Diclofenac – Uses, Dosage & Side Effects

What is Diclofenac?

Diclofenac is a widely used nonsteroidal anti-inflammatory drug (NSAID) that provides pain relief, reduces inflammation, and lowers fever. It is available both by prescription and over the counter, depending on the dosage and formulation. Common forms include tablets, capsules, gel, patches, suppositories, and injectable solutions, making it one of the most versatile and frequently prescribed analgesics worldwide.

Indications (Uses)

Diclofenac is used to treat a broad range of conditions:

• Joint diseases such as osteoarthritis and rheumatoid arthritis
• Acute musculoskeletal pain, including sports injuries and post-surgical pain
• Back pain and spinal disorders
• Menstrual pain (dysmenorrhea)
• Migraine and tension headaches
• Dental pain and post-procedural discomfort
• Inflammatory conditions such as tendinitis and bursitis

Mechanism of Action

Diclofenac works by inhibiting the enzyme cyclooxygenase (COX), which exists in two isoforms: COX-1 and COX-2. Both isoforms are responsible for producing prostaglandins – signaling molecules that promote pain, inflammation, and fever. By blocking prostaglandin synthesis, diclofenac reduces pain signals, suppresses inflammatory responses, and lowers elevated body temperature.

Compared to other NSAIDs, diclofenac shows a slight preference for inhibiting COX-2, which is more directly involved in inflammation. However, COX-1 inhibition also occurs, which can affect the protective lining of the stomach and platelet function, contributing to some of its known side effects.

Dosage and Administration

Dosage varies depending on the form of diclofenac and the condition being treated:

• Oral (tablets/capsules): Typical daily dose of 75–150 mg, divided into 2–3 doses
• Topical (gel/patch): Applied directly to the affected area several times daily – significantly lower systemic absorption
• Injection: Administered under medical supervision, typically 75 mg once daily
• Treatment duration should be kept as short as possible – ideally no more than 7–10 days without medical guidance

Side Effects

Like all NSAIDs, diclofenac can cause side effects, particularly with prolonged or high-dose use:

Common Side Effects

• Stomach upset, nausea, and vomiting
• Diarrhea or constipation
• Headache and dizziness

Rare but Serious Side Effects

• Gastric ulcers and gastrointestinal bleeding
• Increased risk of heart attack and stroke with long-term use
• Kidney damage (nephrotoxicity), especially in patients with pre-existing kidney disease
• Elevated liver enzymes or liver damage
• Allergic reactions, including skin reactions in rare cases

Contraindications

Diclofenac should not be used in patients with:

• Known hypersensitivity to diclofenac or other NSAIDs
• Active peptic ulcers or gastrointestinal bleeding
• Severe renal, hepatic, or cardiac impairment
• The third trimester of pregnancy
• Concurrent use of anticoagulants (e.g., warfarin) without medical supervision

Drug Interactions

Diclofenac may interact with several other medications:

• Anticoagulants (e.g., warfarin, heparin): increased risk of bleeding
• Other NSAIDs or corticosteroids: increased risk of gastrointestinal irritation
• ACE inhibitors and diuretics: reduced antihypertensive efficacy
• Lithium and methotrexate: elevated plasma levels and increased risk of toxicity

Additional Notes

Patients with known cardiovascular conditions should consult a physician before using diclofenac. Topical formulations such as gels and patches are preferred for localized pain, as they significantly reduce systemic exposure and the associated risk of side effects. In many countries, low-dose diclofenac products (e.g., 25 mg tablets, topical gel) are available without a prescription, while higher doses require a doctor's authorization.

References

1. European Medicines Agency (EMA): Diclofenac-containing medicines – Assessment report, 2013. Available at: www.ema.europa.eu
2. Brunton L, Hilal-Dandan R, Knollmann B. Goodman & Gilman's The Pharmacological Basis of Therapeutics. 13th edition. McGraw-Hill Education, 2018.
3. National Institute for Health and Care Excellence (NICE): Non-steroidal anti-inflammatory drugs. NICE Evidence Review, 2021. Available at: www.nice.org.uk