- Email: [email protected]
ANTAGONISM OF THE EFFECTS OF MIDAZOLAM ON PHRENIC NERVE ACTIVITY IN THE DOG BY RO15-1788 AND RO15-3505
Br. J. Anaath. (1984), 56,1161
ANTAGONISM OF THE EFFECTS OF MIDAZOLAM ON PHRENIC NERVE ACTIVITY IN THE DOG BY RO15-1788 AND RO15-3505 G. GORDON, E. M. GRUNDY, D. AL-KHUDHAIRI, D. J. ANDERSON AND J. G. WHITWAM
SUMMARY
thfrr m i ryi m H n v f nf rrtiim rrf thf prt-inn nf midpTninm 1 aiigjpiitinfl riiat Knth nntugnnren: haA p Hiirai-inn nf
action at least as long as that of midazolam.
f
The discovery of specific benzodiazepine receptors (Mohler and Okada, 1977; Squires and Braestrup, 1977) was followed by the identification of two benzodiazepine receptors BZi and BZ2 (Braestrup and Nielsen, 1980) and the demonstration of endogenous benzodiazepine antagonists, the ($carbolines (Braestrup and Nielsen, 1981). These studies lead to the search for synthetic benzodiazepine antagonists and one such compound, Ro 15-1788 (Hunkeleretal., 1981),has been shown to antagonize the effects of both Ro 11-3128 (3-methylclonazepam) (Darragh, Lambe and Brick, 1981; Darragh et al., 1981) and diazepam (O'Boyle et al., 1983) in man. However, it has been suggested that in high doses Ro 15-1788 may itself have benzodiazepine-like properties and could be a partial agonist (Nutt, Cowen and Little, 1982). The present study investigated the effects of Ro 15-1788 and of the more recently introduced Ro 15-3 50 5 on the depression of phrenic nerve activity induced by midazolam. This drug was chosen as the test benzodiazepine because it is administered in water, free of other vehicles, it has a relatively short half-life and, unlike diazepam, its metabolites are G. GORDON, M J . , CH.B., F.F.A.R.CS., E. M. GRUNDY, B.SC, M.B.,
CH.B., M.R.CJ"., F.F-A.R.CS. (Department of Anaesthetics); D. J. ANDERSON, BJHARM., PH.D., M.P.S., M.LBIOL.; Hammersmith
Hospital, Du Cane Road, London W12 OHS. D. AL-KHUDHATJU, M.B., OLB., F.F.A.R.C.S.I., Northwick Park Hospital, Watford Road, Harrow, Middlesex HA1 3UJ. J. G. WHTTWAM, MJI., CH.B., FH.D., F.R.C.P., F.F.A.R.CS., Department of Anaesthetics, Royal Postgraduate Medical School, Du Cane Road, London W120HS. Correspondence to G. G.
Downloaded from http://bja.oxfordjournals.org/ at University of Birmingham on August 27, 2015
Experiments were performed on 14 anarnthftized, artificially ventilated dogs, in which efferent activity in the phrenic nerve was recorded and blood-gas tensions, arterial pH and core temperature were controlled. Doses of miHnTnlam between 0.2mgkg~' and 2mgkg~ 1 abolished phrenic nerve activity for periods between 30 and 90min. Rol5-1788 in doses between O.Mmgkg"1 and lmgkg" 1 and Rol5-3505 0.2-2mgkg"' reversed the effects of miHpTrdpm on phrenic nerve activity. Prior administration of these drugs either abolished or greatly inhibited the action of miHpminm When the preparations were observed for up to 2 h,
cleared as rapidly as the parent compound (Allonen, Ziegler and Klotz, 1981; Smith, Eadie and O'Rourke Brophy, 1981). In addition, data on its effects on phrenic nerve activity in dogs were already available (Whitwam et al., 1980; AlKhudhairi, Askitopoulou and Whitwam, 1982). In man, midazolam and diazepam cause a comparable degree of respiratory depression (Forster et al., 1980; Power, Morgan and Chakrabarti, 1983). MATERIALS AND METHODS
Ro 15-1788 was provided as a fine powder by Roche Products Ltd. Ten milligram was suspended in each 1 ml of a solution of 5% acacia with the addition of polyoxyethylene sorbiton mono oleate 0.1 ml to each 10 ml of suspension. Ro 15-3505 was presented in»a 2:3 water:organic solution of pharmacologically inert materials, the full formulation of which is not available for general publication. Experiments were performed on 14 mongrel dogs (mean weight 16.65 kg) anaesthetized with methohexitone lOmgkg"1 i.v. followed by a 1% solution of a-chloralose, administered initially as a bolus dose of 3 ml kg"1 and then by a continuous infusion of 2mlkg~Ih~I. Suxamethonium 1 1-2 mg kg" h"1 was administered i.v. and the lungs ventilated artificially with oxygen-enriched air via a a cuffed endotracheal tube. Catheters were inserted to the inferior vena cava via a femoral vein, and to a femoral artery. Therightphrenic nerve was exposed in the neck and part of it was dissected free from surrounding tissues, desheathed and cut distally, immersed in mineral oil and mounted on bipolar silver-silver chloride electrodes to record efferent © The Macmillan Press Ltd 1984
