European Journal of Clinical Pharmacology © by Springer-Verlag 1977
Europ. J. clin. Pharmacol. 11, 345-349 (1977)
Diazepam Actions and Plasma Concentrations Following Ethanol Ingestion S.M. MacLeod, H.G. Giles, G. Patzalek, J.J. Thiessen, and E.M. Sellers Clinical Institute of the Addiction Research Foundation, 33 Russell Street, Toronto and the Faculties of Medicine and Pharmacy, University of Toronto, Toronto, Ontario, Canada
Summary. In eight normal volunteers, the combination of ethanol (0.5 g/kg) and diazepam (10 mg) administered orally produced a greater decrease in motor performance on a pursuit rotor than diazepam alone. The pharmacologic effect of diazepam was enhanced by 73% and this potentiation was associated with significantly greater diazepam concentrations (p < 0.01) than after diazepam alone. The failure to observe any increase in the concentrations of the principal metabolite, Ndesmethyl diazepam, during the period of enhanced pharmacologic effect precludes any change in the demethylating metabolic process as being responsible. The data suggest (0.10 > p > 0.05) a trend to a smaller volume of distribution of diazepam when ethanol is administered prior to diazepam ingestion. The subjects showed acute tolerance to the effects of diazepam. Lower plasma concentrations on the ascending side of the plasma diazepam concentration versus time profile were linked with the same pharmacologic responses associated with a greater drug concentration on the descending portion, of the same curve. Key words: Diazepam, ethanol, plasma levels, interaction, motor performance.
Diazepam has enjoyed unprecedented acceptance as an anxiolytic drug in large part because of its apparent freedom from adverse effects. There can be little doubt, however, that it has significant pharmacologic effects on cognitive and psychomotor performance [1-12]. Haffner and his co-workers  have compared the mental and psychomotor effects of diazepam and ethanol but greater interest has fo-
cused on interactions between these agents [3-12]. Most studies have indicated that the combination of diazepam and ethanol produced greater decrement in psychomotor performance than either agent alone . These interactions are generally arithmetically additive although potentiation has sometimes been reported and occasional studies have failed to document any interaction between diazepam and ethanol [4, 5]. Methodological differences complicate the interpretation and comparison of ethanol-diazepam interaction studies. Linnoila and his co-workers have carried out several studies on the interaction between diazepam and ethanol, all showing an additive, deleterious effect on psychomotor performance with doses of diazepam ranging from 5 to 10 mg and doses of ethanol ranging from 0.5 to 0.8 g/kg [6-10]. Increased effects were most marked on tests of complex reaction time and motor skill co-ordination. Subject self assessment of psychomotor performance was also impaired. Since the maximum effect preceded peak levels of blood ethanol it was suggested that the ethanol-diazepam interaction occurred at a receptor level . The interaction of ethanol and diazepam could reflect a modification of absorption, distribution or biotransformation of either drug. However, it has been shown that diazepam does not affect blood ethanol concentrations nor does it influence the biotransformation of ethanol [13, 14]. Peak serum levels of diazepam are normally achieved 1 to 2 hours after a single oral dose and bioavailability has been reported as ranging between 75%  and close to 100% . Since the greatest interaction of oral diazepam and ethanol in man is seen within the first hour, it was felt that ethanol might be accelerating the absorption of diazepam. Some data suggesting this has been reported by Linnoila  but the
hypothesis was later retracted on evidence that seems inadequate from a methodological standpoint [121. The present study was intended to resolve this conflict by determining whether there may be a significant influence of ethanol upon the absorption or distribution of diazepam. Motor performance and plasma diazepam concentrations were concurrently assessed with and without ethanol pretreatment.
Material and Methods
Experiments examined the effects of ethanol in a dose of 0.5 g/kg on the absorption and pharmacologic actions of diazepam as measured by pursuit rotor performance in young healthy male volunteers, aged 18 to 25 (mean weight = 62.1 kg, range = 56 to 74.5 kg) who were recruited through advertisement. Subjects were free of drugs and had normal renal and hepatic function. Once entered into the study, subjects were randomly assigned in a balanced cross-over study to one of two treatments on each of two different occasions separated by one week. The two treatments were: a) Diazepam 10rag p.o.; or b) Ethanol 0.5 g/kg p. o. over 15 min followed immediately by diazepam 10 mg p. o. Diazepam was always given to patients following an 8 hour fast (ethanol pretreatment excepted) and food was withheld for at least two hours following drug dosing. Following the administration of diazepam, blood samples of 5 ml each were drawn through a forearm vein from an indwelling cannula at 0, 2.5, 5, 7.5, 10, 12.5, 15, 30, 45 min and 1, 2, 3, 4, 6 and 8 hours. Serum ethanol concentrations were measured by gas-liquid chromatography. Diazepam was analyzed by an adaptation of the method of Arnold  employing flurazepam hydrochloride as the internal standard. Aliquots were analyzed on either a Hewlett-Packard 5710A or a 7620A gas chromatograph equipped with a nickel-63 electron capture detector and an HP-3380 integrator. The column used was 3% OV-17 on chromosorb W, 80-100 mesh, 183 cm by 2 mm I. D. The temperatures of the injector, oven, and detector were 300 °, 255 ° and 300 ° respectively. The standard curve is linear over the range 10-500 ng of diazepam/ml of plasma although dilution is required for solutions with concentrations above 300 ng/ml. Diazepam-H 3 was recovered from blank plasma with an efficiency of 93 + 1% (S. D., n = 6) of the theoretical value. The analysis of replicates indicates a variable error (standard deviation) ranging from 12% at the lower limit to 3% at the upper limit.
