Download Mexiletine guidelines

Mexiletine for Non-Dystrophic
Myotonia: the National Hospital for
Neurology and Neurosurgery
Prescription Guidelines
Consultants: Professor M. Hanna, Consultant Neurologist, Dr D. Fialho,
Consultant Neurophysiologist, Dr E Matthews, Consultant Neurologist, Dr K
Savvatis, Consultant Cardiologist.
Specialist Nurse: Natalie James.
Clinical Fellows: Dr K Suetterlin, Dr Oliver Watkinson.
Date for Guideline Review January 2021 .
Suetterlin K, Bugiardini E, Kaski JP, et al. Long -term Safety and Efficacy of
Mexiletine for Patients with Skeletal Muscle Channelopathies. JAMA Neurol.
2015;72(12):1531-1533. doi:10.1001/jamaneurol.2015.2338.
1 Prior to Mexiletine prescription:
1.1 Ensure baseline ECG normal, enquire about cardiac symptoms and/or
history of cardiac disease (especially history of myocardial infarction
in the previous 2 years, history of congestive heart failure, sinus or AV
node disease).
1.2 Check no drug interactions with existing medication.
1.3 If possibility of hepatic or renal impairment, check baseline
LFT/U&E/Coagulation and consider liaising with appropriate specialty
prior to mexiletine prescription.
1.4 If pre-existing reflux consider investigation and or treatment e.g. H.
pylori eradication as symptoms may be exacerbated by mexiletine.
2 Refer or discuss with cardiology prior to prescription if:
2.1 Abnormal baseline ECG (1st degree or higher AV-block, prolonged QRS
duration).
2.2 Any cardiac history.
3 Counselling of patients:
3.1 Dyspepsia is by far the most common adverse effect (37%). Other
adverse effects reported in audited patients whilst taking mexiletine
(without clear alternative precipitant) included headache 8%,
palpitations 6%, nausea 5%, tremor 1.5%.
3.2 Incidence of significant cardiac or other, adverse effect very low (none
in our audit of 63 patients with mean follow up 4.8 years). However,
patient should be counselled to seek urgent medical attention if they
develop any cardiac symptoms, particularly if suggestive of syncope,
arrhythmia, angina or heart failure and highlight that they are taking
mexiletine.
3.3 Mexiletine is relatively contraindicated post myocardial infarction, if
MI occurs whilst on mexiletine its cessation must be discussed with a
cardiologist.
4 Dose Titration:
Adequate dose titration is necessary to determine efficacy and slow dose
titration seems to improve tolerability. Start with 100mg mexiletine
once daily and increase by 100mg per week to a maximum of 200mg
three times a day or dose at which symptom control is adequate whichever is the lesser amount.
4.1 If dyspepsia limits dose titration consider additional
pharmacotherapy (e.g. omeprazole) to facilitate reaching sufficient
mexiletine dose for adequate treatment trial (200mg TDS).
4.2 In refractory cases and where adverse effects allow, consider further
dose titration to a total of 800mg mexiletine daily. However, patients
should be counselled about the higher risk of side effects associated
with this dose (e.g. dyspepsia).
5 Monitoring of patients on Mexiletine
5.1 Repeat ECG after initial dose titration complete (approximately 2
weeks after stabilised at effective dose).
5.2 Repeat ECG if significant dose change.
5.3 Repeat ECG if any concern over cardiac symptom and consider referral
to Cardiology.
5.4 If mexiletine dose unchanged, no new cardiac symptoms, interacting
medications or other related patient concerns then routine annual
monitoring ECG not indicated (based on audit).
6 When to discuss or refer patients on mexiletine to a cardiologist
6.1 If significant ECG change e.g. atrial fibrillation, heart block.
6.2 If any new cardiac symptom e.g. arrhythmia, syncope, dyspnoea.