Pathogenesis of Symptoms in Prostatic Hyperplasia
To thoroughly understand the pharmacology of antiandrogen agents, it is essential to clearly understand the pathogenesis of the conditions for which they are prescribed. Benign prostatic hyperplasia (BPH) is accompanied by a gradual enlargement of the organ.
Because the prostate gland anatomically surrounds the prostatic urethra, its excessive growth inevitably leads to narrowing of the urethral lumen. As a result of this mechanical compression, the main clinical manifestation of the disease develops: persistent urinary obstruction. Therapeutic strategies for this condition are aimed either at relaxing the musculature surrounding the urethra or at directly reducing the volume of hyperplastic tissue.
Classification of Antiandrogen Drugs
Antiandrogen medications represent a broad pharmacological group aimed at suppressing the effects of male sex hormones. Fundamentally, the mechanisms of action in this group are divided into two main pathways:
- Disruption of androgen hormone synthesis. This category includes enzyme system inhibitors that prevent the formation of active hormone forms (a prominent example being finasteride).
- Blockade of androgen-receptor binding. These drugs compete with hormones for binding to specific cellular receptors, preventing already synthesized androgens from exerting their biological effects.
Mechanism of Action of Finasteride
Finasteride (known under the trade name Proscar) is a classic inhibitor of androgen synthesis. Its pharmacodynamics are strictly tied to the 5-alpha-reductase enzyme.
A crucial characteristic of the drug is its tissue specificity—its primary action unfolds locally, directly within the tissues of the prostate gland.
The chain of pharmacological effects of finasteride is as follows:
- The drug binds to the 5-alpha-reductase enzyme and blocks its activity.
- As a result of this enzymatic blockade, the conversion of regular testosterone into its most active form—dihydrotestosterone (DHT)—is severely impaired.
- A sharp drop in the concentration of active dihydrotestosterone leads to a decrease in hormonal stimulation of prostate cells.
- The reduction in cell proliferative activity logically culminates in a decrease in the physical size of the prostate gland and improved urine flow.
Alternative Approach: Alpha-1 Blockers
In addition to finasteride, which reduces gland volume, medications that affect smooth muscle tone are actively used in the treatment of BPH. Long-acting agents (e.g., doxazosin and terazosin) are considered drugs of choice in this niche. This group also includes prazosin and tamsulosin.
Mechanism of action in BPH:
- They selectively bind to $\alpha_{1A}$-adrenergic receptors.
- This receptor subtype is abundantly localized in the smooth muscle of the prostate gland itself, as well as in the prostatic urethra and the bladder neck area.
- Receptor blockade causes marked relaxation of the smooth musculature.
- This leads to a functional widening of the urethral lumen and rapid improvement in urine outflow, without directly affecting testosterone secretion or prostate volume.