In vitro cytotoxicity as a marker of hypersensitivity to sulphamethoxazole in patients with HIV

Novel bioactivation mechanism of reactive metabolite formation from phenyl methyl-isoxazoles

Recently, we described a series of phenyl methyl-isoxazole derivatives as novel, potent, and selective inhibitors of the voltage-gated sodium channel type 1.7 (Bioorg Med Chem Lett 21:3871-3876, 2011). The lead compound, 2-chloro-6-fluorobenzyl [3-(2,6-dichlorophenyl)-5-methylisoxazol-4-yl]carbamate, showed unprecedented GSH and cysteine reactivity associated with NADPH-dependent metabolism in trapping studies using human liver microsomes. Additional trapping experiments with close analogs and mass spectra and NMR analyses suggested that the conjugates were attached directly to the 5'-methyl on the isoxazole moiety. We propose a mechanism of bioactivation via an initial oxidation of the 5'-methyl generating a stabilized enimine intermediate and a subsequent GSH attack on the 5'-methylene. Efforts to ameliorate reactive metabolite generation were undertaken to minimize the potential risk of toxicity. Formation of reactive metabolites could be significantly reduced or prevented by removing the 5'-methyl, by N-methylation of the carbamate; by replacing the nitrogen with a carbon or removing the nitrogen to obtain a carboxylate; or by inserting an isomeric 5'-methyl isoxazole. The effectiveness of these various chemical modifications in reducing GSH adduct formation is in line with the proposed mechanism. In conclusion, we have identified a novel mechanism of bioactivation of phenyl 5-methyl-isoxazol-4-yl-amines. The reactivity was attenuated by several modifications aimed to prevent the emergence of an enimine intermediate. Whether 5'-methyl isoxazoles should be considered a structural alert for potential formation of reactive metabolites is dependent on their context, i.e., 4'-nitrogen.

Influence of NAT2 polymorphisms on sulfamethoxazole pharmacokinetics in renal transplant recipients

The sulfamethoxazole (SMX)-trimethoprim drug combination is routinely used as prophylaxis against Pneumocystis pneumonia during the first 3 to 6 months after renal transplantation. The objective of this study was to examine the impact of N-acetyltransferase 2 (NAT2) and CYP2C9 polymorphisms on the pharmacokinetics of SMX in 118 renal transplant recipients. Starting on day 14 after renal transplantation, patients were administered 400 mg/day-80 mg/day of SMX-trimethoprim orally once daily. On day 14 after the beginning of SMX therapy, plasma SMX concentrations were determined by a high-performance liquid chromatography method. The SMX area under the concentration-time curve from 0 to 24 h (AUC(0-24)) for 15 recipients with the NAT2 slow acetylator genotype (NAT2 5/ 6, - 6/ 6, - 6/ 7, and - 7/ 7) was significantly greater than that for 56 recipients with the NAT2 rapid acetylator genotype (homozygous for NAT2 4) (766.4 ± 432.3 versus 537.2 ± 257.5 μg-h/ml, respectively; P = 0.0430), whereas there were no significant differences in the SMX AUC(0-24) between the CYP2C9 1/ 1 and - 1/ 3 groups. In a multiple regression analysis, the SMX AUC(0-24) was associated with NAT2 slow acetylator polymorphisms (P = 0.0095) and with creatinine clearance (P = 0.0499). Hepatic dysfunction in NAT2 slow acetylator recipient patients during the 6-month period after SMX administration was not observed. SMX plasma concentrations were affected by NAT2 polymorphisms and renal dysfunction. Although standard SMX administration to patients with NAT2 slow acetylator polymorphisms should be accompanied by monitoring for side effects and drug interaction effects from the inhibition of CYP2C9, SMX administration at a low dose (400 mg) as prophylaxis may not provide drug concentrations that reach the level necessary for the expression of side effects. Further studies with a larger sample size should be able to clarify the relationship between SMX plasma concentration and side effects.

Drug allergy: an updated practice parameter

Adverse drug reactions (ADRs) result in major health problems in the United States in both the inpatient and outpatient setting. ADRs are broadly categorized into predictable (type A and unpredictable (type B) reactions. Predictable reactions are usually dose dependent, are related to the known pharmacologic actions of the drug, and occur in otherwise healthy individuals, They are estimated to comprise approximately 80% of all ADRs. Unpredictable are generally dose independent, are unrelated to the pharmacologic actions of the drug, and occur only in susceptible individuals. Unpredictable reactions are subdivided into drug intolerance, drug idiosyncrasy, drug allergy, and pseudoallergic reactions. Both type A and B reactions may be influenced by genetic predisposition of the patient

A novel two-step hierarchical quantitative structure-activity relationship modeling work flow for predicting acute toxicity of chemicals in rodents

BACKGROUND

Accurate prediction of in vivo toxicity from in vitro testing is a challenging problem. Large public-private consortia have been formed with the goal of improving chemical safety assessment by the means of high-throughput screening.

OBJECTIVE

A wealth of available biological data requires new computational approaches to link chemical structure, in vitro data, and potential adverse health effects.

METHODS AND RESULTS

A database containing experimental cytotoxicity values for in vitro half-maximal inhibitory concentration (IC(50)) and in vivo rodent median lethal dose (LD(50)) for more than 300 chemicals was compiled by Zentralstelle zur Erfassung und Bewertung von Ersatz- und Ergaenzungsmethoden zum Tierversuch (ZEBET; National Center for Documentation and Evaluation of Alternative Methods to Animal Experiments). The application of conventional quantitative structure-activity relationship (QSAR) modeling approaches to predict mouse or rat acute LD(50) values from chemical descriptors of ZEBET compounds yielded no statistically significant models. The analysis of these data showed no significant correlation between IC(50) and LD(50). However, a linear IC(50) versus LD(50) correlation could be established for a fraction of compounds. To capitalize on this observation, we developed a novel two-step modeling approach as follows. First, all chemicals are partitioned into two groups based on the relationship between IC(50) and LD(50) values: One group comprises compounds with linear IC(50) versus LD(50) relationships, and another group comprises the remaining compounds. Second, we built conventional binary classification QSAR models to predict the group affiliation based on chemical descriptors only. Third, we developed k-nearest neighbor continuous QSAR models for each subclass to predict LD(50) values from chemical descriptors. All models were extensively validated using special protocols.

CONCLUSIONS

The novelty of this modeling approach is that it uses the relationships between in vivo and in vitro data only to inform the initial construction of the hierarchical two-step QSAR models. Models resulting from this approach employ chemical descriptors only for external prediction of acute rodent toxicity.

