Spiramycin concentrations in plasma and genital-tract secretions after intravenous administration in the ewe

Uterine infections are associated with reduced fertility in ruminant species. Spiramycin is a macrolide antibiotic potentially active against most of the microorganisms isolated from secretions of infected genital tracts. The present work investigated the ability of systemically administered spiramycin to enter genital secretions, by determining the disposition kinetics of the antibiotic in both plasma and uterine genital secretions. Five healthy ovariectomized ewes were given a single intravenous (i.v.) injection of spiramycin, at a dose of 20 mg/kg. Plasma and genital secretion samples were collected at predetermined intervals for 5 days post-injection. Blood was collected from the jugular vein while mucus was obtained by inserting polyurethane sponges into the vagina. The spiramycin concentration peak in genital-tract secretions was obtained 2.53 +/- 0.63 h after the i.v. administration. The mean residence time was significantly longer (P less than 0.01) in the mucus (18.31 +/- 3.24 h) than in plasma (6.99 +/- 2.53 h). An average mucus to plasma ratio of 7.87 +/- 3.00 was calculated from the area under concentration-time curves covering the period under study. These data indicate that after systemic administration to ewes, spiramycin is rapidly found in genital-tract secretions, at concentrations which are sufficiently high and persistent to suggest its use in the treatment of post-partum uterine infections.