Paroxetine and fluoxetine

Charlier, C., Broly, F., Lhermitte, M., Pinto, E., Ansseau, M., and Plomteux, G., Polymorphisms in the CYP 2D6 gene association with plasma concentrations of fluoxetine and paroxetine, Ther. Drug Monit. 25(6), 738-742, 2003. 

Describe the advantages that fluoxetine and paroxetine offer over typical antidepressants. 

Selective serotonin reuptake inhibitor (SSRI) Currently, the most widely used antidepressants (e.g., fluoxetine and paroxetine). 

Increased plasma concentrations of TCAs and symptoms of toxicity may occur when fluoxetine and paroxetine are added to a TCA regimen. 

SSRIs—fluvoxamine, fluoxetine, and paroxetine, more than sertraline and citalopram Inhibition of metabolism at CYP2D6 isoenzyme TCA toxicity due to up to 10-fold increase in TCA levels with coadministration Lower TCA dose Baumann, 1996... 

There are several antipsychotics that are substrates to CYP2D6 (von Bahr et ah, 1991 Jerling et ah, 1996 Ring et ah, 1996 (Fang and Gorrod, 1999 Flockhart and Oesterheld, 2000) (Table 26.3). Moreover, several antipsychotics may act as inhibitors of CYP2D6-mediated biotransformation. These include thioridazine, chlorpromazine, haloperidol, fluphenazine, and pimozide (Desta et ah, 1998 Shin et ah, 1999). Of particular salience is the fact that the serotonin selective reuptake inhibitors (SSRIs) fluoxetine and paroxetine are metabolized to a significant extent by this isoenzyme. 

The initial reports from open studies (Artigas et al. 1994 Blier and Bergeron 1995) suggest that the combination is associated with improved efficacy with probable faster onset of action. This rapid response was reported with augmentation of fluoxetine and paroxetine, and more recently with nefazodone (Bakish et al. 1997), but interestingly not with sertraline or low doses of fluvoxamine. These results needed to be confirmed in placebo-controlled studies, and the reports from large studies do indeed find an acceleration of response measured as time to response and possible superiority of action with some antidepressants at the end of treatment (Perez et al. 1997 Tome de la Granja et al. 1997). 

SSRIs such as fluoxetine and paroxetine may inhibit the metabolism of antipsychotics, increasing their plasma levels and the chance for toxicity ( 517, 518). While antipsychotics may inhibit the metabolism of tricyclic antidepressants, or, in turn, have their metabolism inhibited by tricyclic antidepressants, the clinical relevance is uncertain. 

Of interest, treatment with hypericum is more expensive than with TCAs. Although it is somewhat less expensive than fluoxetine and paroxetine, depending on the formulation of hypericum used, its cost is comparable with that of sertraline. 

Fluvoxamine, fluoxetine, and paroxetine have nonlinear pharmacokinetics, which means that dose increases lead to disproportionately greater increases in plasma drug levels (25). In contrast, citalopram and sertraline have linear pharmacokinetics. For these reasons, dose increases with fluvoxamine, fluoxetine, and paroxetine can lead to greater than proportional increases in concentration-dependent effects such as serotonin-mediated adverse effects (e.g., nausea) and inhibition of specific CYP enzymes. 

Because reboxetine and bupropion share with desipramine the ability to block the NE uptake pump, some clinician may want to combine them with an SSRI. Bupropion, however, should be used cautiously with fluvoxamine, fluoxetine, and paroxetine because these three antidepressants inhibit one or more CYP enzymes to a substantial degree at their lowest, usually effective antidepressant dose. Therefore, the dose of bupropion should be kept low and TDM could be used to ensure that unusually high levels of bupropion or its active metabolites do not develop. 

There is a great disparity of current knowledge regarding the effects of antidepressants on GYP enzymes. There have been almost no studies to test the potential effects of TCAs, MAOIs, and trazodone on GYP enzymes. There has only been one study with bupropion but it demonstrated that bupropion produces substantial inhibition of GYP 2D6 comparable with the effect of fluoxetine and paroxetine. In contrast to studies in these antidepressants, there have been extensive in vitro and in vivo studies of SSRIs, nefazodone, and venlafaxine. 

