Simultaneous determination of trimethoprim and sulfamethoxazole in dried plasma and urine spots.

Background: Trimethoprim-sulfamethoxazole (TMP-SMX) is an antimicrobial drug combination commonly prescribed in children and adults. The study objectives were to validate and apply an HPLC–MS/MS method to quantify TMP-SMX in dried plasma spots (DPS) and dried urine spots (DUS), and perform a comparability analysis with liquid matrices. Results: For TMP the validated range was 100–50,000 ng/ml for DPS and 500–250,000 ng/ml for DUS; for SMX, the validated range was 1000–500,000 ng/ml for both DPS and DUS. Good agreement was noted between DPS/DUS and liquid plasma and urine samples for TMP, while only modest agreement was observed for SMX in both matrices. Conclusion: A precise, accurate and reproducible method was developed to quantify TMP-SMX in DPS and DUS samples.