Sedative Plasma Concentrations and Delirium Risk in Critical Illness.

BACKGROUND: The relationship between plasma concentration of sedatives and delirium is unknown. OBJECTIVE: We hypothesized that higher plasma concentrations of lorazepam are associated with increased delirium risk, whereas higher plasma concentrations of dexmedetomidine are associated with reduced delirium risk. METHODS: This prospective cohort study was embedded in a double-blind randomized clinical trial, where ventilated patients received infusions of lorazepam and dexmedetomidine. Plasma concentrations of these drugs and delirium assessments were measured at least daily. A multivariable logistic regression model accounting for repeated measures was used to analyze associations between same-day plasma concentrations of lorazepam and dexmedetomidine (exposures) and the likelihood of next-day delirium (outcome), adjusting for same-day mental status (delirium, coma, or normal) and same-day fentanyl doses. RESULTS: This critically ill cohort (n = 103) had a median age of 60 years (IQR: 48-66) with APACHE II score of 28 (interquartile range [IQR] = 24-32), where randomization resulted in assignment to lorazepam (n = 51) or dexmedetomidine (n = 52). After adjusting for same-day fentanyl dose and mental status, higher plasma concentrations of lorazepam were associated with increased probability of next-day delirium (comparing 500 vs 0 ng/mL; odds ratio [OR] = 13.2; 95% CI = 1.4-120.1; P = 0.02). Plasma concentrations of dexmedetomidine were not associated with next-day delirium (comparing 1 vs 0 ng/mL; OR = 1.1; 95% CI = 0.9-1.3; P = 0.45). CONCLUSIONS: In critically ill patients, higher lorazepam plasma concentrations were associated with delirium, whereas dexmedetomidine plasma concentrations were not. This implies that the reduced delirium risk seen in patients sedated with dexmedetomidine may be a result of avoidance of benzodiazepines, rather than a dose-dependent protective effect of dexmedetomidine.

New up-conversion luminescence in molecular cyano-substituted naphthylsalophen lanthanide(iii) complexes.

A new naphthylsalophen and its 3 : 2 ligand-to-lanthanide sandwich-type complexes were isolated. When excited at 380 nm, the complexes display the characteristic metal-centred emission for NdIII, ErIII and YbIII. Upon 980 nm excitation, in mixed lanthanide and the Er complexes, Er-centred upconversion emission at 543 and 656 nm is observed, with power densities as low as 2.18 W cm-2.

Tariquidar, a selective P-glycoprotein inhibitor, does not potentiate loperamide's opioid brain effects in humans despite full inhibition of lymphocyte P-glycoprotein.

BACKGROUND: Loperamide, a potent opioid, has been used as an in vivo probe to assess P-glycoprotein activity at the blood-brain barrier, because P-glycoprotein inhibition allows loperamide to cross the blood-brain barrier and exert its central opioid effects. In humans, studies with nonselective and moderately potent inhibitors resulted in mild opioid effects but were confounded by the concurrent inhibition of loperamide's metabolism. The authors studied the effect of the highly selective, potent P-glycoprotein inhibitor tariquidar on loperamide's central opioid effects. METHODS: In a randomized, double-blind, crossover study, nine healthy subjects received on 2 study days oral loperamide (32 mg) followed by an intravenous infusion of either tariquidar (150 mg) or placebo. Central opioid effects (pupil diameter, sedation) were measured for 12 h, and blood samples were drawn up to 48 h after drug administration to determine plasma loperamide concentrations and ex vivo P-glycoprotein activity in T lymphocytes. Values for pupil diameter and loperamide concentrations were plotted over time, and the areas under the curves on the tariquidar and placebo study day were compared within each subject. RESULTS: Tariquidar did not significantly affect loperamide's central effects (median reduction in pupil diameter area under the curve, 6.9% [interquartile range, -1.4 to 12.1%]; P = 0.11) or plasma loperamide concentrations (P = 0.12) but profoundly inhibited P-glycoprotein in lymphocytes by 93.7% (95% confidence interval, 92.0-95.3%). CONCLUSION: These results suggest that despite full inhibition of lymphocyte P-glycoprotein, the selective P-glycoprotein inhibitor tariquidar does not potentiate loperamide's opioid brain effects in humans.

