Which statement best describes nifedipine's pharmacologic class when used as a tocolytic?

• A. It is a calcium channel blocker
• B. It is a beta-adrenergic agonist
• C. It is an NSAID
• D. It is a prostaglandin analog

Answer: (A)

Nifedipine used as a tocolytic works by blocking calcium channels in smooth muscle. By inhibiting L-type calcium channels, it reduces calcium entry into uterine muscle cells, lowering intracellular calcium and causing the myometrium to relax. This direct effect on smooth muscle makes it a calcium channel blocker, which is why this option is the best description of its pharmacologic class for this use.

Other choices don’t fit as well. Beta-adrenergic agonists relax smooth muscle through sympathetic stimulation but come with significant maternal and fetal side effects such as tachycardia and hyperglycemia. NSAIDs tocolytics work by inhibiting prostaglandin synthesis, which can delay labor but carry risks like effects on fetal circulation (e.g., ductus arteriosus) and other neonatal issues. Prostaglandin analogs promote labor by stimulating contractions and cervical ripening, not by relaxing the uterus.