Pharmacokinetics of dextromoramide in surgical patients

The pharmacokinetics of the narcotic analgesic dextromoramide was investigated by means of a specific GC-MS method in 9 patients who were given a single oral dose of the drug (7.5 mg) together with an anticholinergic before undergoing minor orthopedic surgery. Dextromoramide was rapidly absorbed from the gastrointestinal tract, with peak plasma levels between 68 and 177 micrograms/L usually achieved within 0.5-4.0 h after dosing. In 5 patients, the decline of plasma concentrations after the peak followed a biphasic pattern, with half-lives of 0.4-1.6 h for the first phase and 6.3-21.8 h for the terminal phase. In the remaining patients, no clear-cut biphasic pattern was seen and half-lives calculated over the period between 4 h and 10 h after administration ranged from 1.5 to 4.7 h. Apparent clearance and volume of distribution values ranged from 0.06 to 0.36 1.h-1.kg-1 and from 0.6 to 2.4 l.kg-1, respectively. Less than 0.06% of the dose was excreted unchanged in urine within 8 h of administration. The concentration of the drug in a CSF sample collected 1 h after dosing was below the limit of detection (2 micrograms/L) in all subjects.