Personal exposure assessment of pesticides in residents: The association between hand wipes and urinary biomarkers.

BACKGROUND: Residential exposure to pesticides may occur via inhalation of airborne pesticides, direct skin contacts with pesticide-contaminated surfaces, and consumption of food containing pesticide residues. The aim was to study the association of dermal exposure to pesticides between the use and non-use periods, between farmer and non-farmer families and between dermal exposure and the excretion of metabolites from urine in residents living close to treated agricultural fields. METHODS: In total, 112 hand wipes and 206 spot urine samples were collected from 16 farmer and 38 non-farmer participants living within 50 m from an agricultural field in the Netherlands. The study took place from May 2016 to December 2017 during the use as well as the non-use periods of pesticides. Hand wipes were analysed for the parent compound and urines samples for the corresponding urinary metabolite of five applied pesticides: asulam, carbendazim (applied as thiophanate-methyl), chlorpropham, prochloraz and tebuconazole. Questionnaire data was used to study potential determinants of occurrence and levels of pesticides in hand wipes according to univariate and multivariate analysis. RESULTS: Carbendazim and tebuconazole concentrations in hand wipes were statistically significantly higher in the pesticide-use period compared to the non-use period. In addition, especially during the use periods, concentrations were statistically significantly higher in farmer families compared to non-farmer families. For asulam, chlorpropham and prochloraz, the frequency of non-detects was too high (57-85%) to be included in this analysis. The carbendazim contents in urine samples and hand wipes were correlated on the first and second day after taking the hand wipe, whereas chlorpropham was only observed to be related on the second day following the spray event. CONCLUSIONS: Concentrations in hand wipes were overall higher in pesticide use periods compared to non-use periods and higher in farmer families compared to non-farmer families. Only for carbendazim a strong correlation between concentrations in hand wipes and its main metabolite in urine was observed, indicating dermal exposure via contaminated indoor surfaces. We expect this to be related to the lower vapour pressure and longer environmental lifetime of carbendazim compared to the other pesticides studies.

Developmental patterns in human blood-brain barrier and blood-cerebrospinal fluid barrier ABC drug transporter expression.

When drugs exert their effects in the brain, linear extrapolation of doses from adults could be harmful for children as the blood-brain barrier (BBB) and blood-CSF barrier (BCSFB) function is still immature. More specifically, age-related variation in membrane transporters may impact brain disposition. As human data on brain transporter expression is scarce, age dependent [gestational age (GA), postnatal age (PNA), and postmenstrual age (PMA)] variation in immunohistochemical localization and staining intensity of the ABC transporters P-glycoprotein (Pgp), breast cancer resistance protein (BCRP), and multidrug resistance-associated proteins 1, 2, 4, and 5 (MRP1/2/4/5) was investigated. Post mortem brain cortical and ventricular tissue was derived from 23 fetuses (GA range 12.9-39 weeks), 17 neonates (GA range 24.6-41.3 weeks, PNA range 0.004-3.5 weeks), 8 children (PNA range 0.1-3 years), and 4 adults who died from a wide variety of underlying conditions. In brain cortical BBB, immunostaining increased with age for Pgp and BCRP, while in contrast, MRP1 and MRP2 staining intensity appeared higher in fetuses, neonates, and children, as compared to adults. BCSFB was positively stained for Pgp, MRP1, and MRP2 and appeared stable across age, while BCRP was not detected. MRP4 and MRP5 were not detected in BBB or BCSFB. In conclusion, human BBB and BCSFB ABC membrane transporters show brain location and transporter-specific maturation.

Toxicokinetics of a urinary metabolite of tebuconazole following controlled oral and dermal administration in human volunteers.

