Metabolism of drugs. XVI. The metabolic fate of methylhexabital (5-cyclohexenyl-3,5-dimethylbarbituric acid). 6. Studies on the reduction of 3-keto-MHB (5-(3-oxo-1-cyclohexenyl)-3,5-dimethylbarbituric acid) and on pharmacological activity of the biotransformation products of methylhexabital from the urine of rabbits.