Respiratory and sedative effects of clobazam and clonazepam in volunteers

Transcription

1 Br. J. clin. Pharmac. (199), 29, Respiratory and sedative effects of clobazam and clonazepam in volunteers J. D. WILDIN, B. J. PLEUVRY, G. E. MAWER, T. ONON & L. MILLINGTON Department of Physiological Sciences, University of Manchester, Oxford Road, Manchester M13 9PT 1 The respiratory and psychomotor effects of two benzodiazepines used mainly as anticonvulsants were compared in healthy volunteers, using a double-blind placebo controlled design. 2 Clobazam (1 and 2 mg) produced significantly fewer psychomotor side effects than clonazepam (.5 and 1 mg). Neither drug at either dose affected the ventilatory response to C2. 3 Although clonazepam produced significant effects on psychomotor performance, these did not correlate with plasma drug concentration. 4 Our studies provide further evidence that at the doses chosen clobazam is considerably less sedating than clonazepam. Further investigation is required into the tolerance profile of both drugs in patients. Keywords clobazam clonazepam ventilatory response to CO2 psychomotor tests Introduction Clobazam and clonazepam are benzodiazepines widely used as adjunctive therapy in epilepsy. There are numerous reports in the literature concerning the effects of these drugs individually and in comparison with other benzodiazepines (Gudgeon & Hickey, 1981; Hindmarch, 1979). Cull & Trimble (1985) compared the two agents in volunteers, but the same subjects did not receive both clonazepam and clobazam. Furthermore, the benzodiazepine was administered chronically over a 2 week period and only a single dose of each drug was included. Clobazam has a 1-5 structure, unlike the classical 1-4 structure possessed by clonazepam and most other benzodiazepines including diazepam. This seems to confer unusual properties such as enhancement at low dosage of psychomotor performance which is normally depressed by these drugs. It is less sedative than typical 1-4 benzodiazepines in chronic dosage (Cull & Trimble, 1985). In order to determine the selectivity of these two drugs, at conventional starting doses, they have been compared in a range of psychomotor 169 tests, using a double-blind crossover design. Some oral benzodiazepines depress the ventilatory response to carbon dioxide (Pleuvry et al., 198; Rudolph et al., 1978; Utting & Pleuvry, 1975), but little work has been done in this respect with clonazepam and clobazam. Thus, the ventilatory response to carbon dioxide has been investigated. The correlation between changes in performance and plasma drugs concentration has also been determined. Methods Clobazam and clonazepam were administered to healthy volunteers in a five period, doubleblind, crossover study. The doses selected were recommended starting doses for adult patients with epilepsy (British National Formulary, 1989). The treatments were presented as identical opaque capsules containing clobazam 1 or 2 mg, clonazepam.5 or 1 mg or placebo and administered in a random sequence.

2 17' J. D. Wildin et al. Volunteers Ten volunteers (six male) aged years, kg were assessed by medical examination with biochemical and haematological screening. The details of the study were explained and written informed consent was obtained. Anyone taking regular medication (with the exception of oral contraceptives), smokers and women who were pregnant or intended to become pregnant were excluded. The experiment had approval from the University Ethics Committee. The subjects were fasted from the night before dosage and fruit juice only was allowed on the following morning not less than 2 h before ingestion of the drug capsules. Food and fluid were permitted 4 h after ingestion of the capsules, but the subjects were asked to abstain from coffee and alcohol from the day before and until 24 h after dosage. Each volunteer was asked to attend on five separate occasions and received the treatments described. At least 7 days elapsed between successive treatments. Psychomotor performance Psychomotor performance was assessed using the 'Leeds Psychomotor Tester'. Two tests were carried out independently. In the choice reaction time test the subject was required to scan a semi-circle of six lights each adjacent to a corresponding button. The