Generic Name

Citalopram

Mechanism

Citalopram is a selective serotonin‑reuptake inhibitor (SSRI).
• Primary action: Inhibits the presynaptic serotonin transporter (SERT), increasing synaptic 5‑HT concentration.
• Secondary effects: Modestly potentiates 5‑HT₁A receptor activity; minimal antagonism at histamine, α₁‑adrenergic, or muscarinic receptors, which accounts for its favorable side‑effect profile.
• Result: Enhanced serotonergic neurotransmission leads to mood elevation and anxiolysis after several weeks of therapy.

Pharmacokinetics

• Absorption: Rapid, ~60 % bioavailability; peak plasma levels at ~3–4 h post‑dose.
• Food effect: Minimal.
• Distribution: Highly protein‑bound (~94 % to albumin; 73 % to α‑1‑acid glycoprotein).
• Metabolism: Primarily hepatic via CYP2C19, 3A4, and 2D6 to active N‑desmethyl‑citalopram.
• Elimination: Renal excretion of metabolites (~80 %); half‑life ~30 h (steady‑state ~40 h).
• Special populations:
• Renal impairment: No dose adjustment needed.
• Hepatic impairment: Use low‑dose titration; monitor for hepatotoxicity.
• Genetic polymorphisms: Poor CYP2C19 metabolizers may experience higher plasma levels—consider dose adjustment.

Indications

• Major depressive disorder (MDD).
• Generalized anxiety disorder (GAD).
• Obsessive‑compulsive disorder (OCD) (off‑label, used cautiously).
• Panic disorder (off‑label).

Contraindications

• Contraindications:
• Known hypersensitivity to citalopram or other SSRIs.
• Concomitant use with monoamine oxidase inhibitors (MAOIs) within 14 days.
• Significant QT prolongation or arrhythmia.
• Severe hepatic impairment.
• Warnings:
• Suicidal ideation in patients <25 yr; monitor closely.
• Serotonin syndrome risk when combined with serotonergic agents.
• QTc prolongation; caution with drugs that also prolong QT (e.g., ondansetron, quinidine).
• Hyponatremia—especially in elderly or those on diuretics.
• Pregnancy Category C—use only if benefits outweigh risks.

Dosing

• Administration: Take in the morning; at the same time daily.
• Steady‑state: Achieved ≈5 days; full therapeutic benefit typically seen at 4–6 weeks.

Adverse Effects

Common (≥10 %):
• Nausea, dry mouth, insomnia, sexual dysfunction (decreased libido, anorgasmia).
• Diarrhea, dizziness, increased sweating.

Serious (≤1 %):
• Serotonin syndrome (hyperreflexia, tremor, clonus, confusion).
• QT interval prolongation → torsades de pointes.
• Hyponatremia → confusion, seizures.
• Severe rash / Stevens–Johnson syndrome (rare).
• Bleeding (especially with aspirin, warfarin).

Monitoring

• Baseline & periodic:
• ECG if QTc prolongation risk or concurrent QT‑prolonging agents.
• Serum electrolytes (Na⁺), especially in elderly or diuretic users.
• Liver function tests if hepatic impairment or in pregnancy.
• During therapy:
• Monitor for signs of serotonin syndrome, especially during dose escalation or drug interactions.
• Assess suicidality at every visit for patients <25 yr.
• Laboratory work‑up: Not routinely required for most patients, but advisable if clinically indicated.

Clinical Pearls

• Avoid abrupt discontinuation: Even after 8 weeks of therapy, taper over ≥4 weeks to prevent discontinuation syndrome (nausea, dizziness, flu‑like symptoms).
• CYP2C19‑poor metabolizers: Because the parent drug is metabolized to the active metabolite, use a lower starting dose (e.g., 10 mg) and monitor plasma levels if available.
• Drug‑drug interactions:
• MAOIs: Avoid concurrent therapy; wait ≥14 days after the last MAOI dose.
• NSAIDs/warfarin: ↑ bleeding risk—consider gastro‑protective agents.
• St. John’s wort: Reduces citalopram levels via CYP induction—caution advised.
• Age & renal function: No dose adjustment for renal impairment, but monitor for increased sensitivity in elderly due to reduced hepatic clearance.
• Pregnancy & lactation: Category C; cross‑placental transfer occurs; counsel about potential neonatal serotonin syndrome if used near delivery.
• Elderly patients: Begin at 10 mg q.d. and titrate slowly; watch for orthostatic hypotension and fall risk.

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