Renal Clearance Rate Research Articles

Sylatron: A Pegylated Interferon for Use in Melanoma

To review the currently available literature on peginterferon alfa-2b (pegIFN [Sylatron]), including its role in therapy and toxicity for adjuvant treatment of locally advanced melanoma. A literature search was performed of PubMed and the American Society of Clinical Oncology abstracts from 1976 to February 2012, using the primary search terms peginterferon alfa-2b, interferon, Sylatron, and melanoma. All available English-language articles and trials that described the pharmacology, pharmacokinetics, pharmacodynamics, clinical activity, or safety profile of pegIFN were reviewed. PegIFN was approved in March 2011 for the adjuvant treatment of node-positive melanoma. Interferon (IFN) is commonly used in patients with melanoma who remain at high risk for relapse following surgery; however, the optimal scheduling and dose are not agreed upon. Pegylation of IFN involves conjugation with polyethylene glycol. Following subcutaneous injection of pegIFN, the rate of absorption, renal and cellular clearance, and immunogenicity are reduced. As a result of the extended serum half-life, once-weekly administration is feasible, compared with the daily and/or thrice weekly dosing of IFN. When compared with observation alone in patients with resected stage III melanoma, pegIFN demonstrated a significant increase in relapse-free survival, with a marginal impact on overall survival. The most common adverse events were as expected with IFN and included fatigue, increased liver enzymes, pyrexia, headache, anorexia, myalgia, nausea, chills, depression, and injection site reactions. A large Phase 3 study is underway to further assess outcome and toxicity differences between pegIFN weekly and low-dose IFN thrice weekly. PegIFN is a modified version of the previously approved interferon indicated for the adjuvant treatment of melanoma. Although the safety profile remains similar between the pegylated and non-pegylated forms, once-weekly administration is feasible secondary to an extended serum half-life and may have improved convenience for the patient.

Continuous Renal Replacement Therapy Clearance Rate for Salicylate Toxicity in Multi-System Trauma

The management of patients with concomitant xenobiotic toxicity and multisystem trauma can be complex. While hemodialysis is generally the modality of choice for extracorporeal elimination of salicylates, the potential for large volume shifts and hypotension may pose a risk in patients with traumatic brain injury. An alternative therapy to hemodialysis is continuous renal replacement therapy, which has slower clearance rates than hemodialysis, but has decreased adverse effects in cases of traumatic brain injury. However, there are few published reports of clearance rates of salicylates using continuous renal replacement therapy. We report a case of multisystem trauma with concomitant intentional salicylate overdose in which continuous renal replacement therapy was employed. The salicylate clearance rate that was obtained in this case was 7.5 mL/minute using continuous veno-venous hemodiafiltration, a form of continuous renal replacement therapy.

Peptide-mediated Cell and In Vivo Delivery of Antisense Oligonucleotides and siRNA

Antisense oligonucleotides and short interfering RNAs (siRNAs) are nucleic acids-targeting reagents for gene expression modulation that are being developed as drugs for many applications. A number of useful synthetic nucleic acids analogues have been introduced recently to greatly improve their properties for use as therapeutics. However, their full effectiveness in cells and in vivo has often only been realized through development of suitable nonviral delivery systems. Among these, a range of natural and synthetic peptides have been found useful for enhancing cellular uptake and/or cell targeting of oligonucleotide analogues and siRNA. Such peptides are synthetically conjugated, used as noncovalent complexes, or used in combination with polymer, liposomal or exosome formulation techniques. This review begins by describing the modes of action of antisense reagents and siRNA and goes on to focus on recent advances in their peptide-mediated cell and in vivo delivery and how peptide use has influenced drug development. The review discusses the challenges associated with understanding the physiological and toxicological aspects of peptide-mediated delivery. Developments towards clinical use are also highlighted, with particular emphasis on peptide conjugates of oligonucleotide analogues used for treatment of neuromuscular diseases.