lights were illuminated individually on a random basis. As soon as the subject detected a light he lifted his finger from the base position button and, as quickly as possible, was expected to press the appropriate response button thus extinguishing the light. This provided the total response time (light on to light off) and the recognition component (light on to finger lifted). The difference between the two was designated movement time. Thirty stimuli were presented. The critical flicker fusion threshold (CFFT) (Hindmarch, 1979) was used as an index of arousal. The subjects were required to detect flicker in a set of four light emitting diodes in foveal fixation at 1 m. A mean of six thresholds was taken, three with gradually increasing frequency of flicker where the point that perceived flickering stops was recorded and three with a decreasing frequency of flicker where the point that perceived flickering starts was recorded. The digit symbol substitution test (Wechsler, 1944) involved substituting symbols for digits according to the code given in the box at the top of the page. The number of symbols correctly substituted in a 9 s period was counted. The volunteers reported their subjective condition on visual analogue scales. Sedation was measured using a 1 mm scale marked at one end 'wide awake' and at the other 'nearly asleep'; similarly coordination was registered between extremes of 'well co-ordinated' and 'clumsy'. Postural sway Subjects were asked to stand on an electronic sway meter. This consisted of a wooden circular platform resting on a resilient rubber plate, into which had been embedded four pressure transducers spaced 9 apart. Cutout shapes attached to the top of the platform ensured that the subjects' feet were positioned consistently so that measurements were repeatable. This resembled the equipment used by Patat & Foulhoux (1986). Volunteers were asked to stand erect and motionless for two 1 min periods, one with eyes open and one with eyes closed. The output from the pressure transducers was recorded as a variable line in the anterior-posterior and left-right directions on two separate recording potentiometers (Rikadenki). This contrasts with the computerised system used by Patat & Foulhoux (1986) who required a complex analysis of the components of postural deviation. Each potentiometer record was analysed via a graphics tablet attached to an Apple II computer. By tracing the potential record, the program calculated the mean deviation from a straight line joining the start and stop potentials. This value was used to represent the relative sway of the individual. The machine was calibrated by determining the potential change produced by a 1 kg mass placed over each sway sensor. Ventilatory response to C2 The ventilatory response to CO2 was measured using a Bell closed circuit spirometer (Ealing). The soda lime canister was removed from the spirometer circuit and the cylinder filled with 5% CO2 in oxygen. Following a maximal expiration, the subject was connected to the spirometer and after initial deep inspiration, was allowed to breathe quietly into the apparatus. Rebreathing took place for not more than 4 min. Gases were sampled at the mouthpiece and measured continuously by an infrared analyser (Morgan) before being returned to the circuit. The CO2 analyser was connected to a recording potentiometer (Rikadenki). End tidal pco2 (Kpa) was measured from the trace. Minute volume was plotted against end tidal pco2. The slope of the best straight line and the 3 1 min-' volume intercept were calculated. This method was based on that of Read (1967) with certain modifications. Read (1967) used an initial concentration of 7% C2, thus equilibrium

