Rifampin alone and in combination with trimethoprim in chemoprophylaxis for infections due to Haemophilus influenzae type b.

The efficacy of rifampin in eradicating Haemophilus influenzae type b from the pharynx of colonized individuals was assessed for 1,467 close contacts of 291 children hospitalized with invasive infections due to H. influenzae type b. Twenty-six percent of all contacts were carrying H. influenzae type b in the pharynx, and 52% of contacts younger than age five had throat cultures positive for this organism. Four different regimens of rifampin were studied and compared with placebo for efficacy in eradication of carriage of H. influenzae type b. The most effective dosage was 20 mg of rifampin/kg given once daily for four days. This schedule was associated with eradication of carriage in 96.2% of 52 colonized, compliant contacts. Carriage of H. influenzae type b was eradicated in 90.9% of the 22 colonized contacts who were younger than age five. Significantly lower rates of carriage eradication were seen with other regimens of rifampin. Potential problems associated with widespread rifampin usage are reviewed.