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Medroxyprogesterone Acetate for Veterinary Use
by Barbara Forney, VMD
Medroxyprogesterone acetate, MPA, is long-acting synthetic progesterone. It is used commonly in women as an injectable contraceptive. Oral MPA is used in women to treat bleeding disturbances associated with the menstrual cycle. MPA blocks the secretion of pituitary hormones and has a marked effect on ACTH and cortisol release. MPA also has an anti insulin effect and decreases testosterone in male humans and male dogs.
MPA historically has been used for estrus suppression in the female, for behavioral management of intact male dogs and cats and to manage feline psychogenic dermatitis and alopecia. There are many side effects associated with MPA use in dogs and cats and recent literature has focused on the use of alternative drugs. All use of MPA in dogs and cats is extra-label and it should be used only when other treatment options have been tried and found unsuccessful.
MPA is used for estrus suppression in performance horse mares and to diminish inappropriate sexual behavior in "studish" geldings. There also is some thought that progestins such as MPA may calm the behavior of "hot" horses. This is an extrapolation based on work done with progestins in other species.
Although the published studies on its use do not show any effect on estrus suppression, there are many practitioners who feel that they have seen a positive response. Anecdotally, there are some mares that respond well to MPA and others that do not seem to respond at all. The gold standard drug for estrus suppression in the mare is altrenogest.
Medroxyprogesterone Acetate Side Effects
- Dogs and cats:
Permanent local alopecia from SC injection. Increased appetite or thirst, obesity, lethargy, personality changes. Uterine pathology, cystic hyperplasia, pyometra. Mammary development, lactation and neoplasia. Adrenocortical suppression. Diabetes mellitus. Acromegaly has been reported in dogs.
There is very little literature regarding the use of MPA in the horse. No reports of side effects have been found.
- MPA should not be used in dogs or cats under the following conditions; prior to puberty, during pregnancy, during a pseudo pregnancy, during diestrus, in the presence of uterine bleeding, during a prolonged heat and in animals with diabetes.
- MPA can suppress adrenal function. The use of exogenous corticosteroids may be necessary in conditions of abnormal stress.
Rifampin may decrease the activity of progestins. The clinical significance of this possible interaction is unknown.
No information regarding overdose was found in the literature.
About the Author
Dr. Barbara Forney is a veterinary practitioner in Chester County, Pennsylvania. She has a master's degree in animal science from the University of Delaware and graduated from the University of Pennsylvania School of Veterinary Medicine in 1982.
She began to develop her interest in client education and medical writing in 1997. Recent publications include portions of The Pill Book Guide to Medication for Your Dog and Cat, and most recently Understanding Equine Medications published by the Bloodhorse.
Dr. Forney is an FEI veterinarian and an active member of the AAEP, AVMA, and AMWA.
You can purchase books by Dr. Forney at www.exclusivelyequine.com
Wedgewood Pharmacy's compounded veterinary preparations are not intended for use in food and food-producing animals.