Vincenza Santoro

Clinically relevant pharmacokinetic drug interactions with second-generation antidepressants: An update

BACKGROUND The second-generation antidepressants include selective serotonin reuptake inhibitors (SSRIs), serotonin and norepinephrine reuptake inhibitors (SNRIs), and other compounds with different mechanisms of action. All second-generation antidepressants are metabolized in the liver by the cytochrome P450 (CYP) enzyme system. Concomitant intake of inhibitors or inducers of the CYP isozymes involved in the biotransformation of specific antidepressants may alter plasma concentrations of these agents, although this effect is unlikely to be associated with clinically relevant interactions. Rather, concern about drug interactions with second-generation antidepressants is based on their in vitro potential to inhibit > or = 1 CYP isozyme. OBJECTIVE The goal of this article was to review the current literature on clinically relevant pharmacokinetic drug interactions with second-generation antidepressants. METHODS A search of MEDLINE and EMBASE was conducted for original research and review articles published in English between January 1985 and February 2008. Among the search terms were drug interactions, second-generation antidepressants, newer antidepressants, SSRIs, SNRIs, fluoxetine, paroxetine, fluvoxamine, sertraline, citalopram, escitalopram, venlafaxine, duloxetine, mirtazapine, reboxetine, bupropion, nefazodone, pharmacokinetics, drug metabolism, and cytochrome P450. Only articles published in peer-reviewed journals were included, and meeting abstracts were excluded. The reference lists of relevant articles were hand-searched for additional publications. RESULTS Second-generation antidepressants differ in their potential for pharmacokinetic drug interactions. Fluoxetine and paroxetine are potent inhibitors of CYP2D6, fluvoxamine markedly inhibits CYP1A2 and CYP2C19, and nefazodone is a substantial inhibitor of CYP3A4. Therefore, clinically relevant interactions may be expected when these antidepressants are coadministered with substrates of the pertinent isozymes, particularly those with a narrow therapeutic index. Duloxetine and bupropion are moderate inhibitors of CYP2D6, and sertraline may cause significant inhibition of this isoform, but only at high doses. Citalopram, escitalopram, venlafaxine, mirtazapine, and reboxetine are weak or negligible inhibitors of CYP isozymes in vitro and are less likely than other second-generation antidepressants to interact with co-administered medications. CONCLUSIONS Second-generation antidepressants are not equivalent in their potential for pharmacokinetic drug interactions. Although interactions may be predictable in specific circumstances, use of an antidepressant with a more favorable drug-interaction profile may be justified.

Effect of aripiprazole augmentation of serotonin reuptake inhibitors or clomipramine in treatment-resistant obsessive-compulsive disorder: a double-blind, placebo-controlled study.

Based on the evidence that aripiprazole added to serotonin reuptake inhibitors (SRIs) or clomipramine in treatment-resistant obsessive-compulsive disorder (OCD) has reported promising results, the present 16-week, double-blind, randomized, placebo-controlled trial had the aim to explore the efficacy of aripiprazole add-on pharmacotherapy on clinical symptoms and cognitive functioning in a sample of treatment-resistant OCD patients receiving SRIs. After clinical and neurocognitive assessments, patients were randomly allocated to receive, in a double-blind design, 15 mg/d of aripiprazole or a placebo. A final sample of 30 patients completed the study. The results obtained indicate that aripiprazole added to stable SRI treatment substantially improved obsessive-compulsive symptoms as measured by changes on the Yale-Brown Obsessive Compulsive Scale total score and subscores (obsessions, P = 0.007; compulsions, P = 0.001; total score, P < 0.0001). Regarding cognitive functions, improvement was observed in some explored areas, such as attentional resistance to interference (Stroop score, P = 0.001) and executive functioning (perseverative errors, P = 0.015). The findings provide evidence that aripiprazole augmentation of SRIs/clomipramine treatment is well tolerated and may be proposed as an effective therapeutic strategy to improve outcome in treatment-resistant OCD.

Effect of aripiprazole augmentation of clozapine in schizophrenia: A double-blind, placebo-controlled study

