Flibanserin

Flibanserin (brand name Addyi) is an oral medication approved for the treatment of hypoactive sexual desire disorder (HSDD) in premenopausal women. It is the first drug in its class indicated specifically to enhance sexual desire in women.

Flibanserin is used to treat HSDD, a condition characterized by low sexual desire that causes distress or interpersonal difficulty. It should be taken once daily at bedtime.

The mechanism of action involves modulation of central nervous system neurotransmitters—acting as a serotonin 5-HT_1A receptor agonist and 5-HT_2A receptor antagonist—to restore balance between excitatory and inhibitory signaling pathways in the brain.

CYP2C19 is the primary enzyme responsible for the metabolism of flibanserin in the liver. As a member of the cytochrome P450 family, CYP2C19 helps convert the drug into inactive metabolites that can be excreted from the body.

Variations in the CYP2C19 gene can alter enzyme activity—ranging from no function (poor metabolizer) to increased function (ultrarapid metabolizer). These changes affect how quickly flibanserin is cleared, influencing drug levels in the bloodstream.

Genetic variations in CYP2C19 give rise to different metabolizer phenotypes. Ultrarapid or rapid metabolizers clear flibanserin more quickly, potentially reducing its effectiveness, while poor metabolizers clear it slowly, increasing the risk of higher blood levels and adverse effects.

Ultrarapid Metabolizer

• Effect on drug levels: Lower systemic flibanserin concentrations.
• Clinical consequence: Potentially reduced efficacy in improving sexual desire.
• Side effects: Similar to normal metabolizers; no increase in severity or frequency expected.

Rapid Metabolizer

• Effect on drug levels: Moderately lower blood levels of flibanserin.
• Clinical consequence: Possible modest decrease in therapeutic response.
• Side effects: Typical side effects; no significant change in risk profile.

Normal Metabolizer

• Effect on drug levels: Expected standard flibanserin concentrations.
• Clinical consequence: Usual efficacy in treating HSDD.
• Side effects: Common adverse effects such as dizziness, somnolence, and hypotension; generally mild to moderate.

Intermediate Metabolizer

• Effect on drug levels: Moderately higher flibanserin concentrations.
• Clinical consequence: Slightly increased risk of side effects.
• Side effects: Mild to moderate dizziness or sedation may occur more frequently.

Poor Metabolizer

• Effect on drug levels: Significantly elevated systemic concentrations.
• Clinical consequence: Higher risk of adverse reactions due to drug accumulation.
• Side effects: Increased incidence and severity of hypotension, syncope, dizziness, and sedation.

Indeterminate / Not Available

• Effect on drug levels: Unknown impact due to uncharacterized genotype.
• Clinical consequence: No specific guidance; follow standard dosing with clinical monitoring.
• Side effects: Unknown; monitor for typical adverse events.

CYP2C19 Dosing Guideline

Examples of alternative approaches mentioned in clinical practice include bremelanotide (Vyleesi®), an injectable melanocortin receptor agonist approved for premenopausal HSDD, as well as non-pharmacologic strategies such as counseling and behavioral therapy.

• FDA – Table of Pharmacogenetic Associations