Which drug is likely to cause severe upset stomach and heartburn as an adverse effect?

Mexiletine is known to cause gastrointestinal disturbances, including severe upset stomach and heartburn, as part of its adverse effect profile. This drug is a class 1B antiarrhythmic agent primarily used to treat ventricular arrhythmias. When administering mexiletine, it is important to monitor the patient's gastrointestinal response because the drug can irritate the stomach lining or increase gastric acidity, leading to discomfort or heartburn.

The other drugs listed have different adverse effect profiles. Amiodarone primarily affects the respiratory and thyroid systems, Digoxin can lead to nausea and vomiting but is less associated with severe stomach upset, and Propranolol, a beta-blocker, may cause gastrointestinal issues, but they are typically less severe compared to those associated with mexiletine. Understanding the specific adverse effects linked to each medication helps in managing patient care effectively and addressing any symptoms that arise during treatment.