Long-Term Stability of a Fixed-Dose Doxazosin and Finasteride Combination Formulation

Author(s):  Mengesha Abebe, Hess Jared

Issue:  Sep/Oct 2026 - Volume 30, Number 5
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Abstract:  BACKGROUND: Lower urinary tract symptoms (LUTS) secondary to benign prostatic hyperplasia (BPH) are commonly treated with a1-adrenoreceptor antagonists, 5a-reductase inhibitors, or a combination of both. The development of a fixed-dose doxazosin (DOX) and finasteride (FIN) formulation in a single dosage form is expected to improve efficacy, lower cost, and improve adherence to the treatment of male LUTS/BPH.

OBJECTIVE: The study aims to determine the stability of a fixed-dose combination formulation containing doxazosin (1 mg) and finasteride (5 mg).

METHODS: We conducted long-term stability studies of a fixed-dose DOX-FIN combination capsule. A stability-indicating HPLC method was developed and used to determine DOX and FIN in combination capsules simultaneously. DOX-FIN capsules were stored at 4°C, 25°C, and 40°C for 12 months. Samples were analyzed periodically using the HPLC method. RESULTS: The HPLC analysis showed that both DOX and FIN amounts remained above 90% of the initial values after 1 year when the capsules were stored at 4°C and 25°C. An elevated temperature (40°C) is not a recommended storage condition for the compounded capsules. Even at 40 °C, doxazosin stability remains above 90% up to 30 days, and finasteride remains above 90% up to 90 days.

CONCLUSION: Long-term stability studies indicated that the combination of doxazosin and finasteride remained stable, with 90% of the drug still present in the formulation after one year for capsules stored at 4°C and 25°C.

Related Keywords: Mengesha Abebe, Hess Jared, Doxazosin, Finasteride, Fixed-dose combination, Long-term stability

Related Categories: PEER-REVIEWED, STABILITIES, COMPATIBILITIES, UROLOGY/URINARY TRACT

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