Acetylator phenotype and genotype in HIV-infected patients with and without sulfonamide hypersensitivity

Adverse reactions to sulfonamides occur at a higher frequency in patients infected with the human immunodeficiency virus (HIV) than noninfected patients. Some studies have suggested that patients with the slow acetylator phenotype are predisposed to these reactions, whereas other studies suggest that the slow acetylator genotype is not a predisposing factor. To rationalize these seemingly contradictory observations, the authors determined the N-acetyltransferase 2 (NAT2) genotype and phenotype in patients with and without a history of hypersensitivity reactions to sulfonamides. HIV-infected patients with a history of a delayed-type hypersensitivity reaction to trimethoprim-sulfamethoxazole were enrolled, along with a group of AIDS patients with no history of hypersensitivity (delayed or immediate). NAT2 phenotype was determined in both groups using dapsone, while the genotype was determined using a polymerase chain reaction-restriction fragment length polymorphism assay. Ten of 14 patients (71%) with a history of hypersensitivity exhibited the slow acetylator phenotype, while 8 of 14 patients (57%) without such a history exhibited this same phenotype (odds ratio [OR] = 1.9, 95% confidence interval [CI] = 0.4-9.0; p = 0.69, Fisher's Exact Test). While 9 of 14 patients (64%) with a history of hypersensitivity exhibited a slow acetylator genotype, only 4 of 14 patients (29%) without such a history exhibited this genotype (ns). There were more instances of discordance between deduced and actual phenotype in the nonhypersensitive patients (n = 4) than in the hypersensitive patients (n = 1). The reported higher frequency of the slow acetylator phenotype among patients with a history of hypersensitivity to sulfonamides does not appear to be explained by metabolic changes that would cause discordance between acetylator genotype and phenotype.     

A discordance between cytochrome P450 2D6 genotype and phenotype in patients undergoing methadone maintenance treatment

AIMS: To assess CYP2D6 activity and genotype in a group of patients undergoing methadone maintenance treatment (MMT). METHODS: Blood samples from 34 MMT patients were genotyped by a polymerase chain reaction-based method, and results were compared with CYP2D6 phenotype (n = 28), as measured by the molar metabolic ratio (MR) of dextromethorphan (DEX)/dextrorphan (DOR) in plasma. RESULTS: Whereas 9% of patients (3/34) were poor metabolizers (PM) by genotype, 57% (16/28) were PM by phenotype (P < 0.005). Eight patients, who were genotypically extensive metabolizers (EM), were assigned as PM by their phenotype. The number of CYP2D6*4 alleles and sex were significant determinants of CYP2D6 activity in MMT patients, whereas other covariates (methadone dose, age, weight) did not contribute to variation in CYP2D6 activity. CONCLUSIONS: There was a discordance between genotype and in vivo CYP2D6 activity in MMT patients. This finding is consistent with inhibition of CYP2D6 activity by methadone and may have implications for the safety and efficacy of other CYP2D6 substrates taken by MMT patients.     

A discordance of the cytochrome P450 2C19 genotype and phenotype in patients with advanced cancer

AIMS: To examine the relationship between cytochrome P450 2C19 (CYP2C19) genotype and expressed metabolic activity in 16 patients with advanced metastatic cancer. METHODS: Individual CYP2C19 genotypes were determined by PCR-based amplification, followed by restriction fragment length analysis, and compared with observed CYP2C19 metabolic activity, as determined using the log hydroxylation index of omeprazole. RESULTS: All 16 patients had an extensive metabolizer genotype. However, based on the antimode in a distribution of log omeprazole hydroxylation indices from healthy volunteers, four of the patients had a poor metabolizer phenotype and there was a general shift of the remaining 12 patients towards a slower metabolic phenotype. This suggests a reduction in metabolic activity for all patients relative to healthy volunteers. A careful analysis of patient medical records failed to reveal any drug interactions or other source for the observed discordance between genotype and phenotype. CONCLUSIONS: There are no previous reports of a 'discordance' between genotype and expressed enzyme activity in cancer patients. Such a decrease in enzyme activity could have an impact on the efficacy and toxicity of chemotherapeutic agents and other drugs, used in standard oncology practice.     

