Eur J Clin Pharmacol (1990) 38:157-160
© Springer-Verlag 1990
Lack of interaction between disuifiram and alprazolam in alcoholic patients B. Diquet 1, L. G u j a d h u r 2, D. Lamiable 3, D. Warot 1, H. H a y o u n 4, and H. Choisy 3 1 D6partement de Pharmacologie Clinique Laboratoire de Pharmacocin6tique, H6pital de la Pitid-SalpetriOre,Paris, 2 Centre Hospitalier Sp6cialis6, Saint-Egr~ve, 3 Laboratoire de Pharmacologie, Facult6 de M6decine, Reims and 4 Laboratoires Upjohn, Paris, France
Sunnnary. Certain interactions between disulfiram and benzodiazepines, especially diazepam and chlordiazepoxide, have previously been reported. The influence of disulfiram on the pharmacokinetics of alprazolam, a triazolobenzodiazepine, metabolized by hepatic microsomal oxidation, has been evaluated in 11 chronic alcoholic patients (6 males, 5 females) undergoing treatment for the alcohol withdrawal syndrome. Each patient received alprazolam 2 mg on the first day (control) followed by two weeks of treatment with disulfiram 0.5 g/d, and then further oral dose of alprazolam 2 rag. No significant change was found in any of the kinetic parameters. Thus, a therapeutic dose of disulfiram did not significantly alter the clearance or half-life of alprazolam in chronic alcoholic patients. Key words: alprazolam, disulfiram; drug interaction, pharmacokinetics, alcoholism
The objectives in the treatment of alcohol withdrawal syndrome include the relief of symptoms, treatment of seizures, hallucinations, delirium and rehabilitation. For this purpose, benzodiazepines and disulfiram are often used concomitantly during alcohol withdrawal [1, 2]. First-line medications for the treatment of alcohol withdrawal syndrome involve benzodiazepines [3] such as diazepam or chlordiazepoxide because they result in sedation, and may also inhibit the development of seizures and delirium tremens or shorten the duration of delirium tremens. More recently, alprazolam, a triazolobenzodiazepine, has been studied during alcoholic withdrawal and seems to possess much the same activity as that of diazepare [4] or chlordiazepoxide [5] in such case. Disulfiram is also widely used in the treatment of alcoholism. It has been shown to inhibit in-vitro acetaldehyde dehydrogenase which metabolizes ethanol to acetic acid. Depending on the dose, disulfiram also inhibits numerous other enzymes such as dopamine beta-hydroxylase [6]. Concurrent ingestion of alcohol and disulfiram might lead
to an enzymatic inhibition and might account for some of the physiologic disturbances of the alcohol-Antabuse ®reaction. Moreover, disulfiram may prolong the half-life of several psychotropic drugs in animal, such as phenytoin [7], thiopenthal [8], or in man, such as some benzodiazepines [9]. Regarding the latter, a study was performed [9] in healthy individuals and in alcoholics, comparing three benzodiazepines (chlordiazepoxide, diazepam and oxazepare), after a fortnight of disulfiram therapy, in order to determine whether this would influence the pharmacokinetics of the concomitantly used benzodiazepines. The half-lives of chlordiazepoxide and diazepam significantly increased (84% and 37% respectively after disulfiram therapy), while the clearance significantly decreased (54% and 41% respectively). Only minimal changes in either parameters were noticed with oxazepam. The aim of this study was thus to detect the possible existence of drug interaction between alprazolam and disulfiram, since interactions have been evidenced in several studies including alprazolam, e.g. with cimetidin [10-12]. Moreover, the kinetics of alprazolam varies in the elderly [13] in case of hepatic impairment [14], obesity [15], or smoking [16].
Methods
Subjects Only patients requiring treatment with disulfiram were to be included. All patients had given their signed informed consent. Patients could not be included in case of any clinical or biological evidence of hepatic impairment such as one of the following: SGOT over 25 IU, SGPT over 25 IU, prothrombine time expressed as Quick's time under 80% of control values, albuminemia under 35 g. 1-1, total bilirubin over 10 rag. 1-1, alkaline phosphatases over 20 IU. 1 1, those weighing over 25% of their ideal weight calculated according to Lorenz' formula, or subjects intending to stop, start, or change markedly their smoking habits during the trial. The day before the first dose of alprazolam the absence of alcohol intake was assessed by the nurse.
