Biochemical and diagnostic classification and serum drug levels: relation to antidepressive effect of imipramine

The relationship between clinical effect of imipramine (IP) in 39 depressed patients and biochemical distinction, serum drug levels, and diagnostic classification was investigated retrospectively. Based on pretreatment plasma ratios of tryptophan and tyrosine to competing amino acids, which reflect the availability of the precursor amino acids to the brain, the patient sample was separated in two halfparts. The one group with low net availability of tryptophan and tyrosine improved significantly more than the other group with comparable mean serum drug levels. In the former group there was no association between clinical improvement and serum drug levels, whereas in the latter group the patients with serum IP plus desipramine (DMI) above 180 ng/ml improved significantly more than patients with lower levels. There was an indication that a serum ratio of IP:DMI below 0.2 was associated with a poor response. Patients classified as nonendogenous depressives by means of the Newcastle II scale showed about the same response pattern as endogenous depressives with comparable plasma amino acid profiles and serum drug levels. Based on amino acid patterns and serum drug levels only half of the patients received an optimal therapy on the applied schematic dosage schedule. Thus, biochemical classification rather than diagnostic may be a useful remedy for the adjustment of serum IP plus DMI to appropriate levels in individual depressives.