Pharmacogenetics of antipsychotic adverse effects: Case studies and a literature review for clinicians

Case Report: Pharmacogenetics Applied to Precision Psychiatry Could Explain the Outcome of a Patient With a New CYP2D6 Genotype

Precision medicine applied to psychiatry provides new insight into the promising field of precision psychiatry. Psychotic disorders are heterogeneous, complex, chronic, and severe mental disorders. Not only does the prognosis and the course of the disease vary among patients suffering from psychotic disorders, but the treatment response varies as well. Although antipsychotic drugs are the cornerstone of the treatment of schizophrenia, many patients only partially respond to these drugs. Furthermore, patients often experience adverse events which can lead to poor treatment adherence. Interindividual variability in drug response could be related to age, gender, ethnicity, lifestyle factors, pharmacological interactions, obesity, and genetics, all of which influence the process of drug metabolism. Commonly prescribed antipsychotics are metabolized by cytochrome P450 (CYP450) enzymes, and CYP450 genes are highly polymorphic. Pharmacogenetic testing is increasingly being used to predict a patient's drug response and could help to find the most appropriate therapy for an individual patient. In this report, we describe a psychotic patient who did not receive adequate clinical follow-up and subsequently presented adverse events, which could be explained by his pharmacogenetic profile and the drug interactions resulting from the polypharmacy prescribed.

Antipsychotic Polypharmacy

Physicians who treat patients with schizophrenia frequently encounter complex clinical situations not fully addressed by published treatment guidelines. Some of these situations lead to antipsychotic polypharmacy, often prescribed when clinical and social obstacles prevent access to clozapine and patients have had suboptimal responses to nonclozapine monotherapy. We offer our perspective on the place of antipsychotic polypharmacy in the current treatment guidelines for patients with schizophrenia. We summarize data on the prevalence of antipsychotic polypharmacy and describe common clinical situations in which this practice is encountered, along with the pharmacological underpinnings of this practice. We briefly review evidence on common risks of antipsychotic polypharmacy and describe the limited evidence for the possible benefits of such practice. Moreover, we take a look at alternative antipsychotic augmentation strategies that address all domains of psychosis.

Associations between the LEP -2548G/A Promoter and Baseline Weight and between LEPR Gln223Arg and Lys656Asn Variants and Change in BMI z Scores in Arab Children and Adolescents Treated with Risperidone

Data on baseline (antipsychotics-naïve) age, weight, and height, and change in these at 3 subsequent follow-up time points up to 313.6 days (95% CI 303.5-323.7) were collected from 181 risperidone-treated children and adolescents (mean age 12.58 years, SD 4.99, range 2.17-17.7) attending a pediatric neurology clinic in Saudi Arabia. Owing to differences in genotypic distributions in the subsamples, results are reported for the white Arab population (n = 144). Age- and gender-normed body mass index (BMI)-standardized z scores (BMI z) were calculated (LMSgrowth program). Linear regression was performed for baseline weight and BMI z, while change in BMI z was assessed using random effects ordered logistic regression. The following single nucleotide polymorphisms (SNPs) were analyzed: rs7799039 in the LEP promoter, rs1805094 (previously rs8179183), rs1137100 and rs1137101 in the LEPR, and rs1414334 in HTR2C. We found a nominally significant association between rs7799309 and baseline weight, adjusting for height, age, gender, and diagnosis (A/G, p = 0.035, β = -3.62 vs. G/G). The rs1137101 (G/G, p = 0.018, odds ratio [OR] = 4.13 vs. A/A) and rs1805094 C allele carriers (p = 0.019, OR = 0.51) showed nominally significant associations with change in BMI z categories. Our data support and replicate previous relevant associations for these variants (including with weight gain when on risperidone), whilst being the first report of such associations in patients of Arab ethnicity.

Antipsychotic Trials in Schizophrenia from India: A Systematic Review and Meta-analysis

Ethnic and regional variations have been found in the pharmacological treatment response. Though many efficacy studies have been conducted in India for antipsychotic treatment modalities of schizophrenia, there is a lack meta-analytic data of the existing literature from India. This study aimed to conduct a systematic review and meta-analysis of the antipsychotic treatment trials of schizophrenia in the Indian context. All controlled trials from India evaluating the clinical efficacy of antipsychotics in patients with schizophrenia were evaluated and 28 trials were included in the metanalysis. Effect sizes were computed using Cohen's 'd' and risk of bias was evaluated. Meta analysis revealed superiority of first generation antipsychotics over placebo (mean effect size of 1.387, confidence interval of 1.127 to 1.648). Second generation antipsychotics were marginally better than first generation antipsychotics (effect size 0.106, confidence intervals 0.009 to 0.204). There was improvement in the methodology of the trials over time (Kendall tau=0.289, P=0.049), though no statistically significant increase in trial duration and sample size was noted. There is lack of data on long term efficacy of antipsychotic in schizophrenia from India. First generation antipsychotics have demonstrated benefits over placebo in patients with schizophrenia in the Indian context, though marginally lesser than second generation ones.

Opening Pandora’s box in the UK: a hypothetical pharmacogenetic test for clozapine

Clozapine is a uniquely efficacious antipsychotic drug in treatment-resistant schizophrenia. Its use is restricted due to adverse effects including a rare but dangerous reduction in neutrophils (agranulocytosis) and the mandatory hematological monitoring this entails in many countries. We review the statistical, ethical and legal issues arising from a hypothetical pharmacogenetic test for clozapine, using the UK as an exemplary case for consideration. Our key findings include: a consideration of the probabilistic results that a pharmacogenetic test may return; the impact on drug licensing; and the potential for pharmacogenetic tests for clozapine being used without consent under the UK’s legal framework. We make recommendations regarding regulatory changes applicable to the special case of pharmacogenetic testing in clozapine treatment.