Acetylator phenotype and serum levels of sulfapyridine in patients with inflammatory bowel disease

Summary Twenty-eight outpatients receiving sulfasalazine for inflammatory bowel disease were monitored. Assessment of acetylator phenotype according to the percentage of acetylated sulfapyridine in serum provided a clear distinction between rapid and slow acetylators. In comparison, the percentage of acetylated sulfapyridine in saliva or urine was a less precise index of phenotype. Determination of saliva concentrations of sulfapyridine and N⁴-acetylsulfapyridine did not provide a reliable estimate of serum levels. Slow acetylators had significantly higher serum concentrations of sulfapyridine (21.9±14.0 [SD] µg/ml) than rapid acetylators (8.8±4.3 µg/ml) and had a higher incidence of toxicity (not statistically significant,p>0.05). Serum concentrations of sulfapyridine were significantly higher in patients with symptoms of toxicity (23.2±15.9 µg/ml) than those without (13.9±9.5 µg/ml) (p<0.05). However, serum concentrations of total sulfapyridine (sulfapyridine plus N⁴-acetylsulfapyridine) were not significantly different in patients with (32.9±21.2 µg/ml) or without (22.8±12.0 µg/ml) toxicity (p>0.05). For all patients serum concentrations of sulfapyridine (total sulfapyridine) ranged from 3.5 to 73.1 (5.7 to 95.1) µg/ml in patients with controlled disease and 6.3 to 38.0 (14.0 to 54.7) µg/ml in patients with active disease. A significant correlation between clinical status of disease and serum drug concentrations was only apparent for rapid acetylators (p<0.05). The daily sulfasalazine dosage (mg/kg of body weight, log value) and serum drug concentrations (log values) were highly correlated (p<0.05). For clinical evaluation of inflammatory bowel disease patients determination of serum sulfapyridine concentrations appears to be more important for monitoring toxicity than therapeutic efficacy of sulfasalazine. Assessment of acetylator status appears to be useful for predicting serum sulfapyridine levels in patients receiving sulfasalazine therapy.     

Interaction between saquinavir soft-gel and rifabutin in patients infected with HIV

AIMS: To evaluate the potential pharmacokinetic interaction between the HIV protease inhibitor saquinavir and rifabutin. METHODS: Fourteen HIV-infected patients provided full steady-state pharmacokinetic profiles following administration of rifabutin alone (300 mg once daily) or saquinavir soft-gel formulation (1200 mg three times daily) plus rifabutin (300 mg once daily) in this open label, partially randomized study. RESULTS: Coadministration of saquinavir and rifabutin resulted in a reduction in saquinavir AUC(0,8 h) and C(max)(0,8 h) of 47% (95% CI 30, 60%) and 39% (95% CI 11, 59%), respectively. Rifabutin AUC(0,24 h) and C(max)(0,24 h) was increased by an average of 44% (95% CI 17, 78%) and 45% (95% CI 14, 85%), respectively. Saquinavir in combination with rifabutin was well tolerated. Gastrointestinal intolerance and asymptomatic increases in liver enzymes were the only adverse events of note. CONCLUSIONS: Administration of rifabutin with saquinavir may decrease the efficacy of this HIV protease inhibitor.     

Acetylation genotype and phenotype in patients with systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is a chronic autoimmune disease affecting various tissues and organs. In the studies on SLE etiopathogenesis, a potential role of genetically determined impairment of xenobiotic metabolism has been emphasized. N-acetyltransferase 2 enzyme (NAT2) exhibits gene polymorphism and the acetylation rate with NAT2 involvement varies from person to person. The study on acetylation phenotype was carried out using isonicotinic acid hydrazide (isoniazid) as a model drug, while NAT2 alleles were determined by the polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) assays. Among patients with SLE, NAT2*4/NAT2*6 and NAT2*5/NAT2*5 genotypes occurred most frequently, while NAT2*4/NAT2*6 and NAT2*5/NAT2*6 prevailed in the control group. The concordance of 96.8% was achieved between acetylation phenotype and NAT2 genotype in the group of SLE patients studied. Conclusion: Acetylation polymorphism appears not to be an important risk factor in SLE.     