158
B. Diquet et al.: Disulfiram and alprazolam in alcoholics
I. Pharmacokinetics parameters of alprazolam in alcoholic patients before (control) and after a fortnight disulfiram therapy Table
Student's t test level of significance
351
_
Control
Disulfiram
Cm~x (ng-ml)
32.6 (19.8-46.8) (7.2)
28.6 (21.3-39.7) (4.7)
NS
oJ
tm~ (min)
119 (30-240) (63)
142 (90-240) (52)
NS
oJ
tl/2 (h)
10.1 (3.31-21.28) (5.21)
9.31 (1.98-27.5) (6.69)
NS
AUC(ng. min. ml-~)
22.6 (14.7-33.4) (6.37)
21.3 (6.4-43.9) (10.4)
NS
i
20
m_
mean (range) and (SD) values
0 Fig.1. Individual modifications of alprazolam C1/F (ml/min x 10) before and after disulfiram treatment
Protocol design Open-label trial. On the first day, patients were given 2 mg alprazolam per os, and samples taken after .5,1,1.5, 2, 3, 4, 6, 9,12, 24, 36, 48, 72 h. One daily disulfiram tablet (0.5 mg) was then administered orally for the following two weeks. On Day 18, a second oral dose of alprazolam was administered and the patients were sampled according to the same schedule. Patients were hospitalized from Day i to Day 3, and from Day 18 to Day 21, and clinical safety was assessed using a daily questionnaire.
rig. m1-1
20
10
5
Assay Plasma levels of alprazolam were determined by High Performance Liquid Chromatography; alprazolam was extracted from plasma (1 ml) in a basic medium with ether. Diazepam was used as internal standard. Plasma extract was injected into a chromatographic system composed of a liquid phase chromatograph (Varian-model 5000) equipped with a Lichrospher 100 CH-8/II column (250 x 4 mm; particle size 5 gm; Merck), fitted to a sample valve (Valco) with a 20 pl loop. The flow-rate of the mobile phase, phosphate buffer (pH - 2.95) - acetonitril (58:42), was 1.1 ml/mn. The effluent was monitored at 226 nm on a variable wavelength detector (Varian-Vafichrom). The ratios between peak heights of alprazolam and internal standard were plotted versus the concentrations of the standards to obtain a calibration curve which was linear in the range 0-40 pg. 1-1. The day to day precision was 3.6% (n = 6) and 3.3% (n = 6) at the concentration of 5 and 20 gg. 1-1 respectively. At the same concentrations, extraction ratio of alprazolam reached 93.8% (1.5) (mean and SD) (n = 6) and 91% (2.6) (n = 6), respectively. No interfering substance was present in chromatograms for the pre-dose plasmas. The limit of detection, measured at a detector sensitivity of 0.01 absorbance unit full scale and allowing a signal-to-noise ratio of 2, was 0.5 gg- 1-1. It should be noticed that metabolites of alprazolam have not been assayed on the basis that they appear in a negligible amount and have a half-life close to that of the parent compound (formation-rate limited?). However, it has been verified using spiked plasma that their presence did not interfere under the described procedure.
Kinetic and calculations Plasma concentrations of alprazolam were analyzed by least-square regression techniques. The exponent from the terminal phase of the plasma concentration curve was used to calculate the elimination haft-life. The experimental area under the plasma concentration curve from time 0 to the last detectable plasma level was determined
"'o
1 ;"i'i
i
9
1'2
2'~
3'6
£8
time (hi
Fig.2. Plasma concentrations of alprazolam (ng/ml) after a 2 mg oral dose, before ( ) and after ( ) a two weeks disulfiram treatment
by the trapezoidal method. The residual area extrapolated to infinity was calculated as the final concentration divided by the exponent beta; the sum of both areas yield to AUC from time 0 to infinity. The clearance was calculated as dose divided by AUC, assuming F = 1. (Data suggested that alprazolam is readily absorbed in man, the bioavailabilityof an oral tablet (at least 92%) being comparable to intravenous administration [17] ). Apparent volume of distribution was calculated as clearance divided by beta. Differences between before and after treatment conditions were determined by Student's paired t test. Differences between pharmacokinetic parameters of alprazolam alone or with disulfiram were determined using an analysis of variance.
