Preparation of valnemulin hydrogen fumarate and its enhanced stability compared with valnemulin hydrochloride

It is necessary to develop a new salt of valnemulin to replace the veterinary antibiotic, e.g. valnemulin hydrochloride, in order to overcome its instability during storage and preparation.

The objective of this study was to prepare a novel organic acid salt, valnemulin hydrogen fumarate, and to investigate its stability compared with valnemulin hydrochloride.

The crystal of valnemulin hydrogen fumarate was prepared by modified crystallization method; the enhanced stabilities of valnemulin hydrogen fumarate were conducted under irradiation and humid conditions, and the experimental results were simulated at AM1 level of calculations.

Valnemulin hydrogen fumarate was more stable than valnemulin hydrochloride. After irradiation for 180 days, the content of valnemulin hydrogen fumarate decreased slightly 2.7%, whereas the content of valnemulin hydrochloride had an obvious decrease of 32.8%. Meanwhile, valnemulin hydrogen fumarate showed better anti-RH (relative humidity) ability than valnemulin hydrochloride. Under conditions of 65% and 85% RH, the absorption values of valnemulin hydrogen fumarate towards water were 0.75% and 1.20% at 48 h, whereas those of valnemulin hydrochloride were 4.50% and 9.71%, respectively.

The enhanced stability of valnemulin hydrogen fumarate could be attributed to its good crystallinity in comparison with the amorphous valnemulin hydrochloride.