Effects of narcotic analgesics, especially pethidine and norpethidine, on renal pelvic smooth muscle in patients with hydronephrosis

Relaxation of the renal pelvic smooth muscle is usually attempted as a symptomatic treatment in painful colic of the upper urinary tract. The spasmolytic potency of morphine, pethidine, pentazocine, fentanyl, naloxone and papaverine was evaluated using noradrenaline-contracted pelvic strips from hydronephrotic patients. The order of spasmolytic potency was found to be fentanyl > pethidine = papaverine > pentazocine = naloxone. Morphine produced a dual effect, starting with contraction followed by relaxation. Norpethidine, which is the only metabolite of pethidine occurring in human plasma, had the same relaxing potency as its parent compound, pethidine. Thus, an active metabolite may play a role in the outcome of spasmolytic drug treatment.