OXYPHENBUTAZONE
Clinical safety rating: caution
Comprehensive clinical and safety monograph for OXYPHENBUTAZONE (OXYPHENBUTAZONE).
Oxyphenbutazone is a nonsteroidal anti-inflammatory drug (NSAID) that inhibits cyclooxygenase (COX-1 and COX-2) enzymes, thereby reducing prostaglandin synthesis, which mediates inflammation, pain, and fever.
| Metabolism | Hepatic metabolism via hydroxylation and glucuronidation; major metabolites include oxyphenbutazone glucuronide; minor CYP450 involvement. |
| Excretion | Primarily renal (biliary/fecal minor). Approximately 60-70% excreted in urine as glucuronide conjugates and unchanged drug; 5-10% in feces via bile. |
| Half-life | Terminal elimination half-life ranges from 27 to 64 hours (mean ~50 hours). Prolonged in hepatic or renal impairment; may extend up to 100 hours in elderly. |
| Protein binding | 98-99% bound to plasma albumin. |
| Volume of Distribution | 0.2-0.3 L/kg. Low Vd indicates limited tissue penetration; primarily confined to plasma and extracellular fluid. |
| Bioavailability | Oral: 90-100% (well absorbed). No other clinically relevant routes. |
| Onset of Action | Oral: 30-60 minutes for analgesic effect; anti-inflammatory effect may take 1-2 hours. Peak plasma levels at 2-4 hours. |
| Duration of Action | Analgesic effect lasts 4-6 hours; anti-inflammatory effect persists 12-24 hours due to long half-life and tissue accumulation. |
100-200 mg orally 3-4 times daily, not to exceed 600 mg/day.
| Dosage form | TABLET |
| Renal impairment | Avoid use if CrCl <30 mL/min. For CrCl 30-60 mL/min, reduce dose by 50%. |
| Liver impairment | Contraindicated in severe hepatic impairment (Child-Pugh C). For Child-Pugh A/B, reduce dose by 50% and monitor. |
| Pediatric use | Not recommended for pediatric use due to risk of adverse effects. |
| Geriatric use | Start at lowest effective dose (100 mg 1-2 times daily), with careful monitoring for renal function and adverse reactions. |
| 1st trimester | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
Comprehensive clinical and safety monograph for OXYPHENBUTAZONE (OXYPHENBUTAZONE).
| Breastfeeding | Contraindicated during breastfeeding. M/P ratio unknown; oxyphenbutazone is excreted into breast milk in small amounts but potential for serious adverse effects (e.g., kernicterus in neonates, especially those with G6PD deficiency). |
| Teratogenic Risk | First trimester: Avoid due to risk of cardiovascular defects and gastroschisis. Second/third trimester: Avoid due to risk of premature ductus arteriosus closure, oligohydramnios, and neonatal renal impairment. NSAIDs, including oxyphenbutazone, are associated with increased risk of miscarriage. |
■ FDA Black Box Warning
WARNING: Serious gastrointestinal (GI) adverse events (bleeding, ulceration, perforation) can occur without warning. Increased risk with history of GI ulcer/bleeding, elderly, and smoking. Also, increased risk of cardiovascular thrombotic events (MI, stroke) with long-term use.
| Serious Effects |
Hypersensitivity to oxyphenbutazone or other NSAIDs; history of aspirin-sensitive asthma; active GI bleeding or ulcer; severe renal or hepatic disease; blood dyscrasias; third trimester of pregnancy; concomitant use with other NSAIDs or anticoagulants (relative).
| Precautions | GI toxicity (ulceration, bleeding), cardiovascular risk, renal toxicity, hepatic toxicity (elevated liver enzymes, hepatitis), hematologic effects (agranulocytosis, aplastic anemia, leukopenia), hypersensitivity reactions, fluid retention, and exacerbation of asthma. |
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| Fetal Monitoring |
| Monitor maternal renal function, liver function, and complete blood count regularly. Fetal ultrasound for ductus arteriosus and amniotic fluid index during third trimester if exposure occurs. |
| Fertility Effects | May impair female fertility due to inhibition of prostaglandin synthesis affecting ovulation and implantation. Reversible upon discontinuation. |