Tebuconazole (TEB) is a widely used triazole fungicide, but the toxicokinetics of its human metabolites are not fully described. For proper interpretation of biological monitoring data, knowledge on the metabolism and elimination of the compound is required. A human volunteer study was performed with the aim to describe the time courses of urinary excretion after controlled oral and dermal administration of TEB. Six healthy volunteers (three males and three females) received on separate occasions a single oral dose of 1.5 mg of TEB and a single dermal dose of 2.5 mg during 1 h. In addition to a pre-exposure urine sample, complete urine voids were collected over 48 h post-administration. The main metabolite hydroxy-tebuconazole (TEB-OH) was quantified in each urine sample. Peak excretion rates after oral and dermal administration were reached after 1.4 and 21 h, mean elimination half-lives were 7.8 and 16 h, and recoveries within 48 h were 38% and 1%, respectively. The time courses of excretion were compared to simulations with an established physiologically based toxicokinetic model for TEB that was extended with a parallel model for TEB-OH. Overall, TEB-OH was rapidly excreted into urine after oral exposure, and renal elimination was considerably slower after dermal exposure. Urinary time courses between individuals were similar. The model predictions were in good agreement with the observed time courses of excretion.

The effect of dipyridamole on the pharmacokinetics of metformin: a randomized crossover study in healthy volunteers.

PURPOSE: Concomitant treatment with the glucose-lowering drug metformin and the platelet aggregation inhibitor dipyridamole often occurs in patients with type 2 diabetes mellitus who have suffered a cerebrovascular event. The gastrointestinal uptake of metformin is mediated by the human equilibrative nucleoside transporter 4 (ENT4), which is inhibited by dipyridamole in preclinical studies. We hypothesized that dipyridamole lowers the plasma exposure to metformin. METHODS: Eighteen healthy volunteers (mean age 23 years; 9 male) were randomized in an open-label crossover study. Subjects were allocated to treatment with metformin 500 mg twice daily in combination with dipyridamole slow-release 200 mg twice daily or to metformin alone for 4 days. After a washout period of 10 days, the volunteers were crossed over to the alternative treatment arm. Blood samples were collected during a 10-h period after intake of the last metformin dose. The primary endpoint was the area under the plasma concentration-time curve (AUC0-12h) and the maximum plasma metformin concentration (C max). RESULTS: In healthy subjects, dipyridamole did not significantly affect Cmax nor AUC0-12h of metformin under steady-state conditions. CONCLUSIONS: Previous in vitro studies report that dipyridamole inhibits the ENT4 transporter that mediates gastrointestinal uptake of metformin. In contrast, co-administration of dipyridamole at therapeutic dosages to healthy volunteers does not have a clinically relevant effect on metformin plasma steady-state exposure. This observation is reassuring for patients who are treated with this combination of drugs.

Exposure to total and protein-unbound rifampin is not affected by malnutrition in Indonesian tuberculosis patients.

Nutritional status may have a profound impact on the pharmacokinetics of drugs, yet only few data are available for tuberculosis (TB) drugs. As malnutrition occurs frequently among TB patients, we assessed the effect of malnutrition on the steady-state pharmacokinetics of total and protein-unbound rifampin during the intensive phase of TB treatment. In a descriptive pharmacokinetic study in Bandung, Indonesia, patients received a fixed standard rifampin dose of 450 mg once daily during the intensive phase of TB treatment. A full pharmacokinetic curve for rifampin was recorded, and total and unbound concentrations of rifampin were analyzed in all samples. Rifampin pharmacokinetic parameters were compared between severely malnourished (BMI of <16.0 kg/m(2)), malnourished (BMI of <18.5 kg/m(2)), and well-nourished (BMI of ≥18.5 kg/m(2)) individuals. No difference in total and protein-unbound pharmacokinetic parameters between severely malnourished (n = 7), malnourished (n = 11), and well-nourished (n = 25) patients could be demonstrated. In addition, no significant correlation between BMI and exposure (area under the concentration-time curve from 0 to 24 h [AUC0-24] and maximum concentration of drug in serum [Cmax]) was found. Females had significantly higher total AUC0-24 (geometric mean, 59.2 versus 48.2 h · mg/liter; P = 0.02) and higher unbound AUC0-24 (geometric mean, 6.2 versus 4.8 h · mg/liter; P = 0.02) than males. Overall, a marked 2-fold interindividual variation in the free fraction was observed (7.6 to 15.0%; n = 36). Nutritional status and BMI do not appear to have a major effect on total and protein-unbound pharmacokinetic parameters of rifampin in Indonesian subjects. The large interindividual variability in the free fraction of rifampin suggests that protein-unbound rather than total rifampin concentrations should preferably be used to study exposure-response relationships.