TNF, LTA, HSPA1L and HLA-DR gene polymorphisms in HIV-positive patients with hypersensitivity to cotrimoxazole

AIMS

Sulfamethoxazole in combination with trimethoprim (cotrimoxazole) is used for prophylaxis and treatment of several opportunistic infections in HIV-infected patients. It is associated with a high incidence of hypersensitivity reactions, which is thought to have an immune basis. Genetic polymorphisms in MHC are known to predispose to hypersensitivity reactions to a structurally diverse group of drugs in HIV-positive patients. The aim of the study was to determine whether functional polymorphisms in TNF, LTA, HSPA1L and HLA-DRB1 genes influence the risk of cotrimoxazole hypersensitivity in HIV-infected patients.

METHODS

We genotyped 136 HIV-positive patients with (n = 53) and without (n = 83) cotrimoxazole hypersensitivity using a combination of PCR-based techniques, including PCR-restriction fragment length polymorphisms, PCR-sequence specific oligonucleotides and real-time PCR. Genotypes and the haplotype frequencies were analyzed using the chi(2) test in the Haploview and CLUMP programs.

RESULTS

No statistically significant difference in SNP or haplotype frequencies were found in HIV-infected sulfamethoxazole hypersensitive patients compared with controls.

CONCLUSION

Our data show that MHC polymorphisms are not major predisposing factors for cotrimoxazole hypersensitivity, although we cannot exclude a minor contribution. An environmental factor (i.e., HIV infection) seems to predominate over any of the genetic factors so far investigated in increasing the risk of cotrimoxazole hypersensitivity.

Multiple adduction reactions of nitroso sulfamethoxazole with cysteinyl residues of peptides and proteins: implications for hapten formation

Sulfamethoxazole (SMX) induces immunoallergic reactions that are thought to be a result of intracellular protein haptenation by its nitroso metabolite (SMX-NO mass, 267 amu). SMX-NO reacts with protein thiols in vitro, but the conjugates have not been defined chemically. The reactions of SMX-NO with glutathione (GSH), a synthetic peptide (DS3), and two model proteins, human GSH S-transferase pi (GSTP) and serum albumin (HSA), were investigated by mass spectrometry. SMX-NO formed a semimercaptal (N-hydroxysulfenamide) conjugate with GSH that rearranged rapidly (1-5 min) to a sulfinamide. Reaction of SMX-NO with DS3 also yielded a sulfinamide adduct (mass increment, 267 amu) on the cysteine residue. GSTP was exclusively modified at the reactive Cys47 by SMX-NO and exhibited mass increments of 267, 283, and 299 amu, indicative of sulfinamide, N-hydroxysulfinamide, and N-hydroxysulfonamide adducts, respectively. HSA was modified at Cys34, forming only the N-hydroxysulfinamide adduct. HSA modification by SMX-NO under these conditions was confirmed with ELISA and immunoblotting with an antisulfonamide antibody. It is proposed that cysteine-linked N-hydroxysulfinamide and N-hydroxysulfonamide adducts of SMX are formed via the reaction of SMX-NO with cysteinyl sulfoxy acids. Evidence for a multistep assembly of model sulfonamide epitopes on GSH and polypeptides via hydrolyzable intermediates is also presented. In summary, novel, complex, and metastable haptenic structures have been identified on proteins exposed in vitro to the nitroso metabolite of SMX.

Trimethoprim-sulfamethoxazole exposure alters ex vivo function of B lymphocytes isolated from human immunodeficiency virus-infected patients receiving Zidovudine

STUDY OBJECTIVE

To determine if exposure to trimethoprim-sulfamethoxazole (TMP-SMX) causes a defect in peripheral B-cell function among patients with the human immunodeficiency virus (HIV) who are receiving zidovudine antiretroviral therapy.

DESIGN

Prospective, single-center, single-group, case-crossover design with a 4-week exposure period.

SETTING

University-affiliated infectious diseases outpatient clinic.

PATIENTS

Fourteen HIV-infected adult men receiving zidovudine, who had CD4(+) cell counts above 350 cells/mm(3) and undetectable viral loads.

INTERVENTION

Patients were administered a 28-day course of TMP 160 mg-SMX 800 mg/day (one double-strength tablet/day). Peripheral blood mononuclear cells (PBMCs) were obtained and isolated before and after exposure to TMP-SMX. Cells were cultured ex vivo with three mitogens of differing immunologic properties: pokeweed mitogen ([PWM] T-cell-dependent B-cell mitogen), Staphylococcus aureus Cowan ([SAC] T-cell-independent B-cell mitogen), and phytohemagglutinin A ([PHA] T-cell mitogen). Functionality of the B and T lymphocytes was then assessed.

MEASUREMENTS AND MAIN RESULTS

Proliferative capacity, cytokine secretion, and antibody production were measured and compared before and after TMP-SMX exposure. Reduced proliferative capacities of both PBMC and B cells stimulated with mitogens were observed at the 3-day culture time point in response to PWM, PHA, and SAC (p=0.029, 0.028, and 0.026, respectively). Proliferative capacity at day 7 of culture was not significantly different for any condition examined. Cytokine production was not altered by combination drug exposure after 10 days of culture when cells were stimulated with either PWM or PHA. Although antibody responses to PWM and PHA were similar, total immunoglobulin G concentration was lower in cells stimulated with SAC in samples obtained after TMP-SMX regimen completion compared with those obtained before exposure (p=0.005).

CONCLUSION

Although these data were affected by limitations in power and study design, they suggest that peripheral B-lymphocyte function is altered as a result of TMP-SMX exposure in HIV-infected patients concurrently receiving zidovudine. Further study of this effect is warranted.

HIV Tat potentiates cell toxicity in a T cell model for sulphamethoxazole-induced adverse drug reactions

HIV infection results in severe immune dysfunction with ensuing sequelae that includes characteristic opportunistic infections. Pneumocystis pneumonia (PCP) is one of the most common of these infections and is routinely treated with sulphamethaxazole (SMX). Although this drug is known to cause hypersensitivity adverse drug reactions (ADRs) in 0.1% of the general population, the incidence of these ADRs increases tenfold in the HIV-positive population. The HIV-1 trans-activator of transcription (HIV-1 Tat) together with the drug metabolite sulphamethaxazole-hydroxylamine (SMX-HA) have both been reported to be factors in these hypersensitivity ADRs. In this study, we use an inducible, Tat-expressing vector system to show that the level of Tat expression contributes to the cellular sensitivity of Jurkat T cells to SMX-HA. We further demonstrated that apoptosis is the likely mechanism by which this occurs. Thus, our data provide insight into the significant increase of SMX-related ADRs during the transition between HIV-1 infection and AIDS.

