Scientific Poster Session III - Case Reports

Case Reports
  Monday, October 14, 2024
  01:00 PM–02:30 PM

Abstract

Introduction: Use of cytochrome P450 (CYP) 3A4 enzyme-inducers, including primidone, is contraindicated with ticagrelor. In patients with acute coronary syndromes (ACS), reviewing home medications prior to P2Y₁₂ inhibitor administration is not always feasible. With a previous report describing stent thrombosis with concomitant primidone, the purpose of this report is to determine the impact of primidone on ticagrelor’s pharmacodynamic profile utilizing the VerifyNow platelet aggregation assay.

Case: An 83-year-old man presented to an outside hospital with complaints of chest pain and diagnosed with a non ST-elevation myocardial infarction. On day one of admission, he received ticagrelor 180 mg and was continued on 90 mg twice daily. On day seven, he transferred and underwent left heart catheterization receiving two drug-eluting stents to the left anterior descending coronary artery. The drug-drug interaction between the patient’s prior-to-admission primidone 50 mg three times daily and ticagrelor was discovered by the team’s pharmacist. A VerifyNow assay 23 hours after the last ticagrelor dose resulted as 76 P2Y₁₂ reaction units (PRU). Eight hours later, he was switched to clopidogrel with a 600 mg loading dose followed by 75 mg once daily.

Discussion: The case provides evidence regarding use of primidone in a patient with ACS receiving ticagrelor. The findings contrast with a report demonstrating ticagrelor failure when combined with primidone. One explanation could be CYP2C19 phenotype variability. CYP2C19 metabolizes primidone to phenobarbital, with phenobarbital primarily responsible for primidone’s CYP enzyme-inducing properties. Patients who are CYP2C19 rapid metabolizers, in theory, have higher levels of phenobarbital compared with slow or normal metabolizers, with this patient plausibly representing the latter group.

Conclusion: Out of an abundance of caution, primidone use with ticagrelor should be avoided to reduce stent thrombosis risk. If ticagrelor must be used in combination with primidone, PRU levels should be monitored to ensure adequate antiplatelet activity.

Presenting Author

Matthew Rockhold PharmD
WVU Medicine

Authors

Jordan Lacoste PharmD
WVU Medicine

Thomas Szymanski PharmD
WVU Medicine