Mechanisms of drug reactions: the metabolic track

Oral Adverse Drug Reactions to Cardiovascular Drugs

A great many cardiovascular drugs (CVDs) have the potential to induce adverse reactions in the mouth. The prevalence of such reactions is not known, however, since many are asymptomatic and therefore are believed to go unreported. As more drugs are marketed and the population includes an increasing number of elderly, the number of drug prescriptions is also expected to increase. Accordingly, it can be predicted that the occurrence of adverse drug reactions (ADRs), including the oral ones (ODRs), will continue to increase. ODRs affect the oral mucous membrane, saliva production, and taste. The pathogenesis of these reactions, especially the mucosal ones, is largely unknown and appears to involve complex interactions among the drug in question, other medications, the patient’s underlying disease, genetics, and life-style factors. Along this line, there is a growing interest in the association between pharmacogenetic polymorphism and ADRs. Research focusing on polymorphism of the cytochrome P450 system (CYPs) has become increasingly important and has highlighted the intra- and inter-individual responses to drug exposure. This system has recently been suggested to be an underlying candidate regarding the pathogenesis of ADRs in the oral mucous membrane. This review focuses on those CVDs reported to induce ODRs. In addition, it will provide data on specific drugs or drug classes, and outline and discuss recent research on possible mechanisms linking ADRs to drug metabolism patterns. Abbreviations used will be as follows: ACEI, ACE inhibitor; ADR, adverse drug reaction; ANA, antinuclear antigen; ARB, angiotensin II receptor blocker; BAB, beta-adrenergic blocker; CCB, calcium-channel blocker; CDR, cutaneous drug reaction; CVD, cardiovascular drug; CYP, cytochrome P450 enzyme; EM, erythema multiforme; FDE, fixed drug eruption; I, inhibitor of CYP isoform activity; HMG-CoA, hydroxymethyl-glutaryl coenzyme A; NAT, N-acetyltransferase; ODR, oral drug reaction; RDM, reactive drug metabolite; S, substrate for CYP isoform; SJS, Stevens-Johnson syndrome; SLE, systemic lupus erythematosus; and TEN, toxic epidermal necrolysis.

Drug Hypersensitivity Syndrome Caused by Minocycline

Background:

Minocycline is a commonly prescribed drug for the treatment of acne. Its use is generally not associated with systemic side effects.

Objective:

To describe a case of minocycline-induced drug hypersensitivity syndrome in a 20-year-old Japanese woman.

Methods and Results:

Following 2 months of minocycline treatment, the patient developed skin lesions composed of exudative maculopapules, purpuratous macules, and target-like, erythema multiforme-like plaques over most of her body. In addition, she had fever, abnormal liver function tests, eosinophilia, and atypical lymphocytosis. Laboratory tests indicated no elevation of antibody titers against cytomegalovirus, Epstein-Barr virus, and human herpesvirus 6. Her ongoing exposure to minocycline was stopped, and treatment with oral prednisolone was begun. Her signs, symptoms, and laboratory abnormalities then began to resolve. Subsequently, the syndrome was observed to return briefly in response to an oral challenge with minocycline.

Conclusions:

Minocycline is able to elicit a drug hypersensitivity syndrome that can resemble infectious mononucleosis. This drug reaction can be treated effectively by cessation of exposure to this drug and steroid therapy.

Safety assessment in pediatric studies

It typically takes many years before an association of a drug with a rare, serious adverse reaction is established. As related to pediatric drug use, evidence is even more erratic, as most drugs are used off labels. To enhance child safety, there is an urgent need to develop robust and rapid methods to identify such associations in as timely a manner as possible. In this chapter, several novel methods, both clinically based pharmacoepidemiological approaches and laboratory-based methods, are described.

