Clinical consequences of the biphasic elimination kinetics for the diuretic effect of furosemide and its acyl glucuronide in humans

Furosemide as a functional marker of acute kidney injury in ICU patients: a new role for an old drug

New pharmacokinetics insight suggests that the furosemide pharmacology occurring in ICU patients with AKI is similar, but not equal to that described in chronic stable renal patients. Even if the diuretic response to furosemide is expressed by a steep dose-response curve positively correlated with renal function, pharmacodynamic limitations occur when creatinine clearance is < 20 ml/min or urine output is < 500 ml/12 h. In such cases, other factors specifically due to acute tubular injury can interfere with the furosemide-induced diuretic output. As modality of administration recent reports and metanalysis, even if not conclusive, suggest that for the same given dose a continuous infusion of furosemide was superior in diuretic response. For septic shock patients on CVVHDF where treatment adds an additional clearance of furosemide the maximum diuretic response is achieved by a continuous infusion of 20 mg/h of furosemide. At this infusion rate the reached plasma level was < 20 mg/L, a range considered safe and not ototoxic. Therefore, the severity of AKI establishes whether a patient will respond to furosemide. In this review we summarized all these recent updates, also suggesting that the diuretic response under continuous infusion may allow assessing glomerular and tubular functions with increased reliability than a bolus dose. However, validation studies are still needed to support continuous infusion as a stress test.

Urine volume as a predicting factor for furosemide clearance during continuous infusion in AKI septic shock patients on hemodiafiltration

BACKGROUND

This study assessed the contribution of intracorporeal (IC) and extracorporeal clearance (EC) of furosemide in patients with septic acute kidney injury (AKI), and the relationship between plasma concentrations and urine volume.

METHODS

Prospective cohort observational study of 15 patients with septic AKI undergoing continuous veno-venous hemodiafiltration (CVVHDF) divided according to urine volume (< 500 ml/12 h, Oliguria group, n = 5; > 500 ml/12 h, Diuresis group, n = 10) during continuous infusion of furosemide (120 mg/12 h) at steady-state condition. Plasma and effluent furosemide concentrations were determined by high-performance liquid chromatography (HPLC)-mass spectrometry every 12 h for 48 h.

RESULTS

Furosemide plasma concentrations and total body clearance (TBC) were 6.14 mg/l and 22.1 ml/min for the Oliguria group, and 2.63 mg/l and 54.4 ml/min for the Diuresis group, respectively (p < 0.05). When urine volume was < 500 ml/24 h, the furosemide plasma concentrations peaked at the potentially toxic value of 13.0 mg/l. Furosemide EC was not relevant for the Diuresis group, but it represented 18% of TBC for the Oliguria group. Furosemide plasma concentrations correlated positively with dose infusion for both groups (r = 0.728 and 0.685, p < 0.05), and negatively with urine volume only for the Diuresis (r = - 0.578, p < 0.01) but not for the Oliguria group (r = - 0.089, p = 0.715).

CONCLUSIONS

For patients with urine volume > 500 ml/12 h continuous infusion of furosemide up to 480 mg/24 h leads to increasing urine volume, which can predict furosemide plasma levels within its safety range. When the urine volume is lower, the furosemide plasma levels are increased beyond any further diuretic efficacy.

The role of the c-Jun N-terminal kinases 1/2 and receptor-interacting protein kinase 3 in furosemide-induced liver injury

1. The mechanisms of furosemide (FS) hepatotoxicity were explored in mice. Specifically, C57Bl/6 J mice were treated with 500 mg FS/kg bodyweight, and c-Jun N-terminal kinase (JNK) activation and receptor-interacting protein kinase 3 (RIP3) expression were measured by western blotting. Co-treatment with FS and the JNK inhibitor SP600125 was also performed, and FS-induced liver injury was compared in wild-type and RIP3 knockout (KO) mice. 2. JNK phosphorylation and RIP3 expression were increased in livers from the FS-treated mice as early as 6 h after treatment and persisted until at least 24 h. JNK phosphorylation was also observed in primary mouse hepatocytes and human HepaRG cells treated with FS. 3. Phosphorylated JNK translocated into mitochondria in livers, but no evidence of mitochondrial damage was observed. 4. SP600125-treated mice, SP600125 co-treated primary mouse hepatocytes and RIP3 KO mice were not protected against FS hepatotoxicity. These data show that, although JNK activation and RIP3 expression are induced by FS, neither contributes to the liver injury.