Association of the diplotype configuration at the N-acetyltransferase 2 gene with adverse events with co-trimoxazole in Japanese patients with systemic lupus erythematosus

Although co-trimoxazole (trimethoprim-sulphamethoxazole) is an effective drug for prophylaxis against and treatment of Pneumocystis pneumonia, patients often experience adverse events with this combination, even at prophylactic doses. With the aim being to achieve individual optimization of co-trimoxazole therapy in patients with systemic lupus erythematosus (SLE), we investigated genetic polymorphisms in the NAT2 gene (which encodes the metabolizing enzyme of sulphamethoxazole). Of 166 patients with SLE, 54 patients who were hospitalized and who received prophylactic doses of co-trimoxazole were included in the cohort study. Adverse events occurred in 18 patients; only two experienced severe adverse events that lead to discontinuation of the drug. These two patients and three additional ones with severe adverse events (from other institutions) were added to form a cohort sample and were analyzed in a case-control study. Genotype was determined using TaqMan methods, and haplotype was inferred using the maximum-likelihood method. In the cohort study, adverse events occurred more frequently in those without the NAT2*4 haplotype (5/7 [71.4%]) than in those with at least one NAT2*4 haplotype (13/47 [27.7%]; P = 0.034; relative risk = 2.58, 95% confidence interval = 1.34-4.99). In the case-control study the proportion of patients without NAT2*4 was significantly higher among those with severe adverse events (3/5 [60%]) than those without severe adverse events (6/52 [11.5%]; P = 0.024; odds ratio = 11.5, 95% confidence interval = 1.59-73.39). We conclude that lack of NAT2*4 haplotype is associated with adverse events with co-trimoxazole in Japanese patients with SLE.

Safety and toxicity of sulfadoxine/pyrimethamine: implications for malaria prevention in pregnancy using intermittent preventive treatment

Plasmodium falciparum infection during pregnancy is strongly associated with maternal anaemia and low birth weight, contributing to substantial morbidity and mortality in sub-Saharan Africa. Intermittent preventive treatment in pregnancy with sulfadoxine/pyrimethamine (IPTp-SP) has been one of the most effective approaches to reduce the burden of malaria during pregnancy in Africa. IPTp-SP is based on administering >or=2 treatment doses of sulfadoxine/pyrimethamine to pregnant women at predefined intervals after quickening (around 18-20 weeks). Randomised, controlled trials have demonstrated decreased rates of maternal anaemia and low birth weight with this approach. The WHO currently recommends IPTp-SP in malaria-endemic areas of sub-Saharan Africa. However, implementation has been suboptimal in part because of concerns of potential drug toxicities. This review evaluates the toxicity data of sulfadoxine/pyrimethamine, including severe cutaneous adverse reactions, teratogenicity and alterations in bilirubin metabolism. Weekly sulfadoxine/pyrimethamine prophylaxis is associated with rare but potentially fatal cutaneous reactions. Fortunately, sulfadoxine/pyrimethamine use in IPTp programmes in Africa, with 2-4 treatment doses over 6 months, has been well tolerated in multiple IPTp trials. However, sulfadoxine/pyrimethamine should not be administered concurrently with cotrimoxazole given their redundant mechanisms of action and synergistic worsening of adverse drug reactions. Therefore, HIV-infected pregnant women in malaria endemic areas who are already receiving cotrimoxazole prophylaxis should not also receive IPTp-SP. Although folate antagonist use in the first trimester is associated with neural tube defects, large case-control studies have demonstrated that sulfadoxine/pyrimethamine administered as IPTp (exclusively in the second and third trimesters and after organogenesis) does not result in an increased risk of teratogenesis. Folic acid supplementation is recommended for all pregnant women to reduce the rate of congenital anomalies but high doses of folic acid (5 mg/day) may interfere with the antimalarial efficacy of sulfadoxine/pyrimethamine. However, the recommended standard dose of folic acid supplementation (0.4 mg/day) does not affect antimalarial efficacy and may provide the optimal balance to prevent neural tube defects and maintain the effectiveness of IPTp-SP. No clinical association between sulfadoxine/pyrimethamine use and kernicterus has been reported despite the extensive use of sulfadoxine/pyrimethamine and related compounds to treat maternal malaria and congenital toxoplasmosis in near-term pregnant women and newborns. Although few drugs in pregnancy can be considered completely safe, sulfadoxine/pyrimethamine - when delivered as IPTp - has a favourable safety profile. Improved pharmacovigilance programmes throughout Africa are now needed to confirm its safety as access to IPTp-SP increases. Given the documented benefits of IPTp-SP in malaria endemic areas of Africa, access to this treatment for pregnant women should continue to expand.

Immunological principles of T-cell-mediated adverse drug reactions in skin

Drug hypersensitivity reactions in skin are an immune-mediated phenomenon associated with significant patient mortality and morbidity. Antigen-specific T cells, which have been isolated from the peripheral circulation and target organs of hypersensitive patients, are thought to propagate and regulate the development of clinical symptoms. The investigation of clinical cases with respect to the basic cellular and chemical mechanisms that underpin drug hypersensitivity has resulted in: i) the need to redress some aspects of present immunological dogma; and ii) additional fundamental immunological questions. Thus, the aim of this review article is to summarise present opinion on how and why drugs initiate a pathogenic T-cell response in a small section of the population and subsequently reflect on gaps in basic immunology and where future research might lead.

Roles of endogenous ascorbate and glutathione in the cellular reduction and cytotoxicity of sulfamethoxazole-nitroso

Sulfamethoxazole (SMX) is an effective drug for the management of opportunistic infections, but its use is limited by hypersensitivity reactions, particularly in HIV-infected patients. The oxidative metabolite SMX-nitroso (SMX-NO), is thought to be a proximate mediator of SMX hypersensitivity, and can be reduced in vitro by ascorbate or glutathione. Leukocytes from patients with SMX hypersensitivity show enhanced cytotoxicity from SMX metabolites in vitro; this finding has been attributed to a possible "detoxification defect" in some individuals. The purpose of this study was to determine whether variability in endogenous ascorbate or glutathione could be associated with individual differences in SMX-NO cytotoxicity. Thirty HIV-positive patients and 23 healthy control subjects were studied. Both antioxidants were significantly correlated with the reduction of SMX-NO to its hydroxylamine, SMX-HA, by mononuclear leukocytes, and both were linearly depleted during reduction. Controlled ascorbate supplementation in three healthy subjects increased leukocyte ascorbate with no change in glutathione, and significantly enhanced SMX-NO reduction. Ascorbate supplementation also decreased SMX-NO cytotoxicity compared to pre-supplementation values. Rapid reduction of SMX-NO to SMX-HA was associated with enhanced direct cytotoxicity from SMX-NO. When forward oxidation of SMX-HA back to SMX-NO was driven by the superoxide dismutase mimetic, Tempol, SMX-NO cytotoxicity was increased, without enhancement of adduct formation. This suggests that SMX-NO cytotoxicity may be mediated, at least in part, by redox cycling between SMX-HA and SMX-NO. Overall, these data indicate that endogenous ascorbate and glutathione are important for the intracellular reduction of SMX-NO, a proposed mediator of SMX hypersensitivity, and that redox cycling of SMX-HA to SMX-NO may contribute to the cytotoxicity of these metabolites in vitro.

