Evaluation of the effects of venlafaxine and pregabalin on the carbon dioxide inhalation models of Generalised Anxiety Disorder and panic

Biochemical challenges for testing novel anti-panic drugs in humans

Current medications for panic disorder each carry significant limitations that indicate the need for novel anxiolytics. The high costs and low success rates of drug development demand that testing trials be efficient. Lab panicogenic challenges in humans allow for the rapid biochemical induction of panic symptoms and hence an efficient means of testing potential anti-panic drugs. This paper describes ideal characteristics of lab panicogens, reviews the validity and utility of various biochemical panicogenic agents, identifies key outcome measures for studies of novel anti-panic drugs, and makes broad recommendations for labs wishing to perform such studies. We conclude by presenting a four-tiered hierarchy of panicogens that matches each against ideal characteristics and reflects our recommendations for their laboratory use.

Multiple-dose clinical pharmacology of the selective orexin-1 receptor antagonist ACT-539313

AIMS

Compounds that selectively target orexin-1 receptors may be beneficial for the treatment of various disorders. The role of selective orexin-1 receptor antagonists (1-SORAs) in addictive behavior and stress/anxiety-related disturbances has been demonstrated in animals. ACT-539313, an orally active, potent 1-SORA, has been assessed in a clinical single-ascending dose study and exhibited good safety and tolerability. In the two reported studies on ACT-539313, multiple-dose pharmacokinetics (PK), pharmacodynamics (PD), safety, and tolerability were investigated and in a proof-of-mechanism study a CO₂ challenge was applied as pharmacological model for induction of anxiety and panic symptoms (sequential inhalation of air, 7.5% CO₂, and 35% CO₂).

METHODS

Two double-blind, placebo-controlled, randomized, multiple-dose studies included 58 healthy male and female subjects. In Study 1, multiple-ascending oral doses of 30, 100, and 200 mg twice daily (b.i.d.) ACT-539313 were investigated in 3 dose groups of 8 or 12 subjects (of whom 2 received placebo per dose group). Study 2 was conducted as a randomized two-way crossover design, enrolling 21 male and 9 female subjects who received 200 mg ACT-539313 or matching placebo b.i.d. for 2.5 days followed by a CO₂ challenge, with a washout period in between. PK, PD (objective and subjective measures of sedation, alertness, effects on central nervous system (CNS), and anxiety/panic symptoms), safety, and tolerability were assessed.

RESULTS

At steady state, ACT-539313 was rapidly absorbed with a median time to maximum plasma concentration of 1.8-2.3 h and eliminated with a mean half-life of 3.8-6.5 h. Overall exposure increased dose-proportionally. In Study 1, PD effects confirmed activity of ACT-539313 on the CNS, without consistent or marked effects of sedation, reduced alertness or visuo-motor impairment. In the CO₂ challenge, cortisol concentrations were lower during initial air inhalation after treatment with ACT-539313 compared to placebo, while no difference was detected after CO₂ inhalation. Trends for lower scores in subjective anxiety assessments were observed for ACT-539313. Besides reports of stress related to the challenge, the most frequently reported adverse events were somnolence and headache. No clinically relevant effects in other safety assessments were observed.

CONCLUSIONS

Multiple-dose administration of ACT-539313 was safe and well tolerated up to multiple doses of 200 mg b.i.d. The drug's PK properties as well as the pattern of a decrease in stress-related symptoms after the CO₂ challenge support further investigations of ACT-539313.

Experimental Drugs for Panic Disorder: An Updated Systematic Review

Several effective pharmacological therapies for panic disorder (PD) are available, but they have some drawbacks, and unsatisfactory outcomes can occur. Expanding the variety of anti-panic medications may allow for improving PD treatment. The authors performed an updated systematic review of preclinical and clinical (Phase I–III) pharmacological studies to look for advances made in the last six years concerning novel-mechanism-based anti-panic compounds or using medications approved for nonpsychiatric medical conditions to treat PD. The study included seven published articles presenting a series of preclinical studies, two Phase I clinical studies with orexin receptor (OXR) antagonists, and two clinical studies investigating the effects of D-cycloserine (DCS) and xenon gas in individuals with PD. The latest preclinical findings confirmed and expanded previous promising indications of OXR1 antagonists as novel-mechanism-based anti-panic compounds. Translating preclinical research into clinical applications remains in the early stages. However, limited clinical findings suggested the selective OXR1 antagonist JNJ-61393115 may exert anti-panic effects in humans. Overall, OXR1 antagonists displayed a favorable profile of short-term safety and tolerability. Very preliminary suggestions of possible anti-panic effects of xenon gas emerged but need confirmation with more rigorous methodology. DCS did not seem promising as an enhancer of cognitive-behavioral therapy in PD. Future studies, including objective panic-related physiological parameters, such as respiratory measures, and expanding the use of panic vulnerability biomarkers, such as hypersensitivity to CO₂ panic provocation, may allow for more reliable conclusions about the anti-panic properties of new compounds.