The simultaneous prescription of two or more antipsychotic drugs in combination is a common treatment strategy for those patients who have demonstrated a suboptimal response to clozapine; nevertheless, evidence suggesting potential advantages of combination treatment with clozapine plus one antipsychotic in terms of efficacy and tolerability are still sparse. The present 24-week double-blind, randomized, placebo-controlled trial of adjunctive aripiprazole to clozapine therapy in schizophrenia was aimed to explore the efficacy of aripiprazole add-on pharmacotherapy on clinical symptomatology and cognitive functioning in a sample of patients with treatment-resistant schizophrenia receiving clozapine. After clinical and neurocognitive assessments patients were randomly allocated to receive, in a double-blind design, either up to 15 mg/day of aripiprazole or a placebo. A final sample of thirty-one patients completed the study. The results obtained indicate that aripiprazole added to stable clozapine treatment showed a beneficial effect on the positive and general psychopathological symptomatology in a sample of treatment-resistant schizophrenia patients. Regarding executive cognitive functions, aripiprazole augmentation of clozapine had no significant effects. The findings provide evidence that aripiprazole augmentation of clozapine treatment is well-tolerated and may be of benefit for patients who are partially responsive to clozapine monotherapy; further double-blind, placebo-controlled trials in a larger number of patients are required to evaluate the therapeutic potential of aripiprazole augmentation of clozapine.

Interactions between Antiepileptics and Second-Generation Antipsychotics

Introduction: Pharmacokinetic and pharmacodynamic drug interactions (DIs) can occur between antiepileptics (AEDs) and second-generation antipsychotics (SGAPs). Some AED and SGAP pharmacodynamic mechanisms are poorly understood. AED–SGAP combinations are used for treating comorbid illnesses or increasing efficacy, particularly in bipolar disorder. Areas covered: This article provides a comprehensive review of the interactions between antiepileptics and second-generation antipsychotics. The authors cover pharmacokinetic AED–SGAP DI studies, the newest drug pharmacokinetics in addition to the limited pharmacodynamic DI studies. Expert opinion: Dosing correction factors and measuring SGAP levels can help to compensate for the inductive properties of carbamazepine, phenytoin, phenobarbital and primidone. Further studies are needed to establish the clinical relevance of combining: i) AED strong inducers with amisulpride, asenapine, iloperidone, lurasidone and paliperidone; ii) valproate with aripiprazole, asenapine, clozapine and olanzapine; iii) high doses of oxcarbazepine (≥ 1500 mg/day) or topiramate (≥ 400 mg/day) with aripiprazole, lurasidone, quetiapine, risperidone, asenapine and olanzapine. Two pharmacodynamic DIs are beneficial: i) valproate–SGAP combinations may have additive effects in bipolar disorder, ii) combining topiramate or zonisamide with SGAPs may decrease weight gain. Three pharmacodynamic DIs contributing to decreased safety are common: sedation, weight gain and swallowing disturbances. A few AED–SGAP combinations may increase risk for osteoporosis or nausea. Three potentially lethal but rare pharmacodynamic DIs include pancreatitis, agranulocytosis/leukopenia and heat stroke. The authors believe that collaboration is needed from drug agencies and pharmaceutical companies, the clinicians using these combinations, researchers with expertise in meta-analyses, grant agencies, pharmacoepidemiologists and DI pharmacologists for future progression in this field.

Effect of adjunctive lamotrigine treatment on the plasma concentrations of clozapine, risperidone and olanzapine in patients with schizophrenia or bipolar disorder.

The effect of lamotrigine on the steady-state plasma concentrations of the atypical antipsychotics clozapine, olanzapine, and risperidone was investigated in patients with schizophrenia or bipolar disorder stabilized on chronic treatment with clozapine (200-500 mg/day; n = 11), risperidone (3-6 mg/day; n = 10) or olanzapine (10-20 mg/day; n = 14)). Lamotrigine was titrated up to a final dosage of 200 mg/day over 8 weeks, and pharmacokinetic assessments were made at baseline and during treatment weeks 6 and 10, at lamotrigine dosages of 100 and 200 mg/day respectively. The plasma concentrations of clozapine, norclozapine, risperidone, and 9-hydroxy-risperidone did not change significantly during treatment with lamotrigine. The mean plasma concentrations of olanzapine were 31 ± 7 ng/mL at baseline, 32 ± 7 ng/mL at week 6, and 36 ± 9 ng/mL at week 10, the difference between week 10 and baseline being statistically significant (P < 0.05). Adjunctive lamotrigine therapy was well tolerated in all groups. These findings indicate that lamotrigine, at the dosages recommended for use as a mood stabilizer, does not affect the plasma levels of clozapine, risperidone, and their active metabolites. The modest elevation in plasma olanzapine concentration, possibly due to inhibition of UGT1A4-mediated olanzapine glucuronidation, is unlikely to be of clinical significance.

Effect of topiramate on plasma concentrations of clozapine, olanzapine, risperidone, and quetiapine in patients with psychotic disorders.

