Severe anemia secondary to a probable drug interaction between zidovudine and valproic acid

Drug-drug interactions and clinical considerations with co-administration of antiretrovirals and psychotropic drugs

Psychotropic medications are frequently co-prescribed with antiretroviral therapy (ART), owing to a high prevalence of psychiatric illness within the population living with HIV, as well as a 7-fold increased risk of HIV infection among patients with psychiatric illness. While ART has been notoriously associated with a multitude of pharmacokinetic drug interactions involving the cytochrome P450 enzyme system, the magnitude and clinical impact of these interactions with psychotropics may range from negligible effects on plasma concentrations to life-threatening torsades de pointes or respiratory depression. This comprehensive review summarizes the currently available information regarding drug-drug interactions between antiretrovirals and pharmacologic agents utilized in the treatment of psychiatric disorders-antidepressants, stimulants, antipsychotics, anxiolytics, mood stabilizers, and treatments for opioid use disorder and alcohol use disorder-and provides recommendations for their management. Additionally, overlapping toxicities between antiretrovirals and the psychotropic classes are highlighted. Knowledge of the interaction and adverse effect potential of specific antiretrovirals and psychotropics will allow clinicians to make informed prescribing decisions to better promote the health and wellness of this high-risk population.

Understanding and preventing drug-drug and drug-gene interactions

Concomitant administration of multiple drugs can lead to unanticipated drug interactions and resultant adverse drug events with their associated costs. A more thorough understanding of the different cytochrome P450 isoenzymes and drug transporters has led to new methods to try to predict and prevent clinically relevant drug interactions. There is also an increased recognition of the need to identify the impact of pharmacogenetic polymorphisms on drug interactions. More stringent regulatory requirements have evolved for industry to classify cytochrome inhibitors and inducers, test the effect of drug interactions in the presence of polymorphic enzymes, and evaluate multiple potentially interacting drugs simultaneously. In clinical practice, drug alert software programs have been developed. This review discusses drug interaction mechanisms and strategies for screening and minimizing exposure to drug interactions. We also provide future perspectives for reducing the risk of clinically significant drug interactions.

Clinical implications and management of drug-drug interactions between antiretroviral agents and psychotropic medications

Medications used in the treatment of human immunodeficiency virus (HIV) often have drug-drug interactions which complicate treatment of psychiatric illnesses in HIV-infected patients. Protease inhibitors (PIs) and non-nucleoside reverse transcriptase inhibitors (NNRTIs) are the two classes of HIV medications most likely to be involved with interactions, with the majority occurring via the cytochrome P450 (CYP450) system. These interactions can result in either increased or decreased exposure to psychotropic and antiretroviral medications, often requiring dosage adjustments and increased monitoring. This article reviews some of the major drug interactions with antiretroviral agents.

Anemia secondary to valproic acid therapy in a 13-year-old boy: a case report

INTRODUCTION

Valproic acid is a commonly used anti-epileptic drug. Hematological toxicities are among the occasionally observed adverse effects of this medication.

CASE PRESENTATION

We present the case of a 13-year-old Caucasian boy who demonstrated mild anemia 12 months after the introduction of valproic acid therapy. A bone marrow biopsy revealed maturation arrest of proerythroblasts.

CONCLUSION

Prompt diagnosis and valproic acid discontinuation resulted in the patient's recovery.

Adverse events caused by drug interactions involving glucuronoconjugates of zidovudine, valproic acid and lamotrigine, and analysis of how such potential events are discussed in package inserts of Japan, UK and USA

BACKGROUND AND OBJECTIVE

As pharmacokinetic drug interactions frequently cause adverse events, it is important that the relevant information is given in package inserts (PIs). We previously analysed the provision of PIs for HMG-CoA reductase inhibitors and Ca antagonists, for which metabolism by cytochrome P450 could be a major interaction mechanism. In this article, we focus on interactions involving glucuronoconjugates because many drugs and their metabolites undergo this conjugation.

METHODS

We reviewed clinical drug interactions related to glucuronoconjugates, focusing on reports of adverse events. Then, we picked out three important drugs (zidovudine, valproic acid and lamotrigine), and examined how the literature information is reflected in the relevant PIs in Japan, UK and USA.

RESULTS AND DISCUSSION

Pharmacokinetic interactions related to glucuronoconjugates were found with 33 drug combinations. Of these, five combinations induced clear adverse events: (i) severe anaemia due to zidovudine and caused by interaction with valproic acid, (ii) recurrence/increased frequency of seizure or increased manic states from a reduction in therapeutic effects of valproic acid caused by panipenem, (iii) meropenem or (iv) ritonavir and (v) of lamotrigine caused by oral contraceptives. Analysis of PIs showed a lack of description of the interaction of zidovudine with valproic acid in the Japanese PI. The UK PI mentioned this interaction without quantitative data, whereas full information was given in the US PI. A lack of description was also present on the interaction between valproic acid with ritonavir, reported in 2006, in the PIs of all three countries. For the interactions involving valproic acid and panipenem or meropenem, even though marked reduction of blood valproic acid level has been reported, no quantitative data were provided in any of the PIs.

