Alpha blocker

Alpha-blockers, α-blockers, or α-adrenergic-antagonists are pharmacological agents that act as receptor antagonists of α-adrenergic receptors (α-adrenoceptors).^[1]

Classification

• α₁-blockers or antagonists act at α₁-adrenoceptors
• α₂-blockers or antagonists act at α₂-adrenoceptors

When the term "alpha blocker" is used without further qualification, it sometimes refers to α₁-blockers, and sometimes refers to agents that act at both types of receptors.

Examples of non-selective α-adrenergic blockers include:

• Phenoxybenzamine
• Phentolamine
• Tolazoline
• Trazodone
• Typical and atypical antipsychotics

Selective α₁-adrenergic blockers include:

• Alfuzosin
• Doxazosin
• Prazosin
• Tamsulosin
• Terazosin
• Silodosin

Selective α₂-adrenergic blockers include:

• Atipamezole
• Idazoxan
• Mirtazapine
• Yohimbine

The agents carvedilol and labetalol are both α- and β-blockers.

Uses

α-Blockers are used in the treatment of several conditions, such as Raynaud's disease, hypertension, and scleroderma.^[2]

α-Blockers can also be used to treat anxiety and panic disorders, such as generalized anxiety disorder, panic disorder, or posttraumatic stress disorder (PTSD). While most commonly used to treat hypertension (usually in conjunction with diuretics when other treatments are ineffective), they are also often used to treat the symptoms of BPH (benign prostatic hyperplasia).

Prazosin is an alpha1-receptor antagonist. Raskind and colleagues^[3] studied the efficacy of prazosin for PTSD among Vietnam combat veterans in a 20-week double-blind crossover protocol with a two-week drug washout to allow for return to baseline.^[3] The CAPS and the Clinical Global Impressions-Change scale (CGI-C) were the primary outcome measures. Patients who were taking prazosin had a robust improvement in overall sleep quality (effect size, 1.6) and recurrent distressing dreams (effect size, 1.9). In each of the PTSD symptom clusters the effect size was medium to large: 0.7 for reexperiencing or intrusion, 0.6 for avoidance and numbing, and 0.9 for hyperarousal. The reduction in CGI-C scores (overall PTSD severity and function at endpoint) also reflected a large effect size (1.4). Prazosin appears to have promise as an effective treatment for PTSD-related sleep disturbance, including trauma-related nightmares, as well as overall Anxiety and PTSD symptoms.

See also

• Beta blocker

References

1. alpha-Adrenergic Blockers at the US National Library of Medicine Medical Subject Headings (MeSH)
2. "Alpha blockers - MayoClinic.com".
3. Raskind MA, Peskind ER, Kanter ED, et al: Reduction of nightmares and other PTSD symptoms in combat veterans by prazosin: a placebo controlled study. American Journal of Psychiatry 160:371–373, 2003[Abstract/Free Full Text]