Results
E l e v e n p a t i e n t s (6 m a l e s a n d 5 f e m a l e s ) a g e d b e t w e e n 33 a n d 56 y e a r s h a v e b e e n i n c l u d e d . A s s h o w n o n T a b l e 1, n o significant d i f f e r e n c e a p p e a r e d b e t w e e n a n y o f t h e a l p r a z o l a m kinetics p a r a m e t e r s b e f o r e a n d a f t e r c h r o n i c t r e a t m e n t w i t h disulfiram. A l p r a z o l a m c l e a r a n c e (Fig. 1), as well as t h e a r e a u n d e r t h e e x p e r i m e n t a l p o i n t s e x t r a p o l a t e d to infinity shows g r e a t v a r i a b i l i t y in b o t h p h a s e s o f t h e trial ( t a b l e I): 22.6 (6.37) n g . m i n . m 1 - 1 o n D a y I a n d
B. Diquet et al.: Disulfiram and alprazolam in alcoholics 21.3 (10.4)ng.min-m1-1 after the second oral dose. Neither the clearance over t v, 94.9 (26.2) vs 112 (77.1) ml.min -1, nor the half-life, 10.09 (5.21) vs 9.31 (6.69) h, differs significantly before and after treatment with disulfiram. The administration of disulfiram had no effect on the experimental peak plasma concentration or the experimental time to peak concentration (Fig. 2): 32.6 (7.2) vs 28.6 (4.7) btg. ml-1 (NS) and 112 (63) vs 142 (52.1) min (NS). Regarding safety, no relevant side effect was observed, except moderate somnolence occurring in three patients.
Discussion Previous reports suggest that the pharmacokinetics of benzodiazepines which undergo hepatic microsomal oxidative metabolism are more susceptible to alterations than those drugs which are eliminated via conjugatives processes. Coadministration of cimetidine as well as hepatic dysfunction have been shown to prolong the elimination of diazepam and desmethyldiazepam both of which are oxidatively metabolized [18]. Conversely the glucuronidation of lorazepam is not substantially altered [19]. Alprazolam is metabolized by hydroxylation to form the 4-hydroxy and alpha-hydroxy derivatives and coadministration of cimetidine prolongs the half-life of alprazolam and reduces its clearance [20]. From a basic research point of view the most surprising is that the oxidation of diazepam is affected whereas in this study that of alprazolam is not. An hypothesis might be the involvement of different isozymes of P-450 cytochromes. Results observed support the hypothesis suggesting a lack of interaction between alprazolam and disulfiram in alcoholic patients, since no difference appeared regarding any of alprazolam elimination-related parameters. For a drug with a low hepatic extraction ratio, clearance might decrease and half-life increase with enzyme inhibition but the availability is essentially unaltered. The hepatic clearance of alprazolam being low, an increase of elimination half-life was expected. As previously reported [9] the half-lives of diazepam and chlordiazepoxide were respectively prolonged by about 37% and 84% in the presence of disulfiram. If these proportions are applied to alprazolam, elimination half-life would reach 22 h, which is obviously not the case here, as the mean value observed in this study is very close to that mentioned in the literature, i. e. 10-16 h [21, 22]. Disulfiram being an old product and despite its frequent use, few data are known about its pharmacokinetics and metabolism in humans. The first and rapid metabolic reaction after the administration is its reduction to diethyl dithiocarbamate (DDC) [23]. Further metabolism of D D C can lead to the formation of its methylester, carbon disulphide or copper bis (diethyl-dithiocarbamate) formed by complexation of D D C with proteinbound copper ions present in plasma. Urinary metabolites are the S-glucuronide of D D C and inorganic sulphate. The reported half-life of 70 min for DDC, whereas disulfiram is reduced within 4 min indicated that the D D C is
