Medical Termination of Pregnancy in Queens: Drugs, Timing and Treatment Protocols

Medical termination of pregnancy (MTP) in queen cats should be approached according to the timing of mating or confirmed pregnancy and the physiological changes occurring during gestation. The available therapeutic approaches can broadly be divided into two stages: intervention shortly after copulation, within approximately one week of mating, and treatment approximately 25–30 days after pregnancy has been confirmed. The choice of approach should be based on the gestational stage, clinical circumstances, and veterinary assessment. 

Early Intervention: Within One Week of Mating 

During the early post-coital period, estrogenic agents have been used to interfere with reproductive events. In cats, ovum transport through the reproductive tract takes approximately 4–5 days after the coitus to reach the isthmus. Administration of estrogen around 40 hours after coitus slows ovum transport and may result in degenerative changes. This may relate to changes in the glandular endometrium, which after estrogen treatment resembles the late proliferative rather than secretory phase¹. 

Despite this mechanism, estrogen should not be used blindly. Treatment may cause serious adverse effects, including bone marrow suppression, aplastic anaemia, leukopenia, and estrus behaviour. The provided clinical guidance specifically cautions against indiscriminate estrogen use because of the possibility of blindness in a queen cat. 

Treatment After Confirmed Pregnancy¹ 

For queens presented approximately 25–30 days after confirmed pregnancy, several pharmacological approaches are described, including prostaglandins, antiprolactin or dopamine agonists, and progesterone antagonists. These agents may be used individually or in combination depending on the clinical situation. 

Prostaglandins¹ 

Prostaglandin-F2 alpha (PGF2α) has luteolytic and uterotonic properties. Synthetic prostaglandin analogues such as cloprostenol have been used for pregnancy termination in cats. However, PGF2α requires considerable caution because effects on other body systems may include hypersalivation, bradycardia, reflex defecation, urination, and emesis. 

Premedication approximately 15 minutes before administration of a prostaglandin analogue may include atropine sulphate, prifinium bromide, or metopimazine to reduce adverse effects. 

Antiprolactin or Dopamine Agonists 

Prolactin acts as a luteotropic hormone in queen cats. Its concentration begins to rise around day 35 of gestation and continues through parturition and the first four weeks of lactation. Reducing prolactin can therefore reduce progesterone and lead to fetal absorption or abortion¹. 

Dopamine agonists such as bromocriptine and cabergoline are used for this purpose. Cabergoline has a longer half-life than bromocriptine and is associated with fewer reported side effects in the provided content. Its pharmacological profile includes stronger stimulation of 5HT2B receptors and preferential binding to D2 receptors¹. 

Progesterone Antagonists 

Progesterone supports pregnancy by promoting endometrial development and placental attachment while maintaining uterine quiescence. Progesterone receptor antagonists occupy progesterone receptors and interfere with these normal reproductive activities. 

Aglepristone (AGL), a progesterone receptor antagonist, has been reported as an option for preventing pregnancy in cats². 

Corticosteroid Approach 

Dexamethasone has abortifacient effects and has been used for mid-gestational pregnancy termination in bitches. Oral administration and lower cost are potential advantages. However, although 100% effectiveness has been reported in dogs, there is no corresponding report for cats in the provided content¹. Therefore, findings from dogs should not be directly extrapolated to queens. 

Combination Therapy 

Combining agents may be considered with the aim of improving abortifacient efficacy while limiting adverse effects and reducing the need for repeated injections or clinical visits. The combination of the PGF analogue cloprostenol with the dopamine agonist cabergoline has been reported to induce abortion or complete fetal resorption³. 

The combination of aglepristone and cloprostenol has also been reported to increase late-term pregnancy termination rates in queens². Similarly, combined misoprostol and aglepristone treatment in mid-term pregnancy has been described as more effective than either agent alone⁴. 

The combined use of prostaglandin and antiprolactin drugs can result in complete fetal reabsorption within 6–8 days⁴. 

Practical Clinical Considerations 

The timing of treatment is central to MTP in queens. Early post-coital intervention and treatment after confirmed pregnancy involve different therapeutic approaches. Before selecting a protocol, the veterinarian should establish the mating history, confirm pregnancy where appropriate, determine gestational stage, and consider the potential adverse effects associated with each therapeutic option. 

Medical termination should therefore be individualized rather than approached as a single fixed protocol, with veterinary supervision throughout treatment. 

References 

1. Sunil P, Singh K, Biswas N, Kumar S, Dwivedi P, Srivastava N, Khan MH. Medical Termination of Pregnancy in Queen. Animal Reproduction Update. 2024 Jul 1;4(2):19. https://www.researchgate.net/profile/Sunil-Parmar-7/publication/384226126 

2. Karakas Alkan K, Alkan H, Tez G, Kanca H. Aglepristone and cloprostenol combination in the termination of late-term pregnancy in queens. Journal of feline medicine and surgery. 2020 Oct;22(10):907-15. https://journals.sagepub.com/doi/pdf/10.1177/1098612X19892087 

3. Rajalakshmi R, Arunmozhi N, Monica G, Umamageswari J, Sarath T, Reena D, Kumar RS, Sridevi P, Krishnakumar K. Combination of anti-prolactin and luteolytic drugs for medical termination of mid-term pregnancy in queen cats. https://www.luvas.edu.in/haryana-veterinarian/download/harvet2022-march/9.pdf 

4. Ay SS, Aslan S, Önyay F, Kaya D, Koldaş E, Arslan S, Fındık M. Effect of oral misoprostol, alone or in combination with aglepristone, on mid-term pregnancy termination in cats. Journal of feline medicine and surgery. 2019 Aug;21(8):714-22. https://journals.sagepub.com/doi/pdf/10.1177/1098612X18797139