Plasma concentrations following single doses of morphine sulfate in oral solution and rectal suppository

Plasma concentrations of morphine and morphine-3-glucuronide (morphine's major metabolite) were determined following single 10-mg doses of morphine sulfate in oral solution and rectal suppository. Ten patients with pain secondary to cancer were given a single 10-mg dose of oral morphine sulfate in an oral solution or rectal suppository on sequential days. Blood samples were collected at time zero and periodically for 4.5 hours after administration. Plasma concentrations of morphine and morphine-3-glucuronide were determined using liquid chromatography with electrochemical detection. Higher mean concentrations of morphine were achieved with the rectal suppository than with the oral solution at all time points, and the overall mean plasma morphine concentration for the entire 4.5-hour period was significantly higher for the rectal suppository than for the oral solution. There were no significant differences between dosage forms in mean morphine-3-glucuronide concentrations at individual time points or over the entire period. A single dose of morphine sulfate in a rectal suppository was better absorbed than in an oral solution. Further studies are needed to compare the clinical efficacy of these dosage forms under steady-state conditions.