fenfluramine hydrochloride: clinical use

Prescribing considerations

• Initiation and supervision should be by a clinician experienced in treating epilepsy.
• Prescribe and dispense through the controlled access programme; use for weight management is not permitted.
• Review renal and hepatic function, particularly with stiripentol.
• Assess appetite, weight, eating-disorder history, sedation, mood, seizure frequency, serotonergic medicines and glaucoma risk.
• Avoid abrupt withdrawal because seizures or status epilepticus may increase.

Contraindications and cautions

• Hypersensitivity to fenfluramine or an excipient
• Aortic or mitral valvular heart disease
• Pulmonary arterial hypertension
• Concurrent or recent MAOI use

Monitoring

• Obtain a baseline echocardiogram to exclude valvular disease and pulmonary hypertension.
• Repeat echocardiography regularly during treatment and after stopping.
• Monitor weight, appetite, seizure frequency, somnolence, mood, suicidal ideation, serotonin toxicity and acute visual symptoms.
• Investigate abnormal echocardiographic findings promptly with cardiology input and reassess benefit versus risk.

Clinical pharmacology

Fenfluramine releases serotonin and acts at 5-HT1D, 5-HT2A and 5-HT2C receptors and the sigma-1 receptor. It is extensively metabolised to active norfenfluramine, mainly through CYP1A2, CYP2B6 and CYP2D6, with elimination predominantly in urine.

Formulation and product differences

• The UK product is a clear, colourless, cherry-flavoured oral solution.
• Packs include a press-in bottle adaptor and graduated oral syringes.
• The solution is compatible with most enteral feeding tubes and a ketogenic diet.
• It contains parabens, a small amount of glucose and trace sulfur dioxide, which may matter in hypersensitivity or glucose-galactose malabsorption.
• Use within 3 months after opening; do not refrigerate or freeze.

Oral solution

Route: Oral

Strengths: 2.2 mg/mL