Influence of NAT2 polymorphisms on sulfamethoxazole pharmacokinetics in renal transplant recipients

Genetic polymorphisms of pharmacogenomic VIP variants in the Hui population from Ningxia Province of China

Pharmacogenomics has been widely used to study the very important pharmacogenetic (VIP) variants among different populations. However, there is little pharmacogenomic information about the Chinese Hui population. Our research aimed to reveal the outstandingly different loci in the Hui population, and provide a theoretical foundation for personalized drug use in the Hui population, so as to facilitate more effective treatment of diseases. This study genotyped 53 VIP variants of 26 genes in 200 independent Hui individuals based on the Pharmacogenetics and Pharmacogenomics Knowledge Base (PharmGKB). Remarkable differences in the genotype and allele frequencies between the Hui and 26 other populations from the 1000 Genomes Project were assessed using the χ² test. The genotype and allele frequencies of single nucleotide polymorphisms (SNPs) in PTGS2 (rs20417), NAT2 (rs1801280), NAT2 (rs1208), ACE (rs4291), and CYP2D6 (rs1065852) were considerably different in the Hui population compared with those in the other 26 populations. Besides, using the PharmGKB database, we identified several VIP variants that may alter the drug metabolism of ibuprofen, rofecoxib (PTGS2), captopril (ACE), citalopram, and escitalopram (CYP2D6). We also discovered other variants associated with adverse reactions to cisplatin and cyclophosphamide (NAT2). Our study indicated that the loci of PTGS2 (rs20417), NAT2 (rs1801280 and rs1208), ACE (rs4291), and CYP2D6 (rs1065852) in the Hui population were obviously different from those in the other 26 populations, which provides reliable information for predicting drug efficacy. Besides, it supplements the pharmacogenomic knowledge of the Hui population and lays the foundation for the individualized treatment for the Hui population.

Sulfamethoxazole-trimethoprim-induced liver injury and genetic polymorphisms of NAT2 and CYP2C9 in Taiwan

OBJECTIVES

Sulfamethoxazole-trimethoprim (SMX-TMP) is one of the most frequently used antibiotics. SMX is metabolized by N-acetyltransferase (NAT) and cytochrome P450 2C9 (CYP2C9) to nontoxic or toxic intermediates. Little is known about the association between genetic variations of these enzymes and SMX-TMP-induced liver injury (SILI). The aim of this study was to explore the genetic polymorphisms of NAT2 and CYP2C9 and the susceptibility to SILI in a Han Chinese population.

METHODS

A total of 158 patients with SILI and 145 controls were recruited in this study. PCR-based genotyping with matrix-assisted laser desorption ionization-time of flight was used to assay the major NAT2 and CYP2C9 genotypes including NAT2 rs1495741, rs1041983, rs1801280, CYP2C9 rs1799853, rs1057910 and rs4918758.

RESULTS

The SILI group had a higher frequency of the NAT2 rs1495741 variant AA genotype and rs1041983 variant TT genotype than the controls (42.4 vs. 25.5%; P = 0.008, and 40.5 vs. 25.5%; P = 0.022, respectively). The SILI group had more slow acetylators than the controls (43.7 vs. 25.5%; P = 0.001). There were no significant differences in the genetic variations of CYP2C9 between the SILI and control groups. After adjusting for confounding factors, the NAT2 slow acetylators still had an increased risk of SILI (adjusted OR: 2.49; 95% confidence interval: 1.46-4.24; P = 0.001), especially in those with hepatocellular and mixed type SILI.

CONCLUSIONS

NAT2 slow acetylators are associated with a higher risk of SILI in the Han Chinese population. However, CYP2C9 genetic polymorphisms are not associated with the susceptibility to SILI.

Role of N-acetyltransferase 2 gene polymorphism in the human pathology

Nowadays multiple heterogeneous chemicals affect the human body. They include drugs, household chemicals, dyes, food supplements and others. The human organism can modify, inactivate, and eliminate the chemicals by biotransformation enzymes. But it is well known that biotransformation can lead to toxification phenomenon. Individuals differ from each other by the rate of chemical modification that promotes accumulation of toxins and carcinogens in some patients. An N-acetyltransferase 2 enzyme participates in the aromatic amines second phase metabolism. This work reviews the acetyltransferase gene polymorphism possible role in diseases development including drug-induced organs damage.