Clinical sedation scores as indicators of sedative and analgesic drug exposure in intensive care unit patients.

BACKGROUND: It is unclear how best to measure sedative/analgesic drug exposure in the clinical care of critically ill patients. Large doses and prolonged use of sedatives and analgesics in the intensive care unit (ICU) may lead to oversedation and adverse effects, including delirium and long-term cognitive impairment. These issues are of particular concern in elderly patients (aged > or =65 years), who account for at least half of all ICU admissions and nearly two thirds of ICU days. OBJECTIVE: This pilot study explored the relationships between clinical sedation scores, sedative/analgesic drug doses, and plasma drug concentrations in critically ill patients, the majority of whom were elderly. METHODS: This was a prospective, observational study conducted in a 500-bed, tertiary care community hospital. Study patients included a cohort of mechanically ventilated, medical ICU patients who were admitted to the hospital between April and June 2004 who required use of fentanyl, lorazepam, or propofol. Sedative/analgesic medications were administered according to clinical guidelines. Patients' sedation levels were measured twice daily using the Richmond Agitation-Sedation Scale (RASS). Dosing of fentanyl, lorazepam, and propofol was recorded. Blood was sampled twice daily for up to 5 days to analyze plasma drug concentrations. To specifically evaluate the effects of acute, extended (rather than chronic) sedative and analgesic exposure, the study focused on an ICU population receiving these agents for at least 48 hours but <2 weeks. RESULTS: Eighteen medical ICU patients (11 females, 7 males; mean [SD] age, 66.1 [18.1] years) on mechanical ventilation comprised the study cohort. Fifteen patients were aged >62 years, and 11 of those were aged > or =71 years. Plasma drug concentrations (median and interquartile range) were as follows: fentanyl--2.1 ng/mL, 0.9-3.4 ng/mL; lorazepam--266 ng/mL, 112-412 ng/mL; and propofol--845 ng/mL, 334-1342 ng/mL. Maximum concentrations were 3- to 12-fold higher than medians (fentanyl, 7.3 ng/mL; lorazepam, 3108 ng/mL; propofol, 10,000 ng/mL). Medication doses were only moderately correlated with RASS scores (Spearman rho): fentanyl--rho = -0.39, P = 0.002; lorazepam--rho = -0.28, P = 0.001; and propofol--rho = -0.46, P < 0.001. Plasma drug concentrations of fentanyl and lorazepam demonstrated moderate correlations with sedation scores (fentanyl--rho = -0.46, P = 0.002; lorazepam: rho = -0.49, P < 0.001), while propofol concentrations correlated poorly with sedation scores (rho = -0.18, P = 0.07). Associations between interval drug doses and plasma concentrations were as follows: fentanyl, rho = 0.84; lorazepam, rho = 0.76; and propofol, rho = 0.61 (all, P < 0.001). Instructive examples of discrepant dose versus plasma concentration profiles and drug interactions are provided, including 3 cases with patients aged > or =64 years. CONCLUSIONS: Elderly patients are commonly encountered in the ICU setting. Only moderate correlations existed between clinical sedation levels and dose or plasma concentration of sedative/analgesic medications in this study population. Further work is needed to understand appropriate and feasible measures of exposure to sedatives/analgesics relating to clinical outcomes.

Pharmacogenetics of plasma efavirenz exposure after treatment discontinuation: an Adult AIDS Clinical Trials Group Study.