BRITISH JOURNAL OF ANAESTHESIA
1162
physiological saline solution before and after each injection. RESULTS
Phrenic nerve activity
In these preparations, anaesthetized with chloralose in which arterial blood-gas tensions were carefully controlled, midazolam 0.2mgkg-1 i.v. caused severe depression of phrenic nerve activity (PNA) for periods up to 40min (fig. 1). Higher doses caused a longer period of depression, but even with a dose of 2 mg kg"1 the maximum duration of significant PNA depression was less than 90 min (Whitwam etal., 1980). In the doses used, neither Ro 15-1788 nor Ro 153505 when administered first, produced any significant change in PNA. When midazolam 0.2-2mgkg- 1 was administered after either antagonist it did not abolish PNA, but rather produced either no change in PNA (fig. 2) or at most a transient decrease in activity of between 25 and 80%, which returned to control values within 15 min (fig. 3). Subsequent observation for periods up to 2 h showed no further decrease in PNA, suggesting that the action of the antagonist was at least as long as midazolam. When administered after midazolam, both Ro 15-1788 0.06-0.75mgkg-1 and Ro 15-3505 0.2mgkg-1 or 2mgkg"' produced a rapid reversal of the effect of midazolam on PNA (figs 4, 5). Control values were reached within 10 min of their administration, and there was no evidence of a return of agonist activity. The administration of the Ro 15-1788 solvent 0.006-0.075 ml kg"1 was not associated with any significant alteration in PNA. Cardiovascular changes
Following the administration of midazolam 0.2 mg kg"1 there was a 6% decrease in mean arterial
lUlJJUU.
IPNA
PNA I H l H t l
1
1 10s
Midazolam 02 mg kg"1
£
'
45
60
Time (min)
FlO. 1. The effect of a m'ngV dose of midazolam on efferent phrenic nerve activity in one dog. PNA»» Phrenic nerve activity; IPNA = integrated phrenic nerve activity.
Downloaded from http://bja.oxfordjournals.org/ at University of Birmingham on August 27, 2015
activity which was processed through a preamplifier (Tektronix 122) rectified, integrated (Neurolog NL 703) and displayed. PaOz , Pacc>2 j arterial pH and core temperature were maintained within the ranges.21.4-35.6kPa, 5.1-6.7kPa, 7.25-7.39 and 37-39°C, respectively. During each investigation these values were maintained within narrow limits and during each period of observation they were returned to the control values measured at the start in each preparation, by changes in ventilation, Flch or the administration of sodium bicarbonate. The phrenic nerve activity and its integrated signal were displayed on an oscilloscope (Tektronix 565) and, together with the ECG, beat-by-beat heart rate, intravascular pressures and intratracheal pressure, recorded on an ultraviolet recorder (SE Laboratories type 2115). Total activity in the phrenic nerve per minute was calculated by multiplying the peak height of the integrator output by the frequency of the bursts of activity per minute. Either Ro 15-1788 (six dogs) or Ro 15-3505 (eight dogs) was administered in any one preparation. In the latter group, six animals received midazolam 0.2 mgkg- 1 or 2 mgkg-1 initially, followed in each case by the same dose of Ro 15-3505. In the remaining animals in this group, the administration sequence was reversed: Ro 15-3505 1 or 2 mgkg-1 was followed by midazolam 0.2 mgkg"1 or 2 mgkg"1. In the Ro 15-1788 group, in order to determine the effect, if any, of the solvent, each dose of the antagonist was preceded by the administration of a volume of solvent equal to that of the succeeding Ro 15-1788. Three animals received midazolam 2 mgkg- 1 initially, followed by Ro 15-1788 0.06-0.75 mgkg"1, while in the remaining dogs midazolam 2mgkg- 1 was preceded by Ro 15-1788 0.15-1.0 mgkg- 1 . Ah* drugs were administered via the catheter in the inferior vena cava, which was flushed with
MIDAZOLAM AND BENZODIAZEPINE ANTAGONISTS
IPNA
)MiMUk
MMKkkAm
PNA
{llMJUUl
1163
tdLMU.
UAJJiA
*-
Time (min) Ro 15-3505 1mgkg' 1
Midazolam 0.2 mgkg" 1
FIG. 2. The effects on efferent phrenic nerve activity of Ro 15-3505 and midazolam. PNA = phrenic nerve activity; IPNA = integrated phrenic nerve activity.