Drug-drug interactions between rosuvastatin and oral antidiabetic drugs occurring at the level of OATP1B1.

Organic anion-transporting polypeptide 1B1 (OATP1B1) is an important hepatic uptake transporter, of which the polymorphic variant OATP1B1*15 (Asn130Asp and Val174Ala) has been associated with decreased transport activity. Rosuvastatin is an OATP1B1 substrate and often concomitantly prescribed with oral antidiabetics in the clinic. The aim of this study was to investigate possible drug-drug interactions between these drugs at the level of OATP1B1 and OATP1B1*15. We generated human embryonic kidney (HEK)293 cells stably overexpressing OATP1B1 or OATP1B1*15 that showed similar protein expression levels of OATP1B1 and OATP1B1*15 at the cell membrane as measured by liquid chromatography-tandem mass spectrometry. In HEK-OATP1B1*15 cells, the V(max) for OATP1B1-mediated transport of E(2)17ß-G (estradiol 17ß-d-glucuronide) was decreased >60%, whereas K(m) values (Michaelis constant) were comparable. Uptake of rosuvastatin in HEK-OATP1B1 cells (K(m) 13.1 ± 0.43 µM) was nearly absent in HEK-OATP1B1*15 cells. Interestingly, several oral antidiabetics (glyburide, glimepiride, troglitazone, pioglitazone, glipizide, gliclazide, and tolbutamide), but not metformin, were identified as significant inhibitors of the OATP1B1-mediated transport of rosuvastatin. The IC(50) values for inhibition of E(2)17ß-G uptake were similar between OATP1B1 and OATP1B1*15. In conclusion, these studies indicate that several oral antidiabetic drugs affect the OATP1B1-mediated uptake of rosuvastatin in vitro. The next step will be to translate these data to the clinical situation, as it remains to be established whether the studied oral antidiabetics indeed affect the clinical pharmacokinetic profile of rosuvastatin in patients.

Transfer of uremic solutes across the human term placenta: An ex vivo study in the dual-side perfused cotyledon.

INTRODUCTION: An increasing number of women becomes pregnant while suffering from chronic kidney disease (CKD). As a result of decreased renal function, uremic solutes circulate at high levels in the maternal circulation. This study aimed to acquire more knowledge about the placental transfer of uremic solutes across the human placenta. METHODS: Placental transfer was studied in healthy term placentas, via the ex vivo dual-side human cotyledon perfusion technique (closed-closed set-up for both maternal and fetal circulations). Uremic solute concentrations in maternal and fetal perfusates were measured via LC-MS/MS over 180 min of perfusion. RESULTS: We found that the studied compounds demonstrated different degrees of placental transfer. Fetal-to-maternal perfusate ratios at t = 180 min were for anthranilic acid 1.00 ± 0.02, indole-3-acetic acid 0.47 ± 0.08, hippuric acid 0.36 ± 0.18, l-arabinitol 0.33 ± 0.04, indoxyl sulfate 0.33 ± 0.11, neopterin 0.28 ± 0.14 and kynurenic acid 0.13 ± 0.03. All uremic solutes studied also emerged in the perfusates when cotyledons were perfused in the absence of uremic solute concentrations added to the maternal reservoir. For kynurenin these concentrations were so high, it complicated the calculation of a transfer ratio for the exogenously administered compound. DISCUSSION: After 180 min of exposure the extent of placental transfer differs substantially for the solutes studied, reflecting different transfer rates. Future studies should investigate to what extent specific uremic solutes reach the fetal circulation in vivo and how they may interfere with organ function and development of the unborn child.

Curcumin-induced fibroblast apoptosis and in vitro wound contraction are regulated by antioxidants and heme oxygenase: implications for scar formation.

