A meta-analysis of the serotonin1A (5-HT1A) receptor partial agonist of the azapirone class as an anxiolytic drug for the treatment of major depressive disorder (MDD) has not previously been reported.

We carried out a systematic review of the literature available in PubMed, the Cochrane Library database and PsycINFO up to 12 October 2013, and conducted a meta-analysis of randomized controlled trials (RCTs) comparing 5-HT1A agonists with placebo and RCTs of 5-HT1A agonist augmentation therapies for MDD treatment. We calculated the risk ratio (RR), number needed to treat (NNT)/number needed to harm (NNH) and 95% confidence intervals (CIs).

Fifteen RCTs comparing 5-HT1A agonists with placebo (total n = 2469, four studies with buspirone, seven with gepirone, three with ipsapirone and one with zalospirone) were identified. Pooled 5-HT1A agonists had significantly more responders (RR 0.74, 95% CI 0.65–083, p < 0.00001, NNT = 6, 12 trials, n = 1816) than placebo. Pooled 5-HT1A agonists were superior to placebo in discontinuation due to inefficacy (RR 0.49, p = 0.02, NNH = 16, p = 0.03, 10 trials, n = 1494) but were inferior to placebo in discontinuation due to side-effects (RR 1.88, p < 0.0001, NNH = 17, p = 0.001, 13 trials, n = 2196). However, all-cause discontinuation was similar in both groups (RR 0.99, p = 0.85, 14 trials, n = 2402). Four 5-HT1A agonist augmentation studies were identified (total n = 365, three buspirone studies and one tandospirone study). There were no statistically significant effects of 5-HT1A agonist augmentation therapies on response rate (RR 0.98, p = 0.85, four trials, n = 341). 5-HT1A agonist-related side-effects including gastrointestinal symptoms, dizziness, insomnia, palpitation, paresthesia and sweating were greater than with placebo (p < 0.00001 to p = 0.03).

Our results suggest that 5-HT1A agonist has a more beneficial effect on MDD than placebo, but has several side-effects.

Positron emission tomography and post-mortem studies of the number of somatodendritic 5-hydroxytryptamine1A (5-HT1A) autoreceptors in raphé nuclei have found both increases and decreases in depression. However, recent genetic studies suggest they may be increased in number and/or function. The current study examined the effect of buspirone on the electroencephalographic (EEG) centroid frequency, a putative index of somatodendritic 5-HT1A receptor functional status, in a cohort of medication-free depressed patients and controls.

A total of 15 depressed patients (nine male) and intelligence quotient (IQ)-, gender- and age-matched healthy controls had resting EEG recorded from 29 scalp electrodes prior to and 30, 60 and 90 min after oral buspirone (30 mg) administration. The effect of buspirone on somatodendritic 5-HT1A receptors was assessed by calculating the EEG centroid frequency between 6 and 10.5 Hz. The effect of buspirone on postsynaptic 5-HT1A receptors was assessed by measuring plasma growth hormone, prolactin and cortisol concentrations.

Analysis of variance revealed a significantly greater effect of buspirone on the EEG centroid frequency in patients compared with controls (F1,28 = 6.55, p = 0.016). There was no significant difference in the neuroendocrine responses between the two groups.

These findings are consistent with an increase in the functional status of somatodendritic, but not postsynaptic, 5-HT1A autoreceptors, in medication-free depressed patients in line with hypotheses based on genetic data. This increase in functional status would be hypothesized to lead to an increase in serotonergic negative feedback, and hence decreased release of 5-HT at raphé projection sites, in depressed patients.