PNA
__f
_t
10i
5
Sotvem 0.1 mg kg' 1
"
Ro 15-1788 Imgkg^ 1
10
•
30
'
90
Time (min) Midazolam 2 mgkg' 1
FIG. 3. The effects of the solvent, Ro 15-1788 and midazolflm on efferent phrenic nerve activity. PNA = Phrenic nerve activity; IPNA — integrated phrenic nerve activity.
PNA 1
10 s Midazolam 2 mgkg- 1
Time (nun)
'
tt1
•
30
Ro 15-1788 1mgkg' 1
FIG. 4. The effects on efferent phrenic nerve activity of midazolam and Ro 15-1788. PNA = Phrenic nerve activity; IPNA — integrated phrenic nerve activity.
PNA
IIIMHll ^
II
,|IM"VM
5
10 s
15
» ' '
30
Time (min) Midazolam 0.2 mgkg- 1
Ro 15-3505 0.2 mgkg' 1
Fro. 5. The effects on efferent phrenic nerve activity of mida7nlnm and Ro 15-3505. PNA = phrenic nerve activity; IPNA = integrated phrenic nerve activity.
Downloaded from http://bja.oxfordjournals.org/ at University of Birmingham on August 27, 2015
IPNA
BRITISH JOURNAL OF ANAESTHESIA
1164 pressure (n.s.). The subsequent administration of Ro 15-3505 0.2 mgkg- 1 caused an increase in mean arterial pressure to within 1 % of control values. Because of the variation in the dose of Ro 15-1788, statistical analysis could not be applied to the cardiovascular changes in this part of the study. However, the administration of midazolam caused the expected slight decrease in mean values which returned to control values following Ro 15-1788. There was never any overshoot in arterial pressure.
In conclusion, this study demonstrated the effectiveness of Ro 15-3505 and Ro 15-1788 in antagonizing the effects of midazolam. Effective specific benzodiazepine antagonists may soon be available for clinical use. REFERENCES
Al-Khudhairi, D., Askitopoulou, H., and Whitwam, J. G. (1982). Acute "tolerance" to the central respiratory effecu of midazolam in the dog. Br. J. Anaatk., 54, 953. Allonen, H., Ziegier, G., and Klotz, U. (1981). Effect kinetics of midazolam; a new hypnotic benzodiazepine. Clin. Pharmacol. 7Tk*r.,30,653. Braestrup, C , and Nielsen, M. (1980). Multiple benzodiazepine receptors. Trends Nruro. Sd., (Dec.), 301. (1981). GABA reduce* binding of 3H-methyl carboline-3 carboxylate to brain benzodiazepine receptors. Natur*(Lond.), 294,472. Darragh, A., Lambe, R., and Brick, I. (1981). Reversal of benzodiazepine induced sedation by intravenous Ro 15-1788. Lanctt, 2,1042. Scully, M., O'Boyle, C , and Wilson Downie, W. (1981X Investigation in man of the efficacy of a benzodiazepine antagonist Ro 15-1788. Lanctt, 2, 8. Fonter, A., Gardez, J. P., Suter, P. M., and Gemperle, M. (1980). Respiratory depression by miHnTnlnm and diazepam. Antsthaioiogy, 53,194. Hunkeler, W., Mohler, M., Pieri, L., Pole, P., Bonetti, E., Cumin, R., Schaffner, R., and Haefeley, W. (1981). Selective antagonists of benzodiazepines. Nantrt (Loud.), 290, 514.
