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A study of some of the pharmacologic actions of fentanyl citrate
TOXICOLOGY
AND
APPLIED
PHARMACOLOGY
6, 48-62
(1964)
A Study of Some of the Pharmacologic of Fentanyl Citrate J. F. Biological
Research
GARDOCKI
Department, Fort
AND
JOHN
YELNOSKY
Research Division, McNeil Washington, Pennsylvania
Received
February
Actions
Laboratories,
Incorporated,
25,1963
Neuroleptanalgesia can be successfully induced in man and experimental animals with Innovan@, a mixture of droperidol and fentanyl citrate (DeCastro and Mundeleer, 19.5’9; Marsboom et al., 1963). It has been used in conjunction with nitrous oxide for the induction and maintenance of general anesthesia in man (Holderness et al., 1963). The usefulness of this preparation is due in part to the pharmacologic properties of fentanyl citrate. The pharmacology of droperidol has been described elsewhere (Janssen et al., 1963; Yelnosky et al., 1964). The biological activity of the mixture is the subject of another paper (Yelnosky and Gardocki, 1964). The chemistry of fentanyl citrate has been described by Janssen (1962). He found this compound to be a potent morphine-like analgesic. The structural relationship to other known analgesics is presented in Fig. 1. Fentanyl citrate, N-( I-phenethyl-4-piperidinyl)propionanilide dihydrogen citrate), is a white crystalline material which is soluble in water (2.55%) and methyl alcohol. The molecular weight is 528.59. The melting point is 149-151°C. This paper is concerned with some of the pharmacologic properties of fentanyl citrate and its comparison to morphine. METHODS
Analgesic Activity The effect of fentanyl citrate and morphine on the response of mice to a noxious stimulus was assayed by a modification of Haffner’s method as described by Bianchi and Franceschini (1954). Our modification consists of recording the presence or absence of vocalization, in addition to the presence or absence of biting the arterial clamp, placed at the base of the tail of a mouse for a 30-second period. This change in procedure permits the differentiation of a morphine-like analgesic effect (block of vocalization and biting) from the general depressant effect of the potent butyrophenone tranquilizers (variable block of biting only). This modified assay was used to study the effect of droperido1 on the analgesic activity of fentanyl citrate. The results of these interaction studies will be reported in another publication (Yelnosky and Gardocki, 1964). Since the EDsO’s for both the block of vocalization and the biting are the same in the case of morphine-like analgesics, a single EDso is presented. The time of peak effects was obtained by determining the percentage block of vocalization and biting at 4, 10, 15, 30, 45, and 60 minutes following the administration of a fixed dose of the experimental drug. The test substances were administered subcutaneously to 17-21 g male mice of the Swiss-Webster strain. Groups of 10 mice 48
PHARMACOLOGY
OF
FENTANYL
49
CITRATE
Fentanyl Citrate
Meperidine
NH, Anileridine FIG. 1. Structural
relationship
of fentanyl citrate to meperidine and anileridine.
were used per dose level or time period studied. The quanta1 responsewas analyzed statistically by the method of Litchfield and Wilcoxon (1949). Behavioral EJ7ectsand Toxicity The effects of fentanyl citrate and morphine were studied in mice following subcutaneous and intravenous administration. Doses employed ranged from those which produced minimal gross behavioral changes to those which were lethal. Fentanyl citrate was administered intramuscularly to dogs over a wide range of nonlethal doses. Mice. Male mice weighing 17-22 g, of the Swiss-Webster strain were used. Ten mice were used at each dosagelevel studied. The mice were observed during the course of the day of administration and at intervals thereafter for a period of 3 days. The observations of the mice included changes from normal behavioral patterns as well as signs of neurologic deficit and autonomic dysfunction. All of the LDSO’sand 95% fiducial limits of the drugs described in this paper were calculated according to the method of Litchfield and Wilcoxon (1949). Dogs. As the behavior of mongrel dogs is considerably more variable than that of a purebred strain of rodents, the procedure for studying the effects of fentanyl citrate was modified for use with this species.The dogs were mongrels of mixed sexesand weighed from 7.0 to 12.9 kg.
50
J. F. GARDOCKI
AND
JOHN
YELNOSKY
TWO dogs were brought into the observation room and allowed approximately 30 minutes to become accustomed to their new environment and the observer. At the end of this period an assessment was made of the animal’s spontaneous motor activity, gait, responsiveness to auditory and noxious stimuli (pinching of toes with forceps), the respiratory rate and depth, and heart rate. Following administration of the drug, changes in these parameters as well as any other detectable signs of drug effect were recorded. In addition, the effectiveness of nalorphine in antagonizing the depressant properties of the drug, and atropine in reversing the bradycardia induced by the drug, was determined.
Constipating
Effects
The method of David et aE. (1957) was used to determine the relative constipating effect of fentanyl citrate and morphine. Doses administered were approximately equivalent to the analgesic EDjo and 10 and 20 times this amount of either drug, respectively. Ten male mice were used per dose level; the test substance was administered subcutaneously. A group of 10 male mice injected with distilled water served as controls. The mice were placed in individual cages with wire mesh bottoms, and fecal pellets were collected below on a paper dish. The number of fecal pellets excreted by each mouse was determined at hourly intervals for a 6-hour period. Food and water were available ad libitum during the duration of the test. Emetic Activity The emetic activity of fentanyl citrate and morphine was determined in dogs. Forty mongrel dogs of mixed sexes, weight range 5.4-10.8 kg, were divided into four groups of 10 dogs each. Groups A and B received, intramuscularly, doses of 1 and 2.5 mg/kg of fentanyl citrate respectively. Groups C and D received similar doses of morphine. Four days later, the groups that had received fentanyl citrate were then injected with similar doses of morphine and those animals treated with morphine were injected with fentanyl citrate in comparable doses. A single emetic episode was regarded as a positive response. The animals were observed for a period of 60-90 minutes following administration of the drug. Neuromuscular
Transmission
Studies were carried out according to the method of Paton and Zaimus (1949). The experiments were conducted in a group of three anesthetized cats. Two animals were anesthetized with chloralose (80 mg/kg, intravenously) following induction of anesthesia with ether; the third cat was anesthetized with urethane, 1000 mg/kg intraperitoneally. The sciatic nerve was divided and the tibialis anterior was stimulated by applying supramaximal shocks (4-6 volts, 0.2 msec duration) to the peripheral end of the sciatic nerve through platinum electrodes. The nerve was stimulated at lo-second intervals by means of an American Electronic Laboratories stimulator model 104A. An isometric steel spring myograph was used to record the tension of the muscle twitch on smoked paper. Intravenous injection of the compound was made through a cannula inserted into the femoral vein. Respiratory
Effects
The effects of fentanyl citrate on respiration was determined in 6 anesthetized dogs (sodium pentobarbital, 30 mg/kg, i.v.). Respiratory rate and tidal volume,
PHARMACOLOGY
OF FENTANYL
CITRATE
51
from which minute volume was calculated, were determined with an Anderson respirometer which was connected to a tracheal cannula. Blood pressure was recorded from a carotid artery with a mercury manometer. Fentanyl citrate was administered intravenously via a cannulated femoral vein. Each dog was given a dose of 0.01, 0.02, and 0.04 mg/kg of fentanyl citrate spaced 15-30 minutes apart. The respiratory effects of morphine were studied in 3 dogs in doses of 0.5 and 2 mg/kg given 15 minutes apart. Blood Pressure, Heart Rate, and Electrocardiogram
(ECG)
These studies were carried out in dogs artifically respired to eliminate cardiovascular effects secondary to respiratory depression. The dogs were anesthetized with sodium pentobarbital (30 mg/kg, i.v.). Blood pressure from a carotid artery was recorded on smoked paper with a mercury manometer or on a Sanborn model 150 recorder with a Sanborn pressure transducer. Effects of the compounds on heart rate, cardiac rhythm, and conduction were determined from lead II electrocardiograms. In some tests, dogs with a bilaterial cervical vagotomy were used. Compounds were injected into a cannulated femoral vein. Femoral Blood Flow Effects of fentanyl citrate on femoral blood flow were determined in dogs anesthetized with pentobarbital (30 mg/kg, i.v.). Blood flow was measured with a Shipley-Wilson rotameter connected to a femoral artery. Compounds were injected into the rubber tubing distal to the rotameter in a volume of 0.1 ml. Initial intravenous injections of heparin (5 mg/kg) and pontamine fast pink (50 mg/kg) were given to prevent cIotting. Additional injections of heparin (5 mg/kg) were administered intermittently throughout the experimental period. The perfusion pressure was measured with a Sanborn pressure transducer placed distal to the rotameter. Recordings of the perfusion pressure and femoral blood flow were made on a Sanborn model 150 recorder. Femoral vascular bed resistance was calculated in peripheral resistance units (PRU) according to the formula: PRU = mean arterial blood pressure (expressed in mm Hg) divided by femoral blood flow (expressed in ml/min) . Dosage Form In all the studies described in this paper, the citrate salt of fentanyl and sulfate salt of morphine were used. Aqueous solutions of these compounds and all other test drugs were employed. Doses are expressed in milligrams of the salt of the compound studied per kilogram. All solutions were freshly prepared before each experiment. RESULTS
Analgesic Activity Onset and duration. As can be seen from Table 1, an analgesic effect was observed at 4 minutes after the subcutaneous administration of 0.1 mg of fentanyl citrate per kilogram. Maximum activity occurred at 10-15 minutes after the injection of the drug. The analgesic effect of fentanyl citrate was no longer in evidence 30 minutes after injection.
