Head-to-head clinical analysis & difference comparison: details on mechanism of action, dosing, half-life, interactions, and maternal-fetal safety.
PHENYLBUTAZONE vs 8-HOUR BAYER
Clinician-reviewed, head-to-head comparison of mechanism, dosing, pharmacokinetics, and safety profiles.
Last clinically reviewed: July 2026 · OpiCalc Medical Review Team
Phenylbutazone is a nonsteroidal anti-inflammatory drug (NSAID) that inhibits cyclooxygenase (COX) enzymes, reducing prostaglandin synthesis, thereby causing anti-inflammatory, analgesic, and antipyretic effects. It also inhibits leukocyte migration and lysosomal enzyme release.
Irreversibly acetylates cyclooxygenase-1 (COX-1) and cyclooxygenase-2 (COX-2), inhibiting prostaglandin and thromboxane A2 synthesis, leading to analgesic, antipyretic, anti-inflammatory, and antiplatelet effects.
Relief of pain and inflammation in ankylosing spondylitis,Acute gouty arthritis,Osteoarthritis,Rheumatoid arthritis (short-term management),Off-label: Use in veterinary medicine for musculoskeletal disorders
Relief of pain, fever, and inflammation,Reduction of risk of myocardial infarction in patients with previous MI or unstable angina,Prevention of recurrent ischemic stroke or transient ischemic attack
Oral: 100-200 mg three times daily with food; maximum 600 mg/day. For acute gout: initial 400 mg followed by 200 mg every 4-6 hours for 1-2 days, then reduce.
325-650 mg every 8 hours for pain/fever; 81-325 mg daily for cardiovascular prophylaxis.
Terminal elimination half-life is 50–65 hours, but exhibits dose-dependent kinetics; can extend to 72–100 hours with repeated dosing or in elderly.
15-20 hours (terminal elimination half-life) for salicylate at therapeutic concentrations; prolonged to 20-30 hours at high doses due to saturation of hepatic metabolism (zero-order kinetics).
Hepatic metabolism via CYP2C9 and CYP3A4; major metabolite is oxyphenbutazone; minor pathways include hydroxylation and glucuronidation.
Hepatic hydrolysis by esterases to salicylic acid, which is primarily conjugated in the liver via glucuronidation and glycine conjugation (salicyluric acid), with minor oxidation by cytochrome P450 (CYP2C9) to gentisic acid.
Primarily hepatic metabolism; renal excretion of metabolites (<1% unchanged). Biliary/fecal excretion accounts for ~20% of total elimination.
Renal excretion of conjugated salicylate metabolites (75% as salicyluric acid, 10% as salicyl phenolic glucuronide, 5% as salicyl acyl glucuronide, 5% as gentisic acid); 10% free salicylate; approximately 10% eliminated in feces via bile.
98–99% bound, primarily to albumin.
80-90% bound to albumin; binding is concentration-dependent and saturable.
0.05–0.1 L/kg, indicating limited extravascular distribution; increased in hypoalbuminemia.
0.15-0.2 L/kg for salicylate; distributes into synovial fluid, CNS, and placental tissues; Vd increases in acidosis.
Oral: 100% absorbed, though systemic availability may be reduced by first-pass metabolism (bioavailability ~90%). Intramuscular: near 100%.
Oral: Approximately 100% for immediate-release, but extended-release may have slightly reduced absorption (relative bioavailability 85-90% compared to immediate-release).
GFR 10-50: use 50% of normal dose. GFR <10: contraindicated due to accumulation of active metabolite oxyphenbutazone.
Avoid in severe renal impairment (Cr Cl <30 m L/min). Use with caution and monitor for bleeding in moderate impairment. Reduce dose or extend interval.
Child-Pugh A: no adjustment. Child-Pugh B: reduce dose by 50%. Child-Pugh C: contraindicated due to risk of hepatotoxicity.
Avoid in severe hepatic impairment. Use with caution in moderate impairment; monitor liver function.
Not recommended in children under 14 years due to risk of Reye-like syndrome and hypersensitivity; safety and efficacy not established.
Not recommended in children <12 years for viral infections due to Reye's syndrome risk (contraindicated).
Initiate at lowest effective dose (100 mg once or twice daily); monitor closely for fluid retention, GI bleeding, and renal impairment; avoid long-term use.
Increased risk of GI bleeding and renal impairment; use lowest effective dose, monitor renal function and signs of bleeding.
WARNING: Aplastic anemia, agranulocytosis, and other blood dyscrasias have been associated with phenylbutazone. Use only when other NSAIDs have failed due to serious adverse effects. Monitor blood counts regularly. Risk is dose-related and increased with prolonged use.
