Prediction of steady-state plasma concentrations and individual dosage regimens of tricyclic antidepressants from a single test dose

Drug dose prediction with flexible test doses

This article presents the first known practical method to apply one-compartment pharmacokinetic modeling to prediction of doses for drugs from one or more blood-drug concentrations, without requiring approximations or a computer. It should be useful for regulating doses of orally administered CNS drugs whose effects develop over a day or more, e.g., lithium, antidepressants, and anticonvulsants. Pharmacokinetic calculations for sequences of one, two, and three test doses are condensed into graphs that can be rapidly applied for clinical purposes. These graphs account for dose division, blood sampling time, and drug elimination rate; they show that the ratio of the steady-state day-mean drug level to the test-drug blood level is independent of the half-life if the test level is about a day after the last test dose. The calculations show the same value as experimental measurements for the ratio between steady-state serum lithium level and serum lithium level measured after a test dose. A rational strategy for drug-loading doses is discussed.

Tricyclic antidepressants: contemporary issues for therapeutic practice

The clinical pharmacology of tricyclic antidepressants is reviewed, with an emphasis on recent findings. These medications have become the treatment of choice for the majority of depressed patients. Their efficacy is limited by lack of vigor and precision in dosage. Pharmacokinetic aspects are addressed which affect the rationale for selective use and interpretation of plasma concentration monitoring. These include nonlinearity, active metabolites, plasma protein binding and age effects. Specific indications for therapeutic drug monitoring occur with patients who fail to respond, those at risk because of age, medical condition or polypharmacy, and to check compliance. Integration of knowledge concerning pharmacokinetics and plasma levels with clinical response will aid in making appropriate pharmacotherapeutic decisions.

Correction of blood drug levels for changes over the day

A graph-based method is presented to compensate for the influence of variations in drug dosage schedules and blood sampling times upon the blood concentrations of drugs whose elimination half-life is between 7 and 48 hours. This method permits the clinician to interpret blood drug levels drawn at nonstandard times, and to correct blood drug levels for how the daily dose was divided. This method is expected to improve the convenience of monitoring blood drug levels.

Serum concentration of depot neuroleptics in tardive dyskinesia

Using radioimmunoassay techniques, serum levels of depot neuroleptics, fluphenazine and flupenthixol, were estimated in two groups of chronic schizophrenic patients with, and without, tardive dyskinesia. There were high significant difference in dose-related serum levels of either drug between the groups. The hypothesis that patients with tardive dyskinesia develop the syndrome because they do not metabolise neuroleptics as efficiently as those without the syndrome was not supported by the data.