Drug Induced Hypersensitivity and the HLA Complex

Drug-induced hypersensitivity reactions are of major concern and present a burden for national healthcare systems due to their often severe nature, high rate of hospital admissions and high mortality. They manifest with a wide range of symptoms and signs, and can be initiated by a wide range of structurally diverse chemical compounds. The pathophysiological mechanisms underlying hypersensitivity reactions are not well understood, but it is thought that they are immune mediated. MHC region on Chromosome 6 contains many genes with immune function. Classical MHC molecules are highly polymorphic cell surface glycoproteins whose function is to present peptide antigens to T cells. In addition to conferring protection from some diseases, HLA alleles are also associated with an increased risk of other diseases, including drug-induced hypersensitivity. Pharmacogenetic approach to predict the risk of drug-induced hypersensitivity has been established for several drugs. We will discuss the progress of hypersensitivity pharmacogenetics over the last few years and focus on current efforts of the international community to develop consortia which aim to standardize disease phenotypes and to identify affected individuals through international collaborations. In addition, we will discuss the clinical utility of HLA typing as predictive or diagnostic testing for drug-induced hypersensitivity.

Establishing causality in pediatric adverse drug reactions: use of the Naranjo probability scale

Carbamazepine hypersensitivity syndrome is a rare, life-threatening condition. Its diagnosis is critical to avoid future exposure to aromatic anticonvulsants. Pediatricians rarely use a systematic approach to establish the cause of drug reactions in the clinical setting. We describe the use of the Naranjo adverse drug reaction probability scale to establish causality in three cases of suspected anticonvulsant hypersensitivity syndrome with the aim of introducing clinicians to this effective tool. Our analysis reveals that this method is useful, but also highlights potential areas for its improvement.

Anticonvulsant hypersensitivity syndrome: cross-reactivity with tricyclic antidepressant agents

BACKGROUND

Aromatic anticonvulsant agents such as carbamazepine and phenytoin can induce anticonvulsant hypersensitivity syndrome (AHS) at a frequency of 1 in 10,000 to 1 in 1,000 treated patients. The hypersensitivity syndrome is a potentially life-threatening adverse drug reaction with multiorgan involvement, and incidental reexposure must be strictly avoided. Patients and treating physicians must be informed and educated about the causal drug and its potential immunologic or toxicologic cross-reactivity with other compounds. It has been well established that for future antiepileptic drug therapy, carboxamides (carbamazepine and oxcarbazepine), phenytoin, and barbiturates (phenobarbital and primidone) have to be avoided owing to their high degree of cross-reactivity. Other anticonvulsant agents, such as valproic acid, benzodiazepines, and gabapentin, may be prescribed.

OBJECTIVES

To present the clinical data for and to describe the potential cross-reactivity between aromatic anticonvulsant and tricyclic antidepressant agents in patients with carbamazepine- and phenytoin-induced AHS.

METHODS

The knowledge of cross-reactivity among aromatic anticonvulsant agents mainly emerged from clinical experience and observations because diagnostic challenge tests are not advisable. Thirty-six patients with the diagnosis of AHS were instructed to contact our unit if the symptoms relapsed.

RESULTS

Despite better knowledge of AHS, one third of the patients had avoidable recurrences after exposure to cross-reactive drugs. Besides the known cross-reactivity among aromatic anticonvulsant agents, we observed a recurrence of the hypersensitivity syndrome in 5 patients after the administration of tricyclic antidepressant agents.

CONCLUSION

The important potential cross-reactivity between aromatic anticonvulsant and tricyclic antidepressant drugs should be brought to the attention of treating physicians.

Reações cutâneas graves adversas a drogas: aspectos relevantes ao diagnóstico e ao tratamento - Parte II

