Comparison of the analgesic efficacy and plasma concentrations of high-dose intra-articular and intramuscular morphine for knee arthroscopy.
OBJECTIVE
It is important to provide good postoperative analgesia after discharge from day case surgery. The usefulness of intra-articular morphine for analgesia after day case knee arthroscopy remains controversial. A large dose of morphine intra-articularly may provide a good long-lasting analgesia, but its efficacy and pharmacokinetics are not known and may be no better than intramuscular morphine. We compared the effect of 10 mg intra-articular and intramuscular morphine for 24 h post-injection in a randomized double-blind study.


METHODS
Forty adults undergoing knee arthroscopy were recruited and received either 10mg morphine intra-articularly or intramuscularly. Our primary outcome was overall visual analogue assessment of pain (0-100 mm scale where 0 is no pain and 100 is worst possible pain) between 4 h (on discharge) and 24 h (post-operatively). Plasma morphine concentrations were measured at 15 min, and 1, 2, 4 and 24 h. The use of additional analgesia was noted.


RESULTS
The assessment of pain experienced between discharge (4 h) and 24 h was significantly better in the intra-articular (n = 20; mean+/-SD: 18+/-19) than the intramuscular (n = 19; mean+/-SD: 34+/-20) group (P = 0.027). The number of patients consuming any additional analgesia between discharge and 24 h was significantly lower in the intra-articular morphine group (P = 0.038), with 4 (20%) patients in the intra-articular group and 11 (60%) patients in the intramuscular group consuming supplementary analgesia. There were no differences in plasma morphine concentrations between the groups.


CONCLUSIONS
A large dose of intra-articular morphine provided better analgesia than the same dose of intramuscular morphine, low plasma morphine levels suggesting a peripheral mechanism.
Raj
N
N
University Hospital of Wales, Department of Anaesthetics and Intensive Care Medicine, Cardiff, UK. naveenraj@doctors.org.uk
Sehgal
A
A
Hall
J E
JE
Sharma
A
A
Murrin
K R
KR
Groves
N D
ND
D000328:Adult; D000698:Analgesia / Q000379:methods*; D000701:Analgesics, Opioid / Q000008:administration & dosage* / Q000097:blood / Q000493:pharmacokinetics; D001182:Arthroscopy / Q000379:methods; D004305:Dose-Response Relationship, Drug; D004311:Double-Blind Method; D005260:Female; D006801:Humans; D007270:Injections, Intra-Articular / Q000379:methods; D007273:Injections, Intramuscular / Q000379:methods; D007719:Knee Joint / Q000187:drug effects / Q000601:surgery*; D008297:Male; D008875:Middle Aged; D009020:Morphine / Q000008:administration & dosage* / Q000097:blood / Q000493:pharmacokinetics; D010147:Pain Measurement / Q000187:drug effects* / Q000379:methods; D010149:Postoperative Pain / Q000517:prevention & control*; D013997:Time Factors; D016896:Treatment Outcome
D000701:Analgesics, Opioid; D009020:Morphine