Question

A patient has a positive PPD skin test with 16 mm of induration. Based on a review of his history, physical examination, and other diagnostic studies you prescribe isoniazid. Which of the following is NOT a side effect that should be anticipated?

a. drug-induced rash
b. drug-induced fever
c. diarrhea
d. elevated liver enzymes
e. neuropathy

Answer 1

Diarrhea is not typically expected as a side effect of isoniazid, unlike drug-induced rash, fever, elevated liver enzymes, and neuropathy, which are documented side effects (option c).

Step-by-step explanation:

A patient has a positive PPD skin test with 16 mm of induration, and isoniazid has been prescribed. Not all side effects are equally likely with isoniazid usage. Diarrhea is not typically anticipated as a direct side effect of isoniazid, whereas the other listed options—drug-induced rash, drug-induced fever, elevated liver enzymes, and neuropathy—are documented side effects of this medication.

Isoniazid is known to inhibit the synthesis of mycolic acid, essential for the mycobacterial cell wall, thus exhibiting toxicity specifically to mycobacteria. Among its side effects, hepatotoxicity (manifesting as elevated liver enzymes), neurotoxicity (which can lead to neuropathy), and hematologic toxicity are well-documented. Meanwhile, side effects such as diarrhea are more commonly related to gastrointestinal irritants or infections rather than isoniazid.

Hence, the answer is option c.