3 occurred more rapidly and end tidal pco2 more closely mirrored brain tissue pco2. However, in our previous experience this had proved extremely stressful to volunteers, often inducing headaches and dyspnoea. Blood pressure and pulse rate Systolic and diastolic blood pressure were measured using the Copal printing/auto-inflation digital sphygmomanometer. The same arm was used for all readings and the same observer made all measurements. It was attempted to ensure that the positioning of the arm cuff was identical on each occasion. Readings were taken at stage 1 and stage 5. Timing A blood sample was taken via a catheter inserted into an arm vein and all the tests described above were performed shortly before drug administration, half hourly for the next 2 h and then at hourly intervals until 8 h after administration. Blood clotting in the catheter was prevented by flushing with heparinised saline (2u ml- 1) after each sample had been taken. The catheter was removed at 8 h. A further set of tests were performed 24 h after drug administration and a 1 ml blood sample was taken by venepuncture. Blood was collected in potassium oxalate tubes, mixed and centrifuged. The plasma was removed and stored at -2 C until assayed for benzodiazepines. Assays Clobazam was extracted from plasma and plasma concentrations measured by. the method of Caccia et al. (1979) using gas chromatography with electron capture. There were certain modifications. The stationary phase was (3%) SP225DA on 8/1 Supelcoport, using N2 as the carrier gas. Elution time for clobazam was 8 min. Diazepam was used as internal standard. Drug recovery using this method was (% ± s.d., n = 4) and was consistent for high and low concentrations of the drug. Clonazepam was assayed by a modification of the method of Badcock & Pollard (1982) using diazepam as internal standard. The stationary phase was 3% SP215DA on 1/12 Supelcoport as the support, with N2 as the carrier gas flowing at 6 ml min1. Drug recovery was (% ± s.d., n = 4) at both high and low concentrations. N-desmethylclobazam was assayed under the same conditions by a modification of the method of Greenblatt (1979). Retention time for N- desmethylclobazam was 14 min. Anticonvulsant benzodiazepines in volunteers 171 Statistics Measurements of response at each time were expressed as the difference between the postand pre-treatment (zero time) values. In the preliminary analysis measurement from different times were pooled and differences due to treatments were assessed without regard to time. Similarly, differences due to time were assessed without regard to treatments. If either revealed significance (P <.5) then differences due to treatment were assessed separately at each time. Since the sequence of treatment was random, the effects of treatments and sequence could not be resolved. Significance was judged from the variance ratio (F) derived from analysis of variance. Results Significant effects of clobazam compared with placebo were found on four of- the sixteen tests (CFlFT, visual analogue scales and L-R postural sway). Significant effects of clonazepam were found on nine of the sixteen tests. The results for critical flicker fusion threshold are shown in Figure 1. Subjects given placebo showed a decrease in threshold frequency throughout the experimental day. This was not significant at any one time and had returned to control values by the following morning. Similar results were obtained from subjects given clobazam 1 mg. The higher dose of clobazam produced a significantly (P <.5) greater decrease than placebo over the first 2 h. Clonazepam.5 mg also tended to decrease flicker fusion threshold but this failed to reach significance compared with placebo. The higher dose of clonazepam caused a decrease in the threshold frequency for most of the day, with a deficit still apparent the next morning. This was significantly different from placebo at 1-7 h and from clobazam 2 mg at 2 and 5 h. Other pairwise comparisons were not made. There was a slight increase in recognition time over the day in placebo-treated subjects (Figure 2). Neither dose of clobazam produced changes that were significantly different from placebo, although low dose clobazam tended to shorten recognition time. The low dose of clonazepam tended to increase recognition time but only 1. mg clonazepam produced a significant increase above placebo and above clobazam 2 mg. Recovery after the second hour was rapid. As with the previous two tests, subjects given placebo showed a decrease in their performance

