Effect of anxiolytic drug silexan on sleep - a narrative review

OBJECTIVES

Silexan is an orally administered, proprietary essential oil from Lavandula angustifolia with significant anxiolytic and sleep improving properties. Here we present a narrative review that provides an overview of the available evidence of the effects of silexan on sleep.

METHODS

We start with a summary of the pharmacological background and continue with presenting sleep-related results from controlled clinical trials with silexan. Then we report on a meta-analysis of item 'insomnia' from the Hamilton Anxiety Scale, which includes data from all randomised, placebo-controlled clinical trials with silexan in which the scale was administered. Finally, we summarise the results of a mediation analysis that was performed to elucidate the pathway of the effect of silexan on sleep.

RESULTS

In randomised, placebo-controlled trials in patients suffering from anxiety disorders silexan had a significant anxiolytic effect and improved sleep along with recovery from anxiety. Mediation analysis demonstrates that more than 98% of the effect of silexan on sleep was mediated by its anxiolytic effect while the direct effect on sleep was marginal.

CONCLUSIONS

Silexan improves sleep as a result of its anxiolytic effect.

Silexan does not affect driving performance after single and multiple dose applications: Results from a double-blind, placebo and reference-controlled study in healthy volunteers

Anxiolytic drugs often have sedative effects that impair the ability to drive. Our double-blind, randomized crossover trial investigated the effect of Silexan, a non-sedating, anxiolytic herbal medicinal product, on driving performance in healthy volunteers. Part 1 aimed at demonstrating equivalence between 80 mg/d Silexan and placebo. Part 2 was performed to demonstrate superiority of 160 and 320 mg Silexan over 1 mg lorazepam and included a placebo arm for assay sensitivity. Driving performance was assessed in a validated, alcohol-calibrated simulator test. The primary outcome was the standard deviation of the lane position (SDLP). Secondary outcomes included driving errors and sleepiness. Fifty and 25 subjects were randomized in Parts 1 and 2, respectively. In Part 1, Silexan 80 mg was confirmed to be equivalent to placebo after single administration (equivalence range: δ = ±2 cm). The 95% confidence interval (CI) for the SDLP marginal mean value difference Silexan-placebo for single administration was -1.43; +1.38 and thus similar to the 95% CI of -1.45; +0.79 cm for 7 days' multiple dosing. In Part 2, 95% CIs for SDLP marginal mean value differences to lorazepam were -8.58; -5.42 cm for Silexan 160 mg and -8.65; -5.45 cm for 320 mg (p < 0.001). Confirmatory results were supported by secondary outcomes, where results for Silexan were comparable to placebo and more favorable than for lorazepam. The study demonstrates that single doses of up to 320 mg Silexan and multiple doses of 80 mg/d have no adverse effect on driving performance.

Pharmacological basis of the anxiolytic and antidepressant properties of Silexan®, an essential oil from the flowers of lavender

Silexan®, a proprietary essential oil manufactured by steam distillation from Lavandula angustifolia flowers showed pronounced anxiolytic effects in patients with subthreshold anxiety disorders and was also efficacious in patients with Generalized Anxiety disorder (GAD). Moreover, evidences for antidepressant-like properties of Silexan® have been observed in anxious patients suffering from comorbid depressive symptoms and in patients with mixed anxiety-depression disorder (ICD-10 F41.2). In accordance with the clinical data Silexan® is active in several behavioral models in rodents at rather low concentrations indicating potent anxiolytic and antidepressive properties. As possible mechanism of action a moderate inhibition of voltage dependent calcium channels (VDCC) has been found showing some similarities to the anxiolytic drug pregabalin. However, while pregabalin mainly inhibits P/Q-type channels by binding to a modulatory subunit, Silexan® moderately inhibits mainly T-type and N-type channels and to some extent P/Q-type channels. Unlike pregabalin Silexan® is free of hypnotic or sedative side effects and seems to be devoid of any abuse potential. With respect to its specific antidepressant like properties Silexan® improves several aspects of neuroplasticity which seems to be the common final pathway of all antidepressant drugs. As a potential mechanism of its effects on neuroplasticity an activation of the transcription factor CREB via activation of intracellular signaling kinases like PKA and MAPK has been found. Since the concentrations of Silexan® needed to inhibit VDCC function and to improve neuroplasticity are quite similar, the effects of Silexan® on PKA or MAPK could constitute a common intracellular signaling cascade leading to VDCC modulation as well as CREB activation and improved neuroplasticity.

Efficacy of Silexan in subthreshold anxiety: meta-analysis of randomised, placebo-controlled trials

Subthreshold psychiatric disorders do not fully meet the diagnostic criteria of syndromal disorders but may be associated with comparable disability. To investigate the anxiolytic effect of Silexan, an active substance from lavender oil for oral administration, in patients with subthreshold anxiety, a meta-analysis that included all published trials with Silexan in this indication was performed. Three randomised, placebo-controlled trials in subthreshold anxiety disorders (anxiety disorder not otherwise specified, restlessness and agitation, mixed anxiety and depressive disorder) were included. Eligible participants with a baseline Hamilton Anxiety Rating Scale (HAMA) total score ≥ 18 points received 1 × 80 mg/day Silexan or placebo for 10 weeks. Outcomes included the HAMA, the Pittsburgh Sleep Quality Index, the Zung Self-rating Anxiety Scale, the Clinical Global Impressions questionnaire and the SF-36 health status inventory. Data were analysed using meta-analysis based on pooled raw data of individual patients (random effects models). A total of 697 patients were assessed for efficacy. Silexan was superior to placebo in reducing the HAMA total score during 10 weeks' treatment [mean value difference, 95% confidence interval: 3.83 (1.28; 6.37) points]. Superiority was comparably pronounced for psychic and somatic anxiety as well as for observer- and self-rated anxiety. Silexan had a beneficial effect on sleep (secondary to the anxiolytic effect) without causing sedation and improved the patients' health-related quality of life. Adverse event incidence in both treatment groups was comparable [risk ratio: 1.06 (0.85; 1.33)]. Silexan has a significant and clinically meaningful anxiolytic effect in subthreshold anxiety. The results cannot be generalised to other lavender oil products.