S. M. MacLeod et al.: Diazepam Actions and Plasma Concentrations
Motor performance was tested by assessing the subject's ability to follow a light around the circular track (diameter = 22.9 cm) of a photoelectric rotary pursuit instrument (Layfayette Instrument Co., Lafayette, Indiana, U. S. A.) moving at 40 r. p. m. at 1/2, 1, 11/2, 2, 4 and 6 hours after each dose of diazepam. In every instance the test procedure for pursuit rotor performance was identical. The subject was allowed two minutes of practice time and this was followed by 3, 60-second determinations with 20-second rest periods between each determination. Following these 3 determinations, a rest of 60 sec was allowed and this was followed by 3 further 60-second determinations with 20-second rests. The diazepam plasma concentration versus time profiles for the individual subjects could best be fitted by a two-compartment open model with first order absorption and unassumed availability (F). The resultant parameters of the following equations were evaluated by non-linear regression analysis employing the iterative sub-routine GAUSHS on an IBM 370/165 computer. Cp = (B-A)e -kac + Ae -~c - Be -~c ka Dose (VJF)(a-~)
= t - t lag
Z(~-k21) (ka-c 0
Z( -k21) (ka-[3)
Figure la presents the time-concentration data for diazepam taken alone and diazepam taken following ethanol pretreatment. Without exception, at each sample time, the mean plasma diazepam concentration was found to be higher in patients pretreated with ethanol (pooled t test p < 0.001). Figure lb shows the plasma diazepam concentrations measured between 0 and 45 min. There was no diazepam measurable with or without ethanol pretreatment at the time intervals 2.5 and 5.0 rain. Following the appearance of measurable concentrations of diazepam at 7.5 min the levels measured in subjects following ethanol pretreatment were consistently slightly higher than those found without ethanol. Table 1 presents the pharmacokinetic parameters estimated; c~, ~, k21, ka, V1/F and tlag. There were no significant differences in any of these parameters when treatments were compared using t
S. M. MacLeod et al.: Diazepam Actions and Plasma Concentrations 600,
g % 400
o c o Q)
Fig. la. Mean plasma diazepam concentrations following ingestion of diazepam alone (Open Circles) and diazepam following pretreatment with ethanol 0.5 g/kg (Closed Circles) (n = 8)
E 500 uo
g 300 C)
E ~- 200
~ $ 0
Fig. lb. Mean plasma diazepam concentrations in the first 45 min following ingestion of diazepam alone (Open Circles) and diazepam following pretreatment with ethanol 0.5 g/kg (Closed Circles) (n = 8)
1. Mean (+ SD) Fitted Pharmacokinetic Parameters For Diazepam With And Without Ethanol Pretreatment (See Text For Details)
Diazepam & ethanol
ct(hr -1) 13 (hr -1)
0.99 (0.15) 0.00042 (0.00066) 0.14 (0.048) 9900 (970) 0.81 (0.12) 0.11 (0.025)
0.80 (0.19) 0.0060 (0.011) 0.12 (0.061) 8600 (1600) 0.82 (0.31) 0.11 (0.024)
N.S. N.S. N.S. N.S. N.S. N.S.
V1/F (ml) ka (hr -1) tjag (hr)
Paired Student's t-test; level of confidence
not significant at the 95%
tests although a weakly significant trend (0.10 > p > 0.05) to a smaller V1/F after ethanol pretreatment was calculated. This tendency may suggest a decrease in the initial apparent distribution space and/or an increase in diazepam bioavailability. Figure 2 presents the effects of ethanol alone, diazepam alone and ethanol and diazepam together on motor performance as determined by the pursuit rotor test. The mean decrement in pursuit rotor performance for each 60-second period is plotted on the ordinate against mean plasma diazepam or blood ethanol concentrations plotted on the abscissa. The central loop indicates the effects of ethanol on pursuit rotor performance, and clearly demonstrates the development of acute tolerance. The mean decrement of 4 seconds in performance seen at a blood ethanol concentration of 55 mg% on the ascending limb of the loop should be contrasted with a mean decrement of 11/2 seconds at the same blood ethanol concentration on the descending limb. The arrows in this case represent the chronological direction. It should be mentioned that the effect of ethanol alone on motor performance was measured in a different group of subjects from those in the present study and these results have been previously reported . The middle loop represents the effect of diazepam alone on pursuit rotor performance and it appears that a dose of 10 mg of diazepam produces a greater decrement than does a dose of ethanol alone of 0.5 g/kg. This loop also indicates a development of acute tolerance as evidenced by a 7.5-second decrement in performance at a plagma diazepam concentration of 360 ng/ml on the ascending limb with no decrement at the same plasma diazepam concentration at a later time. Following ethanol pretreatment, the same dose of diazepam produces a much more dramatic decrement in motor performance and again the development of acute tolerance is demonstrated. It is noteworthy that all three of these motor performance-drug concentration loops have a similar pattern suggesting that diazepam and ethanol alone or in combination may act in a similar manner pharmacologically. Figure 3 plots the mean decrement in pursuit rotor performance on the ordinate against time following the administration of oral diazepam alone and of oral diazepam following ethanol pretreatment. After oral diazepam, impairment was maximal at 60 min and normal skills had returned at 120 min. When ethanol was given prior to oral diazepam the overall pattern of impairment was largely unchanged; however, return to normal skills was delayed untill some point between 120 and 240 min and the maximum decrement in performance was increased at 60 min by approximately 80%.
