Pharmacokinetic interaction between diltiazem and nortriptyline.

OBJECTIVE

Case report of a pharmacokinetic interaction between diltiazem and nortriptyline.

METHODS

Determination of plasma nortriptyline concentrations by HPLC. Calculation of nortriptyline clearances and half-life by formulae used routinely in therapeutic drug monitoring.

RESULTS

The average plasma concentration of nortriptyline at steady state (Css) divided by the amount of nortriptyline administered per time rose significantly in a patient with concomitant administration of diltiazem, suggesting increased bioavailability and/or decreased clearance of nortriptyline.

CONCLUSIONS

There is a significant pharmacokinetic interaction between diltiazem and nortriptyline, which is probably due to a reduction in the first pass clearance of nortriptyline, leading to an increase in its bioavailability.