52
J.
F.
GARDOCKI
AND
JOHN
TABLE ONSET
AND DURATION MALE
ALBINO
citrate
1
ACTIVITY
As ASSAYED
MICE
OF FENTANYL
BY A MODIIT~D
% Blockade
Dose, S.C. (w/kg)
Compound Fentanyl Morphine
OF ANALGESIC
0.1
20
YELNOSKY
of biting
CITRATE
AND
HAI?FNER’S
MORPHIYE
IN
PROCEDURE
and vocalization;
4
10
)6
30
30 -
50 -
50 40
10
time
50
in minutes -45
60
80
30
The peak activity of morphine occurred at 45 minutes after injection of 20 mg/ kg of the narcotic. The duration of action at this dosage level of morphine appears to be greater than 1 hour. Potency. The EDS0 and 95% fiducial limits for fentanyl citrate were calculated to be 0.08 (0.045-0.142) mg/kg and for morphine 15 (12-20) mg/kg (Tables 2 and 4). Behavior and T.oxicity Mice. The effects of fentanyl citrate and morphine observed at the analgesic and lethal doses following subcutaneous injection of the respective drugs are presented in Tables 2 and 3. In general, the well-known effects of morphine were also seen with fentanyl citrate: increase in spontaneous motor activity, circling, increased response to touch, Straub tail reaction, mydriasis, increased muscle tone, respiratory depression, and convulsions. The intensity and duration of these effects were dose related. The onset of the behavioral effects of fentanyl citrate (0.1-1.0 mg/kg) was TABLE ANALGESIC
AND
BEHAVIORAL
FENTANYL
Dose Compound Fentanyl
(m/k)
EFFECTS CITRATE
Time in minutes post drug
AND
2
OBSERVED
FOLLOWING
MORPHINE
IN MALE
Number of mice
DOSES
OF
MICE
Behavioral effects
% Blockade
1.0
10
10
100
Marked tivity, Straub
0.50
10
10
100
Same as above
0.10
10
10
so
Moderate tivity,
0.05
10
10
30
Slight
0.01
10
10
10
Same as above
30
4.5
10
90
Extreme increase in motor activity, circling, Straub tail, increased muscle tone, and sensitivity to touch
20 15
45 45
10 IO
80 50
Same
10
45
10
20
S
45
10
0
citrate
Morphine
SUBCUTANEOUS ALBINO
increase in motor increased muscle tail, and circling increase in motor Straub tail, circling
increased
motor
actone,
ac-
activity
as above
Same as above but less intense Moderate increase in above effect Slight to moderate increase increase in motor activity, Straub tail
PHARMACOLOGY
MORTALITY
53
CITRATE
TABLE 3 RESPONSE CURVF,S AND BEHAVIORAL EWECTS OBSERVED FOLLOWING SUBCIJTANE~US ADMINISTRATION OF FENTANYL CITRATE AND MORPHINE IN MALE ALBINO MICE
Compound
Dose (w/kg)
Fentanyl citrate
300 200
Number of mice 10
% Mortality 100
50 10
10 10
80 60 40 20
8 5 4 3 2 1
10
0
10
10 10
0 20 40 0 0
600 500 400 350 300 200
10
70
10 10
70 20 10
10
0
10
0
10 10
0
10
0
10
0
100
Morphine
OF FENTANYL
50 45 40 30
10 10
10 10
10
0
Behavioral
effects
Depression followed by marked stimulation, Straub tail, increased muscle tone, clonic convulsions, hind limb paralysis, cornea1 blanching. Death or recovery followed as indicated Marked stimulation, increased motor activity, circling, Straub tail, increased responsiveness to touch and auditory stimuli, increased muscle tone. Where death occurred it was generally preceded by clonic convulsions Marked increase in motor activity, circling, Straub tail, extreme increase in muscle tone, impairment of reflexes (pinna, pain, corneal, righting) mydriasis, exophthalmos, increased response to touch. Where death occurred it was preceded by clonic convulsions Same as above but shorter in duration
less pronounced
and
evident within l-2 minutes after injection of the drug. The latency with morphine (S-20 mg/kg) was approximately S-10 minutes. The duration of behavioral changes with fentanyl citrate, 1.0 mg/kg, was approximately 1 hour, and with near lethal and lethal doses greater than 4 but less than 16 hours. The duration with morphine at 20 mg/kg is approximately 2% hours, but less than 24 hours. All deaths occurred within 24 hours following administration of either morphine or fentanyl citrate. Three additional differences were noted between fentanyl citrate and morphine in mice. In the lethal dose range, blanching of the cornea and initial depression followed by stimulation were seen with fentanyl citrate, but not with morphine. The mortality dose response curve obtained with fentanyl citrate differed from that seen with morphine as shown in Table 3. Deaths were observed at doses of approximately one-fifteenth the calculated LDbO. The cause of these deaths observed in doses of 3-4 mg/kg of fentanyl citrate appears to be respiratory depression. Similar doses of morphine did not produce any mortality outside of the primary lethal dose range. A biphasic mortality dose response curve was also observed following intravenous administration. The calculated LDc,,‘s and 95% fiducial limits for fentanyl citrate and morphine following intravenous and subcutaneous administration are to be found in Table 4. Fentanyl citrate was found to be more toxic than morphine in mice.
citrate
b Therapeutic
@ In parentheses:
Morphine
Fentanyl
Compound
index:
95%
fiducial limits. LD,, mg/kg . ED,,, w/kg
Intravenous Subcutaneous
Intravenous Subcutaneous
Route
ACUTE
5 10
6 15
Number of dosage levels
TOXICITY
50 100
60 150
Number of mice
TABLE 4 OF FENTANYL CITRATE
270 470
11.2 62 (221-311) (420-526)
(7.4-16.8) (27-142)
LDRoa (w/kg)
AND MORPHINE
IN MICE
15
0.08
(0.045-0.142) (12-20)
Pioa (mw’kd -
31.3
77.5
Therapeutic index”
2
2 2 z
2
2
y % u
z F3 F: 7:
4 w
PHARMACOLOGY
OF
FENTANYL
CITRATE
55
the calculated LD5,, and 95% fiducial Following subcutaneous administration, limits for fentanyl citrate is 62(27-142) mg/kg and that for morphine 470 (4205 26) mg/kg. The therapeutic index (LD 50:ED50) for fentanyl citrate following subcutaneous administration is 775 and that for morphine 31.3.
Behavioral
Efects
Dogs. Intramuscular administration of 0.0125, 0.025, 0.050, 0.10, 0.20, and 1.0 mg/kg of fentanyl citrate produced similar effects at all dose levels. The primary difference between dose levels was an accentuation of the effects with an increase in dose. Within 10 minutes after the administration of fentanyl citrate the following signs were in evidence: decreased motor activity, ataxia, decreased responsiveness to auditory and painful stimuli, bradycardia, respiratory depression (occasionally tachypnea was observed), salivation, and defecation. The duration of these effects was from 40 minutes after 0.0125 mg/kg to more than 6 but less than 20 hours with a dose of 1.0 mg/kg. Nalorphine, of the central citrate. Three sulted in an citrate.
1.0 mg/kg intravenously, was administered at the peak of depression nervous system following doses of 0.10 and 0.20 mg/kg of fentanyl dogs were used at each dosage level. The injection of nalorphine reimmediate reversal of the central depression induced by fentanyl
The effect of atropine in antagonizing the bradycardia induced by fentanyl citrate was studied in two dogs injected with 1.0 mg/kg of the analgesic. The intravenous injection of 0.1 mg/kg of atropine resulted in an immediate return of heart rate to the control rate, i.e., from 60 per minute to 160 per minute.
Constipating
Effect
Both fentanyl citrate and morphine were found to suppress the output of fecal pellets in mice. In approximately equivalent analgesic doses and ten times this amount morphine appears to have a greater constipating effect. However, the duration of this effect appears to be greater with fentanyl citrate. At twenty times an equivalent analgesic dose morphine has both a greater effect and duration of action, as shown in Table 5.
Emetic Activity AS is readily apparent from Table 6, fentanyl citrate in doses of 1.0 and 2.5 mg/kg is devoid of emetic activity in dogs. Similar doses of morphine produced a 60-90s response in a total of 40 dogs. Following morphine, emesis was generally observed within 15 minutes after the administration of the drug. One of the dogs in group D receiving 2.5 mg/kg of fentanyl citrate was found dead 48 hours following administration of the drug. Since the dog was found dead, advanced autolysis precluded the determination of the cause of death. All the other animals recovered from the effects of morphine and fentanyl citrate within 24 hours. In a supplementary study, one group of two dogs was injected with a dose of 5 mg of fentanyl citrate per kilogram, and another
56
J.
