Quantitation of brinzolamide in dried blood spots by a novel LC-QTOF-MS/MS method

•Sensitive LC-QTOF-MS/MS method for the determination of brinzolamide in DBS.•DBS can be the ideal matrix for drugs with high distribution into RBCs.•DBS concentration correction was suggested, due to hematocrit effect.•The validated method was applied to samples obtained from patients.

In the current study, a rapid and sensitive LC-QTOF-MS/MS method for the determination of brinzolamide in dried blood spots (DBS) was developed and validated. This novel sample collection, storage and transfer technique was suitable for analyzing a drug with high distribution into red blood cells and negligible plasma levels. The method included an isocratic mobile phase consisting of methanol and 10 mM ammonium formate (90:10, v/v) and detection in positive electrospray mode (ESI+). The flow rate was adjusted to 0.350 mL/min yielding retention times of 1.7 min for both brinzolamide and internal standard (IS) rabeprazole on a Cyano analytical column, respectively. The validation of the proposed method over the concentration range 0.500–20.0 μg/mL was performed in compliance with EMEA and FDA guidelines, assessing all major performance characteristics. Inter- and intra- assay precisions were less than 14%, while inter- and intra- assay accuracies varied from 92.2 to 111%. No matrix effect was observed and the mean brinzolamide extraction recovery was 93.5%. The method was successfully applied to real DBS samples from patients in steady state condition, receiving brinzolamide ophthalmic suspension 1% (w/v) for several months. Initial concentrations were corrected due to hematocrit effect, using image processing algorithm written in Matlab.

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