As reações cutâneas graves adversas à droga são as que geralmente necessitam de internação hospitalar, por vezes em unidade de terapia intensiva ou de queimados, com observação minuciosa dos sinais vitais e da função de órgãos internos. O objetivo é descrever estas reações facilitando o seu reconhecimento e tratamento. Fazem parte deste grupo a Síndrome de Hipersensibilidade à Droga (SHD), a Pustulose Exantemática Generalizada Aguda (PEGA), a Necrose Cutânea induzida por Anticoagulante, as Vasculites de Pequenos Vasos (VPV), a Vasculite de Hipersensibilidade ao Propiltiouracil (VHP) e as Reações tipo Doença do Soro (RDS). A SHD tem-se tornado de elevada relevância clínica devido ao uso amplo dos anticonvulsivantes aromáticos e da dapsona, utilizada no tratamento de doenças como a acne e a hanseníase. A PEGA é determinada principalmente pelos derivados beta-lactâmicos e tem como principal diagnóstico diferencial a psoríase pustulosa generalizada. As VPV tegumentares podem refletir uma doença multissistêmica subjacente, com danos graves em órgãos nobres, como os rins, pulmões e sistema hematológico, com morbidade elevada e possível letalidade. Abordamos as características clínicas e o tratamento destas reações adversas à droga.

Idiosyncratic toxicity associated with potentiated sulfonamides in the dog

Idiosyncratic toxicity to potentiated sulfonamides occurs in both humans and dogs, with considerable clinical similarities. The syndrome in dogs can consist of fever, arthropathy, blood dyscrasias (neutropenia, thrombocytopenia, or hemolytic anemia), hepatopathy consisting of cholestasis or necrosis, skin eruptions, uveitis, or keratoconjunctivitis sicca. Other manifestations seen less commonly include protein-losing nephropathy, meningitis, pancreatitis, pneumonitis, or facial nerve palsy. The pathogenesis of these reactions is not completely understood, but may be due to a T-cell-mediated response to proteins haptenated by oxidative sulfonamide metabolites. Our laboratory is working on tests to characterize dogs with possible idiosyncratic sulfonamide reactions, to include ELISA for anti-drug antibodies, immunoblotting for antibodies directed against liver proteins, flow cytometry for drug-dependent anti-platelet antibodies, and in vitro cytotoxicity assays. The management of idiosyncratic sulfonamide toxicity involves client education to identify clinical signs early and allow rapid drug discontinuation, supportive care to include possibly ascorbate and glutathione precursors, and avoidance of subsequent re-exposure. It is important to realize that only antimicrobial sulfonamides, such as sulfamethoxazole, sulfadiazine, and sulfadimethoxine, share this clinical syndrome. There is no evidence for cross-reactivity with drugs that have different underlying structures but share a sulfonamide moiety, such as acetazolamide, furosemide, glipizide, or hydrochlorthiazide.

Detection and analysis of intracytoplasmic cytokines in peripheral blood mononuclear cells in patients with drug-induced liver injury

BACKGROUND/AIMS

Idiosyncratic immune response to drugs causes two types of liver injury, cholestasis or hepatitis. However, the underlying immune mechanisms of drug-induced liver injury are presently unclear.

METHODS

We examined the cytokine production of peripheral blood mononuclear cells (PBMCs) from 17 patients with drug-induced liver injury and healthy controls during their incubation with and without the drug by flow cytometry. We also analyzed the cytokine production in PBMCs from eight patients after stimulation with the drug-pulsed HepG2 lysates to examine the possibility that the drug or its metabolites conjugated with a putative molecule derived from HepG2 cells might be more immunogenic.

RESULTS

Among several cytokines produced by the drug or the drug-pulsed HepG2 lysates, interferon-gamma production from CD8+ cells was associated with hepatocellular injury, and tumor necrosis factor-alpha production from CD14+ cells was with cholestasis. Especially, the latter was apparent when the drug-pulsed HepG2 lysates were used as stimulants, suggesting that a complex consist of the drug, or its metabolite, and a putative molecule derived from HepG2 cells might be more immunogenic than the drug itself.

CONCLUSIONS

The analysis of intracytoplasmic cytokine in PBMCs after stimulation with the drug or the drug-pulsed HepG2 lysates is useful to analyze the immune mechanism underlying drug-induced liver injury.

