PURPOSE: To obtain a transport-release system containing an opioid analgesic encapsulated in phospholipid-based liposome, capable of controllably releasing the analgesic so as to improve therapeutic activity with no concomitant tachyphylaxis. CONSTITUTION: This liposome transport-release system is obtained by encapsulating a 14-hydroxymorphinan-based substance such as butorphanol, naloxone, meperidine, morphine or pentazocine in a liposome composed of a phospholipid and cholesterol. This system affords pain-freed state duration at least double (esp. at least four times) those of non-encapsulated analgesic injection compositions, specifically for 4h or longer, esp. 12-24h.
LIPOSOME TRANSPORTATION-RELEASE SYSTEM OF OPIOID ANALGESIC