Pharmacokinetics of buprenorphine following constant rate infusion for postoperative analgesia in dogs undergoing ovariectomy

Comparison of the Transdermal and Intravenous Administration of Buprenorphine in the Management of Intra- and Postoperative Pain in Dogs Undergoing a Unilateral Mastectomy

The aim of this prospective clinical study was to evaluate the effectiveness of transdermal patches of buprenorphine as an alternative route for the management of perioperative pain in dogs undergoing a unilateral mastectomy. Our hypothesis was that the transdermal route would allow the obtainment of an analgesic plan comparable to that of the injectable administration. Twelve dogs were divided in two groups. In the BupreP group (six dogs), buprenorphine patches were applied 40 h before the start of the surgery, guaranteeing a dosage of 5−6 μg/kg/h. In the BupreI group (six dogs), 20 μg/kg of buprenorphine was administered intravenously 30 min before the induction of anesthesia, and this was repeated every 6 h for 24 h. The main physiological parameters, sedation scores (0 = no sedation; 11 = deep sedation), and pain scores were monitored from 30 min before the surgery to 24 h after the end of anesthesia. All p values < 0.05 were defined as statistically significant. Thirty minutes before the surgery, the sedation scores were higher in BupreI (score = 10) compared to the BupreP group (score = 1). Moreover, during the mastectomy, the mean arterial pressure significantly increased in both groups even if nobody required additional analgesia. In the postoperative period, the pain scores did not show statistically significant differences between the two groups, maintaining values below the pain threshold at all times of the study. In conclusion, the transdermal administration of buprenorphine could guarantee an analgesic quality equal to that of the injectable route.

Pharmacokinetics of a high-concentration formulation of buprenorphine (Simbadol) in male dogs

OBJECTIVE

To describe the pharmacokinetics of buprenorphine in dogs following administration of a high-concentration formulation of buprenorphine.

STUDY DESIGN

Prospective, randomized, crossover study.

ANIMALS

A total of six healthy male intact Beagle dogs, aged 9-13 months and weighing 10.3 ± 1.4 kg (mean ± standard deviation).

METHODS

Dogs were randomized to be administered buprenorphine (0.12 mg kg^-1; Simbadol, 1.8 mg mL^-1) via the intravenous (lateral saphenous) or subcutaneous (dorsal interscapular) route followed by the alternative route of administration after a 14 day interval. Blood was sampled before administration and at set times up to 72 hours after injection. Plasma buprenorphine concentration was measured using liquid chromatography-tandem mass spectrometry.

RESULTS

A three-compartment model with zero or biphasic rapid and slow first-order input in (intravenous or subcutaneous data, respectively) and first-order elimination from the central compartment best fitted the data. The rapid first-order input accounted for 63% of the dosage absorption. Typical values (% interindividual variability) for the three compartment volumes were 900 (33), 2425 (not estimated) and 6360 (28) mL kg^-1. The metabolic and two distribution clearances were 25.7 (21), 107.5 (74) and 5.7 (61) mL minute^-1 kg^-1. The absorption half-life for the fast absorption phase was 8.9 minutes with a 0.7 (103) minute delay. The absorption half-life for the slow absorption phase was 347 minutes with a 226 (42) minute delay. Median (range) bioavailability calculated from noncompartmental analysis was 143 (80-239)%. Calculated terminal half-life was 963 minutes.

CONCLUSIONS AND CLINICAL RELEVANCE

The high-concentration formulation of buprenorphine administered subcutaneously had a large volume of distribution and a rapid absorption phase followed by slower, delayed absorption. The high estimate of bioavailability should be interpreted with caution as values above 100% are most commonly related to experimental issues.

Pharmacokinetics and analgesic effects of intravenous, intramuscular or subcutaneous buprenorphine in dogs undergoing ovariohysterectomy: a randomized, prospective, masked, clinical trial

BACKGROUND

Buprenorphine is used for canine postoperative pain management. This study aimed to describe the pharmacokinetics and evaluate the analgesic efficacy of buprenorphine (Simbadol, 1.8 mg/mL) administered by different routes in dogs undergoing ovariohysterectomy. Twenty-four dogs were included in a randomized, prospective, masked, clinical trial. Buprenorphine (0.02 mg/kg) was administered intravenously (IV), intramuscularly (IM) or subcutaneously (SC) (n = 8/group) 0.5 h before general anesthesia with propofol-isoflurane. Carprofen (4.4 mg/kg SC) was administered after anesthetic induction and before ovariohysterectomy. Pain was scored using the short-form Glasgow composite pain scale for dogs (SF-GCPS). Dogs were administered morphine (0.25 mg/kg IV) when SF-GCPS scores were ≥ 5/20. Blood sampling was performed up to 720 min after drug administration. Plasma buprenorphine and norbuprenorphine concentrations were analyzed using liquid chromatography mass spectrometry. Pharmacokinetics of buprenorphine was described using a non-compartmental model (PK Solver 2.0). Statistical analysis was performed using linear mixed models and Fisher's exact test (p < 0.05).

RESULTS

Pain scores were significantly higher than baseline after IV (0.5-2 h), IM (0.5-3 h) and SC (0.5-4 h) but not among groups. Prevalence of rescue analgesia was significantly higher in SC (7/8 dogs) than IV (2/8) but not different between IV and IM (3/8) or IM and SC. The frequency of rescue analgesia was not significantly different among groups (IV = 2, IM = 5 and SC = 9). Norbuprenorphine was not detected. For IV, IM and SC administration, clearance was 1.29, 1.65 and 1.40 L/hour/kg, volume of distribution was 6.8, 14.2 and 40.1 L/kg, the elimination half-life was 3.7, 5.7, 22 h, and the area under the plasma concentration-time curved extrapolated to infinity was 15.7, 12.4 and 16.4 ng/mL/hour, respectively. Bioavailability for IM and SC was 62.6 and 40%, respectively. Maximum plasma concentrations of buprenorphine were 6.2 and 1.3 ng/mL at 0.14 and 0.33 h after IM and SC administration, respectively.

CONCLUSIONS

The route of administration influences the analgesic efficacy of buprenorphine in dogs. SC administration of buprenorphine failed to provide clinical analgesia due to erratic drug absorption. At the doses administered, the IV and IM routes are preferred for postoperative analgesia.