Allopurinol

[pharout]

I have an interesting question for everyone: When using allopurinol to prevent gout, is it more important to adjust the daily dose based on renal function of the patient or to treat to a uric acid level of <6 despite renal function? I have always been taught to renally adjust doses for different CrCl levels, but unsure why? Side effects are relatively mild, renal toxicity of active metabolite is rare, so why? I was just informed today by one of our internal med docs that he worked in renal clinic and was told to treat the uric acid level and do not worry about renal function. The main reason is that uric acidemia is more renally toxic than the drug itself. I've got this question out to my nephrology colleague and let you know the outcome. Any thoughts? I think it is an interesting question as it contradicts any logic I had toward renal dosage adjustment for allopurinol.

[the old merlin]

Bearing in mind that part of the longterm treatment is drinking plenty of water (around 3l/day) to maintain good kidney function, I would have thought that the uric acid levels were more important.

That's a "thought"; not based on good scientific data.

However I subsequently looked in the BNF (our standard reference book, Pharout) and it confirms my view that keeping the uric acid levels down is the object of the exercise.

However, I'm not sure what one would do with a patient with poor renal function who developed frequent attacks. Given the possibility of Colchicine causing renal damage itself, one wouldn't want to use it too often. Again BNF says stick with Allopurinol (albeit in reduced dose), but monitor toxic possibilities, especially liver function.

Also, given the long half-life of Allopurinol, why would you bother titrating very finely? You're not using it for acute treatment.

[Pharmanaut]

Originally Posted by the old merlin

Bearing in mind that part of the longterm treatment is drinking plenty of water (around 3l/day) to maintain good kidney function, I would have thought that the uric acid levels were more important.

That's a "thought"; not based on good scientific data.

However I subsequently looked in the BNF (our standard reference book, Pharout) and it confirms my view that keeping the uric acid levels down is the object of the exercise.

However, I'm not sure what one would do with a patient with poor renal function who developed frequent attacks. Given the possibility of Colchicine causing renal damage itself, one wouldn't want to use it too often. Again BNF says stick with Allopurinol (albeit in reduced dose), but monitor toxic possibilities, especially liver function.

Also, given the long half-life of Allopurinol, why would you bother titrating very finely? You're not using it for acute treatment.

Check your PMR if you are dispensing colchicine. I've had a patient who was getting them monthly as a repeat. Looked like it was getting swept up with the "Repeat all" button on the computer. Had a word with the Dr who removed the repeat flag off his record.

[pharout]

I have confirmed the above with my colleague. Basically, the nephrotoxic uric acidemia and incidence of hypertension in ckd resulting from hyperuricemia, trump the dose adjustment of the med based on renal function. So you would target a uric acid level <6, no matter what the renal function of the pt. This has also been backed by our rheumatology dept as well. There is more data recently linking hyperuricemia to onset of HTN, so this is an emerging concern. If a pt has renal compromise, you can simply titrate allopurinol by 50mg qD in 2-3 week intervals and monitor serum creatinine as well.

[the old merlin]

Originally Posted by Pharmanaut

Check your PMR if you are dispensing colchicine. I've had a patient who was getting them monthly as a repeat. Looked like it was getting swept up with the "Repeat all" button on the computer. Had a word with the Dr who removed the repeat flag off his record.

Good point.
And make sure the patient understands how they should be taken. In my prescribing advisor days I had to defend a GP who was being (rightly) cautious about prescribing a migraine treatment (not Migril!). The patient was under the impression it should be taken regularly and was most abusive about the GP until I was able to put her right. So angry that she rang the PCT to find "the top person about prescribing"!

[Pharmanaut]

Originally Posted by the old merlin

Good point.
And make sure the patient understands how they should be taken. In my prescribing advisor days I had to defend a GP who was being (rightly) cautious about prescribing a migraine treatment (not Migril!). The patient was under the impression it should be taken regularly and was most abusive about the GP until I was able to put her right. So angry that she rang the PCT to find "the top person about prescribing"!

Did you see the report on someone developing green blood by mis-dosing (not sure if it was mis-use) with Sumatriptan. Probably thats why the max dose is printed on the labels in Pharmacy Manager now.