Interactions o f Some Street Drugs

Blake B. C o ldw ell1’2 , B arry H. T hom as and K eith Bailey

In Canada, alcohol presents the greatest hazard of all the psychoactive, addicting drugs (13). The most common drugs ingested with alcohol are the barbiturates (6, 7, 11). While the toxicity of ethanol-barbiturate combinations has been well documented (1, 12), the biochemical and physiological changes associated with this toxicity are not thoroughly understood. The widespread use of marihuana has focused attention on its potential for causing harmful effects in man. One area, that of its interaction with other drugs, has received some attention in our laboratories (2). The purpose of this paper is to review, briefly, our laboratory studies with animals concerning the inter­actions of alcohol and marihuana components with other CNS drugs. We believe these observations may help to explain, at least in part, some of the pharmacological and toxicological effects of such drug combinations observed in man.

ALCOHOL AND BARBITURATES

A cute ToxicityEthanol (15% w/v) and barbiturates were administered simultaneously by the intraperitoneal route to overnight-fasted, male albino rats of the Wistar strain. The 24-hr LD50 values of the barbiturates were determined at ethanol doses of 0, 2, 3 and 4 g/kg. The effect of ethanol (3g/kg) on barbiturate sleeping time was also investi­gated. The results of these studies are summarized in Figures 1 and 2.

The presence of ethanol produced a dose-dependent decrease in the LD50 values of all five barbiturates examined (thiopental, pentobarbital, amobarbital, pheno­barbital and barbital); the effect being most pronounced with the more slowly metabolized hypnotics. Similarly, ethanol greatly prolonged the barbiturate sleeping time, the effect being most pronounced with the long-acting members (16).

1Drug Research Laboratories, Health Protection Branch, Health and Welfare Canada, Ottawa, Canada, K1A 0L2.2 Many persons have contributed to the investigations reviewed in this paper, especially Drs.G.S. Wiberg, H. L. Trenholm, B. H. Thomas, K. Bailey and L. Whitehouse, and Messrs. C. J. Paul, G. Solomonraj and W. Zeitz.

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454 B. B. Coldwell, B. H. Thomas, e t al.

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Figure 1 The effects o f ethanol on the 24 hour LD 50 o f barbiturates in rats. Figures on the abscissa are doses o f ethanol (g/kg).

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Figure 2 The effect o f ethanol (ip, 3g/kg, 15% w /v aqueous solution) on the median sleeping time induced by ip administration o f threshold hypnotic doses o f thiopental (thio, 30mg/kg), pentobarbital (pent, 30mg/kg), amobarbital (amo, 60mg/kg), and sub- threshold hypnotic doses o f phenobarbital (pheno, 50mg/kg), and barbital (barb, 125mg/kg) to groups o f 15-20 rats. The barbiturates were administered alone (mm) and simultaneously with ethanol (nrn).

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We have investigated the effect of an acute dose of ethanol (3g/kg as a 15% w/v solution) on the pharmacokinetics of pentobarbital (15) and phenobarbital (3). With both barbiturates, the presence of ethanol caused elevated brain levels of the pharmacologically active unchanged drug. This increase was due to alcohol inhibition of barbiturate biotransformation to polar metabolites. These observations are summarized in Figures 3, 4, 5, and 6. Figure 3 shows that many tissues had higher levels of radioactivity, emanating from 14C-pentobarbital, when ethanol was administered with the drug. Figure 4, summarizing the urinary excretion data for the major metabolites of pentobarbital, indicates that ethanol caused a marked reduction in the excretion of M-l, believed to be 5-ethyl-5-(l-methyl-3-carboxypropyl) bar­bituric acid, and an increase in M-IV, 5-ethyl-5-(3-hydroxy-l-methylbutyl) barbituric acid. Figure 5 shows the effect of ethanol on the level of radio-activity in the liver and brain of rats administered 14C-phenobarbital, alone and with ethanol. Figure 6 illustrates that ethanol-treated rats excreted less p-hydroxy-phenobarbital, the major metabolite of phenobarbital, than the control animals.

