Pharmaceutical excipients refer to the substances used in the production and formulation of medicines. They perform multiple functions in pharmaceutical preparations and are likely to affect the quality, safety and effectiveness of drugs.
Pharmaceutical excipients can be classified into natural, semi-synthetic and fully synthetic compounds according to their sources. And based on their use, excipients can be divided into diluents, binders, disintegrants (https://www.formulationbio.com/products/disintegrant-excipients.html), lubricants, glidants and anti-caking agents, wetting agents and solubilizers.
Among all varieties of excipients, how to select the most appropriate ones for a specific drug formulation project? The guidelines below should be taken into consideration.
The compatibility of the main drug and the excipients should be studied.
When screening and researching drugs with new chemical structures, attention should be paid to the investigation of the interaction between the main drug and the excipients. The excipients should have stable properties with no physiological activity, no influence on the content determination of the main drug and no adverse effect on the dissolution and absorption of the drug. According to the above principles, when we select excipients, we must first conduct research on the compatibility of the main drug and excipients. Through preliminary investigation, we can understand the excipient-to-excipient interaction and excipient-to-drug interaction, to avoid the selection of excipients with adverse interactions in prescription design.
For lack of relevant research data, compatibility studies can be conducted. For example, for solid oral preparations, several kinds of excipients can be selected at first, and then mix the main drug and excipients with a certain proportion, and put them under strong light (4500±500Lux), high temperature (60℃) and high humidity (90±5 %) conditions for 10 days, and finally use HPLC to check whether the content and related substances changed before and after placing. When necessary, the active pharmaceutical ingredients (APIs) and excipients can be used for parallel control experiments to judge whether it is the change of the API itself or the influence of the excipients. If conditions permit, experiments such as hot plate (DTA or DSC) can be used to determine whether the main drug interacts with the excipients.
The selection of excipients should be quality centric.
The choice of excipients should first consider the mechanism of action of the drug. Second, the excipients chosen should meet the characteristics and requirements of the dosage form. Third, it is a must to study the effect of the excipient’s physical and chemical properties on the preparation. Changes in the excipient’s physical and chemical properties may affect the quality of the preparation in terms of viscosity, particle size and distribution, fluidity, moisture, pH, etc. For the polymer materials used in sustained and controlled release formulations, changes in molecular weight and viscosity may have a significant impact on the release behavior of drugs. Therefore, according to the characteristics of the preparation and the route of administration of the drug, the physicochemical properties of the excipients in the prescription that may affect the quality of the preparation should be analyzed. If necessary, the corresponding quality control standards should be formulated, and attention should be paid to the selection of appropriate sources of supply to ensure the stability of the quality of excipients.
It should be noted that although some excipients pass the short-term compatibility test without problems, new degradation impurities may appear after 3-6 months of accelerated test. On the contrary, sometimes the compatibility study is first problematic, everything gets fine after adjusting the ratio. For instance, captopril (captopril) and magnesium stearate are incompatible, but the tablet with high drug content (100mg) and magnesium stearate are stable, while tablets with low drug content (2 mg) showed significant incompatibility. Therefore, the results of the compatibility test between raw materials and excipients cannot fully represent the stability under real conditions.
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