The major distinguishing characteristic among the SSRIs is CYP enzyme inhibition. Fluvoxamine, fluoxetine, and paroxetine produce substantial inhibition of one or more CYP enzymes, whereas citalopram and sertraline do not (Table 7-29). In fact, fluvoxamine, fluoxetine, and paroxetine have all caused fatal drug-drug interactions via such CYP enzyme inhibition (339, 496, 497). 

The meta-analysis of all studies comparing clomipramine or SRIs with placebo for the treatment of OCD found that the active drug produced a better result in every trial. We then calculated the effect size and the statistical significance for clomipramine alone and fluvoxamine alone. Their results showed a highly significant effect for both drugs (Table 13-10 and Table 13-11). There were also several studies with sertraline, fluoxetine, and paroxetine that demonstrated similar results (219, 220, 221, 222. 223,. 224, 225 and 226). 

St. John s wort (Hypericum perforatum) is a perennial wildflower indigenous to Europe, North Africa, and western Asia (Fig. 1) and has been used for medicinal purposes for over two millennia. As far back as the early 16th century, St. John s wort was used primarily to treat anxiety, depression, and sleep disorders. In the late 20th and early 21st century, St. John s wort has been recommended for the treatment of mild to moderate depression (7). In support of its use for the treatment of mild to moderate depression, a number of clinical trials have demonstrated that St. John s wort has comparable efficacy to the tricyclic antidepressants (i.e., imipramine) and selective serotonin reuptake inhibitors (e.g., fluoxetine and paroxetine) (8-13). 

Fluoxetine and paroxetine inhibit cytochrome CYP P-450 2D6 and thus may affect metabolism of some opioids, e.g. codeine, 0) codone and tramadol, that are partly metabolised by CYP2D6, many antipsychotic drugs and tricyclic antidepressants. 

Fluoxetine and paroxetine are potent inhibitors of the CYP2D6 isoenzyme, and this contributes to potential drug interactions (see drug interactions). In contrast, fluvoxamine is an inhibitor of CYP3A4, whereas citalopram, escitalopram, and sertraline have more modest CYP interactions. 

Selective serotonin reuptake inhibitors (SSRIs) [P] Fluoxetine and paroxetine inhibit CYP2D6 and decrease metabolism of antidepressants metabolized by this enzyme (eg, desipramine). Citalopram, sertraline, and fluvoxamine are only weak inhibitors of CYP2D6, but fluvoxamine inhibits CYP1A2 and CYP3A4 and thus can inhibit the metabolism of antidepressants metabolized by these enzymes. 

Selective serotonin reuptake inhibitors (SSRIs) [P] Fluoxetine and paroxetine inhibit CYP2D6 and increase concentrations of timolol, propranolol, metoprolol, carvedilol, and labetalol. 

FIGURE 6—15. Some serotonin selective reuptake inhibitors (SSRIs) are inhibitors of CYP450 2D6. Fluoxetine and paroxetine are potent inhibitors of 2D6, and fluvoxamine, sertaline, and citalopram are weak inhibitors of 2D6. 

Concentrations of nefazodone and its metabolites can be increased by fluoxetine and paroxetine (SEDA-20, 9). Combinations of serotonin agents produce serotonin toxicity, and a case of serotonin syndrome occurred when nefazodone (200 mg/day) was combined with fluoxetine (40 mg/day) in a 50-year-old man (109). The toxic symptoms settled 3 days after withdrawal of both antidepressants. 

SSRIs ATOMOXETINE t plasma concentrations and risk of adverse effects (abdominal pain, vomiting, nausea, fatigue, irritability) Atomoxetine is a selective norepinephrine reuptake inhibitor, t plasma concentrations due to inhibition of CYP2D6 by fluoxetine and paroxetine (potent), fluvoxamine and sertraline (less potent) and escitalopram and citalopram (weak) Avoid concurrent use. The interaction is usually severe with fluoxetine and paroxetine... 

Fluoxetine and paroxetine may not be tolerated when switching or augmenting... 

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