Alpha receptors are present in prostatic smooth muscle which when activated, result in increased tone, narrowing the prostate and bladder neck, resulting in urinary flow obstruction.
Examples of alpha-blockers include:
TamsulosinAlfuzosinDoxazosinTerazosinKey adverse effects include:
Hypotension and postural hypotensionDrowsinessHeadachesDry mouthDyspnoea5-alpha reductase inhibitorsAndrogens do not directly cause BPH, but they are required for BPH to occur. Testosterone is converted into dihydrotestosterone (DHT) by the enzyme 5-alpha reductase which binds to receptors on prostatic cells and has proliferative and apoptotic effects.
Examples of 5-alpha reductase inhibitors include:
FinasterideDutasterideKey adverse effects include:
Sexual dysfunction – decreased libido, erectile dysfunction, ejaculation disordersGynaecomastia and breast tendernessUrinary Urgency: DrugsAntimuscarinic drugsAnticholinergic drugs inhibit the parasympathetic nervous system by preventing the binding of acetylcholine (ACh) to its receptors in synapses. Anticholinergic drugs can be divided into antimuscarinic and antinicotinic drugs (e.g. muscle relaxants).
Stimulating muscarinic receptors leads to the constriction of the bladder detrusor muscles, leading to an increased desire to pass urine. Therefore, preventing this can help in urge incontinence.
Example antimuscarinic drugs are:
OxybutyninDarifenacinTolterodineSolifenacinFesoterodineSince they inhibit the parasympathetic nervous system, they can cause troublesome side effects including dry mouth, blurred vision, drowsiness, an increased risk of dementia, constipation and urinary retention.
MirabegronMirabegron is a beta-3 agonist. Stimulation of the beta-3 receptor leads to detrusor muscle relaxation, which reduces the desire to pass urine, hence making it useful in the management of urge incontinence.
Key adverse effects are:
ConstipationHeadacheNauseaArrhythmiaDizzinessErectile Dysfunction: DrugsPhosphodiesterase-5 (PDE-5) inhibitorsPhosphodiesterase-5 (PDE-5) inhibitors lead to increases in cyclic GMP (cGMP) resulting in smooth muscle relaxation in blood vessels. They are used in erectile dysfunction and pulmonary hypertension.
Example drugs are:
Sildenafil (Viagra) – short-acting, usually 1 hour before sexual activityTadalafil (Cialis) – longer activity, lasts up to around 36 hoursContraindications include:
Nitrates and similar drugs (e.g. nicorandil) due to the risk of severe hypotensionHypotensionRecent myocardial infarctionUncontrolled arrhythmiaUncontrolled hypertensionKey side effects include:
HeadachesFlushingNasal congestionVision problems – discontinue if they occur:Cyanopsia – blue tint to visionNon-arteritic anterior ischaemic optic neuropathyAuthorFY1 doctor working in North West England.
MB ChB with Honours (2024, University of Manchester). MSc Clinical Immunology with Merit (2023, University of Manchester).