Molecule

Drug Groups

approved

Description

Citalopram hydrobromide belongs to a class of antidepressant agents known as selective serotonin-reuptake inhibitors (SSRIs). Despite distinct structural differences between compounds in this class, SSRIs possess similar pharmacological activity. As with other antidepressant agents, several weeks of therapy may be required before a clinical effect is seen. SSRIs are potent inhibitors of neuronal serotonin reuptake. They have little to no effect on norepinephrine or dopamine reuptake and do not antagonize α- or β-adrenergic, dopamine D₂ or histamine H₁ receptors. During acute use, SSRIs block serotonin reuptake and increase serotonin stimulation of somatodendritic 5-HT_1A and terminal autoreceptors. Chronic use leads to desensitization of somatodendritic 5-HT_1A and terminal autoreceptors. The overall clinical effect of increased mood and decreased anxiety is thought to be due to adaptive changes in neuronal function that leads to enhanced serotonergic neurotransmission. Side effects include dry mouth, nausea, dizziness, drowsiness, sexual dysfunction and headache. Side effects generally occur within the first two weeks of therapy and are usually less severe and frequent than those observed with tricyclic antidepressants. Citalopram is approved for treatment of depression. Unlabeled indications include mild dementia-associated agitation in nonpsychotic patients, smoking cessation, ethanol abuse, obsessive-compulsive disorder (OCD) in children, and diabetic neuropathy. Citalopram has the fewest drug-drug interactions of the SSRIs.

Indication

For the treatment of depression. Unlabeled indications include: treatment of mild dementia-associated agitation in nonpsychotic patients, smoking cessation, ethanol abuse, obsessive-compulsive disorder (OCD) in children, and diabetic neuropathy.

Pharmacology

Citalopram is one of a class of antidepressants known as selective serotonin reuptake inhibitors (SSRIs). It is used to treat the depression associated with mood disorders. It is also used on occassion in the treatment of body dysmorphic disorder and anxiety. The antidepressant, antiobsessive-compulsive, and antibulimic actions of citalopram are presumed to be linked to its inhibition of CNS neuronal uptake of serotonin. In vitro studies show that citalopram is a potent and selective inhibitor of neuronal serotonin reuptake and has only very weak effects on norepinephrine and dopamine neuronal reuptake. Citalopram has no significant affinity for adrenergic (α₁, α₂, β), cholinergic, GABA, dopaminergic, histaminergic, serotonergic (5HT_1A, 5HT_1B, 5HT₂), or benzodiazepine receptors; antagonism of such receptors has been hypothesized to be associated with various anticholinergic, sedative, and cardiovascular effects for other psychotropic drugs. The chronic administration of citalopram was found to downregulate brain norepinephrine receptors, as has been observed with other drugs effective in the treatment of major depressive disorder. Citalopram does not inhibit monoamine oxidase.

Toxicity

Symptoms most often accompanying citalopram overdose, alone or in combination with other drugs and/or alcohol, included dizziness, sweating, nausea, vomiting, tremor, somnolence, and sinus tachycardia. In more rare cases, observed symptoms included amnesia, confusion, coma, convulsions, hyperventilation, cyanosis, rhabdomyolysis, and ECG changes (including QTc prolongation, nodal rhythm, ventricular arrhythmia, and very rare cases of torsade de pointes). Acute renal failure has been very rarely reported accompanying overdose. Withdrawal symptoms include flu-like symptoms, insomnia, nausea, imbalance, sensory changes and hyperactivity.

Affected Organisms

Biotransformation

Citalopram is metabolized mainly in the liver via N-demethylation to its principle metabolite, demethylcitalopram. Other metabolites include didemethylcitalopram, citalopram N-oxide, and a deaminated propionic acid derivative. Cytochrome P450 (CYP) 3A4 and 2C19 isozymes appear to be principally involved in producing demethylcitalopram. Demethylcitalopram appears to be further N-demethylated by CYP2D6 to didemethylcitalopram. Citalopram metabolites possess little pharmacologic activity in comparison to their parent compound and do not likely contribute to the clinical effect of the drug.

Absorption

Rapidly and well absorbed from the GI tract. Peak plasma concentrations occur within 4 hours of a single orally administered dose. Bioavailability is 80% following oral administration. Food does not affect absorption.

Half Life

35 hours

Protein Binding

80% based on in vitro studies.

Elimination

The systemic clearance of citalopram was 330 mL/min, with approximately 20% of that due to renal clearance. Citalopram is metabolized to demethylcitalopram (DCT), didemethylcitalopram (DDCT), citalopram-N-oxide, and a deaminated propionic acid derivative.

Distribution

* 12 L/kg
Citalopram is highly lipophilic and likely widely distributed throughout the body.

References

External Links