Downloaded from http://bja.oxfordjournals.org/ at University of Birmingham on August 27, 2015
DISCUSSION
This study showed that Ro 15-1788 and Ro 15-3505 are effective antagonists of the central respiratory effects of midazolam, and that they have no significant intrinsic effects in the doses used. It also showed that pre-treatment with both of these antagonists abolishes, or greatly inhibits, the effects of the subsequent administration of midazolam. The problem with this type of experimental work is that only one dose of any one drug may be studied in one preparation in one day. The data presented here do not allow any conclusions to be drawn about the potencies of these drugs with respect to midazolam, nor can any conclusion be drawn about the precise duration of action of the two drugs. Suffice it to say that doses of both antagonist drugs comparable to those of midazolam were effective and that there was never any evidence of a return of the effects of midazolam within the known timecourse of the action of these drugs in these preparations (30-90 min). Hence, the durations of action of both drugs are presumably comparable to that of midazolam. The present study on animals was concerned with a specific action of only one benzodiazepine, midazolam, a drug which, in successive doses, is known to induce the rapid development of tolerance in these animals (Al-Khudhairi, Askitopoulou and Whitwam, 1982). Darragh and colleagues (1981) found that combined oral doses of Ro 15-1788 200 mg and the benzodiazepine 3-methylclonazepam 8mg in human volunteers caused effective antagonism of the psychomotor effects of the benzodiazepine, while the same group (Darragh, Lambe and Brick, 1981) found in volunteers that, following combined oral doses of Ro 15-1788 100 mg and 3methylclonazepam 35 mg, the eventual onset of sedation was reversed by a further dose of Ro 15-1788 20 mg i.v. More recently, O'Boyle and colleagues (1983) have shown that a dose of Ro 15-1788 200 mg
in man attenuated markedly or abolished the various effects of diazepam (psychomotor, amnesic and affective). However, the doses were administered orally, simultaneously and in a ratio of 200 mg: 20 mg, that is 10:1. Midazolam is approximately twice as potent as diazepam (Whitwam, personal communication). In the present study, doses as small as Ro 15-1788 0.06 mgkg"1 and Ro 15-3505 1 0.2mgkg- i.v. were capable of preventing or reversing the effects of midazolam up to 2mgkg"1 i.v., that is, effective dose ratios of 0.03:1 and 0.1:1, respectively. However, the present study is not comparable to the oral studies on human volunteers, but perhaps similar results could have been achieved with smaller oral doses of Ro 15-1788 because the precise dose requirements of the various antagonists drugs and benzodiazepines are not accurately known. Naloxone-induced reversal of the effects of opiates may be accompanied by a large rebound increase in arterial pressure (Tanaka, 1974). However, reversal of the effects of midazolam by Ro 153505 was accompanied by small increases in arterial pressure (5%) and heart rate (1%), which were not statistically significant.
MIDAZOLAM AND BENZODIAZEPINE ANTAGONISTS
Pharm.,19,271. Squires, R. F., and Braestrup, C. (1977). Benzodiazepine recepton in the rat brain. Naturt (Land.), 266, 732. Tanaka, G. (1974). Hypertensive reaction to nalozone.
J.A.M.A., 228,25. Whitwam, J. G., Scott, W., Kurimoto, S., Orchard, C , and Chakrabarti, M. (1980). Cardiovascular effects of midazolam (Ro21-3981)inthedog. Br. J. Anaath., 52.954P.
ANTAGONISME DES EFFETS DU MIDAZOLAM SUR L'ACTTVTTE DU NERF PHRENIQUE CHEZ LE CHEIN PAR LE Ro 15-1788 ET Ro 15-3505 RESUME
Les etudes ont et£ fahes sur 14 chiens endormis et ventQcs •r^ifift^llfrnrnT chez qui l'activiti eff£rente du nerf phrenique a tti enregistrce, les gaz du sang, le pH art£riel et la temperature centrale etant controles. Des doses de miHiiTnlom comprises entre O^mgkg"1 et 2mgkg~ 1 supprimatent ractivite du nerf phreniquepourdesdureesallantde30a90min. Le Ro 15-1788, a des doses de 0,06-1 mgkg-' et le Ro 15-3505 a des doses de 0,2—2mgkg"1 anmilai^nr les effets du midazolam sur l'actrvit£ du nerf phrenique. Une administration prealable de ces agents supprimait ou inbibait fortement l'action du midazolam. Lorqu'on poursuivait l'etude jusqu'a deux heure*, il n'y avait pas de signes de reapparhion de l'action du midazolam, ce qui permet de penser que les deux antagonistes ont une duree d'action au mnin« f*ra\* acclle du midazolam.
ANTAGONISMO DE LOS EFECTOS DEL MIDAZOLAN SOBRE LA ACITVIDAD DEL NERVIO FRENICO EN EL PERRO POR Ro 15-1788 Y Ro 15-3505 SUMARIO
Se Uevaron a cabo experimentos en 14 perros anestesiados artificiahnente ventilfldos en los cuales se registro la actividad eferente del nervio frenico y se controlaron las t
Downloaded from http://bja.oxfordjournals.org/ at University of Birmingham on August 27, 2015
Mohler, H., and Okada, T. (1977). Benzodiazepine receptor: Demonstration in the central nervous system. ScUnce, 198, 849. Nutt, D., Cowen, P., and Little, M. (1982). Unusual interactions of benzodiazepine receptor antagonists. Naturt (Land.), 29S, 436. CBoyk, C , Lambe, R., Darragh, A., Taffe, W., Brick, I., and Kenny, M. (1983). Ro 15-1788 antagonizes the effects of diazepam in man without affecting its bioavailability. Br. J. Anaesth., 55, 349. Power, S. H., Morgan, M., and Chakrabarti, M. K. (1983). Carbon dioxide response curves following midazolam and diazepam. Br. J. Anaath., 55,837. Smith, M. T., Eadie, M. J., and O*Rourke Brophy, T. (1981). The phannacokinetics of rniAa-m\am in man. Eur. J. Gin.
