Purinol300 mg

Established / FDA-Approved Uses

• Chronic gout and gouty arthritis: Long-term management of hyperuricemia in patients with moderate-to-severe recurrent gout, tophaceous gout, or gout with joint destruction, uric acid nephrolithiasis, or nephropathy. Purinol is not indicated for treating an acute gout attack and should not be started during one.
• Secondary hyperuricemia of malignancy (tumor lysis syndrome): Management and prevention of hyperuricemia in patients with leukemia, lymphoma, and other malignancies receiving cancer chemotherapy that causes rapid cell turnover and elevated serum/urinary uric acid.
• Recurrent calcium oxalate kidney stones: Management of recurrent calcium oxalate calculi in patients with hyperuricosuria, when fluid intake and dietary measures alone have failed.

Not Indicated For

• Asymptomatic hyperuricemia (uric acid elevation alone without gout, stones, or malignancy-related risk) is generally not treated with Purinol unless a specific indication above applies.
• Treatment of an acute gout flare - other agents (NSAIDs, colchicine, corticosteroids) are used for the acute attack itself.

Each tablet contains Allopurinol INN 100 mg or 300 mg as the active ingredient.

Purinol is an oral xanthine oxidase inhibitor used for the long-term control of hyperuricemia associated with gout, certain cancer chemotherapy regimens, and recurrent calcium oxalate kidney stones. By reducing the production of uric acid rather than increasing its excretion, Purinol lowers serum urate levels over time, which helps prevent the formation of urate crystals in joints and tissues and reduces the frequency of gout flares with continued use. It is taken as a once-daily or divided-dose oral tablet and is intended for chronic, ongoing management rather than treatment of an acute attack.

Purinol belongs to the Xanthine Oxidase Inhibitor class of anti-gout / uric acid-lowering agents.

Mechanism

Allopurinol and its active metabolite, oxypurinol (alloxanthine), inhibit xanthine oxidase, the enzyme responsible for converting hypoxanthine to xanthine and xanthine to uric acid. By blocking this final step in purine metabolism, Allopurinol lowers plasma and urinary uric acid concentrations, unlike uricosuric agents that increase renal excretion.

Pharmacokinetics

• Absorption: About 80-90% of an oral dose is absorbed from the gastrointestinal tract.
• Metabolism: Extensively metabolized in the liver to oxypurinol, the major active metabolite, which itself has a long half-life and sustained xanthine oxidase-inhibiting activity.
• Half-life: Allopurinol itself has a short plasma half-life (1-2 hours), but oxypurinol has a much longer half-life (approximately 15-30 hours in patients with normal renal function), allowing effective once-daily dosing.
• Excretion: Oxypurinol is eliminated renally; excretion is prolonged in renal impairment, requiring dose adjustment.

Give Purinol by mouth, preferably after food, with plenty of water. Doses over 300 mg/day are usually divided through the day unless the prescriber specifies a single daily dose. Swallow tablets whole; do not crush without checking with a pharmacist. Continue treatment even between gout flares - it is a preventive, long-term therapy, not a treatment for an ongoing attack.

Major Interactions

• Azathioprine and mercaptopurine (6-MP): Purinol markedly inhibits the xanthine oxidase-mediated breakdown of these drugs, raising their blood levels and risk of severe, potentially life-threatening bone marrow suppression. If co-administration is unavoidable, the dose of azathioprine or mercaptopurine must be reduced to about one-quarter to one-third of the usual dose, with close monitoring.
• Ampicillin/amoxicillin: Combined use with Purinol is associated with a significantly higher incidence of skin rash; consider alternative antibiotics where possible.
• Warfarin and other oral anticoagulants: Purinol may potentiate anticoagulant effect; monitor INR more closely when starting, stopping, or changing the dose of Purinol.
• Thiazide diuretics: May increase the risk of hypersensitivity reactions to Purinol, particularly in patients with impaired renal function.
• ACE inhibitors: Concurrent use with Purinol has been associated with an increased risk of hypersensitivity reactions.
• Cyclophosphamide and other cytotoxic agents: Increased risk of bone marrow suppression when combined with Purinol.
• Theophylline: Purinol can reduce clearance of theophylline, raising its plasma level; monitoring is advised with prolonged or high-dose use.
• Didanosine: Purinol increases didanosine plasma concentrations; concurrent use is generally avoided.

Common

• Skin rash (see Precautions - any rash warrants prompt medical review and possible discontinuation)
• Nausea, vomiting, diarrhea, or other mild gastrointestinal upset
• Increased frequency of gout attacks when first starting therapy
• Headache, drowsiness

Less Common / Serious

• Severe hypersensitivity reactions, including Stevens-Johnson syndrome, toxic epidermal necrolysis, and DRESS syndrome (see Precautions and Warnings)
• Abnormal liver function tests, hepatitis
• Bone marrow suppression (leukopenia, thrombocytopenia)
• Renal impairment or worsening of existing renal function

Pregnancy: Data on the use of Purinol in human pregnancy are limited. Purinol should be used during pregnancy only if clearly needed and the potential benefit to the mother justifies the potential risk to the fetus; a physician should be consulted before use.

