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Macrolides, ketolides and fluoroquinolones as well as other classes of antimicrobial agents have been associated with prolongation of cardiac repolarisation. This effect is most notable with erythromycin, clarithromycin, gatifloxacin, moxifloxacin, levofloxacin and telithromycin. All of these agents produce a blockage of the HERG channel dependent potassium current in myocyte membranes resulting in a prolonged QTc interval which may give rise to polymorphic ventricular tachycardia, Torsades de Pointes or ventricular fibrillation. The risk of malignant arrhythmias is increased by concomitant usage with Type Ia or III anti-arrhythmic agents or with other drugs that prolong the QTc interval or have competitive metabolic routes. Electrolyte disturbances or underlying cardiac disease also increase the risk of ventricular arrhythmias. The best clinical outcome indicator is the incidence of the associated arrhythmias. The rough rank order of risk with these agents, albeit with limited and incomplete data, is in decreasing order; erythromycin, clarithromycin, gatifloxacin, levofloxacin and moxifloxacin. Telithromycin outcomes for associated arrhythmia are yet to be determined. The essential point is that the overall risk of ventricular arrhythmias is very small with these agents but can be reduced further by avoiding their usage for patients with other multiple risk factors for Torsades de Pointes.

A susceptibility survey of 537 strains of the Bacteroidesfragilis group from eight centers in the United States was continued at the Tufts New England Medical Center in 1982. The results were compared with those of 755 organisms analyzed in 1981. Nine antimicrobial agents were tested by an agar dilution method. The respective percentages of resistance for 1981 and 1982 were as follows (%): cefoxitin, 8 and 10; moxalactam, 22 and 12; cefotaxime, 54 and 48; cefoperazone, 57 and 54; piperacillin, 12 and 7; clindamycin, 6 and 3; metronidazole, 0 and 0; chloramphenicol, 0 and 0; and tetracycline, 63 and 59. Regional differences in resistance rates were found. Declines in resistance to moxalactam, piperacillin, and clindamycin were noted at the participating hospitals. An outbreak of cefoxitin resistance was noted at the Tufts New England Medical Center, where the rate increased from 14 to 30%. The various species of the B. fragilis group had differing patterns of resistance; B. fragilis was the most susceptible species. Significant cross resistance among the beta-lactam agents was found. These data indicate the need to determine the susceptibility patterns of the B. fragilis group organisms within each hospital.

The minimal inhibitory concentrations of nine antimicrobial agents was determined for over 750 clinical isolates of the Bacteroides fragilis group of anaerobic bacteria collected from nine centers in the United States during 1981. High resistance rates were documented for cefoperazone, cefotaxime, and tetracycline. Cefoxitin had the best activity of the 3-lactam antibiotics, whereas moxalactam and piperacillin had good activities. The resistance rate for clindamycin was 6%. There were no metronidazole-or chloramphenicol-resistant isolates encountered. There were significant differences in susceptibility among the various species of the B. fragilis group, particularly with moxalactam, cefoxitin, and clindamycin. Clustering of clindamycin-, piperacillin-, and cefoxitin-resistant isolates was observed at different hospitals. The variability of resistance rates with the