Small Animal Clinical Pharmacology - CYF MEDICAL DISTRIBUTION

CHAPTER 23 DRUGS AND REPRODUCTION
Mechanism of action
All progestins have the following broad effects.
● Transformation of proliferative endometrium to
secretory endometrium.
● Enhancement of myometrial hypertrophy.
● Inhibition of spontaneous uterine contraction.
● Negative feedback inhibition on the secretion of
pituitary gonadotropins.
● Insulin antagonism.
● Antiestradiol and glucocorticoid activity with
resultant adrenal suppression.
Different progestins may also exert an antiandrogenic
effect, depending on their antigonadotrophic and androgenic
receptor-binding ability. Medroxyprogesterone
acetate, megestrol acetate, delmadinone acetate, clormadinone
acetate and cyproterone acetate have been successfully
tested for that purpose in the dog.
Clinical applications
In females
● Estrus suppression in bitches.
● Estrus postponement in the bitch and queen.
● Prevention of abortion in the bitch and queen.
● Treatment of infertility with shortened interestrus
intervals.
In males
● Suppression of libido in male dogs.
● Treatment of prostatic hyperplasia in dogs.
Treatments that have been used include:
• progesterone in oil 2 mg/kg IM every 72 h, which will maintain
serum progesterone at 10 ng/mL or higher (it can be measured
by laboratory assays to assess adequacy of supplementation),
but this may cause dystocia and masculinization of female
fetuses
• in some countries, when available: oral micronized progesterone,
10–20 mg/kg every 8 h, until 58 d of pregnancy
• synthetic oral progestin altrenogest: 0.088 mg/kg daily (this
drug cannot be measured by progesterone assays)
Treatment of infertility with shortened interestrus intervals in
the bitch
• Megestrol acetate (2 mg/kg for 8 consecutive days) or
clormadinone acetate (0.5 mg/kg for 8 consecutive days) have
been used successfully to treat infertility associated with
shortened interestrus intervals (