Fluvoxamine Maleate (Page 6 of 12)

6.9 Postmarketing Reports

The following adverse reactions have been identified during post-approval use of Fluvoxamine Maleate Tablets. Because these reactions are reported voluntarily from a population of uncertain size, it is not always possible to reliably estimate their frequency or establish a causal relationship to drug exposure.

Voluntary reports of adverse reactions in patients taking Fluvoxamine Maleate Tablets that have been received since market introduction and are of unknown causal relationship to Fluvoxamine Maleate Tablets use include: acute renal failure, agranulocytosis, amenorrhea, anaphylactic reaction, angioedema, aplastic anemia, bullous eruption, Henoch-Schoenlein purpura, hepatitis, ileus, pancreatitis, porphyria, Stevens-Johnson syndrome, toxic epidermal necrolysis, vasculitis, and ventricular tachycardia (including torsades de pointes).

7 DRUG INTERACTIONS

7.1 Potential Interactions with Drugs that Inhibit or are Metabolized by Cytochrome P450 Isoenzymes

Multiple hepatic cytochrome P450 isoenzymes are involved in the oxidative biotransformation of a large number of structurally different drugs and endogenous compounds. The available knowledge concerning the relationship of fluvoxamine and the cytochrome P450 isoenzyme system has been obtained mostly from pharmacokinetic interaction studies conducted in healthy volunteers, but some preliminary in vitro data are also available. Based on a finding of substantial interactions of fluvoxamine with certain of these drugs [see later parts of this section and also Warnings and Precautions (5) ] and limited in vitro data for CYP3A4, it appears that fluvoxamine inhibits several cytochrome P450 isoenzymes that are known to be involved in the metabolism of other drugs such as: CYP1A2 (e.g., warfarin, theophylline, propranolol, tizanidine), CYP2C9 (e.g., warfarin), CYP3A4 (e.g., alprazolam), and CYP2C19 (e.g., omeprazole).

In vitro data suggest that fluvoxamine is a relatively weak inhibitor of CYP2D6.

Approximately 7% of the normal population has a genetic code that leads to reduced levels of activity of CYP2D6. Such individuals have been referred to as “poor metabolizers” (PM) of drugs such as debrisoquin, dextromethorphan, and tricyclic antidepressants. While none of the drugs studied for drug interactions significantly affected the pharmacokinetics of fluvoxamine, an in vivo study of fluvoxamine single-dose pharmacokinetics in 13 PM subjects demonstrated altered pharmacokinetic properties compared to 16 “extensive metabolizers” (EM): mean Cmax , AUC, and half-life were increased by 52%, 200%, and 62%, respectively, in the PM compared to the EM group. This suggests that fluvoxamine is metabolized, at least in part, by CYP2D6. Caution is indicated in patients known to have reduced levels of CYP2D6 activity and those receiving concomitant drugs known to inhibit this cytochrome P450 isoenzyme (e.g., quinidine).

The metabolism of fluvoxamine has not been fully characterized and the effects of potent cytochrome P450 isoenzyme inhibition, such as the ketoconazole inhibition of CYP3A4, on fluvoxamine metabolism have not been studied.

A clinically significant fluvoxamine interaction is possible with drugs having a narrow therapeutic ratio such as pimozide, warfarin, theophylline, certain benzodiazepines, omeprazole and phenytoin. If Fluvoxamine Maleate Tablets are to be administered together with a drug that is eliminated via oxidative metabolism and has a narrow therapeutic window, plasma levels and/or pharmacodynamic effects of the latter drug should be monitored closely, at least until steady-state conditions are reached [see Contraindications (4), Warnings and Precautions (5)].

7.2 CNS Active Drugs

Antipsychotics: See Warnings and Precautions (5.2).

Benzodiazepines: See Warnings and Precautions (5.8).

Alprazolam: See Warnings and Precautions (5.8).

Diazepam: See Warnings and Precautions (5.8).

Lorazepam: A study of multiple doses of fluvoxamine maleate (50 mg b.i.d.) in healthy male volunteers (N=12) and a single dose of lorazepam (4 mg single dose) indicated no significant pharmacokinetic interaction. On average, both lorazepam alone and lorazepam with fluvoxamine produced substantial decrements in cognitive functioning; however, the coadministration of fluvoxamine and lorazepam did not produce larger mean decrements compared to lorazepam alone.

Alcohol: Studies involving single 40 g doses of ethanol (oral administration in one study and intravenous in the other) and multiple dosing with fluvoxamine maleate (50 mg b.i.d.) revealed no effect of either drug on the pharmacokinetics or pharmacodynamics of the other. As with other psychotropic medications, patients should be advised to avoid alcohol while taking Fluvoxamine Maleate Tablets.

Carbamazepine: Elevated carbamazepine levels and symptoms of toxicity have been reported with the coadministration of fluvoxamine maleate and carbamazepine.

Clozapine: See Warnings and Precautions (5.8).

Lithium: As with other serotonergic drugs, lithium may enhance the serotonergic effects of fluvoxamine and, therefore, the combination should be used with caution. Seizures have been reported with the coadministration of fluvoxamine maleate and lithium.

Methadone: See Warnings and Precautions (5.8).

Monoamine Oxidase Inhibitors: See Dosage and Administration ( 2.4, 2.5), Contraindications (4), Warnings and Precautions (5.2).

Pimozide: See Contraindications (4), Warnings and Precautions (5.6).

Ramelteon: See Warnings and Precautions (5.8).

Serotonergic Drugs: See Dosage and Administration ( 2.4, 2.5), Contraindications (4), Warnings and Precautions (5.2).

Tacrine: In a study of 13 healthy, male volunteers, a single 40 mg dose of tacrine added to fluvoxamine 100 mg/day administered at steady-state was associated with five- and eight-fold increases in tacrine Cmax and AUC, respectively, compared to the administration of tacrine alone. Five subjects experienced nausea, vomiting, sweating, and diarrhea following coadministration, consistent with the cholinergic effects of tacrine.

Thioridazine: See Contraindications (4), Warnings and Precautions (5.4).

Tizanidine: See Contraindications (4), Warnings and Precautions (5.5).

Tricyclic Antidepressants (TCAs): Significantly increased plasma TCA levels have been reported with the coadministration of fluvoxamine maleate and amitriptyline, clomipramine or imipramine. Caution is indicated with the coadministration of Fluvoxamine Maleate Tablets and TCAs; plasma TCA concentrations may need to be monitored, and the dose of TCA may need to be reduced.

Triptans: There have been rare postmarketing reports of serotonin syndrome with use of an SSRI and a triptan. If concomitant treatment of fluvoxamine with a triptan is clinically warranted, careful observation of the patient is advised, particularly during treatment initiation and dose increases [see Warnings and Precautions (5.2)].

Sumatriptan: There have been rare postmarketing reports describing patients with weakness, hyperreflexia, and incoordination following the use of a selective serotonin reuptake inhibitor (SSRI) and sumatriptan. If concomitant treatment with sumatriptan and an SSRI (e.g., fluoxetine, fluvoxamine, paroxetine, sertraline) is clinically warranted, appropriate observation of the patient is advised.

Tryptophan: Tryptophan may enhance the serotonergic effects of fluvoxamine, and the combination should, therefore, be used with caution. Severe vomiting has been reported with the coadministration of fluvoxamine maleate and tryptophan [see Warnings and Precautions (5.2)].

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