The pharmacokinetic properties of
benzalazine ((2-hydroxy-5-[(4-carboxyphenyl)azo]
benzoic acid, CAS 64896-26-0), a new agent for the treatment of
ulcerative colitis and
Crohn's disease of the large intestine, were investigated. From jejunal loops of rats in situ no noteworthy absorption of
benzalazine was observed. All attempts to demonstrate metabolic conversion of
benzalazine in mucosal homogenate of the small intestine of rats were without any success. In faecal
suspensions, the half-life of the metabolic conversion of
benzalazine was determined as 15 min and the formation of the metabolite
5-aminosalicylic acid (5-ASA) was demonstrated qualitatively. 72 h after single
oral administration of 300 mg
benzalazine/kg b.w. to rats, an average of 71.83% of the administered dose was recovered in urine and faeces. Only a small amount of unmetabolized
benzalazine was excreted with urine and faeces (0.75% and 1.47% of the administered dose, respectively). The
benzalazine metabolite 5-ASA and the 5-ASA metabolite acetyl-
5-aminosalicylic acid (Ac-5-ASA) were excreted mainly with the faeces (29.22% and 20.66% of the administered dose, respectively) and only in small amounts with the urine (2.54% and 11.06% of the administered dose, respectively).