Comparison of pharmacokinetic procedures for dosing lithium based on analysis of prediction error

Population Pharmacokinetic Analyses of Lithium: A Systematic Review

BACKGROUND AND OBJECTIVES

Even though lithium has been used for the treatment of bipolar disorder for several decades, its toxicities are still being reported. The major limitation in the use of lithium is its narrow therapeutic window. Several methods have been proposed to predict lithium doses essential to attain therapeutic levels. One of the methods used to guide lithium therapy is population pharmacokinetic approach which accounts for inter- and intra-individual variability in predicting lithium doses. Several population pharmacokinetic studies of lithium have been conducted. The objective of this review is to provide information on population pharmacokinetics of lithium focusing on nonlinear mixed effect modeling approach and to summarize significant factors affecting lithium pharmacokinetics.

METHODS

A literature search was conducted from PubMed database from inception to December, 2016. Studies conducted in humans, using lithium as a study drug, providing population pharmacokinetic analyses of lithium by means of nonlinear mixed effect modeling, were included in this review.

RESULTS

Twenty-four articles were identified from the database. Seventeen articles were excluded based on the inclusion and exclusion criteria. A total of seven articles were included in this review. Of these, only one study reported a combined population pharmacokinetic-pharmacodynamic model of lithium. Lithium pharmacokinetics were explained using both one- and two-compartment models. The significant predictors of lithium clearance identified in most studies were renal function and body size. One study reported a significant effect of age on lithium clearance. The typical values of lithium clearance ranged from 0.41 to 9.39 L/h. The magnitude of inter-individual variability on lithium clearance ranged from 12.7 to 25.1%. Only two studies evaluated the models using external data sets.

CONCLUSIONS

Model methodologies in each study are summarized and discussed in this review. For future perspective, a population pharmacokinetic-pharmacodynamic study of lithium is recommended. Moreover, external validation of previously published models should be performed.

How to initiate lithium therapy: a systematic review of dose estimation and level prediction methods

BACKGROUND

Throughout the past decades, several methods have been developed to achieve therapeutic lithium blood levels as quick and safe as possible. The present study will systematically review the methods developed and studied for lithium dose estimation or level prediction at the initiation of therapy.

METHODS

A systematic computerized Medline search was performed for papers published in English, French or Dutch between 1966 and April 2012 describing or studying methods for dosing lithium or predicting the lithium level on a certain dosage. References of relevant articles were screened for additional papers.

RESULTS

Of 273 unique references retrieved, 65 met the inclusion criteria. Apart from the empirical titration method, 38 predictive methods for initiating lithium were identified. These methods can be classified into two categories: the a priori predictive methods, and the test-dose predictive methods requiring the administration of a test dose of lithium prior to starting treatment.

LIMITATIONS

The methodological strength was not taken into account for a study to be included in the review.

CONCLUSIONS

The most important distinction between the empirical titration method and the predictive methods appears to be the shorter time the latter need to achieve the targeted lithium level. The vast majority of predictive methods, however, show inconsistent or poor results or have not been replicated since their initial description. The empirical titration method, although not extensively studied, appears to be a time-honored method that can be recommended for use in daily clinical practice.

A review of lithium dosing methods

Lithium's narrow therapeutic range, concentration-effect relationship, and large differences in interindividual disposition make it an attractive candidate for predictive dosing methods. Lithium disposition is influenced by a number of factors, including patient characteristics, renal function, and concomitant drug therapies. These factors are accounted for, in varied degrees, in the different dosing methods available. One a priori method takes many of these factors into account and appears to have better reliability than others that ignore nonrenal influences on lithium disposition. The lack of data on pharmacokinetic values in different populations limits the usefulness of many of the single-point methods. Better data on the disposition of lithium in differing populations would greatly enhance the utility of both the a priori and single-point methods. Several multipoint methods, which estimate an individual's pharmacokinetic values, have also been described. These appear to be the most reliable, although they are time consuming and may delay the initiation of therapy. A well-designed Bayesian approach to the dosing of lithium, although not currently available, would be the most useful.