USE OF CT1341 ANAESTHETIC ('SAFFAN') IN MONKEYS

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1 Laboratory Animals (1973) 7, USE OF CT1341 ANAESTHETIC ('SAFFAN') IN MONKEYS by P. G. BOX AND K. R. ELLIS Glaxo Research Ltd, Research Farm, Breakspear Road South, Harejield, Uxbridge, Middlesex SUMMARY An intramuscular dose of 12 mg/kg of this steroid anaesthetic produced sedation in cynomolgus monkeys, and higher doses (up to 60 mg/kg) produced light anaesthesia lasting up to 3 hours. Surgical anaesthesia could be induced by a single injection of 120 mg/kg, or by an intramuscular injection of 18 mg/kg followed by 6-12 mg/kg intravenously. No clinical or pathological effects were observed after daily use of the anaesthetic for 4 weeks. DIE ANWENOUNG VON OEM BETAUBUNGSMITTEL CT 1341 ('SAFFAN') BEl AFFEN Eine intramuskulare Dosis von 12 mg/kg dieses steroiden Betaubungsmittels wirkte sedativ bei Cynomolgusaffen, und grossere Dosen (bis zu 60 mg/kg) erzeugten leichte Narkose die bis zu 3 Stunden vorhielt. Man konnte chirurgische Narkose mit einer einzigen Injektion von 120 mg/kg hervorrufen, oder durch eine intramuskullire Injektion von 18 mg/kg, gefolgt von 6-12 mgt kg die intravenos gegeben wurden. Nach taglicher 4 wochenlanger Anwendung dieses Betaubungsmittels konnte man keine klinischen oder pathologischen Foigen beobachten. L'EMPLOI DE L'ANESTHESIQUE CT 1341 ('SAFFAN') SUR LES SINGES Dne dose intramusculaire de 12 mg/kg de cet anesthesique steroide causa it une sedation dans les singes cynomolgus, et des doses augmentees (jusqu'a 60 mg/kg) resultaient en anesthesie legere durant jusqu'a 3 heures. Une anesthesie chirurgique pouvait etre achevee par une seule injection de 120 mg/kg, ou par une injection intramusculaire de 18 mg/kg sui vie par 6-12 mg/kg introduit endoveineusement. Apres une application quotidienne de cet anesthesique pendant 4 semaines aucun effet clinique ou pathologique fut observe. The handling of monkeys for experimental purposes frequently requires that they be sedated or anaesthetised. A preparation which will induce this condition when injected by the intramuscular route is to be preferred since

2 162 P. G. BOX AND K. R. ELLIS it may be given before removing the monkey from its cage. This eliminates the hazard of handling fully conscious monkeys. Phencyclidine satisfies this requirement and its use in monkeys has been described by Spalding & Heyman (1962) and Rutty & Thurley (1962). CT1341 ('Saffan' and 'Althesin'; Glaxo Laboratories Ltd, Greenford Road, Greenford, Middlesex) is a new steroid anaesthetic recently introduced for human and veterinary use. Its composition, pharmacology and toxicology in animal species including the monkey have been described by Child et al. (1971) who showed that when administered by the intravenous route CTI341 has a wide therapeutic index. The work now presented describes the results obtained in using CT] 34] as an alternative to phencyclidine in monkeys. MATERIALS AND METHODS Animals Cynomolgus monkeys (Macaca irus) of either sex were used, of bodyweight up to 3,6 kg. Anaesthetic The CT1341 used throughout this work was standard production material identical to that described by Child et al. (1971), containing a total of 12 mg/ml steroid (9 mg alphaxalone and 3 mg alphadolone acetate). Housing The monkeys were housed 1 or 2 per cage in aluminium-alloy cages of internal dimensions 61 X 61 X 76 cm (24 X 24 X 30 in). Each cage was fitted with a crush-type back enabling the animals to be brought forward to the front bars and restrained either for catching or for intramuscular injection. Inectjion of anaesthetic Intramuscular irifection. Each monkey was restrained as described, a hind leg grasped through the bars, and material injected into the muscles of the thigh. When carrying out this procedure care was taken to ensure that the anaesthetic was injected deep into the muscle layers. This was to eliminate the possibility of inadvertant intermuscular or subcutaneous deposition of the preparation causing it to be only slowly absorbed and therefore less effective (Evans, Aspinall & Hendy, 1972). Intravenous injection. Except for the single occasion that this particular method was being investigated, intravenous injection was only carried out in monkeys previously sedated by intramuscular injection. The external saphaenous, femoral or radial veins were used, the saphaenous being preferred. For the saphaenous and radial veins a 0 51 X 13 mm (25 gauge X! in) needle was used, and for the femoral a 0 91 X 25 mm (20 gauge X 1 in) needle.

