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Medroxyprogesterone Acetate for Dogs, Cats, and Horses

By Barbara Forney, VMD

Commonly prescribed for: Estrus suppression in the female, for behavioral management of intact male dogs and cats, and to manage feline psychogenic dermatitis and alopecia

Species: Dogs, Cats, and Horses

Therapeutic Class: Long-acting Synthetic Progesterone


Basic Information

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.

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.

Horses

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, and personality changes. Uterine pathology, cystic hyperplasia, pyometra, mammary development, lactation, and neoplasia. Adrenocortical suppression. Diabetes mellitus. Acromegaly has been reported in dogs.
  • Horses: There is very little literature regarding the use of MPA in the horse. No reports of side effects have been found.

Precautions

  • 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.
  • Drug Interactions
  • Rifampin may decrease the activity of progestins. The clinical significance of this possible interaction is unknown.

Overdose

No information regarding overdose was found in the literature.

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