Table 1.
Pharmacokinetics of selected opioids.
| Opioid | Plasma protein binding (%) | Volume of distribution (l/kg) | Half-life (t1∕2) | Phase I metabolism | Phase II metabolism | Major metabolites |
|---|---|---|---|---|---|---|
| Morphine | 30 | 245 | 3 | CYP3A | UGT2B7 | Morphine-3-glucuronide (M3G)—neuroexcitatory effects |
| Morphine-6-glucuronide (M6G)—analgesic effect | ||||||
| Hydromorphone | 20 | 91.5 | 2.6 | UGT2B7 | Hydromorphone-3-glucuronide | |
| UGT1A3 | ||||||
| Fentanyl | 84 | 4 | 3.5 | CYP3A | Norfentanyl-inactive | |
| Tramadol | 20 | 2.6 | 6.7 | CYP3A | Nortramadole-inactive | |
| CYP2D6 | O-desmethyltramadol-active | |||||
| Oxycodone | 45 | 2.6 | 3.7 | CYP3A | UGT2B7 | Oxymorphone |
| CYP2D6 | Noroxycodone | |||||
| Methadone | 85–90 | 1–8 | 8–59 | CYP3A | No active metabolites | |
| Codeine | 7–25 | 3–6 | 3–4 | CYP3A | UGT2B7 | Codeine-6-glucuronide (C6G) |
| CYP2D6 | Morphine | |||||
| Norcodeine | ||||||
| Tapentadol | 20 | 540 | 4 | CYP2D6 | UGT1A9 | No active metabolites |
| CYP2C9 | UGT2B7 | |||||
| CYP2C19 | ||||||
| Pethidine | 40 | 3–5 | 4 | CYP2D6 | Norpethidine (neurotoxic, analgesic effect) | |
| CYP3A | ||||||
| CYP2C19 | ||||||
| Dextropropoxyphene | 70–80 | 16 | 15 | CYP3A | Nordextropropoxyphene | |
| Buprenorphine | 96 | 188–335 | 3–4 | CYP3A4 CYP2C8 |
UGT1A1 UGT1A3 UGT2B7 |
Norbuprenorphine Buprenorphine-3-glucuronide Norbuprenorphine-3-glucuronide |