Pharmacokinetics of rectal compared to intramuscular paracetamol in children undergoing minor surgery

Objectives : Although paracetamol is a widely accepted and safe analgesic, guidelines regarding its definite analgesic dose are lacking. This study was, therefore, undertaken to compare the pharmacokinetics of paracetamol when administered by two routes, viz, intramuscular and rectal, in children undergoing minor surgery.
Design : Randomized, controlled, assessor-blind, comparative clinical trial.
Materials and Methods: Following Institutional Ethics Committee approval and valid consent, children undergoing minor surgery were randomized to receive paracetamol either intramuscularly or rectally. Blood samples were collected at fixed intervals for estimation of drug levels.
Results : Fifty children (43 boys, 7 girls; ages 3 to 12 years; weight 10 to 40 kg) were enrolled in the study. 26 patients were randomized to receive paracetamol intramuscularly (mean dose 14.8 ± 0.9 mg/kg) and 24 to receive the paracetamol as a rectal suppository (mean dose 29.5 ± 1.4 mg/kg). Complete pharmacokinetic analysis was possible in only 29 patients, as the blood samples of the others were either not received or were inadequate for analysis. The mean maximum plasma concentration (C_max ) with rectal paracetamol (n = 13) was 6.04 ± 2.21 mg/ml with a T_max of 2.5 ± 0.89 h, while with intramuscular paracetamol (n = 16), the C_max was 10.34 ± 7.09 mg/ml and the T_max 1.47 ± 0.64 h. The area under the concentration-time curve (AUC_0-12 ) was 42.26 ± 22.29 µg.h/ml and 43.60 ± 26.45 µg.hr/ml for rectal and intramuscular paracetamol, respectively. Patients in the intramuscular group needed rescue medication earlier as compared to those in the rectal group (P < 0.05).
Conclusion : Although the drug levels achieved with rectal paracetamol were less than that achieved with intramuscular administration, it was higher than the lower limit for analgesic effect (3-5 µg/ml). Patients who received paracetamol intramuscularly needed rescue medication earlier compared to those receiving paracetamol rectally, indicating a more prolonged duration of action with rectally administered paracetamol. Hence, rectal paracetamol can be used as a safe, effective, and more acceptable analgesic alternative in children.