Duration of Analgesia from Intramuscular Diclofenac (Voltaren)
A single 75 mg intramuscular dose of diclofenac provides effective pain relief for approximately 6-7 hours in adults with acute pain. 1, 2
Evidence for Duration of Action
The median duration of analgesia from IM diclofenac 75 mg is approximately 6.7 hours, based on systematic review data of postoperative pain studies 3
Higher doses (100 mg) extend the duration slightly to approximately 7.2 hours, though this requires splitting into multiple injection sites given the 75 mg per injection limit 3
IM diclofenac demonstrates a fast onset of action (peak analgesia within 30 minutes) combined with this prolonged duration, making it superior to many narcotic combinations for acute pain conditions 2, 4
Clinical Context and Dosing
The standard IM dose is 75 mg per injection, with a minimum interval of 12 hours between doses and a maximum daily dose of 150 mg (two 75 mg injections) 1
For acute severe pain requiring repeated dosing, the second 75 mg dose can be administered after 12 hours if pain returns 1
In controlled trials for acute musculoskeletal injuries, 99.3% of patients achieved 50% pain reduction within 30 minutes with IM diclofenac, demonstrating both rapid onset and robust efficacy 4
Important Clinical Considerations
IM administration is preferred over IV for most clinical settings, as it provides rapid analgesia without the technical complexity and dilution error risks of IV administration 1
The relatively short plasma elimination half-life (1.5 hours) does not correlate with duration of analgesia, as diclofenac persists in synovial fluid and tissues 5
For pain lasting beyond 6-7 hours, transition to oral diclofenac (50 mg three times daily or 100 mg sustained-release twice daily) is appropriate rather than repeated IM injections 1
Safety Parameters
Do not exceed 150 mg total daily dose by any route, as higher doses significantly increase gastrointestinal and renal toxicity without additional analgesic benefit 1
Avoid in patients with active peptic ulcer disease, severe heart failure, renal impairment (CrCl <10 mL/min), or third trimester pregnancy 1
Patients ≥65 years require gastroprotection with a proton pump inhibitor when using diclofenac 1