Effects of the postpartum period on nortriptyline pharmacokinetics

The objective of this research was to investigate sequential serum levels and level/dose ratios of the tricyclic antidepressant nortriptyline (NTP) through the first 17 postpartum weeks. The initial NTP dose was given immediately postpartum to 16 mothers and increased gradually to 70 mg over the first week. A dose of 75 mg was prescribed until adjustment according to serum levels. Serum levels of NTP and its metabolites Z- and E-OH-NTP were determined. At postpartum Week 2, the women developed a mean level/dose (L/D) ratio for NTP of 1.11 (range 0.37 to 3.23), and subsequently experienced an increase in the L/D ratios which continued through Week 6. At Week 8, the NTP L/D ratios declined, and became relatively stable at Week 11 and beyond. For postpartum women treated with NTP, side effect profiles should be carefully followed during the first 6 weeks after delivery as a clinical marker for elevation of serum levels. Since our highest L/D ratios for NTP occurred at Week 6, a serum level is recommended at this time. If the dose needs to be lowered to maintain a nontoxic level, a repeat serum level should be obtained at Week 11, at which time an increase in dose may be required.