BACKGROUND: Efavirenz has a long plasma half-life and a low genetic barrier to resistance. Simultaneously stopping treatment with all agents in efavirenz-containing regimens may result in functional efavirenz monotherapy that selects for drug-resistant human immunodeficiency virus type 1. Lower plasma efavirenz clearance is associated with a cytochrome P450 2B6 gene (CYP2B6) polymorphism (516G-->T) that is more frequent among African American individuals than among European American individuals. METHODS: We characterized relationships between this polymorphism and predicted plasma efavirenz concentration-time profiles after discontinuation of therapy with use of data obtained from subjects receiving therapy. Pharmacokinetic parameters were estimated using population-based methods. Concentrations after discontinuation of therapy were predicted from subject-specific estimates. RESULTS. Median estimated efavirenz half-lives were 23, 27, and 48 h for patients with CYP2B6 position 516 GG (78 patients), GT (60), and TT (14) genotypes, respectively (P<.001). After therapy was stopped, plasma efavirenz concentrations in patients with GG, GT, and TT genotypes were predicted to exceed 46.7 ng/mL (the estimated protein-adjusted 95% inhibitory concentration for wild-type virus) for a median of 5.8 days (interquartile range [IQR], 4.4-8.3 days), 7.0 days (IQR, 5.0-8.0 days), and 14 days (IQR, 11.1-21.2 days), respectively (P<.001). Plasma efavirenz levels were predicted to exceed 46.7 ng/mL for >21 days in 5% of subjects with GG genotype, 5% of subjects with GT genotype, and 29% of subjects with TT genotype. CONCLUSIONS: The CYP2B6 position 516 TT genotype or a prolonged measured elimination half-life may predict increased risk of developing drug resistance among patients who discontinue efavirenz-containing regimens. This has implications for strategies to safely discontinue antiretroviral regimens while avoiding the emergence of drug resistance.

Pharmacogenetics of nevirapine-associated hepatotoxicity: an Adult AIDS Clinical Trials Group collaboration.

Associations have been reported between an MDR1 variant and responses to nonnucleoside reverse-transcriptase inhibitors. We explored associations between MDR1, CYP2B6, and CYP3A polymorphisms and nevirapine hepatotoxicity. Among participants in a randomized study in South Africa (FTC-302), MDR1 3435C-->T was significantly associated with decreased risk of hepatotoxicity (risk ratio, 0.30; P=.016).

The erythromycin breath test reflects P-glycoprotein function independently of cytochrome P450 3A activity.

BACKGROUND: The erythromycin breath test (ERBT) has been widely used as a phenotypic measure of cytochrome P450 (CYP) 3A activity in individuals, as well as its modulation by inhibitors or inducers. However, it is not entirely clear what this measure actually reflects because, in addition to CYP3A, animal studies suggest that P-glycoprotein is also involved in erythromycin's hepatic disposition. Thus studies were undertaken to determine the effect of tariquidar, a potent P-glycoprotein inhibitor that does not affect CYP3A activity, on the ERBT and on the CYP3A-mediated metabolism of midazolam, a non-P-glycoprotein substrate. METHODS: A randomized, double-blind, 2-way crossover trial was performed in 8 healthy subjects involving the intravenous administration of either placebo or tariquidar (150 mg over a period of 30 minutes) on 2 study days 2 weeks apart. On both days, a 1-hour ERBT was performed, followed by determination of midazolam's systemic clearance after a 1-mg intravenous dose. RESULTS: Tariquidar increased the ERBT 1-hour value in all subjects (median, 2.1% [interquartile range (IQR), 1.9% to 3.3%] versus 5.4% [IQR, 3.7% to 7.8%] for placebo and tariquidar, respectively; P = .012), representing a median 2.3-fold (IQR, 1.9- to 3.0-fold) increase. By contrast, midazolam's systemic clearance after tariquidar was unchanged (median change, -4.6% [IQR, -10.2% to 10.7%]; P = .78). CONCLUSIONS: Hepatic P-glycoprotein is an important determinant of the ERBT and a potentially confounding factor in interpreting the meaning of the trait measure. In addition, the results demonstrate the dynamic interplay between hepatic drug metabolism and transport of dual CYP3A/P-glycoprotein substrates.

Pharmacogenetics of efavirenz and central nervous system side effects: an Adult AIDS Clinical Trials Group study.

