CITALOPRAM — citalopram hydrobromide tablet
State of Florida DOH Central Pharmacy
Antidepressants increased the risk compared to placebo of suicidal thinking and behavior (suicidality) in children, adolescents, and young adults in short-term studies of major depressive disorder (MDD) and other psychiatric disorders. Anyone considering the use of citalopram hydrobromide or any other antidepressant in a child, adolescent, or young adult must balance this risk with the clinical need. Short-term studies did not show an increase in the risk of suicidality with antidepressants compared to placebo in adults beyond age 24; there was a reduction in risk with antidepressants compared to placebo in adults aged 65 and older. Depression and certain other psychiatric disorders are themselves associated with increases in the risk of suicide. Patients of all ages who are started on antidepressant therapy should be monitored appropriately and observed closely for clinical worsening, suicidality, or unusual changes in behavior. Families and caregivers should be advised of the need for close observation and communication with the prescriber. Citalopram hydrobromide is not approved for use in pediatric patients. (See WARNINGS: Clinical Worsening and Suicide Risk , PRECAUTIONS: Information for Patients and PRECAUTIONS: Pediatric Use .)
Citalopram hydrobromide, USP is an orally administered selective serotonin reuptake inhibitor (SSRI) with a chemical structure unrelated to that of other SSRIs or of tricyclic, tetracyclic, or other available antidepressant agents. Citalopram hydrobromide, USP is a racemic bicyclic phthalane derivative designated (±)-1-(3-dimethylaminopropyl)-1-(4-fluorophenyl)-1,3-dihydroisobenzofuran-5-carbonitrile, hydrobromide with the following structural formula:
The molecular formula is C20 H22 BrFN2 O and its molecular weight is 405.35.
Citalopram hydrobromide, USP occurs as a fine, white to off-white powder. Citalopram hydrobromide, USP is sparingly soluble in water and soluble in ethanol.
Citalopram hydrobromide, USP are available only in tablet dosage form.
Citalopram tablets, USP, 10 mg are film-coated, oval tablets containing citalopram hydrobromide, USP in strengths equivalent to 10 mg citalopram base. Citalopram tablets, USP, 20 mg and 40 mg, are film-coated, oval, scored tablets containing citalopram hydrobromide, USP in strengths equivalent to 20 mg or 40 mg citalopram base. The tablets also contain the following inactive ingredients: copolyvidone, corn starch, glycerin, lactose monohydrate, magnesium stearate, microcrystalline cellulose, polyvinyl alcohol, polyethylene glycol, sodium starch glycolate, talc and titanium dioxide. Iron oxides are used as coloring agents in the light orange (10 mg) and pink (20 mg) tablets.
The mechanism of action of citalopram hydrobromide as an antidepressant is presumed to be linked to potentiation of serotonergic activity in the central nervous system (CNS) resulting from its inhibition of CNS neuronal reuptake of serotonin (5-HT). In vitro and in vivo studies in animals suggest that citalopram is a highly selective serotonin reuptake inhibitor (SSRI) with minimal effects on norepinephrine (NE) and dopamine (DA) neuronal reuptake. Tolerance to the inhibition of 5-HT uptake is not induced by long-term (14-day) treatment of rats with citalopram. Citalopram is a racemic mixture (50/50), and the inhibition of 5-HT reuptake by citalopram is primarily due to the (S)-enantiomer.
Citalopram has no or very low affinity for 5-HT1A , 5-HT2A , dopamine D1 and D2 , α1 -, α2 — and β-adrenergic, histamine H1 , gamma aminobutyric acid (GABA), muscarinic cholinergic, and benzodiazepine receptors. Antagonism of muscarinic, histaminergic, and adrenergic receptors has been hypothesized to be associated with various anticholinergic, sedative, and cardiovascular effects of other psychotropic drugs.
The single- and multiple-dose pharmacokinetics of citalopram are linear and dose-proportional in a dose range of 10 to 60 mg/day. Biotransformation of citalopram is mainly hepatic, with a mean terminal half-life of about 35 hours. With once daily dosing, steady-state plasma concentrations are achieved within approximately one week. At steady-state, the extent of accumulation of citalopram in plasma, based on the half-life, is expected to be 2.5 times the plasma concentrations observed after a single dose. The tablet and oral solution dosage forms of citalopram hydrobromide are bioequivalent.
Absorption and Distribution
Following a single oral dose (40 mg tablet) of citalopram, peak blood levels occur at about 4 hours. The absolute bioavailability of citalopram was about 80% relative to an intravenous dose, and absorption is not affected by food. The volume of distribution of citalopram is about 12 L/kg and the binding of citalopram (CT), demethylcitalopram (DCT) and didemethylcitalopram (DDCT) to human plasma proteins is about 80%.
Metabolism and Elimination
Following intravenous administrations of citalopram, the fraction of drug recovered in the urine as citalopram and DCT was about 10% and 5%, respectively. 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. In humans, unchanged citalopram is the predominant compound in plasma. At steady-state, the concentrations of citalopram’s metabolites, DCT and DDCT, in plasma are approximately one-half and one-tenth, respectively, that of the parent drug. In vitro studies show that citalopram is at least 8 times more potent than its metabolites in the inhibition of serotonin reuptake, suggesting that the metabolites evaluated do not likely contribute significantly to the antidepressant actions of citalopram.
In vitro studies using human liver microsomes indicated that CYP3A4 and CYP2C19 are the primary isozymes involved in the N-demethylation of citalopram.
Age — Citalopram pharmacokinetics in subjects ≥ 60 years of age were compared to younger subjects in two normal volunteer studies. In a single-dose study, citalopram AUC and half-life were increased in the subjects ≥ 60 years old by 30% and 50%, respectively, whereas in a multiple-dose study they were increased by 23% and 30%, respectively. 20 mg/day is the maximum recommended dose for patients who are greater than 60 years of age (see WARNINGS and DOSAGE AND ADMINISTRATION), due to the risk of QT prolongation.