3 STEROID ANAESTHETIC FOR MONKEYS 163 Calculation of dose Where the weight of any animal was not known exactly it was estimated and the dose calculated on this basis. Once anaesthetised the animal was weighed and the actual dose calculated and recorded. Selection of dose rate Experience in using CT1341 in other species had indicated that an intramuscular dose of 18 mg/kg was likely to be effective. Accordingly for the 1st experiment 4 groups of monkeys were prepared. The doses chosen were 12, 18, 24 and 36 mg/kg. In a 2nd experiment, to determine the dose required to produce complete surgical anaesthesia or even death, larger doses (60 and 120 mg/kg) were used. In some instances this required the anaesthetic to be injected at more than one site. Course of anaesthesia In order to determine the course of sedation and anaesthesia obtained the induction and recovery periods were divided into stages as follows: Induction A. Loss of righting reflex. B. Relaxation with slight trembling. C. Loss of muscle tone of limbs and body. D. Loss of palpebral reflex. E. Complete surgical anaesthesia. Recovery F. Return of muscle trembling. G. Return of voluntary movement capability. H. Return of righting reflex. T. Conscious response to approach by attendant. J. Return of capability to walk or climb. K. Complete clinical recovery. The time taken to reach each of these points in individual resting monkeys was recorded. Complete surgical anaesthesia (stage E) was defined as that state at which the animal failed to react to any external stimulus. The loss of the palpebral reflex (stage D) was achieved considerably earlier in the induction sequence than the stage at which response to skin pinching or metallic sound was lost, although at this stage the animal was completely relaxed. Thus for simple procedures such as blood sampling to be performed stage D would probably be adequate, but for surgery complete surgical anaesthesia (stage E) would be desirable.

4 164 P. G. BOX AND K. R. ELLIS Method of administration Both single- and multiple-dose programs were investigated. Single initial dosing, with no reinforcement was achieved by intramuscular injection only, by intravenous injection only, or by intramuscular followed by a single intravenous injection. Multiple or continual dosing-maintenance of anaesthesia-was achieved by intramuscular followed by repeated intravenous injections. An initial intramuscular dose of 18 mg/kg was given followed by an intravenous dose of 12 mg/kg as soon as the animal was relaxed. The animal was then observed and at the first sign of muscle trembling a further dose of 12 mg/ kg was given intravenously. This procedure was repeated for periods of 4t-6 hours. During this time the femoral artery was cannulated and blood pressure measured with pressure transducer connected to a 2-channel physiological recorder. Body temperature and respiration rate After a single intramuscular injection of CTl341 (18 mg/kg), rectal temperatures of 3 monkeys were recorded at 15-minute intervals over a period of 5 hours. Identical records were made in 3 monkeys given a single intramuscular dose of phencyclidine (3 mg/kg). In this experiment the respiration rates in both groups of animals were recorded every 15 min utes. Repeated daily dosing In order to determine the clinical and toxicological effect upon animals of long-term repeated daily dosage of both CTl341 and phencyclidine, 9 monkeys were selected and divided into 3 groups each of 3 animals. Group A were injected daily for 4 consecutive periods of 5 days each with CT1341 at a dose rate of 18 mg/kg. Group B were injected in the same manner with phencyclidine at a dose of 3 mg/kg. Group C acted as uninjected controls. The weights of all animals were recorded daily and at the end of the 4-week period the animals were killed, perfused with acetic acid-formol saline solution and specimens of brain, liver and kidney removed for histological examination. RESULTS Table 1 shows the course of anaesthesia obtained after different intramuscular doses of CTt341. The results show that CTl341 when administered as a single intramuscular injection induced anaesthesia of a sufficient degree for minor procedures such as blood sampling, throat swabbing, and injection to be carried out. However, full surgical anaesthesia in 100 % of animals was not produced below a dose of 120 mg/kg.