Lactation: Purinol and its active metabolite oxypurinol are excreted into breast milk. Because effects on the nursing infant have not been fully established, Purinol should be used during breastfeeding only under medical supervision, weighing the benefits of treatment against potential risk to the infant.

Severe Hypersensitivity Reactions

Purinol can rarely cause severe, potentially fatal hypersensitivity reactions, including Stevens-Johnson syndrome, toxic epidermal necrolysis, and DRESS syndrome (drug reaction with eosinophilia and systemic symptoms). These reactions may present with fever, skin rash, blistering, mucosal lesions, lymphadenopathy, and organ involvement. Purinol should be discontinued immediately and permanently at the first sign of rash or other symptoms suggesting hypersensitivity, and medical attention should be sought without delay.

HLA-B*5801 Genetic Risk

Carriers of the HLA-B*5801 allele have a substantially increased risk of severe hypersensitivity reactions to Purinol. This allele is more prevalent in certain populations, including some Asian ancestries (e.g., Han Chinese, Thai, Korean). Genetic screening for HLA-B*5801 before starting Purinol is recommended by some guidelines in these higher-risk populations.

Timing Around Acute Gout Attacks

Purinol should not be started during an acute attack of gout, as this may worsen or prolong the attack; therapy is typically initiated only after the acute episode has resolved. Paradoxically, starting Purinol can itself precipitate an acute gout flare due to mobilization of urate stores; low-dose colchicine or an NSAID is often used as prophylaxis during the first several months of therapy.

Other Precautions

• Use with caution and at reduced doses in patients with renal or hepatic impairment.
• Periodic monitoring of liver function, renal function, and blood counts is advisable, especially with long-term use.
• Purinol may cause drowsiness; use caution when driving or operating machinery until individual response is known.
• Maintain adequate fluid intake during treatment.

Reported overdose experience with Purinol is limited. Suspected overdose may present with gastrointestinal upset or other exaggerated adverse effects. There is no specific antidote. In case of suspected overdose, seek immediate medical attention or contact a poison control center; general supportive measures and adequate hydration are used, and hemodialysis can effectively remove Purinol and its active metabolite if clinically indicated. Do not attempt to manage a suspected overdose at home.

Store at room temperature (below 30°C), away from light and moisture. Keep out of reach of children.

Renal Impairment

Dose reduction is required because oxypurinol, the active metabolite, is renally excreted and accumulates in renal impairment, increasing toxicity risk. Lower starting doses and slower titration are used, with dosing intervals or amounts adjusted according to creatinine clearance under medical supervision.

Hepatic Impairment

Use with caution; lower doses may be required, and periodic liver function monitoring is recommended.

Elderly

Older adults often have reduced renal function; start at the lower end of the dosing range and titrate cautiously, with monitoring of renal function.

Pediatric Use

See Pediatric Uses section.

Populations at Genetic Risk

Patients of certain ancestries (e.g., Han Chinese, Thai, Korean) carrying the HLA-B*5801 allele are at higher risk of severe hypersensitivity reactions; genetic testing before starting Purinol is recommended by some guidelines in these groups (see Precautions and Warnings).

Purinol is generally used as a long-term, often lifelong, maintenance therapy for chronic gout and recurrent hyperuricemia-related conditions, since stopping treatment typically allows uric acid levels to rise again. For prevention of hyperuricemia during cancer chemotherapy, Purinol is usually given for a defined short course around the treatment period. Duration should be determined by the prescribing physician based on the indication and response to therapy.

Xanthine oxidase inhibitors; Antigout / uric acid-lowering agents.

Allopurinol and its major active metabolite, oxypurinol, inhibit the enzyme xanthine oxidase, which normally converts hypoxanthine to xanthine and then xanthine to uric acid. By blocking this pathway, Allopurinol reduces the synthesis of uric acid, lowering serum and urinary urate concentrations and reducing the tendency for urate crystal deposition in joints and tissues.

C

The established pediatric use of Purinol is for the management of hyperuricemia secondary to malignancy in children receiving chemotherapy for leukemia, lymphoma, and other cancers, using weight-based dosing under specialist supervision (commonly around 10 mg/kg/day in divided doses, not exceeding 800 mg/day, with age-based dose bands used in some regimens for children age 6-10 years and under 6 years). Primary gout is rare in children, and the safety and efficacy of Purinol for chronic primary gout in the pediatric population have not been established; use in this setting should be guided by a pediatric specialist.