Lamotrigine in mood disorders: Flash survey on prescribing habits and blood tests practices.

OBJECTIVE: Therapeutic drug monitoring for lamotrigine is poorly documented in bipolar and depressive disorders. In order to evaluate its use among French psychiatrists, we explored prescribing habits, therapeutic monitoring and dosage adjustment of lamotrigine through a flash survey. METHODS: A survey was broadcasted by the network of Expert Centers for Bipolar Disorder and Resistant Depression and by the Collegial of Psychiatry of the Assistance publique des Hôpitaux de Paris. Questions concerned the frequency of prescribing depending on the mood disorder, the frequency of plasma levels, therapeutic monitoring, dosage adjustment and the limitation represented by dermatological risk. RESULTS: Of the 99 hospital psychiatrists who responded, 66 practiced in a university hospital and 62 for more than 5years. Overall, lamotrigine was more frequently prescribed for type 2 bipolar disorder (often: 51%) than for type 1 bipolar disorder (often: 22%). Dermatotoxicity was a major barrier to prescribing for 15% (n=13) of respondents. Nearly two-thirds of prescribers (61%, n=59) measured lamotrigine, of which 50% (n=29) systematically. However, 40% of them did not have an opinion on the optimal plasma concentration. In total, 22% (n=13) always adjusted the dosage according to the result. The first argument for dosage adjustment was clinical response for 80% (n=47) of prescribers, adverse effects for 17% (n=10) and plasma levels for only 4% (n=2). CONCLUSION: While many psychiatrists report using plasma dosage of lamotrigine, few use the plasma level result to adapt dosage and many have no opinion of the target values for plasma concentrations. This illustrates the lack of data and recommendations regarding the use of therapeutic pharmacological monitoring of lamotrigine in bipolar and depressive disorders.

Valproate, divalproex, valpromide: Are the differences in indications justified?

In many countries, valproate is indicated for epilepsy only, whereas its derivative divalproex (DVP) and valpromide (VPM) are indicated for bipolar disorders only. DVP is composed of sodium valproate and valproic acid (VA) in a 1:1 molar ratio and VPM is a prodrug completely hydrolyzed in the gastric tract to VA. Whatever the drug, the absorbed and active substance is the valproate ion. In this article, we reviewed the potential reasons that might justify these different indications. We performed a literature review of comparative studies of efficacy, pharmacokinetic parameters, side effects and costs for VPA, DVP, and VPM. We found only studies comparing VA with DVP. None of the eight efficacy studies found differences in epilepsy or mood disorders. The ten studies of side effects reported a difference in terms of gastrointestinal effects, but inconsistently. The United States (US) summary of product characteristics and kinetic comparison studies reported bioequivalence between DVP and VA, but a longer Tmax for DVP, likely due to its gastro-resistant galenic form. VPM summary of product characteristics and pharmacokinetic studies revealed a lower bioavailability (80% vs. 100% for VA) and a delayed Tmax. There is an additional cost for using DVP or VPM as compared to VA (respectively +177% and +77% in France). The differences in indications between valproate derivatives do not seem justified. Interchangeability between VA and DVP in bipolar disorders seems possible, at identical dosage. VPM would require a closer dosing schedule and a 20% reduction in dosage when switching to valproate.

Cytochromes P450 and P-Glycoprotein Phenotypic Assessment to Optimize Psychotropic Pharmacotherapy: A Retrospective Analysis of Four Years of Practice in Psychiatry.

Altered cytochromes P450 enzymes (CYP) and P-glycoprotein transporter (P-gp) activity may explain variabilities in drug response. In this study, we analyzed four years of phenotypic assessments of CYP/P-gp activities to optimize pharmacotherapy in psychiatry. A low-dose probe cocktail was administered to evaluate CYP1A2, 2B6, 2D6, 2C9, 2C19, 3A4, and P-gp activities using the probe/metabolite concentration ratio in blood or the AUC. A therapeutic adjustment was suggested depending on the phenotyping results. From January 2017 to June 2021, we performed 32 phenotypings, 10 for adverse drug reaction, 6 for non-response, and 16 for both reasons. Depending on the CYP/P-gp evaluated, only 23% to 56% of patients had normal activity. Activity was decreased in up to 57% and increased in up to 60% of cases, depending on the CYP/P-gp evaluated. In 11/32 cases (34%), the therapeutic problem was attributable to the patient's metabolic profile. In 10/32 cases (31%), phenotyping excluded the metabolic profile as the cause of the therapeutic problem. For all ten individuals for which we had follow-up information, phenotyping allowed us to clearly state or clearly exclude the metabolic profile as a possible cause of therapeutic failure. Among them, seven showed a clinical improvement after dosage adaptation, or drug or pharmacological class switching. Our study confirmed the interest of CYP and P-gp phenotyping for therapeutic optimization in psychiatry.