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Sunday, July 27, 2025

Diclofenac


Diclofenac is a non-steroidal anti-inflammatory drug (NSAID) that exhibits analgesic, anti-inflammatory, and antipyretic properties. It is widely prescribed across the globe for the symptomatic treatment of pain and inflammation associated with musculoskeletal, rheumatic, and post-operative conditions. Diclofenac is available in numerous formulations including oral tablets, topical gels, eye drops, suppositories, and parenteral injections, allowing for broad clinical versatility. Despite its efficacy, it is associated with significant gastrointestinal, cardiovascular, and renal risks, especially when used long-term or in high doses.

Pharmacological Classification

  • Therapeutic Class: Analgesic, Anti-inflammatory

  • Pharmacological Class: Non-steroidal anti-inflammatory drug (NSAID)

  • ATC Code: M01AB05

  • Chemical Class: Phenylacetic acid derivative

  • Legal Status: Prescription-only medicine (Rx) in many countries, OTC in low doses and topical forms in some jurisdictions

Mechanism of Action

Diclofenac works primarily by inhibiting cyclooxygenase (COX) enzymes—both COX-1 and COX-2—which are involved in the biosynthesis of prostaglandins, key mediators of pain, inflammation, and fever.

  • Inhibition of COX-2 leads to reduced inflammation and pain.

  • Inhibition of COX-1, while contributing to efficacy, is associated with gastrointestinal side effects due to its role in protecting gastric mucosa and platelet function.

  • Diclofenac has higher selectivity for COX-2 than some other traditional NSAIDs (e.g., ibuprofen, naproxen), but less than selective COX-2 inhibitors like celecoxib.

Therapeutic Indications

Oral and Injectable Forms

  • Osteoarthritis

  • Rheumatoid arthritis

  • Ankylosing spondylitis

  • Acute musculoskeletal pain (e.g., sprains, strains, back pain)

  • Postoperative pain

  • Dysmenorrhea (painful periods)

  • Migraine attacks

  • Gout (acute flare)

  • Renal colic

Topical Forms (gel, patch, solution)

  • Local relief of pain and inflammation in:

    • Osteoarthritis of superficial joints (e.g., knees, fingers)

    • Soft tissue injuries (e.g., tendinitis, sprains, bruises)

Ophthalmic Formulations

  • Prevention and treatment of post-operative ocular inflammation (e.g., after cataract surgery)

  • Treatment of non-infectious conjunctivitis

Rectal Suppositories

  • Suitable for patients unable to take oral medication

  • Used in post-operative pain, migraine, or menstrual pain

Formulations and Dosages

  • Oral tablets (immediate or modified-release): 25 mg, 50 mg, 75 mg, 100 mg

  • Topical gel or cream: 1% or 2% (e.g., Voltaren Emulgel)

  • Ophthalmic drops: 0.1% diclofenac sodium

  • Rectal suppositories: 50 mg, 100 mg

  • Injectable (IM or IV): 75 mg/3 mL (e.g., Voltaren injection)

Oral Dosage (Adults)

  • Typical dose: 50–75 mg two or three times daily

  • Modified-release: 75–100 mg once or twice daily

  • Maximum daily dose: Typically 150 mg/day

Note: Use the lowest effective dose for the shortest duration necessary to minimize adverse effects.

Contraindications

  • Known hypersensitivity to diclofenac or other NSAIDs

  • History of gastrointestinal bleeding or perforation related to previous NSAID therapy

  • Active peptic ulcer disease

  • Severe hepatic or renal impairment

  • Congestive heart failure (NYHA II–IV)

  • Established ischemic heart disease, peripheral arterial disease, or cerebrovascular disease (for systemic forms)

  • Pregnancy (especially third trimester)

  • Children under certain age thresholds (depending on formulation)

Precautions and Warnings

  • Cardiovascular risk: Increased risk of serious CV events including MI, stroke, particularly at high doses and prolonged use

  • Gastrointestinal risk: May cause ulcers, bleeding, perforation; co-prescription of PPIs advised in high-risk patients

