Impact of highly concentrated contaminants on the quality of oxygen 93 % produced by pressure swing adsorption.

A zeolite based pressure swing adsorption (PSA) module designed to produce medicinal oxygen with 90 - 96 % oxygen content was exposed to high input concentrations and high total amounts of CO (17.7 %, 44 mol), CO2 (16.5 %, 23 mol), NO2 (0.98 %, 2 mol), NO (6.2 %, 6 mol) and SO2 (4.2 %, 6 mol). In addition the system was operated with up to 35 % argon in the feed gas. An empirical model was developed to describe the dependence of the oxygen concentration in the product on the oxygen concentration in the input. If the oxygen concentration in the feed gas was reduced below 18 % by dilution, the oxygen concentration in the product fell under the 90 % threshold. Additional effects were observed with NO, NO2 and SO2 which are apparently due to chemical reactions on the adsorbent. These effects consisted of a further decrease in the oxygen concentration measured in the product and could not be reversed by excessive regeneration of the module with air. Under the experimental conditions used, only CO was detected in the product. Appropriate CO monitoring of the input gas is considered a possible remedy for PSA modules in order to ascertain the pharmaceutical quality of the oxygen produced.

Effects of OCT1 polymorphisms on the cellular uptake, plasma concentrations and efficacy of the 5-HT(3) antagonists tropisetron and ondansetron.

After uptake into liver cells, the antiemetic drugs tropisetron and ondansetron undergo metabolic inactivation by cytochrome P450 2D6 (CYP2D6). We investigated whether the hepatic organic cation transporter 1 (OCT1; SLC22A1) mediates cellular uptake and whether common OCT1 loss-of-function polymorphisms affect pharmacokinetics and efficacy of both drugs. Both tropisetron and ondansetron inhibited ASP(+) uptake in OCT1-overexpressing HEK293 cells. Overexpression of wild-type, but not OCT1 loss-of-function variants, significantly increased tropisetron uptake. Correspondingly, patients with two loss-of-function OCT1 alleles had higher tropisetron plasma concentrations (n=59, P<0.04) and higher clinical efficacy (n=91, P=0.009) compared with carriers of fully active OCT1. Overexpression of OCT1 did not increase ondansetron uptake. Nevertheless, OCT1 genotypes correlated with pharmacokinetics (n=45, P<0.05) and clinical efficacy (n=222, P<0.02) of ondansetron, the effect size of OCT1 genotypes on pharmacokinetics and efficacy was greater for tropisetron than for ondansetron. In conclusion, in addition to the known effects of CYP2D6, OCT1 deficiency may increase efficacy of tropisetron and potentially of ondansetron by limiting their hepatic uptake.

The effects of genetic polymorphisms in the organic cation transporters OCT1, OCT2, and OCT3 on the renal clearance of metformin.

Organic cation transporters (OCTs) can mediate metformin transmembrane transport. We explored metformin pharmacokinetics in relation to genetic variations in OCT1, OCT2, OCT3, OCTN1, and MATE1 in 103 healthy male Caucasians. Renal clearance varied 3.8-fold and was significantly dependent on creatinine clearance (r(2) = 0.42, P < 0.0001), age (r(2) = 0.09, P = 0.002), and OCT1 polymorphisms. Carriers of zero, one, and two low-activity OCT1 alleles (Arg61Cys, Gly401Ser, 420del, or Gly465Arg) had mean renal clearances of 30.6, 33.1, and 37.1 l/h, respectively (P = 0.04, after adjustment for creatinine clearance and age). Immunohistochemical staining of human kidneys demonstrated OCT1 expression on the apical side of proximal and distal tubules. Increased renal clearance, in parallel with the known decreased hepatic uptake, may contribute to reduced metformin efficacy in low-activity genotypes. Renal OCT1 expression may be important not only in relation to metformin but with respect to other drugs as well.

Relative impact of genotype and enzyme induction on the metabolic capacity of CYP2C9 in healthy volunteers.

