The effect of intramuscular administration of medroxy progesterone acetate (MPA) on electrocardiographic alterations of female dogs

Progestins are useful for hormonal prevention of pregnancy in humans and animals. Progestrone and medroxy progestrone acetate are used for treatment of premenopausal syndrome and decreasing complications of estrogen therapy after menopause. Prescription of progesterone in dogs is usually done to control or delay estrus. If this drug is used at anestrous it will inhibit the gonadotropin excretion beyond the basic level and it will prevent cycle from happening again in proestrus or at the beginning of estrus progesterone will prevent ovulation. Use of progesterone is not totally safe in bitches. It can cause several problems such as cystic endometrial hyperplasia and pyrometera. In this study the effects of medroxy progestrone acetat (MPA) on electrocardiographic changes are evaluated. After nutritional and environmental uniformity and other evaluations, the animals were divided into two groups with six bitches in each group. MPA was used at 10 mg/kg for the first group and 20 mg/kg for the second group. An ECG was recorded from the first group in time zero. MPA was injected intramuscularly and immediately after ECG recording and the time of injection was noted. Another ECG was recorded 0.5 and 2 hours after injection. The same process was repeated for the second group. It was observed that MPA at 20 mg/kg increased the heart rate and consequently PR interval and RR interval were decreased significantly in normal range. Also administration of drug at 10 mg/kg decreased the heart rate and increased PR interval, QT interval and RR interval significantly in normal range. It is probable that these observations are the result of MPAs dose dependent vasodilatory nature that induces the heart to exhibit compensative reactions such as increasing heart rate.