Mirabegron and Its Beta Agonist Activity – Case Scenario
A 76 year old female has a history of urinary urgency and frequency. About a month ago she was started on mirabegron. She has been tried on tolterodine and oxybutynin. Tolterodine did not work that well for her so it was discontinued. Oxybutynin did help some, but she was so bothered by dry eyes and dry mouth that she would rather deal with the urinary symptoms. Remember that both oxybutynin and tolterodine are anticholinergics.
At the visit 1 month ago, she visited her PCP and she was started on mirabegron 50 mg daily for overactive bladder. At that time, her vital signs were pulse = 83 BPM and blood pressure =138/84.
At presentation today she notes that her symptoms have improved some. This medication was somewhat expensive for her, but she was ok with the cost of the medication as long as it was helping some. Her vital signs had changed significantly at her visit today. Her blood pressure was 149/91. Pulse was 88 BPM.
If you remember the mechanism of action of mirabegron, this should help you remember its adverse effect profile. Mirabegron is primarily a beta-3 agonist, but if we get into a situation where we have more effect on beta-1, we can contribute to hypertension and possibly tachycardia. We would want to rule out other causes for the rise in blood pressure. If she is on blood pressure medication, patient adherence is usually the place that I start with. In a 76 year old, depending upon the patient, we may have a little more relaxed blood pressure goals in this patient.
Another important point; the PCP started the dose of mirabegron at 50 mg. As doses go higher, we generally tend to lose selectivity for the receptors that we want. The usual starting dose of mirabegron is 25 mg per day.
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