The metabolism of phenothiazine in the neonatal calf: identification of drug-polypeptide conjugates from urine.

The presence of a polypeptide conjugate fraction in the urine of young calves after oral dosing with phenothiazine has been confirmed. Four different polypeptide conjugates, containing up to six amino acids attached to phenothiazine or leucophenothiazone via the carboxyl terminal of the chain, have been isolated, characterized and sequenced. In addition, several minor polypeptide conjugates have been observed. The literature pertaining to polypeptide conjugates of drugs has been reviewed and the importance of this metabolic route in neonatal animals discussed.