Gene of acetyltransferase has polymorphisms associated with two haplotypes of  fast and slow substrate acetylation. Gene alleles combine in three genotypes: fast, intermediate, and slow acetylators. Acetylation rate plays a significant role in side effects development during tuberculosis treatment and cancer pathogenesis. Recently, new data described the role of enzyme in development of non-infectious diseases in the human. Scientists consider that slow acetylation genotype in combination with high xenobiotic load result in accumulation of toxic substances able to damage cells.

Therefore, acetyltransferase genotyping helps to reveal risk groups of cancer and non-infectious disease development and to prescribe more effective and safe doses of drugs. 

Functional Characterization of the Effects of N-acetyltransferase 2 Alleles on N-acetylation of Eight Drugs and Worldwide Distribution of Substrate-Specific Diversity

Variability in the enzymatic activity of N-acetyltransferase 2 (NAT2) is an important contributor to interindividual differences in drug responses. However, there is little information on functional differences in N-acetylation activities according to NAT2 phenotypes, i.e., rapid, intermediate, slow, and ultra-slow acetylators, between different substrate drugs. Here, we estimated NAT2 genotypes in 990 Japanese individuals and compared the frequencies of different genotypes with those of different populations. We then calculated in vitro kinetic parameters of four NAT2 alleles (NAT2^∗4, ^∗5, ^∗6, and ^∗7) for N-acetylation of aminoglutethimide, diaminodiphenyl sulfone, hydralazine, isoniazid, phenelzine, procaineamide, sulfamethazine (SMZ), and sulfapyrizine. NAT2^∗5, ^∗6, and ^∗7 exhibited significantly reduced N-acetylation activities with lower Vmax and CLint values of all drugs when compared with NAT2^∗4. Hierarchical clustering analysis revealed that 10 NAT2 genotypes were categorized into three or four clusters. According to the results of in vitro metabolic experiments using SMZ as a substrate, the frequencies of ultra-slow acetylators were calculated to be 29.05–54.27% in Europeans, Africans, and South East Asians, whereas Japanese and East Asian populations showed lower frequencies (4.75 and 11.11%, respectively). Our findings will be helpful for prediction of responses to drugs primarily metabolized by NAT2.

Risk factors associated with increased discontinuation rate of trimethoprim-sulfamethoxazole used as a primary prophylaxis for Pneumocystis pneumonia: A retrospective cohort study

BACKGROUND

The use of trimethoprim-sulfamethoxazole (TMP-SMX) for Pneumocystis pneumonia (PcP) prophylaxis is often discontinued owing to adverse drug reactions. Half-dosage of TMP-SMX (40/200 mg daily) is considered more tolerable than the conventional dosage (80/400 mg daily). However, patient background characteristics that are associated with the discontinuation of TMP-SMX prophylaxis and suitable for reduced dosage remain unclear. In this study, we aimed to identify the risk factors for the discontinuation of and efficacy of different doses of TMP-SMX prophylaxis in patients with creatinine clearance higher than 30 mL/min.

METHODS

We retrospectively evaluated 318 immunocompromised non-human immunodeficiency virus (HIV)-infected patients (194 men and 124 women; median age, 68.5 [interquartile range, 59-75] years) who underwent TMP-SMX therapy as a primary PcP prophylaxis between July 2014 and August 2019. The patients were segregated into two groups on the basis of dosage: single-strength (SS; n = 244) and half-strength (HS; n = 74) groups. We evaluated PcP occurrence, TMP-SMX discontinuation rate, and discontinuation-related risk factors in these groups.

RESULTS

PcP did not occur in either group. The univariate and multivariate Cox proportional hazards models revealed that the SS dosage and renal function (e.g. serum creatinine and creatinine clearance) were independently associated with prophylaxis discontinuation. At 24 weeks, the HS group presented significantly lower discontinuation rates than the SS group (P = 0.019, log-rank test). In the SS group, patients with mild renal impairment (e.g. serum creatinine ≥0.78 mg/dL or creatinine clearance ≤64.26 mL/min) presented significantly higher TMP-SMX discontinuation rates than those without such an impairment (P < 0.05, log-rank test with Bonferroni correction). This difference was not significant in the HS group.

