Tricyclic Antidepressant: HPLC Analysis of Doxepin in 'Aponal 100' Tablets

Importance of the Topic

Tricyclic antidepressants such as doxepin remain important in clinical therapy despite newer drug classes. Reliable quantification in pharmaceutical formulations ensures dose accuracy, patient safety, and compliance with regulatory standards. High-performance liquid chromatography (HPLC) methods with optimized columns and conditions are essential to achieve robust, reproducible results.

Study Objectives and Overview

This application note details the development and validation of an HPLC method for analyzing doxepin in 'Aponal 100' tablets. The goals were to separate doxepin from related tricyclic amines and excipients, confirm peak identity via standard comparison, and demonstrate method stability under routine laboratory conditions.

Methodology and Instrumentation

The analysis used an Agilent 1100 Series HPLC system equipped with a Zorbax Eclipse XDB-C18 column (3.5 µm, 4.6 × 75 mm) and matching guard cartridge. Mobile phase A consisted of 0.025 M KH2PO4 buffer at pH 7; phase B was methanol. A gradient from 67% B to 85% B over 15 minutes at 1.0 mL/min was applied, with column temperature maintained at 25 °C and autosampler at 4 °C to prevent sample degradation. UV detection was set at 210 nm. Injection volume was 5 µL.

Main Results and Discussion

The Eclipse XDB-C18 column delivered sharp, symmetrical peaks for basic tricyclic amines by minimizing secondary interactions. Chromatograms showed baseline resolution between doxepin and related compounds (protriptyline, nortriptyline, imipramine, amitriptyline, trimipramine). Extracts from 'Aponal 100' matched the standard retention time for doxepin, with no interference from tablet excipients. Method reproducibility and peak stability were confirmed over multiple injections.

Benefits and Practical Applications

• High selectivity and peak shape for basic biogenic amines at neutral pH.
• Rapid analysis time (17 minutes total run).
• Minimal sample decomposition due to refrigerated autosampler.
• Reliable identification and quantification of doxepin in tablet dosage forms.

Future Trends and Potential Applications

Further developments may include coupling to mass spectrometry for enhanced sensitivity and specificity, miniaturized columns for faster throughput, and automated sample preparation to streamline routine quality control. Expanding the method to other tricyclic antidepressants or complex biological matrices is also feasible.

Conclusion

The presented HPLC method using the Eclipse XDB-C18 column is a robust, accurate procedure for the determination of doxepin in pharmaceutical tablets. It achieves clear separation, fast analysis, and consistent performance, supporting quality control needs in pharmaceutical laboratories.

Reference

Udo Huber, Adebayo O. Onigbinde. Tricyclic Antidepressant: HPLC Analysis of Doxepin in 'Aponal 100' Tablets. Agilent Technologies Application Note 5988-7627EN, 2002.