Allergic adverse reactions to sulfonamides

Antimicrobial sulfonamides were the first antimicrobial agents used effectively to treat infectious diseases. However, because they may cause severe adverse drug reactions (ADRs) and because more effective agents have since been developed, sulfonamides now are used for only a few indications in specific groups, such as AIDS patients. Skin reactions, from benign rash to potentially lethal toxidermias, are the most frequent ADRs to sulfonamides. Other major ADRs include acute liver injury, pulmonary reactions, and blood dyscrasias. Although the mechanisms involved have not been fully elucidated, reactive metabolites appear to play a pivotal role. The hydroxylamine and nitroso metabolites of sulfamethoxazole, the most frequently used sulfonamide today, can bind covalently to proteins because of their chemical reactivity, resulting in the induction of specific adverse immune responses. Therefore, changes in the activity of metabolic and detoxification pathways are associated with a greater risk for developing allergic reactions to sulfonamides. Allergies to sulfonamides, particularly sulfamethoxazole (often used in combination with trimethoprim as co-trimoxazole), are more frequent in AIDS patients, but the reason for this increased risk is not fully understood. No valid tools are available to predict which patients have a greater risk for developing allergies to sulfonamides. Diagnosis is essential to avoid a possible evolution toward severe reactions and readministration of the offending drug. In patients who absolutely require further treatment, successful desensitization may be achieved.

Monotherapy versus polytherapy for epilepsy: a multicenter double-blind randomized study

PURPOSE

Monotherapy has been the gold standard in epilepsy treatment for the last 20 years, partly because of the reputation for increased toxicity of polytherapy. However, monotherapy and polytherapy have not been compared in a double-blind clinical trial. Open trials that compared the two treatments were not optimally designed and compared the two at unequal drug loads (i.e., at nonequivalent dosages). We report on a double-blind clinical trial in which a combination of carbamazepine (CBZ) and valproate (VPA) was compared with CBZ monotherapy. Patients started with equal drug loads, and neurotoxicity was the primary outcome measure.

METHODS

The 130 adult patients with untreated generalized tonic-clonic and/or partial seizures were randomized to equal drug loads of either monotherapy (400 mg CBZ per day) or polytherapy (200 mg CBZ plus 300 mg VPA per day). Outcome was measured by seizure counts, clinimetric epilepsy scales, and neuropsychological tests at baseline, at 2 and 12 months, and irregularly between 2 and 12 months.

RESULTS

No statistical differences were found between the two treatments in the reduction of seizure frequencies, in overall neurotoxicity, or in overall systemic toxicity. The frequencies and clinimetric scores of certain adverse effects did differ (e.g., more monotherapy patients remained sedated, and more polytherapy patients gained weight). Fewer polytherapy patients withdrew because of adverse effects (14 vs. 22%), although this did not reach statistical significance (p=0.15). Neuropsychological assessment did not show significant differences.

CONCLUSIONS

No differences were found in overall neurotoxicity between monotherapy and polytherapy.

Hypersensitivity reactions during therapy with the nucleoside reverse transcriptase inhibitor abacavir

BACKGROUND

Hypersensitivity reactions consist of a variable group of clinical findings and have been described for a wide variety of chemical compounds.

OBJECTIVE

This review characterizes the clinical profile of hypersensitivity to the nucleoside reverse transcriptase inhibitor abacavir sulfate.

METHODS

We performed a retrospective medical review of pooled adverse events data from approximately 200,000 patients who received abacavir in clinical trials, through expanded-access programs, or by prescription from 1996 through 2000. Screened cases of hypersensitivity were classified as either definitive or probable. Definitive cases were identified when initial symptoms resolved on interruption of abacavir therapy and returned on reintroduction of abacavir therapy.

