Gout Treatment. Combined vs Allopurinol alone.

We want to see which type of medication regime would best help patients with poorly controlled gout. One option is to increase the dose of their normal medication (Allopurinol 300mg) or to add in a second drug (Probenecid), with the aim being to compare the reduction in the level of uric acid (i.e. good response is where uric acid levels fall below 0.36, and this correlates well with better gout control), plus which regime is better tolerated by the patient. It is unblinded, therefore the participants will know which regime they are taking. They are assigned into the group taking Allopurinol 600mg (high dose-one drug group) or those taking 300mg with Probenecid (combined drug group). Patients will be followed up for 6weeks, with uric acid levels performed before, and after this 6week period. Hypothesis: - We hypothesise that higher doses of Allopurinol will more effectively control chronic gout (measured for this study as obtaining lower serum urate levels, but for patients this means fewer gout 'flares') compared to their pre-trial dose of Allopurinol (300mg). - Our second hypothesis is that higher dose Allopurinol will be as well tolerated by individuals as their pre-trial dose of 300mg, with no significant deterioration in their kidney function. - Thirdly, those regimes using a higher dose of Allopurinol will not be inferior to the addition of another agent, in this case Probenecid.