The psychopharmacology of epilepsy

Epilepsy affects 1% of the world's population and is defined as two or more unprovoked seizures. Psychiatric conditions (depression, psychosis, anxiety, and attention deficit hyperactivity disorder (ADHD)) may coexist and are linked to negative seizure outcomes and poorer quality of life. There is an increasing body of evidence to suggest a bidirectional relationship between epilepsy and psychiatric disorders, which may imply shared pathophysiologic mechanisms. Extensive research has examined neurobiologic and neuroanatomic substrates for this association revealing some interesting similarities. Psychiatric disorders in people with epilepsy often go underdiagnosed and undertreated, due to fears of exacerbating psychiatric symptoms or provoking seizures, which may cause delays in optimal management. This chapter covers psychiatric conditions in epilepsy largely focusing on depressive disorders and psychotic disorders. Anxiety and ADHD in association with epilepsy are also discussed. Epidemiology, pathophysiologic mechanisms, and pharmacotherapies used to treat epilepsy and psychiatric disorders are also covered.

Pharmacotherapy in Generalized Anxiety Disorder: Novel Experimental Medicine Models and Emerging Drug Targets

Many pharmacological and psychological approaches have been found efficacious in patients with generalized anxiety disorder (GAD), but many treatment-seeking patients will not respond and others will relapse despite continuing with interventions that initially had beneficial effects. Other patients will respond but then stop treatment early because of untoward effects such as sexual dysfunction, drowsiness, and weight gain. There is much scope for the development of novel approaches that could have greater overall effectiveness or acceptability than currently available interventions or that have particular effectiveness in specific clinical subgroups. 'Experimental medicine' studies in healthy volunteers model disease states and represent a proof-of-concept approach for the development of novel therapeutic interventions: they determine whether to proceed to pivotal efficacy studies and so can reduce delays in translating innovations into clinical practice. Investigations in healthy volunteers challenged with the inhalation of air 'enriched' with 7.5% carbon dioxide (CO₂) indicate this technique provides a validated and robust experimental medicine model, mirroring the subjective, autonomic, and cognitive features of GAD. The anxiety response during CO₂ challenge probably involves both central noradrenergic neurotransmission and effects on acid-base sensitive receptors and so may stimulate development of novel agents targeted at central chemosensors. Increasing awareness of the potential role of altered cytokine balance in anxiety and the interplay of cytokines with monoaminergic mechanisms may also encourage the investigation of novel agents with modulating effects on immunological profiles. Although seemingly disparate, these two approaches to treatment development may pivot on a shared mechanism in exerting anxiolytic-like effects through pharmacological effects on acid-sensing ion channels.

Biological markers for anxiety disorders, OCD and PTSD: A consensus statement. Part II: Neurochemistry, neurophysiology and neurocognition

OBJECTIVE

Biomarkers are defined as anatomical, biochemical or physiological traits that are specific to certain disorders or syndromes. The objective of this paper is to summarise the current knowledge of biomarkers for anxiety disorders, obsessive-compulsive disorder (OCD) and posttraumatic stress disorder (PTSD).

METHODS

Findings in biomarker research were reviewed by a task force of international experts in the field, consisting of members of the World Federation of Societies for Biological Psychiatry Task Force on Biological Markers and of the European College of Neuropsychopharmacology Anxiety Disorders Research Network.

RESULTS

The present article (Part II) summarises findings on potential biomarkers in neurochemistry (neurotransmitters such as serotonin, norepinephrine, dopamine or GABA, neuropeptides such as cholecystokinin, neurokinins, atrial natriuretic peptide, or oxytocin, the HPA axis, neurotrophic factors such as NGF and BDNF, immunology and CO2 hypersensitivity), neurophysiology (EEG, heart rate variability) and neurocognition. The accompanying paper (Part I) focuses on neuroimaging and genetics.

CONCLUSIONS

Although at present, none of the putative biomarkers is sufficient and specific as a diagnostic tool, an abundance of high quality research has accumulated that should improve our understanding of the neurobiological causes of anxiety disorders, OCD and PTSD.

Evaluating psychological interventions in a novel experimental human model of anxiety

Inhalation of 7.5% carbon dioxide increases anxiety and autonomic arousal and provides a novel experimental model of anxiety with which to evaluate pharmacological and psychological treatments for anxiety. To date several psychotropic drugs including benzodiazepines, SSRIs and SNRIs have been evaluated using the 7.5% CO2 model; however, it has yet to be used to evaluate psychological interventions. We compared the effects of two core psychological components of mindfulness-meditation (open monitoring and focused attention) against general relaxation, on subjective, autonomic and neuropsychological outcomes in the 7.5% CO2 experimental model. 32 healthy screened adults were randomized to complete 10 min of guided open monitoring, focused attention or relaxation, immediately before inhaling 7.5% CO2 for 20 min. During CO2-challenge participants completed an eye-tracking measure of attention control and selective attention. Measures of subjective anxiety, blood pressure and heart rate were taken at baseline and immediately following intervention and CO2-challenge. OM and FA practice reduced subjective feelings of anxiety during 20-min inhalation of 7.5% CO2 compared to relaxation control. OM practice produced a strong anxiolytic effect, whereas the effect of FA was more modest. Anxiolytic OM and FA effects occurred in the absence of group differences in autonomic arousal and eye-movement measures of attention. Our findings are consistent with neuropsychological models of mindfulness-meditation that propose OM and FA activate prefrontal mechanisms that support emotion regulation during periods of anxiety and physiological hyper-arousal. Our findings complement those from pharmacological treatment studies, further supporting the use of CO2 challenge to evaluate future therapeutic interventions for anxiety.

