Do Alcohol & Renal Failure Affect Drug Metabolism?

Alcohol can affect the metabolism of drugs in several ways. It can reduce the metabolism of other drugs, or it can increase the metabolism of other drugs. Alcohol use can turn some drugs into toxic substances. The kidneys, however, do not metabolize drugs but rather filter many drugs out of the blood. Renal failure can cause the drugs to build up in the body. You should always discuss your prescription and non-prescription drugs with your doctor or pharmacist if you drink alcohol or have renal failure.

Basics of Drug Metabolism

• The liver metabolizes nutrients such as protein and carbohydrates, as well as alcohol and many drugs. To metabolize means to break down into simpler molecules. The body can use these simpler molecules or it can clear them out of the body, such as through the kidneys, The liver metabolizes substances by making enzymes. Different enzymes metabolize different substances. By affecting the way the liver works and the enzymes it makes, drugs can interfere with each other's metabolism in several different ways.

Effects of Alcohol on Drug Metabolism

• The National Institute on Alcohol Abuse and Alcoholism (NIAAA) lists four ways alcohol can interact with other drugs:

  1) The enzyme that metabolizes alcohol may also metabolize another drug. The presence of alcohol in the blood can reduce the metabolism of the other drug.
  2) Chronic alcohol use may activate enzymes that metabolize other drugs.
  3) Chronic alcohol use may also activate enzymes that turn drugs into harmful substances.
  4) Alcohol may increase the effects of other sedatives and narcotic drugs.

  The fourth effect does not pertain to the metabolism of other drugs. However, those who use alcohol should keep it in mind if they take sedatives or narcotic painkillers like morphine.

Significance of Reduced Drug Metabolism

• The enzyme aldehyde dehydrogenase metabolizes most of the alcohol ingested by occasional users. Having a drink of alcohol may prevent aldehyde dehydrogenase from metabolizing other substances. The reduced metabolism of another drug can cause that drug to build up in the blood. The buildup can cause side effects and symptoms of overdose. For example, according to NIAAA and information published in Pharmacist's Letter/Prescriber's Letter (PL/PL), a drink of alcohol can reduce the metabolism of tricyclic antidepressants, increasing their sedative effects.

Importance of Increased Drug Metabolism

• Chronic use of alcohol can activate enzymes that speed up the metabolism of some drugs. The information in PL/PL notes that chronic drinking can have the opposite effect on the metabolism of tricyclic antidepressants as occasional drinking. By increasing the metabolism of these drugs, chronic use of alcohol may cause the need for higher doses to get the right therapeutic effect.

Renal Failure

• The kidneys remove excess fluid, minerals and waste from your blood. Where the liver metabolizes many drugs, the kidneys remove most drugs and their metabolites from the blood and pass them out of the body in the urine. If the kidneys begin to fail, then so does their ability to remove drugs and their metabolites from the blood. These substances can build up in the body, along with the other harmful substances the kidneys normally remove. The kidney failure itself along with the ever-higher levels of drugs in the blood will cause serious symptoms.

Drug Dosing in Renal Failure

• Renal failure generally requires reduced dosages of most drugs. Renal failure occurs in degrees, from mild to severe. For most drugs, doctors adjust the dosage based on clinical measures of kidney function. A study published in "American Family Physician" in 2007 provides dosage adjustments for many drugs keyed to the most commonly used measures of renal function. In general, the more severe the renal failure, the lower the dose of the drug.