Pharmacokinetics in individual subjects is determined by genes and environment. The relative contributions of enzyme induction and inherited genomic variation to cytochrome P450 enzyme 2C9 (CYP2C9) activity are unknown. In 130 volunteers, CYP2C9 activity was measured in vivo using tolbutamide as a probe drug. Tolbutamide was administered orally, and the pharmacokinetics of the drug was analyzed twice--before and after four doses of 450 mg rifampin. Mean total apparent clearances (Cl/F) in the genotype groups CYP2C9*1/*1, *1/*2, *1/*3, *2/*3, and *3/*3 before rifampin were 0.78, 0.74, 0.52, 0.40, and 0.13 l/h, respectively. After rifampin administration, these clearances increased in all genotype groups by a median factor of 1.9 (range 1.1-4.8). The combined effects of genes and environment could be predicted by a simple additive model. Thus, enzyme induction resulted in an approximately twofold difference in CYP2C9 activity, irrespective of the CYP2C9 genotypes. But the difference in activity levels between the CYP2C9*1/*1 and *3/*3 genotypes before the administration of rifampin was sixfold.

Interindividual variation in the pharmacokinetics of Delta9-tetrahydrocannabinol as related to genetic polymorphisms in CYP2C9.

The impact of the CYP2C9 polymorphism on the pharmacokinetics of orally administered 9-tetrahydrocannabinol (THC) was studied in 43 healthy volunteers. THC pharmacokinetics did not differ by CYP2C9*2 allele status. However, the median area under the curve of THC was threefold higher and that of 11-nor-9-carboxy-9-tetrahydrocannabinol was 70% lower in CYP2C9*3/*3 homozygotes than in CYP2C9*1/*1 homozygotes. CYP2C9*3 carriers also showed a trend toward increased sedation following administration of THC. Therefore, the CYP2C9*3 variant may influence both the therapeutic and adverse effects of THC.

Population pharmacokinetics of sevoflurane in conjunction with the AnaConDa: toward target-controlled infusion of volatiles into the breathing system.

BACKGROUND: The Anesthetic Conserving Device (AnaConDa) uncouples delivery of a volatile anesthetic (VA) from fresh gas flow (FGF) using a continuous infusion of liquid volatile into a modified heat-moisture exchanger capable of adsorbing VA during expiration and releasing adsorbed VA during inspiration. It combines the simplicity and responsiveness of high FGF with low agent expenditures. We performed in vitro characterization of the device before developing a population pharmacokinetic model for sevoflurane administration with the AnaConDa, and retrospectively testing its performance (internal validation). MATERIALS AND METHODS: Eighteen females and 20 males, aged 31-87, BMI 20-38, were included. The end-tidal concentrations were varied and recorded together with the VA infusion rates into the device, ventilation and demographic data. The concentration-time course of sevoflurane was described using linear differential equations, and the most suitable structural model and typical parameter values were identified. The individual pharmacokinetic parameters were obtained and tested for covariate relationships. Prediction errors were calculated. RESULTS: In vitro studies assessed the contribution of the device to the pharmacokinetic model. In vivo, the sevoflurane concentration-time courses on the patient side of the AnaConDa were adequately described with a two-compartment model. The population median absolute prediction error was 27% (interquartile range 13-45%). CONCLUSION: The predictive performance of the two-compartment model was similar to that of models accepted for TCI administration of intravenous anesthetics, supporting open-loop administration of sevoflurane with the AnaConDa. Further studies will focus on prospective testing and external validation of the model implemented in a target-controlled infusion device.

Population pharmacokinetics of melphalan and glutathione S-transferase polymorphisms in relation to side effects.