Objectives: To investigate the effect of topiramate on the steady-state plasma concentrations of the second-generation antipsychotics-clozapine, olanzapine, risperidone, and quetiapine-in patients with schizophrenia or bipolar disorder. Methods: Thirty-eight outpatients on long-term treatment with clozapine (250-500 mg/d, n = 10), olanzapine (10-20 mg/d, n = 12), risperidone (3-6 mg/d, n = 9), or quetiapine (200-600 mg/d, n = 7) received adjunctive topiramate, gradually titrated up to a final dosage of 200 mg/d for 6 weeks. Pharmacokinetic assessments were made at baseline and at the end of treatment weeks 4 and 8 at topiramate dosages of 100 and 200 mg/d, respectively. Results: Plasma concentrations of clozapine and its metabolite (norclozapine), olanzapine, risperidone and its metabolite (9-hydroxy-risperidone), and quetiapine were not significantly modified during concomitant administration of topiramate. Adjunctive topiramate therapy was well tolerated in all groups. Conclusions: These findings indicate that topiramate, at the dosages recommended for use as a mood stabilizer, does not affect the plasma levels of the new antipsychotics-clozapine, olanzapine, risperidone, and quetiapine.

Drug dosage individualization based on a random-effects linear model.

This article investigates drug dosage individualization when the patient population can be described with a random-effects linear model of a continuous pharmacokinetic or pharmacodynamic response. Specifically, we show through both decision-theoretic arguments and simulations that a published clinical algorithm may produce better individualized dosages than some traditional methods of therapeutic drug monitoring. Since empirical evidence suggests that the linear model may adequately describe drugs and patient populations, and linear models are easier to handle than the nonlinear models traditionally used in population pharmacokinetics, our results highlight the potential applicability of linear mixed models to dosage computations and personalized medicine.

Therapeutic Drug Monitoring of Quetiapine: Effect of Coadministration with Antiepileptic Drugs in Patients with Psychiatric Disorders

Antiepileptic agents, particularly those with mood-stabilizing properties, are increasingly used in the manage- ment of psychiatric disorders and may be prescribed in combination with antipsychotics. Aim of the present study was to evaluate the pharmacokinetic interaction between various antiepileptics and quetiapine, a second-generation antipsychotic, in psychiatric patients, by using data from a therapeutic drug monitoring service. Steady-state plasma concentrations of quetiapine were compared in patients treated with quetiapine alone (controls, n=35) and in patients comedicated with val- proic acid (n=19), lamotrigine (n=16), carbamazepine (n=6), topiramate (n=6) and oxcarbazepine (n=5). The six groups were matched for sex, age and daily dose of quetiapine. Dose-normalized plasma concentrations of quetiapine were sig- nificantly lower in the carbamazepine group than in the control group (p<0.001), while there were no differences in plasma quetiapine concentrations between the valproic acid, lamotrigine, topiramate or oxcarbazepine groups and the con- trol group. In 5 patients assessed on and off carbamazepine comedication, dose-normalized plasma concentrations of quetiapine were significantly lower during combination therapy than on quetiapine alone (p<0.01). By contrast, no appre- ciable changes in plasma levels of quetiapine were found in the 8 and 6 patients assessed on and off valproic acid or lamo- trigine comedication, respectively. These findings confirm that carbamazepine decreases markedly steady-state plasma concentrations of quetiapine, presumably by inducing its CYP3A4-mediated biotransformation. Conversely, concomitant administration of therapeutic doses of valproic acid, lamotrigine, topiramate or oxcarbazepine does not appear to affect significantly plasma levels of quetiapine.

Low-Dose of Bergamot-Derived Polyphenolic Fraction (BPF) Did Not Improve Metabolic Parameters in Second Generation Antipsychotics-Treated Patients: Results from a 60-days Open-Label Study

Objectives: The nutraceutical approach to the management of metabolic syndrome (MetS) might be a promising strategy in the prevention of cardio-metabolic risk. Low-dose bergamot-derived polyphenolic fraction (BPF) has been proven effective in patients with MetS, as demonstrated by a concomitant improvement in lipemic and glycemic profiles. The present study was aimed to further explore, in a sample of subjects receiving second generation antipsychotics (SGAs), the effects on body weight and metabolic parameters of a low dose of BPF (500 mg/day) administered for 60 days. Methods: Twenty-eight outpatients treated with SGAs assumed BPF at single daily dose of 500 mg/day for 60 days. Body weight, BMI, fasting levels of glucose, total cholesterol, high density lipoprotein cholesterol, low density lipoprotein cholesterol and triglycerides were determined; moreover, Brief Psychiatric Rating Scale (BPRS) was administered. Results: Low-dose BPF administration did not change clinical and metabolic parameters, as well as clinical symptoms in the study sample. At the end of the trial, among completers (n = 24) only nine patients (37.5%) reached an LDL reduction >0 but <50%. Conclusions: Our results demonstrate that patients treated with SGAs may need higher BPF doses for obtaining the positive effects on body weight and metabolic parameters previously found in the general population at lower doses.