1165
ANTAGONISM OF THE EFFECTS OF MIDAZOLAM ON PHRENIC NERVE ACTIVITY IN THE DOG BY RO15-1788 AND RO15-3505 G. GORDON, E. M. GRUNDY, D. AL-KHUDHAIRI, D. J. ANDERSON AND J. G. WHITWAM
SUMMARY
thfrr m i ryi m H n v f nf rrtiim rrf thf prt-inn nf midpTninm 1 aiigjpiitinfl riiat Knth nntugnnren: haA p Hiirai-inn nf
action at least as long as that of midazolam.
f
The discovery of specific benzodiazepine receptors (Mohler and Okada, 1977; Squires and Braestrup, 1977) was followed by the identification of two benzodiazepine receptors BZi and BZ2 (Braestrup and Nielsen, 1980) and the demonstration of endogenous benzodiazepine antagonists, the ($carbolines (Braestrup and Nielsen, 1981). These studies lead to the search for synthetic benzodiazepine antagonists and one such compound, Ro 15-1788 (Hunkeleretal., 1981),has been shown to antagonize the effects of both Ro 11-3128 (3-methylclonazepam) (Darragh, Lambe and Brick, 1981; Darragh et al., 1981) and diazepam (O'Boyle et al., 1983) in man. However, it has been suggested that in high doses Ro 15-1788 may itself have benzodiazepine-like properties and could be a partial agonist (Nutt, Cowen and Little, 1982). The present study investigated the effects of Ro 15-1788 and of the more recently introduced Ro 15-3 50 5 on the depression of phrenic nerve activity induced by midazolam. This drug was chosen as the test benzodiazepine because it is administered in water, free of other vehicles, it has a relatively short half-life and, unlike diazepam, its metabolites are G. GORDON, M J . , CH.B., F.F.A.R.CS., E. M. GRUNDY, B.SC, M.B.,
CH.B., M.R.CJ"., F.F-A.R.CS. (Department of Anaesthetics); D. J. ANDERSON, BJHARM., PH.D., M.P.S., M.LBIOL.; Hammersmith
Hospital, Du Cane Road, London W12 OHS. D. AL-KHUDHATJU, M.B., OLB., F.F.A.R.C.S.I., Northwick Park Hospital, Watford Road, Harrow, Middlesex HA1 3UJ. J. G. WHTTWAM, MJI., CH.B., FH.D., F.R.C.P., F.F.A.R.CS., Department of Anaesthetics, Royal Postgraduate Medical School, Du Cane Road, London W120HS. Correspondence to G. G.
Downloaded from http://bja.oxfordjournals.org/ at University of Birmingham on August 27, 2015
Experiments were performed on 14 anarnthftized, artificially ventilated dogs, in which efferent activity in the phrenic nerve was recorded and blood-gas tensions, arterial pH and core temperature were controlled. Doses of miHnTnlam between 0.2mgkg~' and 2mgkg~ 1 abolished phrenic nerve activity for periods between 30 and 90min. Rol5-1788 in doses between O.Mmgkg"1 and lmgkg" 1 and Rol5-3505 0.2-2mgkg"' reversed the effects of miHpTrdpm on phrenic nerve activity. Prior administration of these drugs either abolished or greatly inhibited the action of miHpminm When the preparations were observed for up to 2 h,
cleared as rapidly as the parent compound (Allonen, Ziegler and Klotz, 1981; Smith, Eadie and O'Rourke Brophy, 1981). In addition, data on its effects on phrenic nerve activity in dogs were already available (Whitwam et al., 1980; AlKhudhairi, Askitopoulou and Whitwam, 1982). In man, midazolam and diazepam cause a comparable degree of respiratory depression (Forster et al., 1980; Power, Morgan and Chakrabarti, 1983). MATERIALS AND METHODS
Ro 15-1788 was provided as a fine powder by Roche Products Ltd. Ten milligram was suspended in each 1 ml of a solution of 5% acacia with the addition of polyoxyethylene sorbiton mono oleate 0.1 ml to each 10 ml of suspension. Ro 15-3505 was presented in»a 2:3 water:organic solution of pharmacologically inert materials, the full formulation of which is not available for general publication. Experiments were performed on 14 mongrel dogs (mean weight 16.65 kg) anaesthetized with methohexitone lOmgkg"1 i.v. followed by a 1% solution of a-chloralose, administered initially as a bolus dose of 3 ml kg"1 and then by a continuous infusion of 2mlkg~Ih~I. Suxamethonium 1 1-2 mg kg" h"1 was administered i.v. and the lungs ventilated artificially with oxygen-enriched air via a a cuffed endotracheal tube. Catheters were inserted to the inferior vena cava via a femoral vein, and to a femoral artery. Therightphrenic nerve was exposed in the neck and part of it was dissected free from surrounding tissues, desheathed and cut distally, immersed in mineral oil and mounted on bipolar silver-silver chloride electrodes to record efferent © The Macmillan Press Ltd 1984
