Effect of hyperthermia on acute chloroquine toxicity in rabbits

EUROPEAN JOURNAL OF PHARMACOLOGY 25 (1974) 210-215. NORTH-HOLLAND PUBLISHING COMPANY

EFFECT

OF HYPERTHERMIA

ON ACUTE CHLOROQUINE IN RABBITS

TOXICITY

E. AYITEY-SMITH, G.L. BOYE, N. NICHANI and R.A. LEWIS Department of Pharmacology, University of Ghana Medical School, P.O.B. 4236, Accra, Ghana Received 3 July 1973

Accepted 22 October 1973

E. AYITEY-SMITH, G.L. BOYE, N. NICHANI and R.A. LEWIS, Effect of hyperthermia on acute chloroquine toxicity in rabbits, European J. Pharmacol. 25 (1974) 210-215. The problem of sudden and unexpected death after the parenteral administration of a therapeutic dose of chloroquine in febrile patients was investigated using rabbits. Hyperthermia was produced in both conscious and anaesthetized rabbits using a Megatherm Junior diathermy machine. Lead II of the electrocardiogram, respiration and blood pressure were monitored during slow i.v. injection of chloroquine. In hyperthermic rabbits, striking cardiac arrhythmias, circulatory collapse and death occurred at a dose level 1/3 as great as in normal rabbits. Animals that had been heated and allowed to cool before the injection, tolerated 2/3 of the lethal dose for normal rabbits, and twice as much as the hyperthermic rabbits. Hyperthermia Diathermy

Cardiovascular Chloroquine toxicity

1. Introduction In tropical Africa, the widespread prevalence of malaria has led to the frequent use of chloroquine. The drug is often given by injection, especially to infants with fever. In the last decade, the toxicity o f chloroquine has been studied in both the acute (Cann and Verhulst, 1961; Kiel, 1964; Carson et al., 1967; Michael and Aiwazzadeh, 1970) and chronic (Whitsnant et al., 1963; Hughes et al., 1971) aspects. Cann and Verhulst (1961) described four cases in which children who ingested large doses of chloroquine died of cardiovascular and respiratory complications within two and a half hours. Similar reports by Michael and Aiwazzadeh (1970) describe deaths due 1o cardiotoxic action of chloroquine. Moreover, there are numerous unpublished observations, from various parts of Africa, of sudden death soon after the i.m. injection o f the standard dose of chloroquine into children with high fever due to malaria. In fact, many pediatric units have specified that personnel should not inject chloroquine until the patient's fever

Arrhythmias Rabbits

has been lowered by cold sponging or the administration of an antipyretic. The purpose o f this investigation was to ascertain the role of fever in determining the toxicity o f chloroquine, to explore the cause of death in such cases, and to see if there was a justification for the clinical practice of lowering temperature before the injection of chloroquine.

2. Materials and methods 2.1. General procedure

Experiments were performed using male and female rabbits weighing 2 . 3 - 3 . 0 kg. The animals were kept in an animal house where they were fed a standard diet. There were 2 separate experiments. In the first study, the animals were not anaesthetized, while in the second study, anaesthesia was used. The conscious rabbits were restrained on a wooden

E. A yitey-Smith et al., Hypertherrnia and chloroquine toxicity frame and placed between the electrodes of a Megatherm Junior diathermy machine. This machine produces short radio waves which penetrate and generate heat in the internal organs without causing tissue damage (Stacy et al., 1955). The temperature of the animals was measured with a clinical thermometer inserted into the rectum. The process was discontinued when the temperature had risen 4°F. The difference between the mean lethal dose was compared according to the Student's t-test (Steel and Torrie, 1960) and were considered to be statistically significant when p was less than 0.05.

A). Respiration was recorded with a bellows pneumograph.

3. Results 3.1. Lethal dose o f ehloroquine In the conscious control rabbits, the lethal dose of chloroquine was 51 mg/kg body weight (table 1). In the anaesthetized control rabbits, where the rate of Table 1 Chloroquine toxicity in conscious rabbits (mg/kg).