F. GARDOCKI
AND
JOHN
TABLE COPI’STJPATING
EFFECT
OF FENTANYL
Dose (mg/k) 0.08 0.80
Compound Fentanyl citrate
1.60
Morphine
5
CITRATE
ADMINISTRATION
IN
Number of mice
AND MALE
ACTIVITY
M~RPIIINE ALBINO
ED50
equivalent
10
1
2-4
4-6
66.2
38.4 35.9 69.3
43.5 25.7 48.7
48 92.4 89.6
0 0 83
10
10
100
10
20
100
94.5
10
10
10
1
100
10
20
100
CITRATE IN MONGREL
AND
6 MORPHINE
Drug Fentanyl citrate Fentanyl citrate Morphine Morphine
FOLLOWING
DOGS (CROSSOVER
Series Ia Dose (w/k) 1.0 2.5 1.0 2.5
O-2
12
OF FENTANYL
SUBCUTANEOUS
5% Inhibition of Fecal pellet output: time in hours
120 240
ADMINISTRATION
Group A B C D
FOLLOWING MICE
Approximate analgesic
TABLE EMETIC
YELNOSKY
INTRAMUSCULAR
STUDY)
Series II I.E.* (%‘o) 0 0 90 70
Drug Morphine Morphine Fentanyl citrate Fentanyl citrate
1.E.b (%I 60 78 0 0
a Time lapse between Series I and II, 4 days. b I.E., Incidence of emesis.
group of 2 dogs received 10 mg of fentanyl citrate per kilogram. Neither emesisnor mortality was observed in either group. Neuromuscular Transmission Intravenous injection of fentanyl citrate to anesthetized cats in doses of 0.010, 0.020, 0.040, 0.080, and 0.16 mg/kg was found to have no effect-neither depression nor enhancement-on the contraction of the tibialis anterior muscle in responseto electrical stimulation of its motor nerve. This finding is of particular interest since it becamenecessary to artificially respire the cats as a result of the severe respiratory depression induced by fentanyl citrate. Control drug studies with succinylcholine were performed. This drug at a dose of 0.030 mg/kg was found to produce a marked decreasein the twitch tension in each of the two cats tested. Respiratory Effects Fentanyl citrate caused a reduction in respiratory minute volume following intravenous dosesof 0.010-0.040 mg/kg. The immediate decreasein minute volume was due to both a decreasein respiratory rate and tidal volume. After 1 or 2 minutes the reduction in minute volume was the result of either a decreasein rate or a decrease in depth of respirations. Maximal depression was seen within 1 minute after the injection of fentanyl citrate, and marked recovery occurred within 5 minutes (Table 7). A fall in blood pressurewas observed at the lowest dose. However, at the higher
PHARMACOLOGY
OF FENTANYL
TABLE EFFECTS
OF FENTANYL
CITRATE
AND
MORPHINE
IN ANESTHETIZED
7 ON RESPIRATORY
Compound Fentanyl
Morphine
citrate
MINUTE
VOLUME
DOGS Mean
Number of dogs
57
CITRATE
% decrease in minute volume: time in minutes after injection of compound
Dose, i.v. (mdkd
1
5
10
6
0.01 0.02 0.04
51.2 83.6 97.6
17.1 28.8 29.5
9.0 16.6 21.2
4
0.5 2.0
-
29.5
14.0 36.3
27.1
doses, after a transient fall in blood pressure, there was a short-lasting hypertensive effect associated with marked respiratory depression. A hypertensive effect was not seen in dogs artificially ventilated, and therefore, this response was considered to be a manifestation of a sympathetic response secondary to hypoxia. Four dogs were given nalorphine (1 mg/kg, i.v.) during periods of apnea caused by injections of 0.70 ( 1 dog) and 0.80 mg/kg of fentanyl citrate (3 dogs). Nalorphine caused an immediate and complete reversal of the depressant effects of fentanyl citrate. Morphine, in doses of 0.5-2.0 mg/kg, also caused a decrease in respiratory minute volume (Table 7). In two of four dogs this was an immediate effect. In two other dogs respiratory depression was preceded by a transient period of hyperpnea. Typical hypertensive effects were produced by morphine. Hyperpnea following intravenous injections of morphine in dogs has been reported by Schmidt and Livingston (1933) and the respiratory depressant effects of morphine in anesthetized dogs using an Anderson respirometer have been described by Shemano et al. (1961). Blood Pressure, Heart Rate, and ECG Effects Each of 3 dogs was given 2 doses of fentanyl citrate (0.0025 and 0.005 mg/kg) spaced 15 minutes apart. The blood pressure and heart rate changes were slight. The maximal effect on blood pressure was a 20% decrease. The heart rate was unchanged in 2 dogs and was decreased from 140 to 100 in 1 dog. There was no evidence in the electrocardiograms of abnormal pacemaker activity or interference with intra-auricular or intraventricular conduction. Twelve additional dogs were studied at 3 higher dosage levels, from 0.01 to 0.04 mg of fentanyl citrate per kilogram. Each dog was observed for 30 minutes after the injection of compound. Fentanyl citrate caused an immediate fall in blood pressure in all the dogs; maximal effects occurred within 10 minutes, occasionally later, and the blood pressure remained below the control level for the duration of the observation period. Morphine was tested in 9 dogs at doses from 0.50 to 2.0 mg/kg, and in each instance produced an immediate maximal fall in blood pressure followed by partial recovery and a sustained hypotensive effect lasting as long as 30 minutes. The results are shown in Table 8. Both compounds produced bradycardia. This effect occurred within 2 minutes after drug injection and lasted for the duration of the observation period. The results are shown in Table 8. Atropine (0.1 or 0.5 mg/kg, i.v.) immedi-
58
J.
F. GARDOCKI
AND
JOHN
YELNOSKY
ately reversed the bradycardia produced by fentanyl citrate and morphine, 0.04 and 2 mg/kg, respectively. Electrocardiograms from 3 dogs receiving 0.010 mg and 3 dogs given 0.040 mg of fentanyl citrate per kilogram were studied for evidence of ectopic pacemaker activity and for changes in intra-auricular and intraventricular conduction. Two ventricular premature contractions were noted in 1 dog given 0.010 mg of fentanyl citrate per kilogram; however, no abnormal pacemaker activity was noted in any of the other tests. There was a prolongation of the P-R interval TABLE EFFECTS
OF FENTANYL
AND
Number of dogs
Compound Fentanyl
CITRATE
citrate
Morphine
a SE, standard
error
MORPHINE
0.01
3 3 3
0.50
PRFSURE
AND
Maximal % decrease in blood pressure
Dose, i.v. (w/kg)
4 3 5
8 ON BLOOD
Mean
0.02 0.04 1 .o
2 .o
SEa
25.3 34.3 49.8
2 k 2
40.9 64.2 75.3
2
k k
HEART
RATE
IN DOGS
Maximal % decrease in heart rate Mean
SE
7.3 5.7 5.7
42.3 49.3 56.4
* 12.0 IL 9.3 2 8.5
7.8
30.7 42.3 43 .o
k 12.6
15.9
6.6
2
10.1
2
3.4
of the mean.
observed in 1 dog after a 0.010 mg/kg dose and in all the dogs after the 0.040 mg/kg dose. The changes in P-R interval were noted during periods of marked bradycardia and were due to a prolongation of the P-R segment. No ectopic pacemaker activity was observed in any of the dogs (9) given morphine. An increase in the P-R interval due to a prolongation of the P-R segment was seen in 1 dog after a dose of 1 mg and in 2 dogs after a dose of 2 mg of morphine per kilogram. The increases in the P-R interval again occurred at the time of marked bradycardia. TABLE EFFECT
Number of dogs
OF FENTANYL
Dose, i.v. h&g)
4 3 5 a SE. standard
0.01
0.02 0.04 error
CITRATE
ON HEART
Nonvagotomized maximal % in heart Mean 42.3 49.3 56.4
RATE
9 IN VACOTOMIZED
dogs, decrease rate
AND
Vagotomized maximal % in heart
SE”
Mean
& 12.0 k 9.3 2 8.5
11.3
6.8 24.0
NONVACOTOMIZED
DOGS
dogs, decrease rate SE
P
2 2.1 * 2.2 k 3.8
< 0.05 < 0.05 < 0.05
of the mean.
Subsequent tests were undertaken to determine whether hypotension, bradycardia, and the prolongation of the P-R interval were secondary to enhanced vagal activity. A significantly greater reduction in heart rate was observed in nonvagotomized dogs after fentanyl citrate, but there was no significant difference in the blood pressure effects (Tables 9 and 10). A prolongation in P-R interval was seen in only 1 of 5 dogs following the injection of 0.040 mg of fentanyl citrate per kilogram. Typical hypotensive effects were obtained with fentanyl citrate (0.04 mg/kg) in 4 dogs pretreated with Clistin@, a potent antihistamine, and in 4 dogs pretreated with
PHARMACOLOGY
OF FENTANYL
59
CITRATE
atropine (1 mg/kg, i.v.). In each test it was shown that the blocking agent was capable of abolishing or markedly reducing the depressor effects of histamine or of acetylcholine, respectively, which were greater than would have been expected from a dose (0.04 mg/kg) of fentanyl citrate. In four additional tests, 4 dogs were each given 4 doses of fentanyl citrate at 30minute intervals. The first dose produced a sustatined hypotensive effect. Subsequent doses had little or no effect on the blood pressure indicating the rapid development of EFFECT OF FENTANYL
Number of dogs
Dose,
i.v.
b-cdkd
4 3 5 a SE, standard
0.01 0.02 0.04 error
TABLE 10 CITRATE ON BLEND PRESSURE IN VAGOTOMIZED Nonvagotomized dogs, maximal % decrease in blood pressure Mean
SEU
25.3 34.3 40.4
f 7.3 f 5.7 -c- 4.9
AND NONVAG~TOMIZED
DOGS
Vagotomized dogs, maximal % decrease in blood pressure Mean 2 1.3 25.7 33.9
SE
P
-+ 1.6 t 2.7 + 3.9
> 0.05 > 0.05 > 0.05
of the mean.