In all of these experiments, no metabolites of pentobarbital or phenobarbital were detected in the brain and the barbiturate blood:brain ratios were similar in alcohol and non-alcohol treated rats. Thus the enhanced levels of radioactivity in the brains of the ethanol-treated animals is due to the unchanged drug, which could account for some of the toxicity of ethanol-barbiturate combinations. Further, there is no evidence that an intoxicating dose of ethanol facilitated the passage of the bar­biturates from blood to brain (4). While the barbiturates do not affect the rate at which ethanol disappears from the blood, they appear to cause changes in the blood and brain concentrations of acetaldehyde and acetone in ethanol-treated animals (5). These effects may also contribute to the toxicity.

* P<0.05

P harm a co k in e tic Investiga tio ns

Figure 3 Tissue distribution o f radioactivity expressed as pentobarbital (IJg/g w et weight) in groups o f three rats 3 hours after ip injection o f 1 ̂ C-pentobarbital (30mg/kg) and either 15% ethanol (3 s /k s .K ^ j or saline control (CD). The figures are means with standard errors.

456 B. B. Coldwell, B. H. Thomas, et al.

Figure 4

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Figure 6

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The cumulative excretion o f pentobarbital and its m etabolites in rat urine after either pentobarbital and ethanol (PB+E) or pentobarbital and saline control (PB). The figures, expressed as a percentage o f the dose o f 14C-pentobarbital (30mg/kg), are means with standard errors. The dose o f ethanol was 3g/kg (7.5% w /v solution in saline) and both drugs were administered orally. N=6.

T IM E (H)

Radioactivity in liver (A) and brain (B), expressed as phenobarbital (/Jg/g w et weight) from rats treated orally with 14C-phenobarbital (SOmg/kg), alone ( - • - ) , and with ethanol (3g/kg, 7.5% w /v aqueous solution, - 0 - ) . Each po in t represents the mean± standard error in 4 animals.% DOSE EXCRETEO IN URINE

Cumulative excretion o f phenobarbital (A) and p-hydroxyphenobarbital (B) in rat urine, expressed as percentages o f the dose o f ̂̂ C-phenobarbital administered (50mg/kg, orally) alone (—%-) cind with ethanol (3g/kg, 7.5% w/v aqueous solution, ~0~). Each po in t represents the meanistandard error o f three animals.

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ALCOHOL AND OTHER DRUGS

A m phetam ineThe effect of ethanol on the toxicity and metabolism of amphetamine in male Swiss Webster mice was investigated. The mouse was chosen because amphetamine metabolism in this species proceeds to a significant extent through the oxidative pathways which are believed to predominate in man (8). Amphetamine exhibits a biphasic LD50 response in mice (9, 10). In our experiments ethanol (3g/kg) reduced the mortality caused by low doses of amphetamine but did not significantly alter the lethality of high doses. Urinary excretion studies indicated that ethanol inhibited amphetamine metabolism (Table I).

TABLE I Effect o f Ethanol (E) on the Urinary Excretion o f Amphetamine (A ) and Metabolites*>b

Compound A a + e 2 a + e 3Amphetamine 43.9 ±3.6 64.4 ± 5.1 68.6 ± 1.4p-Hydroxyamphetamine 3.7 ± 0.6 2.2 ± 0.2 1.9 ±0.3p-Hydroxyamphetamine glucuronide 14.4 ±0.8 8.5 ± 0.4 4.7 ± 0.3Hippuric acid 20.6 ± 2.3 19.3 ± 1.8 18.9 ± 1.6Unknown I 1.5 ± 0.3 1.5 ±0.6 1.0 ± 0.5Unknown II 15.9 ±4.9 4.2 ± 3.3 4.9 ± 2.1Total dose excreted, % 70.6 62.2 55.9aIn the 6 hour period immediately following ip administration to non-grouped mice.

b 14C-d-Amphetamine sulfate (lOmg/kg) was administered alone or with ethanol (15% w/v aqueous solution) at 2 (E2) and 3 (E3)g/kg. The results are expressed as a percentage (mean ± S.E.) of the total amount o f radioactivity excreted in 6 hours.

