Study leaders Dr. Simon Avery and Dr. Kang-Nee Ting of the University of Nottingham in Britain and Malaysia, in collaboration with Richard Pleass now at the University of Liverpool, indicated the natural variation of a patient's levels of the amino acid, tryptophan, had a marked bearing on how they responded to quinine treatment.
It appeared the lower the levels of tryptophan, the more likely it was the patients would suffer side-effects and because tryptophan is an essential amino acid -- which the body cannot produce -- it must be gotten from food.
An earlier study of the researchers found quinine -- used in a yeast model -- could block take-up of tryptophan, causing quinine toxicity in cells.
The study, published in the Journal of Antimicrobial Chemotherapy, discovered quinine levels in patients receiving treatment for malaria were linked to the patients' levels of tryptophan. They were also able to show that the incidence of adverse reaction to quinine was significantly lower in patients with high levels of tryptophan, the study said.