Allopurinol is an oral prescription medication for the treatment of gout, a form of arthritis that produces severe pain and inflammation in joints. Gout occurs when blood and urine levels of uric acid become elevated leading to the deposition of urate crystals in the joints of the ankles, knees, hands, wrists and big toe. Allopurinol effectively treats gout by lowering uric acid levels, but its interactions with certain vitamins and other medications may lead to adverse effects.
Antibiotics
Patients who take allopurinol in combination with the penicillin antibiotics amoxicillin or ampicillin may have skin rashes more frequently than they would if the drugs were not combined. Doctors don't know what causes this adverse interaction.
Antidiabetics
Chlorpropamide is a prescription medication that can effectively lower blood sugar in patients with type 2 diabetes. Diabetic patients with impaired kidney function may be at increased risk of hypoglycemia if they take allopurinol in combination with chlorpropamide. This is because allopurinol increases chlorpropamide's plasma half-life, a measure of the amount of time chlorpropamide remains in circulation in the bloodstream.
Anticoagulants
Anticoagulant medications make it difficult for the blood to clot. Patients taking anticoagulants are at risk of heavy bleeding from even slight injuries such as those that may occur while shaving or flossing the teeth. The anticoagulant medications acenocoumarol, anisindione, dicumarol and warfarin all interact with allopurinol in such a way that their anticoagulant effect is enhanced. This means that patients who take allopurinol with any of these anticoagulants need to be especially careful not to incur any kind of cut or bruise.
Immunosuppressants
Azathioprine and cyclosporine are prescription immunosuppressants that can treat severe rheumatoid arthritis and help to prevent rejection of a transplanted kidney. Both work by diminishing the activity of the immune system, and both have serious side effects associated with them. Allopurinol, in combination with azathioprine or cyclosporine, hinders the ability of the liver to metabolize these immunosuppresants, and therefore their blood levels remain high for prolonged periods of time. Sustained high blood levels of these immunosuppressants increase the patient's risk of serious side effects.
Vitamins
Patients taking allopurinol should be aware that large doses of vitamin C may increase the possibility of kidney stone formation. In addition, large doses of vitamin B-3, also called niacin, may compromise the effectiveness of allopurinol and make the patient's gout condition more serious.
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