Investigation of the urinary excretion of pethidine and five of its metabolites in man using selected ion monitoring

The urinary excretion in man of pethidine and five of its metabolites (norpethidine, pethidinic acid, norpethidinic acid, p-hydroxypethidine and pethidine N-oxide) after a single intramuscular dose has been investigated using analytical procedures based on selected ion monitoring. New methods for the determination of p-hydroxypethidine and pethidine N-oxide have been developed, and the selectivity and sensitivity of the procedures are discussed. Only some 5% of the administered dose was excreted as unchanged pethidine. The mean urinary excretion of norpethidine was 16.4%. Pethidinic acid and norpethidinic acid constituted the major fraction of the dose excreted in urine. The total excretion of pethidinic acid and norpethidinic acid was 41.7 and 23.2%, respectively. Pethidine N-oxide constituted less than 0.5% of the excreted amount, and p-hydroxypethidine could only be detected in the urine of two of the patients. A mean total recovery of about 90% of the dose was found in urine as pethidine and the five metabolites.