Potential Deleterious Effects Following the First Dose of Medroxyprogesterone Acetate as a Contraceptive in Cats

The aim of the present work was to investigate the deleterious effects of the first dose of medroxyprogesterone acetate (MPA) on the female genital system of cats. The study was conducted on 315 cats of different breeds who received their first dose (75 mg) of MPA as a contraceptive. Complete animal identification and stage of estrus were documented at admission. Physical, radiographic and ultrasonographic examinations were done on cats that expressed deleterious manifestations. All of the presented cats received an overdose of MPA during the estrous phase of the estrous cycle. Out of 315 cats who received their first dose of MPA, 27 (8.6 %) demonstrated varied deleterious effects related to the female genital system. Deleterious effects were reported within 15–90 days, including pyometra (n=10, 37.0%), endometritis (n=8, 29.6%), mammary gland hyperplasia (n=4, 14.8 %), cystic endometrial hyperplasia (n=3, 11.2%) and ovarian cyst (n=2, 7.4%). The incidence of these adverse effects increased with age. Persian cats seem to be more susceptible than other cat breeds. Long haired cat breeds seem to be more susceptible to adverse effects following injection of exogenous progestins (MPA) than short haired breeds (Siamese and Egyptian mau). Deleterious effects of MPA occurred following the first overdose. It is advised to use MPA as a contraceptive in the recommended dose during the inter-estrous or anestrous phase.