  • Renal impairment: May cause reversible renal function deterioration, especially in volume-depleted or elderly patients

  • Hepatotoxicity: Regular monitoring of liver function recommended during long-term therapy

  • Hematological effects: Rare cases of anemia, leukopenia, thrombocytopenia

  • Anaphylaxis and bronchospasm: Especially in NSAID-sensitive asthma patients

  • Skin reactions: Rare but serious conditions such as Stevens-Johnson syndrome, toxic epidermal necrolysis

Adverse Effects

Common (1–10%)

  • Dyspepsia

  • Nausea

  • Abdominal pain

  • Headache

  • Dizziness

  • Elevated liver enzymes

  • Rash

  • Fluid retention or peripheral edema

Uncommon to Rare (<1%)

  • GI ulcers or bleeding

  • Hypertension

  • Myocardial infarction

  • Stroke

  • Renal impairment

  • Tinnitus

  • Photosensitivity reactions

  • Asthma exacerbation

Drug Interactions

Increased Risk of GI Bleeding

  • Anticoagulants (e.g., warfarin)

  • Antiplatelets (e.g., clopidogrel, aspirin)

  • SSRIs (e.g., sertraline, fluoxetine)

  • Corticosteroids (e.g., prednisolone)

Increased Risk of Renal Toxicity

  • ACE inhibitors and ARBs (e.g., ramipril, losartan)

  • Diuretics (e.g., furosemide, thiazides)

  • Cyclosporine

Reduced Antihypertensive Effect

  • Beta-blockers

  • ACE inhibitors

  • Diuretics

Methotrexate

  • Diclofenac may reduce renal clearance of methotrexate, increasing toxicity

Lithium and Digoxin

  • Diclofenac may elevate serum levels of both

CYP Interactions

  • Diclofenac is metabolized by CYP2C9; caution with inhibitors (e.g., fluconazole) or inducers (e.g., rifampin)

Use in Special Populations

Pregnancy

  • Contraindicated during third trimester: Risk of premature closure of ductus arteriosus, delayed labour, fetal renal toxicity

  • Use in first and second trimesters only if absolutely necessary

Lactation

  • Present in breast milk in small amounts

  • Short-term use of low doses considered compatible with breastfeeding, but avoid prolonged use

Pediatrics

  • Oral and topical forms available for age-specific use (consult national guidelines)

  • Avoid injectable forms in children unless clearly indicated

Elderly

  • Higher risk of adverse effects

  • Use with caution; consider renal function, comorbidities, and concurrent medications

Comparison With Other NSAIDs (No Tables)

Diclofenac vs. Ibuprofen

  • Diclofenac has stronger anti-inflammatory effects, making it preferred for arthritis

  • Ibuprofen has lower cardiovascular risk, safer for long-term use

  • Both carry GI risks, mitigated by co-prescription with a PPI

Diclofenac vs. Naproxen

  • Naproxen has longer half-life, allowing for twice-daily dosing

  • Naproxen associated with lower CV risk, but higher GI risk

  • Diclofenac better tolerated topically and offers faster pain relief in acute conditions

Diclofenac vs. Celecoxib (COX-2 inhibitor)

  • Celecoxib has lower GI risk, but similar CV risks

  • Diclofenac is cheaper and more widely available

  • Celecoxib may be safer in patients with GI history if CV risk is low

Patient Counseling Points

  • Take with or after food to reduce stomach upset

  • Avoid alcohol and report any signs of GI bleeding (e.g., black stools, vomiting blood)

  • Do not take other NSAIDs concurrently (e.g., ibuprofen, naproxen)

  • Report symptoms like shortness of breath, chest pain, vision changes, or unusual fatigue

  • Apply topical forms only on intact skin, and avoid exposure to sunlight or UV light

  • For gel/cream: Wash hands after application unless treating the hands themselves

  • For eye drops: Use strictly as directed and avoid contamination of the dropper

  • Store all forms at room temperature and keep out of reach of children




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