Side Effects of Zyloprim (Allopurinol) for Kidney Damage Prevention

My husband is on 300 mg a day of zyloprim for the treatment of gout, even though to his knowledge he has never had an actual gout attack. The only way he found out was when he had a blood test done for what turned out to be a problem with his knee, that was fixed through arthroscopic surgery.  He has been on zyloprim for about 5 years.  Is this normal?  When he asks his doctor, he tells him it is to prevent any possible kidney damage.

Significantly abnormally elevated uric acid blood levels can lead to damage to the tissues of the kidney (called urata nephropathy) and kidney stones.  Allopurinol (zyloprim) is used to return the uric acid blood level to normal and avoid the risk of kidney damage, whether or not a patient has ever had gouty arthritis.