A Southern Thai case–control study compared 26 patients with phenytoin cutaneous adverse reactions and 78 tolerant controls. Decreased CYP2C9 function was associated with risk (OR 7.89) and HLA-B*40:06 with OR 6.26, alongside lower haemoglobin and higher white-cell counts. No HLA marker survived Bonferroni correction and missing laboratory data prevented multivariable analysis, so these are exploratory signals rather than a ready screening rule.
Key findings
- Decreased CYP2C9 function had OR 7.89 (95% CI 1.81–34.49; p=.006) and HLA-B*40:06 OR 6.26 (95% CI 1.59–24.69; p=.009). Mean haemoglobin was 11.73 versus 13.48 g/dL, haematocrit 35.94% versus 40.29%, and WBC 10.19 versus 7.75×10^3/µL. No HLA association survived Bonferroni correction.
Why this matters globally
The findings prioritise markers for multicentre Southeast Asian validation where allele frequencies differ from Europe. Implementation requires sensitivity, specificity, predictive value, cost and safe treatment alternatives.
Thai researcher contribution
Researchers from Prince of Songkla, Ramathibodi–Mahidol, Burapha and Thai hospitals studied Southern Thai patients directly, contributing population-specific pharmacogenomic evidence.
Limitations to consider
Only 26 cases produced wide intervals and high false-positive or false-negative risk. Multiple testing, missing data, unadjusted confounding and uncertain timing mean blood-count differences may reflect illness or indication rather than susceptibility.