tolerance to the blood pressure effects of fentanyl citrate. Responses to intravenous injections of epinephrine (1 p.g/kg, i.v.) before and after the development of tolerance were compared and there was no indication of adrenergic blockade. In all instances, the response to epinephrine appeared to be potentiated. Typical hypertensive responses were observed after intravenous injections of DMPP, a potent ganglionic stimulant. Efiects on Femoral Blood Flow Intra-arterial injections of 0.010 and 0.050 mg of fentanyl citrate had no effect on femoral blood flow. Injections of 0.20 mg caused a decrease in vascular resistance of 14.4 and 32.6%; however, this represented a dose of approximately 0.020 mg/kg, which is an extremely high dose. DISCUSSION
The pharmacologic profile of fentanyl citrate indicates that this drug is a very potent morphine-like analgesic. It differs from morphine by its short duration of analgesic activity, lack of emetic activity, and minimal hypotensive activity. The behavioral effects in mice-increased spontaneous motor activity, circling, Straub tail reaction, mydriasis, increased muscle tone, hypersensitivity to touch, and death due to respiratory depression-were seen with both fentanyl citrate and morphine. A comparison of the analgesic EDSO’s for the two compounds indicates that fentanyl citrate is 188 times as potent as morphine on a weight basis. The therapeutic index in mice for fentanyl citrate is 775 and for morphine 31.3. The cornea1 blanching observed in mice with lethal doses of fentanyl citrate is probably due to a sympathetic discharge secondary to respiratory depression. A sympathetic discharge was observed to occur following respiratory depression in dogs. Cornea1 blanching is characteristically observed in mice following injection of high doses of sympathomimetic amines. The biphasic nature of the mortality dose response curve is probably due to respira-
60
J.
F.
GARDOCKI
AND
JOHN
YELNOSKY
tory depression. As can be seen from Table 3, maximum number of deaths occurred at a dose of 3 mg/kg. With increasing doses, closely spaced, there was noted a precipitous fall off in mortality, and at twice the aforementioned dose all of the animals survived. The absence of a similar curve for morphine may simply be due to the choice of the doses employed. Janssen and Jageneau (1958) reported similar curves for morphine in rats. These authors found that deaths following low doses of morphine were more readily prevented by nalorphine than were deaths following high doses of the analgesic. They ascribe death with low doses of morphine to a mechanism which is antagonized by nalorphine, e.g., respiratory depression. Studies on the mechanism of the biphasic mortality dose response curve are currently in progress and will be reported upon completion. The upper portion of the biphasic mortality dose response curve has been used to calculate an LDSO and subsequently the therapeutic index for fentanyl citrate. Since the anticipated use of this drug is in general anesthesia, the problem of respiratory depression from low doses of fentanyl citrate is readily circumvented by artificial respiration which is generally employed during anesthesia. As mentioned, effects of low doses of fentanyl citrate are readily antagonized by nalorphine. Both fentanyl citrate and morphine have a constipating effect in mice. Morphine appears to be more active than fentanyl citrate at approximately equivalent analgesic doses, but it also has a shorter duration of action than fentanyl citrate. With a twentyfold increase in dose, morphine is more active and also has a longer duration of action. Behavioral studies in dogs further extended the similarities between fentanyl citrate and morphine, The reversal of the fentanyl citrate-induced depression of the central nervous system by nalorphine, a specific morphme antagonist, is one of the major points common to fentanyl citrate and morphine. In addition, atropine antagonized the bradycardia induced by fentanyl citrate as it does the bradycardia observed following morphine. The vagi have been observed to play a major role in the bradycardia due to fentanyl citrate since the effectiveness of fentanyl citrate in producing bradycardia, in bilaterally vagotomized dogs, is significantly reduced. According to Schmidt and Livingston (1933) and McCrea and Meek (1926), the vagi also play a major role in the mechanism of the bradycardia due to morphine. One of the most notable differences between fentanyl citrate and morphine is the absence of emetic activity with fentanyl citrate. Similar doses of morphine produce a 60-90y0 incidence of emesis in the dosage range studied. The respiratory depressant properties of fentanyl citrate appear to be due to a central effect as observed in the experiments in cats. No effect on neuromuscular transmission could be observed in the presence of severe respiratory depression. The results of our studies on the hypotensive effect of fentanyl citrate have ruled out several possible mechanisms which could account for the lowering of the blood pressure observed with this drug. It does not appear probable that fentanyl citrate exerts a cholinergic or histamine-like effect since neither vagotomy nor pretreatment with either atropine or an antihistamine, Clistin @, blocked the hypotensive response. Peripheral vasodilation does not account for the hypotension as demonstrated by the absence of a significant change on the femoral vascular bed resistance following intraarterial injection of fentanyl citrate. Respiratory depression is not responsible for the
PHARMACOLOGY OF FENTANYL
CITRATE
61
depressor effect of the drug since this effect occurs when the animal is artificially
respired. Neither ganglionic nor adrenergic blockade can account for the hypotensive effect of fentanyl citrate. These possible mechanisms are excluded because (1) the increased vagal activity following fentanyl citrate is reversed by severing the preganglionic vagal fibers; (2) respiratory depression is accompanied by a marked hypertension; (3) fentanyl citrate does not antagonize the pressor response of epinephrine or DMPP. Studies on the hypotensive effect of fentanyl citrate are being continued. It should be noted, however, that the lowest doses used in the cardiovascular studies, 0.0025 and 0.005 mg/kg, which had little effect on the blood pressure in dogs, represents about 2 and 4 times the recommended human dose. The lack of hypotensive activity in the clinical dose of the drug is indicated in a report by Holderness et al. (1963). SUMMARY Fentanyl citrate is an analgesic that is particularly well suited for use in anesthesia because of its (1) high potency, (2) rapid onset and short duration of action, (3) absence of emetic activity, and (4) minimal hypotensive activity after intravenous administration. As with other morphinelike analgesics, the effects of fentanyl citrate are readily antagonized by nalorphine. Bradycardia is also easily reversed with atropine. ACKNOWLEDGMENTS We are indebted to Dr. A. P. Roszkowski for his study of the effects of fentanyl citrate on neuromuscular transmission, and to Mrs. R. H. Katz and Miss R. W. Ervin for their assistance in these studies. REFERENCES BIANCHI, C., and FRANCESCHINI,J. (1954). Experimental observations on Haffner’s method for testing analgesic drugs. Brit. 1. Pkarmacol. 9, 280-284. DAVID, A., LEITH-ROSS, F., and VALLANCE, D. K. (1957). Antitussive and other pharmacological properties of the diethylaminoethoxyethyl ester of au-diethylphenylacetic acid (oxeladin) . J. Pkarm.
Pkarmacol.
9, 446-458.
DECASTRO, J., and MUNDELEER, P.
(1959). Anethesie sans barbituriques. La neuroleptanalgesie. 16, 1022-1056. HOLDERNESS,M. C., CHASE, P. E., and Damps, R. D. (1963). Use of a narcotic analgesic and a butyrophenone with nitrous oxide for general anesthesia. Anesthesiology 94, 336-340. JANSSEN, P. A. (1962). A review of the chemical features associated with strong morphine-like activity. Brit. J. Anaestkesia 94, 260-267. JANSSEN, P. A., and JAGENEAU, A. H. (1958). Comparative analgesic activity, acute toxicity and tolerance development in rats for R875, morphine, pethidine and methadone. J. Pkarm. Pkurmacol. 10, 14-21. JANSSEN, P. A., NIFXEGEERS, C. J., SCHELLEKENS, K. H., VERBRUCGEN, F. J., and VAN NEUTEN, J. M. (1963). The pharmacology of Dehydrobenzperidol (R4749), a new potent and short acting neuroleptic agent chemically related to Haloperidol. Arzneimittel-forsck. 13, 205-211. LITCHFIELD, J. T., JR., and WILCOXON, F. (1949). A simplified method of evaluating dose-effect experiments. J. Pkarmacol. Exptl. Tkerup. 96, W-113. MCCREA, F. D., and MEEK, W. J. (1926). Action of morphine in slowing the pulse. J. Pkarmacol. Anestkesie,
Exptl.
Tkerap.
Analgesic,
Reanimation
99, 361-366.
MARSBOOM, R., MORTELMANS, J., and VERCRUYSSE,J. (1963). Neuroleptanalgesia in monkeys. Vet. Record 76, 132-133. PATON, W. D. M., and Z-us, E. J. (1949). The pharmacological actions of polymethylene bistrimethylammonium salts. Btit. J. Pkarmacol. 4, 381-400. SCHMIDT, C. F., and LIVINGSTON, A. E. (1933). The action of morphine on the mammalian circulation. J. Pkarmacol. Exptl. Therap. 47, 411-441.