159 more stable in human blood. When a therapeutic dose of disulfiram is administered, the patient is reported to remain susceptible to the ethanol sensitizing effect of the drug for up to 12 h [2]; however, by that time the blood concentration of both disulfiram and metabolite would have long since become negligible. Since 90% of the dose taken is eliminated in the urine within 72 h (data supplied by the manufacturing firm of disulfiram [Esp6ral ®] ), it has been taken for granted that, in accordance with a study already mentioned [9], the "active species" (DDC?) plasma levels become stable after a two-week therapy. As no simple and reliable assay of disulfiram or metabolite was made available, patient's compliance to therapy had to be assumed. This assumption does not seem unrealistic considering the strong motivation of patients entering the trial. Anyway, a lack of compliance could explain the unexpected lack of kinetic interaction. Disulfiram does not alter the kinetics of alprazolam absorption, and in spite of the trend for the time to peak to occur later after disulfiram therapy, the difference did not reach significance level. Benzodiazepines have a wide therapeutic index and an increase in plasma concentration is usually of little clinical significance. However, amongst benzodiazepines, alprazolam as well as oxazepam shows lower risk of pharmacokinetic interaction with disulfiram during alcohol withdrawal therapy. Whether or not this lack of interaction is clinically relevant remains to be demonstrated. It would be interesting to conduct other studies in view to compare efficacy and safety of these drugs on a chronic regimen in such patients.
Acknowledgement: The authors thank Mrs Mistral C. (Research Nurse) for her expert technical assistance.
References 1. Baekeland F, Lundwann KL (1977) Engaging the alcoholic in treatment and keeping him here. In: Kissin B, Beigleter H, eds: The biology of alcoholism, vol. 5, Treatment and rehabilitation of the chronic alcoholic. Plenum Press, New York, pp 161-195 2. Baekeland F, Lundwall L and Kissin B (1975) Methods for the treatment of chronic alcoholism: A critical appraisal, in: Gibbin RJ, Israel Y, Kalant H, Popham RE, Schmidt W and Smart RG, eds: Recent advances in alcohol and drug problems, vol 2. Wiley and Sons, New York, pp 247-327 3.Sellers EM, Naranjo CA (1986) New benzodiazepines for the treatment of alcohol withdrawal. Psychopharmacol Bull 22: 8892 4. Kolin IS, Linet OI (1981) Double blind comparison of alprazolam and diazepam for subchronic withdrawal from alcohol. J Clin Psychiatry 42:16%173 5. McLendon DM, Fabre LF (1979) A double-blind comparison of the anxiolytic efficacy of alprazolam and chlordiazepoxide hydrochloride in the chronic withdrawal from alcohol. Curr Ther Res 26:430-439 6. Goldstein M, Anagnoste B, Lauber E, McKereghan MR (1964) Inhibition of dopamine-beta-hydroxylase by disulfiram. Life Sci 3:763-767 7. Olesen OV (1966) Disulfiram (Antabuse) as inhibitor of phenytoin metabolism. Acta Pharmacol Toxico124:317-322 8. Giarman NJ, Nick FH, White JM (1951) Prolongation of thiopental anesthesia in the mouse by premedication with tetraethylthiuram disulfide (Antabuse). Science 114:36-36
160 9. McLeod SM, Sellers EM, Giles HG, Billings B J, Martin PR, Greenblatt DJ, Marsham JA (1978) Interaction of disulfiram with benzodiazepines. Clin Pharmacol Ther 24:583-589 10. Abernethy DR, Greenblatt DJ, Divoll M, Moschitto LJ, Harmatz JS, Shader RI (1983) Interaction of cimetidine with the triazolobenzodiazepines alprazolam and triazolam. Psychopharmacology 80:275-278 11. Desager JR Pourbaix S, Dumont E, Harvengt C (1984) Metabolic interaction of cimetidine with alprazolam and triazolam after repeated doses. Arch Int Pharmacodyn Ther 270 (1): 170 (abstr) 12. Pourbaix S, Desager JR Huljoveu R, Smith R, Harvengt C (1985) Pharmacokinetic consequences of long term coadministration