Systematic evaluation of the 'efficacy-effectiveness gap' in the treatment of depression with venlafaxine and duloxetine

Psychopharmacological properties and therapeutic profile of the antidepressant venlafaxine

Major depression (MD) is one of the most common psychiatric disorders worldwide. Currently, the first-line treatment for MD targets the serotonin system but these drugs, notably the selective serotonin reuptake inhibitors, usually need 4 to 6 weeks before the benefit is felt and a significant proportion of patients shows an unsatisfactory response. Numerous treatments have been developed to circumvent these issues as venlafaxine, a mixed serotonin-norepinephrine reuptake inhibitor that binds and blocks both the SERT and NET transporters. Despite this pharmacological profile, it is difficult to have a valuable insight into its ability to produce more robust efficacy than single-acting agents. In this review, we provide an in-depth characterization of the pharmacological properties of venlafaxine from in vitro data to preclinical and clinical efficacy in depressed patients and animal models of depression to propose an indirect comparison with the most common antidepressants. Preclinical studies show that the antidepressant effect of venlafaxine is often associated with an enhancement of serotonergic neurotransmission at low doses. High doses of venlafaxine, which elicit a concomitant increase in 5-HT and NE tone, is associated with changes in different forms of plasticity in discrete brain areas. In particular, the hippocampus appears to play a crucial role in venlafaxine-mediated antidepressant effects notably by regulating processes such as adult hippocampal neurogenesis or the excitatory/inhibitory balance. Overall, depending on the dose used, venlafaxine shows a high efficacy on depressive-like symptoms in relevant animal models but to the same extent as common antidepressants. However, these data are counterbalanced by a lower tolerance. In conclusion, venlafaxine appears to be one of the most effective treatments for treatment of major depression. Still, direct comparative studies are warranted to provide definitive conclusions about its superiority.

Antidepressant treatment effects and country income: meta-regression analysis of individual participant data from duloxetine trials

OBJECTIVE

In recent decades, significant numbers of pharmaceutical trials have gradually been relocated to low- and middle-income countries. However, there is little evidence regarding the transferability of trial outcomes across countries. Analysing duloxetine randomised controlled trials (RCTs) conducted in different countries, we investigated whether per capita gross national income (GNI) and healthcare expenditure (HE) are associated with pre-post mean changes of depression severity and differences in duloxetine-placebo effect sizes.

METHOD

Meta-analyses included RCTs investigating duloxetine efficacy in patients with depression. Individual participant data (IPD) from multi-centre duloxetine trials were provided by the manufacturer. Data extracted from published reports also entered analyses in case of trials conducted in only one country. A meta-regression approach was applied to analyse associations of GNI and HE with standardised pre-post mean change using raw score standardisation (SMCR) and comparative effect size, that is, the mean differences (MD) in pre-post effect size between duloxetine and placebo treatment.

RESULTS

23 trials with 8417 randomised participants entered analyses. Regression coefficients indicated a negative linear relationship of SMCR with GNI (z-standardised β = -3.61, R²  = 14.8%, p < 0.001) and HE (β = -4.72, R²  = 24.8%, p < 0.001) for participants treated with duloxetine. Similar associations were found for placebo treatment (GNI: β = -3.52, R²  = 23.8%, p < 0.001; β = -3.34, R²  = 21.0% p < 0.001). Neither GNI nor HE was associated with the MD between duloxetine and placebo pre-post differences.

CONCLUSIONS

Findings challenge the idea of the universal transferability of antidepressant trial outcomes across countries. Understanding the results of antidepressant RCTs demands more sophisticated clarification of context factors involved in determining effectiveness of antidepressant medication and should be discussed with a view to socio-economic context in their countries of origin.