Fibroblast apoptosis plays a crucial role in normal and pathological scar formation and therefore we studied whether the putative apoptosis-inducing factor curcumin affects fibroblast apoptosis and may function as a novel therapeutic. We show that 25-microM curcumin causes fibroblast apoptosis and that this could be inhibited by co-administration of antioxidants N-acetyl-l-cysteine (NAC), biliverdin or bilirubin, suggesting that reactive oxygen species (ROS) are involved. This is supported by our observation that 25-microM curcumin caused the generation of ROS, which could be completely blocked by addition of NAC or bilirubin. Since biliverdin and bilirubin are downstream products of heme degradation by heme oxygenase (HO), it has been suggested that HO-activity protects against curcumin-induced apoptosis. Interestingly, exposure to curcumin maximally induced HO-1 protein and HO-activity at 10-15 microM, whereas, at a concentration of >20-microM curcumin HO-1-expression and HO-activity was negligible. NAC-mediated inhibition of 25-microM curcumin-induced apoptosis was demonstrated to act in part via restored HO-1-induction, since the rescuing effect of NAC could be reduced by inhibiting HO-activity. Moreover pre-induction of HO-1 using 5-microM curcumin protected fibroblasts against 25-microM curcumin-induced apoptosis. On a functional level, fibroblast-mediated collagen gel contraction, an in vitro wound contraction model, was completely prevented by 25-microM curcumin, while this could be reversed by co-incubation with NAC, an effect that was also partially HO-mediated. In conclusion, curcumin treatment in high doses (>25 microM) may provide a novel way to modulate pathological scar formation through the induction of fibroblast apoptosis, while antioxidants, HO-activity and its effector molecules act as a possible fine-tuning regulator.

Urine collection methods for non-toilet-trained children in biological monitoring studies: Validation of a disposable diaper for characterization of tebuconazole exposure.

Young children differ from adults in their exposure and susceptibility to environmental chemicals (e.g. pesticides) because of various factors such as behavior, diet and physiology. Their heightened vulnerability to environmental stressors makes it important to obtain appropriate urine samples for exposure characterization. However, collecting urine from non-toilet-trained children has been shown to be methodologically and practically challenging. Four urine collection approaches were tested: a disposable diaper, a urine bag, a collection pad and the clean catch. The success rate and the user rating of each method was evaluated. The success rates were 67%, 21%, 17% and 4% for the disposable diaper, urine bag, collection pad and clean catch, respectively. The average user ratings on a 0-10 (0 = inconvenient, 10 = convenient) scale were 9.0, 4.7, 7.3 and 2.5, respectively. Subsequently, the best rated method, the disposable polyacrylate diaper was tested with hydroxy-tebuconazole as an exposure biomarker for the fungicide tebuconazole and creatinine for urine density adjustment. After LC-MS/MS analysis, the recoveries of hydroxy-tebuconazole in the range of 0.05-25 ng/mL were on average 106%, and for creatinine 87%. Precisions (relative standard deviation) were for both 3%. The overall procedure including collection and extraction was assessed, resulting in three out of seven positive samples. Based on this study, the disposable diaper is a suitable method for urine collection of non-toilet-trained children for biomonitoring of tebuconazole. This method can serve as a basis for extension to other substances of interest.

Experimental study of diclofenac and its biliary metabolites on anastomotic healing.

