Page 988 - Small Animal Internal Medicine, 6th Edition

960 PART VIII Reproductive System Disorders

Prostaglandins effects are generally seen (mild vulvar bleeding, anorexia,
After confirmation of pregnancy, the natural prostaglandin panting, polydipsia, polyuria). Some bitches become mark-
VetBooks.ir PGF 2α (Lutalyse [Pharmacia]) has been administered to edly polydipsic and polyuric. Its efficacy, few and transient
side effects, low cost, availability, and ease of administra-
bitches and queens to lyse the corpora lutea and evacuate the
uterus, causing pregnancy termination. Prostaglandins are
finances are limited. Oral doses of 0.2 mg/kg bid until fetal
associated with physical side effects that reflect the physio- tion have made dexamethasone the agent of choice when
logic effects of endogenous prostaglandins and include loss (confirmed ultrasonographically) occurs can be used.
emesis, salivation, tachypnea, diarrhea, urination, trembling, Abbreviated diestrus results. Because of the immunosup-
and nesting behavior. These reactions diminish in severity pressant effects of dexamethasone, postabortion metritis can
and duration as treatment progresses. The onset of vaginal occur; clients should be warned to monitor for its signs
discharge is often the first indicator that pregnancy termina- (malodorous discharge, lethargy, anorexia, fever).
tion has begun. Natural prostaglandins must be given for a
significant length of time (often >7 days), adding to the Dopaminergic Compounds
overall cost of therapy. A dosage of 0.1 mg/kg SC q8h for 2 Dopaminergic agents such as cabergoline (Dostinex, Phar-
days, followed by 0.2 mg/kg SC q8h to effect, is recom- macia) are very effective if given later in pregnancy (>40 days
mended for induction of abortion in the bitch. Synthetic gestation) but in small animals can be difficult to dose without
prostaglandins may have fewer side effects and require a compounding. Cabergoline is available in generic tablets that
shorter treatment period and are now preferred by this contain 0.5 mg (500 µg) of drug. Cabergoline inhibits pro-
author to the natural prostaglandins. Cloprostenol (Estru- lactin, a potent luteotroph, and can result in 100% efficacy
mate [ICI, UK]), a synthetic prostaglandin, is dosed at if given 40 days after the LH surge at 5 µg/kg PO q24h for
1-3 µg/kg SC q48h for 3+ doses and has been successful in 7 to 9+ days. The combination of a synthetic prostaglandin
terminating pregnancy in bitches and queens after 30 days’ and a dopaminergic agent are most efficacious. Cloprostenol
gestation. Although prostaglandins are not approved for use (1-3 µg/kg SC given on days 1 and 3) and cabergoline (5 µg/
in domestic dogs or cats, they are recognized as a standard kg PO q24h) for 2 to 10 days to effect is the author’s preferred
of care. Administration of prostaglandins in the clinic rather protocol for canine pregnancy termination; in the queen PGF 2α
than by owners at home is advised because of their narrow at 2.5 mg/cat SC q 24h and cabergoline 50 µg/cat PO q 24h
therapeutic window, but pregnancy termination can be per- is highly effective within 3-6 days.
formed on an outpatient basis, especially with synthetic
prostaglandins. Successful termination of pregnancy and Antiprogestational Agents
evacuation of fetuses must be confirmed with ultrasound. Antiprogestational agents, mifepristone (RU486, Mifeprex
Combination prostaglandin therapy in the bitch with [Danco]) and aglepristone (Alizine [Virbac]), are noted to
intravaginal misoprostol, prostaglandin E2 (Cytotec [Searle]), be very effective (85%-100%) in pregnancy termination and
can reduce the mean time to abortion to under 5 days. Com- lack the severe side effects noted with some other agents.
bination therapies appear to act synergistically: PGF 2α at Aglepristone blocks uterine progesterone receptors; serum
0.1 mg/kg to 0.2 mg/kg SC q8h in combination with intra- progesterone levels remain unchanged. These products do
vaginal misoprostol at 1 to 3 µg/kg q24h (100 µg tablet dis- not appear to affect long-term fertility, are rapid in onset, and
solved in 5 mL water) shortened the treatment time to can be given as an outpatient medication. Unfortunately they
induce abortion in dogs by an average of 2 days over PGF 2α are not readily available in the United States and remain very
used alone. Misoprostol is thought to act as a cervical soften- expensive. As these agents become more cost-effective and
ing agent and has prolonged higher blood levels when availability improves, antiprogestational agents may eventu-
administered intravaginally rather than orally. Side effects ally become the treatment of choice in the United States.
(nausea, cramping, diarrhea) are minimized with intravagi- Aglepristone has the best efficacy used early in gestation
nal administration as well. (21-45 days). In the bitch, aglepristone is dosed at 10 mg/kg
The prognosis for resumption of estrous cycles and suc- SC, given twice, 24 hours apart. No more than 5 mL of the
cessful pregnancies after prostaglandin-induced abortion is 30 mg/mL solution should be given in one SC site, owing to
good. Most bitches experience a return to proestrus 4 months tissue irritation. In the queen, aglepristone is dosed at 15 mg/
(abbreviated diestrus) after prostaglandin-induced abortion. kg SC given twice, 24 hours apart; the higher dose is due to
The onset of estrous cycles in the queen is more variable, poorer bioavailability and faster metabolic clearance in the
reflecting the influence of length of daylight on a seasonally feline. After 45 days gestation, combination therapy with
polyestrous species. cloprostenol and cabergoline is advised.
Dexamethasone
Dexamethasone has more recently been administered to PREPARTUM DISORDERS
terminate pregnancy in bitches. Dexamethasone is thought
to have a direct antiprogesterone effect or to increase endo- DRUG THERAPY DURING PREGNANCY
metrial and placental prostaglandin synthesis and release. The pharmacologic armament for treating reproductive
When used in pregnancies less than 40 days, only mild side disorders is not large, especially if limited to those drugs