Low-Dose Morphine Less Effective Than Diclofenac or Acetaminophen for Renal Colic
Am Fam Physician. 2016 Oct 15;94(8):665.
Which analgesics are most effective in providing significant pain relief in patients who are passing kidney stones in the emergency department?
This is a good example of how a well-done study can lead to erroneous conclusions. The comparator most likely to be effective here—titrated morphine—was used at a low dose and found to be less effective than intramuscular diclofenac or intravenous paracetamol (acetaminophen). (Level of Evidence = 1b)
These authors randomly assigned more than 1,600 patients who presented to an emergency department with suspected kidney stones and pain severity of at least 4 out of 10 to receive 75 mg of intramuscular diclofenac (n = 548), 1 g of intravenous paracetamol (n = 548), or 0.1 mg per kg of intravenous morphine (n = 549). All patients had intravenous lines started and received intravenous or intramuscular placebo (each patient received one active injection and two placebo injections). They did not give any intravenous fluids until 30 minutes after the initial treatment and then only at the discretion of the treating physician. Approximately 80% of the patients in each group had a confirmed stone, and approximately 3% had no imaging performed.
After 30 minutes, nearly two-thirds of the patients in each group experienced at least a 50% reduction in their pain intensity (68%, 66%, and 61%, respectively; P = .04). The authors report that 3% of morphine-treated patients experienced adverse events compared with 1% with each of the other treatments. What happened after the first 30 minutes? The median pain score for each group at 90 minutes was 0. The median time to a pain score of less than 2 out of 10 was 60 minutes, regardless of treatment. Approximately 10% of patients who received diclofenac required rescue analgesia compared with approximately 20% of patients who received the other analgesics. The authors report that two weeks after treatment, no additional adverse events occurred. The study was too small to identify potentially serious adverse events, such as kidney failure, gastrointestinal bleeding, and so forth. Regarding the morphine dose, it was probably too low to be a realistic comparator. The benefit with morphine is that you can rapidly titrate up the dose to get nearly 100% pain relief quickly.
Study design: Randomized controlled trial (double-blinded)
Funding source: Government
Setting: Emergency department
Reference: Pathan SA, Mitra B, Straney LD, et al. Delivering safe and effective analgesia for management of renal colic in the emergency department: a double-blind, multigroup, randomised controlled trial. Lancet. 2016;387(10032):1999–2007.
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