Melphalan is associated with severe side effects such as mucositis, diarrhea, and myelosuppression. We investigated how much the individual severity of these side effects is predicted by pharmacokinetics. In addition, we studied glutathione S-transferase GSTM1, GSTT1, and GSTP1 polymorphisms in relation to adverse events. A high interindividual pharmacokinetic variability was observed in 84 patients. There was a linear correlation between creatinine and melphalan clearance (P=0.0004). Patients treated with a dose > or = 70 mg/m(2) had a 23-fold increased risk to develop mucositis (P<0.001) and a 12-fold increased risk to develop diarrhea (P<0.001) compared with lower doses. The GSTP1 codon 105 polymorphism may be relevant for development of mucositis and the GSTT1 deletion may predict diarrhea, but these findings require confirmation. Melphalan-induced side effects were significantly dependent only on dose. Therapeutic drug monitoring or genotyping for GST does not appear to be very helpful in optimizing therapy with melphalan.

Genetic variation in the renal sodium transporters NKCC2, NCC, and ENaC in relation to the effects of loop diuretic drugs.

There is little data on genetic predictors of loop diuretic efficacy in humans. Therefore, we investigated the diuretic effects of single oral doses of bumetanide, frusemide, and torsemide in a crossover study in 97 healthy Caucasians in relation to genetic variation in the renal sodium transporters NKCC2 (coded by SLC12A1), NCC (SLC12A3), and ENaC (three subunits coded by SCNN1A, SCNN1B, and SCNN1G). The NCC alanine 264 allele (Gly264Ala) and the most frequent SCNN1B haplotype were associated with stronger diuresis, indicating lower reabsorbing function of these alleles. The variant alleles of the tightly coupled polymorphisms rs5723 (Leu649Leu) and rs5729 in SCNN1G were associated with weaker diuresis, indicating higher activity. Extended haplotype homozygosity implied evolutionary selection of the NCC alanine 264 allele. In conclusion, acute diuretic effects of loop diuretics were affected by genetic variation in sodium transporters that, in the nephron, are located distally from NKCC2.

Pharmacokinetics of mirtazapine: enantioselective effects of the CYP2D6 ultra rapid metabolizer genotype and correlation with adverse effects.

Enantiomerically pure drugs and genotyping are promising approaches to achieve optimization in antidepressant therapy. Mirtazapine is a mixed noradrenergic serotoninergic antidepressant used as a racemate. We analyzed pharmacokinetics of its enantiomers in relation to CYP2D6 genotype and in relation to its adverse effects. Mirtazapine was enantioselectively absorbed from the gut with a rate constant of 0.2 min-1 for S+, but 0.08 min-1 for R- mirtazapine. Kinetics of R- mirtazapine was only marginally dependent on CYP2D6 genotype, but total clearance of the S+ enantiomer were 1.3, 2.3, and 3.4 L min-1 in poor, extensive, and ultrarapid metabolizers of CYP2D6 substrates with apparent substantial first-pass metabolism in rapid and ultrarapid metabolizers. Mirtazapine effects on heart rate and blood pressure correlated much more strongly with R- then with S+ concentrations, whereas sedation correlated similarly with both enantiomers. At least concerning some adverse effects, it might be worthwhile to study further mirtazapine enantiospecifically.

Genetic variation at the CYP2C locus and its association with torsemide biotransformation.

In 97 unselected volunteers and two additional homozygous carriers of CYP2C9(*)3, we investigated the oral clearance of torsemide in relation to 37 polymorphisms at the CYP2C gene locus. Torsemide total oral clearance was linearly associated with the number of CYP2C9(*)3 alleles (geometric mean: 59, 40 and 20 ml/min in carriers of no, one and two alleles) and so were the methyl- and ring-hydroxylation but not the carboxylation clearance. Haplotypes including the CYP2C9(*)3 allele were similarly associated with the clearances but no other variant and no haplotype not including the CYP2C9(*)3 variant. The extended haplotype length (EHL) of the CYP2C9 haplotypes was positively associated with higher activity of the gene product. Torsemide total oral clearance was predictable with r(2)=82.1% using plasma concentrations at 0.5, 1, 2 and 24 h. In conclusion, torsemide's biotransformation strongly depended on the CYP2C9(*)3 variant but no other. Higher clearance CYP2C9 haplotypes appear to be evolutionarily selected.

Region specific distribution of levomepromazine in the human brain.

