The single-dose pharmacokinetics and pharmacodynamics of oxycodone administered by the intravenous and rectal routes were determined in 12 adult cancer patients with moderate to severe cancer pain (visual analog scale [VAS] score, approximately 5). Oxycodone was administered by the intravenous and rectal routes with open drug administration and a cross-over design. After single-dose intravenous administration (7.9 +/- 1.5 mg, mean +/- SD), the mean (+/- SD) terminal half-life was 3.4 h (+/- 1.1), the mean (+/- SD) plasma clearance was 45.4 L/h (+/- 10.1), and the mean (+/- SD) volume of distribution in the terminal phase was 3.0 L/kg (+/- 1.1). After rectal oxycodone (30 mg), the mean (+/- SD) absorption lag time was 0.52 h (+/- 0.29) and the mean (+/- SD) absolute bioavailability was 61.6% (+/- 30.2%). Intravenous oxycodone was associated with a rapid onset of pain relief (5-8 min) in contrast to the 0.5- to 1.0-h delay observed after rectal administration. However, rectal oxycodone provided analgesia of much longer duration (approximately 8-12 h) than did intravenous oxycodone (approximately 4 h). There were no significant differences (P > 0.05) in the incidence and severity of side effects between intravenous and rectal oxycodone. The marked interindividual variation observed in the pharmacokinetics and pharmacodynamics of oxycodone in this study emphasizes the need for individualized dosing regimens.