Vascular time-activity variation in patients undergoing 123I-MIBG myocardial scintigraphy: implications for quantification of cardiac and mediastinal uptake

PurposeFor the quantification of cardiac 123I-metaiodobenzylguanidine (MIBG) uptake, the mediastinum is commonly used as a reference region reflecting nonspecific background activity. However, variations in the quantity of vascular structures in the mediastinum and the rate of renal clearance of 123I-MIBG from the blood pool may contribute to increased interindividual variation in uptake. This study examined the relationship between changes in heart (H) and mediastinal (M) counts and the change in vascular 123I-MIBG activity, including the effect of renal function.MethodsFifty-one subjects with ischemic heart disease underwent early (15 min) and late (4 h) anterior planar images of the chest following injection of 123I-MIBG. Vascular 123I-MIBG activity was determined from venous blood samples obtained at 2 min, 15 min, 35 min, and 4 h post-injection. From the vascular clearance curve of each subject, the mean blood counts/min per ml at the time of each acquisition and the slope of the clearance curve were determined. Renal function was expressed as the estimated creatinine clearance (e-CC) and the estimated glomerular filtration rate (e-GFR). Relations between H and M region of interest (ROI) counts/pixel, vascular activity, and renal function were then examined using linear regression.ResultsChanges in ROI activity ratios between early and late planar images could not be explained by blood activity, the slope of the vascular clearance curves, or estimates of renal function. At most 3% of the variation in image counts could be explained by changes in vascular activity (p = 0.104). The e-CC and e-GFR could at best explain approximately 1.5% of the variation in the slopes of the vascular clearance curve (p = 0.194).ConclusionThe change in measured H and M counts between early and late planar 123I-MIBG images is unrelated to intravascular levels of the radiopharmaceutical. This suggests that changes in M counts are primarily due to decrease in soft tissue activity and scatter from the adjacent lungs.

A rapid computational filter for predicting the rate of human renal clearance

In silico models that predict the rate of human renal clearance for a diverse set of drugs, that exhibit both active secretion and net re-absorption, have been produced using three statistical approaches. Partial Least Squares (PLS) and Random Forests (RF) have been used to produce continuous models whereas Classification And Regression Trees (CART) has only been used for a classification model. The best models generated from either PLS or RF produce significant models that can predict acids/zwitterions, bases and neutrals with approximate average fold errors of 3, 3 and 4, respectively, for an independent test set that covers oral drug-like property space. These models contain additional information on top of any influence arising from plasma protein binding on the rate of renal clearance. Classification And Regression Trees (CART) has been used to generate a classification tree leading to a simple set of Renal Clearance Rules (RCR) that can be applied to man. The rules are influenced by lipophilicity and ion class and can correctly predict 60% of an independent test set. These percentages increase to 71% and 79% for drugs with renal clearances of <0.1 ml/min/kg and >1 ml/min/kg, respectively. As far as the authors are aware these are the first set of models to appear in the literature that predict the rate of human renal clearance and can be used to manipulate molecular properties leading to new drugs that are less likely to fail due to renal clearance.

Urinary dopamine excretion and renal responses to fenoldopam infusion in blacks and whites.

Dopamine is an endogenous natriuretic amine that contributes to the maintenance of sodium homeostasis. Deficiencies in the renal production of dopamine and the action of dopamine on renal tubular receptors have been observed in human hypertension and may contribute to salt sensitivity of blood pressure. Ethnic differences in the sodium-to-dopamine relationship may contribute to the higher prevalence of salt sensitivity in blacks. The authors assessed dopaminergic activity in two studies. In the first, daytime and nighttime excretion of sodium and dopamine were compared in 11 black and 17 white normotensive patients. No racial difference in the rate of sodium or dopamine excretion during either period was observed. In the second study, a graded infusion of the dopamine-1 receptor agonist, fenoldopam, was performed in 14 black and 17 white normotensive patients. There was no racial difference in the natriuretic responses. Previously described lower rates of renal free water clearance and potassium excretion in blacks compared with whites were maintained during fenoldopam infusion, suggesting that dopamine is not a mediator of those differences. The authors conclude that there are no race-related differences in dopamine excretion or activity in normotensive patients.