of cometidine and triazolobenzodiazepine, alprazolam and triazolam, in healthy subjects. Int J Clin Phamacol Ther Toxicol 23: 447-451 13. Greenblatt D J, Divoll M, Abernethy DR, Moschitto LJ, Smith RB, Shader RI (1983) Alprazolam kinetics in the elderly - relation to antipyrine disposition. Arch Gen Psychiatry 40:287-290 14. Juhl RR VanThiel DH, Dittert LW, Smith RB (1984) Alprazolam pharmacokinetics in alcoholic liver disease. J Clin Pharmaco124: 113-119 15. Abernethy DR, Greenblatt D J, Divoll M, Smith RB, Shader RI (1983) The influence of obesity on the pharmacokinetics of oral alprazolam and triazolam. Clin Pharmacokinet 9:117-183 16. Smith RB, Gwill PR, Wright CE (1983) Single - and multiple dose pharmacokinetics of oral alprazolam in healthy smoking and non smoking men. Clin Pharm 3:139-143 17. Smith RB, Kroboth PB, Vanderlugt ST, Phillips SR Suhl RP (1984) Pharmacokinetics and pharmacodynamics of alprazolam
B. Diquet et al.: Disulfiram and alprazolam in alcoholics after oral and I. V. administration. Psychopharmacology 84: 452456 18. Klotz V, Reimann I (1980) Delayed clearance of diazepam due to cimetidine. N Engl J Med 302:1012-1014 19. Patwardhan R, Yarborough GW, Desmond PV, Johnson RF, Schenker S, Speeg KV (1980) Cimetidine spares the glucuronidation of lorazepam and oxazepam. Gastroenterology 79: 912916 20. Greenblatt D J, Abernethy DR, Divoll M, Smith RB, Shader RI (1983) Old age, cimetidine and disposition of alprazolam and triazolam. Clin Pharmacol Ther 33:253 21. Abernethy DR, Greenblatt, D J, Divoll M, Shader RJ (1983) Pharmacokinetics of alprazolam. J Clin Psychiatry 44:45-47 22. Greenblatt D J, Divoll M, Abernethy DR, Ochs HR, Shader RI (1983) Clinical Pharmacokinetics of the newer benzodiazepiues. Clin Pharmacokinet 8:233-252 23. Cobby J, Mayersohn M, Selliah S (1977) J Pharmacol Exp Ther 202:724 Received: July 22,1987 Accepted in revised form: August 21, 1989 Dr. B. Diquet D6partement de Pharmacologie Clinique Laboratoire de Pharmacocin6tique Pavillon Hemey H6pital de la Piti6-Salpatri~re Boulevard de l'H6pital F-75651 Paris C6dex 13, France
© Springer-Verlag 1990
Lack of interaction between disuifiram and alprazolam in alcoholic patients B. Diquet 1, L. G u j a d h u r 2, D. Lamiable 3, D. Warot 1, H. H a y o u n 4, and H. Choisy 3 1 D6partement de Pharmacologie Clinique Laboratoire de Pharmacocin6tique, H6pital de la Pitid-SalpetriOre,Paris, 2 Centre Hospitalier Sp6cialis6, Saint-Egr~ve, 3 Laboratoire de Pharmacologie, Facult6 de M6decine, Reims and 4 Laboratoires Upjohn, Paris, France
Sunnnary. Certain interactions between disulfiram and benzodiazepines, especially diazepam and chlordiazepoxide, have previously been reported. The influence of disulfiram on the pharmacokinetics of alprazolam, a triazolobenzodiazepine, metabolized by hepatic microsomal oxidation, has been evaluated in 11 chronic alcoholic patients (6 males, 5 females) undergoing treatment for the alcohol withdrawal syndrome. Each patient received alprazolam 2 mg on the first day (control) followed by two weeks of treatment with disulfiram 0.5 g/d, and then further oral dose of alprazolam 2 rag. No significant change was found in any of the kinetic parameters. Thus, a therapeutic dose of disulfiram did not significantly alter the clearance or half-life of alprazolam in chronic alcoholic patients. Key words: alprazolam, disulfiram; drug interaction, pharmacokinetics, alcoholism