BRITISH JOURNAL OF ANAESTHESIA
1162
physiological saline solution before and after each injection. RESULTS
Phrenic nerve activity
In these preparations, anaesthetized with chloralose in which arterial blood-gas tensions were carefully controlled, midazolam 0.2mgkg-1 i.v. caused severe depression of phrenic nerve activity (PNA) for periods up to 40min (fig. 1). Higher doses caused a longer period of depression, but even with a dose of 2 mg kg"1 the maximum duration of significant PNA depression was less than 90 min (Whitwam etal., 1980). In the doses used, neither Ro 15-1788 nor Ro 153505 when administered first, produced any significant change in PNA. When midazolam 0.2-2mgkg- 1 was administered after either antagonist it did not abolish PNA, but rather produced either no change in PNA (fig. 2) or at most a transient decrease in activity of between 25 and 80%, which returned to control values within 15 min (fig. 3). Subsequent observation for periods up to 2 h showed no further decrease in PNA, suggesting that the action of the antagonist was at least as long as midazolam. When administered after midazolam, both Ro 15-1788 0.06-0.75mgkg-1 and Ro 15-3505 0.2mgkg-1 or 2mgkg"' produced a rapid reversal of the effect of midazolam on PNA (figs 4, 5). Control values were reached within 10 min of their administration, and there was no evidence of a return of agonist activity. The administration of the Ro 15-1788 solvent 0.006-0.075 ml kg"1 was not associated with any significant alteration in PNA. Cardiovascular changes
Following the administration of midazolam 0.2 mg kg"1 there was a 6% decrease in mean arterial
lUlJJUU.
IPNA
PNA I H l H t l
1
1 10s
Midazolam 02 mg kg"1
£
'
45
60
Time (min)
FlO. 1. The effect of a m'ngV dose of midazolam on efferent phrenic nerve activity in one dog. PNA»» Phrenic nerve activity; IPNA = integrated phrenic nerve activity.
Downloaded from http://bja.oxfordjournals.org/ at University of Birmingham on August 27, 2015
activity which was processed through a preamplifier (Tektronix 122) rectified, integrated (Neurolog NL 703) and displayed. PaOz , Pacc>2 j arterial pH and core temperature were maintained within the ranges.21.4-35.6kPa, 5.1-6.7kPa, 7.25-7.39 and 37-39°C, respectively. During each investigation these values were maintained within narrow limits and during each period of observation they were returned to the control values measured at the start in each preparation, by changes in ventilation, Flch or the administration of sodium bicarbonate. The phrenic nerve activity and its integrated signal were displayed on an oscilloscope (Tektronix 565) and, together with the ECG, beat-by-beat heart rate, intravascular pressures and intratracheal pressure, recorded on an ultraviolet recorder (SE Laboratories type 2115). Total activity in the phrenic nerve per minute was calculated by multiplying the peak height of the integrator output by the frequency of the bursts of activity per minute. Either Ro 15-1788 (six dogs) or Ro 15-3505 (eight dogs) was administered in any one preparation. In the latter group, six animals received midazolam 0.2 mgkg- 1 or 2 mgkg-1 initially, followed in each case by the same dose of Ro 15-3505. In the remaining animals in this group, the administration sequence was reversed: Ro 15-3505 1 or 2 mgkg-1 was followed by midazolam 0.2 mgkg"1 or 2 mgkg"1. In the Ro 15-1788 group, in order to determine the effect, if any, of the solvent, each dose of the antagonist was preceded by the administration of a volume of solvent equal to that of the succeeding Ro 15-1788. Three animals received midazolam 2 mgkg- 1 initially, followed by Ro 15-1788 0.06-0.75 mgkg"1, while in the remaining dogs midazolam 2mgkg- 1 was preceded by Ro 15-1788 0.15-1.0 mgkg- 1 . Ah* drugs were administered via the catheter in the inferior vena cava, which was flushed with
MIDAZOLAM AND BENZODIAZEPINE ANTAGONISTS
IPNA
)MiMUk
MMKkkAm
PNA
{llMJUUl
1163
tdLMU.
UAJJiA
*-
Time (min) Ro 15-3505 1mgkg' 1
Midazolam 0.2 mgkg" 1
FIG. 2. The effects on efferent phrenic nerve activity of Ro 15-3505 and midazolam. PNA = phrenic nerve activity; IPNA = integrated phrenic nerve activity.