4 172 J. D. Wildin et al. U Tinw (b), Figure 1 Changes in critical flicker fusion threshold (Hz ± s.e. mean) after placebo (A), clobazam 1 (), 2 mg () and clonazepam.5 (e), 1 mg (u) in 1 subjects. * indicates a significant (P <.5) difference from placebo. I- r 9 ; ; i. jl 3:._ :. i,i 'I; 1 fi-:* e-% 1- :i '5. 7 Th.li.1.11 Figure 2 Changes in recognition time (s ± s.e. mean) after placebo (A), clobazam 1 (), 2 mg () and clonazepam.5 (), 1 mg (-) in 1 subjects. * indicates a significant (P <.5) difference from placebo. in the DSST throughout the trial day (Figure 3). Neither dose of clobazam further affected performance in this test. Both doses of clonazepam significantly reduced performance, with the higher dose having a greater and more persistent effect. This significantly exceeded the effect of the higher dose of clobazam at 1, 2 and 4 h. Subjects receiving placebo generally improved in wakefulness during the day (Figure 4)-peaks coinciding with lunch and the end of the experimental day. Similar results were obtained for subjects given clobazam 1 mg. Higher dose clobazam, and both doses of clonazepam decreased subjective feelings of wakefulness. Some subjects receiving clonazepam 1 mg had to be awakened to undertake tests. A similar pattern of effects was seen with the dexterity scale except that low doses of clobazam tended to improve dexterity. Postural sway Measurements of postural sway with eyes open and eyes closed showed very similar results, and

5 Anticonvulsant benzodiazepines in volunteers ~~~~~~~~ Time tlh) Figure 3 Changes in DSST (no. of symbols substituted ± s.e. mean) after placebo (A), clobazam 1 (), 2 mg () and clonazepam.5 (), 1 mg (e) in 1 volunteers. * indicates a significant (P <.5) difference from placebo. 15 I -J5 E ; :3 - R' 15 7 &,-a I h h -t Figure 4 Changes in subjective assessment by visual analogue scale of wakefulness (mm ± s.e. mean) by placebo (A), clobazam 1 () and 2 mg (), and clonazepam.5 (), 1 mg (m) in 1 volunteers. * indicates a significant (P <.5) difference from placebo. hence only the eyes open results are shown. A significant increase in sway after clobazam was observed at one time point only (1 h, 1 mg). Clonazepam lower dose significantly increased anterior-posterior postural sway at 1 h, and with the higher dose this effect persisted for 5 h (Figure 5). Left-right sway was less adversely affected with high dose clonazepam increasing sway for only the first 3 h. Ventilatory response to CO2 In the doses used, neither clobazam nor clonazepam produced any effect on the slope or the intercept of the ventilation (I min-') (%) CO2-' curve. Similarly, no effects on pulse, blood pressure or body temperature were seen. Plasma concentrations After clobazam, maximal plasma concentrations were reached at 1.3 ±.2 h (1 mg) and at h (2 mg). After clonazepam maximal concentrations were reached at 2.2 ±.3 h (.5 mg) and at 2 ±.6 h (1. mg). These results are shown in Figure 6. The ratio of the area under the concentration-time curves (AUCO, 24) high dose/low dose was 2.31 ±.78

6 174 J. D. Wildin et al. Figure 5 Changes in sway with eyes open in the anterior-posterior plane by placebo (A), clobazam 1 (o) and 2 mg (), and clonazepam.5 (-) and 1 mg (v). * significantly different from placebo (P <.5). Sway is measured as the mean deviation from a mean point in arbitrary units ± s.e. mean (n = 1). In this plane a 1 kg mass at the extremity of the platform produced a deviation of units. for clobazam and 2.4 ±.98 for clonazepam. Two subjects showed very low concentrations of clonazepam after the.5 mg dose. They were excluded from the pharmacokinetic analysis. The concentrations of N-desmethylclobazam were low in all subjects and did not exceed 2 ng ml-'. Discussion Clobazam had little or no effect on a wide range of psychomotor and subjective tests, when compared with placebo. In some cases the effect of clobazam was to improve the score (e.g. 1 mg clobazam on recognition time and visual analogue scale for dexterity), when compared with placebo. Several volunteers taking clobazam spontaneously reported not drowsiness but a mild sense of detachment. These results support previous work by other workers (Parrott, 1982; Robinson et al., 1981; Steiner-Chaskel & Lader, 1981). The tests differed in their sensitivity to the effects of these drugs. For example, although recognition time was affected markedly by clonazepam, the movement time was not significantly prolonged. This demonstrates that once the light was perceived the subject had no significant deficit in his motor ability. The greatest persistence of clonazepam