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Protection beyond the packaging (how to keep moisture out of tablets)

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There are many factors to be considered in the quest for drug quality assurance.These include environmental moisture, stability and packaging solutions.If all of these aspects are addressed throughout the manufacturing and storage processes, the product can be isolated and protected from all possible threats to quality and efficacy.

In addressing the issue of moisture, consideration should be given to the formulation and coating of the product (i.e., capsule or table), to the transport and storage of the product from manufacturer to consumer, and to the treatment and storage of the product by the patient.There are safeguards that can be taken at each step to minimise degradation of the product by ingress of moisture.Long-term stability testing of stored material has been the subject of much research with design of primary packaging and choice of dessicants being considered the key defences against degradation and loss of efficacy.The design and composition of the drug product itself can also affect the moisture sensitivity of the final dosage form and needs to be considered from the outset.

Inside the tablet

Excipient selection and core formulation do influence the stabiliity of moisture sensitive drugs and compounds.Water can be present in formulations as a free and mobile form which can react with other materials, or in a bound form that is essentially unreactive.For example pre-gelatinized maize starch 1500 has a relatively high moisture content of 14%, as measured by loss on drying.It is, however, less reactive than other excipients with lower moisture content, e.g., mycrocrystallince cellulose or dicalcium phosphate.Many studies have shown that Starch 1500 improves product stability, and this is believed to be by the material acting as a moisture scavenger, sequestering free water that may be present in the formulation.

Film coating

The right film coating formulation can provide a functional barrier to improve the stability of moisture sensitive substances, by reducing the moisture vapour transmission rate (MTR).While conventional hydroxypropylmethyl cellulose(HPMC) based coatings do impeded the ingress of moisture when compared with a uncoated tablet, it has been shown that coatings that utilize polyvinyl alcohol (PVA) as the film-forming polymer show significantly less ingress of moisture. Opadry amb II, a high performance moisture barrier film coating and marketed by Colorcon, is the first fully formulated PVA-based immediate release system without polyethylene glycol (PEG) that delivers the three-fold advantage of high productivity, low impurity levels and a superior tablet finish. Tablets coated with Opadry amb II exhibit a high-gloss, quality appearance with well-defined logos.

Packaging

Several studies have shown that film coating may be more important than the final packaging of oral dosage forms.Colourcon, for example, assessed the degradation of three different packaging configurations:Alclar blisters, aluminium foil-foil and high density polyethylene bottles with dessicant.Clavulanic acid/amoxicillin tablets were tested and the uncoated and HPMC-coated products showed marked degradation under all packaging scenarios, whereas tablets coated with Opadry amba II showed superior stability in all packagings.Such tests affirm that film coating offers marked benefits in preventing moisture from degrading tablets.The benefits of the right film coatings become more important when consideration is given to what happens once the pharmaceutical product reaches the patient.After the dosage form has been dispensed by a pharmacist, it is not unusual for the tablets to be transferred out of their packaging to a pill sorter, or for a patient simply to place their medication into any convenient container – or even a clothing pocket.Under such circumstances, the longevity of a product is highly dependent on the formulation itself and the application of one or more protective coatings.

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