An overview of psychotropic drug-drug interactions

Antipsychotic prescribing practices following withdrawal of concomitant carbamazepine

OBJECTIVE

The goal of this study was to examine provider prescribing habits following carbamazepine discontinuation and to assess for the presence of antipsychotic-related adverse drug reactions due to the loss of car-bamazepine-related induction of the cytochrome P450 enzyme (CYP) 3A4 and p-glycoprotein.

METHODS

A retrospective chart review of patient records from January 2006 through December 2007 at the Veterans Affairs (VA) San Diego Healthcare System was done, which focused on the co-prescription of carbamazepine and a second-generation (atypical) antipsychotic (aripiprazole, quetiapine, risperidone) that is significantly affected by CYP3A4/p-glycoprotein induction. The cases in which carbamazepine was discontinued while the antipsychotic was continued during the 2-year time frame were then analyzed further. Data were collected concerning documentation of antipsychotic-related adverse drug reactions that occurred after carbamazepine was discontinued and prescribers' responses to carbamazepine discontinuation.

RESULTS

Nine patients were identified who had concomitant prescriptions for carbamazepine and a second-generation antipsychotic and who then discontinued carbamazepine. In only one case did the provider initially decrease the dose of the antipsychotic when carbamazepine was discontinued. Two patients experienced akathisia 3 weeks after carbamazepine was discontinued.

CONCLUSIONS

Many providers are not adjusting the dose of second-generation antipsychotics after discontinuation of a CYP3A4/p-glycoprotein inducer, placing patients at risk for adverse drug reactions. In addition to provider education, mechanisms need to be integrated into the current prescription processing software to alert providers of kinetic changes related to medication discontinuation. In addition, when discontinuing carbamazepine in patients who are being concomitantly treated with a second-generation antipsychotic that is a CYP3A4/p-glycoprotein substrate, providers should arrange for patient follow-up 2-4 weeks after carbamazepine discontinuation to evaluate patients for antipsychotic-related adverse drug reactions.

Effects of aging on the human taste system

Losses in taste perception as well as distortions of gustatory function occur with greater frequency in older individuals, and these changes are exacerbated by certain medical conditions, pharmacologic interventions, radiation, and exposure to toxic chemicals. Medications, especially drug-drug interactions, are the most significant yet underappreciated contributors to taste disorders in the elderly. Taste disorders frequently occur when the fraction of an orally administered drug dose that reaches the systemic circulation is markedly increased due to inhibition (by a coadministered drug) of the efflux transporter P-glycoprotein and/or inhibition of the cytochrome P450 metabolism system, which normally limit systemic availability of drugs. The supratherapeutic plasma drug concentrations that result from drug-drug interactions can induce a taste from the blood side of taste cells (intravascular taste), alter taste cell biochemistry, and/or modify other aspects of the taste pathways.

Attention-deficit-hyperactivity disorder: an update

Attention-deficit-hyperactivity disorder (ADHD) is a common neuropsychiatric disorder that impairs social, academic, and occupational functioning in children, adolescents, and adults. In patients with ADHD, neurobiologic research has shown a lack of connectivity in key brain regions, inhibitory control deficits, delayed brain maturation, and noradrenergic and dopaminergic dysfunction in multiple brain regions. The prevalence of this disorder in the United States is 6-9% in youth (i.e., children and adolescents) and 3-5% in adults. Prevalence rates for youth are similar worldwide. Children with ADHD are at greater risk than children without ADHD for substance abuse and delinquency whether or not they receive drug therapy; however, early treatment with psychoeducation as well as drug therapy and/or behavioral intervention may decrease negative outcomes of ADHD, including the rate of conduct disorder and adult antisocial personality disorder. Drug therapy is effective for all age groups, even preschoolers, and for late-onset ADHD in adults. Stimulants, such as methylphenidate and amphetamine, are the most effective therapy and have a good safety profile; although recent concerns of sudden unexplained death, psychiatric adverse effects, and growth effects have prompted the introduction of other therapies. Atomoxetine, a nonstimulant, has no abuse potential, causes less insomnia than stimulants, and poses minimal risk of growth effects. Other drug options include clonidine and guanfacine, but both can cause bradycardia and sedation. Polyunsaturated fatty acids (fish oil), acetyl-L-carnitine, and iron supplements (for youth with low ferritin levels) show promise in improving ADHD symptoms. As long-term studies show that at least 50% of youth are nonadherent with their drug therapy as prescribed over a 1-year period, long-acting formulations (administered once/day) may improve adherence. Comorbid conditions are common in patients with ADHD, but this patient population can be treated effectively with individualized treatment regimens of stimulants, atomoxetine, or bupropion, along with close monitoring.

Venlafaxine metabolism as a marker of cytochrome P450 enzyme 2D6 metabolizer status

INTRODUCTION

One of the major enzymes of the cytochrome P450 drug-metabolizing system, CYP2D6, shows a high degree of genetic polymorphism and variability in activity. Based on the degree of CYP2D6 activity, individuals can be broadly classified as poor metabolizers (PMs) or extensive metabolizers (EMs); the metabolism of CYP2D6 substrates differs among PMs and EMs. The metabolism of various drugs that are substrates of CYP2D6 has been used as a marker for metabolic phenotype, calculating the plasma or urinary metabolic ratio of the parent compound to its metabolite. The current analysis evaluates the use of the O-desmethylvenlafaxine-venlafaxine ratio (ODV/VEN) after administration of VEN, a CYP2D6 substrate, for determining CYP2D6 metabolic phenotype in healthy adults receiving VEN.