PNA
__f
_t
10i
5
Sotvem 0.1 mg kg' 1
"
Ro 15-1788 Imgkg^ 1
10
•
30
'
90
Time (min) Midazolam 2 mgkg' 1
FIG. 3. The effects of the solvent, Ro 15-1788 and midazolflm on efferent phrenic nerve activity. PNA = Phrenic nerve activity; IPNA — integrated phrenic nerve activity.
PNA 1
10 s Midazolam 2 mgkg- 1
Time (nun)
'
tt1
•
30
Ro 15-1788 1mgkg' 1
FIG. 4. The effects on efferent phrenic nerve activity of midazolam and Ro 15-1788. PNA = Phrenic nerve activity; IPNA — integrated phrenic nerve activity.
PNA
IIIMHll ^
II
,|IM"VM
5
10 s
15
» ' '
30
Time (min) Midazolam 0.2 mgkg- 1
Ro 15-3505 0.2 mgkg' 1
Fro. 5. The effects on efferent phrenic nerve activity of mida7nlnm and Ro 15-3505. PNA = phrenic nerve activity; IPNA = integrated phrenic nerve activity.
Downloaded from http://bja.oxfordjournals.org/ at University of Birmingham on August 27, 2015
IPNA
BRITISH JOURNAL OF ANAESTHESIA
1164 pressure (n.s.). The subsequent administration of Ro 15-3505 0.2 mgkg- 1 caused an increase in mean arterial pressure to within 1 % of control values. Because of the variation in the dose of Ro 15-1788, statistical analysis could not be applied to the cardiovascular changes in this part of the study. However, the administration of midazolam caused the expected slight decrease in mean values which returned to control values following Ro 15-1788. There was never any overshoot in arterial pressure.
In conclusion, this study demonstrated the effectiveness of Ro 15-3505 and Ro 15-1788 in antagonizing the effects of midazolam. Effective specific benzodiazepine antagonists may soon be available for clinical use. REFERENCES
Al-Khudhairi, D., Askitopoulou, H., and Whitwam, J. G. (1982). Acute "tolerance" to the central respiratory effecu of midazolam in the dog. Br. J. Anaatk., 54, 953. Allonen, H., Ziegier, G., and Klotz, U. (1981). Effect kinetics of midazolam; a new hypnotic benzodiazepine. Clin. Pharmacol. 7Tk*r.,30,653. Braestrup, C , and Nielsen, M. (1980). Multiple benzodiazepine receptors. Trends Nruro. Sd., (Dec.), 301. (1981). GABA reduce* binding of 3H-methyl carboline-3 carboxylate to brain benzodiazepine receptors. Natur*(Lond.), 294,472. Darragh, A., Lambe, R., and Brick, I. (1981). Reversal of benzodiazepine induced sedation by intravenous Ro 15-1788. Lanctt, 2,1042. Scully, M., O'Boyle, C , and Wilson Downie, W. (1981X Investigation in man of the efficacy of a benzodiazepine antagonist Ro 15-1788. Lanctt, 2, 8. Fonter, A., Gardez, J. P., Suter, P. M., and Gemperle, M. (1980). Respiratory depression by miHnTnlnm and diazepam. Antsthaioiogy, 53,194. Hunkeler, W., Mohler, M., Pieri, L., Pole, P., Bonetti, E., Cumin, R., Schaffner, R., and Haefeley, W. (1981). Selective antagonists of benzodiazepines. Nantrt (Loud.), 290, 514.
