Adult: Initially, 400-600 mg daily in divided doses for the 1st 48 hours, then reduce to minimum effective dose, usually 200-300 mg daily in divided doses. Use the lowest effective dose for the shortest possible duration required to control symptoms. Treatment recommendations may vary among countries (refer to local or specific product guidelines). Elderly: Use the lowest effective dose for the shortest possible duration.
Renal Impairment
Severe: Contraindicated.
Hepatic Impairment
Severe: Contraindicated.
Administration
Phenylbutazone Should be taken with food.
Contraindications
Hypersensitivity. History of asthma, urticaria, or allergic-type reaction to aspirin or other NSAIDs; active or history of peptic ulcer or haemorrhage; history of previous NSAID-induced gastrointestinal bleeding or perforation; symptoms or history of inflammatory bowel disease; blood dyscrasias, haemorrhagic diathesis; severe heart failure; pulmonary impairment, pulmonary oedema or pulmonary hypertension; thyroid disease; Sjogren's syndrome. Severe renal and hepatic impairment. Pregnancy (3rd trimester). Concomitant use with other NSAIDs including COX-2 inhibitors.
Special Precautions
Patient with uncontrolled hypertension, peripheral arterial disease, established ischaemic heart disease, mild to moderate CHF, cerebrovascular disease; risk factors for CV disease (e.g. diabetes, smoking, hyperlipidaemia); history of gastrointestinal disease; active or history of bronchial asthma; SLE, mixed connective tissue disease. Avoid use in women attempting to conceive. Mild to moderate renal and hepatic impairment. Elderly. Pregnancy (1st-2nd trimester) and lactation.
Adverse Reactions
Significant: Blood dyscrasias, oedema, Na and fluid retention, jaundice, hepatitis; aseptic meningitis (particularly in patients with SLE or mixed connective tissue diseases); acute bronchospasm attacks (in patients with active or history of bronchial asthma). Cardiac disorders: CHF. Ear and labyrinth disorders: Tinnitus, vertigo. Endocrine disorders: Goitre. Eye disorders: Optic neuritis, visual disturbances. Gastrointestinal disorders: Nausea, vomiting, diarrhoea, flatulence, constipation, dyspepsia, abdominal pain, ulcerative stomatitis, exacerbation of colitis and Crohn's disease. General disorders and administration site conditions: Malaise. Investigations: Decreased thyroid hormones, abnormal hepatic function tests. Rarely, increased serum transaminases. Nervous system disorders: Headache, dizziness, drowsiness, paraesthesia. Psychiatric disorders: Confusion, depression, hallucinations. Renal and urinary disorders: Rarely, haematuria, proteinuria, renal insufficiency, acute renal failure. Skin and subcutaneous tissue disorders: Photosensitivity. Vascular disorders: Hypertension. Potentially Fatal: Serious CV thrombotic events (e.g. stroke, MI), gastrointestinal reactions (e.g. bleeding, ulceration, perforation). Rarely, serious skin reactions (e.g. Stevens-Johnson syndrome, toxic epidermal necrolysis, exfoliative dermatitis).
Patient Counseling Information
This drug may cause drowsiness, dizziness and visual disturbances, if affected, do not drive or operate machinery.
Monitoring Parameters
Monitor CBC, LFTs, and renal function periodically (if treatment is continued for >1 week). Assess for weight gain or oedema, bleeding, bruising, and gastrointestinal adverse events.
Overdosage
Symptoms: Nausea, vomiting, epigastric pain, gastrointestinal bleeding, peptic ulceration; headache, tinnitus, deafness, dizziness, drowsiness, disorientation, excitation, fainting, hyperventilation, sweating, agitation, convulsions (occasional), coma; anaemia, leucopenia, thrombocytopenia, hypoprothrombinaemia; hypotension, hypertension (occasional), tachycardia, cardiac arrhythmias; adult respiratory distress syndrome, cyanosis; metabolic acidosis, respiratory alkalosis, hyperglycaemia, hypocalcaemia; hepatotoxicity (e.g. elevated transaminases, jaundice, hepatic necrosis); urinary retention, renal toxicity, acute renal failure, red discolouration of urine. Rarely, diarrhoea. Management: Symptomatic and supportive treatment. Monitoring for 36 hours may be necessary due to the delayed effects. May perform gastric lavage and administer activated charcoal within 1 hour of ingestion. In case of frequent or prolonged convulsions, administer IV diazepam. Assess and correct electrolytes, pH, and blood gases as required. Ensure adequate urine output. Observe renal and hepatic function. Manage hypotension with fluids, ensuring not to overhydrate. Perform cardiac monitoring in symptomatic patients. Charcoal haemoperfusion may be considered in severe cases.
Drug Interactions
Increased risk of gastrointestinal bleeding with antiplatelet agents (e.g. aspirin), corticosteroids, anticoagulants (e.g. warfarin) and SSRIs. May reduce the effects of antihypertensive agents (e.g. ACE inhibitors, β-blockers) and mifepristone. May increase the risk of nephrotoxicity with diuretics (e.g. loop diuretics, thiazide and thiazide-like diuretics). Decreased enteral absorption with colestyramine. May increase the serum concentrations of lithium, digoxin and methotrexate. May enhance the nephrotoxic effects of ciclosporin and tacrolimus. Concomitant use with misoprostol may result in CNS adverse effects (e.g. dizziness, headache, transient diplopia). May enhance the effects and duration of effects of oral antidiabetic drugs. Potentially Fatal: Increased risk of adverse effects with other NSAIDs including COX-2 selective inhibitors.
Food Interaction
May potentiate the CNS effects of alcohol.
Action
Description: Mechanism of Action: Phenylbutazone, a pyrazolone derivative, is a non-steroidal anti-inflammatory drug (NSAID) with antipyretic, analgesic, and uricosuric properties. Pharmacokinetics: Absorption: Readily absorbed from the gastrointestinal tract. Time to peak plasma concentration: Approx 2 hours. Distribution: Crosses the placenta; enters breast milk (small amounts). Plasma protein binding: 98%. Metabolism: Extensively metabolised in the liver via oxidation and conjugation with glucuronic acid to oxyphenbutazone and γ-hydroxyphenbutazone. Excretion: Via urine (approx 1% as unchanged drug); bile (approx 10% as metabolites). Elimination half-life: 70 hours.
Chemical Structure
Phenylbutazone Source: National Center for Biotechnology Information. PubChem Compound Summary for CID 4781, Phenylbutazone. https://pubchem.ncbi.nlm.nih.gov/compound/Phenylbutazone. Accessed Sept. 23, 2024.
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