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Int J Pharm. 2007 Oct 1;343(1-2):131-40. Epub 2007 May 18.

Vitrification from solution in restricted space: formation and stabilization of amorphous nifedipine in a nanoporous silica xerogel carrier.

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  • 1National Institute of Chemistry, Hajdrihova 19, 1000 Ljubljana, Slovenia.

Abstract

PURPOSE:

The goal was to find thermodynamic criteria that must be satisfied in order to prevent formation of crystalline state of drugs within a confined space (e.g., nanopores of inorganic solid). Similarly, criteria that lead to stabilization of amorphous drug within such pores were investigated.

METHODS:

In the theoretical part, the classical thermodynamics of nucleation is applied to the conditions of a restricted space. The theoretical findings are verified using porous silica as a carrier and nifedipine as a model drug. The amorphicity of the latter is checked using XRD and thermal analysis (DTA, DSC) in combination with BET measurements.

RESULTS:

It is shown that there exists a critical pore radius of a host below which the entrapped substance will solidify in an amorphous form. There also exists a critical pore radius below which the entrapped amorphous solid will not be able to crystallize. Specifically, incorporation of NIF into a silica xerogel with an average pore diameter of about 2.5 nm produces and stabilizes its amorphous form.

CONCLUSION:

Entrapment of drugs into solid nanoporous carriers could be regarded as a potentially useful and simple method for production and/or stabilization of non-crystalline forms of a wide range of drugs.

PMID:
17590546
[PubMed - indexed for MEDLINE]
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