[Lethal drug interactions of the new antiviral, sorivudine, with anticancer prodrugs of 5-fluorouracil]

A life-threatening drug-drug interaction between capecitabine and brivudine in a patient with metastatic breast cancer

In the current report we present the case of a patient experiencing a life-threatening drug-drug interaction involving the concurrent administration of capecitabine and brivudine. A 65- year-old female with metastatic breast cancer was commenced on brivudine for Herpes Zoster, while on capecitabine treatment, by a physician unfamiliar with the potential repercussions of this drug-drug interaction. As a result, she developed skin rash, severe oral mucositis, and severe and prolonged pancytopenia. These side effects were attributed to a serious interaction of capecitabine with brivudine, resulting in inhibition of dihydropyrimidine dehydrogenase. The patient was admitted for supportive care including intravenous hydration, parenteral nutrition, mouth care solutions, fluconazole, antimicrobial therapy, filgrastim, red blood cell and platelet transfusions. She successfully recovered and was discharged on the 26^th day after her admission. Drug-drug interactions can be serious, even life-threatening; thus the physicians should be cautious when prescribing new drugs.

Looking back to move forward: a twenty-year audit of herpes zoster in Asia-Pacific

Background

Herpes zoster (HZ) is a prevalent viral disease that inflicts substantial morbidity and associated healthcare and socioeconomic burdens. Current treatments are not fully effective, especially among the most vulnerable patients. Although widely recommended, vaccination against HZ is not routine; barriers in Asia-Pacific include long-standing neglect of adult immunisation and sparse local data. To address knowledge gaps, raise awareness, and disseminate best practice, we reviewed recent data and guidelines on HZ from the Asia-Pacific region.

Methods

We searched PubMed, Scopus, and World Health Organization databases for articles about HZ published from 1994 to 2014 by authors from Australia, China, Hong Kong, India, Indonesia, Japan, Korea, Malaysia, New Zealand, the Philippines, Singapore, Taiwan, Thailand, and Vietnam. We selected articles about epidemiology, burden, complications, comorbidities, management, prevention, and recommendations/guidelines. Internet searches retrieved additional HZ immunisation guidelines.

Results

From 4007 retrieved articles, we screened-out 1501 duplicates and excluded 1264 extraneous articles, leaving 1242 unique articles. We found guidelines on adult immunisation from Australia, India, Indonesia, Malaysia, New Zealand, the Philippines, South Korea, and Thailand.

HZ epidemiology in Asia-Pacific is similar to elsewhere; incidence rises with age and peaks at around 70 years – lifetime risk is approximately one-third. Average incidence of 3–10/1000 person-years is rising at around 5% per year. The principal risk factors are immunosenescence and immunosuppression. HZ almost always causes pain, and post-herpetic neuralgia is its most common complication. Half or more of hospitalised HZ patients have post-herpetic neuralgia, secondary infections, or inflammatory sequelae that are occasionally fatal. These disease burdens severely diminish patients’ quality of life and incur heavy healthcare utilisation.

Conclusions

Several countries have abundant data on HZ, but others, especially in South-East Asia, very few. However, Asia-Pacific countries generally lack data on HZ vaccine safety, efficacy and cost-effectiveness. Physicians treating HZ and its complications in Asia-Pacific face familiar challenges but, with a vast aged population, Asia bears a unique and growing burden of disease. Given the strong rationale for prevention, most adult immunisation guidelines include HZ vaccine, yet it remains underused. We urge all stakeholders to give higher priority to adult immunisation in general and HZ in particular.

Electronic supplementary material

The online version of this article (doi:10.1186/s12879-017-2198-y) contains supplementary material, which is available to authorized users.

Lethal Toxicity After 5-Fluorouracil Chemotherapy and Its Possible Relationship to Dihydropyrimidine Dehydrogenase Deficiency: A Case Report and Review

5-fluorouracil (5-FU) is a chemotherapeutic agent widely used in the treatment of solid malignancies, especially in colorectal cancer. A characteristic note seen with its use is the considerable interindividual variation in the incidence and severity of the toxicities seen among patients. We report the case of a 55-year old woman who presented with severe, lethal toxicity to standard doses of 5-fluorouracil (5-FU) and folinic acid. We discuss the known clinical determinants of toxicity. We also discuss the possible molecular factors implicated in the variable toxicity seen to 5-FU, especially in regards to dihiyropyrimidine dehydrogenase, a pivotal enzyme in the metabolism of 5-FU.

