Diclofenac is a prototypical non-steroidal anti-inflammatory drug (NSAID) of the phenylacetic acid class, widely used in the Indian market for its potent analgesic, anti-inflammatory, and antipyretic properties. It is a non-selective inhibitor of cyclooxygenase (COX) enzymes, with a preferential inhibition of COX-2. It is extensively used for acute and chronic pain management, particularly in musculoskeletal and arthritic conditions. The 'NA' designation typically refers to the Sodium salt, which is the most common and rapidly absorbed form.
Adult: Oral (Sodium/Potassium salt): 75-150 mg per day in 2-3 divided doses. Sustained/Extended Release: 100 mg once daily. Topical Gel (1%): Apply 2-4 g to affected area 3-4 times daily. IM Injection: 75 mg once or twice daily (short-term use).
Note: Take oral tablets with or after food to reduce GI upset. Swallow SR/ER tablets whole, do not crush or chew. For topical gel, apply to clean, intact skin; wash hands after application; do not apply to wounds, infected skin, or under occlusive dressings unless directed. IM injection should be given deep into gluteal muscle.
Diclofenac exerts its therapeutic effects primarily by inhibiting the enzyme prostaglandin-endoperoxide synthase, commonly known as cyclooxygenase (COX). COX exists in two isoforms: COX-1 (constitutive, involved in gastric cytoprotection and platelet function) and COX-2 (inducible, involved in inflammation, pain, and fever). Diclofenac is a non-selective NSAID but shows a relative preference for inhibiting COX-2 over COX-1. By inhibiting COX, it blocks the conversion of arachidonic acid to prostaglandin G2 and subsequently to prostaglandin H2, the precursor for various prostanoids (PGE2, PGI2, thromboxane A2). The reduction in prostaglandin E2 (PGE2) at the site of injury leads to decreased vasodilation, edema, and sensitization of pain receptors.
Pregnancy: Category C (first and second trimester): Use only if potential benefit justifies potential risk to fetus. Avoid in third trimester (Category D) due to risk of premature closure of ductus arteriosus, delayed labor, and potential renal dysfunction in neonate.
Driving: May cause dizziness, vertigo, fatigue, or visual disturbances. Patients should be cautioned about operating machinery or driving if affected.
| Aspirin, other NSAIDs | Increased risk of GI ulceration and bleeding; pharmacodynamic antagonism. | Major |
| Anticoagulants (Warfarin, Acenocoumarol) | Increased risk of bleeding due to antiplatelet effect and displacement from protein binding. | Major |
| Anti-platelets (Clopidogrel, Aspirin) | Additive risk of bleeding. | Major |
| ACE Inhibitors (Ramipril, Enalapril), ARBs (Losartan) | Reduced antihypertensive effect; increased risk of renal impairment. | Moderate |
| Diuretics (Furosemide, Hydrochlorothiazide) | Reduced diuretic and antihypertensive efficacy; increased nephrotoxicity risk. | Moderate |
| Lithium | Increased serum lithium levels and toxicity risk due to reduced renal clearance. | Major |
| Methotrexate | Increased methotrexate levels and toxicity risk (especially with high-dose MTX). | Major |
| Cyclosporine, Tacrolimus | Increased risk of nephrotoxicity. | Major |
| Corticosteroids (Prednisolone) | Markedly increased risk of GI ulceration and bleeding. | Major |
| SSRIs (Fluoxetine, Sertraline) | Increased risk of upper GI bleeding. | Moderate |
| Antidiabetics (Glibenclamide, Metformin) | May potentiate hypoglycemic effect; monitor blood glucose. | Moderate |
| Quinolone Antibiotics (Ciprofloxacin) | Increased risk of CNS stimulation and seizures. | Moderate |
Same composition (Diclofenac (NA)), different brands: