PHARMACOKINETICS AND PHARMACODYNAMICS OF OXYCODONE WHEN GIVEN INTRAVENOUSLY AND RECTALLY TO ADULT PATIENTS WITH CANCER PAIN

The single-dose pharmacokinetics and pharmacodynamics of oxycodone adm inistered by the intravenous and rectal routes were determined in 12 a dult cancer patients with moderate to severe cancer pain (visual analo g scale [VAS] score, approximately 5). Oxycodone was administered by t he intravenous and rectal routes with open drug administration and a c ross-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 w as 3.0 L/kg (+/- 1.1). After rectal oxycodone (30 mg), the mean (+/- S D) absorption lag time was 0.52 h (+/- 0.29) and the mean (+/- SD) abs olute 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 (approxi mate to 8-12 h) than did inhavenous oxycodone (approximate to 4 h). Th ere were no significant differences (P > 0.05) in the incidence and se verity of side effects between inhavenous and rectal oxycodone. The ma rked interindividual variation observed in the pharmacokinetics and ph armacodynamics of oxycodone in this study emphasizes the need for indi vidualized dosing regimens.