Ethnic differences in responses to disease modifying drugs.

BACKGROUND AND
OBJECTIVE: The UK has a growing South Asian population. In the South Asian population of Bradford people appear to be less tolerant of disease-modifying anti-rheumatic drugs (DMARDs). One reason for this may be poor communication during patient education, which is generally designed for white North European people. Our objective was to obtain information on DMARDs that were used, the duration of their use and reasons for their discontinuation between ethnic groups.
METHODS: Retrospective data were obtained from the inception of a clinical database in August 1993 to July 2001 using 'DMARD' as the main search item; a total of 5479 DMARD prescriptions were represented in the data. A subset of the data so obtained was cross-checked against the patient records. Inaccuracies in start and stop dates prior to January 1997, together with other reasons (such as incomplete data), resulted in a final data set of 2356 drugs. The drugs had been given to 1391 patients. Overwhelmingly, the two main ethnic groups were North European (1191 patients) and South Asian (193 patients).
RESULTS: The final data set was based on the following drugs: azathioprine (179); antimalarials (chloroquine and hydroxychloroquine) (407); corticosteroids (648); D-penicillamine (61); methotrexate (459); sulphasalazine (493); and sodium aurothiomalate (96). Survival analysis showed that age and drug type were important variables influencing the duration of time spent on a drug before discontinuation. For age, drug survival was better for the older age group [log rank test, chi2(3) = 29.1, P < 0.0001]. For drug, survival was best for steroids, followed in decreasing order by sulphasalazine, methotrexate, sodium aurothiomalate, azathioprine, antimalarials and D-penicillamine [chi2(6) = 99.3, P < 0.00001). For all drugs, the main ethnic groups differed, with a 12-month survival rate of drugs in the North European group of 0.742 (95% confidence interval 0.693-0.791) and the South Asian group of 0.665 (95% confidence interval 0.645-0.684) [log rank test, chi2(1) = 18.19, P < 0.00001]. As the two main ethnic groups differed with respect to age and drug type, further survival analysis adjusting for these variables confirmed a significant difference between the two ethnic groups. The main reasons for terminating the DMARD differed between the groups: people of South Asian origin were more likely to discontinue the drug because of rashes, lack of efficacy and worry about the potential side-effects of the drug.
CONCLUSIONS: People of South Asian ethnic status terminate DMARD therapy sooner than North Europeans. The reasons for this difference are not clear but may concern problems with effective communication, cultural differences in attitudes to chronic illness or genetic polymorphisms in drug metabolism.