Famotidine and Vyvanse: Safety and Monitoring
Famotidine and Vyvanse (lisdexamfetamine) can be safely taken together without dosage adjustments, as there are no known pharmacokinetic or pharmacodynamic interactions between H2-receptor antagonists and amphetamine-based stimulants. However, baseline cardiovascular assessment is warranted before initiating Vyvanse, regardless of famotidine co-administration.
No Drug-Drug Interaction Expected
Famotidine does not interact with CNS stimulants through hepatic metabolism. Famotidine is eliminated primarily through the kidneys (approximately 70%) as the parent compound, with minimal hepatic metabolism 1.
Lisdexamfetamine is converted to d-amphetamine through enzymatic hydrolysis in the blood, not through cytochrome P450 pathways. This rate-limited biotransformation occurs independently of hepatic enzyme systems 2, 3.
Famotidine has demonstrated no clinically important drug interactions in clinical practice, with studies showing it does not impair the clearance of other medications metabolized through different pathways 1, 4.
Cardiovascular Monitoring Considerations
While the combination is safe, standard cardiovascular monitoring for Vyvanse applies regardless of famotidine use:
Assess baseline cardiovascular status before initiating Vyvanse. This includes blood pressure, heart rate, and screening for cardiac risk factors, as amphetamines produce dose-related increases in blood pressure and heart rate 5.
Lisdexamfetamine produces peak cardiovascular effects (increased mean arterial blood pressure, heart rate) approximately 1-3 hours after administration, with effects lasting 10-12 hours 5, 2.
Monitor blood pressure and heart rate periodically during treatment, particularly during dose titration (typical range 30-70 mg daily) 6.
Clinical Pitfalls to Avoid
Do not confuse famotidine with proton pump inhibitors (PPIs). While PPIs can interact with antiplatelet agents like clopidogrel through CYP2C19 inhibition, H2-receptor antagonists like famotidine do not cause this interaction 7.
Do not assume all acid-suppressing medications behave similarly. The FDA specifically notes that H2 blockers and antacids do not interfere with medications metabolized by CYP2C19, unlike certain PPIs 7.
Be aware that famotidine's antisecretory activity begins within 1 hour and lasts 10-12 hours, which overlaps with Vyvanse's duration of action but does not create any interaction concerns 1.
Dosing Recommendations
No dosage adjustment of either medication is required when used together. Standard dosing applies for both agents 1, 2.
Vyvanse: Typical starting dose 20-30 mg once daily in the morning, titrated by 10 mg weekly to maximum 70 mg daily 8.
Famotidine: Standard dosing for acid suppression (20-40 mg) can be maintained without modification 1.