effects was seen in the flicker fusion (CFF) test (Figure 1). This contrasts with the brief duration of effect and rapid recovery seen with recognition time (Figure 2). The CFF response appeared to parallel the plasma concentration of clonazepam (Figure 6b). Other responses (DSST, recognition time) waned whilst the concentration remained high. This may indicate that acute tolerance, which has been recognised with other benzodiazepines (Crawford et al., 1987), develops to the effects of clonazepam on some functions but not on others. Alternative explanations are less likely. The rapid waning of the effect of 1 mg clonazepam on recognition time (Figure 2) is unlikely to be caused by the concentration falling below a critical threshold since the mean concentration at 3 h exceeded that at 2 h (Figure 6b). Similarly, a more rapid fall in the concentration of drug in venous plasma than in brain would lead to the unexpected presence of psychomotor effects rather than early recovery. Within subject correlations between plasma concentrations and effect were generally very weak. This supports previous findings by Congdon & Forsythe (198) who found that in patients, dose was unrelated to effect in terms of seizure scores, and Froscher & Engels (1986) who observed in discussion following a paper on tolerance to clonazepam that there was no correlation between clonazepam serum levels and side effects. The mild effects of clobazam made concentration/effect analysis impractical. Graphical plots of response (DSST, recognition time) against plasma concentration of clonazepam were prepared in the expectation of observing a hyster-

7 Anticonvulsant benzodiazepines in volunteers 175 a 6 5 C 4 a) c E 3 2 nn - b 4 5 Time (h) 4- P4_ C a) co CL a) N Time (h) Figure 6 (a) Plasma concentrations (ng ml-' + s.c. mean) of clobazam (1 and 2 mg) after oral dose in 1 volunteers and (b) plasma concentrations of clonazepam (ng ml-' ± s.e. mean) (.5 and 1 mg) after oral dose in 1 volunteers. esis loop. However, this was observed in one subject only. Generally there was a lack of observations during the rising phase of plasma concentration. As with clobazam, correlation between effect and the concentration of its major metabolite (N-desmethylclobazam) was not assessed. Pullar et al. (1987) showed that only small amounts (1-2 ng ml-') of N- desmethylclobazam were to be expected from a single dose of clobazam. Comparable plasma concentrations to these have been shown to produce virtually no effect on psychomotor performance in humans (Davies et al., 1985). Further work with higher doses of clobazam is necessary before concentration/response relationships can be described. Neither drug at either dose had any effect on the ventilatory response to CO2 despite the fact that many of the recipients of clonazepam 1 mg had to be awakened to undertake the tests. This suggests that the displacement of the ventilatory response to CO2 seen with other benzodiazepines is not simply due to sedation as has been suggested for some other drugs (Eddy et al., 197). The doses given in this study are those given

8 176 J. D. Wildin et al. in the first weeks of anti-epileptic therapy, when drugs are being introduced to the patient, and when adverse effects are most likely to be reported. Clobazam maintenance therapy often remains around the 2 mg day- ' mark for patients with epilepsy, and so this dose could be considered therapeutic. The relative lack of effect from clobazamn in this study suggests that patients should have few problems relating to CNS depression with this drug. Clonazepam by contrast appears likely to produce a higher incidence of drowsiness and sedation during the first few weeks of therapy. Unless tolerance to these effects is substantial it is likely that CNS References depression caused by clonazepam will increase as the dose is increased towards the usual adult daily maintenance dose of 4-8 mg (British National Formulary, 1989). It is concluded that clobazam is relatively free from CNS depressant actions when compared with clonazepam at the doses recommended for the commencement of anti-epileptic drug treatment. The authors would like to thank Miss J. Preece for assistance in performing the assays for clobazam and clonazepam, Mrs K. Bond for word-processing the text, and