Oral oxycodone-induced respiratory depression during normocapnia and hypercapnia: a pharmacokinetic-pharmacodynamic modeling study.

The widely prescribed opioid oxycodone may cause lethal respiratory depression. We compared the effects of oxycodone on breathing and antinociception in healthy young volunteers. After pharmacokinetic/pharmacodynamic modelling, we constructed utility functions to combine the wanted and unwanted endpoints into a single function. We hypothesized that the function would be predominantly negative over the tested oxycodone concentration range. Twenty-four male and female volunteers received 20 (n=12) or 40 (n=12) mg oral oxycodone immediate-release tablets. Hypercapnic ventilatory responses (visit 1) or responses to three nociceptive assays (pain pressure, electrical and thermal tests; visit 2) were measured at regular intervals for 7 hours. Pharmacokinetic/pharmacodynamic analyses, that included carbon dioxide kinetics, stood at the basis of the utility function: probability of antinociception minus probability of respiratory depression. Oxycodone had rapid onset/offset times (30-40 min) with potency values (effect-site concentration causing 50% of effect) ranging from 0.05 to 0.13 ng/mL for respiratory variables obtained at hypercapnia and antinociceptive responses. Ventilation at an extrapolated end-tidal carbon dioxide partial pressure of 55 mmHg, was used for creation of three utility functions, one for each of the nociceptive tests. Contrary to expectation, the utility functions were close to zero or positive over the clinical oxycodone concentration range. The similar or better likelihood for antinociception relative to respiratory depression may be related to oxycodone's receptor activation profile or to is high likeability that possibly alters the modulation of nociceptive input. Oxycodone differs from other μ-opioids, such as fentanyl, that have a consistent negative utility.