Can alfuzosin (alpha-1 adrenergic receptor blocker) affect smooth muscle function in blood tests?

From the Guidelines

Alfuzosin does not directly affect blood tests that measure smooth muscle function. Alfuzosin is an alpha-1 adrenergic receptor blocker primarily used to treat benign prostatic hyperplasia (BPH) by relaxing smooth muscle in the prostate and bladder neck, as stated in the AUA guideline on management of BPH 1. While it acts on smooth muscle tissue, it doesn't interfere with laboratory blood tests that assess smooth muscle markers or function.

Key Points to Consider

• The mechanism of action of alfuzosin involves blocking alpha-1 receptors, preventing norepinephrine from binding to these receptors in smooth muscle cells, which leads to muscle relaxation but doesn't alter blood biomarkers related to smooth muscle in laboratory testing.
• According to the guideline, alpha-blocker therapy, including alfuzosin, is based on the hypothesis that clinical BPH is partly caused by alpha1-adrenergic-mediated contraction of prostatic smooth muscle, resulting in bladder outlet obstruction 1.
• The use of alfuzosin has been extensively investigated for the treatment of LUTS, with meta-analyzed data suggesting that alfuzosin is similarly effective in partially relieving symptoms as other alpha blockers, producing on average a 4-to-6 point improvement in the AUA Symptom Index 1.

Important Considerations for Patients Taking Alfuzosin

• Alfuzosin can cause orthostatic hypotension (a drop in blood pressure when standing up) due to its vasodilatory effects on vascular smooth muscle.
• If you're scheduled for blood pressure measurements as part of your evaluation, it's essential to inform your healthcare provider that you're taking alfuzosin, as it may influence blood pressure readings.

From the FDA Drug Label

Alfuzosin is a selective antagonist of post-synaptic alpha1-adrenoreceptors, which are located in the prostate, bladder base, bladder neck, prostatic capsule, and prostatic urethra. The dynamic component is a function of the smooth muscle tone in the prostate and its capsule, the bladder neck, and the bladder base as well as the prostatic urethra. The smooth muscle tone is regulated by alpha-adrenergic receptors. Alfuzosin exhibits selectivity for alpha1-adrenergic receptors in the lower urinary tract Blockade of these adrenoreceptors can cause smooth muscle in the bladder neck and prostate to relax, resulting in an improvement in urine flow and a reduction in symptoms of BPH

Alfuzosin's effect on smooth muscle function can be detected in blood tests indirectly by measuring the improvement in urine flow and reduction in symptoms of BPH. However, there is no direct information in the provided drug label that alfuzosin affects smooth muscle function in blood tests. 2

From the Research

Effect of Alfuzosin on Smooth Muscle Function

• Alfuzosin is a selective and competitive alpha(1)-adrenoceptor antagonist that decreases the sympathetically controlled tone of prostatic smooth muscle 3, 4.
• It acts by reducing the tone of prostatic, prostatic capsule, bladder base, and proximal urethral smooth muscle, thereby reducing urethral pressure and resistance, bladder outlet resistance, and symptoms associated with benign prostatic hyperplasia 4.
• The combination of alfuzosin and tadalafil exerts an additive relaxant effect on human detrusor and prostatic tissues in vitro, suggesting a potential therapeutic benefit in the treatment of lower urinary tract symptoms 5.

Mechanism of Action

• Alfuzosin's mechanism of action involves the selective blockade of alpha-1 adrenergic receptors, which reduces the contraction of smooth muscle in the prostate and bladder neck 3, 4.
• The drug's effect on smooth muscle function is thought to be mediated by its ability to reduce the tone of these muscles, rather than by altering the contractile properties of the muscle itself 4.
• Desensitization of alpha-1 adrenergic receptor-mediated vascular smooth muscle contraction has been observed in rabbit aorta, suggesting that prolonged exposure to alpha-1 adrenergic receptor agonists can lead to a loss of sensitivity to these agents 6.

Clinical Implications

• Alfuzosin has been shown to be effective in improving symptoms associated with benign prostatic hyperplasia, including urinary flow rate and quality of life 3, 4.
• The drug's ability to reduce the tone of smooth muscle in the prostate and bladder neck makes it a useful therapeutic option for the treatment of lower urinary tract symptoms 3, 4.
• The combination of alfuzosin and tadalafil may offer an additive therapeutic benefit in the treatment of lower urinary tract symptoms, although further clinical studies are needed to confirm this 5.