OBJECTIVE: The aim of this study was to examine concentrations of levomepromazine and its metabolite desmethyl-levomepromazine in different regions of human brain and in relationship to drug-free time. METHODS: Drug concentrations were measured in up to 43 regions of 5 postmortem human brains of patients previously treated with levomepromazine. To enable statistical comparison across brain regions several smaller brain areas were put together to form larger brain areas (cortex cerebri, limbic system, cerebellum, basal ganglia, thalamus). Mean values of drug concentrations in these larger brain areas were used in a repeated measurement ANOVA to analyze for region specific distribution. The elimination half-life in brain tissue was estimated with a NONMEM population kinetic analysis using the mean value of all brain regions of an individual case. RESULTS: Levomepromazine and desmethyl-levomepromazine appear to accumulate in human brain tissue relative to blood. Mean concentrations differed largely between individual brains, in part due to differences in dose of drug, duration of treatment and drug-free time before death. There was an apparent region-specific difference in levomepromazine concentrations with highest values in the basal ganglia (mean 316 ng/g) and lowest values in the cortex cerebri (mean 209 ng/g). The elimination half-life from brain tissue is longer than from blood and was calculated to be about one week. Similar results were obtained with desmethyl-levomepromazine. CONCLUSIONS: Levomepromazine shows a region-specific distribution in the human brain with highest values in the basal ganglia. This might be the consequence of low expression of the metabolic enzyme Cyp2D6 in the basal ganglia. If this finding is true also for other neuroleptic drugs it might increase our understanding of preferential toxicity of neuroleptic drugs against basal ganglia structures and higher volumes of basal ganglia of neuroleptic-treated patients. Furthermore, patients exposed to levomepromazine cannot be considered to be free of residual effects of the drug for a number of weeks after withdrawal.

Pharmacokinetics of doxepin and desmethyldoxepin: an evaluation with the population approach.

OBJECTIVE: Little information on the population pharmacokinetics of the tricyclic antidepressant doxepine and its pharmacologically active metabolite desmethyldoxepine is available. However, a more individualised drug therapy may be feasible if the influence of various patient characteristics on plasma concentration was known. PATIENTS AND METHODS: We retrospectively analysed pharmacokinetic therapeutic drug-monitoring data in 114 psychiatric patients (79 females, 35 males) treated with doxepine for a period of 22-306 days, mostly due to major depression. The data were analysed using the computer program NONMEM. For both, doxepine and its metabolite desmethyldoxepine, a one-compartment model was chosen. Pharmacokinetic parameters clearance (CL/F) and volume of distribution (V/F) of doxepine and desmethyldoxepine were modelled in terms of both random and fixed effects. RESULTS: The fit of the model to the concentration-time data was significantly improved when V/F was expressed as a function of weight ( P<0.05) and CL/F as a function of age ( P<0.05). Co-medication that inhibits P(450) isoenzymes lowered CL/F of doxepine by 15%. CONCLUSION: The analysis indicates that the factors age and, to some extent, body weight may be a guidance for individual doxepine dose regimens, which however needs confirmation in prospective clinical trials linking pharmacokinetics and therapeutic effect. Co-medication may represent only a minor important covariate.

A cell-kinetic model of CD34+ cell mobilization and harvest: development of a predictive algorithm for CD34+ cell yield in PBPC collections.

