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

• Main Authors: Christine Doran, PharmD (Author), Michael Moro, MEd (Author), Jennifer Green, DO (Author), Kristen N. Gardner, PharmD, BCPP (Author)
• Format: Book
• Published: American Association of Psychiatric Pharmacists, 2021-01-01T00:00:00Z.
• Subjects: article
• Online Access: Connect to this object online.
• Notes: 2168-9709; 10.9740/mhc.2021.01.019
• Keywords: rifamycin; rifabutin; rifapentine; valproate; pharmacokinetic; valproic acid; Neurosciences. Biological psychiatry. Neuropsychiatry; RC321-571; Pharmacy and materia medica; RS1-441
• Source: Mental Health Clinician, Vol 11, Iss 1, Pp 19-22 (2021)

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.