Pharmacokinetics and serum bactericidal activities of quinolones in combination with clindamycin, metronidazole, and ornidazole.

To enhance the antimicrobial spectrum of the quinolones against anaerobic organisms and gram-positive bacteria, we investigated in two studies the parenteral combinations of ciprofloxacin (200 mg) and ofloxacin (200 mg) with metronidazole (500 mg) or clindamycin (600 mg) and the oral combinations of enoxacin (400 mg) and fleroxacin (400 mg) with metronidazole (400 mg), clindamycin (300 mg), or ornidazole (500 mg) (only with fleroxacin). The pharmacokinetics and serum bactericidal activities (SBAs) against 5 aerobic and 2 anaerobic species (total, 58 strains) were determined in two groups of 10 healthy volunteers by using a randomized crossover study design. The additions of metronidazole, clindamycin, and ornidazole did not affect the pharmacokinetics of the quinolones. The combination of clindamycin with ciprofloxacin, ofloxacin, and, to a lesser extent, fleroxacin resulted in an increase of the SBA against gram-positive strains (mean peak titers): Staphylococcus aureus, ciprofloxacin alone, 1:5.5; ciprofloxacin-clindamycin, 1:19.9; ofloxacin alone, 1:3.6; ofloxacin-clindamycin, 1:17.5; fleroxacin alone, 1:4.3; fleroxacin-clindamycin, 1:8.1; Streptococcus pneumoniae (fleroxacin and enoxacin were not tested), ciprofloxacin alone, 1:2.0; ciprofloxacin-clindamycin, 1:53; ofloxacin alone, 1:2.6; and ofloxacin-clindamycin, 1:49.2. The high SBA of quinolones against gram-negative bacteria was not affected by the combinations; however, relatively low activities against Pseudomonas aeruginosa were detected. In general, against anaerobic bacteria, low bactericidal activities were determined in both studies (mean peak titers ranged from 1:2.1 to 1:3.1; mean trough titers range from 1:2.0 to 1:2.9). In clinical settings with severe mixed infections, a parenteral therapy consisting of modern quinolones together with clindamycin or imidazole derivatives seems to be active and offers no obvious interactions.

Combination effects of ciprofloxacin, clindamycin, and metronidazole intravenously in volunteers.

Despite the broad antibacterial spectrum of ciprofloxacin, most anaerobic organisms are resistant to the drug, whereas several gram-positive organisms are only moderately susceptible. Thus, in some clinical situations, combined treatment with ciprofloxacin and metronidazole or clindamycin could be useful. Therefore, the pharmacokinetics and serum bactericidal activities of ciprofloxacin in combination with clindamycin or metronidazole were investigated using a randomized crossover study design in 10 healthy volunteers. Ciprofloxacin (200 mg) was administered alone and in combination with clindamycin (600 mg) or metronidazole (500 mg); all drugs were given intravenously over 30 minutes. Serum and urine concentrations of the substances were measured using standard methods (high-performance liquid chromatography or gas chromatography). Blood samples for determination of serum bactericidal activity against five different aerobic and two anaerobic bacterial species (a total of 58 strains) were obtained one hour and six hours after drug infusion. All values were statistically analyzed by use of the Student t test.