Gender — In three pharmacokinetic studies (total N=32), citalopram AUC in women was one and a half to two times that in men. This difference was not observed in five other pharmacokinetic studies (total N=114). In clinical studies, no differences in steady-state serum citalopram levels were seen between men (N=237) and women (N=388). There were no gender differences in the pharmacokinetics of DCT and DDCT. No adjustment of dosage on the basis of gender is recommended.
Reduced hepatic function — Citalopram oral clearance was reduced by 37% and half-life was doubled in patients with reduced hepatic function compared to normal subjects. Citalopram hydrobromide 20 mg/day is the maximum recommended dose for hepatically impaired patients (see WARNINGS and DOSAGE AND ADMINISTRATION), due to the risk of QT prolongation.
CYP2C19 poor metabolizers – In CYP2C19 poor metabolizers, citalopram steady-state Cmax and AUC was increased by 68% and 107%, respectively. Citalopram hydrobromide 20 mg/day is the maximum recommended dose in CYP2C19 poor metabolizers due to the risk of QT prolongation (see WARNINGS and DOSAGE AND ADMINISTRATION).
CYP2D6 poor metabolizers — Citalopram steady-state levels were not significantly different in poor metabolizers and extensive metabolizers of CYP2D6.
Reduced renal function — In patients with mild to moderate renal function impairment, oral clearance of citalopram was reduced by 17% compared to normal subjects. No adjustment of dosage for such patients is recommended. No information is available about the pharmacokinetics of citalopram in patients with severely reduced renal function (creatinine clearance < 20 mL/min).
In vitro enzyme inhibition data did not reveal an inhibitory effect of citalopram on CYP3A4, -2C9, or -2E1, but did suggest that it is a weak inhibitor of CYP1A2, -2D6 and -2C19. Citalopram would be expected to have little inhibitory effect on in vivo metabolism mediated by these enzymes. However, in vivo data to address this question are limited.
CYP3A4 and CYP 2C19 inhibitors: Since CYP3A4 and CYP 2C19 are the primary enzymes involved in the metabolism of citalopram, it is expected that potent inhibitors of CYP3A4 (e.g., ketoconazole, itraconazole and macrolide antibiotics) and potent inhibitors of CYP2C19 (e.g., omeprazole) might decrease the clearance of citalopram. However, coadministration of citalopram and the potent CYP3A4 inhibitor ketoconazole did not significantly affect the pharmacokinetics of citalopram. Citalopram hydrobromide 20 mg/day is the maximum recommended dose in patients taking concomitant cimetidine or another CYP2C19 inhibitor because of the risk of QT prolongation (see WARNINGS and DOSAGE AND ADMINISTRATION).
CYP2D6 Inhibitors: Coadministration of a drug that inhibits CYP2D6 with citalopram hydrobromide is unlikely to have clinically significant effects on citalopram metabolism, based on the study results in CYP2D6 poor metabolizers.
Clinical Efficacy Trials
The efficacy of citalopram hydrobromide as a treatment for depression was established in two placebo-controlled studies (of 4 to 6 weeks in duration) in adult outpatients (ages 18 to 66) meeting DSM-III or DSMIII-R criteria for major depression. Study 1, a 6-week trial in which patients received fixed citalopram hydrobromide doses of 10, 20, 40 and 60 mg/day, showed that citalopram hydrobromide at doses of 40 and 60 mg/day was effective as measured by the Hamilton Depression Rating Scale (HAMD) total score, the HAMD depressed mood item (Item 1), the Montgomery Asberg Depression Rating Scale and the Clinical Global Impression (CGI) Severity scale. This study showed no clear effect of the 10 and 20 mg/day doses, and the 60 mg/day dose was not more effective than the 40 mg/day dose. In study 2, a 4-week, placebo-controlled trial in depressed patients, of whom 85% met criteria for melancholia, the initial dose was 20 mg/day, followed by titration to the maximum tolerated dose or a maximum dose of 80 mg/day. Patients treated with citalopram hydrobromide showed significantly greater improvement than placebo patients on the HAMD total score, HAMD item 1 and the CGI Severity score. In three additional placebo-controlled depression trials, the difference in response to treatment between patients receiving citalopram hydrobromide and patients receiving placebo was not statistically significant, possibly due to high spontaneous response rate, smaller sample size, or, in the case of one study, too low a dose.
In two long-term studies, depressed patients who had responded to citalopram hydrobromide during an initial 6 or 8 weeks of acute treatment (fixed doses of 20 or 40 mg/day in one study and flexible doses of 20 to 60 mg/day in the second study) were randomized to continuation of citalopram hydrobromide or to placebo. In both studies, patients receiving continued citalopram hydrobromide treatment experienced significantly lower relapse rates over the subsequent 6 months compared to those receiving placebo. In the fixed-dose study, the decreased rate of depression relapse was similar in patients receiving 20 or 40 mg/day of citalopram hydrobromide.
Analyses of the relationship between treatment outcome and age, gender and race did not suggest any differential responsiveness on the basis of these patient characteristics.
Comparison of Clinical Trial Results
Highly variable results have been seen in the clinical development of all antidepressant drugs. Furthermore, in those circumstances when the drugs have not been studied in the same controlled clinical trial(s), comparisons among the results of studies evaluating the effectiveness of different antidepressant drug products are inherently unreliable. Because conditions of testing (e.g., patient samples, investigators, doses of the treatments administered and compared, outcome measures, etc.) vary among trials, it is virtually impossible to distinguish a difference in drug effect from a difference due to one of the confounding factors just enumerated.
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