OBJECTIVES: Efavirenz is an effective antiretroviral agent, but central nervous system side effects occur commonly, and population (racial) differences in pharmacokinetics and response have been reported. Efavirenz is metabolized by cytochrome P4502B6 (CYP2B6). We investigated whether polymorphisms in CYP2B6, CYP3A4, CYP3A5, and MDR1 were associated with efavirenz central nervous system side effects and pharmacokinetics. DESIGN: Twenty-four week cohort from a randomized study. METHODS: Adult AIDS Clinical Trials Group study A5097s examined relationships between central nervous system side effects and efavirenz plasma concentration-time profiles in HIV-infected subjects. Efavirenz plasma pharmacokinetics were estimated by a population-based method. Central nervous system symptoms were assessed by questionnaires and neuropsychological testing. RESULTS: Study subjects included 89 (57%) European-Americans, 50 (32%) African-Americans, and 15 (10%) Hispanics. The CYP2B6 T/T genotype at position 516 (GlnHis) was more common in African-Americans (20%) than in European-Americans (3%), and was associated with greater efavirenz plasma exposure (P < 0.0001). The median efavirenz [area-under-the-curve] (0-24 h) according to G/G, G/T, and T/T genotype was 44 (n = 78), 60 (n = 60), and 130 (n = 14) mug.h/ml, respectively (P < 0.0001). The CYP2B6 G516T genotype was also associated with central nervous system symptoms at week 1 (P = 0.036). Analysis of DNA from other subjects confirmed population differences in frequency of the G516T variant. No associations were apparent with the other polymorphisms studied. CONCLUSIONS: A CYP2B6 allelic variant that is more common in African-Americans than in Europeans-Americans was associated with significantly greater efavirenz plasma exposure during HIV therapy. Inter-individual differences in metabolism may, in part, explain susceptibility to efavirenz central nervous system side effects.

Genotype-phenotype associations for common CYP3A4 and CYP3A5 variants in the basal and induced metabolism of midazolam in European- and African-American men and women.

CYP3A activity in adults varies between individuals and it has been suggested that this has a genetic basis, possibly related to variant alleles in CYP3A4 and CYP3A5 genes. Accordingly, genotype-phenotype associations were investigated under constitutive and induced conditions. Midazolam's systemic and oral clearances, and the erythromycin breath test (ERBT) were determined in 57 healthy subjects: 23 (11 men, 12 women) European- and 34 (14 men, 20 women) African-Americans. Studies were undertaken in the basal state and after 14-15 days pretreatment with rifampin. DNA was characterized for the common polymorphisms CYP3A4*1B, CYP3A5*3, CYP3A5*6 and CYP3A5*7 by direct sequencing, and for exon 21 and exon 26 variants of MDR1 by allele-specific, real-time polymerase chain reaction. In 95% of subjects, the basal systemic clearance of midazolam was unimodally distributed and variability was less than four-fold whereas, in 98% of the study population, oral clearance varied five-fold. No population or sex-related differences were apparent. Similar findings were observed with the ERBT. Rifampin pretreatment markedly increased the systemic (two-fold) and oral clearance (16-fold) of midazolam, and the ERBT (two-fold) but the variabilities were unchanged. No associations were noted between these phenotypic measures and any of the studied genotypes, except for oral clearance and its fold-increase after rifampin. These were related to the presence of CYP3A4*1B and the inversely linked CYP3A5*3 polymorphism, with the extent of induction being approximately 50% greater in CYP3A5*3 homozygotes compared to wild-type subjects. In most healthy subjects, variability in intestinal and hepatic CYP3A activity, using midazolam as an in-vivo probe, is modest and common polymorphisms in CYP3A4 and CYP3A5 do not appear to have important functional significance.

In vivo comparisons of constitutive cytochrome P450 3A activity assessed by alprazolam, triazolam, and midazolam.

BACKGROUND: Previous studies have not demonstrated good correlations between various presumed phenotypic measures of in vivo cytochrome P450 (CYP) 3A activity. However, in reality, few have used appropriate and validated in vivo probes that consider the complexities of CYP3A. Accordingly, the disposition of 3 closely related benzodiazepines with extensive and similar CYP3A-mediated metabolism characteristics but different pharmacokinetics was investigated, and correlations between the drugs were examined. METHODS: The single-dose oral clearances of alprazolam, midazolam, and triazolam and the systemic clearances of the latter 2 drugs were separately determined in 21 healthy subjects (10 men) according to a randomized experimental design with a minimum 1-week period between the individual studies. An erythromycin breath test was also performed. RESULTS: After intravenous administration, systemic clearance varied 3-fold compared with a 6-fold range in clearance after an oral dose for all 3 drugs. However, mean values differed markedly between the drugs, with the systemic clearance of midazolam being almost double that of triazolam (383 +/- 73 mL/min versus 222 +/- 54 mL/min). Oral clearances were even more dissimilar: alprazolam, 75 +/- 36 mL/min; triazolam, 360 +/- 195 mL/min; and midazolam, 533 +/- 759 mL/min. Estimates of CYP3A-mediated extraction by the intestine and liver indicated approximately equal contributions by both organs but larger values for midazolam than for triazolam, and these differences accounted for the differences in oral bioavailability, 30% +/- 13% versus 55% +/- 20%, respectively. Statistically significant ( P = .001 to .004) correlations between the 3 drugs' oral clearances ranged from 0.60 to 0.68 ( r s value), whereas the correlation for the systemic clearances of midazolam and triazolam was 0.66 ( P = .001). No statistically significant relationships were observed between any of the clearance parameters and the erythromycin breath test. CONCLUSION: Despite alprazolam, midazolam, and triazolam having markedly different pharmacokinetic characteristics, statistically significant correlations were present between the oral and systemic clearances of the 3 drugs, consistent with a major involvement of CYP3A in their metabolism and elimination. However, the magnitude of the coefficients of determination ( r s ) was such to suggest that an in vivo probe approach, even with the use of valid phenotypic trait values, will be unable to accurately and reliably predict the pharmacokinetic behavior of another CYP3A substrate, as determined by the enzyme's constitutive activity.