Combination exposure to zidovudine plus sulfamethoxazole-trimethoprim diminishes B-lymphocyte immune responses to Pneumocystis murina infection in healthy mice

We have previously shown that zidovudine plus sulfamethoxazole-trimethoprim exposure decreases immune cell populations in the bone marrow of healthy mice by inducing apoptosis. The hypothesis of the current work was that this toxicity would have an adverse impact on the immune response. To determine this, BALB/c mice were treated with zidovudine, sulfamethoxazole-trimethoprim, the combination of both drugs, or vehicle only (control) via oral gavage for 21 days. On day 4 after dosing completion, the mice were infected intratracheally with 1x10(7) Pneumocystis murina organisms. Immune cell populations (in lung digest, bronchoalveolar lavage fluid, tracheobronchial lymph node, and bone marrow samples), the lung Pneumocystis burden, and serum Pneumocystis-specific antibody titers were determined at days 6, 10, and 20 postinfection. While total bone marrow cellularity was recovered by day 6 postinfection in the combination exposure group, B-cell numbers did not recover until 10 days postinfection, primarily due to the persistent depletion of the late pre-B-cell phenotype. The numbers of CD4+ and CD8+ T cells, as well as the numbers of total B cells and activated B cells in tracheobronchial lymph nodes, were decreased at days 10 and 20 as a result of zidovudine plus sulfamethoxazole-trimethoprim exposure compared to the numbers in the control group. No significant differences in lung lavage or lung digest cell populations were observed. There was a trend of a delay in Pneumocystis clearance in the combination treatment group, and Pneumocystis-specific serum immunoglobulin G titers were reduced at day 20 postinfection. Together, these data indicate that the combination of zidovudine and sulfamethoxazole-trimethoprim adversely affects the humoral immune response to Pneumocystis.

Differential toxicity of reactive metabolites of clindamycin and sulfonamides in HIV-infected cells: influence of HIV infection on clindamycin toxicity in vitro

Hypersensitivity adverse drug reactions are much more common among patients with acquired immunodeficiency syndrome (AIDS) than in the general population. High rates of hypersensitivity reactions to clindamycin have been noted. To investigate the role of reactive metabolites in these reactions, the authors studied toxicity of clindamycin and sulphamethoxazole (SMX) and their metabolites in uninfected and human immunodeficiency virus (HIV)-infected MOLT3 cells. Infected and uninfected cells were incubated with clindamycin or sulphamethoxazole hydroxylamine in increasing concentrations; reactive metabolites were generated by coincubation of cells and drug with murine microsomes and a microsomal activating system. Over a concentration range of 0 to 400 microM SMX-HA, there was a significant concentration-dependent increase in cell death in HIV-infected compared to uninfected cells (28%+/-3% vs 8%+/-5% at 400 microM, P < .05). In contrast, coincubation of cells with clindamycin, microsomes, and a microsomal activating system, as well as combinations of primaquine or pyrimethamine, was not associated with an increase in cell death among infected compared to uninfected cells. No concentration-toxicity was demonstrated. These data support the role of reactive metabolites in adverse drug reactions to sulfonamides during HIV infection, whereas alternate mechanism(s) may be responsible for increased rates of adverse drug reactions to clindamycin among patients with AIDS.

Role of bioactivation in drug-induced hypersensitivity reactions

Drug-induced hypersensitivity reactions are a major problem in both clinical treatment and drug development. This review covers recent developments in our understanding of the pathogenic mechanisms involved, with special focus on the potential role of metabolism and bioactivation in generating a chemical signal for activation of the immune system. The possible role of haptenation and neoantigen formation is discussed, alongside recent findings that challenge this paradigm. Additionally, the essential role of costimulation is examined, as are the potential points whereby costimulation may be driven by reactive metabolites. The relevance of local generation of metabolites in determining the location and character of a reaction is also covered.

Reactive oxygen species generation and its role in the differential cytotoxicity of the arylhydroxylamine metabolites of sulfamethoxazole and dapsone in normal human epidermal keratinocytes

Cutaneous drug reactions (CDR) are responsible for numerous minor to life-threatening complications. Though the exact mechanism for CDR is not completely understood, evidence suggests that bioactivation of drugs to reactive oxygen or nitrogen species is an important factor in the initiation of these reactions. Several CDR-inducing drugs having an arylamine functional group, such as sulfamethoxazole (SMX) and dapsone (DDS), undergo bioactivation to reactive arylhydroxylamine metabolites. These metabolites can generate cellular oxidative stress by forming reactive oxygen species (ROS). Several studies have demonstrated a higher cytotoxicity with DDS hydroxylamine (DDS-NOH) compared to SMX hydroxylamine (SMX-NOH). To investigate the role of differential ROS generation in the higher cytotoxicity of DDS-NOH, hydroxylamine metabolites of SMX and DDS were synthesized and ROS formation by these metabolites determined. DDS-NOH and its analogues/metabolites consistently resulted in higher ROS formation as compared to SMX-NOH. However, comparison of the ROS generation and cytotoxicity of a series of arylhydroxylamine analogues of DDS did not support a simple correlation between ROS generation and cell death. Numerous ROS scavengers were found to reduce metabolite-induced ROS formation, with differences in the potency between the agents. The decrease in DDS-NOH-induced ROS generation in NHEK with ascorbic acid, N-acetylcysteine, Trolox, and melatonin was 87, 86, 44, and 16%, respectively. Similarly, the cytotoxicity and adduct formation of DDS-NOH in NHEK was reduced in the presence of ascorbic acid. In summary, these studies show that arylhydroxylamine metabolites of SMX/DDS induce ROS generation in NHEK, though such generation is not directly related to cytotoxicity.

