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The early bactericidal activity of streptomycin
P R Donald1, F A Sirgel, A Venter
1Department of Paediatrics, University of Stellenbosch, Cape Town, South Africa.
Setting:
Patients with sputum smear-positive, newly diagnosed pulmonary tuberculosis studied at Tygerburg Hospital, Cape Town, for their early response to streptomycin (SM).
Objective:
To determine the standard early bactericidal activity (EBA), namely the fall in viable counts of tubercle bacilli in 16-hour sputum collections during the first 2 days of treatment with SM.
Design:
Patients were randomised to logarithmically spaced daily doses of 7.5, 15 or 30 mg/kg SM. A comparison by standard biological assay methods was then made with previous estimations of the EBA of paromomycin in doses of 7.5 and 15 mg/kg.
Results:
An EBA of 0.133 obtained with 30 mg/kg SM differed significantly from zero (P = 0.0009), while the EBAs of 0.043 with 15 mg/kg and -0.025 with 7.5 mg/kg did not so differ. A linear regression equation of EBA = -0.2587 + 0.2627 log10 dose was obtained with significant slope (P = 0.007). Paromomycin was estimated to be 1.745 more potent than SM with wide 95% confidence limits (0.6-28.6), indicating that it cannot be considered more potent than SM.
Conclusions:
The low EBAs show that SM has low, dose-related, bactericidal activity in cavities, consistent with results from clinical trials. If streptomycin-resistant bacilli are present, paromomycin is probably the aminoglycoside of choice.