Serum and cerebrospinal fluid morphine pharmacokinetics after single doses of intravenous and intramuscular morphine after hip replacement surgery.
OBJECTIVE
To compare the time course of morphine and metabolite concentrations in serum and cerebrospinal fluid (CSF) after intravenous and intramuscular administration after surgery.


METHODS
This was a randomized double-blind, double-dummy study in patients who had undergone hip replacement surgery. Morphine (M, 10 mg) was administered intravenously (IV) or intramuscularly (IM). Arterial blood and CSF samples (from a spinal catheter) were drawn simultaneously at 10, 30, 60, and 120 min after administration. Morphine and metabolites [morphine-3-glucuronide (M-3-G), morphine-6-glucuronide (M-6-G), and normorphine (NM)] were determined by a validated liquid chromatography-tandem mass spectrometry method.


RESULTS
Thirty-eight patients were included: 13 men and 25 women, 20 in the IV, 18 in the IM group. Serum concentrations of M after 10 min were consistently higher after IM than IV, concentrations of M-3-G and M-6-G after IM surpassed those of IV after 45 min. NM was not found. None of the metabolites was found in CSF. CSF morphine concentrations and CSF/serum concentration ratios were consistently higher after IV compared to IM. The mean AUC(CSF)/AUC(serum) (0-120 min) concentration ratios were 0.18 and 0.09 after IV and IM, respectively.


CONCLUSIONS
The uptake of morphine to the CSF was consistently higher after IV administration than after IM already after 10 min. The higher CSF concentration may be caused by an initially higher morphine blood/CSF gradient following IV morphine injection. The pharmacokinetic findings are compatible with a more rapid and extensive initial effect of IV morphine compared with IM.
Dale
O
O
Pain and Palliation Research Group, Department of Circulation and Medical Imaging, Faculty of Medicine, Norwegian University of Science and Technology, Trondheim, Norway. ola.dale@ntnu.no
Thoner
J
J
Nilsen
T
T
Tveita
T
T
Borchgrevink
P C
PC
Klepstad
P
P
D000368:Aged; D000701:Analgesics, Opioid / Q000008:administration & dosage / Q000493:pharmacokinetics*; D019540:Area Under Curve; D019644:Arthroplasty, Replacement, Hip; D002045:Bupivacaine / Q000008:administration & dosage / Q000493:pharmacokinetics; D004311:Double-Blind Method; D005260:Female; D006801:Humans; D007273:Injections, Intramuscular; D007275:Injections, Intravenous; D008297:Male; D008874:Midazolam / Q000008:administration & dosage / Q000493:pharmacokinetics; D008875:Middle Aged; D009020:Morphine / Q000097:blood / Q000134:cerebrospinal fluid / Q000493:pharmacokinetics*; D009022:Morphine Derivatives / Q000097:blood; D010147:Pain Measurement / Q000379:methods; D010149:Postoperative Pain / Q000188:drug therapy; D011182:Postoperative Care / Q000379:methods
D000701:Analgesics, Opioid; D009022:Morphine Derivatives; C035349:morphine-6-glucuronide; D009020:Morphine; C018108:morphine-3-glucuronide; D008874:Midazolam; C010616:normorphine; D002045:Bupivacaine