Slow acetylator phenotype and genotype in HIV-positive patients with sulphamethoxazole hypersensitivity

AIMS: To test the role of acetylator status, and to investigate the reported discrepancy between acetylator phenotype and genotype in HIV-positive patients with sulphamethoxazole (SMX) hypersensitivity. METHODS: Forty HIV-positive patients (32 of whom were SMX-hypersensitive), and 26 healthy volunteers, were genotyped by polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) analysis, and phenotyped using dapsone (50 mg) as a probe, for acetylator status. Sequencing of the NAT2 exon was performed where discrepancy between phenotyping and genotyping was detected. Our results were also pooled with published studies addressing slow acetylator status in HIV-positive SMX-hypersensitive patients. RESULTS: Slow acetylator genotype and phenotype frequencies did not differ between HIV-positive SMX-hypersensitive and nonhypersensitive patients, and healthy controls, which was further confirmed in a meta-analysis of published studies (pooled odds ratio 2.25, 95% confidence interval 0.45, 11.17). Discordance between phenotype and genotype was resolved in four of the subjects by sequencing of the whole NAT2 exon, which revealed rare mutations, leaving three (9%) HIV-positive SMX-hypersensitive patients and one (4%) healthy volunteer who continued to demonstrate the discordance. CONCLUSIONS: Slow acetylator phenotype or genotype is unlikely to predispose to SMX hypersensitivity in HIV-positive patients, although a minor role cannot be excluded. Phenotype-genotype discrepancies are partly due to nondetection of all rare alleles by PCR methodology, and can be circumvented by sequencing of the gene in patients showing a discrepancy.     

Correlation between acetylation phenotype and genotype in Chinese women

OBJECTIVE: The acetylation polymorphism is a common inherited variation in human drug and carcinogen metabolism. Because N-acetyltransferase (NAT2) is important for the detoxification and/or bioactivation of drugs and carcinogens, this polymorphism has important implications in therapeutics and cancer susceptibility. A high correlation between acetylation phenotype and genotype has been demonstrated in several studies. However, no such data exist for Chinese females. The aim of the present study was to compare acetylation phenotype with NAT2 genotype in a population of primarily non-smoking Chinese females. METHODS: In the present study, the correlation between N-acetyltransferase activity and NAT2 genotype was evaluated in 103 unrelated Chinese female controls derived from a hospital-based case-control study of lung cancer in Singapore. Acetylation phenotype and genotype were respectively determined using caffeine and an allele-specific polymerase chain reaction (PCR). RESULTS: The proportions of rapid and slow phenotypes were 78% and 22%, respectively, while the distribution of rapid (heterozygotes and homozygotes combined) and slow acetylator genotypes was 76% and 24%, respectively. The distribution of the various NAT2 genotypes did not differ significantly (chi2 = 1.45, P > 0.05) from that predicted by the Hardy-Weinberg Law. All slow acetylators were accurately predicted (100%), whereas 2 of 80 rapid acetylators were erroneously predicted as slow (2.5%). The overall prediction rate of the PCR-based test for the acetylation phenotype was at 98.1% in our Chinese population. CONCLUSION: Our results suggest that genotyping with PCR may well become the preferred method for the determination of acetylation polymorphism in epidemiological studies in this Asian population.     

