Susceptibility of Neisseria gonorrhoeae to gentamicin, the primary treatment for gonorrhea in Malawi since 1993, was determined by using agar dilution MICs, E-test MICs, disc diffusion, and clinical cure rate. Agar dilution MICs were slightly higher in 1996 than in 1993 isolates, with a concomitant drop in the clinical cure rate. E-test MICs were substantially lower than agar dilution determinations, with only 77.4% within 1 log2 concentration.
PIP: Gentamicin (240 mg single intramuscular dose) was adopted in 1993 as the treatment of choice for gonorrhea in Malawi, following findings of high-level gonococcal resistance to penicillin, tetracycline, and streptomycin. This study sought to assess the clinical efficacy of gentamicin in the treatment of Neisseria gonorrhoeae 2 years after the onset of its widespread use and to evaluate the potential roles of the disc diffusion and E test in the development of a surveillance system for monitoring antimicrobial susceptibility. 206 consecutive men presenting to a sexually transmitted disease clinic in Lilongwe in 1996 and 198 urethritis patients treated at a hospital in Blantyre during 1992-93 were enrolled. The clinical cure rate for gentamicin treatment of gonorrhea was 91.8% in 1996 compared to 95.0% in 1993. The proportion of highly susceptible isolates declined from 17.2% in 1993 to 9.5% in 1996, but the majority of isolates remained in the moderately susceptible category. The E test yielded substantially lower minimum inhibitory concentrations (MICs) than the standard agar dilution assay, with only 77.4% within 1 log2 concentration. Disc diffusion was not helpful in determining the efficacy of gentamicin, since there was little difference in the range of disc diameters at different MICs as determined by agar dilution. Establishment of an MIC that clearly shows resistance to gentamicin was not possible. These findings suggest that the agar dilution assay remains the method of choice for MIC determination, although the less expensive E test may be capable of monitoring antibiotic efficacy under field conditions.