PHARMACOKINETIC STUDIES OF BENZALAZINE

The pharmacokinetic properties of benzalazine ((2-hydroxy-5-[(4-carbox yphenyl) azo]benzoic acid, CAS 64896-26-0), a new agent for the treatm ent of ulcerative colitis and Crohn's disease of the large intestine, were investigated. From jejunal loops of rats in situ no noteworthy ab sorption of benzalazine was observed. All attempts to demonstrate meta bolic conversion of benzalazine in mucosal homogenate of the small int estine of rats were without any success. In faecal suspensions, the ha lf-life of the metabolic conversion of benzalazine was determined as 1 5 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 ad ministered 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 m etabolite 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 t he urine (2.54% and 11.06% of the administered dose, respectively).