Serotonin (5-HT) Antagonist Overview Including Classification

5-Hydroxytryptamine (5-HT) Antagonists

Classification, Mechanism, Indications, Adverse Effects & Drug Interactions
Focus Drugs: Ergotamine, Risperidone, Olanzapine, Ondansetron, Granisetron, Clozapine

Overview of Serotonin (5-HT)

Serotonin: Neurotransmitter derived from tryptophan
Involved in mood, appetite, sleep, nausea, and vasoconstriction
Multiple receptor subtypes (5-HT1 to 5-HT7)

Ergotamine

Class: 5-HT1 Partial Agonist/Antagonist
Mechanism: Vasoconstriction of intracranial vessels
Indications: Acute migraine, cluster headaches
Adverse Effects: Nausea, vasospasm, ischemia
Interactions: Avoid with triptans, CYP3A4 inhibitors

Risperidone

Class: Atypical antipsychotic (5-HT2A > D2 blockade)
Mechanism: Blocks 5-HT2A and dopamine D2 receptors
Indications: Schizophrenia, bipolar disorder
Adverse Effects: EPS, hyperprolactinemia
Interactions: CYP2D6 inhibitors may increase effects

Olanzapine

Class: Atypical antipsychotic
Mechanism: Blocks 5-HT2A, D2, H1, muscarinic receptors
Indications: Schizophrenia, bipolar disorder, depression adjunct
Adverse Effects: Weight gain, sedation, metabolic syndrome
Interactions: CYP1A2 inhibitors (e.g., fluvoxamine)

Clozapine

Class: Atypical antipsychotic
Mechanism: Blocks 5-HT2A, D4 > D2
Indications: Resistant schizophrenia, suicidality
Adverse Effects: Agranulocytosis, seizures, myocarditis
Interactions: CYP1A2/3A4 substrates, avoid bone marrow suppressants

Ondansetron

Class: 5-HT3 Antagonist
Mechanism: Blocks serotonin at vagal nerve terminals & CTZ
Indications: Nausea/vomiting (chemo, surgery)
Adverse Effects: Headache, constipation, QT prolongation
Interactions: QT-prolonging agents

Granisetron

Class: 5-HT3 Antagonist
Mechanism: Similar to ondansetron
Indications: Chemotherapy-induced nausea/vomiting
Adverse Effects: QT prolongation, headache
Interactions: Caution with QT-prolonging drugs

References

Katzung, Basic & Clinical Pharmacology
Goodman & Gilman’s Pharmacological Basis of Therapeutics
Latest clinical guidelines on antipsychotic and antiemetic use

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