S. M. MacLeod et al.: Diazepam Actions and Plasma Concentrations 14
E cD g Q
100 200 300 400 500 MeanPlasmaDiazepamConcentration(ng/ml)
20 40 60 80 100 MeanBlood Ethanol(mg/lOOcc)
Fig. 2. Relationship between decrement in pursuit rotor performance and mean plasma-diazepam and/or blood ethanol concentrations. The mean decrement in pursuit rotor performance per 60 sec is plotted as a function of diazepam or ethanol concentration. The directional arrows indicate the order of the determinations during the study session. The effects of ethanol alone in a dose of 0.5 g/kg (Open Triangles), diazepam alone in a dose of 10 mg (Closed Circles) and the combination of ethanol 0.5 g/kg followed by diazepam 10 mg (Open Circles) are represented (n
9' Time (min)
Fig. 3. The mean decrement in pursuit rotor performance is plotted against the time following the administration of 10mg diazepam orally alone (Open Circles) and following pretreatment with ethanol 0.5 g/kg (Closed Circles) (n = 8)
A comparsion may be made between the fates of ethanol and diazepam after administration of single oral doses. Ethanol is rapidly eliminated from the plasma compartment (mean peak concentration = 850 mg/1 at 45 min, mean concentration at 2 hours = 500 mg/l) while over that same time diazepam primarily undergoes distribution. Therefore, any changes in the plasma diazepam concentration versus time profile are unlikely to be the result of metabolic effects of ethanol or diazepam when single doses are given immediately following ethanol ingestion. Furthermore, the phenomena described above appear well before N-desmethyl diazepam is detectable in plasma and this precludes any change in biotransformation as being responsible for the interaction. In view of the study design, the areas under the entire diazepam concentration versus time curves should be indentical after both treatments. Unfortunately, the data are not adequate to permit a comprehensive characterization of the diazepam curves. Thus, confirmation of the equivalence of the areas under the curves is not possible. In this study, the kinetic data are best described by a two-compartment open model although diazepam kinetics are usually best described by a three-compartment model. As evidenced by the present results, ethanol appears to have affected the availability (F) or initial distribution of diazepam. Since enhanced rate or extent of availability may be caused by improved dissolution, in separate experiments we determined that ethanol (1.5 M) does not influence the dissolution rate of diazepam tablets in hydrochloric acid (0.1 M). This study demonstrates that diazepam alone or in combination with ethanol is able to produce measurable and reproducible decrements in motor performance as assessed by the pursuit rotor test. It has also been shown that acute tolerance develops to this effect of diazepam in the presence or absence of ethanol. Peak concentrations of ethanol in serum were reached at 45 min after diazepam dosing and this preceded maximum decrement in pursuit rotor performance following oral diazepam. This finding is in contrast with the observation of Linnoila ; however, a significant decrease in motor performance did occur while ethanol concentration was still rising and it remains possible that the interaction occurs at a central nervous system receptor as has been suggested . Peak plasma concentrations of diazepam after oral dosing were not achieved until 60 rain, the time of maximal decrement in motor performance. Diazepam absorption and distribution thus appear
S. M. MacLeod et al.: Diazepam Actions and Plasma Concentrations
to be more important than ethanol absorption and distribution in determining the observed psychomotor effects of the ethanol-diazepam combination. The alterations observed in motor performance response to diazepam following ethanol pretreatmerit cannot be explained on the basis of altered dissolution, absorption or biotransformation of diazepam. Whitehouse et al.  have shown in rats pretreated with ethanol 3 g/kg, that 60 min after diazepam dosing, brain concentrations of diazepam were 6.4 times control. It is possible that diazepam distribution in man is similarly altered by ethanol. The magnitude of the interaction shown in the present study stresses the need for careful research into diazepam-ethanol interactions in relation to the performance of motor skills such as driving.
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Received: September 27, 1976, and in revised form: January 17, 1977; accepted." January 23, 1977 Dr. S. M. MacLeod Suite 216, Nurses Residence Toronto Western Hospital 399 Bathurst Street Toronto, Ontario M5T 2S8 Canada