CONCLUSION

Five combinations were identified to cause severe adverse events because of interactions related to glucuronoconjugates. This information, including quantitative data, is not always properly provided in the relevant PIs in Japan, UK or USA. PIs should be improved to better inform healthcare providers and thereby help them and their patients.

Monitoring insulin-like growth factors in HIV infection and AIDS

There is a close association between the growth hormone (GH)-insulin-like growth factor I (IGF-I) axis, infection and immunity. Infection with the human immunodeficiency virus (HIV) is often associated with a decrease of the concentrations of IGF-I, IGF-II, IGF-binding protein 3 (IGFBP-3) and an increase of IGFBP-1 and -2. Many investigators have studied the relationship between the GH-IGF-I system and some of the most common characteristics of disease progression, such as decreased CD4 cell counts, weight loss and fat redistribution. Although conditions for restoration of thymic function and lymphopoiesis with GH or IGF-I are still not well defined, many studies led to the development of clinical trials on the therapeutic use of GH, IGF-I and GHRH for the treatment of weight loss or fat redistribution, two problems which persist despite the introduction of highly active antiretroviral therapy. Monitoring IGF-I concentrations during treatment with GH and GHRH is likely to become an essential component of their therapeutic use. IGF-I levels are the first indicator of treatment efficacy and can be used to monitor compliance. High levels of IGF-I are a warning sign for the increased risk of potential adverse effects, such as acromegalic-like symptoms or malignancy. This could lead to a reduction of the therapeutic dose or the temporary interruption of treatment until IGF levels reach a safe range. IGF-I levels are also likely to increase with other hormones used in HIV patients, such as erythropoietin for the treatment of anemia or anabolic androgens in HIV-infected women.

Possible interaction between lopinavir/ritonavir and valproic Acid exacerbates bipolar disorder

OBJECTIVE

To describe a case of exacerbated mania potentially related to an interaction between lopinavir/ritonavir and valproic acid (VPA) and propose a mechanism of action for this interaction.

CASE SUMMARY

A 30-year-old man with bipolar disorder and HIV initiated treatment with lopinavir/ritonavir, zidovudine, and lamivudine. Prior to beginning therapy with these antiretrovirals, he was receiving VPA 250 mg 3 times daily, with his most recent VPA concentration measured at 495 micromol/L. Twenty-one days after starting antiretroviral treatment, he became increasingly manic. His VPA concentration at admission was 238 micromol/L, a 48% decrease. The daily VPA dose was increased to 1500 mg, and olanzapine was introduced. The VPA concentration following this dose escalation was 392 micromol/L, and the patient improved clinically.

DISCUSSION

Fifty percent of VPA is metabolized by glucuronidation, 40% undergoes mitochondrial beta-oxidation, and less than 10% is eliminated by the cytochrome P450 isoenzymes. Ritonavir can induce glucuronidation of several medications including ethinyl estradiol, levothyroxine, and lamotrigine. We believe that ritonavir-mediated induction of VPA glucuronidation resulted in a decrease in VPA concentrations and efficacy. An objective causality assessment suggested that the increased mania was probably related to the decrease in VPA concentration and that a possible interaction exists between lopinavir/ritonavir and VPA.

CONCLUSIONS

A potential interaction exists between VPA and all ritonavir-boosted antiretroviral regimens. Clinicians should monitor patients closely for a decreased VPA effect when these medications are given concomitantly.

Glucuronidation in therapeutic drug monitoring

BACKGROUND

Glucuronidation is a major drug-metabolizing reaction in humans. A pharmacological effect of glucuronide metabolites is frequently neglected and the value of therapeutic drug monitoring has been questioned. However, this may not always be true.

METHODS

In this review the impact of glucuronidation on therapeutic drug monitoring has been evaluated on the basis of a literature search and experience from the own laboratory.

RESULTS

The potential role of monitoring glucuronide metabolite concentrations to optimize therapeutic outcome is addressed on the basis of selected examples of drugs which are metabolized to biologically active/reactive glucuronides. Furthermore indirect effects of glucuronide metabolites on parent drug pharmacokinetics are presented. In addition, factors that may modulate the disposition of these metabolites (e.g. genetic polymorphisms, disease processes, age, and drug-drug interactions) are briefly mentioned and their relevance for the clinical situation is critically discussed.

CONCLUSION

Glucuronide metabolites can have indirect as well as direct pharmacological or toxicological effects. Although convincing evidence to support the introduction of glucuronide monitoring into clinical practice is currently missing, measurement of glucuronide concentrations may be advantageous in specific situations. If the glucuronide metabolite has an indirect effect on the pharmacokinetics of the parent compound, monitoring of the parent drug may be considered. Furthermore pharmacogenetic approaches considering uridine diphosphate (UDP) glucuronosyltransferases polymorphisms may become useful in the future to optimize therapy with drugs subject to glucuronidation.