BACKGROUND: Diclofenac increases the risk of anastomotic leakage, but the underlying mechanism is unknown. As diclofenac is excreted largely as biliary metabolites, the aim of this study was to determine the effect of these metabolites on intestinal anastomoses. METHODS: This was a randomized controlled blinded experiment using 210 male Wistar rats to assess the effect of 'diclofenac bile' on the anastomotic complication score, leak rate and anastomotic strength following oral and parenteral administration of diclofenac. Bile duct and duodenal catheterization techniques were used for diversion and replacement of bile, and biliary diclofenac metabolites were determined. RESULTS: Replacement of control bile with diclofenac bile resulted in higher anastomotic complication scores (P = 0·006) and leakage in five of 18 animals, compared with one of 18 controls (P = 0·089). In turn, following oral diclofenac administration, replacement of diclofenac bile with control bile reduced anastomotic complications (P = 0·016). The leak rate was seven of 15 versus 13 of 17 without replacement (P = 0·127). After intramuscular administration of diclofenac, the reduction in anastomotic complications was not significant when bile was replaced with control bile (P = 0·283), but it was significant when bile was drained without replacement (P = 0·025). Diclofenac metabolites in bile peaked within 2 h after administration. Administration of diclofenac bile resulted in nearly undetectable plasma levels of diclofenac (mean(s.d.) 0·01(0·01) µg/ml) after 120 min. Following oral diclofenac, bile replacement with control bile did not affect the plasma concentration of diclofenac (0·12(0·08) µg/ml versus 0·10(0·05) µg/ml with diclofenac bile; P = 0·869). CONCLUSION: Altered bile composition as a result of diclofenac administration increases the ileal anastomotic complication rate in rats.

Placental disposition of the immunosuppressive drug tacrolimus in renal transplant recipients and in ex vivo perfused placental tissue.

Currently, tacrolimus is the most potent immunosuppressive agent for renal transplant recipients and is commonly prescribed during pregnancy. As data on placental exposure and transfer are limited, we studied tacrolimus placental handling in samples obtained from renal transplant recipients. We found transfer to venous umbilical cord blood, but particularly noted a strong placental accumulation. In patient samples, tissue concentrations in a range of 55-82 ng/g were found. More detailed ex vivo dual-side perfusions of term placentas from healthy women revealed a tissue-to-maternal perfusate concentration ratio of 113 ±â€¯49 (mean ±â€¯SEM), underlining the placental accumulation found in vivo. During the 3 h ex vivo perfusion interval no placental transfer to the fetal circulation was observed. In addition, we found a non-homogeneous distribution of tacrolimus across the perfused cotyledons. In conclusion, we observed extensive accumulation of tacrolimus in placental tissue. This warrants further studies into potential effects on placental function and immune cells of the placenta.

Mild intracellular acidification by dexamethasone attenuates mitochondrial dysfunction in a human inflammatory proximal tubule epithelial cell model.

Septic acute kidney injury (AKI) associates with poor survival rates and often requires renal replacement therapy. Glucocorticoids may pose renal protective effects in sepsis via stimulation of mitochondrial function. Therefore, we studied the mitochondrial effects of dexamethasone in an experimental inflammatory proximal tubule epithelial cell model. Treatment of human proximal tubule epithelial cells with lipopolysaccharide (LPS) closely resembles pathophysiological processes during endotoxaemia, and led to increased cytokine excretion rates and cellular reactive oxygen species levels, combined with a reduced mitochondrial membrane potential and respiratory capacity. These effects were attenuated by dexamethasone. Dexamethasone specifically increased the expression and activity of mitochondrial complex V (CV), which could not be explained by an increase in mitochondrial mass. Finally, we demonstrated that dexamethasone acidified the intracellular milieu and consequently reversed LPS-induced alkalisation, leading to restoration of the mitochondrial function. This acidification also provides an explanation for the increase in CV expression, which is expected to compensate for the inhibitory effect of the acidified environment on this complex. Besides the mechanistic insights into the beneficial effects of dexamethasone during renal cellular inflammation, our work also supports a key role for mitochondria in this process and, hence, provides novel therapeutic avenues for the treatment of AKI.

Diuretic efficacy of high dose furosemide in severe heart failure: bolus injection versus continuous infusion.