None
Risk of bone marrow suppression (aplastic anemia, agranulocytosis); gastrointestinal ulceration and bleeding; renal toxicity (especially in elderly, dehydrated, or those with pre-existing renal impairment); hepatic dysfunction; hypersensitivity reactions; sodium and water retention; increased cardiovascular risk; use lowest effective dose for shortest duration.
Increased risk of gastrointestinal bleeding and ulceration; Reye syndrome in children with viral illness; Hemorrhagic stroke risk with high doses; Impaired renal function in predisposed patients; Bronchospasm in aspirin-sensitive asthma; Anaphylactic reactions; Use caution in patients with hepatic impairment or G6PD deficiency.
Hypersensitivity to phenylbutazone or other NSAIDs; history of aplastic anemia or agranulocytosis; active peptic ulcer disease; severe renal or hepatic impairment; advanced age; concomitant use with other NSAIDs or anticoagulants; pregnancy (third trimester) and lactation.
Known hypersensitivity to NSAIDs or aspirin; Active peptic ulcer disease or GI bleeding; Severe renal impairment (e GFR <30 m L/min); Hemorrhagic diathesis; Children with viral infection (Reye syndrome); Third trimester of pregnancy; Severe hepatic impairment.
Avoid taking with alcohol as it may increase the risk of gastrointestinal bleeding and hepatotoxicity. Grapefruit juice may increase drug levels and toxicity; avoid concurrent consumption. High-fat meals can delay but do not significantly reduce absorption; take with food or milk to minimize gastrointestinal irritation. Maintain adequate hydration unless contraindicated due to fluid retention concerns.
Avoid alcohol; may increase risk of gastrointestinal bleeding. No specific food restrictions, but taking with food can reduce gastric irritation. Avoid high-dose vitamin C supplements as they may increase salicylate levels.
First trimester: Increased risk of cardiovascular malformations and neural tube defects due to inhibition of prostaglandin synthesis. Second and third trimesters: Risk of premature closure of ductus arteriosus, oligohydramnios, and neonatal renal impairment. Avoid in all trimesters unless absolutely necessary.
First trimester: No well-controlled studies. Avoid use unless clearly needed. Second and third trimesters: Aspirin should be avoided due to risk of premature closure of ductus arteriosus, oligohydramnios, and increased risk of maternal and fetal bleeding. High doses may cause constriction of ductus arteriosus in utero and persistent pulmonary hypertension in newborn.
Excreted into breast milk in low concentrations. M/P ratio is approximately 0.1–0.2. Potential for adverse effects in the infant, including platelet dysfunction and renal impairment. Avoid breastfeeding during therapy.
Small amounts of aspirin are excreted in breast milk. M/P ratio not established. Use with caution in breastfeeding women; avoid high doses due to risk of Reye's syndrome in infants and potential for adverse effects on platelet function.
Increased renal clearance and volume of distribution in pregnancy may reduce serum drug levels. However, due to significant teratogenic and fetal risks, use is contraindicated in pregnancy. No dosing adjustment justified.
Pregnancy increases clearance of aspirin; however, dose adjustments are not routinely recommended due to narrow therapeutic index. Use lowest effective dose for shortest duration. Avoid in third trimester.
Phenylbutazone is a nonsteroidal anti-inflammatory drug (NSAID) with potent anti-inflammatory, antipyretic, and analgesic effects, but its use is severely limited due to high risk of serious adverse effects including agranulocytosis, aplastic anemia, and hepatotoxicity. It is reserved for short-term treatment of severe conditions such as ankylosing spondylitis, acute gouty arthritis, and acute exacerbations of rheumatoid arthritis when other therapies are ineffective or contraindicated. Due to its long half-life (50-100 hours), dosing should be carefully adjusted, and complete blood counts (CBC) and liver function tests must be monitored regularly. It inhibits prostaglandin synthesis and can cause sodium and water retention, exacerbating hypertension and heart failure. Avoid concomitant use with other NSAIDs, anticoagulants, or methotrexate due to increased bleeding risk and toxicity.
8-Hour Bayer is enteric-coated aspirin designed for extended release, reducing gastrointestinal irritation. Onset of action is delayed; not suitable for acute pain or rapid antiplatelet effect. Use with caution in patients with history of peptic ulcer disease or on anticoagulants. Monitor renal function in elderly or dehydrated patients. Avoid in children with viral illness due to Reye's syndrome risk.
Take this medication exactly as prescribed; do not exceed the recommended dose or duration of therapy due to risk of serious side effects.,Report any signs of infection (fever, sore throat, mouth ulcers), unusual bleeding or bruising, skin rash, or jaundice immediately.,Avoid alcohol and aspirin-containing products while taking this drug.,This medication may cause dizziness or drowsiness; avoid driving or operating heavy machinery until you know how it affects you.,Use effective contraception if you are of childbearing age; this drug may be harmful to an unborn baby and should not be used in late pregnancy.,Do not take this drug with other NSAIDs (e.g., ibuprofen, naproxen) or corticosteroids without consulting your doctor.
