Introduction The thiopurine metabolites (TPM), 6-Thioguanine nucleotide (6-TGN) and 6-Methylmercaptopurine nucleotide (6-MMPN), have been shown to be useful in monitoring and managing inflammatory bowel disease (IBD) patients on thiopurines. This study set out to determine the overall cost of setting up a TPM service for all of our IBD patients taking thiopurines, whilst assessing any cost savings from the recommended dose adjustments suggested by the results.
Method The gastroenterology department at the Luton and Dunstable University Hospital identified 406 patients with IBD on thiopurine medication. These patients were sent a letter in December 2014 requesting blood tests inclusive of a TPM assessment to be performed before the end of January 2015. The patient’s samples were sent to Birmingham City Hospital for measurement at a cost of £32. Based on published data a thiopurine management algorithm was designed to help guide clinicians in their response to the results. If a change in prescription was recommended by the results the annual prescription cost for the CCG was calculated using the following drug tariff costs: Azathioprine 25 mg (28 tablets) £2.96, Azathioprine 50 mg (56 tablets) £3.19 and 6-Mercaptopurine 50 mg (25 tablets) £50.47.
Results 200 patients attended before the end of January 2015 for the TPM tests there were 156 patients taking AZA and 44 taking 6-MP. The TPM results determined a change in management for 124 (62%) patients, with 76 patients (38%) having no change to their thiopurine drug dose and therefore annual prescription costs. Dose reduction was recommended in 36%, 14% had their dose increased, 13% had their thiopurine drug therapy stopped, and 1 patient had their AZA changed to 6-MP. The annual prescription cost for AZA and 6-MP for the patients in the study was originally £47,065.98. The use of the TPM results in the thiopurine management algorithm led to a reduction in prescription costs to £39,548.78. The total cost of the TPM tests was £6400.00 and therefore the overall saving for the first year of the service was £1117.20.
Conclusion TPM assessment led to a dose adjustment in 62% of the IBD patients on thiopurine therapy. Essentially the costs of introducing this service were covered by the savings in the first year alone, from personalised drug dosage adjustments. In addition to the overall saving of £1117.20 in the first year, there will also be an on-going, year on year, prescription cost saving of £7517.20. These savings could be higher still once the remaining thiopurine patients have completed their TPM review. Future studies will be necessary to assess additional cost savings if the personalised dose adjustments are proven to lead to improved disease control and reduced complication rates.
Disclosure of interest None Declared.