Barbiturates cause enzyme stimulation in the liver, leading to a shortened duration of many drugs.

• A. They do not affect liver enzymes
• B. They cause enzyme stimulation in the liver, shortening the duration of many drugs
• C. They slow metabolism
• D. They are cleared by kidneys only

Answer: (B)

Barbiturates induce hepatic enzymes, which boosts the liver’s ability to metabolize many drugs. When enzyme levels rise, drugs that rely on these enzymes are cleared faster, lowering their plasma concentrations and shortening their duration of action. This is a classic example of enzyme induction in the liver. The other statements don’t fit: not affecting liver enzymes would mean no interaction; slowing metabolism would prolong a drug’s duration; and being cleared by the kidneys only ignores the hepatic enzyme induction that shortens duration.