Changes in cardiovascular function after venlafaxine but not pregabalin in healthy volunteers: a double-blind, placebo-controlled study of orthostatic challenge, blood pressure and heart rate

It is generally thought that venlafaxine raises blood pressure at higher doses; however, some studies have found no effect or a decrease in blood pressure. The aim of this study was to evaluate the cardiovascular (CV) effects of 3 weeks of dosing with venlafaxine, pregabalin and placebo on young healthy adults. Fifty-four participants, of mean age 23.1 years (sd 4.68), 29 male, were randomised into three parallel groups. Each group received one of the three drugs, dosed incrementally over a 3-week period to reach daily doses of 150 mg/day venlafaxine and 200 mg/day pregabalin. Blood pressure sphygmomanometer measurements, heart rate measurements, and orthostatic challenges recorded continuously beat-to-beat were performed weekly over this period and 5 days after treatment cessation. Results showed resting systolic blood pressure (SBP) and resting and standing diastolic blood pressure (DBP) and heart rate (HR) were significantly raised by venlafaxine compared with the pregabalin and placebo groups. SBP drop on standing was larger, the resulting overshoot was smaller, and recovery was slower on venlafaxine. HR recovery was significantly impaired by venlafaxine. CV changes were observed after only 1 week of dosing at 112.5 mg/day. These effects of venlafaxine are likely to be due to its action of noradrenergic reuptake inhibition.

Pregabalin for the treatment of generalized anxiety disorder: an update

A PREVIOUS REVIEW SUMMARIZED WHAT WAS THEN KNOWN ABOUT THE POTENTIAL ROLE OF PREGABALIN IN THE TREATMENT OF PATIENTS WITH GENERALIZED ANXIETY DISORDER (GAD): this review provides an update on its pharmacological properties and presumed mechanism of action, the liability for abuse, and efficacy and tolerability in patients with GAD. Pregabalin has a similar molecular structure to the inhibitory neurotransmitter gamma amino butyric acid (GABA) but its mechanism of action does not appear to be mediated through effects on GABA. Instead, its anxiolytic effects may arise through high-affinity binding to the alpha-2-delta sub-unit of the P/Q type voltage-gated calcium channel in "over-excited" presynaptic neurons, thereby reducing the release of excitatory neurotransmitters such as glutamate. The findings of randomized controlled trials and meta-analyses together indicate that pregabalin is efficacious in both acute treatment and relapse prevention in GAD, with some evidence of an early onset of effect, and broad efficacy in reducing the severity of psychological and physical symptoms of anxiety. It also has efficacy as an augmenting agent after non-response to antidepressant treatment in GAD. Continuing vigilance is needed in assessing its potential abuse liability but the tolerability profile of pregabalin may confer some advantages over other pharmacological treatments in the short term for treatment in patients with GAD.

The effect of a clinically effective and non-effective dose of lorazepam on 7.5% CO₂-induced anxiety

Symptoms of anxiety induced by 7.5% CO₂ inhalation can be attenuated by acute administration of GABA(A) receptor anxiolytics such as lorazepam and alprazolam. This study investigated if these effects are dose-related, by comparing a 0.5 mg dose (considered non-clinically effective) and a 2 mg dose of lorazepam (clinically effective) on 7.5% CO₂ inhalation. Eighteen healthy males (mean age 20.6 years, SD 1.29), judged physically and mentally fit, attended three visits, each one week apart, to take each treatment in a randomised double-blind crossover design. Drugs were given 60 min prior to 20 min air inhalation, followed by 20 min 7.5% CO₂ inhalation. The order of gas presentation was single blind. Subjective ratings using visual analogue scales (VAS) and questionnaires were recorded before and after each inhalation. Blood pressure (BP), heart rate (HR), respiration rate (RR) and expired CO₂ were recorded during each inhalation. Inhalation of 7.5% CO₂ significantly raised BP, HR, RR and expired CO₂. Ratings of feeling like leaving the room were significantly lower on 2 mg compared with 0.5 mg and placebo, and dose-dependent trends were seen in scores for VAS fearful, anxious, stressed, tense, and worried. Results may be indicative of dose-dependent effects of lorazepam in a CO₂ model of anxiety.