Pethidine Solution for Injection 50 mg/ml Dosage and administration Dogs and cats by intramuscular injection: 3.3 mg/kg for premedication prior to surgical procedures and examination, as an adjunct to sedation or anaesthesia, or post-operatively as an analgesic. Horses by intramuscular injection: 2.0 mg/kg for the relief of pain in spasmodic colic.