Comparison of two intravenous anesthetic infusion regimens for alfaxalone in cats.

Objective: To compare the performance of an alfaxalone constant rate intravenous (IV) infusion versus a 3-step IV infusion, both following a loading dose, for the maintenance of a target plasma alfaxalone concentration of 7.6 mg L (effective plasma alfaxalone concentration for immobility in 99% of the population) in cats.

Study Design: Prospective randomized crossover study.

Animals: A group of six healthy, adult male neutered cats.

Methods: Catheters were placed in a jugular vein for blood sampling and in a medial saphenous vein for drug administration. An IV bolus of alfaxalone (2 mg kg) was administered, followed by either 0.2 mg kg minute for 240 minutes (single infusion; SI) or 0.4 mg kg minute for 10 minutes, then 0.3 mg kg minute for 30 minutes, and then 0.2 mg kg minute for 200 minutes (3-step infusion; 3-step). Plasma alfaxalone concentration was measured at six time points during the infusions. Measures of performance were calculated for each infusion regimen and compared using the paired Wilcoxon signed-rank test.

Results: Median (range) absolute performance error, divergence, median prediction error and wobble were 15 (8-19)%, -8 (-12 to -6)% hour, -12 (-19 to -7)% and 10 (8-19)%, respectively, in the SI treatment, and 6 (2-16)%, 0 (-13 to 2)% hour, 1 (-16 to 4)% and 4 (3-6)% respectively, in the 3-step treatment and were significantly smaller in the 3-step treatment than in the SI treatment.

Conclusion And Clinical Relevance: After IV administration of a bolus dose, a 3-step infusion regimen can better maintain stable plasma alfaxalone concentrations close to the target concentration than a single constant rate infusion.