Effect of repeated biopsy sampling on endometrial concentrations of sodium benzylpenicillin following intramuscular injection in pony mares.

Endometrial concentrations of sodium benzylpenicillin were determined in biopsy samples from anoestrous pony mares after intramuscular administration of the penicillin at 22,000 iu/kg. Serum samples, collected at the same time as biopsies, were also assayed for their penicillin content. In experiment 1 a single pair of blood and tissue samples was taken from each mare between five and 360 minutes after injection. In experiment 2 each mare was sampled consecutively six times (between five and 300 minutes) after injection. Both serum and endometrial concentration reached a peak between 15 and 30 minutes after injection. Tissue concentrations were lower than serum, except after 180 minutes in experiment 2. This suggests that at the time intervals used in the present study, serial biopsies eventually caused an increase in the endometrial content of penicillin.