OBJECTIVES: The efficacy of high dose furosemide as a continuous infusion was compared with a bolus injection of equal dose in patients with severe heart failure. BACKGROUND: The delivery rate of furosemide into the nephron has been proved to be a determinant of diuretic efficacy in healthy volunteers. METHODS: In a randomized crossover study we compared the efficacy of a continuous infusion of high dose furosemide (mean daily dosage 690 mg, range 250 to 2,000) versus a single bolus injection of an equal dose in 20 patients with severe heart failure. The patients received an equal dosage, either as a single intravenous bolus injection or as an 8-h continuous infusion preceded by a loading dose (20% of total dosage). RESULTS: Mean (+/- SEM) daily urinary volume (infusion 2,860 +/- 240 ml, bolus 2,260 +/- 150 ml, p = 0.0005) and sodium excretion (infusion 210 +/- 40 mmol, bolus 150 +/- 20 mmol, p = 0.0045) were significantly higher after treatment with continuous infusion than with bolus injection, despite significantly lower urinary furosemide excretion (infusion 310 +/- 60 mg every 24 h, bolus 330 +/- 60 mg every 24 h, p = 0.0195). The maximal plasma furosemide concentration was significantly higher after bolus injection than during continuous infusion (infusion 24 +/- 5 micrograms/ml, bolus 95 +/- 20 micrograms/ml, p < 0.0001). Short-term, completely reversible hearing loss was reported only after bolus injection in 5 patients. CONCLUSIONS: We conclude that in patients with severe heart failure, high dose furosemide administered as a continuous infusion is more efficacious than bolus injection and causes less ototoxic side effects.

Controlled release of rhBMP-2 loaded poly(dl-lactic-co-glycolic acid)/calcium phosphate cement composites in vivo.

The release kinetics of recombinant human bone morphogenetic protein-2 (rhBMP-2) loaded poly(dl-lactic-co-glycolic acid)/calcium phosphate cement (PLGA/Ca-P cement) composites were studied in vivo. RhBMP-2 was radiolabeled with (131)I and entrapped within PLGA microparticles or adsorbed onto the microparticle surface. PLGA microparticles were prepared of high molecular weight (HMW) PLGA (weight average molecular weight [M(w)] 49,100+/-1700) or low molecular weight (LMW) PLGA (M(w) 5,900+/-300) and used for preparation of 30:70 wt.% PLGA/Ca-P cement composite discs. Release of 131I-rhBMP-2 loaded composites was assessed by scintigraphic imaging according to a 2(2) two-level full factorial design in the rat ectopic model during four weeks. In vivo release kinetics varied among formulations. All formulations showed slow release without initial burst, and displayed a linear release from 3 to 28 days. Release of LMW entrapped rhBMP-2 composites (1.7+/-0.3%/day) was significantly faster than release from other formulations (p<0.01). After 28 days, retention within the composites was 65+/-5%, 75+/-4%, 50+/-4% and 70+/-6% of the initial rhBMP-2 for HMW entrapped, HMW adsorbed, LMW entrapped and LMW adsorbed rhBMP-2 composites, respectively. Release from the composite was probably slowed down by an interaction of rhBMP-2 and Ca-P cement after rhBMP-2 release from PLGA microparticles. We conclude that PLGA/Ca-P cement composites can be considered as sustained slow release vehicles and that the release and retention of rhBMP-2 can be modified according to the desired profile to a limited extent.

Vascular effects of loop diuretics.

Although it is generally believed that the beneficial effect of loop diuretics is the result of a rapid increase in diuresis, substantial evidence, from a large number of in vitro and in vivo experiments, has accumulated showing that administration of furosemide causes direct vascular effects, which probably contribute to its acute clinical effects. Several mechanisms are involved in the vascular response to loop diuretics. The role of the renin-angiotensin-adolsterone axis, prostaglandins and the direct vascular effects of loop diuretics on both the arterial and venous parts of the vasculature are discussed.

Thiazide-induced vasodilation in humans is mediated by potassium channel activation.