The objectives in the treatment of alcohol withdrawal syndrome include the relief of symptoms, treatment of seizures, hallucinations, delirium and rehabilitation. For this purpose, benzodiazepines and disulfiram are often used concomitantly during alcohol withdrawal [1, 2]. First-line medications for the treatment of alcohol withdrawal syndrome involve benzodiazepines [3] such as diazepam or chlordiazepoxide because they result in sedation, and may also inhibit the development of seizures and delirium tremens or shorten the duration of delirium tremens. More recently, alprazolam, a triazolobenzodiazepine, has been studied during alcoholic withdrawal and seems to possess much the same activity as that of diazepare [4] or chlordiazepoxide [5] in such case. Disulfiram is also widely used in the treatment of alcoholism. It has been shown to inhibit in-vitro acetaldehyde dehydrogenase which metabolizes ethanol to acetic acid. Depending on the dose, disulfiram also inhibits numerous other enzymes such as dopamine beta-hydroxylase [6]. Concurrent ingestion of alcohol and disulfiram might lead
to an enzymatic inhibition and might account for some of the physiologic disturbances of the alcohol-Antabuse ®reaction. Moreover, disulfiram may prolong the half-life of several psychotropic drugs in animal, such as phenytoin [7], thiopenthal [8], or in man, such as some benzodiazepines [9]. Regarding the latter, a study was performed [9] in healthy individuals and in alcoholics, comparing three benzodiazepines (chlordiazepoxide, diazepam and oxazepare), after a fortnight of disulfiram therapy, in order to determine whether this would influence the pharmacokinetics of the concomitantly used benzodiazepines. The half-lives of chlordiazepoxide and diazepam significantly increased (84% and 37% respectively after disulfiram therapy), while the clearance significantly decreased (54% and 41% respectively). Only minimal changes in either parameters were noticed with oxazepam. The aim of this study was thus to detect the possible existence of drug interaction between alprazolam and disulfiram, since interactions have been evidenced in several studies including alprazolam, e.g. with cimetidin [10-12]. Moreover, the kinetics of alprazolam varies in the elderly [13] in case of hepatic impairment [14], obesity [15], or smoking [16].
Methods
Subjects Only patients requiring treatment with disulfiram were to be included. All patients had given their signed informed consent. Patients could not be included in case of any clinical or biological evidence of hepatic impairment such as one of the following: SGOT over 25 IU, SGPT over 25 IU, prothrombine time expressed as Quick's time under 80% of control values, albuminemia under 35 g. 1-1, total bilirubin over 10 rag. 1-1, alkaline phosphatases over 20 IU. 1 1, those weighing over 25% of their ideal weight calculated according to Lorenz' formula, or subjects intending to stop, start, or change markedly their smoking habits during the trial. The day before the first dose of alprazolam the absence of alcohol intake was assessed by the nurse.
158
B. Diquet et al.: Disulfiram and alprazolam in alcoholics
I. Pharmacokinetics parameters of alprazolam in alcoholic patients before (control) and after a fortnight disulfiram therapy Table
Student's t test level of significance
351
_
Control
Disulfiram
Cm~x (ng-ml)
32.6 (19.8-46.8) (7.2)
28.6 (21.3-39.7) (4.7)
NS
oJ
tm~ (min)
119 (30-240) (63)
142 (90-240) (52)
NS
oJ
tl/2 (h)
10.1 (3.31-21.28) (5.21)
9.31 (1.98-27.5) (6.69)
NS
AUC(ng. min. ml-~)
22.6 (14.7-33.4) (6.37)
21.3 (6.4-43.9) (10.4)
NS
i
20
m_
mean (range) and (SD) values
0 Fig.1. Individual modifications of alprazolam C1/F (ml/min x 10) before and after disulfiram treatment
Protocol design Open-label trial. On the first day, patients were given 2 mg alprazolam per os, and samples taken after .5,1,1.5, 2, 3, 4, 6, 9,12, 24, 36, 48, 72 h. One daily disulfiram tablet (0.5 mg) was then administered orally for the following two weeks. On Day 18, a second oral dose of alprazolam was administered and the patients were sampled according to the same schedule. Patients were hospitalized from Day i to Day 3, and from Day 18 to Day 21, and clinical safety was assessed using a daily questionnaire.