Acetylator phenotyping with sulphadimidine in patients receiving isoniazid

The possible competition of isoniazid for the acetylation of sulphadimidine was studied by comparing the degree of acetylation of urine sulphadimidine (1 g orally) in isoniazid-treated and in isoniazid-untreated patients. The former group (isoniazid 300 mg once daily) consisted of 5 slow and 5 rapid acetylators and the latter group of 5 and 6 respective acetylator phenotypes. In all of the 4-8, 8-12 and 12-24 h urine fractions, the acetylation percentage of sulphadimidine and its distribution pattern were practically unaffected by the isoniazid. This suggests that isoniazid therapy does not interfere significantly with the routine acetylator phenotyping by means of sulphadimidine.     

Meta-analysis: the outcome of anti-viral therapy in HCV genotype 2 and genotype 3 infected patients with chronic hepatitis

Background  Anti-viral therapy seems more successful in HCV genotype 2 than genotype 3-infected patients.
Aim  To report sustained virological response (SVR) rates for HCV-2 and HCV-3 infection.
Methods  Meta-analyses were carried out on SVR data on 2275 patients treated for 24 weeks in eight individual trials and on 968 patients with rapid virological response (RVR) treated for 12–16 weeks or 24 weeks in four studies.
Results  After 24 weeks of therapy, SVR rates were 74% and 68%, respectively, for HCV-2 and HCV-3 genotype patients. Among high viraemics, SVR rate in HCV-2 infection (75%) differed from the 58% value in HCV-3 infection. Among low viraemic patients, respective rates were 79% and 75%. In RVR patients treated for 12–16 or 24 weeks, SVR rates in HCV-2 infection were 83% and 84%, respectively, and in HCV-3 infection 84% and 86%. In patients without RVR treated for 24 weeks, SVR was higher in HCV-2, with a 17.8% weighted difference.
Conclusions  Twenty-four weeks of therapy should remain standard duration for HCV-2 and low viraemic HCV-3 patients. In RVR patients, HCV-3 patients respond to short-treatment as well as HCV-2 patients, irrespective of basal viraemia. Patients without RVR may need longer treatment than the recommended 24 weeks.     

Thiopurine methyltransferase genotype and phenotype status in Japanese patients with systemic lupus erythematosus

We investigated the genotypic status of thiopurine methyltransferase (TPMT) polymorphism to evaluate the possible risk of the toxicity of azathioprine (AZA) in 68 patients with systemic lupus erythematosus (SLE). The allele frequency of TPMT mutation in the SLE group (2.9%) was higher than that in 174 Japanese healthy volunteers (1.1%), although it did not reach statistically significant difference (p=0.23). The mean value of TPMT activities in 51 subjects with TPMT*1/*1 was 40% higher than that of 4 subjects with TPMT*1/*3C in SLE group (18.1+/-6.1 nmol/h/ml packed red blood cells (pRBC) versus 13.2+/-3.2 nmol/h/ml pRBC; p=0.11). Two out of 4 SLE patients with TPMT*1/*3C had been treated with AZA, and one patient showed a leucopenia. The TPMT genotyping before AZA treatment is recommended for Japanese SLE patient group to avoid the AZA-induced adverse events, although detection of the patient with low TPMT activity by genotyping is still imperfect.     