Downloaded from http://bja.oxfordjournals.org/ at University of Birmingham on August 27, 2015
DISCUSSION
This study showed that Ro 15-1788 and Ro 15-3505 are effective antagonists of the central respiratory effects of midazolam, and that they have no significant intrinsic effects in the doses used. It also showed that pre-treatment with both of these antagonists abolishes, or greatly inhibits, the effects of the subsequent administration of midazolam. The problem with this type of experimental work is that only one dose of any one drug may be studied in one preparation in one day. The data presented here do not allow any conclusions to be drawn about the potencies of these drugs with respect to midazolam, nor can any conclusion be drawn about the precise duration of action of the two drugs. Suffice it to say that doses of both antagonist drugs comparable to those of midazolam were effective and that there was never any evidence of a return of the effects of midazolam within the known timecourse of the action of these drugs in these preparations (30-90 min). Hence, the durations of action of both drugs are presumably comparable to that of midazolam. The present study on animals was concerned with a specific action of only one benzodiazepine, midazolam, a drug which, in successive doses, is known to induce the rapid development of tolerance in these animals (Al-Khudhairi, Askitopoulou and Whitwam, 1982). Darragh and colleagues (1981) found that combined oral doses of Ro 15-1788 200 mg and the benzodiazepine 3-methylclonazepam 8mg in human volunteers caused effective antagonism of the psychomotor effects of the benzodiazepine, while the same group (Darragh, Lambe and Brick, 1981) found in volunteers that, following combined oral doses of Ro 15-1788 100 mg and 3methylclonazepam 35 mg, the eventual onset of sedation was reversed by a further dose of Ro 15-1788 20 mg i.v. More recently, O'Boyle and colleagues (1983) have shown that a dose of Ro 15-1788 200 mg
in man attenuated markedly or abolished the various effects of diazepam (psychomotor, amnesic and affective). However, the doses were administered orally, simultaneously and in a ratio of 200 mg: 20 mg, that is 10:1. Midazolam is approximately twice as potent as diazepam (Whitwam, personal communication). In the present study, doses as small as Ro 15-1788 0.06 mgkg"1 and Ro 15-3505 1 0.2mgkg- i.v. were capable of preventing or reversing the effects of midazolam up to 2mgkg"1 i.v., that is, effective dose ratios of 0.03:1 and 0.1:1, respectively. However, the present study is not comparable to the oral studies on human volunteers, but perhaps similar results could have been achieved with smaller oral doses of Ro 15-1788 because the precise dose requirements of the various antagonists drugs and benzodiazepines are not accurately known. Naloxone-induced reversal of the effects of opiates may be accompanied by a large rebound increase in arterial pressure (Tanaka, 1974). However, reversal of the effects of midazolam by Ro 153505 was accompanied by small increases in arterial pressure (5%) and heart rate (1%), which were not statistically significant.
MIDAZOLAM AND BENZODIAZEPINE ANTAGONISTS
Pharm.,19,271. Squires, R. F., and Braestrup, C. (1977). Benzodiazepine recepton in the rat brain. Naturt (Land.), 266, 732. Tanaka, G. (1974). Hypertensive reaction to nalozone.
J.A.M.A., 228,25. Whitwam, J. G., Scott, W., Kurimoto, S., Orchard, C , and Chakrabarti, M. (1980). Cardiovascular effects of midazolam (Ro21-3981)inthedog. Br. J. Anaath., 52.954P.
ANTAGONISME DES EFFETS DU MIDAZOLAM SUR L'ACTTVTTE DU NERF PHRENIQUE CHEZ LE CHEIN PAR LE Ro 15-1788 ET Ro 15-3505 RESUME
Les etudes ont et£ fahes sur 14 chiens endormis et ventQcs •r^ifift^llfrnrnT chez qui l'activiti eff£rente du nerf phrenique a tti enregistrce, les gaz du sang, le pH art£riel et la temperature centrale etant controles. Des doses de miHiiTnlom comprises entre O^mgkg"1 et 2mgkg~ 1 supprimatent ractivite du nerf phreniquepourdesdureesallantde30a90min. Le Ro 15-1788, a des doses de 0,06-1 mgkg-' et le Ro 15-3505 a des doses de 0,2—2mgkg"1 anmilai^nr les effets du midazolam sur l'actrvit£ du nerf phrenique. Une administration prealable de ces agents supprimait ou inbibait fortement l'action du midazolam. Lorqu'on poursuivait l'etude jusqu'a deux heure*, il n'y avait pas de signes de reapparhion de l'action du midazolam, ce qui permet de penser que les deux antagonistes ont une duree d'action au mnin« f*ra\* acclle du midazolam.
ANTAGONISMO DE LOS EFECTOS DEL MIDAZOLAN SOBRE LA ACITVIDAD DEL NERVIO FRENICO EN EL PERRO POR Ro 15-1788 Y Ro 15-3505 SUMARIO
Se Uevaron a cabo experimentos en 14 perros anestesiados artificiahnente ventilfldos en los cuales se registro la actividad eferente del nervio frenico y se controlaron las t
Downloaded from http://bja.oxfordjournals.org/ at University of Birmingham on August 27, 2015
Mohler, H., and Okada, T. (1977). Benzodiazepine receptor: Demonstration in the central nervous system. ScUnce, 198, 849. Nutt, D., Cowen, P., and Little, M. (1982). Unusual interactions of benzodiazepine receptor antagonists. Naturt (Land.), 29S, 436. CBoyk, C , Lambe, R., Darragh, A., Taffe, W., Brick, I., and Kenny, M. (1983). Ro 15-1788 antagonizes the effects of diazepam in man without affecting its bioavailability. Br. J. Anaesth., 55, 349. Power, S. H., Morgan, M., and Chakrabarti, M. K. (1983). Carbon dioxide response curves following midazolam and diazepam. Br. J. Anaath., 55,837. Smith, M. T., Eadie, M. J., and O*Rourke Brophy, T. (1981). The phannacokinetics of rniAa-m\am in man. Eur. J. Gin.
1165