METHODS

The analysis included data from 2 studies in which healthy adults were classified as either EMs or PMs using established methods (1 genotypic and 1 phenotypic) and were then administered VEN at daily dosages ranging from 75 to 150 mg. Blood plasma samples were taken at various time points, and the ODV/VEN ratio was calculated.

RESULTS

Blood samples from 28 participants in the 2 studies were available for analysis. The ODV/VEN ratio distinguished the EM and PM phenotypes; ratios were 1 or greater for EMs and less than 1 for PMs at 4 hours after dose administration.

CONCLUSIONS

The ratio of ODV/VEN is an effective means of phenotyping individuals according to their CYP2D6 metabolizer status.

Practical guidelines for the use of new generation antipsychotic drugs (except clozapine) in adult individuals with intellectual disabilities

New generation antipsychotic (NGA) drugs introduced to the US market after clozapine (aripiprazole, olanzapine, paliperidone, quetiapine, risperidone, and ziprasidone) are frequently used in individuals with intellectual disabilities (ID). However, there is very limited research to fully establish evidence-based or personalized medicine approaches for their use in this population. These guidelines take a pragmatic approach to establishing frameworks for their use by utilizing the prescribing information and reviewing the available literature on other relevant neuropsychiatric disorders. In the absence of expert consensus guidance and well-controlled comparison trials, we present a set of guidelines to inform initiation, dosing and monitoring of use in adults. Further, in these guidelines we provide practical information on drug-drug interactions and adverse drug reactions, and a brief review of discontinuation syndromes, potential for abuse, use during pregnancy and cost considerations. We also provide drug utilization review forms for each NGA to facilitate implementation of these guidelines, these guidelines provide a practical and necessary resource for practitioners treating psychiatric disorders and challenging behaviors in adult individuals with ID.

An investigation of the behavioral mechanisms of antipsychotic action using a drug-drug conditioning paradigm

Antipsychotic drugs at noncataleptic doses selectively suppress conditioned avoidance response in rats. In our previous study, we had used a two-way active avoidance response paradigm to show that the antipsychotic-induced interoceptive state is one of the mechanisms underlying the avoidance-disruptive effect of antipsychotics. In this study, we sought to further examine this mechanism using a novel drug-drug conditioning procedure. We made use of the fact that both the typical neuroleptic haloperidol and the atypical neuroleptic olanzapine disrupt conditioned avoidance responding, whereas chlordiazepoxide (an anxiolytic) does not. We reasoned that if the antipsychotic interoceptive state is important in causing a disruption on avoidance responding (an index of antipsychotic efficacy), pairing chlordiazepoxide (a cueing drug conditional stimulus) with haloperidol or olanzapine (a cued drug unconditional stimulus) should engender chlordiazepoxide to exhibit this property and behave like an antipsychotic drug. Chlordiazepoxide exhibited an acquired antipsychotic-like property in disrupting avoidance responding after being repeatedly paired with haloperidol, but not with olanzapine. In contrast, it significantly attenuated the antiavoidance efficacy of olanzapine but not haloperidol after being repeatedly paired with these drugs. This study suggests that the haloperidol-induced interoceptive drug state is directly involved in its antiavoidance action, and chlordiazepoxide may attenuate the antiavoidance efficacy of antipsychotics (especially olanzapine). To the extent that the antiavoidance effect predicts clinical effects of antipsychotic treatment, this study suggests that the antipsychotic-induced interoceptive drug state may be an important behavioral mechanism mediating the clinical effects of antipsychotic treatments.

Intramuscular aripiprazole : a review of its use in the management of agitation in schizophrenia and bipolar I disorder

An intramuscular formulation of the atypical antipsychotic aripiprazole (Abilify) has been developed and is approved in the EU for use in agitation and disturbed behaviour associated with schizophrenia. In the US, it is approved for the treatment of agitation associated with schizophrenia or bipolar I disorder (manic or mixed). In large, well designed trials, intramuscular aripiprazole was an effective and generally well tolerated treatment for agitation associated with schizophrenia, schizoaffective disorder, schizophreniform disorder or bipolar I disorder. Intramuscular aripiprazole was more effective than placebo in these patient populations and was noninferior to intramuscular haloperidol in those with agitation associated with schizophrenia and its related disorders. Aripiprazole is associated with a low risk for extrapyramidal symptoms (EPS), cardiac effects, hyperprolactinaemia, weight gain and other metabolic disturbances. Head-to-head trials comparing intramuscular aripiprazole with other intramuscular atypical antipsychotics are required before the relative position of each of these agents can be fully determined. In the meantime, intramuscular aripiprazole, with its favourable tolerability profile, is a valuable treatment option for agitation in patients with schizophrenia, schizoaffective disorder, schizophreniform disorder or bipolar I disorder.