CONCLUSION

Mild renal impairment might increase the risk of discontinuation of conventional TMP-SMX prophylaxis. In patients with a mild renal impairment, the HS dosage may improve tolerability while maintaining prophylactic efficacy.

Living with sulfonamides: a diverse range of mechanisms observed in bacteria

Sulfonamides are the oldest class of synthetic antibiotics still in use in clinical and veterinary settings. The intensive utilization of sulfonamides has been leading to the widespread contamination of the environment with these xenobiotic compounds. Consequently, in addition to pathogens and commensals, also bacteria inhabiting a wide diversity of environmental compartments have been in contact with sulfonamides for almost 90 years. This review aims at giving an overview of the effect of sulfonamides on bacterial cells, including the strategies used by bacteria to cope with these bacteriostatic agents. These include mechanisms of antibiotic resistance, co-metabolic transformation, and partial or total mineralization of sulfonamides. Possible implications of these mechanisms on the ecosystems and dissemination of antibiotic resistance are also discussed. KEY POINTS: • Sulfonamides are widespread xenobiotic pollutants; • Target alteration is the main sulfonamide resistance mechanism observed in bacteria; • Sulfonamides can be modified, degraded, or used as nutrients by some bacteria.

Isolation and characterization of a marine bacterium Vibrio diabolicus strain L2-2 capable of biotransforming sulfonamides

Sulfonamides (SAs) have attracted much attention because of their high detection rates in natural water. In this study, a marine bacterium Vibrio diabolicus strain L2-2 was isolated which could metabolize 9 SAs to a different extent. Compared with SAs and their analogs, SAs with N-oxides of heterocyclic structure were easier to be transformed to their N⁴-acetylated metabolites or their isoxazole ring rearrangement isomers by strain L2-2. And, gene vdnatA and vdnatG were likely to be the key genes in SAs acetylation process, which might code Arylamine N-acetyltransferase. The biotransformation rates of sulfathiazole(STZ), sulfamonomethoxine(SMT), sulfadiazine(SDZ), sulfamethoxazole(SMX) and sulfisoxazole(SIX) could reach 29.39 ± 5.63, 24.97 ± 4.45, 79.41 ± 4.05, 64.64 ± 1.71, 32.82 ± 4.46% in 6 days, respectively. Besides, the overall optimal conditions for SAs biotransformation were less than 100 mg/L for total SAs in neutral or weakly alkaline medium with the salinity of 10-20‰ and additional nutrients like glucose, sucrose or glycerine. Furthermore, toxicity was demonstrated to be significantly reduced after biotransformation. Together, this study introduced a strategy to use V. diabolicus strain L2-2 to realize simultaneous removal and detoxification of multiple SAs in freshwater and seawater, and revealed SAs removal pathways and relevant molecular mechanism.

Physiologically Based Pharmacokinetic Modeling for Trimethoprim and Sulfamethoxazole in Children

OBJECTIVE

The aims of this study were to (1) determine whether opportunistically collected data can be used to develop physiologically based pharmacokinetic (PBPK) models in pediatric patients; and (2) characterize age-related maturational changes in drug disposition for the renally eliminated and hepatically metabolized antibiotic trimethoprim (TMP)-sulfamethoxazole (SMX).

METHODS

We developed separate population PBPK models for TMP and SMX in children after oral administration of the combined TMP-SMX product and used sparse and opportunistically collected plasma concentration samples to validate our pediatric model. We evaluated predictability of the pediatric PBPK model based on the number of observed pediatric data out of the 90% prediction interval. We performed dosing simulations to target organ and tissue (skin) concentrations greater than the methicillin-resistant Staphylococcus aureus (MRSA) minimum inhibitory concentration (TMP 2 mg/L; SMX 9.5 mg/L) for at least 50% of the dosing interval.

RESULTS

We found 67-87% and 71-91% of the observed data for TMP and SMX, respectively, were captured within the 90% prediction interval across five age groups, suggesting adequate fit of our model. Our model-rederived optimal dosing of TMP at the target tissue was in the range of recommended dosing for TMP-SMX in children in all age groups by current guidelines for the treatment of MRSA.