RESULTS

A total of 1803 cases were identified, 1302 in the 30,595 patients participating in clinical trials or the expanded-access program and 501 in patients from the post-marketing experience. On review, 176 (9.8%) of these cases were considered definitive and the remainder probable. Based on the 1302 cases identified in clinical trials or the expanded-access program, the calculated incidence of hypersensitivity was 4.3%. Symptoms reported in > or = 20% of cases of this multiorgan reaction included fever, rash, malaise/fatigue, and gastrointestinal symptoms such as nausea, vomiting, and diarrhea, among others. Respiratory symptoms occurred in 30% of cases and included dyspnea (12%), cough (10%), and pharyngitis (6%). In 90% of cases, hypersensitivity reactions occurred within the first 6 weeks after initiation of abacavir (median time, 11 days); after an initial reaction, rechallenge with abacavir resulted in the reappearance of symptoms within hours of reexposure. Hypotension was present in 25% of these rechallenge reactions. Among patients who received abacavir in clinical trials, the mortality rate was 0.03% (3 per 10,000 patients).

CONCLUSIONS

Hypersensitivity to abacavir is an idiosyncratic reaction and a distinct clinical syndrome characterized predominantly by systemic involvement. It can be expected to appear as a treatment-limiting event in approximately 5% of patients. The appearance of clinical symptoms consistent with this syndrome mandates immediate discontinuation of abacavir. Hypersensitivity to abacavir is an absolute contraindication to subsequent treatment with any formulation that includes this agent.

Drug-induced hypersensitivity syndrome in pediatric patients

The antiepileptic hypersensitivity syndrome is a severe, multiorgan reaction to oral antiepileptics that manifests as fever, rash, lymphadenopathy, and hepatitis. This same reaction pattern also has been described following administration of a few unrelated medications. We report on 11 patients who had drug-induced hypersensitivity syndrome and were admitted to our pediatric service and review 94 cases of this syndrome in pediatric patients identified from the literature. We undertook this study to summarize the findings and alert clinicians to the severe internal organ involvement that can occur with this syndrome.

Induction of delayed-type hypersensitivity to sulfamethoxazole in mice: role of metabolites

Although cutaneous adverse drug reactions (ADRs) are relatively frequent and potentially severe, their mechanisms are poorly understood and no validated predictive experimental model is available. Sulfamethoxazole (SMX) is commonly used to treat infections in HIV-positive patients and severe cutaneous ADRs have been described. This study was undertaken to test whether sensitization to SMX could be achieved in mice using a combination of in vivo and in vitro endpoints. No delayed-type hypersensitivity (DTH) response could be evidenced following SMX injection in the back and subsequent challenge into the footpad or onto the ear. Pretreatment with the enzymatic inducers phenobarbitone and betanaphtoflavone, or depletion in CD4(+) T-lymphocytes were not successful either. In contrast, the injection of SMX/S9 mix in the back and challenge with SMX/S9 mix induced a significant increase in footpad thickness. A significant proliferation of spleen cells from SMX- or SMX/S9 mix-treated mice was evidenced following incubation with SMX/S9 mix, but not SMX alone. This study provides indirect evidence that SMX metabolites are involved and confirms previous in vitro results obtained with lymphocytes from patients with a history of SMX-induced ADRs cultured with murine microsomes. Further investigations using other drugs known to induce similar ADRs are warranted to establish the predictive value of this murine model.

Idiosyncratic reactions: new methods of identifying high-risk patients

This article describes the mechanisms of idiosyncratic drug reactions (IDRs) and provides an analysis of potential methods for identifying patients at high risk for antiepileptic idiosyncratic drug reactions. IDRs may be caused by toxic metabolites, either directly or indirectly (by way of an immunologic response or a free radical-mediated process). Four methods to potentially identify patients at high risk for AED IDRs are discussed: development of an "at-risk" clinical profile for a particular AED: identification of biomarkers that measure the formation of a toxic metabolite by a previously unrecognized bioactivation pathway for a particular AED; identification of biomarkers indicating deficient detoxification abilities [e.g., deficient free radical scavenging enzyme activities or low calculated oxidative protection (COP) ratios 1 and 2]; and identification of at-risk genetic markers. Clinical profiles for patients receiving valproic acid (VPA), felbamate (FBM), and lamotrigine (LTG) and who are at risk for development of AED IDRs are presented. Patients with VPA IDRs have deficient erythrocyte glutathione peroxidase activity, low plasma selenium concentrations, low COP1 ratios, and low COP2 ratios compared with age-matched controls. Patients with FBM-associated aplastic anemia have deficient erythrocyte glutathione peroxidase, superoxide dismutase (SOD), and glutathione reductase activities compared with age-matched controls. Use of at-risk clinical profiles (for VPA, FBM, and LTG) and measurement of erythrocyte glutathione peroxidase activity, erythrocyte SOD activity, and calculation of COP1 and COP2 ratios (for VPA and FBM) are inexpensive, simple methods of identifying high-risk patients for IDRs. Research is needed to further characterize the mechanism of IDRs, to investigate the clinical utility of free radical-scavenging enzyme activity measurement and calculation of COP ratios for other AED IDRs, and to develop additional methods of identifying patients at high risk for AED IDRs.

