Alcohol and Medication Interactions - a combination of alcohol and medication can impair driving and machinery operation abilities

Alcohol Research & Health, Wntr, 1999 by Ron Weathermon, David W. Crabb

Antihistamines. These medications, which are available both by prescription and OTC, are used in the management of allergies and colds. Antihistamines may cause drowsiness, sedation, and low blood pressure (i.e., hypotension), especially in elderly patients (Dufour et al. 1992). Through pharmacodynamic interactions, alcohol can substantially enhance the sedating effects of these agents and may thereby increase, for example, a person's risk of falling or impair his or her ability to drive or operate other types of machinery. As a result of these potential interactions, warning labels on OTC antihistamines caution patients about the possibility of increased drowsiness when consuming the medication with alcohol. Newer antihistamines (i.e., certrizine and loratidine) have been developed to minimize drowsiness and sedation while still providing effective allergy relief. However, these newer medications may still be associated with an increased risk of hypotension and falls among the elderly, particularly when combined with alcohol. Consequently, patients taking nonsedating antihistamines still should be warned against using alcohol.

Barbiturates. These medications are sedative or sleep-inducing (i.e., hypnotic) agents that are frequently used for anesthesia. Phenobarbital, which is probably the most commonly prescribed barbiturate in modern practice, also is used in the treatment of seizure disorders. Phenobarbital activates some of the same molecules in the CNS as does alcohol, resulting in pharmacodynamic interactions between the two substances. Consequently, alcohol consumption while taking phenobarbital synergistically enhances the medication's sedative side effects. Patients taking barbiturates therefore should be warned not to perform tasks that require alertness, such as driving or operating heavy machinery, particularly after simultaneous alcohol consumption.

In addition to the pharmacodynamic interactions, pharmacokinetic interactions between alcohol and phenobarbital exist, because alcohol inhibits the medications breakdown in the liver. This inhibition results in a slower metabolism and, possibly, higher blood levels of phenobarbital. Conversely, barbiturates increase total cytochrome P450 activity in the liver and accelerate alcohol elimination from the blood (Bode et al. 1979). This acceleration of alcohol elimination probably does not have any adverse effect.

Benzodiazepines. Like barbiturates, benzodiazepines (BZDs) are classified as sedative-hypnotic agents and act through the same brain molecules as do barbiturates. Accordingly, as with barbiturates, concurrent consumption of BZDs and moderate amounts of alcohol can cause synergistic sedative effects, leading to substantial CNS impairment. It is worth noting that both barbiturates and benzodiazepines can impair memory, as can alcohol. Consequently, the combination of these medications with alcohol would exacerbate this memory-impairing effect. In fact, this effect sometimes is exploited by mixing alcoholic beverages with BZDs, such as the rapid-acting flunitrazepam (Rohypnol[R]), an agent implicated in date rape (Simmons and Cupp 1998). In addition, the metabolism of certain BZDs involves cytochrome P450, leading to the alcohol-induced changes in metabolism described earlier in this article.