Bayesian model of Hamilton Depression Rating Score (HDRS) with memantine augmentation in bipolar depression

Aim

Presynaptic and post-synaptic glutamatergic modulation is associated with antidepressant activity that takes several weeks to reach a maximal full effect. Limiting mood elevating effects after single drug administration may be the result of compensatory synaptic processes. Therefore, using augmentation treatment with agents having presynaptic and post-synaptic effects on the glutamatergic system, this study aims to evaluate the effect of augmentation therapy on the rate of change in mood elevation in patients with bipolar depression.

Methods

In a pilot study, 29 outpatients with bipolar depression on a stable lamotrigine dose regimen received placebo or memantine pills daily (titrated up by 5 mg week^–1 to 20 mg) in a randomized, double-blind, parallel group, 8 week study. Patients were evaluated weekly using the 17-item Hamilton Depression Rating Score (HDRS) and all data were analyzed simultaneously. Linear, exponential, maximal effect, Gompertz and inverse Bateman functions were evaluated using a Bayesian approach population pharmacodynamic model framework. In these models, differences in parameters were examined across the memantine and placebo augmentation groups.

Results

A Gompertz function with a treatment switch on the parameter describing the speed of HDRS decline (γ, 95% confidence interval [CI]) best described the data (γ_memantine = 1.8, 95% CI 0.9, 3.6), γ_placebo = 1.2, 95% CI 0.5, 3.5)). Between subject variability was identified on baseline HDRS (2.9, 95% CI 1.5, 4.4) and amplitude of score improvement (4.3, 95% CI 2.7, 6.5).

Conclusions

This pharmacodynamic approach identified an increased speed of response after memantine augmentation, compared with placebo augmentation in bipolar depression patients.