MEDICAL MANAGEMENT

Both dogs with open-cervix or closed-cervix pyometra can be successfully treated with medical management. Medical management of pyometra is best performed in patients of appropriate breeding age that are reproductively valuable and free of immediate life-threatening illness, including septicemia, endotoxemia, or organ dysfunction. Closed-cervix pyometra carries an increased risk for complications, primarily uterine rupture.⁴

The initial goal of medical management is to reduce the progesterone stimulation of the uterus, which contributes to making the uterus a favorable environment for bacterial infection. This goal can be achieved by administering medications that promote regression of the progesterone-producing corpora lutea or that block progesterone receptors in the uterus.

Table 1 Selected Therapeutic Protocols for Medically Managing Pyometra in Dogs*

Prostaglandins

Prostaglandin F_2-alpha is the most commonly used medication to medically manage pyometra in dogs. Prostaglandins induce regression of the corpora lutea (luteolysis) through numerous mechanisms, including constriction of blood vessels responsible for oxygen delivery.^6,7 As the corpora lutea regress, progesterone production drops. The reduction in progesterone concentrations promotes relaxation (opening) of the cervix, allowing the uterine contents to escape. Prostaglandins also directly stimulate myometrium contraction, thereby promoting expulsion of the infected uterine contents.³ Although not documented, uterine rupture could occur theoretically if intense myometrial contractions were to precede cervical relaxation.

Dogs treated with injectable prostaglandins frequently demonstrate adverse effects such as abdominal discomfort, vomiting, defecation, urination, tachycardia, restlessness, anxiety, fever, hypersalivation, dyspnea, or panting.⁴ Adverse effects are dosage-dependent and cholinergic-like and result from the systemic stimulatory effects of prostaglandins on smooth muscle elsewhere in the body.⁸ These adverse effects will usually occur within minutes of administration and can persist for up to an hour or more afterward.⁴ The prevalence and severity of adverse effects usually decrease with repeated prostaglandin treatments. An earlier study suggested that intravaginal administration of prostaglandin may be associated with a reduction of adverse effects.⁹ Walking the patient immediately after prostaglandin administration for 20 to 60 minutes can be beneficial in minimizing the severity of these adverse effects.⁴ If the adverse effects are persistent or severe, pretreatment with anticholinergics and antiemetics has been suggested.¹⁰ Rarely, more serious adverse effects, including cardiac arrhythmias, and anaphylactic shock, have been reported.⁴

Both natural and synthetic prostaglandin formulations have been used to successfully treat pyometra. Their dosages and administration frequencies vary according to the selected protocol. It is important you adhere closely to the recommended prostaglandin product dosing regimen as prostaglandins have narrow safety margins and severe adverse effects can be expected when excessive doses are given. Synthetic prostaglandin formulations, such as cloprostenol, appear to induce fewer adverse effects because of increased specificity for the uterine smooth muscle.³ In a report of 163 dogs with open-cervix pyometra treated medically with prostaglandins alone, 153 dogs responded favorably.⁴

Dopamine agonists

Dopamine agonists have been used in combination with prostaglandins to treat pyometra.¹¹ Dopamine agonists act by inhibiting prolactin production by the pituitary gland. Prolactin is luteotrophic. Repeated administration of prolactin inhibitors will induce a rapid drop in plasma progesterone concentrations.¹² Thus, a reduction in prolactin concentrations in the blood would be expected to have a synergistic effect with prostaglandins for promoting regression of the corpora lutea. Dopamine agonists cabergoline and bromocriptine have been administered for this purpose.³ Cabergoline is often preferred over bromocriptine because it usually has fewer adverse effects.³ In one study, the combination of cloprostenol and cabergoline was successful in treating 21 of 22 patients with open cervix pyometra.¹¹ In another study involving both open and closed cervical cases, 24 of 29 patients were successfully treated with this combination.¹³