Rapid Clot Formation and Abnormal Fibrin Structure in a Symptomatic Patient Taking Fenfluramine: A Case Report

• Published in: Angiology 2001-05, Vol.52 (5), p.361-366
• Main Authors: Carr, Marcus E., Carr, Sheryl L., Martin, Erika J., Johnson, Betty Anne
• Format: Article
• Language: English
• Subjects: Adult; Biological and medical sciences; Blood Coagulation Disorders - chemically induced; Drug toxicity and drugs side effects treatment; Female; Fenfluramine - adverse effects; Fibrin - chemistry; Humans; Medical sciences; Pharmacology. Drug treatments; Prothrombin Time; Time Factors; Toxicity: blood
• ISSN: 0003-3197; 1940-1574
• DOI: 10.1177/000331970105200511

A 35-year-old woman experienced symptomatic calf pain while taking a combination of fenflu ramine and phentermine. All symptoms resolved when the medications were stopped, but pain returned when fenfluramine was restarted. Laboratory evaluation revealed mild elevations of aspartate aminotransferase and lactate dehydrogenase and a remarkably shortened prothrombin time (6.3 seconds). Additional studies revealed that the clots were composed of very thin fibrin fibers. All laboratory abnormalities, including the abnormal fibrin structure, completely resolved when fenfluramin was stopped. Direct addition of fenfluramine or phen termine to normal plasma did not alter either coagulation kinetics or fibrin structure, supporting the concept that the induced changes may have originated at the hepatic level. Clots composed of thin fibers are much more resistant to fibrinolysis, and could potentially put such patients at risk for thrombotic complications. This is the first report of clotting abnormalities associated with fenfluramine use. Subsequent to its use in this patient, fenfluramine was removed from clinical use due to reports of acquired valvular heart disease.