-Hydrochlorothiazide and indapamide are thought to exert their hypotensive efficacy through a combined vasodilator and diuretic effect, but in vivo evidence for a direct vascular effect is lacking. The presence and mechanism of a direct vascular action of hydrochlorothiazide in vivo in humans were examined and compared with those of the thiazide-like drug indapamide. Forearm vasodilator responses to infusion of placebo and increasing doses of hydrochlorothiazide (8, 25, and 75 microg. min-1. dL-1) into the brachial artery were recorded by venous occlusion plethysmography. Dose-response curves were repeated after local tetraethylammonium (TEA) administration to determine the role of potassium channel activation and, in patients with the Gitelman syndrome, to determine the role of the thiazide-sensitive Na-Cl cotransporter in the vasodilator effect of hydrochlorothiazide. Vascular effects of hydrochlorothiazide were compared with those of indapamide in both normotensive (mean arterial pressure, 85+/-7 mm Hg) and hypertensive (mean arterial pressure, 124+/-16 mm Hg) subjects. At the highest infusion rate, local plasma concentrations of hydrochlorothiazide averaged 11.0+/-1.6 microg/mL, and those of indapamide averaged 7. 2+/-1.5 microg/mL. In contrast to indapamide, hydrochlorothiazide showed a direct vascular effect (maximal vasodilation, 55+/-14%; P=0. 013), which was inhibited by TEA (maximal vasodilation after TEA, 13+/-10%; P=0.02). The response was not dependent on blood pressure and was similar in patients with Gitelman syndrome, indicating that absence of the Na-Cl cotransporter does not alter the vasodilatory effect of hydrochlorothiazide. The vasodilator effect of hydrochlorothiazide in the human forearm is small and only occurs at high concentrations. The mechanism of action is not mediated by inhibition of vascular Na-Cl cotransport but involves vascular potassium channel activation. In contrast, indapamide does not exert any direct vasoactivity in the forearm vascular bed.

Diuretic efficiency of furosemide during continuous administration versus bolus injection in healthy volunteers.

Furosemide delivery rate in the nephron has been reported to be one of the major determinants of diuretic response. In a randomized, crossover double-blind study in eight healthy volunteers, we tested this hypothesis by comparing continuous intravenous infusion of furosemide (infusion rate, 4 mg/hr) during 8 hours after administration of an intravenous loading dose of 8 mg (total dose, 40 mg) with an intravenous bolus injection of 40 mg furosemide. During the study days subjects were rehydrated with isovolumetric amounts of fluid. Mean total urinary volume (Vur), sodium (UNa), potassium, and chloride excretion after 8 and 24 hours were significantly greater after treatment with continuous furosemide infusion when compared with bolus injection, whereas total urinary furosemide excretion showed no differences (Vur bolus versus Vur infusion, 5270 versus 6770 ml/8 hours; UNa bolus versus UNa infusion, 314 versus 430 mmol/8 hours; both p less than 0.001). These findings strongly support the concept of the furosemide delivery rate into the nephron as a determinant of diuretic efficiency.

Hydrochlorothiazide exerts no direct vasoactivity in the human forearm.

BACKGROUND: Recently, hydrochlorothiazide has been shown to relax vascular smooth muscle in vitro in clinically relevant concentrations by the opening of calcium-activated potassium channels, leading to hyperpolarization and consequent closing of voltage-operated calcium channels. Long-term administration of hydrochlorothiazide reduces peripheral vascular resistance in vivo in man. These results indicate that hydrochlorothiazide has hemodynamic activity, and we therefore examined the direct vascular action of this drug in vivo. SUBJECTS AND METHODS: Forearm vasodilator responses to the infusion of a placebo and five increasing doses of hydrochlorothiazide into the brachial artery were recorded by venous occlusion strain-gauge plethysmography (perfused forearm technique) in eight normotensive male volunteers. Venous samples were taken from an ipsilateral antecubital vein at the end of each infusion period to measure the hydrochlorothiazide concentration. RESULTS AND DISCUSSION: Plasma concentrations of hydrochlorothiazide averaged 3.5 +/- 0.3 mu g/ml at the highest infusion rate. This concentration leads to a 60 +/- 10% relaxation in vitro and is more than 10 times the therapeutic plasma concentration. Despite these supratherapeutic levels, we were unable to demonstrate a change in forearm blood flow and vascular resistance. Also, no significant changes were observed in blood pressure and heart rate. CONCLUSION: In contrast to in vitro results, hydrochlorothiazide does not exert any direct vasoactivity in the forearm vascular bed of healthy normotensive male volunteers at (supra)therapeutic plasma concentrations.

