Grapefruit juice and antacids are contraindicators for medications?

• A. Grapefruit juice and antacids
• B. Ibuprofen and acetaminophen
• C. Vitamin C and zinc
• D. Caffeine and sugar

Answer: (A)

Grapefruit juice and antacids affect how many medicines are absorbed and metabolized, so their combination with certain drugs is generally contraindicated. Grapefruit juice blocks intestinal enzymes (notably CYP3A4) and transporters, which normally break down or move drugs across the gut lining. When these are inhibited, drug levels in the bloodstream can rise unexpectedly, increasing the risk of toxicity for medications that rely on gut metabolism or have a narrow safety margin (such as some statins, calcium channel blockers, and certain immunosuppressants).

Antacids, on the other hand, change the stomach’s environment and can bind drugs or minerals, forming less soluble complexes. This can markedly reduce the absorption of drugs like certain antibiotics (tetracyclines, fluoroquinolones) and thyroid hormone, among others. The timing matters: separating antacid use from these medications by a few hours can sometimes prevent the interaction, but for some drugs, coadministration is avoided altogether.

Other listed pairs don’t present the same broad, clinically significant interaction pattern with a wide range of medications, so they aren’t classified as contraindicated in the same way.