CONCLUSION

We successfully developed a pediatric PBPK model of the combination antibiotic TMP-SMX using sparse and opportunistic pediatric pharmacokinetic samples. This novel and efficient approach has the potential to expand the use of PBPK modeling in pediatric drug development.

Insights on sulfamethoxazole bio-transformation by environmental Proteobacteria isolates

Although sulfonamide residues are frequently reported as freshwaters contaminants, information on the ability of native bacteria to modify these synthetic antibiotics is scarce. Our purpose was to investigate the potential of bacteria from different aquatic environments to cleave or transform sulfamethoxazole (SMX) and infer on their ability to reduce the toxicity of this antibiotic. From a collection of about 100 Proteobacteria, 47 strains previously isolated from drinking water, surface water, and wastewater grew in the presence of 200 μM_SMX, and were further studied. Out of these, 14 strains, mostly from mineral drinking water, transformed SMX into equimolar amounts of the lesser toxic derivative N⁴-acetyl-sulfamethoxazole. The highest percentage of SMX transformation was recorded for two strains affiliated to Pseudomonas mandelii. For P. mandelii McBPA4 higher SMX transformation rate and extent were observed in fed-batch (∼8 μM_SMX/h, 81%) than in batch conditions (∼5 μM_SMX/h, 25%), but similar specific transformation rates were found in both cultivation modes (∼20 μmol_SMX/g_{cell dry weight}/h), indicating the dependence of the process on the microbial load. These results evidence that the capacity to transform synthetic antibiotics may be common among bacteria and highlight the potential of environmental bacteria in attenuating the potential adverse effects of pollution with sulfonamides.

Improvement of sulfamethoxazole (SMX) elimination and inhibition of formations of hydroxylamine-SMX and N4-acetyl-SMX by membrane bioreactor systems

Sulfamethoxazole (SMX) has frequently been detected in aquatic environments. In natural environment, not only individual microorganism but also microbial consortia are involved in some biotransformation of pollutants. The competition for space under consortia causing cell-cell contact inhibition changes the cellular behaviors. Herein, the membrane bioreactor system (MBRS) was applied to improve SMX elimination thorough exchanging the cell-free broths (CFB). The removal efficiency of SMX was increased by more than 24% whether under the pure culture of A. faecalis or under the co-culture of A. faecalis and P. denitrificans with MBRS. Meanwhile, MBRS significantly inhibited the formation of HA-SMX, and Ac-SMX from parent compound. Additionally, the cellular growth under MBRS was obviously enhanced, indicating that the increases in the cellular growth under MBRS are possibly related to the decreases in the levels of HA-SMX and Ac-SMX compared to that without MBRS. The intracellular NADH/NAD⁺ ratios of A. faecalis under MBRS were increased whether thorough itself-recycle of CFB or exchanging CFB between the pure cultures of A. faecalis and P. denitrificans, suggesting that the enhancement in the bioremoval efficiencies of SMX under MBRS by A. faecalis is likely related to the increases in the NADH/NAD⁺ ratio. Taken together, the regulation of cell-to-cell communication is preferable strategy to improve the bioremoval efficiency of SMX.

Population Pharmacokinetics of Trimethoprim-Sulfamethoxazole in Infants and Children

Trimethoprim (TMP)-sulfamethoxazole (SMX) is used to treat various types of infections, including community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA) and Pneumocystis jirovecii infections in children. Pharmacokinetic (PK) data for infants and children are limited, and the optimal dosing is not known. We performed a multicenter, prospective PK study of TMP-SMX in infants and children. Separate population PK models were developed for TMP and SMX administered by the enteral route using nonlinear mixed-effects modeling. Optimal dosing was determined on the basis of the matching adult TMP exposure and attainment of the surrogate pharmacodynamic (PD) target for efficacy, a free TMP concentration above the MIC over 50% of the dosing interval. Data for a total of 153 subjects (240 samples for PK analysis) with a median postnatal age of 8 years (range, 0.1 to 20 years) contributed to the analysis for both drugs. A one-compartment model with first-order absorption and elimination characterized the TMP and SMX PK data well. Weight was included in the base model for clearance (CL/F) and volume of distribution (V/F). Both TMP and SMX CL/F increased with age. In addition, TMP and SMX CL/F were inversely related to the serum creatinine and albumin concentrations, respectively. The exposure achieved in children after oral administration of TMP-SMX at 8/40 mg/kg of body weight/day divided into administration every 12 h matched the exposure achieved in adults after administration of TMP-SMX at 320/1,600 mg/day divided into administration every 12 h and achieved the PD target for bacteria with an MIC of 0.5 mg/liter in >90% of infants and children. The exposure achieved in children after oral administration of TMP-SMX at 12/60 and 15/75 mg/kg/day divided into administration every 12 h matched the exposure achieved in adults after administration of TMP-SMX at 640/3,200 mg/day divided into administration every 12 h in subjects 6 to <21 years and 0 to <6 years of age, respectively, and was optimal for bacteria with an MIC of up to 1 mg/liter.