Cytochrome P450 2E1 and 3A activities do not differ between Mexicans and European Americans.

OBJECTIVES: Population differences in the activity of various cytochrome P450 (CYP) enzymes have been demonstrated on the basis of either genetic or environmental determinants. Hispanics are a large demographic group both worldwide and within the United States; hence the possibility of differences in metabolism between one such group-Mexicans-and a European-derived population was determined with respect to CYP2E1 and CYP3A. METHODS: Young healthy Mexican immigrants living in Los Angeles, Calif, who had maintained a traditional diet were compared with previously and identically studied groups of age-, sex-, and weight-matched European Americans who resided in middle Tennessee and ate a "western" diet (15 men and 15 women). In one study carried out in 15 women, the disposition of chlorzoxazone after an oral dose (250 mg) was compared. In the other investigation, all of the 15 subjects were men and received intravenous [(15)N(3)]-labeled midazolam (1 mg) and oral midazolam (2 mg) simultaneously to characterize the disposition of benzodiazepine in the two populations. RESULTS: Plasma concentration-time profiles of chlorzoxazone and its 6-hydroxy metabolite and the 0- to 24-hour urinary recovery of the latter were not different between Mexicans and European Americans. This indicates that CYP2E1 activity is similar in the two populations. Similarly, no significant intergroup differences were noted in the plasma concentration-time profiles of midazolam after either intravenous or oral administration. Accordingly, CYP3A does not appear to be different between Mexicans and European Americans. CONCLUSIONS: Similarity in the metabolism of chlorzoxazone between Mexicans and European Americans suggests that the risk associated with CYP2E1-mediated activation of procarcinogens is not different between these two populations. Likewise, the absence of any difference in the disposition of midazolam indicates that, from a pharmacokinetic standpoint, dosages of drugs metabolized by CYP3A need not be different between Mexicans and European Americans.

Coordinate induction of both cytochrome P4503A and MDR1 by St John's wort in healthy subjects.

BACKGROUND: Many drugs are cosubstrates of cytochrome P450 (CYP) 3A and MDR1; furthermore, their disposition is markedly affected by pretreatment with inducing agents, including St John's wort. Such drug interactions reflect induction of both proteins through a common mechanism involving the steroid X receptor/pregnane X receptor. However, the relative contributions of enhanced metabolism and efflux transport to the overall induction process are unknown. METHODS: The effects of 12 days' pretreatment with St John's wort on the disposition of selected in vivo probe drugs were determined in 21 young healthy subjects. Midazolam after oral and intravenous administration was used to assess CYP3A activity in both the intestinal epithelium and the liver, whereas the disposition of fexofenadine after an oral dose was assumed to be a measure of MDR1 function, and the oral plasma concentration-time profile of cyclosporine (INN, ciclosporin) was considered to reflect both CYP3A and MDR1 activities. RESULTS: St John's wort markedly affected the plasma concentration-time profiles of all of the drugs, with associated increases in their clearance. With midazolam, the enhancement was considerably less after intravenous administration (approximately 1.5-fold) than after oral administration (approximately 2.7-fold), and estimated intestinal and hepatic extraction ratios were higher by approximately 1.2- to 1.4-fold. By contrast, the oral clearances of fexofenadine and cyclosporine were equally increased by approximately 1.6-fold and 1.9-fold, respectively; these changes were both statistically less than for midazolam's oral clearance and greater than its estimated intestinal extraction. CONCLUSIONS: Although the disposition of all 3 drugs was altered by St John's wort, the extent of induction measured by oral clearance was different with CYP3A activity (midazolam), apparently increasing more than MDR1 function (fexofenadine), whereas with cyclosporine the change in oral clearance appeared to be more closely associated with the increase in MDR1 rather than CYP3A, despite the fact that both proteins are importantly involved in its disposition. These discordances indicate that, although a common molecular mechanism may be involved, the quantitative aspects of induction are complex and depend on the particular drug and the relative contributions of CYP3A and MDR1 in its disposition.