Cytochrome P450 activation of arylamines and heterocyclic amines

Arylamines and heterocyclic arylamines (HAAs) are of particular interest because of demonstrated carcinogenicity in animals and humans and the broad exposure to many of these compounds. The activation of these, and also some arylamine drugs, involves N-hydroxylation, usually by cytochrome P450 (P450). P450 1A2 plays a prominent role in these reactions. However, P450 1A1 and 1B1 and other P450s are also important in humans as well as experimental animals. Some arylamines (including drugs) are N-hydroxylated predominantly by P450s other than those in Family 1. Other oxygenases can also have roles. An important issue is extrapolation between species in predicting cancer risks, as shown by the low rates of HAA activation by rat P450 1A2 and low levels of P450 1A2 expression in some nonhuman primates.

Evaluation of the clinical, immunologic, and biochemical effects of nitroso sulfamethoxazole administration to dogs: a pilot study

Sulfonamide antimicrobials such as sulfamethoxazole (SMX) have been associated in humans with hypersensitivity reactions, to include fever, skin eruptions, hepatotoxicity, and blood dyscrasias. These reactions also occur in dogs, the only non-human species known to develop a similar spectrum of sulfonamide hypersensitivity. Sulfonamide hypersensitivity is not well understood, but has been hypothesized to be due to the generation of the reactive oxidative metabolite, nitroso sulfamethoxazole (SMX-NO). SMX-NO, unlike the parent sulfonamide, is cytotoxic in vitro, haptenizes tissue proteins, and is immunogenic in rodents. The purpose of this pilot study was to determine whether SMX-NO, when administered to dogs, would lead to drug-tissue adducts, anti-drug antibodies, antioxidant depletion, or clinical evidence of drug hypersensitivity. Four dogs were randomized to one of four treatments: SMX-NO 1 mg/kg; SMX-NO 3 mg/kg; SMX-NO 10 mg/kg; or vehicle control. Dosing was by the intraperitoneal route, once daily for four consecutive days per week, for 2 weeks total, followed by a third week of observation. Following this, all dogs were challenged with trimethoprim-sulfamethoxazole, 25 mg/kg for 12 h for 2 weeks. No dog developed clinical or biochemical evidence of drug hypersensitivity. Plasma cysteine and leukocyte reduced glutathione were not depleted during dosing; however, ascorbate was significantly depleted by week 2 following SMX-NO at 10 mg/kg. Anti-SMX antibodies (IgG or IgM by ELISA) were not detected in any dogs at any time points. SMX-hemoglobin adducts were detected in the spleen in SMX-NO dosed dogs; however, these adducts were not accompanied by an immunologic or systemic response. The results of this pilot study indicate that SMX-NO dosing in dogs, using a dosing protocol shown to be immunogenic in other species, produces modest ascorbate depletion and hemoglobin adduct formation, but is insufficient to produce an immunologic response or a clinical syndrome of sulfonamide hypersensitivity in this susceptible species.

Plasma Ascorbate Deficiency Is Associated With Impaired Reduction of Sulfamethoxazole-Nitroso in HIV Infection

OBJECTIVE

The objective of these studies was to determine the role of ascorbate deficiency in HIV infection in the defective detoxification of sulfamethoxazole-nitroso, the metabolite thought to mediate sulfonamide hypersensitivity reactions.

METHODS

Fifty-one HIV-infected patients and 26 healthy volunteers were evaluated. Vitamin supplementation histories were obtained, and blood samples were collected for determination of plasma ascorbate, dehydroascorbate, and cysteine concentrations, erythrocyte glutathione concentrations, and plasma reduction of sulfamethoxazole-nitroso in vitro.

RESULTS

Plasma ascorbate concentrations were significantly lower in HIV-positive patients not taking vitamin supplements (29.5 +/- 22.3 microM) than in healthy subjects (54.8 +/- 22.3 microM; P = 0.0005) and patients taking 500-1000 mg of ascorbate daily (82.5 +/- 26.3 microM; P < 0.0001). Plasma ascorbate deficiency was strongly correlated with impaired reduction of sulfamethoxazole-nitroso to its hydroxylamine (r = 0.60, P < 0.0001), and during in vitro reduction, the loss of plasma ascorbate was strongly associated with the amount of nitroso reduced (r = 0.70, P < 0.0001). Ascorbate added ex vivo normalized this reduction pathway. Erythrocyte glutathione concentrations were significantly lower in HIV-positive patients (0.98+/-0.32 mM) than in healthy subjects (1.45+/-0.49 mM; P = 0.001), but this finding was unrelated to ascorbate supplementation. There was trend toward lower plasma cysteine concentrations in patients (8.4+/-3.9 microM) than in controls (10.3+/-4.3 microM), but this trend was similarly unrelated to ascorbate supplementation. Dehydroascorbate concentrations were not significantly higher in HIV-positive patients (7.4+/-10.5%) than in healthy controls (4.0+/-6.2%), even in the subset of patients taking ascorbate (8.4+/-9.4%).

CONCLUSIONS

Ascorbate deficiency is common in HIV-positive patients and is associated with impaired detoxification of sulfamethoxazole-nitroso, the suspected proximate toxin in sulfonamide hypersensitivity. Patients taking daily ascorbate supplements (500-1000 mg) achieved high plasma ascorbate concentrations and did not show this detoxification defect. Ascorbate deficiency (or supplementation) was not associated with changes in glutathione or cysteine concentrations. These data suggest that ascorbate deficiency, independent of thiol status, may be an important determinant of impaired drug detoxification in HIV infection.

Monitoring adverse drug reactions to sulfonamide antibiotics in human immunodeficiency virus-infected individuals

Patients infected with the human immunodeficiency virus (HIV) are at higher risk for adverse drug reactions from trimethoprim-sulfamethoxazole (TMP-SMX) than the HIV-negative population. Studying the HIV-positive population the authors aimed to validate the predictive and diagnostic value of the lymphocyte toxicity assay (LTA) for adverse drug reactions. Patient lymphocytes were analyzed for toxicity to SMX and TMP. Of 35 enrolled HIV patients, 18 had TMP-SMX hypersensitivity syndrome reaction (HSR); 10 tolerated the drug; and 5 had never received the drug. When cases with HSR were compared with controls that tolerated the drugs, cytotoxicity was higher for cases: 29.5% +/- 10.1% versus 19.3% +/- 11.2% for SMX (P < 0.022) and 25.0% +/- 11.9% versus 16.3% +/- 11.0% for TMP (P < 0.04). The authors' proposed threshold value for assigning positive results for TMP and SMX hypersensitivities was 22.5%. The LTA has a strong potential for use as a diagnostic tool to assess TMP-SMX hypersensitivity in HIV-infected individuals. Larger patient populations, as well as in vitro studies are needed to further address the reasons for elevated results in immunocompromised patients and to validate the usefulness of the test.