BACKGROUND: Mobilization and homing of PBPCs are still poorly understood. Thus, a sufficient algorithm for the prediction of PBPC yield in apheresis procedures does not yet exist. STUDY DESIGN AND METHODS: The decline of CD34+ cells in the peripheral blood during apheresis and their simultaneous increase in the collection bag were determined in a prospective study of 18 consecutive apheresis procedures. A cell-kinetic, four-compartment model describing these changes was developed. Retrospective data from 136 apheresis procedures served to further improve this model. A predictive algorithm for the yield was developed that considered the sex, weight, and height of the patient, the number of CD34+ cells in peripheral blood before apheresis, the inlet flow, and the duration of the apheresis. The accuracy of this algorithm was evaluated by comparison of the predicted and the observed yields of CD34+ cells in 105 prospective autologous and 148 retrospective allogeneic apheresis procedures. RESULTS: The correlation between predicted and observed yields was good for the autologous and allogeneic groups with a correlation coefficient (r) of 0.8979 and 0.8311 (p<0.0001), respectively. The regression is described by the equations log (measured value [m]) = 1.0118 + 0.8595 x log (predicted value [p]) for the autologous and log (m) = 2.226 + 0.7559 x log (p) for the allogeneic group. The respective equations for the zero-point regression are log (m) = 1.014 x log (p) and log (m) = 1.026 x log (p). The probability that the measured value was 90 percent or more of the predicted value was 83.8 percent for the autologous and 90.5 percent for the allogeneic apheresis procedures. CONCLUSION: The predictive accuracy of the algorithm and the slope of the zero-point regression curve were higher for allogeneic than autologous PBPC collections. The predictive algorithm may be a useful tool in PBPC harvest, enabling the adaptation of the size of the apheresis to the needs of each patient.

An add-in implementation of the RESAMPLING syntax under Microsoft EXCEL.

The RESAMPLING syntax defines a set of powerful commands, which allow the programming of probabilistic statistical models with few, easily memorized statements. This paper presents an implementation of the RESAMPLING syntax using Microsoft EXCEL with Microsoft WINDOWS(R) as a platform. Two examples are given to demonstrate typical applications of RESAMPLING in biomedicine. Details of the implementation with special emphasis on the programming environment are discussed at length. The add-in is available electronically to interested readers upon request. The use of the add-in facilitates numerical statistical analyses of data from within EXCEL in a comfortable way.

Measurement of free and bound malondialdehyde in plasma by high-performance liquid chromatography as the 2,4-dinitrophenylhydrazine derivative.

We established a method for the detection of free and total (free and bound) malondialdehyde (MDA) in human plasma samples after derivatisation with 2,4-dinitrophenylhydrazine (DNPH). Free MDA was prepared by perchloric acid deproteinisation whereas an alkaline hydrolysation step for 30 min at 60 degrees C was introduced prior to protein precipitation for the determination of total MDA. Derivatisation was accomplished in 10 min at room temperature subsequently chromatographed by HPLC on a reversed-phase 3 microm C(18) column with UV detection (310 nm). The detection limit was 25 pmol/ml for free and 0.3 nmol/ml for total MDA. The recovery of MDA added to different human plasma samples was 93.6% (n=11; RSD 7.1%) for the hydrolysation procedure. In samples from 12 healthy volunteers who underwent a hypoxic treatment (13% O2 for 6 h) we estimated a baseline value of total MDA of 2.16 nmol/ml (SD 0.29) (ambient air) with a significant increase to 2.92 (nmol/ml, SD 0.57; P=0.01) after the end of this physiological oxidative stress challenge. Plasma values of free MDA in these samples were close to our detection limit. The presented technique can easily performed with an isocratic HPLC apparatus and provides highly specific results for MDA as do sophisticated GC-MS methods.

Increased psychological responses and divergent neuroendocrine responses to m-CPP and ipsapirone in patients with panic disorder.

In patients with panic disorder and /or agoraphobia (PDA) an increased sensitivity of central 5-HT2C receptors and a decreased responsiveness of 5-HT1A receptors has been postulated. In the present study, neuroendocrine challenges were performed using oral doses of the non-selective 5-HT2C agonist m-chlorophenylpiperazine (m-CPP) (0.4 mg/kg), the selective 5-HT1A antagonist ipsapirone (0.3 mg/kg), and placebo in 40 patients with PDA and 12 healthy controls in order to compare 5-HT2C and 5-HT1A-specific psychobehavioural and neuroendocrine response patterns. At baseline, all psychobehavioural variables and the plasma concentration of noradrenaline (NE) were significantly increased in the patient group compared to the controls. The administration of m-CPP or ipsapirone was followed by comparable psychological symptoms and, in 55% of all patients, panic attacks. In comparison to the control subjects, patients were characterized by significantly higher psychological reactions to both challenge agents and a significantly higher NE response to m-CPP. In the patient group, there was also a trend towards an increased cortisol response after administration of m-CPP and a decreased cortisol and hypothermia response after administration of ipsapirone compared to the control group. The neuroendocrine findings of our study support earlier reports of opposite changes in the responsiveness of 5-HT2C and 5-HT1A-related receptors in PDA patients. The behavioural hypersensitivity to both, m-CPP and ipsapiron, shows that the provocation of anxiety and other psychological symptoms might be influenced by

Persistence of haloperidol in human brain tissue.

