Conjugation Reactions in the Newborn Infant: The Metabolism of Para-aminobenzoic Acid

Abstract

The metabolism of p-aminobenzoic acid (PAB) was studied by Injecting a dose of lOOmg/kg of the Na salt into 3 newborn premature infants, 2 full-term newborns, 2 infants 5 and 8 weeks old, and 4 children 8 1/2 to 11 years old. In the children PAB iSTrapidly cleared from the serum, chiefly by formation of p-aminohippuric acid (PAH). The 24-hour recovery in the urine lies between 76 and 93% of which 68 to 85% are excreted within the first 4 hours. The chief conjugate in the urine is PAH, which accounts for nearly half of the total. Other metabolites are acetyl-PAB, free PAB, acetyl-PAH, PAB- and acetyl-PAB-glucuronides. In the newborn infants PAB is eliminated tardily from the circulation. The main conjugate formed is acetyl-PAB. PAH, acetyl-PAH, and free PAB are other metabolic products. The excretion in the urine is also delayed so that only about 10% of the given dose appears within the first 4 hours. The 24-hour recovery amounts to between 48 and 70%. Again the major metabolite is acetylated PAB with acetyl- PAH, PAH, and free PAB following in decreasing order. Glucuronides account for only about 7%, acetamidobenzoyl glucuronide prevailing over p-aminobenzoyl glucuronide. As the 2 older infants show, the transition from the pattern in the newborn period to that in children takes place around the 8th week of life.