Pharmacokinetics and dosimetry of cobalt-55 and cobalt-57.

UNLABELLED: The isotopes 55Co and 57Co have been evaluated for PET and SPECT imaging in several clinical brain studies. For clinical application of cobalt, it is important to know the delivered radiation dose. The biodistribution of 55Co in both rat and humans after intravenous (bolus)-administration was studied. Based on pharmacokinetic data, radiation dose calculations according to the MIRD system are presented. By combining present measurements with literature data on 60CoCl2, the radiation dose delivered by 56CoCl2 (T1/2 78.8 days) and 57CoCl2 (T1/2 = 270 days) could be assessed. METHODS: Whole-body Co-PET was performed in two healthy volunteers and one rat after intravenous injection of 37 and 3.7 MBq (1 resp. 0.1 mCi) 55Co, respectively. Blood samples were withdrawn during 300 min in humans. In seven rats the 55Co-biodistribution was determined by postmortem analysis. The residence time of the liver (critical organ) was determined in rats and humans. Blood partition-data of 55Co were assessed resulting in basic pharmacokinetic data in humans. Based on these kinetic data, radiation dose was calculated using the MIRD protocol. RESULTS: In both the humans and the rat, the liver and bladder retained the highest fractions of 55Co (about 50% resp. 40% of the administered dose). The liver residence time in humans was 8.6 hr. The free fraction 55Co in the human plasma was at maximum 12%. The total-body mean transit time was 152 min. The volume of the central compartment = 2.8 liter and the steady-state distribution volume = 48 liter. CONCLUSION: From these results, according to the WHO recommendations for class II studies, 22.2 MBq (0.6 mCi) 55Co and 14.8 MBq (0.4 mCi) 57Co (excluding any radionuclide contamination) can be used.

Saturable pharmacokinetics in the renal excretion of drugs.

The renal excretion of drugs is the result of different mechanisms: glomerular filtration, passive back diffusion, tubular secretion and tubular reabsorption. Of these mechanisms the last 2 are saturable, as they involve carrier transport. This also implies that both tubular secretion and tubular reabsorption are susceptible to competition between similar substrates for a common carrier site. Furthermore, transport via these mechanisms is energy-dependent, so-called active transport, able to concentrate a drug. Tubular secretion takes place in the proximal tubule of the nephron. Many organic compounds are actively secreted, but there are separate carrier systems for anions and cations. Anions appear to be transported actively over the basolateral membrane and by a less efficient non-active carrier-mediated process (facilitated diffusion) over the brush border membrane. As a result of these mechanisms, anions tend to accumulate in proximal tubular cells. For cations, however, the active transport step operates over the brush border membrane, whereas the uptake of the cation in the cell occurs via facilitated diffusion over the basolateral membrane. Active reabsorption is most prominent for many nutrients and endogenous substrates (amino acids, glucose, vitamins), but various exogenous compounds also have a certain affinity for the reabsorptive carrier systems. Uricosuric drugs, for instance, interfere with carrier-mediated reabsorption of urate. The occurrence of saturable excretion routes causes dose-dependent, non-linear pharmacokinetics. In clinical pharmacokinetics, tubular secretion can adequately be described with the use of a Michaelis-Menten equation. This implies that a compound undergoing tubular secretion exhibits a concentration-dependent renal clearance. At low plasma concentrations the clearance will be maximal, and for several drugs may be as high as the effective renal plasma flow. Increasing concentrations cause decreasing renal clearance, until eventually the secretion mechanism becomes fully saturated. Then the excretion of the drug in urine will depend primarily on its net rate of filtration. It is important to realise that the non-linear kinetics will be evident from the plasma kinetics only when the saturable pathway contributes to at least some 20% of the total body clearance. Interactions with other substrates, however, are likely to occur even when only a very small amount of drug is transported by the carrier system. Non-linear kinetics inevitably lead to disproportionate accumulation.(ABSTRACT TRUNCATED AT 400 WORDS)