The efficacy, safety, and pharmacokinetics of intramuscular and oral phenyramidol in patients with low back pain in an emergency department

Authors: HAKAN ERGÜN, ONUR POLAT, N. ARDA DEMİRKAN, MÜGE GÜNALP, SERDAR GÜRLER

Abstract: To compare the efficacy, safety, and pharmacokinetics of oral and intramuscular (i.m.) phenyramidol in patients with low back pain. Materials and methods: Consecutive patients with low back pain were recruited and randomized (5:3) to treatment with either 800 mg oral or i.m. phenyramidol. Pain was assessed by visual analogue scale every 30 min for 2 h. Blood samples were drawn at baseline and every 15 min for 2 h. A 5-point verbal global evaluation scale was performed by both patients and physicians. In addition, the need for rescue analgesics after 2 h was noted. After the acute phase, patients were re-randomized (5:3) to receive either a placebo tablet or a 400 mg phenyramidol tablet 3 times a day for 7 days. Efficacy of the long term treatment was measured by the evaluation of both patients and physicians (with a 5-point verbal global evaluation scale) and by the daily amount of naproxen sodium consumed as the rescue analgesic drug. Results: Seventy-two patients (45F/27M) had a marked improvement in pain scores, with no significant difference between the groups. Sixty-one (39F/22M) patients completed the second phase, in which no difference in any parameter was noted. Seven of 38 patients in phenyramidol group had elevated liver enzymes at the end of the chronic treatment phase which normalized after 1 week. Only the T_{max} pharmacokinetic parameter (C_{max}, T_{max}, t_½, and AUC) was significantly but slightly different between the groups. Conclusion: Liver enzymes should be monitored in patients taking repeated dose of phenyramidol and should not be used in combination with analgesics bearing hepatotoxicity potential, such as paracetamol.

Keywords: Phenyramidol, low back pain, pharmacokinetics, emergency department

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