Safety, efficacy, quality, and stability are the main characteristics of any medicine. To achieve these properties, a thorough knowledge of the physico-chemical properties of the active pharmaceutical ingredient (API) and the individual excipients which form a formulation is required. Although most excipients are pharmacologically inert, they can form chemical and physical interactions with API under different environmental conditions. Potential physical and chemical interactions may affect chemical nature, stability and bioavailability of API and consequently the safety, quality and efficacy of the finished dosage form. Early identification of (in)compatibilities between individual components is therefore one of the main steps in the development of a new pharmaceutical form. During the master's thesis, the physico-chemical compatibility of ibuprofen and paracetamol, the two most commonly used analgesics and antipyretics and individual excipients (fillers, binders, aromas that form granules) for filling into straws was evaluated. The delivery system is primarily intended for pediatric and geriatric patients who experience difficulty swallowing when taking oral medications. In the first phase, we prepared physical mixtures of API and individual excipient in a ratio of 1:1. Differential scanning calorimetry (DSC), known as a rapid method for ascertaining physico-chemical interactions between two components and determining the thermal stability of API, was used to evaluate compatibility. DSC curves of pure API, excipients and physical mixtures were recorded at the time of the preparation. We were mainly interested in the interaction of API (paracetamol or ibuprofen) with an excipient, which is the primary coating in a finished dosage form and is in direct contact with API. Paracetamol crystals in finished dosage form are coated with two coatings. The purpose of the primary coating is to mask the unpleasant taste, and the secondary coating is to facilitate the emptying of the dose out of the straw. Polymer Eudragit® E PO is used as the primary coating and polymer Kollicoat® IR as the secondary coating. In case of ibuprofen granules, the coating is only primary, to mask the unpleasant taste where polymer Eudragit® RL is used. In addition to testing in closed vials at 40 °C and 75 % relative humidity (RH), the mixtures of API and excipient, used as a coating in finished drug were also tested in open vials at 40 °C, 75% RH, and in closed vials at 50 °C. In order to identify potential interactions between components, we compared the DSC curves of individual pure components with DSC curves of prepared mixtures, at the initial time, at the time of preparation of physical mixtures, and after one month of aging. The change in melting point and melting enthalpy of individual substances in the mixture with comparison to pure substances were monitored. We have determined that interactions occur in many physical mixtures, which is inferred from a shift in melting temperature, a change in melting enthalpy, or the disappearance of an endothermic event. No interactions were detected in physical mixtures of paracetamol and talc, erythritol and maltitol. DSC analysis of the physical mixtures of ibuprofen and individual PS showed no interaction between ibuprofen and talc, iron oxide and erythritol. Additional chemical analyzes should be performed to confirm interactions and determine compatibility.
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