Objective To describe the dose-related thermal antinociceptive effects of intravenous (IV) hydromorphone in cats.
Study design Randomized, blinded, crossover design.
Animals Seven adult cats (3.5–7.4 kg), two spayed females, and five neutered males.
Methods Hydromorphone (0.025, 0.05, or 0.1 mg kg−1) was administered IV. Skin temperature and thermal threshold were measured before and at selected time points to 720 minutes post-administration. Statistical analysis of mean thermal threshold and skin temperatures over time for each dose and between doses was by way of a split-plot model and post hoc Bonferroni t-tests. p < 0.05 was considered significant.
Results A significant difference from baseline for mean thermal threshold was identified for the 0.05 mg kg−1 dose (5–80 minutes, peak thermal threshold 46.9 ± 6.2 °C) and 0.1 mg kg−1 dose (5–200 minutes, peak thermal threshold 54.9 ±0.2 °C). The thermal threshold was significantly greater after the 0.1 mg kg−1 dose from 5 to 200 minutes compared to the 0.025 mg kg−1 and 0.5 mg kg−1 doses. The thermal threshold was significantly greater from 35 to 80 minutes for the 0.05 mg kg−1 dose when compared with the 0.025 mg kg−1 dose. Skin temperature was significantly increased from 35 to 140 minutes following the 0.1 mg kg−1 dose.
Conclusions A dose-related antinociceptive effect was demonstrated for IV hydromorphone in cats.
Clinical relevance Hydromorphone at doses less than 0.1 mg kg−1 has a modest antinociceptive effect and a short duration of action. At a dose of 0.1 mg kg−1 IV, onset of analgesia is rapid with a clinically useful duration of effect, but is associated with a rise in skin temperature.