{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,4,13]],"date-time":"2026-04-13T18:51:02Z","timestamp":1776106262434,"version":"3.50.1"},"reference-count":59,"publisher":"MDPI AG","issue":"1","license":[{"start":{"date-parts":[[2026,1,21]],"date-time":"2026-01-21T00:00:00Z","timestamp":1768953600000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["MPs"],"abstract":"<jats:p>Reversed-phase high-performance liquid chromatography (RP-HPLC) remains one of the most widely applied analytical techniques in the development and quality control testing of finished pharmaceutical products. The combination of gradient chromatographic methods with diode-array detection (DAD) enhances selectivity, ensuring accuracy and reliability when testing drugs with diverse chemical properties in a single dosage form (i.e., fixed-dose combination (FDC) products). In this study, an RP-DAD-HPLC method was developed for the quantitative analysis of clofazimine (CFZ) and pyrazinamide (PZA) for inclusion in an FDC topical drug delivery system. Chromatographic separation was achieved using a C18 column (4.6 mm \u00d7 150 mm, 5 \u00b5m particle size) with gradient elution at 1 mL\/min, employing 0.1% aqueous formic acid and acetonitrile (mobile phases). PZA and CFZ were detected at 254 nm and 284 nm, respectively. The method was validated in accordance with ICH Q2 guidelines, assessing specificity (considering interference from solvents, product matrix, and degradation products), linearity (7.8\u2013500.0 \u00b5g\/mL, r2 = 0.9999), system repeatability (%RSD \u2264 2.7%), and intermediate precision (25\u2013500 \u00b5g\/mL, %RSD \u2264 0.85%). Method robustness was evaluated using a three-level Box\u2013Behnken design (BBD) with response surface methodology (RSM) to assess the effects of variations in detection wavelength, mobile phase flow rate, and column temperature.<\/jats:p>","DOI":"10.3390\/mps9010016","type":"journal-article","created":{"date-parts":[[2026,1,21]],"date-time":"2026-01-21T11:11:17Z","timestamp":1768993877000},"page":"16","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":2,"title":["RP-DAD-HPLC Method for Quantitative Analysis of Clofazimine and Pyrazinamide for Inclusion in Fixed-Dose Combination Topical Drug Delivery System"],"prefix":"10.3390","volume":"9","author":[{"ORCID":"https:\/\/orcid.org\/0000-0003-0197-300X","authenticated-orcid":false,"given":"Marius","family":"Brits","sequence":"first","affiliation":[{"name":"Faculty of Health Sciences, Centre of Excellence for Pharmaceutical Sciences (Pharmacen<sup>TM<\/sup>), North-West University, Building G16, 11 Hoffman Street, Potchefstroom 2520, South Africa"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0009-0005-4688-6737","authenticated-orcid":false,"given":"Francelle","family":"Bouwer","sequence":"additional","affiliation":[{"name":"Faculty of Health Sciences, Centre of Excellence for Pharmaceutical Sciences (Pharmacen<sup>TM<\/sup>), North-West University, Building G16, 11 Hoffman Street, Potchefstroom 2520, South Africa"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-2489-1616","authenticated-orcid":false,"given":"Joe M.","family":"Viljoen","sequence":"additional","affiliation":[{"name":"Faculty of Health Sciences, Centre of Excellence for Pharmaceutical Sciences (Pharmacen<sup>TM<\/sup>), North-West University, Building G16, 11 Hoffman Street, Potchefstroom 2520, South Africa"}],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"1968","published-online":{"date-parts":[[2026,1,21]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","unstructured":"Rull\u00e1n, J., Seijo-Montes, R.E., Vaillant, A., and S\u00e1nchez, N.P. 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