Metabolism of xenobiotics of human environments

Xenobiotics have been defined as chemicals to which an organism is exposed that are extrinsic to the normal metabolism of that organism. Without metabolism, many xenobiotics would reach toxic concentrations. Most metabolic activity inside the cell requires energy, cofactors, and enzymes in order to occur. Xenobiotic-metabolizing enzymes can be divided into phase I, phase II, and transporter enzymes. Lipophilic xenobiotics are often first metabolized by phase I enzymes, which function to make xenobiotics more polar and provide sites for conjugation reactions. Phase II enzymes are conjugating enzymes and can directly interact with xenobiotics but more commonly interact with metabolites produced by phase I enzymes. Through both passive and active transport, these more polar metabolites are eliminated. Most xenobiotics are cleared through multiple enzymes and pathways. The relationship between chemical concentrations, enzyme affinity and quantity, and cofactor availability often determine which metabolic reactions dominate in a given individual.

Interaction between capecitabine and brivudin in a patient with breast cancer

BACKGROUND

A 66-year-old woman with metastatic mammary carcinoma, who was being treated with capecitabine, contracted a herpes zoster infection that was treated with the antiviral drug brivudin. A drug-drug interaction between brivudin and capecitabine caused medullar aplasia, serious toxic effects to the intestinal mucous membrane, hand-foot syndrome, onycholysis and dental pigmentation.

INVESTIGATIONS

Physical examination, blood analysis, blood cultures, chest X-ray, bone marrow aspiration and biopsy.

DIAGNOSIS

Serious adverse event secondary to inhibition of dihydropyrimidine dehydrogenase by a drug-drug interaction between capecitabine and brivudin.

MANAGEMENT

Intravenous hydration, imipenem, red blood cell and platelet transfusions, filgrastim, omeprazole, care of the mouth and feet, topical anesthetics, systemic analgesics and parenteral nutrition.

[Molecular toxicological mechanism of the lethal interactions of the new antiviral drug, sorivudine, with 5-fluorouracil prodrugs and genetic deficiency of dihydropyrimidine dehydrogenase]

In 1993, there were 18 acute deaths in Japanese patients who had the viral disease herpes zoster and were treated with the new antiviral drug sorivudine (SRV, 1-beta-D-arabinofuranosyl-(E)-5-(2-bromovinyl)uracil). All the dead patients had received a 5-fluorouracil (5-FU) prodrug as anticancer chemotherapy concomitant with SRV administration. Studies on toxicokinetics in rats and on hepatic dihydropyrimidine dehydrogenase (DPD), a rate-limiting enzyme for 5-FU catabolism in rats and humans, strongly suggested that in the patients who received both SRV and the 5-FU prodrug, tissue levels of highly toxic 5-FU markedly increased as a result of irreversible inactivation of DPD in the presence of NADPH by 5-(2-bromovinyl)uracil (BVU), a metabolite formed from SRV by gut flora in rats and humans. Recombinant human (h) DPD was also irreversibly inactivated by [14C] BVU in the presence of NADPH. MALDI-TOF MS analysis of radioactive tryptic fragments from the radiolabeled and inactivated hDPD demonstrated that a Cys residue located at position 671 in the pyrimidine-binding domain of hDPD was modified with an allyl bromide type of reactive metabolite, dihydro-BVU. Thus artificial DPD deficiency caused by BVU from SRV led to patient deaths when coadministered with the 5-FU prodrug. Human population studies using healthy volunteers have demonstrated that there are poor and extensive 5-FU metabolizers who have very low and high DPD activities, respectively. Administration of a clinical dose of 5-FU or its prodrug to poor 5-FU metabolizers may cause death unless DPD activity is determined using their peripheral blood mononuclear cells prior to the administration of the anticancer drug.

Polymorphisms of metabolizing enzymes and transporter proteins involved in the clearance of anticancer agents

BACKGROUND

The efficacies and toxicities of anticancer agents vary greatly among patients. This is attributable to the activities of drug-metabolizing enzymes and membrane transporters, primarily determined by polymorphisms of the functions of genes encoding these proteins.

DESIGN

We reviewed the available literature on drug-metabolizing enzymes and membrane transporters, especially their physiological functions, genetic and functional polymorphisms, and involvement in metabolism, pharmacokinetics and toxicity of anticancer agents.

