Morphine, pethidine and buprenorphine disposition in the cat

Area of Science:

• Veterinary Pharmacology
• Comparative Pharmacokinetics
• Opioid Analgesics

Background:

• Opioid analgesics are crucial in veterinary medicine.
• Understanding feline pharmacokinetics is essential for safe and effective pain management.
• Limited pharmacokinetic data exists for morphine, buprenorphine, and pethidine in cats.

Purpose of the Study:

• To determine and compare the pharmacokinetics of morphine, buprenorphine, and pethidine in cats.
• To evaluate the influence of intravenous (i.v.) and intramuscular (i.m.) administration on opioid pharmacokinetics.
• To provide data for optimizing analgesic protocols in feline patients.

Main Methods:

• Pharmacokinetic parameters were determined in 10 cats.
• Morphine (0.2 mg/kg) was administered i.v. or i.m.
• Buprenorphine (0.01 mg/kg) was administered i.v. or i.m.
• Pethidine (5 mg/kg) was administered i.m.
• Plasma drug concentrations were measured using HPLC, RIA, and GC.
• Key pharmacokinetic parameters including half-life, MRT, clearance, and volume of distribution were calculated.

Main Results:

• Morphine: t1/2el 76.3 min (i.v.) vs. 93.6 min (i.m.); Clp 24.1 mL/kg/min (i.v.) vs. 13.9 mL/kg/min (i.m.).
• Buprenorphine: t1/2el 416.8 min (i.v.) vs. 380.2 min (i.m.); Clp 16.7 mL/kg/min (i.v.) vs. 23.7 mL/kg/min (i.m.).
• Pethidine (i.m.): t1/2el 216.4 min; Clp 20.8 mL/kg/min.
• Tmax for i.m. morphine, buprenorphine, and pethidine were 15, 3, and 10 min, respectively.

Conclusions:

• The pharmacokinetics of morphine, buprenorphine, and pethidine in cats are generally comparable to those in dogs.
• Cats may exhibit slower clearance of morphine compared to dogs.
• These findings support informed clinical decisions regarding opioid use in feline pain management.