Alfaxalone crossreactivity affecting progesterone concentrations in cats

Alfaxalone is a commonly used anesthetic agent in small animals. In cats, alfaxalone is used as an intramuscular agent to achieve clinically useful sedation or anesthesia, negating need for intravenous treatment, particularly in difficult patients. Molecular structure of alfaxalone is similar to progesterone (P4 ) hormone allowing for activation of GABA A complex through a progesterone receptor. On clinical observation, intact female cats demonstrating signs of estrus, following alfaxalone treatment had serum P4  concentrations suggestive of luteal activity. Concern that alfaxalone may be interfering with the assay, we hypothesized that alfaxalone would crossreact with progesterone assay. Eight domestic shorthair neutered male cats were administered 3 mg/kg of alfaxalone IM. Blood samples were collected at set time points (baseline, 30 and 60 minutes, and 3, 6 and 10 hours). Serum concentrations of P 4 immunoreactivity (IR) were determined using an automated immunoassay system (Immulite 1000). Data were analyzed using repeated measures ANOVA and a Tukey-Cramer multiple comparisons test, with p < 0.05 used for significance. Serum P 4 IR was elevated (p < 0.05) at 30 minutes, 1 hour, and 3 hours compared to baseline and returned to baseline at 6 hours. We concluded that intramuscular alfaxalone treatment in cats may interfere with immunoassay measurement of serum P 4 for up to 6 hours. Caution should be exercised when interpreting serum P 4 IR results in cats treated with alfaxalone.

Keywords: Alfaxalone, progesterone, immunoreactivity, cat

This manuscript was originally published in the journal Clinical Theriogenology Vol 12(3) Sept 2020.  Clinical Theriogenology is the official journal of the Society for Theriogenology (SFT) and the American College of Theriogenologists (ACT).  This content has been reproduced on the IVIS website with the explicit permission of the SFT/ACT.