1. Clinical Overview
Diclofenac (1% w/w) is a topical non-steroidal anti-inflammatory drug (NSAID) widely used in India for the symptomatic relief of localized pain and inflammation. It is a first-line topical therapy for musculoskeletal conditions, offering the advantage of targeted delivery with minimal systemic absorption, thereby reducing the risk of gastrointestinal and cardiovascular adverse events associated with oral NSAIDs. It is a prescription medication in India, available in various gel, spray, and solution formulations.
| Onset | Duration | Bioavailability |
|---|---|---|
| Within 1-2 hours for analgesic effect; anti-inflammatory effect may take several days of regular application. | Approximately 8-12 hours per application. | Topical bioavailability is low, typically < 10% of the applied dose is systemically absorbed. Systemic bioavailability is approximately 6%. |
2. Mechanism of Action
Diclofenac exerts its anti-inflammatory, analgesic, and antipyretic effects primarily through the non-selective, reversible inhibition of the enzyme cyclooxygenase (COX), with a slight preference for COX-2 over COX-1. This inhibition blocks the conversion of arachidonic acid to prostaglandin G2 (PGG2) and subsequently to prostaglandin H2 (PGH2), the precursors of prostanoids including prostaglandins (PGs), prostacyclin, and thromboxanes. The reduction in prostaglandin synthesis, particularly PGE2 and PGI2, at the site of inflammation mediates its therapeutic effects.
3. Indications & Uses
- Symptomatic relief of pain and inflammation in osteoarthritis of superficial joints (e.g., knees, hands)
- Acute musculoskeletal pain (e.g., sprains, strains, sports injuries)
- Localized soft tissue rheumatism (e.g., tendinitis, tenosynovitis, bursitis)
4. Dosage & Administration
Adult Dosage: Apply a thin layer (2-4 grams of gel, approximately the size of a 1-2 rupee coin) to the affected area 3 to 4 times daily. Gently rub in. Do not apply more than 16 grams per day to any single joint (e.g., knee) or 32 grams total per day.
Administration: 1. Wash and dry hands and the affected area before application. 2. Apply a thin layer and gently rub into the skin until absorbed. 3. Do not apply with occlusive dressings unless directed by a physician. 4. Wash hands thoroughly after application unless the hands are the treated area. 5. Avoid contact with eyes, mucous membranes, and broken skin. 6. Do not use with heating pads or hot packs. 7. Allow the gel to dry before covering with clothing.
5. Side Effects
Common side effects may include:
- Application site reactions: pruritus (itching), dryness, erythema (redness), rash, burning sensation, paresthesia (tingling).
- Gastrointestinal: dyspepsia, nausea (more common with large surface area application).
6. Drug Interactions
| Drug | Effect | Severity |
|---|---|---|
| Anticoagulants (Warfarin, Acenocoumarol) | Increased risk of bleeding due to antiplatelet effect and potential displacement from protein binding sites. | Major |
| Anti-platelets (Aspirin, Clopidogrel) | Additive risk of GI bleeding and reduced antiplatelet efficacy of low-dose aspirin. | Major |
| ACE Inhibitors (Ramipril, Enalapril) / ARBs (Losartan) | Reduced antihypertensive efficacy; increased risk of renal impairment, especially in volume-depleted patients. | Moderate |
| Diuretics (Furosemide, Hydrochlorothiazide) | Reduced diuretic and antihypertensive efficacy; risk of nephrotoxicity. | Moderate |
| Lithium | Decreased renal clearance of lithium, leading to increased serum lithium levels and potential toxicity. | Major |
| Methotrexate | Decreased renal clearance of methotrexate, increasing the risk of methotrexate toxicity (myelosuppression). | Major |
| Cyclosporine, Tacrolimus | Increased risk of nephrotoxicity. | Moderate |
| Other NSAIDs (Oral or Topical) | Increased risk of adverse effects (GI, renal, CV) without additive benefit. | Major |
| SSRIs / SNRIs (Fluoxetine, Venlafaxine) | Increased risk of upper GI bleeding. | Moderate |
| Corticosteroids (Oral) | Increased risk of GI ulceration or bleeding. | Moderate |
7. Patient Counselling
- DO apply only to intact skin over the painful/affected area.
- DO wash hands before and after application (unless hands are being treated).
- DO use the smallest amount needed to cover the area with a thin film.
- DO NOT apply to open wounds, cuts, infections, rashes, or eczema.
- DO NOT use with occlusive dressings, bandages, or heating pads unless advised by your doctor.
- DO NOT allow the gel to come into contact with eyes, nose, mouth, or other mucous membranes. If contact occurs, rinse thoroughly with water.
- DO NOT use other NSAID-containing products (oral or topical) concurrently without consulting your doctor.
- DO NOT use for pain for more than 7-10 days without consulting your doctor.
8. Toxicology & Storage
Overdose: Topical overdose is unlikely to cause systemic toxicity due to limited absorption. However, excessive application over large areas could lead to symptoms similar to oral overdose: nausea, vomiting, epigastric pain, GI bleeding, headache, dizziness, drowsiness, tinnitus, apnea, metabolic acidosis, coma, convulsions, acute renal failure, and hepatotoxicity.
Storage: Store at room temperature (15°C to 30°C). Protect from light and moisture. Do not freeze. Keep the tube tightly closed. Keep out of reach and sight of children. Do not use after the expiry date printed on the pack.