DiazepamRecently, we have investigated the effect of ethanol on the pharmacokinetics of diazepam in the rat. Some of the data are summarized in Figure 7. The brains from rats treated with diazepam plus ethanol (3g/kg), compared to those from rats given diazepam alone, contained significantly more unchanged diazepam and mono- hydroxylated derivatives, indicating ethanol inhibition of metabolism.

IsoniazidPreliminary data indicate that ethanol may alter the metabolism of isoniazid in rats. In the presence of ethanol and after oral administration of isoniazid, the excretion of isonicotinic acid and isonicotinoyl glycine was reduced and that of N-acetylisoniazid was increased relative to the amounts excreted by control animals.

A9 tetrahydrocannabinolThe metabolism of this component of marihuana in rats was not altered by the simultaneous administration of ethanol.

458 B. B. Coldwell, B. H. Thomas, et al

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Figure 7 Levels o f diazepam and m etabolites in the brain during the 2 hours follow ing oral administration o f 1 ^C-diazepam (5mg/kg) to rats treated 30 minutes earlier with water (20 ml/kg) or ethanol (3g/kg, 15% w /v aqueous solution). Each poin t repre­sents the mean o f 5 animals. Controls: diazepam, -A-; m onohydroxylated diazepam, - o - ; other metabolites;- O . Ethanol treated: diazepam, - A- ; m ono-hydroxylated diazepam, —m—; other m etabolites,-m -.

CANNABINOIDS AND PENTOBARBITALThe effect o f cannabidiol (CBD), cannabigerol (CBG), cannabinol (CBN), A8-tetra­hydrocannabinol (A8-THC), and A9-tetrahydrocannabinol (A9-THC) on the in vivo metabolism of 14C-pentobarbital was investigated in rats (2). The cannabinoids (20 mg/kg, ip) were administered 30 min prior to either oral or iv treatment with 14C- pentobarbital. The levels of total radioactivity and of unchanged pentobarbital and metabolites were determined in the blood, liver, brain and urine at various times up to 24 hr after dosing. Figure 8 shows the blood radioactivity profiles obtained after treatment with CBD, CBG, A8-THC or A9-THC and 14 C-pentobarbital (30mg/kg, iv). Only CBD had a significant effect on the blood profile. Figure 9 indicates this effect is dose dependent.

SUMMARYIt would appear from these investigations that the metabolism of many drugs may be altered by the presence of ethanol, leading to an enhancement of the pharmacological effects and the increased likelihood of toxic reactions. It has been shown that the

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clearance of some drugs from the blood of human subjects is retarded by the presence of ethanol (14). Our studies in animals suggest that this is most likely due to an inhibition of drug metabolism by ethanol and very probably, in man as in the rat, such inhibition leads to higher brain levels of the drug and enhanced effects on the target

Figure 8 Blood 14C concentration profiles, expressed as mean±SE o f [Jg/ml o f sodium pento­barbital, obtained from groups o f 5 rats treated ip with 20 mg/kg o f cannabidiol (CBD, —0— , cannabigerol (CBG, — A—J, A8-tetrahydrocannabinol /A -THC,-o~), £&-tetrahydrocannabinol (A9-THC, —0— , or vehicle ( -+ -), followed 30 minutes later by ^C -pentobarbital (iv, 30 mg/kg). A-CBD and CBG; B-l$-TH C and t?-THC. Significant differences: CBD vs controls-from 1.5 to 12 hours, CBD > controls (p < 0.01). A9-THC v s controls — a t 0.25 and 1 hour, controls > A 9 -THC (p < 0 .0 5 ) , at 4 hours A9-T H C > controls (p < 0 .0 5 ).

Figure 9 The dose response effect o f cannabidiol (CBD) on blood 14C concentrations, expressed as mean±SE o f /Jg/ml o f sodium pentobarbital, obtained from groups o f 6 rats treated ip with 5 ( -o- ), 10 (—A — , 20 (—0— mg/kg o f CBD, or vehicle (■*■), follow ed 30 minutes later by 14C-pentobarbital (po, 30 mg/kg).Significant differences: 20 mg,/kg vs controls - 1 hour, p < 0 .0 5 ; 3-12 hours, p < 0.01. 10 mg/kg vs controls - 1.5 hours, p < 0.05; 2-12 hours, p < .0 .01. 5 mg/kg vs controls — 6 and 12 hours, p < 0 .0 5 ; 2-4 and 8 hours, p < 0 .0 1 .

