Viscosity and consistence measurements following Ph.B. 2009

Summary

A good knowledge of rheological properties is important for quality and stability assessment of medicines, making-up, and the study of drug release or the choice of a suitable homogenizer. Viscosity is the most often measured quantity. Apparent viscosity of chosen polymeric excipients used in pharmacy particularly as thickeners, stabilizing agents and drug carriers was measured (Methylcellulosum, Hypromellosum, Cellacefatum, Xanthani gummi, Carbomera) and also consistency of semisolids (Vaselinum album, Vaselinum flavum, Adeps lanae, Alcoholum adipis lanae unguentum, Alcoholum adipis lanae cremor, Acoholis cetylici unguentum, Alcoholis ceylici cremor). An effort was made to proceed strictly according to the Ph. B. 2009 with a goal to evaluate critically the pharmacopoeial requirements concerning rheological assessments. The pharmacopoeial texts are not very homogeneous probably due to their different authorship. There are formulations which make compounding, measurement or evaluation difficult or impossible. Most often the inaccuracies are due to incorrect translation of the English original. The methods taking into account the specific properties of polymers should be more applied to compounding. The measurement conditions should be prescribed unambiguously and uniformly. Then the statement of procedure according to the pharmacopoeia will not be controversial.

Key words:
viscosity – apparent viscosity – consistency – viscometers – penetrometers