use of long acting subcutaneous levonorgestrel (LNG) gel depot as an effective contraceptive option for cotton‐top tamarins (Saguinus oedipus)

Cotton‐top tamarins (Saguinus oedipus) are a critically endangered species that have been bred successfully in captivity for many years. For two decades, the Cotton‐top Tamarin SSP© has been challenged with a high rate of reproduction combined with a history of contraceptive failures and nonrecommended births using the current Depo Provera® (medroxyprogesterone acetate) injection followed by MGA (melengestrol acetate) implant contraception combination. To address these issues we have developed and tested the use of levonorgestrel (LNG) as an effective contraception option for cotton‐top tamarins. LNG was delivered in an injectable, gel matrix consisting of polylactic‐co‐glycolic acid, triethyl citrate and N‐methylpyrrolidone. This gel matrix forms a biodegradable depot at the subcutaneous injection site providing slow release of the active ingredient. Gel matrix composition and LNG concentration were adjusted in four gel formulations to maximize the duration of contraceptive efficacy while minimizing immediate post‐injection increases in fecal LNG concentration. LNG treatment (68.44±8.61 mg/kg) successfully eliminated ovarian cycles (fecal pregnanediol‐3‐glucuronide (PdG) and estrone conjugates (E1C)) for 198.8±70.3 days (formulation four; range 19–50 weeks). It was demonstrated that subcutaneous LNG depot injection was an effective, reversible contraceptive option for the management of cotton‐top tamarins in captivity. Zoo Biol 30:498–522, 2011. © 2010 Wiley Periodicals, Inc.