62
J, F. GARDOCKI
AND
JOHN
YELNOSKY
I., WENDEL, H., and Ross, S. D. (1961). A pharmacological comparison of phenazotine hydrobromide and morphine sulfate as narcotic analgesics. J. Pharmacol. Exptl. Therap. 132, 258-263. A study of some of the pharmacologic actions of YELNOSILY, J., and GARDOCKI, J. F. (1964). fentanyl citrate and droperidol. Toxicol. Appl. Pharmacol. 6, 63-70. YELNOSKY, J., KATZ, R., and DIETRICH, E. V. (1964). A study of some of the pharmacologic actions of droperidol. Toxicol. Appl. Pharmacol. 6, 37-47. SHEMANO,
AND
APPLIED
PHARMACOLOGY
6, 48-62
(1964)
A Study of Some of the Pharmacologic of Fentanyl Citrate J. F. Biological
Research
GARDOCKI
Department, Fort
AND
JOHN
YELNOSKY
Research Division, McNeil Washington, Pennsylvania
Received
February
Actions
Laboratories,
Incorporated,
25,1963
Neuroleptanalgesia can be successfully induced in man and experimental animals with Innovan@, a mixture of droperidol and fentanyl citrate (DeCastro and Mundeleer, 19.5’9; Marsboom et al., 1963). It has been used in conjunction with nitrous oxide for the induction and maintenance of general anesthesia in man (Holderness et al., 1963). The usefulness of this preparation is due in part to the pharmacologic properties of fentanyl citrate. The pharmacology of droperidol has been described elsewhere (Janssen et al., 1963; Yelnosky et al., 1964). The biological activity of the mixture is the subject of another paper (Yelnosky and Gardocki, 1964). The chemistry of fentanyl citrate has been described by Janssen (1962). He found this compound to be a potent morphine-like analgesic. The structural relationship to other known analgesics is presented in Fig. 1. Fentanyl citrate, N-( I-phenethyl-4-piperidinyl)propionanilide dihydrogen citrate), is a white crystalline material which is soluble in water (2.55%) and methyl alcohol. The molecular weight is 528.59. The melting point is 149-151°C. This paper is concerned with some of the pharmacologic properties of fentanyl citrate and its comparison to morphine. METHODS
Analgesic Activity The effect of fentanyl citrate and morphine on the response of mice to a noxious stimulus was assayed by a modification of Haffner’s method as described by Bianchi and Franceschini (1954). Our modification consists of recording the presence or absence of vocalization, in addition to the presence or absence of biting the arterial clamp, placed at the base of the tail of a mouse for a 30-second period. This change in procedure permits the differentiation of a morphine-like analgesic effect (block of vocalization and biting) from the general depressant effect of the potent butyrophenone tranquilizers (variable block of biting only). This modified assay was used to study the effect of droperido1 on the analgesic activity of fentanyl citrate. The results of these interaction studies will be reported in another publication (Yelnosky and Gardocki, 1964). Since the EDsO’s for both the block of vocalization and the biting are the same in the case of morphine-like analgesics, a single EDso is presented. The time of peak effects was obtained by determining the percentage block of vocalization and biting at 4, 10, 15, 30, 45, and 60 minutes following the administration of a fixed dose of the experimental drug. The test substances were administered subcutaneously to 17-21 g male mice of the Swiss-Webster strain. Groups of 10 mice 48
PHARMACOLOGY
OF
FENTANYL
49
CITRATE
Fentanyl Citrate
Meperidine
NH, Anileridine FIG. 1. Structural
relationship
of fentanyl citrate to meperidine and anileridine.
were used per dose level or time period studied. The quanta1 responsewas analyzed statistically by the method of Litchfield and Wilcoxon (1949). Behavioral EJ7ectsand Toxicity The effects of fentanyl citrate and morphine were studied in mice following subcutaneous and intravenous administration. Doses employed ranged from those which produced minimal gross behavioral changes to those which were lethal. Fentanyl citrate was administered intramuscularly to dogs over a wide range of nonlethal doses. Mice. Male mice weighing 17-22 g, of the Swiss-Webster strain were used. Ten mice were used at each dosagelevel studied. The mice were observed during the course of the day of administration and at intervals thereafter for a period of 3 days. The observations of the mice included changes from normal behavioral patterns as well as signs of neurologic deficit and autonomic dysfunction. All of the LDSO’sand 95% fiducial limits of the drugs described in this paper were calculated according to the method of Litchfield and Wilcoxon (1949). Dogs. As the behavior of mongrel dogs is considerably more variable than that of a purebred strain of rodents, the procedure for studying the effects of fentanyl citrate was modified for use with this species.The dogs were mongrels of mixed sexesand weighed from 7.0 to 12.9 kg.
50
J. F. GARDOCKI
AND
JOHN
YELNOSKY
TWO dogs were brought into the observation room and allowed approximately 30 minutes to become accustomed to their new environment and the observer. At the end of this period an assessment was made of the animal’s spontaneous motor activity, gait, responsiveness to auditory and noxious stimuli (pinching of toes with forceps), the respiratory rate and depth, and heart rate. Following administration of the drug, changes in these parameters as well as any other detectable signs of drug effect were recorded. In addition, the effectiveness of nalorphine in antagonizing the depressant properties of the drug, and atropine in reversing the bradycardia induced by the drug, was determined.
Constipating
Effects
The method of David et aE. (1957) was used to determine the relative constipating effect of fentanyl citrate and morphine. Doses administered were approximately equivalent to the analgesic EDjo and 10 and 20 times this amount of either drug, respectively. Ten male mice were used per dose level; the test substance was administered subcutaneously. A group of 10 male mice injected with distilled water served as controls. The mice were placed in individual cages with wire mesh bottoms, and fecal pellets were collected below on a paper dish. The number of fecal pellets excreted by each mouse was determined at hourly intervals for a 6-hour period. Food and water were available ad libitum during the duration of the test. Emetic Activity The emetic activity of fentanyl citrate and morphine was determined in dogs. Forty mongrel dogs of mixed sexes, weight range 5.4-10.8 kg, were divided into four groups of 10 dogs each. Groups A and B received, intramuscularly, doses of 1 and 2.5 mg/kg of fentanyl citrate respectively. Groups C and D received similar doses of morphine. Four days later, the groups that had received fentanyl citrate were then injected with similar doses of morphine and those animals treated with morphine were injected with fentanyl citrate in comparable doses. A single emetic episode was regarded as a positive response. The animals were observed for a period of 60-90 minutes following administration of the drug. Neuromuscular
Transmission
Studies were carried out according to the method of Paton and Zaimus (1949). The experiments were conducted in a group of three anesthetized cats. Two animals were anesthetized with chloralose (80 mg/kg, intravenously) following induction of anesthesia with ether; the third cat was anesthetized with urethane, 1000 mg/kg intraperitoneally. The sciatic nerve was divided and the tibialis anterior was stimulated by applying supramaximal shocks (4-6 volts, 0.2 msec duration) to the peripheral end of the sciatic nerve through platinum electrodes. The nerve was stimulated at lo-second intervals by means of an American Electronic Laboratories stimulator model 104A. An isometric steel spring myograph was used to record the tension of the muscle twitch on smoked paper. Intravenous injection of the compound was made through a cannula inserted into the femoral vein. Respiratory
Effects
The effects of fentanyl citrate on respiration was determined in 6 anesthetized dogs (sodium pentobarbital, 30 mg/kg, i.v.). Respiratory rate and tidal volume,
PHARMACOLOGY
OF FENTANYL
CITRATE
51
from which minute volume was calculated, were determined with an Anderson respirometer which was connected to a tracheal cannula. Blood pressure was recorded from a carotid artery with a mercury manometer. Fentanyl citrate was administered intravenously via a cannulated femoral vein. Each dog was given a dose of 0.01, 0.02, and 0.04 mg/kg of fentanyl citrate spaced 15-30 minutes apart. The respiratory effects of morphine were studied in 3 dogs in doses of 0.5 and 2 mg/kg given 15 minutes apart. Blood Pressure, Heart Rate, and Electrocardiogram
(ECG)
These studies were carried out in dogs artifically respired to eliminate cardiovascular effects secondary to respiratory depression. The dogs were anesthetized with sodium pentobarbital (30 mg/kg, i.v.). Blood pressure from a carotid artery was recorded on smoked paper with a mercury manometer or on a Sanborn model 150 recorder with a Sanborn pressure transducer. Effects of the compounds on heart rate, cardiac rhythm, and conduction were determined from lead II electrocardiograms. In some tests, dogs with a bilaterial cervical vagotomy were used. Compounds were injected into a cannulated femoral vein. Femoral Blood Flow Effects of fentanyl citrate on femoral blood flow were determined in dogs anesthetized with pentobarbital (30 mg/kg, i.v.). Blood flow was measured with a Shipley-Wilson rotameter connected to a femoral artery. Compounds were injected into the rubber tubing distal to the rotameter in a volume of 0.1 ml. Initial intravenous injections of heparin (5 mg/kg) and pontamine fast pink (50 mg/kg) were given to prevent cIotting. Additional injections of heparin (5 mg/kg) were administered intermittently throughout the experimental period. The perfusion pressure was measured with a Sanborn pressure transducer placed distal to the rotameter. Recordings of the perfusion pressure and femoral blood flow were made on a Sanborn model 150 recorder. Femoral vascular bed resistance was calculated in peripheral resistance units (PRU) according to the formula: PRU = mean arterial blood pressure (expressed in mm Hg) divided by femoral blood flow (expressed in ml/min) . Dosage Form In all the studies described in this paper, the citrate salt of fentanyl and sulfate salt of morphine were used. Aqueous solutions of these compounds and all other test drugs were employed. Doses are expressed in milligrams of the salt of the compound studied per kilogram. All solutions were freshly prepared before each experiment. RESULTS
Analgesic Activity Onset and duration. As can be seen from Table 1, an analgesic effect was observed at 4 minutes after the subcutaneous administration of 0.1 mg of fentanyl citrate per kilogram. Maximum activity occurred at 10-15 minutes after the injection of the drug. The analgesic effect of fentanyl citrate was no longer in evidence 30 minutes after injection.