rig. m1-1
20
10
5
Assay Plasma levels of alprazolam were determined by High Performance Liquid Chromatography; alprazolam was extracted from plasma (1 ml) in a basic medium with ether. Diazepam was used as internal standard. Plasma extract was injected into a chromatographic system composed of a liquid phase chromatograph (Varian-model 5000) equipped with a Lichrospher 100 CH-8/II column (250 x 4 mm; particle size 5 gm; Merck), fitted to a sample valve (Valco) with a 20 pl loop. The flow-rate of the mobile phase, phosphate buffer (pH - 2.95) - acetonitril (58:42), was 1.1 ml/mn. The effluent was monitored at 226 nm on a variable wavelength detector (Varian-Vafichrom). The ratios between peak heights of alprazolam and internal standard were plotted versus the concentrations of the standards to obtain a calibration curve which was linear in the range 0-40 pg. 1-1. The day to day precision was 3.6% (n = 6) and 3.3% (n = 6) at the concentration of 5 and 20 gg. 1-1 respectively. At the same concentrations, extraction ratio of alprazolam reached 93.8% (1.5) (mean and SD) (n = 6) and 91% (2.6) (n = 6), respectively. No interfering substance was present in chromatograms for the pre-dose plasmas. The limit of detection, measured at a detector sensitivity of 0.01 absorbance unit full scale and allowing a signal-to-noise ratio of 2, was 0.5 gg- 1-1. It should be noticed that metabolites of alprazolam have not been assayed on the basis that they appear in a negligible amount and have a half-life close to that of the parent compound (formation-rate limited?). However, it has been verified using spiked plasma that their presence did not interfere under the described procedure.
Kinetic and calculations Plasma concentrations of alprazolam were analyzed by least-square regression techniques. The exponent from the terminal phase of the plasma concentration curve was used to calculate the elimination haft-life. The experimental area under the plasma concentration curve from time 0 to the last detectable plasma level was determined
"'o
1 ;"i'i
i
9
1'2
2'~
3'6
£8
time (hi
Fig.2. Plasma concentrations of alprazolam (ng/ml) after a 2 mg oral dose, before ( ) and after ( ) a two weeks disulfiram treatment
by the trapezoidal method. The residual area extrapolated to infinity was calculated as the final concentration divided by the exponent beta; the sum of both areas yield to AUC from time 0 to infinity. The clearance was calculated as dose divided by AUC, assuming F = 1. (Data suggested that alprazolam is readily absorbed in man, the bioavailabilityof an oral tablet (at least 92%) being comparable to intravenous administration [17] ). Apparent volume of distribution was calculated as clearance divided by beta. Differences between before and after treatment conditions were determined by Student's paired t test. Differences between pharmacokinetic parameters of alprazolam alone or with disulfiram were determined using an analysis of variance.
Results
E l e v e n p a t i e n t s (6 m a l e s a n d 5 f e m a l e s ) a g e d b e t w e e n 33 a n d 56 y e a r s h a v e b e e n i n c l u d e d . A s s h o w n o n T a b l e 1, n o significant d i f f e r e n c e a p p e a r e d b e t w e e n a n y o f t h e a l p r a z o l a m kinetics p a r a m e t e r s b e f o r e a n d a f t e r c h r o n i c t r e a t m e n t w i t h disulfiram. A l p r a z o l a m c l e a r a n c e (Fig. 1), as well as t h e a r e a u n d e r t h e e x p e r i m e n t a l p o i n t s e x t r a p o l a t e d to infinity shows g r e a t v a r i a b i l i t y in b o t h p h a s e s o f t h e trial ( t a b l e I): 22.6 (6.37) n g . m i n . m 1 - 1 o n D a y I a n d
B. Diquet et al.: Disulfiram and alprazolam in alcoholics 21.3 (10.4)ng.min-m1-1 after the second oral dose. Neither the clearance over t v, 94.9 (26.2) vs 112 (77.1) ml.min -1, nor the half-life, 10.09 (5.21) vs 9.31 (6.69) h, differs significantly before and after treatment with disulfiram. The administration of disulfiram had no effect on the experimental peak plasma concentration or the experimental time to peak concentration (Fig. 2): 32.6 (7.2) vs 28.6 (4.7) btg. ml-1 (NS) and 112 (63) vs 142 (52.1) min (NS). Regarding safety, no relevant side effect was observed, except moderate somnolence occurring in three patients.
