Plasma and Oral Fluid Pharmacokinetics and Pharmacodynamics after Oral Codeine Administration

Abstract

Abstract Background: The ease, noninvasiveness, and safety of oral fluid collection have increased the use of this alternative matrix for drugs-of-abuse testing; however, few controlled drug administration data are available to aid in the interpretation of oral fluid results. Methods: Single oral codeine doses (60 and 120 mg/70 kg) were administered to 19 volunteers. Oral fluid and plasma were analyzed for free codeine, norcodeine, morphine, and normorphine by solid-phase extraction combined with gas chromatography–mass spectrometry (SPE/GC-MS). Physiologic and subjective effects were examined. Results: Mean (SE) peak codeine concentrations were 214.2 ± 27.6 and 474.3 ± 77.0 μg/L in plasma and 638.4 ± 64.4 and 1599.3 ± 241.0 μg/L in oral fluid. The oral fluid-to-plasma ratio for codeine was relatively constant (∼4) from 1 to 12 h. The mean half-life (t1/2) of codeine was 2.2 ± 0.10 h in plasma and 2.2 ± 0.16 h in oral fluid. Significant dose-related miosis and increases in sedation, psychotomimetic effect, and “high” occurred after the high dose. Mean codeine oral fluid detection time was 21 h with a 2.5 μg/L cutoff, longer than that of plasma (12–16 h). Detection times with the proposed Substance Abuse and Mental Health Services Administration cutoff (40 μg/L) were only 7 h. Norcodeine, but not morphine or normorphine, was quantified in both plasma and oral fluid. Conclusions: The disposition of codeine over time was similar in plasma and oral fluid, but because of high variability, oral fluid codeine concentrations did not reliably predict concurrent plasma concentrations. Oral fluid testing is a useful alternative matrix for monitoring codeine exposure with a detection window of 7–21 h for single doses, depending on cutoff concentrations. These controlled drug administration data should aid in the interpretation of oral fluid codeine results.