52
J.
F.
GARDOCKI
AND
JOHN
TABLE ONSET
AND DURATION MALE
ALBINO
citrate
1
ACTIVITY
As ASSAYED
MICE
OF FENTANYL
BY A MODIIT~D
% Blockade
Dose, S.C. (w/kg)
Compound Fentanyl Morphine
OF ANALGESIC
0.1
20
YELNOSKY
of biting
CITRATE
AND
HAI?FNER’S
MORPHIYE
IN
PROCEDURE
and vocalization;
4
10
)6
30
30 -
50 -
50 40
10
time
50
in minutes -45
60
80
30
The peak activity of morphine occurred at 45 minutes after injection of 20 mg/ kg of the narcotic. The duration of action at this dosage level of morphine appears to be greater than 1 hour. Potency. The EDS0 and 95% fiducial limits for fentanyl citrate were calculated to be 0.08 (0.045-0.142) mg/kg and for morphine 15 (12-20) mg/kg (Tables 2 and 4). Behavior and T.oxicity Mice. The effects of fentanyl citrate and morphine observed at the analgesic and lethal doses following subcutaneous injection of the respective drugs are presented in Tables 2 and 3. In general, the well-known effects of morphine were also seen with fentanyl citrate: increase in spontaneous motor activity, circling, increased response to touch, Straub tail reaction, mydriasis, increased muscle tone, respiratory depression, and convulsions. The intensity and duration of these effects were dose related. The onset of the behavioral effects of fentanyl citrate (0.1-1.0 mg/kg) was TABLE ANALGESIC
AND
BEHAVIORAL
FENTANYL
Dose Compound Fentanyl
(m/k)
EFFECTS CITRATE
Time in minutes post drug
AND
2
OBSERVED
FOLLOWING
MORPHINE
IN MALE
Number of mice
DOSES
OF
MICE
Behavioral effects
% Blockade
1.0
10
10
100
Marked tivity, Straub
0.50
10
10
100
Same as above
0.10
10
10
so
Moderate tivity,
0.05
10
10
30
Slight
0.01
10
10
10
Same as above
30
4.5
10
90
Extreme increase in motor activity, circling, Straub tail, increased muscle tone, and sensitivity to touch
20 15
45 45
10 IO
80 50
Same
10
45
10
20
S
45
10
0
citrate
Morphine
SUBCUTANEOUS ALBINO
increase in motor increased muscle tail, and circling increase in motor Straub tail, circling
increased
motor
actone,
ac-
activity
as above
Same as above but less intense Moderate increase in above effect Slight to moderate increase increase in motor activity, Straub tail
PHARMACOLOGY
MORTALITY
53
CITRATE
TABLE 3 RESPONSE CURVF,S AND BEHAVIORAL EWECTS OBSERVED FOLLOWING SUBCIJTANE~US ADMINISTRATION OF FENTANYL CITRATE AND MORPHINE IN MALE ALBINO MICE
Compound
Dose (w/kg)
Fentanyl citrate
300 200
Number of mice 10
% Mortality 100
50 10
10 10
80 60 40 20
8 5 4 3 2 1
10
0
10
10 10
0 20 40 0 0
600 500 400 350 300 200
10
70
10 10
70 20 10
10
0
10
0
10 10
0
10
0
10
0
100
Morphine
OF FENTANYL
50 45 40 30
10 10
10 10
10
0
Behavioral
effects
Depression followed by marked stimulation, Straub tail, increased muscle tone, clonic convulsions, hind limb paralysis, cornea1 blanching. Death or recovery followed as indicated Marked stimulation, increased motor activity, circling, Straub tail, increased responsiveness to touch and auditory stimuli, increased muscle tone. Where death occurred it was generally preceded by clonic convulsions Marked increase in motor activity, circling, Straub tail, extreme increase in muscle tone, impairment of reflexes (pinna, pain, corneal, righting) mydriasis, exophthalmos, increased response to touch. Where death occurred it was preceded by clonic convulsions Same as above but shorter in duration
less pronounced
and
evident within l-2 minutes after injection of the drug. The latency with morphine (S-20 mg/kg) was approximately S-10 minutes. The duration of behavioral changes with fentanyl citrate, 1.0 mg/kg, was approximately 1 hour, and with near lethal and lethal doses greater than 4 but less than 16 hours. The duration with morphine at 20 mg/kg is approximately 2% hours, but less than 24 hours. All deaths occurred within 24 hours following administration of either morphine or fentanyl citrate. Three additional differences were noted between fentanyl citrate and morphine in mice. In the lethal dose range, blanching of the cornea and initial depression followed by stimulation were seen with fentanyl citrate, but not with morphine. The mortality dose response curve obtained with fentanyl citrate differed from that seen with morphine as shown in Table 3. Deaths were observed at doses of approximately one-fifteenth the calculated LDbO. The cause of these deaths observed in doses of 3-4 mg/kg of fentanyl citrate appears to be respiratory depression. Similar doses of morphine did not produce any mortality outside of the primary lethal dose range. A biphasic mortality dose response curve was also observed following intravenous administration. The calculated LDc,,‘s and 95% fiducial limits for fentanyl citrate and morphine following intravenous and subcutaneous administration are to be found in Table 4. Fentanyl citrate was found to be more toxic than morphine in mice.
citrate
b Therapeutic
@ In parentheses:
Morphine
Fentanyl
Compound
index:
95%
fiducial limits. LD,, mg/kg . ED,,, w/kg
Intravenous Subcutaneous
Intravenous Subcutaneous
Route
ACUTE
5 10
6 15
Number of dosage levels
TOXICITY
50 100
60 150
Number of mice
TABLE 4 OF FENTANYL CITRATE
270 470
11.2 62 (221-311) (420-526)
(7.4-16.8) (27-142)
LDRoa (w/kg)
AND MORPHINE
IN MICE
15
0.08
(0.045-0.142) (12-20)
Pioa (mw’kd -
31.3
77.5
Therapeutic index”
2
2 2 z
2
2
y % u
z F3 F: 7:
4 w
PHARMACOLOGY
OF
FENTANYL
CITRATE
55
the calculated LD5,, and 95% fiducial Following subcutaneous administration, limits for fentanyl citrate is 62(27-142) mg/kg and that for morphine 470 (4205 26) mg/kg. The therapeutic index (LD 50:ED50) for fentanyl citrate following subcutaneous administration is 775 and that for morphine 31.3.
Behavioral
Efects
Dogs. Intramuscular administration of 0.0125, 0.025, 0.050, 0.10, 0.20, and 1.0 mg/kg of fentanyl citrate produced similar effects at all dose levels. The primary difference between dose levels was an accentuation of the effects with an increase in dose. Within 10 minutes after the administration of fentanyl citrate the following signs were in evidence: decreased motor activity, ataxia, decreased responsiveness to auditory and painful stimuli, bradycardia, respiratory depression (occasionally tachypnea was observed), salivation, and defecation. The duration of these effects was from 40 minutes after 0.0125 mg/kg to more than 6 but less than 20 hours with a dose of 1.0 mg/kg. Nalorphine, of the central citrate. Three sulted in an citrate.
1.0 mg/kg intravenously, was administered at the peak of depression nervous system following doses of 0.10 and 0.20 mg/kg of fentanyl dogs were used at each dosage level. The injection of nalorphine reimmediate reversal of the central depression induced by fentanyl
The effect of atropine in antagonizing the bradycardia induced by fentanyl citrate was studied in two dogs injected with 1.0 mg/kg of the analgesic. The intravenous injection of 0.1 mg/kg of atropine resulted in an immediate return of heart rate to the control rate, i.e., from 60 per minute to 160 per minute.
Constipating
Effect
Both fentanyl citrate and morphine were found to suppress the output of fecal pellets in mice. In approximately equivalent analgesic doses and ten times this amount morphine appears to have a greater constipating effect. However, the duration of this effect appears to be greater with fentanyl citrate. At twenty times an equivalent analgesic dose morphine has both a greater effect and duration of action, as shown in Table 5.
Emetic Activity AS is readily apparent from Table 6, fentanyl citrate in doses of 1.0 and 2.5 mg/kg is devoid of emetic activity in dogs. Similar doses of morphine produced a 60-90s response in a total of 40 dogs. Following morphine, emesis was generally observed within 15 minutes after the administration of the drug. One of the dogs in group D receiving 2.5 mg/kg of fentanyl citrate was found dead 48 hours following administration of the drug. Since the dog was found dead, advanced autolysis precluded the determination of the cause of death. All the other animals recovered from the effects of morphine and fentanyl citrate within 24 hours. In a supplementary study, one group of two dogs was injected with a dose of 5 mg of fentanyl citrate per kilogram, and another
56
J.