CYP2D6 genotype and phenotype determination in a Mexican Mestizo population

Objective Although CYP2D6 genetic polymorphism plays an important role in interindividual and interethnic variability in drug response, very few pharmacogenetic data are available from Hispanic populations, including Mexicans. For this purpose, this study was undertaken to determine CYP2D6 genotype and phenotype in a healthy Mexican Mestizo population. Methods Genotyping of five CYP2D6 mutant alleles by PCR–RFLP, and CYP2D6*5 and duplicated CYP2D6 alleles by long-PCR was performed in two hundred and forty three Mexican Mestizos. Of these, one hundred subjects were also phenotyped using dextromethorphan as the probe drug. Results The frequency of CYP2D6*2, *3, *4, *5, *10, *17 was 19.34%, 1.44%, 11.21%, 2.67%, 12.45%, and 1.65%, respectively, while duplicated CYP2D6 alleles were found in 12.76% of the 243 genotyped subjects. Among the 100 phenotyped subjects, we identified ten (10%, 95% confidence interval of 4.12–15.9) individuals as poor metabolizers by using the published antimode for Caucasians. The mean log₁₀ dextromethorphan/dextrorphan ratio of the total sample was −2.05. The mean (SD) of the log₁₀ MR in the CYP2D6 subgroups was UM=−2.6 (0.86); EM=−2.09 (0.98); IM=−1.71 (1.06); and PM=0.42 (0.625). These data show a trend toward a smaller mean log MR (higher enzyme activity) as the number of active alleles increases. Conclusions The PM frequency of CYP2D6 in the population studied was 10%, which is very similar to Spanish Caucasians. The observed frequency of the CYP2D6 alleles tested was unique for the Mexican Mestizo sample analyzed, and in accordance to the Caucasian, Asian and African admixture in this population.     

Relationship between NAT1 genotype and phenotype in a Japanese population

NAT1, which biotransforms many carcinogens, is genetically polymorphic. This polymorphism has been postulated as a mechanism for susceptibility differences in cancer, possibly due to NAT1 activity differences. However, the relationship between NAT1 genotype and phenotype is not clear. In our study of 110 Japanese, the frequency of the NAT1*10 allele (0.53, 95% confidence interval 0.46-0.59) was higher than others have observed in Caucasians (0.16). From genotype frequency studies, 26.4% of the subjects belonged to the NAT1*10/*10 genotype, 53.6% to the NAT1*4/*10 genotype and 20% to the NAT1*4/*4 genotype. Neither NAT1*3 nor NAT1*11 genotype was seen in these subjects. In female subjects, we found higher NAT1 activity in NAT1*4/*10 subjects than in NAT1*4/*4 subjects (n = 49; 2.63 versus 2.16 nmol/min/mg protein). NAT1 activity-difference between NAT1*4/*10 and NAT1*10/*10 was not statistically significant. Thus, not only the presence of NAT1*10 allele, but also other factors are suspected of increasing NAT1 activities. After full sequencing of 10 subjects, five individuals having the highest activities and five individuals having the lowest activities, we found NAT1*18A and NAT1*18B to be in the high activity group and the low activity group, respectively. The genotypes containing these variants were heterozygous, i.e. NAT1*4/*18A and NAT1*4/*18B. Due to rare frequencies of these variants, they cannot be considered as other effective, genetic factors on NAT1 activity. Age and tobacco smoking did not affect the relationship between NAT1 genotype and phenotype.     

人类免疫缺陷病毒感染者抗病毒治疗期间病毒载量与免疫学指标的关系

目的 探讨人类免疫缺陷病毒(HIV)感染者抗病毒治疗期间病毒载量(VL)与免疫学指标的关系.方法 建立前瞻性研究队列,选取2018年1月至2019年1月在保定市人民医院治疗的确认为HIV-1感染阳性的感染者200例为研究对象,给予替诺福韦(TDF)+拉米夫定(3TC)+依非韦伦(EFV)高效抗反转录病毒治疗(HAART...     

