What outcome can occur when enzyme induction of phenobarbital occurs with oral contraceptives?

What outcome can occur when enzyme induction of phenobarbital occurs with oral contraceptives?

• A. Decreased blood serum levels of phenobarbital
• B. Increased action of oral contraceptives
• C. Unreliable contraception
• D. Two of the above

Answer: (C)

Enzyme induction speeds up the liver’s drug-metabolizing enzymes. Phenobarbital is a strong inducer, so when it is used with oral contraceptives, the contraceptive steroids are broken down more quickly. This lowers their blood levels and diminishes their ability to prevent ovulation, making contraception unreliable. While phenobarbital itself can have changes in metabolism with chronic use, the main and most clinically important effect in this pairing is the reduced effectiveness of the oral contraceptive.

Enzyme induction speeds up the liver’s drug-metabolizing enzymes. Phenobarbital is a strong inducer, so when it is used with oral contraceptives, the contraceptive steroids are broken down more quickly. This lowers their blood levels and diminishes their ability to prevent ovulation, making contraception unreliable. While phenobarbital itself can have changes in metabolism with chronic use, the main and most clinically important effect in this pairing is the reduced effectiveness of the oral contraceptive.