Hi Neil, that’s a very interesting question about supporting allopurinol with probenecid (often sold under the Probalan brand). Allopurinol works by reducing the amount of uric acid our bodies produce. Probenecid works by encouraging our kidneys to excrete more uric acid in our urine.
Before I comment further, I must apologize, Neil. You originally submitted your question via my Gout Helpdesk (aka the orange Gout Help button). I have to admit I’ve been overwhelmed by the number of tickets in the helpdesk. I’m slowly working through them, but I always give priority to GoutPal members who post directly in the forums. I’ll mark your Helpdesk ticket as ‘Resolved’ and continue to help you in this forum.
Back to allopurinol with probenecid. This is a good idea for some patients, and if your doctor wants to try it, then it’s a good idea if it lowers your uric acid. Having said that, personally, I would ask for another allopurinol increase first.
The reason I say that is because to describe the level as “plateaued” based on one result seems premature to me. This is especially true when you have a significant burden of uric acid crystals. Blood tests only measure dissolved urate. So, if a large number of crystals start to dissolve, blood test results will show slightly higher levels. Your test results went from 0.40 to 0.37 with 150 mg allopurinol daily. This is a 7.5% fall. When I’m thinking about uric acid, I regard the uric acid range as more significant than an individual test result. In essence, any single test result can easily fluctuate by 10% from natural daily fluctuations, dissolving crystals, or both. I believe this is a possible explanation for your static uric acid level.
I’ve seen other cases of allopurinol being supported by probenecid. From memory, these have involved higher allopurinol doses, and static results over more than one increase.
Ultimately, it’s always best to discuss the pros and cons with your doctor and reach a mutually agreed strategy. There are other factors that your doctor might be aware of. Significantly, there might be reasons why he is reluctant to increase allopurinol beyond a relatively low dose. I always recommend that anyone taking any uric acid lowering treatment should combine uric acid blood tests with kidney function and liver function tests. It might be that the results of these persuade your doctor against increasing allopurinol further.
It’s great that your doctor realizes the need to get uric acid lower. It is definitely your best chance of reducing your urate burden, which will shrink your tophi.
I think you have to check that there are no special reasons for restricting your allopurinol dose. Then, the question is if it’s better to increase allopurinol, introduce probenecid, or both. That’s the discussion you need with your doctor.
I hope this helps. If not, please ask for clarification. Otherwise, I look forward to reading the outcome of your visit.