Urine concentrations of five penicillins following oral administration to normal adult dogs.

Penicillin G, penicillin V, ampicillin, hetacillin, and amoxicillin were administered separately per os to clinically normal adult dogs of both sexes at 8-hour intervals for five consecutive 8-hour test periods. All urine was collected from each dog during each test period and was assayed for antimicrobial activity. Daily doses of the antimicrobics used were as follows: penicillin G, 110,000 U/kg of body weight; penicillin V, 77 mg/kg; ampicillin, 77 mg/kg; hetacillin, 77 mg/kg; and amoxicillin, 33 mg/kg. Mean 8-hour urine concentrations (+/- 1 SD) were as follows: penicillin G, 294 +/- 210 U/ml; penicillin V, 148 +/- 98 micrograms/ml; ampicillin, 309 +/- 55 micrograms/ml; hetacillin, 300 +/- 156 micrograms/ml, and amoxicillin 201 +/- 93 micrograms/ml. Among the three antimicrobials administered at the same daily dosage, ie, penicillin V, ampicillin, and hetacillin, the mean urine concentrations of penicillin V were significantly lower (P < 0.01) than were concentrations of ampicillin and hetacillin. The mean urine concentrations of the latter two did not differ significantly (P > 0.05).