2.2. Unanaesthetized rabbits

Control (101 +- I°F)

Heated and cooled (101 -+ I°F)

Hyperthermic (105 -+ I°F)

41.6 48.0 61.3 50.0 56.0 62.0 52.0 39.3

18.7 18.0 34.0 44.2 32.0 24.0 22.0 31.6 41.5 37.0

11.8 10.8 26.2 9.3 11.2 18.4 9.3 32.0 14.0 18.0

Mean

51

30

16

S.D. S.E. P-value

12 4.5

10 3.4 < 0.001

7.6 2.6 < 0.001

Lead II of the electrocardiogram was recorded using a Siemens Cardiomat. Chloroquine was injected at the rate of 1.0 mg/kg body weight/min into the marginal ear vein using a syringe. There were 3 series of trials in this experiment. In the first or control series the animals were not heated before the injection of chloroquine. In the second series the animals were heated and then immediately injected with chloroquine. In the third series, the animals were allowed to cool off over a period of approximately 1 hr before the injection of chloroquine. 2. 3. Anaesthetized rabbits The animals were given an i.p. injection of 1 ml/kg body weight of an aqueous solution of 3% chloralose and 3% pentobarbital. There were 3 series of trials in this experiment. In 1 series the animals were heated but not injected with chloroquine. In the next series the animals were not heated but were injected with chloroquine. In the last series the animals were heated and injected with chloroquine. The chloroquine was infused into a femoral vein at the rate of 0.63 mg/kg body weight/min, using a Harvard model 975 compact infusion pump. In these animals, the electrocardiogram, the respiratory rate and the femoral blood pressure were recorded at 5 min intervals, using an E and M physiograph. The femoral artery and vein of the rabbit were cannulated with polyethylene tubing. 100 i.u. of heparin was injected into the femoral vein. Blood pressure was measured from the femoral artery by means of a linear core pressure transducer (P-1.000

211

Table 2 Chloroquine toxicity in anaesthetized rabbits (mg/kg).

Mean S.D. S.E. P-value

Control (101 -+ I°F)

Hyperthermic (105 -+ I°F)

45.1 56.2 57.8 22.3 74.3 85.7 32.0

13.6 11.0 20.7 14.3 10.8 8.6 42.8

53 22 9.3

17 12 4.9 < 0.001

212

E. A yitey-Smith et al., Hyperthermia and chloroquine toxicity

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Fig. 1. Lead I1 of the E.C.G. in conscious rabbits injected with chloroquine 1.0 mg/kg/min. A, control; B, hyperthermic; and C, heated and then cooled before the start of injection. The n u m b e r below the tracing indicates the n u m b e r of rain after the start of the chloroquine injection.

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Fig. 2. Typical blood pressure, E.C.G. (Lead II) and respiration in unanaesthetized rabbit which was made hyperthermic but was not infused witb chloroquine. The distance in 'mm" between 2 consecutive inspirations is inversely related to the rate (25 m m equals 1 sec). The n u m b e r given below the tracings indicates the min elapsed after heating (5 experiments were performed).

213

E. A yitey.Smith et al., Hyperthermia and chloroquine toxicity

infusion was slightly lower, the lethal dose was 53 mg/kg body weight (table 2). In the hyperthermic animals the lethal dose was 16 mg/kg in the conscious animals, and 17 mg/kg in the anaesthetized rabbits. Thus, fever caused a 3-fold increase in the toxicity of chloroquine. Finally, in the rabbits that were heated and then allowed to cool before the injection of chloroquine, the lethal dose was 30 mg/kg. This figure is intermediate between the lethal dose for the hyperthermic and the control rabbits.

Such striking changes were not seen in the early stages in the electrocardiogram of the normal rabbit (fig. 1A), although an hour after the start of the chloroquine injection there were abnormalities in the electrocardiogram. In the rabbits that were heated and cooled before the injection of chloroquine, bradycardia was seen after 30 min, and partial A - V block after 40 min (fig. 1C).

