We investigated the effects of a range of IV administered doses of omeprazole (0.125 to 2.0 mg/kg of body weight) on gastric pH (monitored by indwelling electrode) and plasma gastrin concentration, compared with those of IV administered ranitidine (1.0 mg/kg) in 4 Welsh mountain-type ponies. Pharmacokinetic variables of IV administered omeprazole also were examined. Episodes of high gastric pH in the basal state obscured the effect of acid suppression on intragastric pH; however, omeprazole induced dose-dependent increase in mean gastric pH (P < 0.01) during the 11 hours after its administration. In the presence of acid-suppressant treatment, plasma gastrin concentration correlated significantly with gastric pH (Spearman's rank correlation coefficient, p = 0.445, P < 0.01), whereas basal pH and plasma gastrin concentration were not correlated. The effect was not great, and a dose-dependency was not found. Intravenously administered omeprazole was subject to two-compartment pharmacokinetics, and there was evidence for saturable steps in the redistribution and elimination phases. Dosage of 0.25 mg/kg induced approximately half-maximal inhibition of basal gastric pH in these ponies and was associated with area under the concentration vs time curve of 0.7 micromoles.h/L, which corresponds reasonably with results of other species. Omeprazole may represent a useful alternative acid-suppressant agent in horses, but further work is required to relate the dose-dependent effects found in this study to well-defined targets of acid suppression in clinical cases.

Withdrawal periods required when doses of 24,000 IU and 66,000 IU of procaine penicillin G/kg body weight were administered to yearling beef steers by intramuscular injection daily for five consecutive days were investigated. These dosages are in excess of product label recommendations, but are in the range of procaine penicillin G dosages that have been administered for the treatment of some feedlot bacterial diseases. The approved dose in Canada is 7,500 IU/kg body weight intramuscularly, once daily, with a withdrawal period of five days. Based on the tissue residue data from this study, the appropriate withdrawal period is ten days for the 24,000 IU/kg body weight dose and 21 days for the 66,000 IU/kg body weight dose when administered intramuscularly to yearling beef steers. In a related study, 18 yearling beef steers received 66,000 IU of procaine penicillin G/kg body weight administered by subcutaneous injection, an extra-label treatment in terms of both dose and route of administration, typical of current practice in some circumstances. Deposits of the drug were visible at subcutaneous injection sites up to ten days after injection, with more inflammation and hemorrhage observed than for intramuscular injections of the same dose. These results suggest that procaine penicillin G should not be administered subcutaneously at high doses; and therefore a withdrawal period was not established for subcutaneous injection.