A case report of olanzapine-induced hypersensitivity syndrome

Hypersensitivity syndrome is defined as a drug-induced complex of symptoms consisting of fever, rash, and internal organ involvement. The hypersensitivity syndrome is well recognized as being caused by anticonvulsants. Olanzapine is an atypical antipsychotic agent whose side effects include sedation, weight gain, and increased creatinine kinase and transaminase levels. To date, there have been no reports of hypersensitivity syndrome related to this drug. A 34-year-old man developed a severe generalized pruritic skin eruption, fever, eosinophilia, and toxic hepatitis 60 days after ingestion of olanzapine. After termination of olanzapine treatment, the fever resolved, the skin rash was reduced, eosinophil count was reduced to normal, and the transaminase levels were markedly reduced. Clinical features and the results of skin and liver biopsies indicated that the patient developed hypersensitivity syndrome caused by olanzapine.

Immunological principles of adverse drug reactions: the initiation and propagation of immune responses elicited by drug treatment

Adverse drug reactions account for between 2 to 5% of all hospital admissions and can prevent the administration of an otherwise effective therapeutic agent. Hypersensitivity or immune-mediated reactions, although less common, tend to be proportionately more serious. There is convincing evidence to implicate the immune system in the pathogenesis of hypersensitivity reactions. Our understanding of the way in which the immune system recognises drugs is based on the hapten hypothesis; the onset of hypersensitivity involves drug bioactivation, covalent binding to proteins, followed by uptake, antigen processing and T cell proliferation. Central to this hypothesis is the critical role of drug metabolism, with the balance between metabolic bioactivation and detoxification being one important component of individual susceptibility. The purpose of this review is to classify drug hypersensitivity reactions in terms of their clinical presentation, and also to consider recent advances in our understanding of the chemical, biochemical and, in particular, cellular immunological mechanisms of hypersensitivity. The following topics are reviewed: (i) drug disposition and cellular metabolism; (ii) mechanisms of antigen processing and presentation; (iii) the role of cytokines and co-stimulatory molecules in the induction and maintenance of a polarised immune response; and (iv) the application of the hapten hypothesis, danger hypothesis and serial triggering model to drug hypersensitivity. A greater understanding of the mechanism(s) of hypersensitivity may identify novel therapeutic strategies and help to combat one of the more severe forms of adverse reactions to drugs.

Value of animal models for predicting hypersensitivity reactions to medicinal products

Although hypersensitivity reactions induced by medicinal products and chemicals are relatively common, few predictive models are available. A major difficulty is our currently limited understanding of the mechanisms involved, and efforts should be paid to better defining drug immunogenicity, hapten formation and immune effector mechanisms. A second difficulty is the multiplicity of clinical manifestations presumably due to varying mechanisms. Available models can only predict a few of these reactions. Anaphylaxis models in guinea-pigs can be only used for the safety assessment of macromolecules which are neither humanized or of human origin, whereas guinea-pig or mouse models can detect the majority of human contact sensitizers. In addition to the extensive validation of existing models, promising avenues of research are expected to be found in the use of novel animal models, particularly those using genetically modified animals, such as transgenic and knock-out mice.