3.2. Effect o f chloroquine on the electrocardiogram in conscious rabbits

Injection of chloroquine into anaesthetized rabbits caused an increase in respiratory rate (fig. 3E). Merely heating anaesthetized rabbits had a similar effect (fig. 2D). Infusion of chloroquine into these hyperthermic animals caused a further increase in the respiratory rate as well as an increase in the depth of respiration (fig. 3F). In the terminal stages of chloroquine infusion, respiration became irregular, depressed and gasping (fig. 4H). The signs of respiratory distress were preceded by changes in the electrocardiogram and by a marked fall in blood pressure (fig. 3F). In the un-

In the hyperthermic rabbits, the injection of chloroquine (fig. IB) was followed by striking changes in the electrocardiogram. At 10 min there was bradycardia, which was followed at 20 min by bigeminal rhythm with prolongation of P - R interval and widening of Q - R - S complex. These changes progressed to ventricular flutter, then fibrillation and death of the animal.

2~

3.3. Effect o f chloroquine on respiration in anaesthetized rabbits

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Fig. 3. Blood pressure Lead 1I of the E.C.G. and respiration in anaesthetized rabbits infused with chloroquine (0.63 mg/kg/min). E, control non-heated, and F, hyperthermic animals. The distance in 'mm' between 2 consecutive inspirations is inversely related to the respiratory rate (25 mm equals 1 sec). The number given below the tracings indicates the min elapsed after the start of the chloroquine injection.

2l 4

E. Ayitey-Smith et al., Hyperthermia and chloroquine toxicity

4. Discussion

G mm/Hg. 4%,,,,.r~,,~

E.C.G.

.

~/,a/~gg~

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mmlHg. 80 0 E.C.G. Rcspiration

/,0 minutes

Fig. 4. Blood pressure, lead 1I of the E.C.G. and respiration in anaesthetized rabbits infused with chloroquine 0.63 mg/kg/ rain. The tracings were obtained from two rabbits (G, control non-heated; and H, hyperthermic) in agonal state (120 and 40 rain respectively after tile start of chloroquine infusion).

anaesthetized rabbits, cardiovascular collapse and respiratory failure led to the occurrence of convulsions. 3.4. Effect o f chloroqu&e on blood pressure and E. C.G. in anaesthetized rabbits

When chloroquine was infused into hyperthermic rabbits, during the first 15 min, there was a fall in systolic and mean blood pressures (fig. 3F). By 30 min, the blood pressure fell to 0, with occasional spikes corresponding to the bigeminal rhythm. Ventricular tachycardia and vascular collapse also occurred in non-heated rabbits infused with chloroquine, but at a later time (fig. 4G). In the anaesthetized rabbits, heated but not infused with chloroquine, there were no obvious cardiovascular changes during 120 min of observation (fig. 2D).

The 3-fold increase in toxicity when chloroquine was injected into hyperthermic rabbits was striking. However, since animals that had been heated and allowed to cool showed a moderate increase in toxicity, it is apparent that the fever produced by diathermy had a deleterious action on the animals, in particular with respect to ability to tolerate chloroquine. This action cannot be explained on the basis of tissue damage (Stacy et al., 1955). Moreover. the greater toxicity of chloroquine in the animals that remained hyperthermic must have been in part due to the deleterious action of fever, and in part due to a direct interaction between fever and chloroquine. Much work has been done on the production of fever by the administration of drugs (Lomax, 1970) but there has been little work on the effect of fever on the toxocity of drugs. Nevertheless, salicylates (Goodman and Gilman, 1970) and ether (Seevers et al., 1938) are known to be more toxic in febrile patients. Curare (Paton and Zaimis, 1951) shows a greater activity with rising temperature. The increased toxicity of drugs in hyperthermia may be related to the increase in the rate of chemical reactions with rising temperature. In the rabbit, conscious or anaesthetized, the most vulnerable organ was the heart. Early in the course of chloroquine injection, abnormalities were seen in the electrocardiogram, and circulatory collapse was associated with marked changes in the rate and rhythm of the heart. Apparently, chloroquine, like quinidine, is an effective agent against cardiac arrhythmias when used in small doses (Bellet, 1961). In our experiments, chloroquine induced arrhythmias only at high dosage in normal rabbits, but at low dosage in hyperthermic rabbits. It has been shown that chloroquine is a potent local anaesthetic (Jindal et al., 1960) and this might explain its action on the heart, since procaine and its derivatives have a pronounced action on the heart. Prolongation of the P - R interval and widening of the Q - R - S complex observed after the injection of chloroquine suggest decreased intraventricular conduction, which could lead to the occurrence of ventricular arrhythmias. Circulatory collapse was due to myocardial depression rather than peripheral vasodilatation because systolic and mean blood pressure fell before the dias-