Suboptimal cotrimoxazole prophylactic concentrations in HIV-infected children according to the WHO guidelines

AIMS

A clinical study was conduct in HIV-infected children to evaluate the prophylactic doses of cotrimoxazole [sulfamethoxazole (SMX) and trimethoprim (TMP)] advised by the WHO.

METHODS

Children received lopinavir-based antiretroviral therapy with cotrimoxazole prophylaxis (200 mg of SMX/40 mg of TMP once daily). A nonlinear mixed effects modelling approach was used to analyse plasma concentrations. Factors that could impact the pharmacokinetic profile were investigated. The model was subsequently used to simulate individual exposure and evaluate different administration schemes.

RESULTS

The cohort comprised 136 children [average age: 1.9 years (range: [0.7-4]), average weight: 9.5 kg (range: [6-16.3])]. A dose per kg was justified by the significant influence of implementing an allometrically scaled body size covariate on SMX and TMP pharmacokinetics. SMX and TPM clearance were estimated at 0.49 l h^-1 /9.5 kg and 3.06 l h^-1 /9.5 kg, respectively. The simulated exposures obtained after administration of oral dosing recommended by the WHO for children from 10 to 15 kg were significantly lower than in adults for SMX and TMP. This could induce a reduction of effectiveness of cotrimoxazole. Simulations show that regimens of 30 mg kg^-1 of SMX and 6 mg kg^-1 of TMP in the 5-10 kg group and 25 mg kg^-1 of SMX and 5 mg kg^-1 of TMP in the 10-15 kg group are more suitable doses.

CONCLUSIONS

In this context of high prevalence of opportunistic infections, a lower exposure to cotrimoxazole in children than adults was noted. To achieve comparable exposure to adults, a dosing scheme per kg was proposed.

Exogenous cofactors for the improvement of bioremoval and biotransformation of sulfamethoxazole by Alcaligenes faecalis

Sulfamethoxazole (SMX), an extensively prescribed or administered antibiotic pharmaceutical product, is usually detected in aquatic environments, because of its incomplete metabolism and elimination. This study investigated the effects of exogenous cofactors on the bioremoval and biotransformation of SMX by Alcaligenes faecalis. High concentration (100mg·L(-1)) of exogenous vitamin C (VC), vitamin B6 (VB6) and oxidized glutathione (GSSG) enhanced SMX bioremoval, while the additions of vitamin B2 (VB2) and vitamin B12 (VB12) did not significantly alter the SMX removal efficiency. Globally, cellular growth of A. faecalis and SMX removal both initially increased and then gradually decreased, indicating that SMX bioremoval is likely dependent on the primary biomass activity of A. faecalis. The decreases in the SMX removal efficiency indicated that some metabolites of SMX might be transformed into parent compound at the last stage of incubation. Two transformation products of SMX, N-hydroxy sulfamethoxazole (HO-SMX) and N4-acetyl sulfamethoxazole (Ac-SMX), were identified by a high-performance liquid chromatograph coupled with mass spectrometer. High concentrations of VC, nicotinamide adenine dinucleotide hydrogen (NADH, 7.1mg·L(-1)), and nicotinamide adenine dinucleotide (NAD(+), 6.6mg·L(-1)), and low concentrations of reduced glutathione (GSH, 0.1 and 10mg·L(-1)) and VB2 (1mg·L(-1)) remarkably increased the formation of HO-SMX, while VB12 showed opposite effects on HO-SMX formation. In addition, low concentrations of GSH and NADH enhanced Ac-SMX formation by the addition of A. faecalis, whereas cofactors (VC, VB2, VB12, NAD(+), and GSSG) had no obvious impact on the formation of Ac-SMX compared with the controls. The levels of Ac-SMX were stable when biomass of A. faecalis gradually decreased, indicating the direct effect of biomass on the formation of Ac-SMX by A. faecalis. In sum, these results help us understand the roles played by exogenous cofactors in eliminating SMX by A. faecalis and provide potential strategies for improving SMX biodegradation.

