[Pharmacology of buprenorphine]

Pharmacokinetics of low-dose and high-dose buprenorphine in cats after rectal administration of different formulations

OBJECTIVES

A prospective experimental study was performed in nine young healthy cats to investigate a pharmacokinetic profile and the clinical relevance of rectally administered buprenorphine. Rectal pH value was measured in all nine cats.

METHODS

Blood was collected 15, 30, 60, 90, 120, 240 and 480 mins and 24 h after the rectal administration of a suppository and a gel at doses between 0.02 mg/kg and 0.1 mg/kg buprenorphine to determine the plasma concentration of buprenorphine. Rectal pH was measured with pH paper.

RESULTS

Upon pharmacokinetic non-compartment analysis of high-dose buprenorphine (0.1 mg/kg), average maximal plasma concentration was found to be 1.13 ng/ml, time to maximal plasma concentration was 45 mins and area under the plasma concentration-time curve was 94.19 ng*min/ml, representing low but potential bioavailability. Mean residual time was 152.2 mins and the half-life was 92.6 mins. A wide range of plasma concentrations within the cohort was measured and two of the cats had to be excluded from statistical analysis owing to incomplete uptake. Vital parameters of all cats were considered to be normal but three of the cats showed mydriasis up to 8 h after application. After the administration of a low-dose suppository or a rectal gel (0.02 mg/kg) within pilot studies, no buprenorphine was detected in cat plasma. Rectal pH in all cats was between 7.7 and 8.

CONCLUSIONS AND RELEVANCE

The rectal application of buprenorphine at a dose of 0.1 mg/kg revealed a potential but weak uptake in cats. Regarding effective concentrations in previous pharmacokinetic investigations, rectal administration is currently not recommended for good provision of opioid analgesia in cats. Pharmacological investigations of formulation and galenics in order to improve the rectal bioavailability of buprenorphine remain to be clarified before further dose-finding and pharmacokinetic/pharmacodynamic studies are performed.

Determination of buprenorphine in plasma by liquid chromatography: application to heroin-dependent subjects

A rapid, sensitive, precise and accurate HPLC assay with UV detection was developed for the determination of buprenorphine (BN) in human plasma. This method involved a two-step extraction in the presence of clothiapine as internal standard. The compounds were chromatographied on a reversed-phase Spherisorb C8 column with a mobile phase consisting of 0.06 M KH2PO4/Na2HPO4 pH 6.4-acetonitrile-triethylamine-Pic B5 (520:480:0.5:15, v/v) and detected at 214 nm. The recovery of BN was greater than 94% with an intra-day relative standard deviation < or = 4.8% and an inter-day relative standard deviation < or = 14.6% at any studied level. Studies of drug stability during sample storage at -20 degrees C and at +4 degrees C did not show any significative degradation of BN. This method was successfully applied to explore the overdose state of heroin-dependent subjects treated by high-dose BN.

[Comparative study of buprenorphine and its combination to ketoprofen or propacetamol for postoperative analgesia in urologic surgery]

OBJECTIVE

To compare the analgesic effect of subcutaneous buprenorphine alone and in combination with propacetamol and ketoprofen following urologic surgery.

STUDY DESIGN

Open randomized clinical trial.

PATIENTS

Sixty ASA II/III patients undergoing urologic surgery.

METHODS

The patients were randomized into three groups to receive either buprenorphine (0.3 mg subcutaneous) on demand (group 1, n = 20), or a combination of buprenorphine (0.3 mg)-propacetamol (2 g)-ketoprofen (100 mg) by intravenous route over 2 hours followed by an infusion of propacetamol (2 g) and ketoprofen (100 mg) at a constant rate over. The remaining 22 hours (group 2, n = 20), or the same loading dose as in group 2 prolonged by a continuous infusion of buprenorphine (0.3 mg), propacetamol (2 g) and ketoprofen (100 mg) over the same period (group 3, n = 20). Visual analogue scale pain scores (0-10) were assessed every hour during the 24 hours of the study. When the VAS score exceeded 5, an additional dose of 0.3 mg of buprenorphine was administered.

RESULTS

Groups were similar for age, surgery, anaesthesia and initial pain levels. Compared to group 1, the onset of analgesia was earlier in groups 2 and 3 at the 1st hour (P < 0.05); the level of analgesia was lower at the 3rd hour (P < 0.05). The maintenance of this analgesia level required constant buprenorphine administration. Buprenorphine requirements were decreased to 56% and 37% in groups 2 and 3 respectively, compared to group 1 (P < 0.05). Incidence of nausea and vomiting was lowered to 15% in group 3 (P < 0.05).

CONCLUSION

A combination of buprenorphine, propacetamol and ketoprofen provides effective postoperative analgesia with a low incidence of nausea and vomiting and decreased requirements of buprenorphine.

[Risk evaluation of oxygen desaturation after buprenorphine or morphine administration during the early postoperative period]

The purpose of this study, conducted in a PACU in the early recovery period of orthopaedic procedures under general anaesthesia, was to compare the time course of O2 arterial saturation (SpO2), measured by pulse oximetry, after the intramuscular administration of either buprenorphine (0.30 mg) or morphine (10 mg). The rate of patients who had an episode of O2 desaturation (defined as a SpO2 under 95%) was similar in both groups: 73% after buprenorphine vs 67% after morphine. The cumulative duration of desaturation episodes was higher following buprenorphine (p < 10(-5). Finally, in patients who had at least one episode of arterial desaturation, the mean duration of these episodes was identical in both groups. However the average number of episodes per patient was significantly higher in the buprenorphine group. These results should lead us to be cautious with the use of buprenorphine during the early recovery period, especially as this as this agent has specific characteristics such as a long duration of action and resistance to naloxone.

[Analgesia by sublingual buprenorphine in extracorporeal kidney lithotripsy]

The efficacy of sublingual buprenorphine given for premedication was assessed in 287 consecutive patients scheduled for extracorporeal shock wave lithotripsy (ESWL). The patients were randomly assigned to three groups. They were given 45 min before starting ESWL 5 mg midazolam orally in group 1 (n = 97), and 5 mg midazolam orally and 0.2 mg sublingual buprenorphine in group 2 (n = 97), and 5 mg midazolam orally and 0.4 mg sublingual buprenorphine in group 3 (n = 93). Analgesia was assessed with a simple three step verbal scale: no pain, moderate pain treated with simple analgesics (Spasfon, Viscéralgine), and exquisite pain requiring general anaesthesia. Sublingual buprenorphine provided good analgesia in 87% of group 2 patients, and 88% of group 3 patients (NS) whereas 70% of group 1 patients experienced no pain (p < 0.05). The incidence of side-effects during the 12 h following ESWL, such as nausea, vomiting and drowsiness, was higher in group 3 (31 patients) than in group 2 (13 patients) (p > 0.01). No clinical respiratory depression occurred, although 11 patients in group 3 complained of drowsiness. It is concluded that premedication with 0.2 mg of sublingual buprenorphine provides efficient analgesia for ESWL and few side-effects.