Effects of Ketoconazole on Glucuronidation by UDP-Glucuronosyltransferase Enzymes

PURPOSE

Ketoconazole has been shown to inhibit the glucuronidation of the UGT2B7 substrates zidovudine and lorazepam. Its effect on UGT1A substrates is unclear. A recent study found that coadministration of irinotecan and ketoconazole led to a significant increase in the formation of SN-38 (7-ethyl-10-hydroxycamptothecine), an UGT1A substrate. This study investigates whether ketoconazole contributes to the increase in SN-38 formation by inhibiting SN-38 glucuronidation.

EXPERIMENTAL DESIGN

SN-38 glucuronidation activities were determined by measuring the rate of SN-38 glucuronide (SN-38G) formation using pooled human liver microsomes and cDNA-expressed UGT1A isoforms (1A1, 1A7 and 1A9) in the presence of ketoconazole. Indinavir, a known UGT1A1 inhibitor, was used as a positive control. SN-38G formation was measured by high-performance liquid chromatograph.

RESULTS

Ketoconazole competitively inhibited SN-38 glucuronidation. Among the UGT1A isoforms screened, ketoconazole showed the highest inhibitory effect on UGT1A1 and UGT1A9. The K(i) values were 3.3 +/- 0.8 micromol/L for UGT1A1 and 31.9 +/- 3.3 micromol/L for UGT1A9.

CONCLUSIONS

These results show that ketoconazole is a potent UGT1A1 inhibitor, which seems the basis for increased exposure to SN-38 when coadministered with irinotecan.

Depletion of latent HIV-1 infection in vivo: a proof-of-concept study

BACKGROUND

Persistent infection in resting CD4+ T cells prevents eradication of HIV-1. Since the chromatin remodeling enzyme histone deacetylase 1 (HDAC1) maintains latency of integrated HIV, we tested the ability of the HDAC inhibitor valproic acid to deplete persistent, latent infection in resting CD4+ T cells.

PROCEDURES

We did a proof-of-concept study in four volunteers infected with HIV and on highly-active antiretroviral therapy (HAART). After intensifying the effect of HAART with subcutaneous enfuvirtide 90 mug twice daily for 4-6 weeks to prevent the spread of HIV, we added oral valproic acid 500-750 mg twice daily to their treatment regimen for 3 months. We quantified latent infection of resting CD4+ T cells before and after augmented treatment by limiting-dilution culture of resting CD4+ T cells after ex-vivo activation.

FINDINGS

The frequency of resting cell infection was stable before addition of enfuvirtide and valproic acid, but declined thereafter. This decline was significant in three of four patients (mean reduction 75%, range 68% to >84%). Patients had slight reactions to enfuvirtide at the injection site, but otherwise tolerated treatment well.

INTERPRETATION

Combination therapy with an HDAC inhibitor and intensified HAART safely accelerates clearance of HIV from resting CD4+ T cells in vivo, suggesting a new and practical approach to eliminate HIV infection in this persistent reservoir. This finding, though not definitive, suggests that new approaches will allow the cure of HIV in the future.

Review: mixing new cocktails: drug interactions in antiretroviral regimens

Current highly active antiretroviral therapy (HAART) for the treatment of HIV infection requires the concomitant administration of three or four different agents, often with a high potential for drug-drug interactions. Additionally, some HIV-positive patients still require concomitant treatment with drugs for opportunistic infections, some require medication to treat unrelated medical conditions and/or the metabolic complications of antiretroviral therapy, others may self-medicate with herbal formulations and/or over-the-counter drugs, and still others many take drugs for recreational reasons or to manage addiction. Therefore, the virtually limitless number of drug combinations that may be taken by patients undergoing treatment of HIV infection makes drug-drug interactions almost inevitable. Managing these interactions is one of the major challenges associated with the multidrug regimens used for HIV therapy. This paper provides an overview of the most common interactions between antiretrovirals in the same and different classes-nucleoside analogue reverse transcriptase inhibitors (NRTI), protease inhibitors (PI), and non-nucleoside reverse transcriptase inhibitors (NNRTI)-by focusing on principles rather than specific interactions. The paper also addresses interactions between these antiretrovirals and other commonly used medications that may be prescribed concomitantly.

Antiretrovirals, Part II: Focus on Non-Protease Inhibitor Antiretrovirals (NRTIs, NNRTIs, and Fusion Inhibitors)

The second in a series reviewing the HIV/AIDS antiretroviral drugs. This review summarizes the non-protease inhibitor antiretrovirals: nucleoside and nucleotide analogue reverse transcriptase inhibitors (NRTIs), the nonnucleoside reverse transcriptase inhibitors (NNRTIs), and cell membrane fusion inhibitors. In an overview format for primary care physicians and psychiatrists, this review presents the mechanism of action, side effects, toxicities, and drug interactions of these agents.