Table 2.
Pharmacology of methylnaltrexone (parameters after repeated intravenous application, healthy volunteers).
| Chemistry | Derivative of naltrexone; molecular weight 436.3 Da; positively charged |
| Receptor antagonism | Peripheral μ-opioid receptor antagonist; 8-fold lower potency at κ-opioid receptor; 120-fold lower potency at δ-opioid receptor |
| Route | Intravenous, subcutaneous, and oral (including enteric-coated) |
| Cmax (ng/mL) | 675 (SD 495–855) (0.3 mg/kg) |
| tmax (h) | 0.10 (SD 0.05–1.15) (0.3 mg/kg) |
| AUC (ng/h*mL) | 353 (SD 262–444) (0.3 mg/kg) |
| t1/2 (h) | 2.9 (SD 2.0–3.8) (0.3 mg/kg) |
| Metabolism | Small percentage undergoes hepatic metabolism (possibly glucuronidation) |
| Active metabolite | None |
| Elimination | 40%–50% renal and unchanged, another 50% fecal elimination |