Drug Interactions And Alcohol

The term alcohol-drug interaction refers to the possibility that alcohol may alter the intensity of the pharmacological effect of a drug, so that the overall actions of the combination of alcohol plus drug are additive, potentiated, or antagonistic. Such interactions can be divided into two broad categories — PHARMACOKINETIC and Pharmacodynamic. Pharmacokinetics are concerned with the extent and rate of absorption of the drugs, their distribution within the body, binding to tis sues, biotransformation (metabolism), and excretion. Pharmacokinetic interactions refer to the ability of alcohol to alter the plasma and tissue concentration of the drug and/or the drug metabolites, such that the effective concentration of the drug at its target site of action is significantly decreased or increased. Pharmacodynamics are concerned with the biochemical and physiological effects of drugs and their mechanisms of action. Pharmacodynamic interactions refer to the combined actions of alcohol and the drug at the target site of action, for example, binding to enzyme, receptor, carrier, or macromolecules. Phar-macodynamic interactions may occur with or without a pharmacokinetic component. For many drugs acting on the central nervous system that exhibit cross-tolerance (a similar tolerance level) with alcohol, pharmacodynamic interactions with alcohol are especially important.

Most drugs are metabolized in the liver by an enzyme system usually designated as the cyto-chrome P450 mixed-function oxidase system, and the liver is the principal site of many alcohol-drug pharmacokinetic interactions. Two major factors— blood flow to the liver and the activity of drug-metabolizing enzymes—strongly influence the overall metabolism of drugs. Biotransformation of drugs that are actively metabolized by liver enzymes mainly depends on the rate of delivery of the drug to the liver. These may be flow-limited drugs, where the liver can transform as much drug as it receives, or capacity-limited drugs, which have a low liver-extraction ratio—their clearance (removal from the blood) primarily depends on the rate of their metabolism by the liver.

There are a number of factors other than the drugs themselves that influence the speed and intensity of alcohol/drug interactions in the human body. These include the patient's sex, weight, age, and race; the presence or absence of food in the stomach; and history of alcohol intake. For example, the levels of alcohol dehydrogenase (ADH), a stomach enzyme that oxidizes alcohol to acetalde-hyde, are lower in women than in men; lower in Asians than in Western Caucasians; and lower in alcoholics than in nonalcoholics. Elderly persons are at greater risk of alcohol/drug interactions than younger adults, because they usually take more prescription medications, are more likely to have a serious illness, and show age-related changes in the absorption and clearance of certain medications.

With regard to stomach contents, food generally slows the rate of alcohol absorption. Consequently, medications that increase the rate of gastric emptying, such as erythromycin (Eryc, Ilotycin) or cisapride (Propulsid), enhance the rate of alcohol metabolism.

Drug Addiction

Drug Addiction

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