F. GARDOCKI
AND
JOHN
TABLE COPI’STJPATING
EFFECT
OF FENTANYL
Dose (mg/k) 0.08 0.80
Compound Fentanyl citrate
1.60
Morphine
5
CITRATE
ADMINISTRATION
IN
Number of mice
AND MALE
ACTIVITY
M~RPIIINE ALBINO
ED50
equivalent
10
1
2-4
4-6
66.2
38.4 35.9 69.3
43.5 25.7 48.7
48 92.4 89.6
0 0 83
10
10
100
10
20
100
94.5
10
10
10
1
100
10
20
100
CITRATE IN MONGREL
AND
6 MORPHINE
Drug Fentanyl citrate Fentanyl citrate Morphine Morphine
FOLLOWING
DOGS (CROSSOVER
Series Ia Dose (w/k) 1.0 2.5 1.0 2.5
O-2
12
OF FENTANYL
SUBCUTANEOUS
5% Inhibition of Fecal pellet output: time in hours
120 240
ADMINISTRATION
Group A B C D
FOLLOWING MICE
Approximate analgesic
TABLE EMETIC
YELNOSKY
INTRAMUSCULAR
STUDY)
Series II I.E.* (%‘o) 0 0 90 70
Drug Morphine Morphine Fentanyl citrate Fentanyl citrate
1.E.b (%I 60 78 0 0
a Time lapse between Series I and II, 4 days. b I.E., Incidence of emesis.
group of 2 dogs received 10 mg of fentanyl citrate per kilogram. Neither emesisnor mortality was observed in either group. Neuromuscular Transmission Intravenous injection of fentanyl citrate to anesthetized cats in doses of 0.010, 0.020, 0.040, 0.080, and 0.16 mg/kg was found to have no effect-neither depression nor enhancement-on the contraction of the tibialis anterior muscle in responseto electrical stimulation of its motor nerve. This finding is of particular interest since it becamenecessary to artificially respire the cats as a result of the severe respiratory depression induced by fentanyl citrate. Control drug studies with succinylcholine were performed. This drug at a dose of 0.030 mg/kg was found to produce a marked decreasein the twitch tension in each of the two cats tested. Respiratory Effects Fentanyl citrate caused a reduction in respiratory minute volume following intravenous dosesof 0.010-0.040 mg/kg. The immediate decreasein minute volume was due to both a decreasein respiratory rate and tidal volume. After 1 or 2 minutes the reduction in minute volume was the result of either a decreasein rate or a decrease in depth of respirations. Maximal depression was seen within 1 minute after the injection of fentanyl citrate, and marked recovery occurred within 5 minutes (Table 7). A fall in blood pressurewas observed at the lowest dose. However, at the higher
PHARMACOLOGY
OF FENTANYL
TABLE EFFECTS
OF FENTANYL
CITRATE
AND
MORPHINE
IN ANESTHETIZED
7 ON RESPIRATORY
Compound Fentanyl
Morphine
citrate
MINUTE
VOLUME
DOGS Mean
Number of dogs
57
CITRATE
% decrease in minute volume: time in minutes after injection of compound
Dose, i.v. (mdkd
1
5
10
6
0.01 0.02 0.04
51.2 83.6 97.6
17.1 28.8 29.5
9.0 16.6 21.2
4
0.5 2.0
-
29.5
14.0 36.3
27.1
doses, after a transient fall in blood pressure, there was a short-lasting hypertensive effect associated with marked respiratory depression. A hypertensive effect was not seen in dogs artificially ventilated, and therefore, this response was considered to be a manifestation of a sympathetic response secondary to hypoxia. Four dogs were given nalorphine (1 mg/kg, i.v.) during periods of apnea caused by injections of 0.70 ( 1 dog) and 0.80 mg/kg of fentanyl citrate (3 dogs). Nalorphine caused an immediate and complete reversal of the depressant effects of fentanyl citrate. Morphine, in doses of 0.5-2.0 mg/kg, also caused a decrease in respiratory minute volume (Table 7). In two of four dogs this was an immediate effect. In two other dogs respiratory depression was preceded by a transient period of hyperpnea. Typical hypertensive effects were produced by morphine. Hyperpnea following intravenous injections of morphine in dogs has been reported by Schmidt and Livingston (1933) and the respiratory depressant effects of morphine in anesthetized dogs using an Anderson respirometer have been described by Shemano et al. (1961). Blood Pressure, Heart Rate, and ECG Effects Each of 3 dogs was given 2 doses of fentanyl citrate (0.0025 and 0.005 mg/kg) spaced 15 minutes apart. The blood pressure and heart rate changes were slight. The maximal effect on blood pressure was a 20% decrease. The heart rate was unchanged in 2 dogs and was decreased from 140 to 100 in 1 dog. There was no evidence in the electrocardiograms of abnormal pacemaker activity or interference with intra-auricular or intraventricular conduction. Twelve additional dogs were studied at 3 higher dosage levels, from 0.01 to 0.04 mg of fentanyl citrate per kilogram. Each dog was observed for 30 minutes after the injection of compound. Fentanyl citrate caused an immediate fall in blood pressure in all the dogs; maximal effects occurred within 10 minutes, occasionally later, and the blood pressure remained below the control level for the duration of the observation period. Morphine was tested in 9 dogs at doses from 0.50 to 2.0 mg/kg, and in each instance produced an immediate maximal fall in blood pressure followed by partial recovery and a sustained hypotensive effect lasting as long as 30 minutes. The results are shown in Table 8. Both compounds produced bradycardia. This effect occurred within 2 minutes after drug injection and lasted for the duration of the observation period. The results are shown in Table 8. Atropine (0.1 or 0.5 mg/kg, i.v.) immedi-
58
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F. GARDOCKI
AND
JOHN
YELNOSKY
ately reversed the bradycardia produced by fentanyl citrate and morphine, 0.04 and 2 mg/kg, respectively. Electrocardiograms from 3 dogs receiving 0.010 mg and 3 dogs given 0.040 mg of fentanyl citrate per kilogram were studied for evidence of ectopic pacemaker activity and for changes in intra-auricular and intraventricular conduction. Two ventricular premature contractions were noted in 1 dog given 0.010 mg of fentanyl citrate per kilogram; however, no abnormal pacemaker activity was noted in any of the other tests. There was a prolongation of the P-R interval TABLE EFFECTS
OF FENTANYL
AND
Number of dogs
Compound Fentanyl
CITRATE
citrate
Morphine
a SE, standard
error
MORPHINE
0.01
3 3 3
0.50
PRFSURE
AND
Maximal % decrease in blood pressure
Dose, i.v. (w/kg)
4 3 5
8 ON BLOOD
Mean
0.02 0.04 1 .o
2 .o
SEa
25.3 34.3 49.8
2 k 2
40.9 64.2 75.3
2
k k
HEART
RATE
IN DOGS
Maximal % decrease in heart rate Mean
SE
7.3 5.7 5.7
42.3 49.3 56.4
* 12.0 IL 9.3 2 8.5
7.8
30.7 42.3 43 .o
k 12.6
15.9
6.6
2
10.1
2
3.4
of the mean.
observed in 1 dog after a 0.010 mg/kg dose and in all the dogs after the 0.040 mg/kg dose. The changes in P-R interval were noted during periods of marked bradycardia and were due to a prolongation of the P-R segment. No ectopic pacemaker activity was observed in any of the dogs (9) given morphine. An increase in the P-R interval due to a prolongation of the P-R segment was seen in 1 dog after a dose of 1 mg and in 2 dogs after a dose of 2 mg of morphine per kilogram. The increases in the P-R interval again occurred at the time of marked bradycardia. TABLE EFFECT
Number of dogs
OF FENTANYL
Dose, i.v. h&g)
4 3 5 a SE. standard
0.01
0.02 0.04 error
CITRATE
ON HEART
Nonvagotomized maximal % in heart Mean 42.3 49.3 56.4
RATE
9 IN VACOTOMIZED
dogs, decrease rate
AND
Vagotomized maximal % in heart
SE”
Mean
& 12.0 k 9.3 2 8.5
11.3
6.8 24.0
NONVACOTOMIZED
DOGS
dogs, decrease rate SE
P
2 2.1 * 2.2 k 3.8
< 0.05 < 0.05 < 0.05
of the mean.
Subsequent tests were undertaken to determine whether hypotension, bradycardia, and the prolongation of the P-R interval were secondary to enhanced vagal activity. A significantly greater reduction in heart rate was observed in nonvagotomized dogs after fentanyl citrate, but there was no significant difference in the blood pressure effects (Tables 9 and 10). A prolongation in P-R interval was seen in only 1 of 5 dogs following the injection of 0.040 mg of fentanyl citrate per kilogram. Typical hypotensive effects were obtained with fentanyl citrate (0.04 mg/kg) in 4 dogs pretreated with Clistin@, a potent antihistamine, and in 4 dogs pretreated with
PHARMACOLOGY
OF FENTANYL
59
CITRATE
atropine (1 mg/kg, i.v.). In each test it was shown that the blocking agent was capable of abolishing or markedly reducing the depressor effects of histamine or of acetylcholine, respectively, which were greater than would have been expected from a dose (0.04 mg/kg) of fentanyl citrate. In four additional tests, 4 dogs were each given 4 doses of fentanyl citrate at 30minute intervals. The first dose produced a sustatined hypotensive effect. Subsequent doses had little or no effect on the blood pressure indicating the rapid development of EFFECT OF FENTANYL
Number of dogs
Dose,
i.v.
b-cdkd
4 3 5 a SE, standard
0.01 0.02 0.04 error
TABLE 10 CITRATE ON BLEND PRESSURE IN VAGOTOMIZED Nonvagotomized dogs, maximal % decrease in blood pressure Mean
SEU
25.3 34.3 40.4
f 7.3 f 5.7 -c- 4.9
AND NONVAG~TOMIZED
DOGS
Vagotomized dogs, maximal % decrease in blood pressure Mean 2 1.3 25.7 33.9
SE
P
-+ 1.6 t 2.7 + 3.9
> 0.05 > 0.05 > 0.05
of the mean.