OBJECTIVE: After discontinuation of neuroleptic drugs, their antipsychotic and antiparkinsonian effects are still present for a prolonged period. It is not known whether the extended effects of neuroleptic drugs in humans are due to the continued presence of drug in brain tissue or to long-lasting drug-induced physiologic changes. The aim of this study was to directly examine haloperidol concentrations in human brain tissue in relation to drug-free time. METHOD: Haloperidol concentrations were measured in five regions (temporal cortex, cingulate gyrus, caudate nucleus, dentate nucleus, corpus callosum) of the postmortem brains of 11 patients previously treated with haloperidol. Haloperidol was analyzed by means of high-performance liquid chromatography with ultraviolet detection. The half-life in brain tissue was estimated by a population kinetic analysis. RESULTS: Haloperidol concentrations in the human brain tissue were 10-30 times higher than optimal serum concentrations used in the treatment of schizophrenia. Haloperidol concentrations appeared to be homogeneously distributed across different brain areas within a single patient. There was no apparent relation between duration of treatment and mean haloperidol concentration. Higher doses of haloperidol seemed to be related to higher concentrations in brain tissue. The elimination half-life from brain tissue was calculated to be 6.8 days. CONCLUSIONS: The results may have implications for clinical treatment decisions and the design of clinical research protocols. Patients exposed to haloperidol cannot be considered to be free of residual effects of the drug for a number of weeks after withdrawal.

Population pharmacokinetics of piritramide in surgical patients.

BACKGROUND: Piritramide is a synthetic opioid used for postoperative analgesia in several European countries. The authors present a mixed-effects model of its population pharmacokinetics in patients undergoing surgery. METHODS: After institutional approval and informed patient consent was obtained, 29 patients who were classified as American Society of Anesthesiologists physical status I or II and aged 21-82 yr were enrolled in the study. They received 0.2 mg/kg piritramide as an intravenous bolus before anesthesia was induced. Central venous blood samples were drawn for as long as 48 h after administration of the drug. The plasma concentration of piritramide was determined by gas chromatography. The concentration-time data were analyzed by mixed-effects modeling. Target-controlled infusions and intermittent bolus regimens were simulated to identify a regimen suitable for patient-controlled analgesia based on population pharmacokinetics and published pharmacodynamic data. RESULTS: The pharmacokinetics of piritramide were described adequately by a linear three-compartment model. Patient age and weight were significant covariates. The values of the pharmacokinetic parameters are: V1 = 50.5 [1], V2 = 150 x (1 + 9.32 x 10(-3) x (age - 47 yr)) [l], V3 = 212 x (1 + 6.37 x 10(-3) x (age - 47 yr)) [l], Cl1 = 0.56 x (1 - 6.14 x 10(-3) x (age - 47 yr)) [l/min], Cl2 = 8.25 x (1 + 2.02 x 10(-2) x (Wt - 74 kg)) [l/min], Cl3 = 0.80 [l/min]. The age of 47 yr and the weight of 74 kg refer to the median values for these factors in the patients studied. Rapid distribution, slow distribution, and elimination half-lives for the median patient are 0.05, 1.34, and 10.43 h, respectively. The context-sensitive half-time after a 24-h infusion is predicted at 10.5 h in a 75-yr-old patient compared with 7 h for the median patient. CONCLUSIONS: Piritramide is distributed extensively and eliminated slowly. The pharmacokinetic profile of the drug allows for intermittent bolus administration even when constant effect compartment concentrations are desirable, e.g., for PLA.