Take with a full glass of water; do not crush or chew the tablet.,Do not use within 7 days before surgery due to bleeding risk.,If used for pain, consult a doctor if symptoms persist for more than 10 days.,Avoid alcohol while taking this medication to reduce stomach bleeding risk.,Seek medical attention for signs of bleeding (black stools, blood in vomit).
"The combination of fenoprofen, a nonsteroidal anti-inflammatory drug (NSAID), with phenylbutazone, another NSAID with potent anti-inflammatory effects, significantly increases the risk of gastrointestinal (GI) adverse effects, including ulceration, bleeding, and perforation. This additive toxicity arises from synergistic inhibition of cyclooxygenase (COX) enzymes, leading to reduced gastroprotective prostaglandin synthesis and impaired platelet aggregation. Clinically, patients may experience increased incidence of gastric mucosal injury, occult blood loss, and potentially life-threatening GI bleeding, particularly in elderly or renally impaired individuals."
"Aprepitant, a moderate CYP3A4 inducer, can accelerate the metabolism of Phenylbutazone, a nonsteroidal anti-inflammatory drug (NSAID) primarily metabolized by CYP3A4 and CYP2C9. This leads to reduced plasma concentrations of Phenylbutazone, potentially diminishing its analgesic and anti-inflammatory efficacy. The interaction may result in inadequate symptom control in patients with chronic inflammatory conditions such as rheumatoid arthritis."
"Phenylbutazone, a nonsteroidal anti-inflammatory drug (NSAID) with potent prostaglandin synthesis inhibition, antagonizes the vasodilatory and antiplatelet effects of epoprostenol, a prostacyclin analog. This occurs because phenylbutazone reduces the production of endogenous prostacyclin and may also compete for receptor binding or downstream signaling, thereby diminishing epoprostenol's therapeutic efficacy in pulmonary arterial hypertension. Clinically, this interaction may lead to increased pulmonary vascular resistance, worsening symptoms, and elevated risk of thrombotic events."
No interactions on record
Explore head-to-head clinical comparisons of other medications in the same therapeutic classes.
Common clinical questions about PHENYLBUTAZONE vs 8-HOUR BAYER, answered by our medical review team.
PHENYLBUTAZONE is a NSAID that works by Phenylbutazone is a nonsteroidal anti-inflammatory drug (NSAID) that inhibits cyclooxygenase (COX) enzymes, reducing prostaglandin synthesis, thereby causing anti-inflammatory, analgesic, and antipyretic effects. It also inhibits leukocyte migration and lysosomal enzyme release.. 8-HOUR BAYER is a NSAID that works by Irreversibly acetylates cyclooxygenase-1 (COX-1) and cyclooxygenase-2 (COX-2), inhibiting prostaglandin and thromboxane A2 synthesis, leading to analgesic, antipyretic, anti-inflammatory, and antiplatelet effects.. They differ in pharmacokinetic profiles, FDA-approved indications, and side effect profiles.
Potency comparisons between PHENYLBUTAZONE and 8-HOUR BAYER depend on the specific clinical indication. These are both NSAID agents and are not directly interchangeable by dose. A physician or clinical pharmacist should guide any therapeutic switching decisions.
The standard adult dose of PHENYLBUTAZONE is: Oral: 100-200 mg three times daily with food; maximum 600 mg/day. For acute gout: initial 400 mg followed by 200 mg every 4-6 hours for 1-2 days, then reduce.. The standard adult dose of 8-HOUR BAYER is: 325-650 mg every 8 hours for pain/fever; 81-325 mg daily for cardiovascular prophylaxis.. Dosing should always be individualized based on indication, renal and hepatic function, age, and other patient factors.
No direct drug-drug interaction has been formally documented between PHENYLBUTAZONE and 8-HOUR BAYER in current clinical databases. However, individual patient risk factors including other medications, organ function, and comorbidities should always be evaluated by a qualified healthcare provider.
The maternal-fetal safety profiles differ. PHENYLBUTAZONE is classified as Category C. First trimester: Increased risk of cardiovascular malformations and neural tube defects due to inhibition of prostaglandin synthesis. Second and third trimesters: Risk of premature. 8-HOUR BAYER is classified as Category C. First trimester: No well-controlled studies. Avoid use unless clearly needed. Second and third trimesters: Aspirin should be avoided due to risk of premature closure of ductus arte. Always consult a maternal-fetal medicine specialist before taking either drug during pregnancy or lactation.