Population differences in S-warfarin metabolism between CYP2C9 genotype-matched Caucasian and Japanese patients.

OBJECTIVE: Our objective was to investigate population differences in the metabolic activity of cytochrome P450 (CYP) 2C9 between genotypically matched Caucasian and Japanese patients by using the unbound oral clearance of S-warfarin as an in vivo phenotypic trait measure. METHODS: Ninety Japanese and 47 Caucasian patients receiving maintenance warfarin therapy were studied. Steady-state plasma unbound concentrations of S-warfarin were measured by a chiral HPLC method coupled with an ultrafiltration technique, and unbound oral clearance for S-warfarin was estimated. By combining plasma unbound concentrations of S-warfarin with the urinary excretion rates of S-7-hydroxywarfarin, the formation clearance of S-7-hydroxywarfarin was also determined. Genotyping of CYP2C9 was performed for 6 distinct alleles (CYP2C9*1, CYP2C9*2, CYP2C9*3, CYP2C9*4, CYP2C9*5, and a T/C transition in intron 2). RESULTS: The frequency distribution of unbound oral clearance for S-warfarin obtained from Japanese patients was shifted toward higher values as compared with that in Caucasian patients. Japanese patients had lower allelic frequencies for the 5 variants than Caucasian patients. When interpopulation comparisons of CYP2C9 activity were made for genotype-matched subjects, Japanese patients with the homozygous CYP2C9*1 (wild-type) genotype (n = 85) had significantly (P <.01) greater median values for unbound oral clearance and formation clearance than Caucasian patients with the corresponding genotype (n = 26), 10.4 mL x min(-1) x kg(-1) versus 4.25 mL x min(-1) x kg(-1) and 0.015 mL x min(-1) x kg(-1) versus 0.010 mL x min(-1) x kg(-1), respectively. In addition, Japanese patients heterozygous for the CYP2C9*3 genotype (n = 4) showed a significantly (P <.05) reduced unbound oral clearance for S-warfarin, by 63%, as compared with Japanese patients possessing the homozygous CYP2C9*1 genotype. By contrast, in Caucasian patients, no significant differences were observed in this parameter between CYP2C9(*)1 homozygous subjects and those with heterozygous CYP2C9(*)2 or CYP2C9(*)3 genotypes. CONCLUSIONS: These findings indicate that population differences in the frequencies of known variant CYP2C9 alleles account only in part for the variability observed in in vivo CYP2C9 activity in different populations. In addition, a gene-dose effect of defective CYP2C9 alleles on the in vivo CYP2C9 activity is evident in Japanese patients but not in Caucasian patients. Further studies are required to identify currently unknown factor(s) (eg, transcriptional regulation) responsible for the large intrapopulation and interpopulation variability in CYP2C9 activity.

Genetic variability in CYP3A5 and its possible consequences.

The cytochrome P450 3A (CYP3A) subfamily members are the most abundant and important drug-metabolizing enzymes in humans, and wide interindividual variability in CYP3A expression and function is present. CYP3A4 alone cannot fully explain the observed constitutive variability because its genetic variants are relatively uncommon and have limited functional significance, whereas CYP3A5 expression in humans is highly variable and may be contributory. However, it is difficult to delineate the relative contribution of CYP3A4 and CYP3A5, and to differentiate their effects on drug metabolism as their protein structure, function and substrates are so similar. By contrast, molecular biology methods provide the ability to identify CYP3A4 and CYP3A5 genotypes with certainty. This review collates currently available data on CYP3A5 polymorphisms, provides information on the population frequency of each genetic variant in major ethnic groups, and describes in vitro and in vivo studies that have attempted to identify genotype-phenotype associations.

