Research Highlight

Question of solubility

doi:10.1038/nindia.2010.148 Published online 26 October 2010

By making water-soluble nanocrystals from a common anti-diabetic herb, an Indian researcher has tried to overcome the challenge faced by most newly released pharmaceutical products — that of their solubility in water.

Water solubility increases the bioavailability of drugs when administered to humans. Earlier research revealed that more than half of the compounds developed by the pharmaceutical industry have poor water solubility.

Methods such as dissolving medical formulations in water–alcohol mixtures, making solid dispersions, changing the pH of the solutions or adding water-soluble carriers such as cyclodextrins have been traditionally used to increase solubility. Alternatively, the particle size of poorly soluble drugs is sometimes reduced to increase their in vivo performance.

Ramaswamy Ravichandran from the Regional Institute of Education in Bhopal has now shown that acids derived from the herb Gymnema sylvestre — a native of the tropical forests of southern and central India — can be converted to nano-sized crystals that have increased solubility in water. Gymnemic acids have established anti-diabetic, anti-sweetener and anti-inflammatory properties, but their bioavailability in drug form was questionable.

Freeze-dried gymnemic acid nanocrystals dissolved almost completely within 15 minutes in water and in buffers of pH 1.2 and 6.8. In contrast, the raw gymnemic acid powder did not dissolve beyond 81%. Physiological tests showed that the nanocrystals provided increased dissolution velocity, enhanced kinetic solubility in water and improved physical stability.

Oral doses of dried gymnemic acid nanocrystals could have improved oral bioavailability, according to Ravichandran. The research could help to increase the bioavailability of other crucial drugs facing similar solubility issues.


  1. Ravichandran, R. Physico-chemical evaluation of gymnemic acids nanocrystals. Int. J. Nanoparticles. 3, 280-296 (2010) | Article