Plasma morphine concentrations during chronic oral administration in patients with cancer pain

Plasma concentrations of morphine were studied in 16 patients with chronic pain due to advanced cancer, treated with regular doses of morphine chloride by the oral route. Doses ranged from 20 to 125 mg every 4 h and a significant, positive, linear correlation was found between dose (range 0.22-3.01 mg/kg) and mean plasma concentration (range 22-364 ng/ml). The profile of the 4 h concentration curve is described and found to be subject to considerable, individual variation. The present investigation supports the experience that good pain relief can be obtained, if individual requirements as to dose and dose interval are taken into consideration.