Allopurinol Side Effects:  Brand names for Allopurinol include Zyloprim and Aloprim.  Allopurinol is used for the prevention of gout as well as for selected other problems related to elevated levels of uric acid. Allopurinol is an inhibitor of the enzyme xanthine oxidase which facilitates the final step in the breakdown of the DNA building blocks called purines into uric acid. Uric acid at high concentrations can precipitate leading to deposition of crystals in joints.  This leads to acute inflammation called gout.  Additional problems associated with hyperuricemia include some types of kidney stones, potential kidney injury and accumulation of uric acid deposits in joints called gouty tophi.  Allopurinol is available in 100 mg and 300 mg tablets/capsules and the usual adult dose is 300 mg daily.  Fortunately, allopurinol has no side effects in most people and is usually well tolerated.  In addition to prevention of acute gout attacks less common indications for use of allopurinol include prevention of recurrent calcium oxalate renal stones and chemotherapy induced hyperuricemia.

Common Allopurinol Side Effects:  Side effects are generally uncommon and the only really common side effect, affecting less than 5 percent of patients is a rash.  Diarrhea is also listed as a common allopurinol side effect.

Serious Allopurinol Side Effects:  Most of the serious Allopurinol side effects are related to allergic or hypersensitivity problems.  Skin reactions can be severe, and include Stevens-Johnson syndrome, exfoliative dermatitis, acute severe pustular exanthematosis, hair loss called allopecia and toxic epidermal necrolysis.  Other hypersensitivity syndromes are also reported.  Hematologic serious allopurinol side effects include myelosuppression, thrombocytopenia, leukopenia, pancytopenia and aplastic anemia.  Liver problems including hepatic necrosis, hepatic impairment and other hepatotoxicity problems are seen infrequently.  Blood vessels can be involved in the hypersensitivity problems that are included in the serious allopurinol side effects and include purpura and vasculitis as well as necrotizing angiitis.  Kidney related serious allopurinol side effects can include renal impairment and renal failure as well as development of kidney stones.  Neurologic issues can include peripheral neuropathy and seizures.  Fortunately, all of these serious allopurinol side effects are uncommon.

Unusual Side Effects:  The most unusual allopurinol side effect is the propensity to develop acute attacks of gout during the initiation of treatment with allopurinol.  This is felt to be related to the abrupt change in serum concentrations of uric acid, and most physicians use a second drug like colchicine in low doses for the first two months of allopurinol therapy to avoid this short term exacerbation.

Drug Interactions:  Aspirin is one of the primary drugs that can interact with allopurinol.  The list of potential drug interactions is extensive and see the manufacturer’s prescribing guidelines for complete information.

Cautions:  With reduced renal function the dose of allopurinol may need to be reduced, and with more severe renal insufficiency caution is advised. Allopurinol should be avoided in patients with prior allopurinol hypersensitivity or negative reactions.  Again, see the manufacturers prescribing guidelines for complete details.

Pregnancy and Lactation Class:  Allopurinol is pregnancy category C, and is felt to be safe for breast feeding women.  Fortunately, gout is rare in premenopausal women, so this is only an issue for the less common allopurinol uses.

Special Considerations:  The propensity for allopurinol to cause acute gouty attacks in the first few weeks of therapy while the uric acid levels are changing abruptly makes it ideal to use a second drug during this initial therapy.  This used to be an inexpensive issue, as generic colchicine was used.  Now with the FDA decision to grant an exclusive patent to Colcrys to market colchicine at a very high price makes this more problematic.

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