A comparative effectiveness analysis of treatment for latent tuberculosis infection using multilevel selection models

AIM

Nine months of isoniazid (9INH) is the gold standard for treatment of latent tuberculosis infection (LTBI). This paper compares the effectiveness of 9 months of isoniazid with 4 months of transitional rifampin (9H4R) to alternative therapies, including 9INH, 6 months of isoniazid (6INH) and 6 months of isoniazid with 4 months of transitional rifampin (6H4R), for treatment of LTBI.

MATERIALS & METHODS

Using an ethnically diverse clinic sample of 552 patients given treatment for LTBI with 9H4R, we use multilevel selection models to examine the adjusted comparative effectiveness of the regimens among ethnic groups that feature distinct genetic predispositions to side effects on INH. For unadjusted/absolute effectiveness, we simulated cost-effectiveness ratios for 4 months of rifampin (4RIF) and compared with bootstrapped confidence intervals for the alternative therapies.

RESULTS

There are variations in the comparative effectiveness across ethnic groups, with the most notable differences for 9H4R. For unadjusted/absolute effectiveness, 4RIF presents the greatest net benefit for US born black and African patients. For all other ethnic groups, 6H4R was the most effective.

CONCLUSION

Patient ethnicity affects tolerance to INH. 9H4R was the most effective LTBI treatment for all ethnicities. However, this result heavily depends on whether adjustments are made for self-selection.

Complications and outcomes of trimethoprim-sulphamethoxazole as chemoprophylaxis for pneumocystis pneumonia in renal transplant recipients

BACKGROUND

Following a pneumocystis pneumonia (PCP) outbreak in our nephrology unit, all transplant patients were offered chemoprophylaxis with trimethoprim-sulphamethoxazole (TMP-SMX) as the first line agent. A high rate of complications was noted. We aimed to quantify TMP-SMX associated adverse events and evaluate its prophylactic benefit in their light. Potential risk factors for complications' development were also investigated.

METHOD

This was an observational study of outcomes in transplant recipients commenced on TMP-SMX prophylaxis for 1year period. End-points were adverse events due to TMP-SMX, the additional medical burden resulting from these events, and PCP diagnosis.

RESULTS

290 patients commenced on TMP-SMX. 110 (38%) developed complications with most common being rise in serum creatinine (Cr) (n = 63, 22%) followed by gastrointestinal symptoms (n = 15, 5%), and leucopenia (n = 5, 2%). PCP incidence fell from 19 cases in 19 months to 2 cases in 12 months. Baseline renal function (P = 0.019) was an independent predictors for developing rise in Cr with TMP-SMX.

CONCLUSION

Use of chemoprophylaxis is an effective strategy in dealing with a PCP outbreak but can lead to a high number of complications. Rises in serum Cr can cause significant concern and increase in the number of investigations.

Cotrimoxazole - optimal dosing in the critically ill

The optimum dosage regimen for cotrimoxazole in the treatment of life threatening infections due to susceptible organisms encountered in critically ill patients is unclear despite decades of the drug's use. Therapeutic drug monitoring to determine the appropriate dosing for successful infection eradication is not widely available. The clinician must utilize published pharmacokinetic, pharmacodynamic, and effective inhibitory concentration information to determine potential dosing regimens for individual patients when treating specific pathogens. Using minimum inhibitory concentrations known to successfully block growth for target pathogens, the pharmacokinetics of both trimethoprim and sulfamethoxazole can be utilized to establish empiric dosing regimens for critically ill patients while considering organ of clearance impairment. The author's recommendations for appropriate dosing regimens are forwarded based on these parameters.