Isoniazid toxicity in health care workers

The toxicity of isoniazid chemoprophylaxis was assessed in 83 health care w orkers (HCWs) receiving a 6-month course, in whom clinical toxicity and liv er function were monitored. Thirty-four HCWs (41%) developed an adverse eve nt; in 26 (76%), toxicity was sufficiently severe to require cessation of t reatment. Of the total, liver function test abnormalities (serum alanine tr ansaminase levels more than two times normal) were evident in 14 subjects, with 8 requiring cessation of therapy. Other symptoms reported included mal aise, nausea with associated anorexia, arthralgia, and rash. Mean time to d evelopment of symptoms was 3 weeks (range, 0.5-6 weeks), with the mean age of those with toxicity not differing significantly from those without (38 v s. 39 years). The high rate of toxicity seen in this study is sufficiently notable that we advocate the use of monthly liver function testing and freq uent review in those receiving isoniazid prophylactic therapy.