Does lithium interact with mirabegron (Myrbetriq)?

Lithium and Mirabegron Interaction

Lithium does not have a clinically significant interaction with mirabegron, and these medications can generally be used together without special precautions. Based on the available evidence, there are no documented direct interactions between lithium and mirabegron (Myrbetriq) that would affect morbidity, mortality, or quality of life.

Pharmacological Considerations

Mirabegron Properties

• Mirabegron is a β3-adrenoceptor agonist used for overactive bladder (OAB) treatment 1
• It has a different mechanism of action from antimuscarinic agents 2
• Common side effects include hypertension, nasopharyngitis, urinary tract infection, and headache 2
• Mirabegron is eliminated through multiple metabolic and excretory pathways, reducing its potential for drug interactions 3

Lithium Properties

• Lithium is primarily used as a mood stabilizer for bipolar disorder 4
• It requires regular monitoring of serum levels 4
• Lithium has known interactions with certain medications, particularly NSAIDs, which should be avoided in patients taking lithium 1

Safety Assessment

Lack of Documented Interactions

• None of the guidelines or research evidence indicates a specific interaction between lithium and mirabegron
• The European Association of Urology guidelines on management of non-neurogenic male lower urinary tract symptoms do not list lithium as having interactions with mirabegron 1
• The pharmacokinetic studies of mirabegron do not mention lithium as a medication with potential interactions 5, 3

Renal Considerations

• Both medications have considerations related to renal function:
  • Lithium requires dose adjustment and careful monitoring in patients with impaired renal function 1
  • Mirabegron exposure increases in patients with renal impairment (31%, 66%, and 118% higher AUC in mild, moderate, and severe impairment, respectively) 5
• However, there is no evidence suggesting that the combination specifically worsens renal outcomes

Cardiovascular Considerations

• Mirabegron can cause hypertension in some patients 2
• The European Heart Journal guidelines on risk of arrhythmia induced by psychotropic medications note that lithium has been associated with bradycardia, T-wave changes, and AV-block 1
• However, there is no evidence suggesting that the combination specifically increases cardiovascular risk

Clinical Recommendations

1. Monitor renal function regularly when using either medication, particularly in patients with pre-existing renal impairment

2. Check lithium levels periodically as recommended for standard lithium therapy (typically maintaining levels between 0.2 to 0.6 mEq/L for maintenance therapy) 1

3. Monitor blood pressure at baseline and periodically during treatment, as mirabegron has been associated with hypertension 2

4. Be aware of the individual side effect profiles of each medication:

   • Mirabegron: hypertension, nasopharyngitis, UTI, headache 2
   • Lithium: tremor, thirst, polyuria, hypothyroidism, weight gain 4

Conclusion

Based on current evidence, lithium and mirabegron can be used concomitantly without specific dose adjustments or extraordinary monitoring beyond what is already recommended for each medication individually. The absence of documented interactions in the literature suggests these medications do not significantly affect each other's efficacy or safety profiles.