A multi-investigator/institutional DNA bank for AIDS-related human genetic studies: AACTG Protocol A5128.

BACKGROUND: An understanding of the relationships among allelic variability and clinical outcomes will be critical if HIV-infected patients are to benefit from the explosion in knowledge in human genomics. Human DNA banks must allow future analyses while addressing confidentiality, ethical, and regulatory issues. METHOD: A multidisciplinary group of clinical investigators, ethicists, data managers, regulatory specialists, and community representatives developed Adult AIDS Clinical Trials Group (AACTG) Protocol A5128. Participants in past or present AACTG clinical trials may contribute DNA. Extraction from whole blood is performed at a central laboratory, where participants' unique identifiers are replaced by randomly assigned identifiers prior to DNA storage. To identify genotype-phenotype relationships, genetic assay results can be temporarily linked to clinical trials data. RESULTS: Institutional review boards in 21 states and Puerto Rico have approved Protocol A5128, and accrual is ongoing. Of the first 4,247 enrollees, 82% are male, 56% are white, 26% are African American, and 15% are Hispanic. Because participants may participate in multiple AACTG protocols, these represent 11,424 cases in 324 different AACTG studies and substudies, with at least 100 participants from 24 different studies. Studies exploring specific genotype-phenotype relationships are underway. CONCLUSION: The AACTG DNA bank will be an important resource for genomic discovery relevant to HIV therapy.

Single plasma concentrations of 1'-hydroxymidazolam or the ratio of 1'-hydroxymidazolam:midazolam do not predict midazolam clearance in healthy subjects.

The 30-minute ratio of 1'-hydroxymidazolam:midazolam plasma concentrations has been used as a measure of midazolam clearance in liver transplant patients. This study determined if a single concentration of 1'-hydroxymidazolam or the ratio of 1'-hydroxymidazolam:midazolam could be used to predict midazolam clearance in healthy subjects. Plasma midazolam and 1'-hydroxymidazolam concentrations from three previous studies were used for analyses. Data obtained predose and at 5, 30, 60, 120, 240, 300, and 360 minutes following intravenous doses of midazolam in 61 adults were divided and used to derive and validate equations to predict midazolam clearance. Equations were derived using linear regression and then validated by comparing predicted to observed clearance. Only one equation was related to midazolam clearance as afunction of 1'-hydroxymidazolam, but it did not predict midazolam clearance (r = 0.29, p = 0.31). Single sampling of 1'-hydroxymidazolam or 1'-hydroxymidazolam:midazolam plasma concentrations cannot be used to predict midazolam clearance in healthy adults.

Limited sampling strategy to predict AUC of the CYP3A phenotyping probe midazolam in adults: application to various assay techniques.

Midazolam clearance is used to phenotype hepatic CYP3A activity but requires multiple plasma samples following a single intravenous dose. The authors evaluated the use of a limited sampling scheme, using different assay techniques to determine the reproducibility of such a strategy in estimating midazolam AUC. Seventy-three healthy adults received midazolam as a single intravenous bolus dose. At least eight plasma samples were collected from each subject and were assayed using either LC/MS/MS or electron capture gas chromatography. Eleven subjects were randomly selected for the training set using stepwise linear regression to determine relationships between midazolam plasma concentrations and AUC. Validation of the predictive equations was done using the remaining 62 subjects. Mean percent error (MPE), mean absolute error (MAE), and root mean square error (RMSE) were calculated to determine bias and precision. Based on the training set, five models were generated with coefficients of determination ranging from 0.87 to 0.95. Validation showed that MPE, MAE, and RMSE values were acceptable for three of the models. Intrasubject reproducibility was good. In addition, training set datafrom one institution were able to predict data from the other two institutions using other assay techniques. Minimized plasma sampling mayprovide a simpler method for estimating midazolam AUC for CYP3A phenotyping. A limited sampling strategy is more convenient and cost-effective than standard sampling strategies and is applicable to more than one assay technique.