Azithromycin is a new subclass of macrolide antibiotics classified as an azalide. This antimicrobial has a similar mechanism of action to the other macrolides (i.e., erythromycin) by binding to the 50 S ribosomal subunit.2 Azithromycin provides broad-spectrum antibiosis against gram-positive and gram-negative bacteria.2 It also has the ability to obtain sustained drug concentrations in tissues much greater than the corresponding plasma concentration.1,3 This study determined the pharmacokinetics of azithromycin (Zithromax®, Pfizer Inc., New York, NY, USA) in ball pythons (Python regius), a species that is representative of the Boidae family. Snakes were administered azithromycin intravenously (IV) to determine distribution and orally (PO) to determine bioavailability and absorption. Seven ball pythons (two males, five females), weighing approximately 0.67–0.96 kg, were used in this experiment. Using a crossover design, each snake was given a single 10 mg/kg IV dose of azithromycin via cardiocentesis. For the oral study, each snake was dosed at 10 mg/kg using the same IV azithromycin preparation. Blood samples were collected prior to dosing and at 1, 3, 6, 12, 24, 48, 72, and 96 h post-azithromycin administration. Plasma t½ for IV and PO dosing was 17 h and 51 h, respectively, and the average oral bioavailability (F) was 77% (±27%). The recommended dose for azithromycin in ball pythons is 10 mg/kg at 48–72 h intervals.
1. Hunter, R.P., M.J. Lynch, J.F. Ericson, et al. 1995. Pharmacokinetics, oral bioavailability, and tissue distribution of azithromycin in cats. J. Vet. Pharmacol. Therap. 18:38–46.
2. Retsema, J., A. Girard, W. Schelkly, et al. 1987. Spectrum and mode of action of azithromycin (CP-62, 993), a new 15-membered-ring macrolide with improved potency against gram-negative organisms. Antimicrob. Agents Chemother. 31:1939–1947.
3. Schentag, J.J. and C.H. Ballow. 1991. Tissue-directed pharmacokinetics. Am. J. Med. 91(Suppl. 3A):5–11.