Tonicity Calculations: An Aid to Understanding

Isotonicity is an important requisite mainly for parenteral aqueous-based pharmaceutical preparations. In addition, ophthalmic, nasal, auricular dosage forms together with irrigations meet such a requirement. The main purpose of this report is to present an advanced informative support to a challenging subject in relation to pharmaceutical formulation. The understanding of the theoretical fundamentals professionally distinguishes the work of the pharmaceutical formulator, which in this way has la possibility to put into practice such information with more knowledge. Such a feature is of certain concern from an informative perspective when specific software or online facilities are used to solve tonicity problems.

Firstly, this paper will give a precise definition of the concepts used. Then, it will introduce the osmometry from a pathophysiological outlook, in order to set such an issue in the context of its practical implications. The necessity to achieve isotonicity will then be dealt with by illustrating the rational processes, including arithmetic calculations, involved in the production of accurate formulations. A critical presentation of the various methods of adjusting the tonicity of a solution (ΔTf, osmotic factor, Equivalent method, V-value) with the use of some simple applied examples will be reported.

Author(s): Valter Travagli

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