Plasma pharmacokinetics, pulmonary disposition, and safety of subcutaneous gamithromycin in alpacas

The study objective was to determine the disposition of gamithromycin in plasma, peripheral blood polymorphonuclear cells (PMNs), pulmonary epithelial lining fluid (PELF), and bronchoalveolar lavage (BAL) cells in alpacas. A single subcutaneous injection of gamithromycin (6.6 mg/kg) was administered to six healthy adult alpacas. At various time points after administration, gamithromycin concentrations were analyzed via LC-MS/MS in plasma, PMNs, PELF, and BAL cells until Day 14 post-injection. Plasma gamithromycin concentrations were measured in all six alpacas; the remaining three body compartments were analyzed in four alpacas. Gamithromycin rapidly concentrated in blood PMNs, BAL cells, and PELF. Shorter T_max , and lower C_max, and AUC were observed in plasma than in the other three compartments. C_max was highest in BAL cells (26001.80 ± 12400.00 ng/ml) and PMNs (2573.00 ± 963.30 ng/ml) compared to PELF (660.80 ± 413.70 ng/ml) and plasma (452.30 ± 196.20 ng/ml). Mean terminal half-lives were 72.60 ± 14.10 h in plasma, 56.60 ± 10.60 h in PELF, 62.80 ± 85.30 h in PMNs, and 93.60 ± 124.80 h in BAL cells. No injection site reactions occurred. One alpaca developed colic but no other adverse reactions were noted. Overall, gamithromycin was highly concentrated in white blood cells and pulmonary fluids/cells. Clinical utilization of gamithromycin in alpacas should be done with caution until further investigation of potential for colic.