Hoechst UK Ltd for financial support for the study. Badcock, R. & Pollard, A. C. (1982). Micro-determination of clonazepam in plasma or serum by electron capture gas liquid chromatography. J. Chromatogr., 23, British National Formulary (1989). Number 17. Chapter 4, Central Nervous System, clobazam p. 146, clonazepam p London: British Medical Association and Royal Pharmaceutical Society of Great Britain. Caccia, S., Ballambio, M., Guiso, G. & Zanini, M. G. (1979). Gas-liquid chromatographic determination of clobazam and N-desmethylclobazam in Plasma. J. Chromatogr., 164, Congdon, P. J. & Forsythe, W. J. (198). Intravenous clonazepam in the treatment of status Epilepticus in children. Epilepsia, 21, Crawford, T. O., Mitchell, J. W. G. & Snodgrass, S. R. (1987). Lorazepam in childhood status epilepticus and serial seizures: effectiveness and tachyphylaxis. Neurology, 37, Cull, C. A. & Trimble, M. R. (1985). Anticonvulsant benzodiazepines and performance. In Clobazamhuman psychopharmacology and clinical applications, eds Hindmarch, I., Stonier, P. D. & Trimble, M. R., Royal Society of Medicine International Congress and Symposium Series No. 74, pp London: Royal Society of Medicine. Davies, I. R., McEwen, J., Pidgeon, A. W., Robinson, J. W. & Stonier, P. D. (1985). Comparison of N-desmethylclobazam and N-desmethyldiazepam, two active benzodiazepine metabolites. In Clobazam-human psychopharmacology and clinical applications, eds Hindmarch, I., Stonier, P. D. & Trimble, M. R. Royal Society of Medicine International Congress and Symposium Series No. 74, pp London: Royal Society of Medicine. Eddy, N. B., Frebel, H., Hahn, K. J. R. & Halbaetz, H. (197). Codeine and its alternatives for pain and cough relief, p. 33. Geneva: World Health Organisation. Froscher, W. & Engels, H. G. (1986). Tolerance to the anticonvulsant effects of clonazepam. In Tolerance to beneficial and adverse effects of antiepileptic drugs, eds Koella, W. P., Frey, H.-H., Froscher, W. & Meinardi, H., pp New York: Raven Press. Greenblatt, D. J. (1979). Determination of clobazam and N-desmethylclobazam in plasma. J. pharm. Sci., 69, Gudgeon, A. C. & Hickey, B. J. (1981). A dose range comparison of clobazam and diazepam: 1- Tests of psychological functions. In Clobazam, eds Hindmarch, I. & Stonier, P. D. Royal Society of Medicine International Congress and Symposium Series Vol. 43, pp London: Royal Society of Medicine. Hindmarch, I. (1979). Some aspects of the effects of clobazam on human performance. Br. J. clin. Pharmac., 7, 77S-82S. Parrott, C. (1982). The effects of clobazam on CFF. Drug Dev. Res. (Suppl), 1, Patat, A. & Foulhoux, P. (1986). Effect on postural sway of various benzodiazepine tranquillisers. Br. J. clin. Pharmac., 2, Pleuvry, B. J., Maddison, S. E., Odeh, R. B. & Dodson, M. E. (198). Respiratory and psychological effects of oral temazepam. Br. J. Anaesth., 52, Pullar, T., Haigh, J. R. M. & Feely, M. P. (1987). Pharmacokinetics of N-desmethylclobazam in healthy volunteers and patients with epilepsy. Br. J. clin. Pharmac., 24, Read, D. J. C. (1967). A clinical method for assessing the ventilatory response to CO2. Aust. Annal. Med., 16, Robinson, R., Gudgeon, A. C. & Hindmarch, I. (1981). Oxazolam, ketazolam and clobazam compared with placebo on tests of psychomotor function. In Clobazam, eds Hindmarch, I. & Stonier, P. D. Royal Society of Medicine International Congress and Symposium Series Vol. 43, pp London: Royal Society of Medicine. Rudolph, M., Geddes, D. M., Turner, S. A. & Saunders, K. B. (1978). Depression of central respiratory drive by nitrazepam. Thorax, 33, 97-1.

9 Anticonvulsant benzodiazepines in volunteers 177 Steiner-Chaskel, N. & Lader, M. H. (1981). Effects of single doses of clobazam and diazepam on psychological functions in normal subjects. In Clobazam. eds Hindmarch, 1. & Stonier, P. D. Royal Society of Medicine International Congress and Symposium Series Vol. 43, pp London: Royal Society of Medicine. Utting, H. J. & Pleuvry, B. J. (1975). Benzoctaminea study of the respiratory effects of oral doses in human volunteers, and interactions with morphine in mice. Br. J. Anaesth., 47, Wechsler,. (1944). The measurement of adult intelligence, 3rd edition, p Baltimore: Williams & Wilkins. (Received 16 May 1989, accepted 1 October 1989)