Opioid delivery in the treatment of cancer breakthrough pain: a review of routes of administration.

Analgesics delivered via the oral route of administration (capsules, tablets, or solutions) are most commonly used to treat cancer breakthrough pain (BTP); however, the effectiveness of oral opioids may be limited by slow gastrointestinal absorption and first-pass metabolic effects. Although the limitations presented by oral opioid delivery are acknowledged and formulations and delivery systems that mirror the temporal characteristics of the majority of cancer BTP episodes are available, short-acting oral opioids are the accepted standard of care. The purpose of this review is to provide an overview of the different routes of opioid administration used in the treatment of cancer BTP and briefly discuss the characteristics of different delivery systems.