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Drugs Used in Urology

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Benign Prostatic Hyperplasia: Drugs

Alpha-blockers

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:

  • Tamsulosin
  • Alfuzosin
  • Doxazosin
  • Terazosin

Key adverse effects include:

5-alpha reductase inhibitors

Androgens 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:

  • Finasteride
  • Dutasteride

Key adverse effects include:

Urinary Urgency: Drugs

Antimuscarinic drugs

Anticholinergic 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:

  • Oxybutynin
  • Darifenacin
  • Tolterodine
  • Solifenacin
  • Fesoterodine

Since 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.

Mirabegron

Mirabegron 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:

  • Constipation
  • Headache
  • Nausea
  • Arrhythmia
  • Dizziness

Erectile Dysfunction: Drugs

Phosphodiesterase-5 (PDE-5) inhibitors

Phosphodiesterase-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 activity
  • Tadalafil (Cialis) – longer activity, lasts up to around 36 hours

Contraindications include:

  • Nitrates and similar drugs (e.g. nicorandil) due to the risk of severe hypotension
  • Hypotension
  • Recent myocardial infarction
  • Uncontrolled arrhythmia
  • Uncontrolled hypertension

Key side effects include:

  • Headaches
  • Flushing
  • Nasal congestion
  • Vision problems – discontinue if they occur:
    • Cyanopsia – blue tint to vision
    • Non-arteritic anterior ischaemic optic neuropathy

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