Cannabinoid receptor agonist 13, a novel cannabinoid agonist: first in human pharmacokinetics and safety

Cannabinoid receptor agonist 13 (CRA13) is a novel cannabinoid (CB) receptor agonist with high affinity and functional activity toward both CB(1) and CB(2) receptors. This phase I study aimed to evaluate the pharmacokinetics, safety, and tolerability of single oral doses of CRA13. Sixty-three of 69 healthy adult males were randomized in seven cohorts (n = 9) to receive 1 to 80 mg of CRA13 or placebo orally in fasted condition. To investigate the diet effect, an independent group (n = 6) was randomized to receive 40 mg of CRA13 after high-fat and high-calorie breakfast in crossover design with a 2-week washout period. Peak plasma concentration (C(max)) ranged from 7.8 to 467.6 ng/ml (1-80 mg). CRA13 was rapidly absorbed and demonstrated linear pharmacokinetics (1-80 mg). Time to reach C(max) (t(max)) was 1.5 to 2 h for all doses in both fasted and fed groups. Administration of 40 mg of CRA13 with food induced approximately 2-fold increase in the C(max) and the area under the concentration-time curve, AUC(0 - tz). The apparent elimination half-life (t(1/2)) was 21 to 36 h and 30 to 41 h for fasted and fed groups, respectively. Dizziness, headache, and nausea were the most frequently reported adverse events (AEs), predominantly at the 40- and 80-mg doses. The incidence of AEs was dose-dependent and mild to moderate. No deaths and serious adverse events were reported. In conclusion, CRA13 was reasonably well tolerated and demonstrated a linear pharmacokinetics over the studied dose range (1-80 mg). Food intake increased CRA13 C(max) and AUC(0 - tz) by approximately 2-fold, whereas t(max) was unaffected.

Mechanistic modelling of tesaglitazar pharmacokinetic data in subjects with various degrees of renal function--evidence of interconversion

WHAT IS ALREADY KNOWN ABOUT THIS SUBJECT

Tesaglitazar, is predominantly metabolized (to an acyl glucuronide of the parent compound) and 20% of given dose is found unchanged in the urine. Acyl glucuronides are know to be unstable and can become hydrolysed back to parent compound, a phenomena called interconversion.

WHAT THIS STUDY ADDS

A likely mechanism (interconversion) for the cause of the increased exposure of tesaglitazar in subjects with impaired renal function. A possible modelling framework to evaluate interconversion without dosing of the metabolite based on the simultaneous analysis of plasma and urine data from a group of subjects with varying renal function. A mechanistic understanding of the pharmacokinetic properties of tesaglitazar and its metabolite. AIMS To develop a mechanistic pharmacokinetic (PK) model for tesaglitazar and its metabolite (an acyl glucuronide) following oral administration of tesaglitazar to subjects with varying renal function, and derive an explanation for the increased plasma exposure of tesaglitazar in subjects with impaired renal function.

METHODS

Data were from a 6-week study in subjects with renal insufficiency and matched controls undergoing repeated oral dosing with tesaglitazar (n = 41). Compartmental population PK modelling was employed to describe the PK of tesaglitazar and its metabolite, in plasma and urine, simultaneously. Two hypotheses were tested to investigate the increased exposure of tesaglitazar in subjects with renal functional impairment: tesaglitazar metabolism is correlated with renal function, or metabolite elimination is reduced in renal insufficiency, leading to increased hydrolysis (interconversion) to the parent compound via biliary circulation.

