Source: Health Products Regulatory Authority (ZA) Revision Year: 2021 Publisher: PHARMACARE LIMITED, Healthcare Park, Woodlands Drive, Woodmead 2191
Category and Class: A 1.2 Psychoanaleptics (antidepressants)
Pharmacotherapeutic group: Selective serotonin reuptake inhibitors
ATC code: N06AB03
The antidepressant and anti-obsessive-compulsive action of fluoxetine is presumed to be linked to its inhibition of central nervous system (CNS) neuronal uptake of serotonin.
Studies at clinically relevant doses in man have demonstrated that fluoxetine blocks the uptake of serotonin into human platelets and
inhibits the neuronal uptake of serotonin into the central nervous system.
Fluoxetine is well absorbed after oral administration.
Fluoxetine is extensively bound to plasma proteins (about 95%) and is widely distributed (volume of distribution: 2 to 40 l/kg). Steady-state plasma concentrations are achieved after dosing for several weeks.
Peak plasma concentration is reached in 6 to 8 hours after a single dose of 40 mg.
Because of the long elimination half-lives of fluoxetine (4 to 6 days) and its major active metabolite, norfluoxetine (4 to 16 days), changes in dose will not be fully reflected in plasma for several weeks (approximately 4 half-lives).
Fluoxetine has a long elimination half-life These long half-lives must be taken into account when doses are titrated or when treatment is stopped.
The disposition of single doses of fluoxetine in healthy elderly patients (>65 years of age) did not differ significantly from that in younger normal subjects. However, given the long half-life and non-linear disposition of the medicine, a single-dose study is not adequate to rule out the possibility of altered pharmacokinetics in the elderly, particularly if they have systemic illness or are receiving multiple medicines for concomitant diseases.
The effects of age upon the metabolism of fluoxetine have been investigated in 260 elderly but otherwise healthy depressed patients (≥60 years of age) who received 20 mg fluoxetine for 6 weeks. Combined fluoxetine plus norfluoxetine plasma concentrations were 209,3 ± 85,7 ng/ml at the end of 6 weeks. No unusual age-associated pattern of adverse events was observed in those elderly patients.
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