The yellow, oblong tablet debossed with SG and a score line on one side and 436 on the reverse is an oral prescription nonsteroidal anti-inflammatory drug (NSAID) containing Naproxen (500 mg).
(Note: Another pill bearing this numerical imprint is a white, round tablet with 436 inside a raised hexagon, which contains Allopurinol 300 mg. Below is the detailed clinical profile for the Naproxen 500 mg (SG 436) formulation).
Pill Identification
Attribute – Specification
- Active Ingredient – Naproxen, USP (500 mg)
- Imprint – SG with a score line on one side; 436 on the reverse
- Color & Shape – Light yellow, oblong / capsule-shaped / rectangular
- Manufacturer – ScieGen Pharmaceuticals, Inc.
- Drug Class – Nonsteroidal Anti-inflammatory Drug (NSAID) / Propionic acid derivative
- Prescription Status – Rx-only (high-strength prescription form)
Mechanism of Action
Naproxen is a non-selective inhibitor of the cyclooxygenase enzyme system:
- COX-1 and COX-2 Inhibition: Naproxen reversibly inhibits both cyclooxygenase-1 and cyclooxygenase-2 isoenzymes.
- Blockade of Prostaglandin Synthesis: By blocking COX enzymes, naproxen prevents the conversion of arachidonic acid into pro-inflammatory prostaglandins, prostacyclin, and thromboxane.
- Analgesic, Anti-inflammatory, and Antipyretic Action: Decreased peripheral prostaglandin synthesis lowers the sensitivity of nociceptors to mechanical and chemical stimuli, mitigates localized tissue swelling/edema, and modulates hypothalamic temperature regulation to reduce fever.
Indications and Clinical Uses
- Arthritic Conditions: Relief of signs and symptoms of osteoarthritis, rheumatoid arthritis, ankylosing spondylitis, and polyarticular juvenile idiopathic arthritis.
- Acute Musculoskeletal Disorders: Management of acute tendonitis, bursitis, sprains, and strains.
- Acute Gouty Arthritis: Rapid reduction of pain and joint inflammation during acute gout flares.
- Mild to Moderate Pain & Primary Dysmenorrhea: Treatment of acute pain episodes and menstrual cramps.
Dosage and Administration
- Dosing should always be titrated to the lowest effective dose for the shortest possible duration to minimize cardiovascular and gastrointestinal risks. Take with food, milk, or an antacid to reduce stomach upset.
- Osteoarthritis, Rheumatoid Arthritis, Ankylosing Spondylitis:
- Standard Adult Dosing: 250 mg to 500 mg orally twice daily (morning and evening).
- Severe Flares: May be increased up to 1,500 mg per day for limited periods under physician supervision.
- Acute Gout:
- Starting Dose: 750 mg initially, followed by 250 mg every 8 hours until the acute attack resolves.
- Analgesia, Dysmenorrhea, Tendonitis/Bursitis:
- Starting Dose: 500 mg initially, followed by 250 mg every 6 to 8 hours as needed.
- Maximum Daily Dose: Total daily dose should not exceed 1,250 mg on the first day or 1,000 mg on subsequent days.
- Renal Impairment: Not recommended in patients with baseline severe renal impairment due to the risk of accelerating renal failure.
Side Effects
Common Adverse Reactions:
- Gastrointestinal: Dyspepsia (heartburn), nausea, epigastric abdominal pain, constipation, bloating, diarrhea
- Central Nervous System: Headache, dizziness, lightheadedness, drowsiness
- Dermatologic / Otic: Tinnitus (ringing in ears), peripheral edema, mild rash, pruritus, ecchymosis (easy bruising)
Serious Adverse Reactions:
- Gastrointestinal ulceration, perforation, and massive bleeding (can occur without warning)
- Myocardial infarction, stroke, or severe worsening of hypertension
- Acute kidney injury, interstitial nephritis, and renal papillary necrosis
- Drug-Induced Liver Injury (DILI) with elevated aminotransferases
- Severe cutaneous adverse reactions (Stevens-Johnson syndrome [SJS], Toxic Epidermal Necrolysis [TEN])
- Severe anaphylactoid reactions (bronchospasm, angioedema)
Key Drug Interactions
- Anticoagulants & Antiplatelets (e.g., Warfarin, Apixaban, Clopidogrel, Aspirin): Synergistically increases the risk of major upper and lower gastrointestinal bleeding.
- ACE Inhibitors, ARBs, and Diuretics: NSAIDs diminish the antihypertensive effect of these agents and substantially increase the risk of acute renal failure when taken together (the “triple whammy” effect with diuretics and renin-angiotensin blockers).
- Lithium & Methotrexate: Naproxen decreases the renal clearance of lithium and methotrexate, leading to elevated serum concentrations and severe toxicity.
- Other NSAIDs / Corticosteroids: Concomitant use with oral steroids or other systemic NSAIDs dramatically multiplies the risk of severe gastric ulceration.
Boxed Warnings and Contraindications
- Cardiovascular Thrombotic Events NSAIDs cause an increased risk of serious and potentially fatal cardiovascular thrombotic events, including myocardial infarction and stroke. This risk may occur early in treatment and increases with higher doses and prolonged duration of use.
- Gastrointestinal Bleeding, Ulceration, and Perforation NSAIDs cause an increased risk of serious gastrointestinal adverse events including bleeding, ulceration, and perforation of the stomach or intestines, which can be fatal. Elderly patients and individuals with a prior history of peptic ulcer disease or GI bleeding face the greatest risk.
Contraindications & Pregnancy Restrictions:
- Coronary Artery Bypass Graft (CABG): Contraindicated for perioperative pain management in the setting of CABG surgery.
- Aspirin Triad / Hypersensitivity: Contraindicated in patients with a history of asthma, urticaria, or allergic-type reactions triggered by aspirin or other NSAIDs.
- Pregnancy (at 20 Weeks and Later): Avoid use at 20 weeks gestation or later due to the risk of fetal renal dysfunction causing oligohydramnios, and avoid entirely at 30 weeks or later due to premature closure of the fetal ductus arteriosus.