Inactivation of human arylamine N-acetyltransferase 1 by the hydroxylamine of p-aminobenzoic acid

Human N-acetyltransferase 1 (NAT1) is a widely distributed enzyme that catalyses the acetylation of arylamine and hydrazine drugs as well as several known carcinogens, and so its levels in the body may have toxicological importance with regard to drug toxicity and cancer risk. Recently, we showed that p-aminobenzoic acid (PABA) was able to down-regulate human NAT1 in cultured cells, but the exact mechanism by which PABA acts remains unclear. In the present study, we investigated the possibility that PABA-induced down-regulation involves its metabolism to N-OH-PABA, since N-OH-AAF functions as an irreversible inhibitor of hamster and rat NAT1. We show here that N-OH-PABA irreversibly inactivates human NAT1 both in cultured cells and cell cytosols in a time- and concentration-dependent manner. Maximal inactivation in cultured cells occurred within 4 hr of treatment, with a concentration of 30 microM reducing activity by 60 +/- 7%. Dialysis studies showed that inactivation was irreversible, and cofactor (acetyl coenzyme A) but not substrate (PABA) completely protected against inactivation, indicating involvement of the cofactor-binding site. In agreement with these data, kinetic studies revealed a 4-fold increase in cofactor K(m), but no change in substrate K(m) for N-OH-PABA-treated cytosols compared to control. We conclude that N-OH-PABA decreases NAT1 activity by a direct interaction with the enzyme and appears to be a result of covalent modification at the cofactor-binding site. This is in contrast to our findings for PABA, which appears to reduce NAT1 activity by down-regulating the enzyme, leading to a decrease in NAT1 protein content.

Plasma cysteine deficiency and decreased reduction of nitrososulfamethoxazole with HIV infection

The aim of these studies was to determine whether HIV-infected patients have a plasma thiol deficiency and whether this is associated with decreased detoxification of the toxic metabolites of sulfamethoxazole. Reduced, oxidized, protein-bound, and total thiol levels were measured in 33 HIV-positive patients and 33 control subjects by an HPLC method utilizing the fluorescent probe bromobimane. The reduction of sulfamethoxazole hydroxylamine and nitrososulfamethoxazole by plasma and the plasma redox balance in the presence of nitrososulphamethoxazole were also determined by HPLC. Reduced plasma cysteine was significantly (p<0.0001) lower in HIV-positive patients (13.0+/-3.0 microM) when compared with control subjects (16.9+/-3.0 microM). Although there was no difference in oxidized, protein-bound, and total cysteine, the thiol/disulfide ratios were lower in HIV-positive patients. Reduced homocysteine was elevated in patients. Plasma from HIV-positive patients was less able to detoxify nitrososulfamethoxazole than control plasma. These findings show that the disturbance in redox balance in HIV-positive patients may alter metabolic detoxification capacity, and thereby predispose to sulfamethoxazole hypersensitivity.

Prospective evaluation of detoxification pathways as markers of cutaneous adverse reactions to sulphonamides in AIDS

The use of sulphonamides is complicated by a high rate of cutaneous reactions in AIDS. Metabolic risk factors have been suspected for these reactions. We conducted a prospective study to evaluate whether glutathione S-transferase M1 null genotype, glutathione deficiency and acetylator status as risk factors. To explain the high frequency of slow acetylator phenotype in AIDS patients, we compared N-acetyltransferase-2 phenotype and genotype in this population. AIDS patients treated with sulphonamides for Pneumocystis carinii pneumonia or toxoplasmosis were followed up for cutaneous reactions. Glutathione S-transferase genotyping, glutathione level determination, N-acetyltransferase-2 genotyping and phenotyping were performed. One hundred and thirty-six AIDS patients were studied. Glutathione S-transferase M1 and T1 null genotypes, intracellular glutathione level, slow acetylator genotype and phenotype were not risk factors for cutaneous sulphonamides reactions. The association of glutathione S-transferase M1 null genotype and the slow acetylator one was a risk factor [Fisher's exact test, odds ratio (OR) = 2.6, 95% confidence interval (CI) = 1.2-5.9; P = 0.02]. A discordance between acetylator genotype and phenotype was found in 35% of patients. This frequency was significantly higher than the 6-7% expected (Fisher's exact test: OR = 7.5, 95% CI = 4.2-13.4; P < 0.0001). Suspected metabolic risk factors for sulphonamides cutaneous reactions were not confirmed prospectively. However, the association of glutathione S-transferase M1 null genotype and the slow acetylator one appeared to increase the risk of reactions. We clearly showed that the acetylation phenotype measured by caffeine probe could be modified by the disease.

Association analysis of drug metabolizing enzyme gene polymorphisms in HIV-positive patients with co-trimoxazole hypersensitivity

The use of co-trimoxazole in HIV-positive patients has been associated with a high frequency (40-80%) of hypersensitivity reactions. This has been attributed to the bioactivation of the sulphonamide component, sulphamethoxazole (SMX), to its toxic hydroxylamine and nitroso metabolites. The aim of this study was to determine whether functionally significant polymorphisms in the genes coding for enzymes involved in SMX metabolism influence susceptibility to SMX hypersensitivity. HIV-positive patients with (n = 56) and without (n = 89) SMX hypersensitivity were genotyped for allelic variants in CYP2C9, GSTM1, GSTT1, GSTP1 and NAT2 using polymerase chain reaction (PCR) and/or PCR-restriction fragment length polymorphism analysis. The CYP2C9*2/*3 genotype and CYP2C9*3 allele frequencies were nine- and 2.5-fold higher in the hypersensitive group compared to non-sensitive patients, respectively, although they were not statistically significant when corrected for multiple testing. There were no differences in the frequencies of the GSTM1 and GSTT1 null genotypes, and the slow acetylator genotype, between hypersensitive and non-sensitive patients, while GSTP1 frequency was lower (although non-significant) in the hypersensitive group [21% versus 32%, odds ratio (OR) = 0.5, Pc = 0.24]. Comparison of the genotype frequencies in HIV-positive and -negative patients showed that the NAT2 slow acetylator genotype frequency in the HIV-positive patients (74%) was significantly (Pc = 0.0003, OR = 2.3) higher than in control subjects (56%). Our results show that genetic polymorphisms in drug metabolizing enzymes are unlikely to be major predisposing factors in determining individual susceptibility to co-trimoxazole hypersensitivity in HIV-positive patients.

A novel lymphocyte toxicity assay to assess drug hypersensitivity syndromes

OBJECTIVES

To validate the novel lymphocyte toxicity assay (LTA) based on the mitochondrial succinate dehydrogenase (SDH) activity vs. the LTA by using trypan blue exclusion and to determine the utility of the assay to confirm drug hypersensitivity syndrome (DHS) to sulphonamides (SMX) and aromatic anticonvulsants.