Concordance between proguanil phenotype and CYP2C19 genotype in Chinese

Objective To investigate whether urinary proguanil (chlorguanide) metabolite ratios incorporating its minor metabolite, 4-chlorophenylbiguanide, define individuals as extensive metabolisers (EMs) or poor metabolisers (PMs) of CYP2C19 more reliably than the standard phenotyping ratio [proguanil/cycloguanil (PG/CG)].Methods Thirty-eight ethnic Chinese subjects ingested 100 mg proguanil, collected urine for 8 h and were genotyped for CYP2C19*1, *2 and *3 alleles. Proguanil metabolite ratios (PG/CG; proguanil/4-chlorophenylbiguanide (PG/CPB); proguanil/(cycloguanil+4-chlorophenylbiguanide) [PG/(CG+CPB)] were determined from the urinary recoveries of proguanil, cycloguanil and 4-chlorophenylbiguanide. Proguanil phenotypes were determined from the ratios using frequency distribution histograms, probit and normal test variable plots.Results Data from 35 subjects were suitable for analysis. Of subjects, 5 were CYP2C19*2/*2, 1 was *2/*3, 21 were *1/*2 and 8 were *1/*1. A rank order of proguanil metabolic ratios was observed, with *1/*1 subjects having the lowest, *1/*2 intermediate and *2/*2, *2/*3 having the highest ratios (P<0.0001). All subjects with PM genotypes were classified as PMs of proguanil by probit analysis of PG/CPB and PG/(CG+CPB) ratios, but not PG/CG.Conclusion A gene-dose effect of CYP2C19 genotype on the conversion of proguanil to cycloguanil and 4-chlorophenylbiguanide has been demonstrated in ethnic Chinese subjects. Complete concordance between PM CYP2C19 genotype and PM phenotype was only achieved with probit analysis of proguanil metabolite ratios that incorporated 4-chlorophenylbiguanide.Work was completed at the Department of Clinical Pharmacology, Royal North Shore Hospital, St Leonards, NSW 2065, Australia.     

Structured treatment interruption in patients infected with HIV: a new approach to therapy

Current antiretroviral regimens are limited by issues of potency, adherence, toxicity, resistance and cost. With these limitations and the realisation that eradication of HIV infection currently is not possible, there is enthusiasm for strategies that allow discontinuation of medications, such as the structured treatment interruption (STI). STI is hypothesised to have benefits in three distinct clinical scenarios: acute treated infection, chronic treated infection with controlled viraemia, and chronic treated infection without controlled viraemia (salvage therapy). In patients with acute treated HIV infection, STI may preserve or enhance cellular immune responses to allow continued virological suppression in the absence of ongoing treatment. The Berlin patient presented with acute HIV infection prior to seroconversion and received antiretroviral therapy. After two treatment interruptions (for intercurrent infections), he permanently discontinued therapy and remained virologically suppressed for 2 years. Investigators from Massachusetts General Hospital described eight patients with acute or early HIV infection who received treatment and then underwent one or two STI. After the STIs, five of eight patients showed enhanced cellular immune responses and continued with virological suppression off treatment for a median of 2.7 years. In patients with chronic treated infection with controlled viraemia, STI may enhance immune responses as in the case of acute infection, or may allow decreased drug exposure and toxicity. Investigators from the National Institutes of Health enrolled 18 patients with chronic HIV infection and virological suppression while taking antiretroviral regimens. With a single STI, all patients rebounded, although one (6%) ultimately continued off therapy with virological suppression. The largest study of STI is the Spanish Swiss Intermittent Treatment Trial in which 128 patients with chronic suppressed HIV infection on antiretroviral therapy underwent four cycles of STI. At 52 weeks, 17% had suppressed viral load levels of <5000 copies/ml in the absence of therapy. In patients with chronic treated infection without controlled viraemia (salvage therapy), STI promotes a shift from resistant to wild-type (i.e. no mutations) virus. In the Hamburg cohort, the shift to wild-type virus was seen in 28 of 45 heavily treatment-experienced patients after an STI. Seventy-two percent of these patients experienced a virological response on a subsequent regimen, although many ultimately experienced virological rebound. In the San Francisco cohort, a shift to wild-type virus was seen in 15 of 17 protease inhibitor-experienced patients and six of these patients achieved virological suppression to <200 copies/ml on a new regimen. Risks associated with STI include increases in viral load levels with the risk of loss of virological control (i.e. failure to resuppress on therapy), repopulation of viral reservoirs and antiretroviral resistance, and decreases in CD4+ cell counts with the risk of loss or dysregulation of immune function and the occurrence of clinical events. Other risks include acute retroviral syndrome and the recurrence of short-term adverse effects. Currently, STI cannot be recommended as part of routine clinical care. Prospective studies are needed to assess the risks and benefits of this strategy in all clinical settings.