Improved buccal delivery of opioid analgesics and antagonists with bitterless prodrugs

Buccal delivery of opioid analgesics and antagonists is a useful way of improving bioavailability relative to the oral route. These compounds taste bitter, however. Various prodrugs of nalbuphine, naloxone, naltrexone, oxymorphone, butorphanol, and levallorphan, in which the 3-phenolic hydroxyl group was esterified, lacked a bitter taste. This taste difference was not due to differences in water solubility, suggesting that for these compounds the phenolic functional group is important for interaction with the taste receptor. In rats, nalbuphine, naloxone, and naltrexone administered buccally as prodrugs exhibited up to 90% bioavailability. In dogs, the bitter taste of buccally administered nalbuphine and naloxone caused salivation and swallowing, and bioavailability was low. Buccal dosing of the prodrugs of these compounds caused no adverse effects and the bioavailability ranged from 35 to 50%, a significant improvement relative to the oral bioavailability, which is 5% or less. The feasibility of buccal prodrug delivery using an adhesive patch formulation was demonstrated.