tolerance to the blood pressure effects of fentanyl citrate. Responses to intravenous injections of epinephrine (1 p.g/kg, i.v.) before and after the development of tolerance were compared and there was no indication of adrenergic blockade. In all instances, the response to epinephrine appeared to be potentiated. Typical hypertensive responses were observed after intravenous injections of DMPP, a potent ganglionic stimulant. Efiects on Femoral Blood Flow Intra-arterial injections of 0.010 and 0.050 mg of fentanyl citrate had no effect on femoral blood flow. Injections of 0.20 mg caused a decrease in vascular resistance of 14.4 and 32.6%; however, this represented a dose of approximately 0.020 mg/kg, which is an extremely high dose. DISCUSSION
The pharmacologic profile of fentanyl citrate indicates that this drug is a very potent morphine-like analgesic. It differs from morphine by its short duration of analgesic activity, lack of emetic activity, and minimal hypotensive activity. The behavioral effects in mice-increased spontaneous motor activity, circling, Straub tail reaction, mydriasis, increased muscle tone, hypersensitivity to touch, and death due to respiratory depression-were seen with both fentanyl citrate and morphine. A comparison of the analgesic EDSO’s for the two compounds indicates that fentanyl citrate is 188 times as potent as morphine on a weight basis. The therapeutic index in mice for fentanyl citrate is 775 and for morphine 31.3. The cornea1 blanching observed in mice with lethal doses of fentanyl citrate is probably due to a sympathetic discharge secondary to respiratory depression. A sympathetic discharge was observed to occur following respiratory depression in dogs. Cornea1 blanching is characteristically observed in mice following injection of high doses of sympathomimetic amines. The biphasic nature of the mortality dose response curve is probably due to respira-
60
J.
F.
GARDOCKI
AND
JOHN
YELNOSKY
tory depression. As can be seen from Table 3, maximum number of deaths occurred at a dose of 3 mg/kg. With increasing doses, closely spaced, there was noted a precipitous fall off in mortality, and at twice the aforementioned dose all of the animals survived. The absence of a similar curve for morphine may simply be due to the choice of the doses employed. Janssen and Jageneau (1958) reported similar curves for morphine in rats. These authors found that deaths following low doses of morphine were more readily prevented by nalorphine than were deaths following high doses of the analgesic. They ascribe death with low doses of morphine to a mechanism which is antagonized by nalorphine, e.g., respiratory depression. Studies on the mechanism of the biphasic mortality dose response curve are currently in progress and will be reported upon completion. The upper portion of the biphasic mortality dose response curve has been used to calculate an LDSO and subsequently the therapeutic index for fentanyl citrate. Since the anticipated use of this drug is in general anesthesia, the problem of respiratory depression from low doses of fentanyl citrate is readily circumvented by artificial respiration which is generally employed during anesthesia. As mentioned, effects of low doses of fentanyl citrate are readily antagonized by nalorphine. Both fentanyl citrate and morphine have a constipating effect in mice. Morphine appears to be more active than fentanyl citrate at approximately equivalent analgesic doses, but it also has a shorter duration of action than fentanyl citrate. With a twentyfold increase in dose, morphine is more active and also has a longer duration of action. Behavioral studies in dogs further extended the similarities between fentanyl citrate and morphine, The reversal of the fentanyl citrate-induced depression of the central nervous system by nalorphine, a specific morphme antagonist, is one of the major points common to fentanyl citrate and morphine. In addition, atropine antagonized the bradycardia induced by fentanyl citrate as it does the bradycardia observed following morphine. The vagi have been observed to play a major role in the bradycardia due to fentanyl citrate since the effectiveness of fentanyl citrate in producing bradycardia, in bilaterally vagotomized dogs, is significantly reduced. According to Schmidt and Livingston (1933) and McCrea and Meek (1926), the vagi also play a major role in the mechanism of the bradycardia due to morphine. One of the most notable differences between fentanyl citrate and morphine is the absence of emetic activity with fentanyl citrate. Similar doses of morphine produce a 60-90y0 incidence of emesis in the dosage range studied. The respiratory depressant properties of fentanyl citrate appear to be due to a central effect as observed in the experiments in cats. No effect on neuromuscular transmission could be observed in the presence of severe respiratory depression. The results of our studies on the hypotensive effect of fentanyl citrate have ruled out several possible mechanisms which could account for the lowering of the blood pressure observed with this drug. It does not appear probable that fentanyl citrate exerts a cholinergic or histamine-like effect since neither vagotomy nor pretreatment with either atropine or an antihistamine, Clistin @, blocked the hypotensive response. Peripheral vasodilation does not account for the hypotension as demonstrated by the absence of a significant change on the femoral vascular bed resistance following intraarterial injection of fentanyl citrate. Respiratory depression is not responsible for the
PHARMACOLOGY OF FENTANYL
CITRATE
61
depressor effect of the drug since this effect occurs when the animal is artificially
respired. Neither ganglionic nor adrenergic blockade can account for the hypotensive effect of fentanyl citrate. These possible mechanisms are excluded because (1) the increased vagal activity following fentanyl citrate is reversed by severing the preganglionic vagal fibers; (2) respiratory depression is accompanied by a marked hypertension; (3) fentanyl citrate does not antagonize the pressor response of epinephrine or DMPP. Studies on the hypotensive effect of fentanyl citrate are being continued. It should be noted, however, that the lowest doses used in the cardiovascular studies, 0.0025 and 0.005 mg/kg, which had little effect on the blood pressure in dogs, represents about 2 and 4 times the recommended human dose. The lack of hypotensive activity in the clinical dose of the drug is indicated in a report by Holderness et al. (1963). SUMMARY Fentanyl citrate is an analgesic that is particularly well suited for use in anesthesia because of its (1) high potency, (2) rapid onset and short duration of action, (3) absence of emetic activity, and (4) minimal hypotensive activity after intravenous administration. As with other morphinelike analgesics, the effects of fentanyl citrate are readily antagonized by nalorphine. Bradycardia is also easily reversed with atropine. ACKNOWLEDGMENTS We are indebted to Dr. A. P. Roszkowski for his study of the effects of fentanyl citrate on neuromuscular transmission, and to Mrs. R. H. Katz and Miss R. W. Ervin for their assistance in these studies. REFERENCES BIANCHI, C., and FRANCESCHINI,J. (1954). Experimental observations on Haffner’s method for testing analgesic drugs. Brit. 1. Pkarmacol. 9, 280-284. DAVID, A., LEITH-ROSS, F., and VALLANCE, D. K. (1957). Antitussive and other pharmacological properties of the diethylaminoethoxyethyl ester of au-diethylphenylacetic acid (oxeladin) . J. Pkarm.
Pkarmacol.
9, 446-458.
DECASTRO, J., and MUNDELEER, P.
(1959). Anethesie sans barbituriques. La neuroleptanalgesie. 16, 1022-1056. HOLDERNESS,M. C., CHASE, P. E., and Damps, R. D. (1963). Use of a narcotic analgesic and a butyrophenone with nitrous oxide for general anesthesia. Anesthesiology 94, 336-340. JANSSEN, P. A. (1962). A review of the chemical features associated with strong morphine-like activity. Brit. J. Anaestkesia 94, 260-267. JANSSEN, P. A., and JAGENEAU, A. H. (1958). Comparative analgesic activity, acute toxicity and tolerance development in rats for R875, morphine, pethidine and methadone. J. Pkarm. Pkurmacol. 10, 14-21. JANSSEN, P. A., NIFXEGEERS, C. J., SCHELLEKENS, K. H., VERBRUCGEN, F. J., and VAN NEUTEN, J. M. (1963). The pharmacology of Dehydrobenzperidol (R4749), a new potent and short acting neuroleptic agent chemically related to Haloperidol. Arzneimittel-forsck. 13, 205-211. LITCHFIELD, J. T., JR., and WILCOXON, F. (1949). A simplified method of evaluating dose-effect experiments. J. Pkarmacol. Exptl. Tkerup. 96, W-113. MCCREA, F. D., and MEEK, W. J. (1926). Action of morphine in slowing the pulse. J. Pkarmacol. Anestkesie,
Exptl.
Tkerap.
Analgesic,
Reanimation
99, 361-366.
MARSBOOM, R., MORTELMANS, J., and VERCRUYSSE,J. (1963). Neuroleptanalgesia in monkeys. Vet. Record 76, 132-133. PATON, W. D. M., and Z-us, E. J. (1949). The pharmacological actions of polymethylene bistrimethylammonium salts. Btit. J. Pkarmacol. 4, 381-400. SCHMIDT, C. F., and LIVINGSTON, A. E. (1933). The action of morphine on the mammalian circulation. J. Pkarmacol. Exptl. Therap. 47, 411-441.
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I., WENDEL, H., and Ross, S. D. (1961). A pharmacological comparison of phenazotine hydrobromide and morphine sulfate as narcotic analgesics. J. Pharmacol. Exptl. Therap. 132, 258-263. A study of some of the pharmacologic actions of YELNOSILY, J., and GARDOCKI, J. F. (1964). fentanyl citrate and droperidol. Toxicol. Appl. Pharmacol. 6, 63-70. YELNOSKY, J., KATZ, R., and DIETRICH, E. V. (1964). A study of some of the pharmacologic actions of droperidol. Toxicol. Appl. Pharmacol. 6, 37-47. SHEMANO,