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Haywood, 2013 Liquid dosage forms extemporaneously prepared from commercially available products - considering new evidence on stability.

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J Pharm Pharm Sci. 2013;16(3):441-55.
Liquid dosage forms extemporaneously prepared from commercially available products - considering new evidence on stability.
Haywood A1, Glass BD.

Abstract at http://www.ncbi.nlm.nih.gov/pubmed/24021292Free full text (PDF) at http://ejournals.library.ualberta.ca/index.php/JPPS/article/view/19411/15507 and attached to this post

Although the world's population is ageing and as a result of this an increasing number of patients are experiencing difficulty in swallowing, there remains a lack of commercially available oral liquids for both these older and paediatric patients. This presents a problem to health care professionals, especially the pharmacist in practice, who is often required to provide a solution for these patients by preparing oral liquids extemporaneously from commercially available products. Preparation of these oral liquids is challenging, both due to the lack of pharmacopoeial and stability-indicating formulae and the fact that their stability is not only determined by the active pharmaceutical ingredient, but also the ability of excipients from the commercial product to interact with each other and the active pharmaceutical ingredient. This increases the complexity of the stability considerations to be taken into account within these oral liquids, highlighting the number of parameters to be considered in the extemporaneous preparation of oral liquids. This paper presents new evidence on the stability of 42 oral liquids prepared from commercially available products, reported on in the literature since the previous review published in 2006. However, unlike the previous review where the stability concerns in 7.2% of the extemporaneously prepared oral liquids were mainly due to interaction between the active pharmaceutical ingredients and the excipients in the commercial product, most of these stability considerations have been recognised and this has resulted in the authors proposing solutions to these problems prior to the extemporaneous preparation of the oral liquid. As such this paper also focuses on the increased level of research that has been undertaken to solve previous issues related to stability, especially in terms of the use of commercial products, which is common practice in the extemporaneous preparation of oral liquids.

13_haywood_stability.pdf

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Altostrata

An earlier paper by these authors on the same subject:
 
J Pharm Pharm Sci. 2006;9(3):398-426.
Stability considerations in liquid dosage forms extemporaneously prepared from commercially available products.
Glass BD1, Haywood A.

Abstract at http://www.ncbi.nlm.nih.gov/pubmed/17207422Free full text at http://www.ualberta.ca/~csps/JPPS9_3/MS_973_Review/MS_973.html PDF http://www.ualberta.ca/~csps/JPPS9_3/MS_973_Review/M_973_Final.pdf (contains info for many benzodiazepines and a few other psychiatric drugs)

The pharmacist, both in community and hospital pharmacy practice, is often challenged with the preparation of a liquid dosage form not available commercially for paediatric patients, those adults unable to swallow tablets or capsules and patients who must receive medications via nasogastric or gastrostomy tubes. Recognising the lack of information available to healthcare professionals, a general discussion of the various parameters that may be modified in preparing these dosage forms and a tabulated summary of the dosage forms presented in the literature is described, which, although not exhaustive, will provide information on the formulation and stability of the most commonly prepared extemporaneous liquid dosage forms. An extensive survey of the literature and investigation of 83 liquid dosage forms revealed that stability considerations were of concern for only 7.2% of these liquid dosage forms, extemporaneously prepared from the following commercially available products: captopril, hydralazine hydrochloride, isoniazid, levothyroxine sodium, phenoxybenzamine hydrochloride and tetracycline hydrochloride. Inclusion of the antioxidant, sodium ascorbate in the liquid dosage form for captopril resulted in improved stability at 4 degrees C. Hydralazine hydrochloride, isoniazid and phenoxybenzamine hydrochloride were adversely affected due to interactions with excipients in the formulation, while the effect of the preservative in lowering the pH in a levothyroxine sodium mixture resulted in decreased stability. Interestingly, the instability in these formulations is primarily due to interactions between the drug substance and the excipients rather than degradation of the active pharmaceutical ingredient by standard routes such as oxidation, hydrolysis, photolysis or thermolysis. This low percentage however illustrates the low risk associated with these dosage forms investigated. It may be concluded that when considering the safety and efficacy of liquid dosage forms prepared extemporaneously, it is thus important to consider not only the stability of the drug substance but the entire formulation.

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