Comparative efficacy of nalidixic acid and ampicillin for severe shigellosis.

Nalidixic acid is effective in vitro against shigellae including strains multiply-resistant to antibiotics. A comparative study of acute shigellosis in infants and children involved 19 patients treated with ampicillin and 17 treated with nalidixic acid. Stool cultures remained positive longer with nalidixic acid treatment than with ampicillin therapy, and clinical response was slower. The rate of response to therapy was correlated with the serum levels of ampicillin. Though nalidixic acid eliminates shigellae from stools more rapidly than with symptomatic therapy alone, it cannot be recommended for routine treatment of acute shigellosis since it has little effect on the natural course of the illness. In special circumstances when dealing with shigellae that are resistant to ampicillin, tetracycline, and chloramphenicol, nalidixic acid may have a limited use.