Mexitil (Mexiletine)

How it works

Mexiletine is a Class IB antiarrhythmic that works by blocking sodium channels in the heart. This slows the abnormal electrical impulses that cause ventricular arrhythmias like VPCs and ventricular tachycardia. Because it targets sodium channels (while sotalol targets potassium channels and beta receptors), the two medications complement each other and can suppress arrhythmias that neither drug controls well alone.

Common dosage

Typically 5–8 mg/kg two to three times daily. The multiple daily doses are necessary because mexiletine is metabolized relatively quickly. Your cardiologist will determine the exact dose and frequency based on Holter monitor results. Giving it with food can help reduce GI side effects.

Dosages vary - your vet will determine the right dose for your dog.

Side effects to watch for

• ●GI upset (nausea, vomiting, reduced appetite) - the most commonly reported side effect; giving it with food usually helps substantially
• ●Tremors or shakiness
• ●Ataxia (wobbliness or unsteadiness)
• ●Lethargy
• ●Rarely: worsening arrhythmias at incorrect doses
• ●Practical note: cost and availability are the biggest real-world hurdles - mexiletine has been subject to periodic shortages and price swings, so ask your cardiologist about backup sourcing before you run low

Drug interactions

• ●Sotalol - commonly and intentionally used together for enhanced arrhythmia control in Dobermans
• ●Other antiarrhythmic drugs - avoid combining with other sodium channel blockers (Class IA or IC) due to increased toxicity risk
• ●Medications that alter stomach pH (antacids, H2 blockers) - can affect mexiletine absorption
• ●Opioids - may slow GI motility and alter mexiletine absorption
• ●Hepatic enzyme inducers (phenobarbital) - can increase mexiletine metabolism, reducing effectiveness

Frequently asked questions