E. A yity.Smith et al., Hyperthermia and chloroquine toxicity

tolic pressure was affected. Similar observations and conclusions were made when chloroquine was injected into dogs (Michael and Aiwazzadeh, 1970). Apparently, the respiratory depression, observed by other workers who injected chloroquine into anaesthetized dogs (Chinyanga and Vartanian, 1972) did not occur in the rabbits until after the cardiovascular changes had appeared. This discrepancy may be due to species difference, difference due to anaesthesia, or difference in the rate o f injection o f chloroquine. The clinical practice o f reducing fever before injecting chloroquine has a sound scientific basis. The recommended dose o f 5 mg/kg o f body weight is probably too close to the lethal dose in febrile individuals in view of the 3-fold increase in toxicity associated with hyperthermia, and the wide variation in toxic dose from one individual to another. When it is necessary to inject chloroquine before the fever can be brought down, the initial dose should be reduced to 2 mg/kg body weight, and repeated after a suitable interval.

References Bellet, S., 1961, Chloroquine in the management of cardiac arrhythmias, Practitioner 186, 19. Cann, H.M. and H.L. Verhulst, 1961, Fatal acute chloroquine poisoning in children, Pediatrics 27, 95.

215

Carson, J.W., M.L. Barringer and R.E. Jones, 1967, Fatal chloroquine ingestion, Pediatrics 40, 449. Chinyanga, H.M. and G.A. Vartanian, 1972, Respiration depression induced by a quinoline derivative, chloroquine, Ghana Med. J. 11, 2. Goodman, L.S. and A. Gilman, 1970, The Pharmacological Basis of Therapeutics, 4th edn. (The MacMillan Company, New York) p. 326. Hughes, J.T., M. Esiri, J.M. Oxbury and C.W.M. Whitty, 1971, Chloroquine myopathy, Quart. J. Med. 64, 85. Jindal, M., M.A. Patel and A.D. Joseph, 1960, Local anaesthetic action of antimalarials, Arch. Intern. Pharmacodyn. Therap. 137 (1-2), 132. Kiel, F.W., 1964, Chloroquine suicide, J. Amer. Med. Assoc. 190, 398. Lomax, P., 1970, Drugs and body temperature, Intern. Rev. Neurobiol. 12, 1. Michael, T.A.D. and S. Aiwazzadeh, 1970, the effects of acute chloroquine poisoning with special reference to the heart, Fundamentals Clin. Cardiol. 79,831. Paton, W.D.M. and E.J. Zaimis, 1951, The action of d-tubocurarine and decamethonium on respiration and other muscles in the cat, J. Physiol. (London) 112, 311. Seevers, M.H., W.H. Cassels and T.J. Becker, 1938, The role of hypercapnia and pyrexia in the production of 'ether convulsions', J. Pharmacol. Exptl. Therap. (proceedings) 63, 33. Stacy, R.W., D.T. Williams, R.E. Worden and R.O. McMorris, 1955, Essentials of Biological and Medical Physics (McGraw-Hill, New York) p. 481. Steel, R.G.D. and J.H. Torrie, 1960, Principles and Procedures of Statistics (McGraw-Hill, New York) p. 99. Whisnant, J.P., R.E. Espinosa, R.R. Kierland and E.A. Lambert, 1963, Chloroquine neuromyopathy, Proc. Staff Meet. Mayo Clin. 38, 50.