3 Metabolism and Excretion Free Online FlashCards

What is drug metabolism?

Metabolism, or biotransformation, is the chemical alteration of a drug by the body.

How can enzyme inhibition affect drug exposure?

Enzyme inhibition slows metabolism and may increase drug exposure; the clinical effect depends on the drug.

What is drug excretion?

Excretion is the removal of a drug or its metabolites from the body.

What three processes handle substances in the kidneys?

In the kidneys, substances may be filtered from blood, secreted into urine, or reabsorbed back into blood.

What does drug clearance measure?

Clearance is the volume of plasma cleared of drug per unit time, not the total amount of drug removed.

What is a drug's elimination half-life?

Elimination half-life is the time required for plasma drug concentration to fall by half during elimination.

What remains after four half-lives with first-order elimination?

With first-order elimination, a constant fraction is removed per interval. After four half-lives, about $6.25\%$ of the starting amount remains.

Where does drug metabolism mainly occur?

Metabolism occurs mainly in the liver, but the intestines, kidneys, blood, and other tissues can also contribute.

What outcomes can drug metabolism produce?

Metabolism can make a drug more water-soluble, inactivate it, produce an active metabolite, or activate an initially inactive prodrug.

What can enzyme induction do to a drug's effects?

Enzyme induction speeds metabolism and may reduce exposure, though faster metabolism can increase effects if the drug is a prodrug.

Which are two nonrenal routes of drug excretion?

Drugs can also leave through bile and feces or through the lungs if they are volatile.

How is clearance calculated in the simplified model?

Clearance equals the rate of drug elimination divided by plasma drug concentration: $CL = \frac{\text{rate of drug elimination}}{\text{plasma drug concentration}}$.