RESULTS

The hypothesis for interconversion was best supported by the data. The population PK model included first-order absorption, two-compartment disposition and separate renal (0.027 l h(-1)) and metabolic (1.9 l h(-1)) clearances for tesaglitazar. The model for the metabolite; one-compartment disposition with renal (saturable, V(max) = 0.19 micromol l(-1) and K(m) = 0.04 micromol l(-1)) and nonrenal clearances (1.2 l h(-1)), biliary secretion (12 h(-1)) to the gut, where interconversion and reabsorption (0.8 h(-1)) of tesaglitazar occurred.

CONCLUSION

A mechanistic population PK model for tesaglitazar and its metabolite was developed in subjects with varying degrees of renal insufficiency. The model and data give insight into the likely mechanism (interconversion) of the increased tesaglitazar exposure in renally impaired subjects, and separate elimination and interconversion processes without dosing of the metabolite.

Diuretics in pediatrics : current knowledge and future prospects

This review summarizes current knowledge on the pharmacology, pharmacokinetics, pharmacodynamics, and clinical application of the most commonly used diuretics in children. Diuretics are frequently prescribed drugs in children. Their main indication is to reduce fluid overload in acute and chronic disease states such as congestive heart failure and renal failure. As with most drugs used in children, optimal dosing schedules are largely unknown and empirical. This is undesirable as it can potentially result in either under- or over-treatment with the possibility of unwanted effects. The pharmacokinetics of diuretics vary in the different pediatric age groups as well as in different disease states. To exert their action, all diuretics, except spironolactone, have to reach the tubular lumen by glomerular filtration and/or proximal tubular secretion. Therefore, renal maturation and function influence drug delivery and consequently pharmacodynamics. Currently advised doses for diuretics are largely based on adult pharmacokinetic and pharmacodynamic studies. Therefore, additional pharmacokinetic and pharmacodynamic studies for the different pediatric age groups are necessary to develop dosing regimens based on pharmacokinetic and pharmacodynamic models for all routes of administration.

Determination of furosemide in plasma and urine using monolithic silica rod liquid chromatography

In the present study we developed a fast and reliable HPLC assay for the determination of the loop diuretic furosemide in plasma and urine, using a Chromolith RP 18e (100 mm x 4.6 mm) monolithic silica rod HPLC column. After liquid-liquid extraction with diethylether plasma or urine samples were separated with a gradient consisting of solvent A (20% acetonitrile) and solvent B (80% acetonitrile), both in 0.25% acetic acid. The flow rate was 3.5 ml/min and the effluent was monitored by fluorescence with excitation at 230 nm and emission at 410 nm. The retention times for the internal standard (naproxen) and for furosemide were 2.1 and 3.7 min, respectively, and total run time was 8 min. The calibration curves were linear between 7.8 and 1000 ng/ml, and within-assay and between-assay coefficients of variation were <6.5% and <10%, respectively. The proposed assay for furosemide in plasma and urine using monolithic silica rod chromatography is fast, sensitive, and reliable, and, thus, well suited for pharmacokinetic studies.

Population pharmacokinetic modeling for enterohepatic recirculation in Rhesus monkey

Enterohepatic recirculation (EHR) occurs via biliary excretion and intestinal reabsorption of a drug. Drug recycling through EHR can lead to a change in pharmacokinetic (PK) properties, such as reduced clearance (CL), extended half-life (T(1/2)) and increased plasma exposure (AUC). As a result, EHR may prolong the pharmacological effect of drugs. In the present study, the compound (Cpd A) was found to exhibit EHR in Rhesus monkeys associated with a reduction in CL (from 3.8 to 0.33 Lh(-1), IV; from 2.3 to 0.4 Lh(-1), PO), and an increase in T(1/2) (from 0.9 to 18 h, IV) and in AUC (from 1.5 to 17.4 microg h/mL, IV; from 2.8 to 16.3 microg h/mL, PO), by comparing the PK in the monkeys via the interruption of EHR (bile-duct cannulation) with that in the intact monkeys. A population four-compartment model was constructed based on recirculation loops incorporating all possible inputs (bile secretion, a lag-time model for gall bladder emptying, routes and amounts of a single dose administration) to fully evaluate the EHR of Cpd A. The plasma concentrations versus time profiles predicted from the model had a good fit to the values observed in the subjects and were further simulated with 90% confidence interval to demonstrate its utility. Thus, the model could be applied as a useful tool to evaluate the drugs or compounds that undergo EHR in different species.

