Rifampin-divalproex drug-drug interaction in an adult patient: A case report

The divalproex (DVP) package insert states that rifampin may increase the oral clearance of valproate by 40% and that valproic acid derivative dose adjustments may be required when starting or stopping rifampin. However, the overall clinical significance of this drug-drug interaction remains unclear given that limited clinical outcome data has been published. This case describes a 52-year-old female with bipolar disorder, borderline personality disorder, and PTSD who was previously stable on a medication regimen consisting of DVP delayed-release 500 mg every morning and 1500 mg every evening (baseline steady-state trough 99.8 mcg/mL). Throughout rifampin therapy for latent tuberculosis treatment, she required an increase in both the frequency of DVP administration, from 2 to 3 times daily, and DVP dose by 75% to maintain clinical stability. Valproic acid trough concentrations ranged from 56.4 to 75.9 mcg/mL during the 4-month course of rifampin. This report supports that the DVP-rifampin interaction may be clinically significant and of a greater magnitude than suggested by the package insert.

Risk Factors for Utilization of Acute Care Services for Lithium Toxicity

OBJECTIVE

This study evaluated risk factors for utilization of acute care services (ACS) (hospitalization or emergency department or urgent care visit) for lithium toxicity and the prevalence of lithium toxicity in a large, ambulatory population.

METHODS

A nested case-control study compared lithium users with ACS utilization for lithium toxicity (case group) to lithium users without toxicity (control group) by using data from Kaiser Permanente Colorado for patients with at least one lithium prescription purchase. Patients in the case group were matched 1:5 with patients in the control group who had purchased lithium within 39 days of the ACS encounter. Possible lithium toxicity, identified by lithium level or diagnosis, was confirmed by chart review. Multivariable, conditional logistic regression analysis was used to identify patient and prescription characteristics associated with ACS utilization for lithium toxicity. The prevalence of lithium toxicity was determined.

RESULTS

Of 3,115 individuals who took lithium, 70 experienced lithium toxicity, with or without ACS utilization, for a prevalence of 2.2%. Identified risk factors for ACS utilization for lithium toxicity included a newly initiated potentially interacting medication (odds ratio [OR]=30.30, 95% confidence interval [CI]=2.32-394.95), a higher number of treated chronic diseases (OR=1.28, CI=1.12-1.45), older age (OR=1.05, CI=1.02-1.09), and higher total daily lithium dose (OR=1.00, CI=1.00-1.00).

CONCLUSIONS

Newly initiated, potentially interacting medications are a major preventable driver of ACS use for lithium toxicity, whereas age, chronic disease, and total daily lithium dose are small but significant factors. Clinicians should use extra caution when initiating a potentially interacting medication.

Review of cariprazine in management of psychiatric illness

Schizophrenia and bipolar disorder are severe and debilitating psychiatric disorders. Despite the availability of numerous antipsychotic drugs, many patients still experience poor outcomes and treatment-limiting adverse side effects. Cariprazine is a novel antipsychotic with unique pharmacodynamic and pharmacokinetic properties. It is both a dopamine type 2 and dopamine type 3 partial agonist with 2 equipotent metabolites, desmethyl cariprazine and didesmethyl cariprazine, of which didesmethyl cariprazine has a half-life of 1 to 3 weeks. The objective of this article is to review the literature regarding efficacy and tolerability of cariprazine in the management of psychiatric disorders to determine its current place in therapy.

Medication prescribing in liver dysfunction

Patients with mental illness often have co-occurring substance abuse which increases the risk for developing cirrhosis, particularly with common etiologies such as hepatitis and alcoholic liver disease. As such, knowledge of how the disease may impact medication prescribing is important. Unfortunately, there is a paucity of data to guide medication prescribing in these patients. Product labeling information should be used in the clinical decision making process. Additionally, clinicians should consider the etiology of disease, adverse effect profile, and pharmacokinetic parameters including solubility, product formulation, protein binding, hydrophilicity, metabolism, bioavailability, extraction ratios, excretion route, and half-life. Thoughtful consideration should be given when prescribing potentially hepatotoxic medications, and those which may increase bleeding risk in patients with coagulopathy. It is essential to ensure every medication has an appropriate indication and carefully evaluate the need for each medication. Overall, more research is necessary to support clinical decision-making with outcomes based research in patients with chronic liver disease.

Schizophrenia and folate pharmacogenetics: Review of the literature regarding folic acid and its pharmacogenetically regulated metabolism in relation to schizophrenia treatments

Folic acid and its metabolism and utilization has become of increasing importance within the field of schizophrenia. Methylenetetrahydrofolate reductase (MTHFR) is the enzyme responsible for the formation of methyltetrahydrofolate (5-methyl THF) from dietary folate. Multiple studies have demonstrated relationships between MTHFR gene variants and schizophrenia. This review discusses these studies, and their findings regarding the relationship between different variants of the MTHFR gene and risk of antipsychotic-related metabolic syndrome, and the relationship between the pharmacogenetics of folate and the negative/cognitive symptoms of schizophrenia.