Bioanalysis of captopril: two sensitive high-performance liquid chromatographic methods with pre- or postcolumn...

Area of Science:

• Analytical Chemistry
• Pharmacology
• Biochemistry

Background:

• Captopril is an antihypertensive drug whose metabolites can be reconverted to the active form.
• Accurate bioanalysis requires quantifying both free captopril and its reducible disulfide metabolites.
• Existing analytical methods may not effectively differentiate or quantify these forms simultaneously.

Purpose of the Study:

• To develop and compare two High-Performance Liquid Chromatography (HPLC) methods for captopril analysis.
• To validate these methods for the bioanalysis of free and total captopril in biological matrices.
• To determine the suitability of each method for specific analytical needs (free vs. total captopril).

Main Methods:

• Development of a precolumn derivatization HPLC method using monobromobimane (MBB) for free captopril.
• Development of a postcolumn reaction HPLC method using o-phthaldialdehyde (OPA) for free and total captopril.
• Validation of both methods in human plasma, with the OPA method also validated in urine, including disulfide reduction steps for total analysis.

Main Results:

• The MBB method achieved a limit of quantitation (LOQ) of 12.5 ng/ml in plasma.
• The OPA method had an LOQ of 25 ng/ml in plasma and 250 ng/ml in urine for total captopril.
• The MBB method was unsuitable for total captopril due to interference from the reducing agent.

Conclusions:

• The precolumn MBB method is superior for free captopril analysis due to simpler immediate derivatization.
• The postcolumn OPA method is highly suitable for total captopril analysis, unaffected by reducing agents or endogenous thiols.
• Both validated methods provide reliable quantification of captopril and its metabolites in biological samples.