Standards of laboratory practice: antidepressant drug monitoring. National Academy of Clinical Biochemistry

Therapeutic drug monitoring (TDM) for certain tricyclic antidepressants (TCAs) and lithium is supported on the basis of clearly defined therapeutic ranges. TDM is of particular importance in individuals whose pharmacokinetic behavior may differ from that of the general population or is changing as the result of aging and maturation. Once steady-state drug concentrations are achieved, serum or plasma specimens should be collected during the terminal drug-elimination phase and separated from cellular blood components immediately. Methods of analysis must be specific for parent drug and active metabolites and demonstrate imprecision (CVs) within 5-10% over the therapeutic range. For support of overdose situations, semiquantitative values for TCAs and quantitative measures of lithium should be available within 1 h, and routine TDM results should be reported within 24 h of receipt in the laboratory. Standardized and rigorous laboratory practices contribute to improved therapeutic management.

Published by Clinical chemistry, 1998. The guideline itself is at the source linked here.

pubmed.ncbi.nlm.nih.gov/9590392/