ABSTRACT
Lumbar spinal fluid and plasma concentrations of morphine were measured by radioimmunoassay after intrathecal administration of 1 mg of morphine (n = 13) or heroin (n = 10). Plasma levels of morphine were measured regardless of 'whether heroin or morphine was injected intrathecally, because of the rapid biotransformation of heroin to morphine in plasma. Significant drug concentrations appeared in plasma after intrathecal heroin (peak concentration 47.8 +/- 9.0 nmol/L, time to peak concentration 10 +/- 2.4 min); after intrathecal morphine plasma drug concentrations were significantly lower (8.1 +/- 1.0 nmol/L; P less than 0.002) and significantly later (216 +/- 39 min; P less than 0.002). Elimination half-life of heroin from spinal fluid (43 +/- 5 min) was significantly shorter than for morphine (73 +/- 5 min; P less than 0.02).
Subject(s)
Heroin/administration & dosage , Morphine/administration & dosage , Aged , Anesthesia, Epidural , Biotransformation , Female , Half-Life , Heroin/blood , Heroin/cerebrospinal fluid , Humans , Injections, Spinal , Male , Middle Aged , Morphine/blood , Morphine/cerebrospinal fluid , Radioimmunoassay , Time FactorsABSTRACT
Nine patients undergoing cardiopulmonary bypass surgery were given either 2 mg diamorphine or 2.5 mg morphine by intrathecal injection. Spinal fluid (sf) samples were collected over 25 min and drug concentrations measured by HPLC. Concentrations in sf were about 4000 times as great as after 1 mg/kg IV morphine. The kinetic properties of morphine and heroin in sf differed; diamorphine was removed from sf much more rapidly than morphine. Lipophilic opiates may be safer for intrathecal use because of the shorter life of substantial drug concentrations in the mobile sf phase.