Acyl glucuronide drug metabolites: toxicological and analytical implications

Although glucuronidation is generally considered a detoxification route of drug metabolism, the chemical reactivity of acyl glucuronides has been linked with the toxic properties of drugs that contain carboxylic acid moieties. It is now well documented that such metabolites can reach appreciable concentrations in blood. Furthermore, they are labile, undergo hydrolysis and pH-dependent intramolecular acyl migration to isomeric conjugates of glucuronic acid, and may react irreversibly with plasma proteins, tissue proteins, and with nucleic acids. This stable binding causes chemical alterations that are thought to contribute to drug toxicity either through changes in the functional properties of the modified molecules or through antigen formation with subsequent hypersensitivity and other immune reactions. Whereas in vitro data on the toxicity of acyl glucuronides have steadily accumulated, direct evidence for their toxicity in vivo is scarce. Acyl glucuronides display limited stability, which is dependent on pH, temperature, nature of the aglycon, and so on. Therefore, careful sample collection, handling, and storage procedures are critical to ensure generation of reliable pharmacologic and toxicologic data during clinical studies. Acyl glucuronides can be directly quantified in biologic specimens using chromatographic procedures. Their adducts with plasma or cell proteins can be determined after electrophoretic separation, followed by blotting. ELISA techniques have been used to assess the presence of antibodies against acyl glucuronide-protein adducts. This review summarizes the most recent evidence concerning biologic and toxicologic effects of acyl glucuronide metabolites of various drugs and discusses their relevance for drug monitoring. A critical evaluation of the available methodology is included.

Enterohepatic circulation: physiological, pharmacokinetic and clinical implications

Enterohepatic recycling occurs by biliary excretion and intestinal reabsorption of a solute, sometimes with hepatic conjugation and intestinal deconjugation. Cycling is often associated with multiple peaks and a longer apparent half-life in a plasma concentration-time profile. Factors affecting biliary excretion include drug characteristics (chemical structure, polarity and molecular size), transport across sinusoidal plasma membrane and canniculae membranes, biotransformation and possible reabsorption from intrahepatic bile ductules. Intestinal reabsorption to complete the enterohepatic cycle may depend on hydrolysis of a drug conjugate by gut bacteria. Bioavailability is also affected by the extent of intestinal absorption, gut-wall P-glycoprotein efflux and gut-wall metabolism. Recently, there has been a considerable increase in our understanding of the role of transporters, of gene expression of intestinal and hepatic enzymes, and of hepatic zonation. Drugs, disease and genetics may result in induced or inhibited activity of transporters and metabolising enzymes. Reduced expression of one transporter, for example hepatic canalicular multidrug resistance-associated protein (MRP) 2, is often associated with enhanced expression of others, for example the usually quiescent basolateral efflux MRP3, to limit hepatic toxicity. In addition, physiologically relevant pharmacokinetic models, which describe enterohepatic recirculation in terms of its determinants (such as sporadic gall bladder emptying), have been developed. In general, enterohepatic recirculation may prolong the pharmacological effect of certain drugs and drug metabolites. Of particular importance is the potential amplifying effect of enterohepatic variability in defining differences in the bioavailability, apparent volume of distribution and clearance of a given compound. Genetic abnormalities, disease states, orally administered adsorbents and certain coadministered drugs all affect enterohepatic recycling.