Pilot study on disposition and pain relief after i.m. administration of meperidine during the day or night

Two groups (four patients each) of sickle cell anemia patients with severe pain were studied. One group comprised patients admitted to emergency unit in the morning (5:40 to 9:15) and the other patients admitted in the evening (18:53 to 22:50). All patients received intramuscular meperidine (1.5 mg/kg). Pain intensity and pain relief were followed for 4 h; blood samples were taken up to 6 h after drug administration. Significant differences in drug disposition were found between the day and night groups, as the elimination half-life was 46% shorter during the night and the total serum clearance was 70% greater during the night. Whereas a positive correlation was found between drug concentration and pain relief for the day group, no such correlation was found for th night group. Even though peak concentrations were higher during the night, analgesia was lower. This pilot study suggests that much higher meperidine doses might be required during the night to achieve equieffective analgesia.