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Multi-unit tablets consist of coated subunits which are embedded in an excipients mixture. As subunits various kinds of particles with defined less-porous surface and a shape being suitable for coating processes are feasible. The functional coating usually being applied in a fluid bed coating process (click here to get more information) provides each subunit with the characteristic desired drug release properties. Very specific release profiles can be generated by changing the composure of the tablet – either equally or by combining different kinds of particles. Also dose strengths can be adapted easily. One possibility is to develop different dose strengths by varying the tablet size keeping the composition the same - no additional development efforts need to be taken. Another option for dose strength variation is the development of dividable multi-unit tablets. Since the release characteristics are related to the single subunits, dividing the tablet does not affect the release characteristics as it is true for monolithic tablets. All these reasons support multi-unit tablets as the preferred type particularly for controlled release dosage forms.
But there are also some challenges with regard to multiparticulate formulations. The main challenges for multiparticulate tablet manufacturing are:
Uniformity of drug content and tablet weight is mainly based on well flowable tabletting mixtures with narrow particle size distribution preventing demixing effects. In case of big sized coated particles size adaptation of the outer phase may be considered which can be managed by granulation. In order to ensure undamaged film coatings and thus reproducible drug release after tablet compression, various impact factors need to be considered.
Different subunits are suitable for multiparticulate sustained release formulations. The critical properties are as follows:
The following table gives an overview of different subunits and their adequacy for particle coating as well as tablet compression:
In general, sustained release dosage forms deliver the active ingredient over up to 24 hours. The objective is to achieve a longer-lasting therapeutic effect with a medication having fewer side effects and a reduced dosing frequency. These factors improve patient compliance and a safe administration of the medication, making the therapy more successful, especially for long term regimens. With sustained release dosage forms, the phase that determines the rate is the precisely controlled drug release, not the absorption phase. Preferably the active is absorbed as soon as it is released. In many cases, a zero order release profile is desired, to keep blood plasma levels as balanced as possible. In cases where a rapid increase of plasma level is desired, the drug is preferably separated into immediate and maintenance doses.
The reduced dosing frequency of sustained release dosage forms is generally accompanied by an increase of the single dosage of the drug. As a result, formulators need to consider more carefully drug safety and to limit the risk of dose-dumping. Special considerations of the active’s physical and chemical properties become more significant in the context of the development of sustained release dosage forms than with immediate release formulations. Sustained release preparations are an advantageous way to treat any indication, e.g. cardiovascular diseases, pain management and diseases of the central nervous system.
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