Discussion Previous reports suggest that the pharmacokinetics of benzodiazepines which undergo hepatic microsomal oxidative metabolism are more susceptible to alterations than those drugs which are eliminated via conjugatives processes. Coadministration of cimetidine as well as hepatic dysfunction have been shown to prolong the elimination of diazepam and desmethyldiazepam both of which are oxidatively metabolized [18]. Conversely the glucuronidation of lorazepam is not substantially altered [19]. Alprazolam is metabolized by hydroxylation to form the 4-hydroxy and alpha-hydroxy derivatives and coadministration of cimetidine prolongs the half-life of alprazolam and reduces its clearance [20]. From a basic research point of view the most surprising is that the oxidation of diazepam is affected whereas in this study that of alprazolam is not. An hypothesis might be the involvement of different isozymes of P-450 cytochromes. Results observed support the hypothesis suggesting a lack of interaction between alprazolam and disulfiram in alcoholic patients, since no difference appeared regarding any of alprazolam elimination-related parameters. For a drug with a low hepatic extraction ratio, clearance might decrease and half-life increase with enzyme inhibition but the availability is essentially unaltered. The hepatic clearance of alprazolam being low, an increase of elimination half-life was expected. As previously reported [9] the half-lives of diazepam and chlordiazepoxide were respectively prolonged by about 37% and 84% in the presence of disulfiram. If these proportions are applied to alprazolam, elimination half-life would reach 22 h, which is obviously not the case here, as the mean value observed in this study is very close to that mentioned in the literature, i. e. 10-16 h [21, 22]. Disulfiram being an old product and despite its frequent use, few data are known about its pharmacokinetics and metabolism in humans. The first and rapid metabolic reaction after the administration is its reduction to diethyl dithiocarbamate (DDC) [23]. Further metabolism of D D C can lead to the formation of its methylester, carbon disulphide or copper bis (diethyl-dithiocarbamate) formed by complexation of D D C with proteinbound copper ions present in plasma. Urinary metabolites are the S-glucuronide of D D C and inorganic sulphate. The reported half-life of 70 min for DDC, whereas disulfiram is reduced within 4 min indicated that the D D C is
159 more stable in human blood. When a therapeutic dose of disulfiram is administered, the patient is reported to remain susceptible to the ethanol sensitizing effect of the drug for up to 12 h [2]; however, by that time the blood concentration of both disulfiram and metabolite would have long since become negligible. Since 90% of the dose taken is eliminated in the urine within 72 h (data supplied by the manufacturing firm of disulfiram [Esp6ral ®] ), it has been taken for granted that, in accordance with a study already mentioned [9], the "active species" (DDC?) plasma levels become stable after a two-week therapy. As no simple and reliable assay of disulfiram or metabolite was made available, patient's compliance to therapy had to be assumed. This assumption does not seem unrealistic considering the strong motivation of patients entering the trial. Anyway, a lack of compliance could explain the unexpected lack of kinetic interaction. Disulfiram does not alter the kinetics of alprazolam absorption, and in spite of the trend for the time to peak to occur later after disulfiram therapy, the difference did not reach significance level. Benzodiazepines have a wide therapeutic index and an increase in plasma concentration is usually of little clinical significance. However, amongst benzodiazepines, alprazolam as well as oxazepam shows lower risk of pharmacokinetic interaction with disulfiram during alcohol withdrawal therapy. Whether or not this lack of interaction is clinically relevant remains to be demonstrated. It would be interesting to conduct other studies in view to compare efficacy and safety of these drugs on a chronic regimen in such patients.
Acknowledgement: The authors thank Mrs Mistral C. (Research Nurse) for her expert technical assistance.
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