A Review of Drug Interactions With Psychiatric Medicines for the Pharmacy Practitioner

With thousands of potential drug interactions, it is next to impossible to remember them all, especially with many people on multiple prescriptions and over-the-counter medications. With the increasing use of psychiatric medicines in the general population, drug interactions may occur without recognition or warning. Pharmacy computer software programs provide help with identifying the majority of potential drug interactions, but these systems are only as good as the user who develops them. Some drug interactions are negligible, whereas others are quite significant. It is most important to remember drug interactions that may have a significant clinical effect. Approximately half of all medications prescribed today are affected by cytochrome P450 enzymes, but other interactions that involve various mechanisms can also be problematic. This review identifies drug interactions that may occur with the most frequently prescribed psychiatric medications and provides a review of selected interactions that may be clinically relevant for the pharmacist to review.

The challenge of managing drug interactions in elderly people

Drug therapy is essential when caring for elderly patients, but clearly it is a double-edged sword. Elderly patients are at high risk of having drug interactions, but the prevalence of these interactions is not well documented. Several types of interactions exist: drug-drug, drug-disease, drug-food, drug-alcohol, drug-herbal products, and drug-nutritional status. Factors such as age-related changes in pharmacokinetics and pharmacodynamics, frailty, interindividual variability, reduced homoeostatic mechanisms, and psychosocial issues need to be considered when drug interactions are assessed. Software can help clinicians to detect drug interactions, but many programmes have not been updated with the evolving knowledge of these interactions, and do not take into consideration important factors needed to optimise drug treatment in elderly patients. Any generated recommendations have to be tempered by a holistic, geriatric, multiprofessional approach that is team-based. This second paper in a series of two on prescribing in elderly people proposes an approach to categorise drug interactions, along with strategies to assist in their detection, management, and prevention.

Historical Review of Carbamazepine for the Treatment of Bipolar Disorder

The management of bipolar disorder has seen significant evolution in terms of the number of treatment options now approved for both the acutely manic phase and the maintenance stages of the illness. In addition, new formulations of traditional agents are available for clinicians to use in their treatment approach. One such example is carbamazepine, which has approval by the United States Food and Drug Administration for the treatment of acute and mixed mania in an extended-release formulation that uses a three-bead delivery system. Although the parent compound has been available for decades, its approval for bipolar disorder is recent despite numerous clinical trials that have supported its use in both the acute and maintenance phases of bipolar disorder. Advantages of the new formulation include less fluctuation in plasma concentration and, in general, improved tolerability. However, issues remain with regard to cytochrome P450 drug-related interactions and the need for therapeutic drug monitoring (e.g., drug concentrations, epoxide metabolite concentrations, hematology, and liver function tests) as part of the treatment and monitoring process. We review the current body of literature describing the use of carbamazepine in bipolar disorder during both the acute and maintenance phases of the disorder, including trials of both monotherapy and combination therapy, as well as findings from trials that included patients with rapid cycling and mixed episodes.

Determination of Lamotrigine and its Metabolites in Human Plasma by Liquid Chromatography-Mass Spectrometry

A method based on electrospray ionization liquid chromatography-mass spectrometry was developed for the quantitative determination of lamotrigine and three of its reported metabolites, lamotrigine-2-N-glucuronide, lamotrigine-2-N-methyl, and lamotrigine-2-N-oxide in human blood plasma. The method utilized sample preparation by precipitation of proteins with acetonitrile, chromatographic separation on a reversed-phase system by gradient elution, and monitoring of the protonated molecular ions. Two internal standards, 3,5-diamino-6-(2-methoxyphenyl)-1,2,4-triazine and morphine-3-glucuronide-D3, were utilized to achieve precise quantification. The method validation comprised a demonstration of an agreement in the quantification of lamotrigine with that of a routine HPLC-UV method. The limits of detection were between 0.05 and 0.16 micromol/L. The method was employed for the measurement of clinical samples collected from 55 patients in steady-state prior to the dose intake (trough level). Lamotrigine and the 2-N-glucuronide were typically detected, while the N-methyl and N-oxide metabolites were detected only rarely. The median lamotrigine plasma level was 24.0 micromol/L (range, 4.3 to 64 micromol/L), the median 2-N-glucuronide level was 2.4 micromol/L (range, <0.05 to 24 micromol/L), and the median lamotrigine 2-N-glucuronide/lamotrigine ratio was 0.11 (range, <0.01 to 0.64). In conclusion, this liquid chromatographic-mass spectrometric method is suitable for simultaneous determination of lamotrigine and its metabolites in human plasma.

Anxiety in medically ill patients

Anxiety disorders and anxiety symptoms are highly prevalent in the general population and more so in the medically ill. They have a number of negative consequences for these patients and may worsen the outcome of the medical illness and increase health care utilization. In the evaluation of these patients, it is of paramount importance to identify the etiology of the anxiety and, in particular, to differentiate primary from secondary anxiety. Management includes medications (especially benzodiazepines and selective serotonin reuptake inhibitors) and psychotherapy (particularly cognitive-behavioral therapy).