What is the recommended frequency for administering diclofenac (Nonsteroidal Anti-Inflammatory Drug (NSAID)) 500mg?

Critical Error: Diclofenac 500mg Does Not Exist

There is no such thing as diclofenac 500mg—this dose does not exist in any formulation and would represent a dangerous overdose. The maximum recommended daily dose of diclofenac by any route is 150 mg/day, making a single 500mg dose more than three times the total daily limit 1, 2, 3.

Standard Diclofenac Dosing

Oral Formulations

• Standard dose: 50 mg two to three times daily (100-150 mg/day total) 2, 3
• Maximum daily dose: 150 mg/day for rheumatoid arthritis; 100-150 mg/day for osteoarthritis and ankylosing spondylitis 2, 4
• Available strengths: 25 mg, 50 mg, 75 mg (extended-release), and 100 mg (extended-release) 2, 3

Injectable Formulations

• Intramuscular dose: 75 mg per injection 1
• Frequency: Every 12 hours minimum interval 1
• Maximum daily dose: 150 mg/day (two 75 mg injections) 1
• Intravenous dose: 18.75-37.5 mg boluses every 6 hours for postoperative pain 1

Typical Dosing Schedules

For Acute Pain

• Immediate-release: 50 mg three times daily with meals 2, 5
• Intramuscular: 75 mg as a single dose for acute renal colic or severe pain 1, 3

For Chronic Inflammatory Conditions

• Standard regimen: 50 mg two to three times daily (total 100-150 mg/day) 2, 4
• Extended-release: 75 mg twice daily or 100 mg once daily 4

For Topical Application (Actinic Keratosis)

• Diclofenac 3% gel: Apply twice daily for 60-90 days 6

Critical Safety Considerations

Absolute Contraindications

• Active peptic ulcer disease 1
• Severe heart failure, liver failure, or history of GI bleeding 1
• Never exceed 150 mg/day by any route, as higher doses significantly increase GI and renal toxicity without additional benefit 1

High-Risk Situations Requiring Extreme Caution

• History of peptic ulcer disease 1
• Age >60 years 1
• Concomitant anticoagulant use (increases bleeding risk 3-6 fold) 1
• Pre-existing cardiovascular disease 1, 3
• Renal impairment (avoid if creatinine clearance <10 mL/min) 1

Monitoring Requirements for Chronic Use

• Baseline and every 3 months: blood pressure, BUN, creatinine, liver function tests, CBC, fecal occult blood 1
• Discontinue if BUN or creatinine doubles 1
• Discontinue if liver function tests increase to 3× upper limit of normal 1

Common Pitfalls to Avoid

Dosing Errors

• Never combine multiple formulations without accounting for total daily dose 1
• Do not exceed 150 mg/day regardless of route or indication 1, 2
• Avoid IV administration errors: Many serious adverse effects are attributed to large IV overdoses due to dilution errors 1

Drug Interactions

• Anticoagulants: Concomitant use increases INR up to 15% and triples bleeding risk—requires close monitoring 1
• Lithium, digoxin, methotrexate, cyclosporin: Significant interactions documented 7
• Aspirin: Reduces diclofenac efficacy 7

Treatment Duration

• Short-term use preferred: Use lowest effective dose for shortest duration 8
• If two NSAIDs fail sequentially: Switch to alternative analgesic approach (opioids, nerve blocks) rather than trying additional NSAIDs 1

Pharmacokinetic Considerations

• Rapid absorption: Peak plasma concentrations occur 1.5-2 hours after oral ingestion 2, 7
• Short half-life: 1.5 hours in plasma, but persists longer in synovial fluid 2, 7
• Extensive protein binding: Binds to plasma albumin 7
• No dose adjustment needed: For elderly, children, or mild-to-moderate renal/hepatic impairment 3, 7