Diclofenac is a prototypical non-steroidal anti-inflammatory drug (NSAID) of the phenylacetic acid class. It is a potent inhibitor of cyclooxygenase (COX) enzymes, particularly COX-2, leading to reduced synthesis of prostaglandins, which are key mediators of pain, inflammation, and fever. The 75mg strength is primarily formulated for sustained release or as a twice-daily dose for moderate to severe pain and inflammatory conditions. It is one of the most widely prescribed and consumed NSAIDs in India due to its efficacy and cost-effectiveness.
Adult: For chronic conditions (RA, OA): 75mg to 150mg per day in 2 or 3 divided doses. The 75mg SR tablet is typically given twice daily. For acute pain/dysmenorrhea: 50mg TDS or 75mg BD initially, then reduce to lowest effective dose.
Note: Take with or immediately after food or a full glass of milk/water to minimize gastric irritation. Swallow the sustained-release tablet whole; do not crush, chew, or break. Can be taken with antacids (but may reduce absorption). Maintain adequate fluid intake.
Diclofenac exerts its therapeutic effects primarily by inhibiting the enzyme cyclooxygenase (COX), which exists in two main isoforms: COX-1 (constitutive, involved in gastric cytoprotection and platelet function) and COX-2 (inducible, upregulated at sites of inflammation). Diclofenac is a non-selective COX inhibitor but shows a relative preference for inhibiting COX-2 over COX-1. This inhibition blocks the conversion of arachidonic acid to prostaglandin G2 and subsequently to prostaglandin H2, the precursor for various prostaglandins (PGE2, PGI2) and thromboxane A2. The reduction in prostaglandin synthesis, particularly PGE2 at inflammatory sites, mediates its anti-inflammatory, analgesic, and antipyretic actions.
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, oligohydramnios, and inhibition of labor. Not recommended for use during labor.
Driving: May cause dizziness, vertigo, visual disturbances, or drowsiness in some patients. Patients should be cautioned about operating machinery or driving until they know how the drug affects them.
| Anticoagulants (Warfarin, Acenocoumarol) | Increased risk of bleeding due to antiplatelet effect and potential displacement from protein binding. | Major |
| Anti-platelets (Aspirin, Clopidogrel) | Additive risk of GI bleeding. | Major |
| Other NSAIDs (including selective COX-2 inhibitors) | Increased risk of GI and renal toxicity without added benefit. | Major |
| ACE Inhibitors (Ramipril, Enalapril), ARBs (Losartan) | Reduced antihypertensive effect; increased risk of renal impairment. | Moderate |
| Diuretics (Furosemide, Hydrochlorothiazide) | Reduced diuretic and antihypertensive efficacy; risk of renal failure. | Moderate |
| Lithium | Increased lithium levels and toxicity due to reduced renal clearance. | Major |
| Methotrexate | Increased methotrexate levels and toxicity (especially with high-dose MTX). | Major |
| Cyclosporine, Tacrolimus | Increased risk of nephrotoxicity. | Major |
| Oral Hypoglycemics (Glibenclamide) | Enhanced hypoglycemic effect; monitor blood glucose. | Moderate |
| Quinolone Antibiotics (Ciprofloxacin) | Increased risk of CNS stimulation and seizures. | Moderate |
| SSRIs (Fluoxetine, Sertraline) | Increased risk of upper GI bleeding. | Moderate |
| Corticosteroids (Prednisolone) | Markedly increased risk of GI ulceration and bleeding. | Major |