460 B. B. Coldwell, B. H. Thomas, e t al.

organs, such as the central nervous system. Investigations on the in vivo interaction of marihuana components with pentobarbital indicate that non-euphoric effects, due to cannabinoids other than A9-THC, which might lead to impairment of function, are a distinct possibility.

REFERENCES1. Bogan, J., and Smith, H. Analytical Investigations o f Barbiturate Poisoning: Description of Methods and a Survey o f Results, Journal o f Forensic Sciences 7, 37 (1967).2. Coldwell, B.B., Bailey, K., Paul, C. J. and Anderson, G. Interaction o f Cannabinoids with Pentobarbital in Rats, Toxicology and A pplied Pharmacology 28, in press (1974).3. Coldwell, B. B., Paul, C. J. and Thomas, B. H. Phenobarbital Metabolism in Ethanol-

Intoxicated Rats, Canadian Journal o f Physiology and Pharmacology, 51, 458 (1973).4. Coldwell, B. B., Trenholm, H. L., Thomas, B. H. and Charbonneau, S. The Effect o f Ethanol

on Phenobarbitone and Pentobarbitone Absorption into Rat Blood and Brain, Journal o f Pharmacy and Pharmacology, 23, 947 (1971).5. Coldwell, B. B., Wiberg, G. S. and Trenholm, H. L. Some Effects of Ethanol on the Toxicity and Distribution o f Barbiturates in Rats, Canadian Journal o f Physiology and Pharmacology. 48, 254 (1970).6. Devenyi, P. and Wilson, M. Barbiturate Abuse and Addiction and their Relationship to

Alcohol and Alcoholism, Canadian Medical Association Journal. 104, 215 (1971).7. Devenyi, P., and Wilson, M. Abuse of Barbiturates in an Alcohol Population, Canadian

Medical Association Journal. 104, 219 (1971).8. Dring, L. G., Smith, R. L. and Williams, R. T. Metabolic Fate o f Amphetamine in Man and

Other Species, Biochemical Journal. 116, 425 (1970).9. Gardocki, J. F., Schuler, M. E. and Goldstein, L. Reconsideration of the Central Nervous System Pharmacology o f Amphetamine. I. Toxicity in Grouped and Isolated Mice, Toxi­cology and A pplied Pharmacology. 8, 550 (1966).

10. George, D. J. and Wolf, H. H. Dose Lethality Curves for d-Amphetamine in Isolated and Aggregated Mice, Life Science 5 , 1583 (1966).

11. Glatt, M. M., The Abuse o f Barbiturates in the United Kingdom, Bulletin on Narcotics 14, 19(1962).12. Gupta, R. C., and Kofoed, J. Toxicological Statistics for Barbiturates, other Sedatives and Tranquillizers in Ontario: A 10-year Survey, Canadian Medical Association Journal. 94, 863

(1966).13. LeDain, G. Interim R eport o f the Commission o f Enquiry into the Non-Medical Use o f Drugs. Queen’s Printer, Ottawa, Canada, 1970.14. Rubin, E., Gang, H., Misra, P. S. and Lieber, C. S. Inhibition o f Drug Metabolism by Acute

Ethanol Intoxication. A Hepatic Microsomal Mechanism, American Journal o f Medicine 49, 801 (1970).

15. Thomas, B. H., Coldwell, B. B., Solomonraj, G., Zeitz W. and Trenholm, H. L. Effect o f Ethanol on the Fate o f Pentobarbital in the Rat, Biochemical Pharmacology 21, 2605(1972).

16. Wiberg, G. S., Coldwell, B. B. and Trenholm, H. L. Toxicity o f Ethanol-Barbiturate Mixtures, Journal o f Pharmacy and Pharmacology 2 1 ,2 3 2 (1969).