METHODS

Incubation of patient lymphocytes, with or without murine hepatic microsomes with anticonvulsants or SMX. The viability of lymphocytes was based on SDH activity that can be measured spectrophotometrically. The percentage of cells displaying cytotoxicity compared to controls (cells treated only with drug) was calculated. Seventy-two immunocompetent and 16 immunocompromised (HIV) patients with DHS to SMX were sampled. The results were validated vs. 26 controls that had not experienced DHS to SMX. Sixty-two patients who had DHS to anticonvulsants were compared with 24 controls that did not have any DHS to the same anticonvulsants.

RESULTS

The results showed a very good percentage of sensitivity 98 and specificity 96 with a kappa-score of 0.96. LTA higher than 13.5% was considered positive for the immunocompetent population and LTA higher than 22% was positive for the immunocompromised population. In two of the 26 controls, LTA was positive.

CONCLUSION

The high quantitative kappa-value 0.96 emphasizes that the novel LTA is at least as good as the trypan blue assay. The latter is labor intensive, time consuming, and prone to human error. The new assay is objective, faster, and has been reproducible in assessing cytotoxicity.

Cytotoxicity of sulfonamide reactive metabolites: apoptosis and selective toxicity of CD8(+) cells by the hydroxylamine of sulfamethoxazole

Treatment with sulfonamide antibiotics in HIV-infected patients is associated with a high incidence (> 40%) of adverse drug events, including severe hypersensitivity reactions. Sulfonamide reactive metabolites have been implicated in the pathogenesis of these adverse reactions. Sulfamethoxazole hydroxylamine (SMX-HA) induces lymphocyte toxicity and suppression of proliferation in vitro; the mechanism(s) of these immunomodulatory effects remain unknown. We investigated the cytotoxicity of SMX-HA via apoptosis on human peripheral blood mononuclear cells and purified cell subpopulations in vitro. CD19(+), CD4(+), and CD8(+) cells were isolated from human peripheral blood by positive selection of cell surface molecules by magnetic bead separation. SMX-HA induced significant CD8(+) cell death (67 +/- 7%) at 100 microM SMX-HA, with only minimal CD4(+) cell death (8 +/- 4%). No significant subpopulation toxicity was shown when incubated with parent drug (SMX). Flow cytometry measuring phosphatidylserine externalization 24 h after treatment with 100 microM and 400 microM SMX-HA revealed 14.1 +/- 0.7% and 25. 6 +/- 4.2% annexin-positive cells, respectively, compared to 3.7 +/- 1.2% in control PBMCs treated with 400 microM SMX. Internucleosomal DNA fragmentation was observed in quiescent and stimulated PBMCs 48 h after incubation with SMX-HA. Our data show that CD8(+) cells are highly susceptible to the toxic effects of SMX-HA through enhanced cell death by apoptosis.

Cellular disposition of sulphamethoxazole and its metabolites: implications for hypersensitivity

1. Bioactivation of sulphamethoxazole (SMX) to chemically-reactive metabolites and subsequent protein conjugation is thought to be involved in SMX hypersensitivity. We have therefore examined the cellular metabolism, disposition and conjugation of SMX and its metabolites in vitro. 2. Flow cytometry revealed binding of N-hydroxy (SMX-NHOH) and nitroso (SMX-NO) metabolites of SMX, but not of SMX itself, to the surface of viable white blood cells. Cellular haptenation by SMX-NO was reduced by exogenous glutathione (GSH). 3. SMX-NHOH and SMX-NO were rapidly reduced back to the parent compound by cysteine (CYS), GSH, human peripheral blood cells and plasma, suggesting that this is an important and ubiquitous bioinactivation mechanism. 4. Fluorescence HPLC showed that SMX-NHOH and SMX-NO depleted CYS and GSH in buffer, and to a lesser extent, in cells and plasma. 5. Neutrophil apoptosis and inhibition of neutrophil function were induced at lower concentrations of SMX-NHOH and SMX-NO than those inducing loss of membrane viability, with SMX having no effect. Lymphocytes were significantly (P<0.05) more sensitive to the direct cytotoxic effects of SMX-NO than neutrophils. 6. Partitioning of SMX-NHOH into red blood cells was significantly (P<0.05) lower than with the hydroxylamine of dapsone. 7. Our results suggest that the balance between oxidation of SMX to its toxic metabolites and their reduction is an important protective cellular mechanism. If an imbalance exists, haptenation of the toxic metabolites to bodily proteins including the surface of viable cells can occur, and may result in drug hypersensitivity.

Desensitization to co-trimoxazole (trimethoprim-sulphamethoxazole) in HIV-infected patients: is patch testing a useful predictor of reaction?

OBJECTIVE

To establish the safety and efficacy of desensitization to co-trimoxazole in hypersensitive HIV-infected subjects. To assess if delayed hypersensitivity (type IV) to co-trimoxazole predicts those unable to be desensitized.

METHOD

desensitization to co-trimoxazole, comprising trimethoprim (T) 0.4 mg and sulphamethoxazole (S) 2 mg initially with doubling dose daily, full strength co-trimoxazole (T/S 160 mg/800 mg) at 10 days. Patch testing with 4.5% and 9% co-trimoxazole in yellow soft paraffin, CMI Multitest.

RESULTS

nineteen patients, 18 male and one female, were recruited and completed the desensitization regime. Of these 80%(15) achieved successful desensitization. Three of those who reacted did so within 18 days. All patients were successfully managed in an outpatient setting. There were no major adverse reactions. Of those reacting none gave a positive patch test to co-trimoxazole and all showed absent delayed type hypersensitivity reactions to recall antigens.

CONCLUSIONS

co-trimoxazole desensitization is a safe and efficacious procedure, with a success rate of 80% using the above regime. Patch testing with co-trimoxazole gives no useful information about those that reacted.

