| toxicity summary | IDENTIFICATION: Fluoxetine is a selective serotonin reuptake inhibitor used as an antidepressant agent. It is soluble in: water, methanol, chloroform and insoluble in hexane, ethyl acetate and benzene. HUMAN EXPOSURE: Main risks and target organs: Fluoxetine is safer in overdose than most other classes of antidepressants. In overdosage, most patients experience only mild neurological and gastroenterological symptoms; significant cardiovascular toxicity is unusual. The serotonergic effects of fluoxetine may be enhanced by combination with other antidepressants, monoamine oxidase inhibitors, carbamazepine or lithium and produce a life-threatening serotoninergic syndrome comprising hyperthermia, tremor and convulsions. Summary of clinical effects: Drowsiness, tremor, headache, blurred vision, dizziness, restlessness, and rarely, seizures and coma. Nausea, vomiting, abdominal pain. Bradycardia, mild hypertension or hypotension. Contraindications: Absolute: Hypersensitivity to fluoxetine. Coadministration of sumatriptan, non-specific monoamine oxidase inhibitors and B-specific monoamine oxidase inhibitors. Relative: Combination therapy with A-specific monoamine oxidase inhibitors or other antidepressants. Pregnancy or lactation. Routes of entry: Oral: Fluoxetine is administered orally. Absorption by route of exposure: Fluoxetine hydrochloride is readily absorbed from the gastrointestinal tract with peak plasma concentrations appearing from 6 to 8 hours after oral administration. The systemic bioavailability is greater than 85 % and does not appear to be affected by food. Distribution by route of exposure: Fluoxetine is widely distributed throughout the body. Plasma protein binding is 94 %. Biological half-life by route of exposure: Fluoxetine has a relatively long and highly variable half-life ranging from 1 to 4 days after a single dose and averaging nearly 70 hours; patients receiving high doses over long periods of time may exhibit prolonged elimination half-lives. The half-life of its active metabolite, norfluoxetine, is about 7 to 9 days. Metabolism: Fluoxetine is extensively metabolized in the liver to a desmethyl metabolite, norfluoxetine, which has activity similar to fluoxetine. Peak plasma concentrations of the active metabolite, norfluoxetine, occur around 76 hours after ingestion. Elimination and excretion: The primary route of elimination appears to be further hepatic metabolism to inactive metabolites which are conjugated and then excreted in the urine. Mode of action: Toxicodynamics: Fluoxetine is a potent inhibitor of serotonin re-uptake by Central Nervous System neurones and may interact with other drugs or circumstances which cause serotonin release. The enhancement of the serotonergic effects may produce a life-threatening serotonin syndrome. Pharmacodynamics: Fluoxetine specifically inhibits neuronal re-uptake of serotonin, thus increasing the concentration of the serotonin at the synapse and reinforcing of serotonergic neuronal transmission. Fluoxetine has little effect on other neurotransmitters. Fluoxetine has no direct effect on the heart. Carcinogenicity: Human studies: there is no evidence of carcinogenicity in patients taking fluoxetine. Teratogenicity: Human studies: a study of 128 women exposed to fluoxetine during the first trimester showed no increase in major fetal malformations. It is not known, however, if the drug is a human teratogen. A neonate whose mother had been taking fluoxetine during most of her pregnancy suffered tachypnea, emesis, continuous crying, irritability, tremor and increased muscle tone; the symptoms resolved within 96 hours. Fluoxetine and norfluoxetine are excreted in breast milk. The effects on the infant are uncertain. Caution should be exercised when fluoxetine is administered to a nursing mother. Interactions: Drug interactions with fluoxetine have been reported with L-tryptophan, L-dopa; monoamine oxidase inhibitors: selegiline, tranylcypromine; tricyclic antidepressants; selective serotonin re-uptake inhibitors: trazodone, zimeldine; benzodiazepines: alprazolam, diazepam; buspirone, lithium, anticonvulsants: carbamazepine, phenytoin, valproate; pentazocine, dextromethorphan, fenfluramine, calcium channel blockers, benztropine, cyproheptadine, clarithromycin. Cannabis, ethanol and LSD. At least 14 days should elapse between discontinuing a MAO-inhibiting antidepressant and introducing fluoxetine. Conversely, because of the long half-life of fluoxetine and its metabolite, norfluoxetine, it is recommended that at least 5 weeks should elapse between discontinuation of fluoxetine and the introduction of a MAO inhibitor. Main adverse effects: The major adverse effects reported with therapeutic doses of fluoxetine are primarily those of headache, insomnia, nausea, and nervousness. Less common adverse effects include tremors, sweating, dry mouth, anxiety, drowsiness, and diarrhea. ANIMAL/PLANT STUDIES: Carcinogenicity: Animal studies: fluoxetine was not carcinogenic in rats and mice at doses ten times the recommended daily dose for 24 months. Teratogenicity: Animal studies: in rats, fluoxetine and norfluoxetine cross the placenta and distribute within the fetus during the periods of organogenesis and postorganogenesis. Levels in fetal tissue are approximately half the corresponding maternal concentrations. Fluoxetine does not impair the fetal growth in rats or rabbits at doses nine and eleven times the maximum daily human dose respectively. Mutagenicity: In vitro: fluoxetine and norfluoxetine did not show mutagenicity in the Ames test. There was no induction of sister-chromatid exchange in the bone marrow of the Chinese Hamster. |
