Question
One month after undergoing surgical spinal fusion because of a traumatic spinal cord injury, a 69-year-old man comes to the physician because of lower abdominal pain. He last voided yesterday. Physical examination shows a suprapubic mass and decreased sensation below the umbilicus. Urodynamic studies show simultaneous contractions of the detrusor muscle and the internal urethral sphincter. Urinary catheterization drains 900 mL of urine from the bladder. Which of the following is the most appropriate pharmacotherapy for this patient’s urinary symptoms?
| A. |
Finasteride
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| B. |
Phenylephrine
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| C. |
Bethanechol
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| D. |
Prazosin
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Show Answer
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Correct Answer � D
Explanation
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Ans-D-Prazosin
Finasteride
Finasteride is used to treat bladder outlet obstruction due to benign prostatic hyperplasia (BPH), as it decreases the size of the prostate. This man is at risk of having BPH, which is common in men > 50 years of age and can cause urinary retention. However, BPH typically has a gradual onset and rarely manifests with acute urinary retention as severe as seen in this patient. Finasteride has no effects on detrusor muscle activity or urinary sphincter contraction and would not be effective for the spastic neurogenic bladder seen in this patient.
Phenylephrine
Phenylephrine is a sympathomimetic alpha-1 agonist, which would increase the smooth muscle tone at the neck of the bladder and the internal urethral sphincter, thereby inducing urinary retention. Phenylephrine would be contraindicated in this patient with an already overactive sphincter muscle and spastic neurogenic bladder.
Bethanechol
Bethanechol can be used to treat bladder hypomotility seen in flaccid neurogenic bladder or postoperative urinary retention. In these cases, the detrusor muscle is not contracting properly, and the addition of a muscarinic agonist will stimulate M3 receptors in the bladder, causing detrusor contraction and improved urinary outflow. This patient’s urinary retention is due to a spastic neurogenic bladder, which would be exacerbated with muscarinic agonists; a muscarinic antagonist could be used instead.
Prazosin
Alpha blockers such as prazosin are the most appropriate pharmacotherapy in patients with spastic neurogenic bladder because of their effects on smooth muscle relaxation of the neck of the bladder and the internal urethral sphincter, which can improve urine outflow. This patient likely had a spinal cord lesion near the level of T10 (decreased sensation below the umbilicus), which is now causing sympathetic stimulation of the urethral sphincter, as evidenced by the urodynamic studies. Alpha blockers are also a first-line therapy in urinary retention due to outflow tract obstruction caused by benign prostatic hyperplasia. The most common side effects of alpha blockers are postural hypotension and headaches.
A lower, sacral lesion would affect the parasympathetic bladder input and lead to a flaccid neurogenic bladder that is unable to contract.