5 STEROID ANAESTHETIC FOR MONKEYS 165 Table 1. Course of anaesthesia in cynomolgus monkeys following a single intramuscular,.-., injection of CT1341. '--',.-.,... -<::,.-.,,.-.,. '--'.. -<:: ;: -6' }. : <:> '--' ;: '--' oj::> Course of anaesthesia (minutes) C -6' '" '" l:: <:> <:l (:l (:l..... induction recovery.. (:l t" l:: ti <..l "l; "l; "l; A B C D E F G H I J K * ' * * * * ' * ] ]6' ]20 ] ] ] ] ' l ] , ,3 36 3,60 33' , ,0 ] , ] ] A loss of righting reflexes; B slight twitching, relaxed; C loss of muscle tone; D loss of palpebral reflex; E full surgical anaesthesia; F trembling; G return of movement capability; H return of righting reflexes; I response to approach; J capable of walking or climbing; K complete recovery. '" Twitched jf stimulated.

6 166 P. G. BOX AND K. R. ELLIS : 2100 ',. g CT1341 _ Phencyclidine0---0 Controls )(a_. )( Time (days) Fig. 1. Average bodyweight of cynomolgus monkeys given repeated phencyclidine. 3 monkeys per group. doses of CT1341 and Fig. 1 shows the daily average bodyweights recorded in the monkeys used in the repeated dosing experiment. The results indicate that the daily administration of CTJ341 and phencyclidine for 5 days out of 7 over a period of 4 weeks appeared to produce no adverse effect on any of the animals apart from a loss in weight of about 7 % over the experimental period. No abnormality was detected histologically in the specimens removed post mortem \ \ U 38 "-!E CT 1341 Phencyclidine Time (hours) Fig. 2. Average body temperature of 3 monkeys arter intramuscular injection of CT1341 and phencyclidine.

7 STEROID ANAESTHETIC FOR MONKEYS 167 Fig. 2 shows the average body temperature recorded in 3 monkeys after single intramuscular doses of CTl341 and phencyclidine. Both preparations caused a marked fall in body temperature during the anaesthetic period which did not return to normal until after the animals were fully recovered. Table 2 shows the respiration rate observed in these animals, which remained regular and within normal limits during the whole period of anaesthesia. Table 2. Respiration rates of monkeys given a single intramuscular (18 mgjkg) and phencyclidine (3 mg/kg). dose of CT1341 CT1341 Phencyclidine Monkey no Time after injection (min) J20 26 Table 3 shows the course of anaesthesia obtained in monkeys after intramuscular followed by intravenous injection of CTl341 at different dose rates. It also shows the course of anaesthesia obtained by a single intravenous injection of 12 mg/kg. The results show that intravenous injection produced full surgical anaesthesia of short duration. Intramuscular injection followed by intravenous injection produced full surgical anaesthesia, the duration of this being controlled largely by the size of the initial intramuscular dose. Anaesthesia could be satisfactorily maintained by additional intravenous injections, a dose of 12 mg/kg extending the period of anaesthesia by minutes. Table 4 shows the blood pressure measurements taken in the monkeys initially anaesthetised by intramuscular injection of CTl341 followed by successive intravenous injections. These results indicate that after each intravenous injection a transitory fall in blood pressure occurred which returned to normal within 3-4 min.

