Small Animal Clinical Pharmacology - CYF MEDICAL DISTRIBUTION

POLYPEPTIDE HORMONES
reproductive male function have been observed with implants
containing the GnRH agonist azagly-nafarelin.
Control of prostatic disease
• Five adult dogs implanted with deslorelin at a dose of 0.5–
1.0 mg/kg showed a signifi cant 50% decrease in prostatic
volume from week 6 to week 44.
Reduction of aggression
• Some studies suggest that prolonged use of deslorelin implants
may reduce aggression in male dogs and cats.
hCG is a high molecular weight glycoprotein secreted by
the chorion of pregnant women and recovered from their
urine. It has mostly LH-like but also has some FSH-like
activity. 1 IU = 1 USP unit. 1 mg ≥1500 USP units. It is
available as a purified biological.
eCG is a high molecular weight glycoprotein secreted by
the endometrial cups of the pregnant mare with a long
(>24 h) half-life. Several products have FSH-like as well as
LH-like activities.
Pharmacokinetics
Data are not available for the dog and cat. In the pig,
distribution half-life to extracellular fluid after intravenous
administration is 2 min and elimination half-life is
13 min.
Adverse effects
● None reported, although naturally occurring GnRH
might induce a hypersensitivity reaction.
● However, when trying to prevent estrus in anestrous
bitches, the use of GnRH agonists, especially deslorelin
implants, may first induce heat as a result of the
stimulatory effect of the drug on the pituitary. Some
studies have shown that concomitant use of progestins
may reduce this adverse reaction but not suppress
it completely.
Contraindications and precautions
None reported.
Known drug interactions
None reported.
Gonadotropins
Gonadotropins include the pituitary gonadotropins,
luteinizing hormone (LH) and follicle-stimulating
hormone (FSH), and the nonpituitary gonadotropins,
human chorionic gonadotropin (hCG) and equine
chorionic gonadotropin (eCG), which is also called
pregnant mare’s serum gonadotropin (PMSG).
EXAMPLES
FSH has two subunits (α = 89 amino acids and β = 115
amino acids). There are a variety of products available,
which are biological products purified from the pituitary
glands of farm animals and therefore contain some LH
activity. 1 mg FSH-P contains 1 Armour unit, which may be
9.4–14.2 IU of FSH.
LH has two subunits (α = 89 amino acids and β = 115
amino acids). LH is no longer available as a commercial
product.
Mechanism of action
The gonadotropins are produced endogenously by
the anterior pituitary and act with other hormones to
promote folliculogenesis, spermatogenesis and steroidogenesis.
They may not have all these effects when
administered parenterally.
Clinical applications
In females
● Estrus induction in the bitch (FSH and hCG, eCG
and hCG).
● Luteinization of follicular cysts (hCG).
● Estrus induction in anestrus queens (FSH and
hCG).
● Ovulation induction in bitches and queens (hCG).
● Stimulation of progesterone release from luteal cells,
including challenge testing to diagnose the presence
of ovarian parenchyma (hCG).
In males
● Stimulation of testosterone release from Leydig cells,
including challenge testing to diagnose the presence
of testicular parenchyma (hCG).
● Cryptorchidism treatment (hCG).
● Enhancement of spermatogenesis (infertile male
dogs): recent data suggest that this treatment is ineffective.
This may be because repeated injections may
lead to immuno-sensitization, thus decreasing the
efficacy of gonadotropin administration.
Formulations and dose rates
IN FEMALES
Estrus induction in bitches
• The most widely studied gonadotropin for estrus induction in
the dog is eCG. Protocols range from daily (20–40 lU/kg) to
weekly (110 lU/kg) injections, often IM. However, premature
luteal failure occurs frequently and, therefore, the pregnancy
rates remain low. Ultrasonographic and histological studies
have demonstrated that ovarian follicular dynamics differ widely
from those at spontaneous estrous cycles. Furthermore, the
likelihood of inducing cystic follicular degeneration is very high.
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