Midodrine Can Cause Bradycardia
Yes, midodrine can cause bradycardia due to reflex parasympathetic stimulation. 1 This is an important side effect that clinicians should monitor for when prescribing this medication.
Mechanism of Bradycardia with Midodrine
Midodrine is a peripheral alpha-1 adrenergic agonist that works by causing vasoconstriction, which increases blood pressure. The bradycardia occurs through the following mechanism:
- When midodrine increases blood pressure through vasoconstriction, it triggers the baroreceptor reflex
- This reflex activates parasympathetic (vagal) stimulation to the heart
- The resulting vagal reflex leads to a slowing of the heart rate 2
Risk Factors for Midodrine-Induced Bradycardia
Patients at higher risk for developing bradycardia with midodrine include those:
- Taking other negative chronotropic agents such as:
- Beta-blockers
- Digoxin
- Non-dihydropyridine calcium channel blockers 1
- Using cardiac glycosides (such as digitalis) 2
- Taking psychopharmacologic agents that can affect heart rate 2
Monitoring and Management
When prescribing midodrine, the following monitoring and management strategies should be implemented:
- Monitor heart rate before and after initiating therapy
- Advise patients to report any symptoms suggesting bradycardia:
- Increased dizziness
- Syncope
- Cardiac awareness
- Pulse slowing 2
- If bradycardia occurs, discontinue midodrine and re-evaluate the patient 2
- Consider alternative treatments for orthostatic hypotension in patients with pre-existing bradycardia or those on other medications that slow heart rate
Dosing Considerations
- Standard dosing: 5-20 mg three times daily 3
- For dialysis patients: 5 mg administered 30 minutes before dialysis session 1, 3
- In patients with renal impairment: Start with a lower dose of 2.5 mg 3, 2
- Schedule the last daily dose at least 4 hours before bedtime to minimize supine hypertension 2
Other Important Side Effects
While monitoring for bradycardia, clinicians should also be aware of other potential adverse effects:
- Supine hypertension (most significant concern)
- Piloerection (goosebumps)
- Scalp itching or tingling
- Urinary retention or urgency
- Gastrointestinal symptoms (nausea, heartburn)
- Headache and sleep disturbances 1
Clinical Pearls
- Midodrine is effectively cleared by hemodialysis with a reduced half-life of 1.4 hours during dialysis 1
- Avoid concomitant use with other alpha-adrenergic agents (ephedrine, pseudoephedrine, phenylpropanolamine) as this may worsen supine hypertension 1, 2
- Midodrine can antagonize the actions of alpha-adrenergic blockers (terazosin, prazosin, doxazosin) and could result in urinary retention 1
- In severe overdose cases, bradycardia can be profound, as reported in a case with heart rate ranging from 43-60 beats/min 4
Remember that while midodrine is an effective treatment for orthostatic hypotension, careful monitoring for bradycardia and other side effects is essential for safe use of this medication.