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Tuberculosis (TB) is believed to affect around 10 million people worldwide. Treatment for TB includes isoniazid and rifampicin, with fixed-dose combination (FDC) recommended for improved patient compliance. Similarly, orally disintegrating tablets (ODTs) are an increasingly popular dosage form that aid compliance since they do not require swallowing. In this study ODTs of isoniazid and rifampicin, either as discrete or FDC doses, were formulated and bioequivalence between single and combination doses compared using in vitro and in silico approaches. Dissolution profiles were compared using FDA advised difference (f1) and similarity (f2) testing in biorelevant media. Rifampicin release from FDCs decreased by approximately 15% in fed-state media (failed f1 and f2), which was attributed to enhanced rifampicin degradation in the presence of isoniazid at lower pH. Apparent permeability (Papp) values derived from Caco-2 transport studies were included alongside dissolution results into a physiologically based pharmacokinetic (PBPK) model, to simulate in vivo bioavailability in healthy subjects. Models showed no difference in bioavailability between formulations or dosing (fasted or fed) state, despite the failures in dissolution-based bioequivalence testing, highlighting shortcomings in f1 and f2 assessment and the strength of PBPK models.

The successful development of compressed ODTs utilises low compression forces to create a porous structure whereby excipients are added to enhance wicking/swelling action or provide strength to the fragile tablet framework. In this work, a systematic investigation comparing materials from two different categories was employed to understand their functionality in binary mixture tablets of the most commonly used diluent mannitol. Cellulose based excipients such as HPC (SSL-SFP), L-HPC (NBD-022) and MCC (Avicel PH-102) were compared with non-cellulosic materials such as PEO (POLYOX WSR N-10) and Crospovidone (XL-10). Pure excipient properties were studied using Heckel Plot, compressibility profile, SEM and XRPD, whereas the prepared binary mixture compacts were studied for hardness, disintegration time and friability. Results from our investigation provide insight into differences encountered in product performance of ODT upon inclusion of additional materials. For example, non-cellulosic excipients Polyox and Crospovidone showed higher plasticity (Py values 588 and 450MPa) in pure form but not in binary mixtures of mannitol. Cellulosic excipients, nonetheless, offer faster disintegration (30 sec) specifically L-HPC and MCC tablets. Disintegration time for tablets with fully substituted-HPC was prolonged (200-500 sec) upon increasing concentration between 1-10% due to gelation/ matrix formation. It can be concluded that despite the reasonably good plasticity of both cellulosic and noncellulosic excipients in pure form, the mechanical strength in binary mixtures is negatively impacted by the fragmentation/ fracture effect of mannitol.

HPLC methods for insulin in official monographs require extended runtimes and elevated temperatures. Inter-laboratory reproducibility of HPLC methods obtained from published literature is an on-going challenge, moreso for peptides. This paper serves as a step-by step guide to troubleshoot and establish a validated HPLC method for insulin at room temperature using simple UV detectors with minimal run times. A modified gradient reversed-phase HPLC was developed for the quantification of recombinant human insulin with UV detection at room temperature. An octadecylsilica column was used as the stationary phase while the mobile phase consisted of solution A: 1mmol sodium sulphate and 0.2% triethylamine in water and solution B: acetonitrile. The developed method was then validated using International Conference on Harmonisation (ICH) guidelines. The calibration curve was linear over a concentration range of 10-1000 µg/mL with correlation coefficient of 0.9993, with average recovery percent of 100.89 ± 1.4% and RSD recovery of 0.01. Insulin retention time was 3.84 ± 0.08 mins, while LOD and LOQ were estimated at 0.63 and 2.0 µg/mL respectively. The developed method conformed to the validation criteria of the ICH guidelines in our laboratories and other independent operator laboratories, and can serve as a rapid and effective method for quantifying insulin from any sample at room temperature using simple detectors.