8 168 P. G. BOX AND K. R. ELLIS Table 3. Course of anaesthesia in cynomolgus monkeys after intramuscular (i.m.) followed by intravenous (i.v.) administration of CT134J. Interval between i.m. and i.v. injections was minutes. Full surgical anaesthesia achieved in all animals after i.v. dose... Recovery times (minutes after intravenous dose) <:l... E,-..,:,-.. S:: <:l '"...;..; ;. '" E::: '- '" I.l ::: <::l.so.j:l ",.J:l -<::l :::,-.. "' "' ',:: >< <:l ;:: '-.J:::l ",--- ",--- E ;. <::l E <:l C <:l f} E}9.... g..., c. '" f} c I::l..., I::l..., E I.l.... ::: ,06 17, ,72 IN J8' J40 ] J ] , J,99 5,0 ] ]' ] DISCUSSION Anaesthesia of sufficient depth to perform minor procedures can be obtained in cynomolgus monkeys by a single intramuscular dose of CT1341 steroid anaesthetic. The speed of induction of anaesthesia is related to the dose given. The duration of anaesthesia appears to be dependent upon the size of the dose given but full surgical anaesthesia is only obtained in 100% of animals with intramuscular injection when very high doses are used (120 mg/kg). Initial sedation achieved by giving CT1341 by intramuscular injection as a precursor to intravenous injection to produce complete anaesthesia is satisfactory. With this method the duration of anaesthesia appears to be related to the size of the initial intramuscular dose. At intramuscular doses varying from mg/kg no signs of respiratory or cardiac embarrassment were seen and in all cases recovery appeared to be uncomplicated. In all experiments animals remained clinically normal throughout. With regard to the effect of both CT1341 and phencyclidine on body temperature, both showed a significant hypothermic effect. It is known that anaesthetics in general have this property and this work confirms the degree to which both these preparations exert this effect. None of the animals appeared to be adversely affected, but it is perhaps worthy of mention that throughout

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10 170 P. G. BOX AND K. R. ELLIS the work they were kept in an environment controlled to maintain a temperature of 24 C (75 F). The repeated-dosing experiment was designed to examine the possibility that daily dosing of monkeys either with phencyclidine or CTl341 can have an adverse clinical or pharmacological effect. Discussion with other workers using monkeys had shown that there appears to be a marked disinclination to anaesthetise monkeys daily since it is considered that this procedure results in poor food intake with consequent loss of weight and deterioration in general condition. The results obtained in this work failed to confirm this belief and showed that the daily administration of both CTl341 and phencyclidine on 5 days out of 7 over a period of 4 weeks failed to produce any observable deterioration in the animals' bodily condition other than a 7 % decrease in weight. No adverse effect upon brain, liver or kidney was determined at the end of the trial period. We deduce from these results that these anaesthetics are safe to use daily in Macaca irus monkeys at the dose rates described. Intramuscular injection followed by one or more intravenous doses ofctl341 would appear to provide a satisfactory method of achieving surgical anaesthesia in the monkey for prolonged periods of time. In monkeys initially anaesthetised by intramuscular injection a number of veins are readily available for intravenous injection besides the femoral vein. These include the external saphaenous and radial vein where this passes over the biceps brachii. These veins were preferred since they are visible and in the relaxed animal accurate venepuncture was found to be relatively easy. Child et al. (1971) showed that different animals vary in their susceptibility to CTl341. Only Macaca irus monkeys were used in this work, and it is possible that slightly differing results could be obtained in other monkey species. However it is considered unlikely that these differences would be more than marginal and therefore it would be reasonable to postulate that the results obtained in this work may be taken as a guide to the use of CTl341 in species of monkeys other than M. irus. ACKNOWLEDGEMENTS We are grateful to Mr S. G. Lake for carrying out the histological examinations of the tissues, and to Mr K. Daniels for technical assistance. REFERENCES Child, K. J., Currie, J. P., Davis, B., Dodds, M. G., Pearce, D. R. & Twissell, D. J. (1971). The pharmacological properties in animals of CT1341-a new steroid anaesthetic agent. British Journal of Anaesthesia 43, 2. Evans, J. M.,Aspinall, K. W. & Hendy, P. G. (1972). Clinical evaluation in cats of a new anaesthetic CT1341. Journal of Small Animal Practice 13, 479. Rutty, D. A. & Thurley, D. C. (1962). Further observations on the use of phenycyclidine in monkeys. Veterinary Record 74, 883. Spalding, V. T. & Heyman, C. S. (1962). The value of phencyclidine in the anaesthesia of monkeys. Veterinary Record 74, 158.