Genotyping of the arylamine N-acetyltransferase polymorphism in the prediction of idiosyncratic reactions to trimethoprim-sulfamethoxazole in infants

The pathogenesis of hypersensitivity to trimethoprim-sulfamethoxazole (TMP-SMX) is supposed to be associated with the slow acetylation phenotype. This pharmacogenetic defect is associated with the mutations of the arylamine N-acetyltransferase (NAT2) encoding gene. The aim of the study was to compare the usefulness of the acetylation phenotype and NAT2 coding genotype in the prediction of idiosyncratic reaction to Cotrimoxazole in infants. The study was carried out in the group of 20 infants, aged 2-12 months (mean age 6.3 months) treated with Cotrimoxazole, administered at 100 mg/kg b.w./24 h doses. In seven children (35%) no adverse effects of the treatment have been observed, whereas in 13 (65%) children various adverse effects occurred as a result of the therapy, such as rash (4 children), granulocytopenia with anemization (5 children) or liver impairment (4 children). The acetylation phenotype of each child was determined on the basis of urine of N-acetyl isoniazid/isoniazid ratio, after ingestion of isoniazid as a model drug. Furthermore we used polymerase chain reaction (PCR) followed by the analysis of restriction fragments length polymorphism (RFLP) technique to identify the known mutant alleles of the NAT2 gene. It has been presumed that the genotype determining fast acetylation contains at least one of wild-type allele. No correlation has been found between the observed adverse effects of Cotrimoxazole and age, gender and acetylation phenotype. However, it has been demonstrated that the risk of adverse effects of Cotrimoxazole is considerably higher in children with mutations of the NAT2 encoding gene. The comparison of the results from PCR-RFLP genotyping with phenotyping suggested that in infants, the NAT2 genotype rather than phenotype provides the basis for the detection of hypersensitivity to TMP-SMX.

Comparison of the in vitro cytotoxicity of hydroxylamine metabolites of sulfamethoxazole and dapsone

The differential incidence of adverse drug reactions (ADR) between trimethoprim-sulfamethoxazole and dapsone might be explained, in part, by differences in the inherent toxicity of the hydroxylamine metabolites of sulfamethoxazole and dapsone. To test this hypothesis, the in vitro cytotoxicities of sulfamethoxazole hydroxylamine, dapsone hydroxylamine, and monoacetyldapsone hydroxylamine were compared using peripheral blood mononuclear cells (PBMC) from healthy volunteers. After 3 hr of exposure to hydroxylamine metabolites, PBMC were washed thoroughly to remove residual hydroxylamine, and viability was assessed 16 hr later by determination of 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) conversion. A concentration-dependent toxicity was observed with each hydroxylamine metabolite. While dapsone hydroxylamine and monoacetyldapsone hydroxylamine were not significantly different, both showed significantly greater cytotoxic potency than sulfamethoxazole hydroxylamine (P < 0.05). This differential potency was not a function of differential stability in aqueous medium and was maintained over time. The effects of red blood cells (RBC), impermeable RBC "ghosts," and RBC lysate on hydroxylamine-induced cytotoxicity were determined using a two-compartment dialysis system. Amelioration of hydroxylamine-dependent cytotoxicity occurred when RBC were included in PBMC incubations. This apparent detoxifying effect was markedly greater using RBC lysate in comparison with impermeable "ghosts" (P < 0.05). No difference in detoxification was observed between sulfamethoxazole hydroxylamine and monoacetyldapsone hydroxylamine. Differences in the inherent cytotoxicity of their hydroxylamine metabolites do not appear to explain the differential incidence of ADR between trimethoprim-sulfamethoxazole and dapsone.

The role of reactive drug metabolites in immune-mediated adverse drug reactions

OBJECTIVE

To highlight recent advances in the understanding of adverse drug reactions (ADRs), with a focus on models outlining interactions between drug metabolism, disease processes, and immunity. Specific mechanisms that identify the metabolic pathways responsible for drug bioactivation to reactive drug metabolites (RDMs) involved in the initiation and propagation of specific immune-mediated hypersensitivity reactions are discussed. Drug classes well known to be associated with immune-mediated ADRs are reviewed and the clinical implications of current research are discussed.

DATA SOURCES

Original experimental research and immunologic review articles relevant to ADR diagnosis and etiology.

DATA EXTRACTION

Results of relevant in vitro experiments and clinical reactions to drug therapy were compiled and reviewed. Critical discoveries concerning the identification of RDMs involved in ADRs were highlighted, with respect to RDM involvement in the production of an immune response to drug haptens.

DATA SYNTHESIS

Drug adverse effects are classified according to clinical characteristics, immune interactions, and mechanistic similarities. Cytochrome P450 bioactivation of drug molecules to RDMs is a prerequisite to many ADRs. An electrophilic metabolite may react with cellular macromolecules (i.e., lipids, proteins, nucleic acids), resulting in direct cellular damage and organ toxicity. Covalent binding of an RDM to cellular macromolecules may also result in the formation of a hapten that is capable of eliciting a cellular or humoral immune response against drug or protein epitopes, culminating in the characteristic symptoms of hypersensitivity reactions. Mechanistic details concerning the identification of stable protein-metabolite conjugates and their interaction with the immune system remain unclear. Genetic imbalance between bioactivation and detoxification pathways, as well as reduced cellular defense against RDMs due to disease or concomitant drug therapy, act as risk factors to the onset and severity of ADRs.

CONCLUSIONS

Adverse reactions to drug therapy cause significant morbidity and mortality. Identification of the pathways involved in drug bioactivation and detoxification may elucidate the potential of chemical agents to induce immune-mediated ADRs. Understanding the mechanisms of ADRs to current xenobiotics is helpful in the prevention and management of ADRs, and may prove useful in the design of novel therapeutic agents with reduced incidence of severe adverse events.

Adverse reactions to trimethoprim-sulfamethoxazole among children with human immunodeficiency virus infection

BACKGROUND

The clinical course of HIV infection is frequently different among infants and children from that in adults. In adults among the most common sources of morbidity related to therapy are adverse drug reactions, notably to trimethoprim-sulfamethoxazole. Although there are case reports of serious adverse reactions to trimethoprim-sulfamethoxazole among infants and children with HIV infection, the precise rate and clinical characteristics of these adverse reactions among HIV-infected children are unknown.

METHODS

We reviewed the clinical records of all children referred to a regional HIV clinic in a 6-year period. Therapy and suspected adverse drug reactions to therapy were reviewed by one of the investigators not involved in patient care. Adverse drug reactions were identified and characterized according to previously established criteria.

RESULTS

During this time 78 children were referred for assessment of possible HIV infection, 45 of whom were ultimately determined to have the infection. Twenty-five were treated with trimethoprim-sulfamethoxazole, 15 (60%) of whom tolerated therapy and 10 (40%) of whom had adverse reactions. The most common type of adverse reaction was erythema multiforme (70%), followed by neutropenia (20%) and Stevens-Johnson syndrome (10%). In two patients a serious adverse reaction to trimethoprim-sulfamethoxazole led to the diagnosis of HIV infection.

CONCLUSIONS

The overall incidence and type of serious adverse reactions to trimethoprim-sulfamethoxazole among infants and children with HIV infection appear to be similar to those among adults.