Diclofenac

Active Ingredient & Mechanism of Action

• Active Ingredient: Diclofenac (commonly formulated as Diclofenac Sodium or Diclofenac Potassium).
• Mechanism: Diclofenac acts primarily by non-selectively inhibiting the cyclooxygenase (COX) enzymes: COX-1 and COX-2:
  1. Inhibition of Prostaglandins: It blocks the synthesis of prostaglandins—chemical mediators that promote inflammation, swelling, fever, and pain signaling throughout body tissues.
  2. COX-2 Selectivity Ratio: Compared to many other traditional non-selective NSAIDs (like ibuprofen or naproxen), diclofenac has a relatively higher affinity for the COX-2 enzyme, contributing to its strong anti-inflammatory potency.

Dosage Forms & Available Formulations

• Oral Tablets & Capsules:
  • Diclofenac Potassium (e.g., Cataflam): Immediate-release formulations (25 mg, 50 mg) designed for rapid absorption and fast onset of acute pain relief.
  • Diclofenac Sodium (e.g., Voltaren): Enteric-coated, delayed-release, or extended-release formulations (50 mg, 75 mg, 100 mg) designed for continuous, steady management of chronic inflammatory joint diseases.
• Topical Formulations: Gels (e.g., Voltaren Emulgel 1% or 2.32%), patches, and solutions for localized joint and muscle pain.
• Rectal Suppositories: 50 mg and 100 mg suppositories for post-operative pain or severe acute pain when oral administration is not feasible.
• Intramuscular (IM) Injection / Intravenous (IV) Infusion: 75 mg / 3 mL ampoules used in hospital or acute care settings for renal colic, severe post-operative pain, or acute trauma.
• Ophthalmic Drops: 0.1% drops used post-cataract surgery to prevent inflammation.

Clinical Indications

• Arthritic Conditions: Symptomatic management of Osteoarthritis, Rheumatoid Arthritis, and Ankylosing Spondylitis.
• Acute Musculoskeletal Disorders: Strains, sprains, tendinitis, bursitis, low back pain, and sports injuries.
• Acute Pain Events: Renal colic (kidney stones), acute gout attacks, dysmenorrhea (severe period pain), dental pain, and post-surgical pain.

Key Pharmacokinetics

• Absorption: Well absorbed from the gastrointestinal tract. Diclofenac potassium dissolves faster in the stomach, yielding faster peak plasma levels ($\sim 30\text{ to }60\text{ minutes}$) compared to enteric-coated diclofenac sodium ($\sim 1.5\text{ to }2.5\text{ hours}$).
• First-Pass Metabolism: Undergoes extensive hepatic first-pass metabolism; only about 50% to 60% of an oral dose reaches systemic circulation unchanged.
• Distribution & Protein Binding: High plasma protein binding ($> 99\%$, primarily to albumin). Accumulates and persists in synovial fluid (joints) at higher concentrations than in blood plasma over extended periods.
• Elimination & Half-Life: Short plasma elimination half-life of 1 to 2 hours. Excreted primarily through the kidneys as glucuronide/sulfate conjugates in urine ($\sim 65\%$) and via bile/feces ($\sim 35\%$).

Administration Guidelines & Dosing Limits

• Taking with Food: Oral tablets should be taken with or after meals with a full glass of water to minimize gastric irritation. Enteric-coated sodium tablets should be swallowed whole (never crushed or chewed).
• Typical Adult Dosing:
  • Acute Pain / Primary Dysmenorrhea: 50 mg of diclofenac potassium 2 to 3 times daily.
  • Osteoarthritis / Rheumatoid Arthritis: 100 mg to 150 mg daily in divided doses (e.g., 50 mg 2 to 3 times daily or a single 100 mg extended-release tablet daily).
• Maximum Daily Dose Limit: 150 mg in 24 hours for adults.

Safety Profile & Critical Warnings

• Boxed Warnings (Black Box Warnings):
  1. Cardiovascular Risk: Like other NSAIDs, diclofenac carries an increased risk of serious cardiovascular thrombotic events, including myocardial infarction (heart attack) and stroke. Due to its higher COX-2 activity, diclofenac carries a higher relative cardiovascular risk than naproxen or low-dose ibuprofen.
  2. Gastrointestinal Risk: Elevated risk of severe GI adverse events, including stomach ulcers, gastrointestinal bleeding, and intestinal perforation, which can be fatal and may occur without warning symptoms.
• Hepatic Safety: Can cause elevations in liver transaminase enzymes (ALT/AST). Periodic liver function monitoring is required during prolonged, high-dose therapy.
• Renal Risk: Can impair renal blood flow, causing fluid retention, worsening hypertension, and acute kidney injury—especially in dehydrated patients or those with pre-existing renal disease.
• Pregnancy Warning: Strictly contraindicated from 20 weeks of pregnancy onward (can cause premature closure of the fetal ductus arteriosus, neonatal pulmonary hypertension, and oligohydramnios).
• Key Drug Interactions:
  • Anticoagulants (e.g., Warfarin, DOACs, Aspirin): Greatly elevates gastrointestinal and systemic bleeding risks.
  • Antihypertensives (ACE Inhibitors, ARBs, Beta-Blockers, Diuretics): Diminishes their blood-pressure-lowering effectiveness and increases kidney toxicity risks.
  • Lithium & Methotrexate: Inhibits renal clearance of these drugs, increasing the risk of toxic drug accumulation.
  • Other NSAIDs / Corticosteroids: Concurrent use increases gastrointestinal ulceration risk without therapeutic benefit.

Note: Diclofenac is a prescription and pharmacy-regulated medication depending on formulation and regional regulations. Dosage schedules, duration of use, and individual cardiovascular, hepatic, or renal risk factors must be thoroughly evaluated by a qualified healthcare professional.