RESULTS

Nine enzymes metabolizing anticancer agents have been shown to have genetic polymorphisms: dihydropyrimidine dehydrogenase, cytochrome P450, NAD(P)H:quinone oxidoreductase 1, N-acetyltransferase 2, thiopurine methyltransferase, glutathione S-transferase, and uridine diphosphate glucuronosyltransferase. Decreased activities of these proteins can cause not only inherited metabolic disorders, but also extraordinarily severe toxicity in cancer patients given chemothearpy. Transporter proteins mediate cellular uptake and secretion of organic anions and cations. These proteins have recently been shown to play critical roles in the clearance of anticancer agents, although relations between patients' genetics backgrounds and the clinical significance of drug actions are poorly understood.

CONCLUSIONS

Further studies should be focused on dosing and selection of anticancer agents, based on the type and extent of metabolic variation among individuals, in order to avoid adverse reactions and therapeutic failure.

Structure-activity relationships of (E)-5-(2-bromovinyl)uracil and related pyrimidine nucleosides as antiviral agents for herpes viruses

A series of (E)-5-(2-bromovinyl)uracil analogues and related nucleosides was synthesized, and their antiviral activities were evaluated. (E)-5-(2-Bromovinyl)-2'-deoxy-L-uridine (L-BVDU, 2), 1-(beta-L-arabinofuranosyl)-(E)-5-(2-bromovinyl)uracil (L-BVAU, 4), (E)-5-(2-bromovinyl)-1-(2-deoxy-2-fluoro-beta-L-ribofuranosyl)uracil (L-FBVRU, 8) and (E)-5-(2-bromovinyl)-1-(2-deoxy-2-fluoro-beta-L-arabinofuranosyl)urac il (L-FBVAU, 10) were synthesized via appropriate 5-iodouracil analogues from L-arabinose. D- and L-Oxathiolane and -dioxolane derivatives 13, 16, 20, 21, and 29-34 were prepared by glycosylation reaction of the oxathiolane and dioxolane intermediates with silylated uracil analogues using TMSI as the coupling agent. The synthesized compounds were evaluated in cell cultures infected with the following viruses: varicella zoster virus (VZV), Epstein Barr virus (EBV), and herpes simplex virus types 1 and 2 (HSV-1 and HSV-2). Among the tested compounds, beta-L-CV-OddU (29), beta-L-BV-OddU (31), and beta-L-IV-OddU (33) exhibited potent in vitro antiviral activity against VZV with EC(50) values of 0.15, 0. 07, and 0.035 microM, respectively, and against EBV with EC(50) values of 0.49, 0.59, and 3.91 microM, respectively.

Preclinical approach for identifying drug interactions

Pharmacokinetic drug interactions may be divided into two categories: induction and inhibition of enzymes involved in the metabolism of a drug. The induction and inhibition of such enzymes result in decreases or increases in the blood concentrations of the drug, causing drug effects to be altered. Cytochrome P450 (P450 or CYP) is an enzyme responsible for the metabolism of a wide variety of drugs, including some anticancer agents. If a drug with a high affinity to bind to a specific form of P450 is given to a patient in combination with other drugs mainly metabolized by this enzyme, the former may potentiate the pharmacological actions of the latter by preventing their metabolism and thus increasing their serum concentration. Alternatively, if a drug inhibits or inactivates essentially all forms of P450 nonspecifically, it may be possible that the pharmacological effects of other drugs used in combination with it will be enhanced. CYP3A4 is one of the major forms of P450 in human liver microsomes. In previous studies using human liver microsomes, docetaxel was determined to be metabolized mainly by this isozyme. Thus it was assumed that inducers and inhibitors of CYP3A4 might affect the pharmacokinetics of docetaxel. In our studies, administration of dexamethasone, a known inducer of CYP3A, to mice resulted in decreases in serum docetaxel concentrations. In contrast, ketoconazole, an inhibitor of CYP3A, is assumed to increase the serum and hepatic concentrations of docetaxel. As an example of a drug which might inhibit the metabolism of other drugs, we found that bis-aceto-ammine-dichloro-cyclohexylamine platinum(IV) (JM216), which is currently being developed as a potential anticancer agent, inhibits essentially all major forms of P450 present in human liver microsomes. Since its inhibition potency is relatively high, careful assessment of the effects of this drug on the metabolism of other drugs appears to be necessary.