Remdesivir (RDV) is the first antiviral drug, approved by the Food and Drug Administration, to treat severe acute respiratory syndrome coronavirus 2. RDV is a relatively new chemical entity, 'ester prodrug', with no reported stability profile.Due to the urgency of its use and thus fast production, it is important to develop a stability-indicating method for its assay. Chromatographic separation was carried out on a C18 column (250 Â 4.6 mm, 5 μm) with dual detection: diode array at 240 nm and fluorescence at λ ex/em 245/390 nm. Isocratic elution of acetonitrile and distilled water (acidified with phosphoric acid, pH 4) in the ratio of 55:45 (v/v), respectively, was used. The linearity range using HPLC-diode array detection was 0.1-15 μg/mL, whereas that using fluorimetric detection was 0.05-15 μg/mL. As per the International Conference on Harmonization guidelines, RDV has been degraded by accelerated alkaline, acidic, neutral hydrolysis, oxidative, heat, and photolytic stress conditions. Possible degradation hypothesis of the parent molecule has been suggested and illustrated. The proposed methods have achieved selective determination of the intact drug with no peaks overlapping in all assumptions. Extensive degradation confirms threatened drug stability at thermal and basic hydrolytic stressing. The developed methods were fully validated and proved suitable for quality control routine analysis of RDV in raw material and pharmaceutical dosage forms.

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A validated and highly selective high-performance thin-layer chromatography (HPTLC) method was developed for the determination of ketorolac tromethamine (KTC) with phenylephrine hydrochloride (PHE) (Mixture 1) and with febuxostat (FBX) (Mixture 2) in bulk drug and in combined dosage forms. The proposed method was based on HPTLC separation of the drugs followed by densitometric measurements of their spots at 273 and 320 nm for Mixtures 1 and 2, respectively. The separation was carried out on Merck HPTLC aluminum sheets of silica gel 60 F254 using chloroform-methanol-ammonia (7:3:0.1, v/v) and (7.5:2.5:0.1, v/v) as mobile phase for KTC/PHE and KTC/FBX mixtures, respectively. Linear regression lines were obtained over the concentration ranges 0.20-0.60 and 0.60-1.95 µg band(-1)for KTC and PHE (Mixture 1), respectively, and 0.10-1.00 and 0.25-2.50 µg band(-1) for KTC and FBX (Mixture 2), respectively, with correlation coefficients higher than 0.999. The method was successfully applied to the analysis of the two drugs in their synthetic mixtures and in their dosage forms. The mean percentage recoveries were in the range of 98-102%, and the RSD did not exceed 2%. The method was validated according to ICH guidelines and showed good performances in terms of linearity, sensitivity, precision, accuracy and stability.

The widespread coronavirus 2019 (COVID-19) pandemic, attributed to the severe acute respiratory syndrome coronavirus-2, has resulted in global lockdowns and excess mortality. Remdesivir (RM) is the first and only antiviral drug that the US Food and Drug Administration (FDA) has approved so far for COVID-19. The treatment protocol involves multidrug combinations, basically depending on RM, in addition to antimicrobials, antipyretics, corticosteroids, and anticoagulants. This study develops and validates sensitive and selective RM screening in spiked human plasma in the presence of commonly co-administered drugs. Hydroxychloroquine, azithromycin, paracetamol, dexamethasone, and anticoagulants (rivaroxaban and edoxaban) have been detected simultaneously with RM in the same biological matrix. Separation has been efficiently achieved by simple reversed phase HPLC with dual detectors. Diode array detector and fluorimetric detection have been used to compare their sensitivity and selectivity. Both assays have been validated according to bioanalytical FDA validation parameters. Chromatographic separation and quantitation of RM along with concomitant drugs instantly bioscreen COVID-19 multiple therapy medication in 10 min run time. Furthermore, the proposed in vitro study takes the lead for prospective testing of possible drug–drug interactions that alter the pharmacokinetic profiles of drugs.

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