Adult outcomes of gestational or adult exposure to perfluorooctanic acid (PFOA) in female CD-1 mice

Rainbow trout (Oncorhynchus mykiss) confined to respirometer-metabolism chambers were dosed with perfluorooctanoate (PFOA) by intra-arterial (i.a.) injection and sampled to obtain concentration time-course data for plasma, urine, and expired water. The data were then analyzed by compartmental modeling to estimate rates of renal and branchial clearance. Averaged across all animals, the renal clearance rate (1.35 mL/h/kg) was more than ten times greater than the branchial clearance rate (0.12 mL/h/kg). The average whole-body elimination half-life was 12.6 d, which is somewhat longer than values obtained in previous studies with smaller trout. The tissue distribution of PFOA was assessed by collecting tissues at the end of chambered exposures and in a separate tissue time-course experiment. From the time-course study it appeared that an internal steady-state was established within 24 h of i.a. injection. Consistent with previous studies, the rank order of PFOA concentration in tissues at steady state was: plasma > liver > kidney > muscle. In a second set of chambered experiments, fish were exposed to PFOA in water to determine the rate of branchial uptake. Branchial uptake rates were too low to assess directly by measuring PFOA concentrations in inspired and expired water. Uptake rate constants (mean 0.19 L/d/kg; 0.1% uptake efficiency) were therefore estimated by compartmental modeling using plasma concentration time-course data and model parameters derived from the elimination experiments. It is clear from this effort that elimination of PFOA by trout occurs primarily via the renal route. This finding is consistent with numerous studies of mammals and suggests that trout possess membrane transporters that facilitate the movement of PFOA from plasma to urine.

A Novel Anti-CD20 IgG-Interferon-α2b Fusion Protein with Potent in Vitro and in Vivo Anti-Lymphoma Activity Made by the Dock-and-Lock (DNL) Method.

BACKGROUND: Interferon-α2b (IFN-α2b) is active alone and in combination with other agents in the therapy of a variety of cancers, including hairy cell leukemia, chronic myelocytic leukemia, follicular lymphoma, and malignant melanoma. As for most cytokines, the pharmacokinetics are a major factor affecting schedule and efficacy. The protein is rapidly degraded, diffuses widely throughout the body, and has a rapid rate of renal clearance. Commercially available IFNs that are pegylated, such as PEG-INTRON and PEGASYS, have increased serum half-life and reduced renal clearance, which augment their biological activity. For therapy of lymphoma and other cancers, fusing IFN-α2 to tumor-targeting antibodies could increase serum half-life and target the IFN-α2 to the tumor, conceivably allowing less frequent and lower dosing with improved therapeutic efficacy and reduced side effects.METHODS: The modular DNL method exploits a pair of distinct protein domains involved in the natural binding between protein kinase A (PKA) and A-kinase anchoring proteins (AKAP), whereby the dimerization-and-docking domain (DDD) of PKA and the anchoring domain (AD) of an interactive AKAP are each fused to a biological entity, resulting in respective DDD- and AD-modules that are readily combined to quantitatively generate stably-tethered structures of defined composition with retained bioactivity. We have selectively combined recombinant DDD-modules comprising IFN-α2b with recombinant AD-modules derived from the anti-CD20 humanized mAb, veltuzumab, and other humanized mAbs to generate complexes comprising four copies of IFN-α2b site-specifically linked to the bivalent IgG.RESULTS: The IgG-AD2 and IFN-α2b-DDD2 modules were expressed in separate myeloma cell cultures and purified from culture broths by Protein A and IMAC, respectively. Combining an IgG-AD2 module with slightly more than 2 molar equivalents of the cytokine-DDD2 module under mild redox conditions resulted in the formation of a covalent complex comprising one IgG and 4 IFN-α2b via the docking of each of the two AD2 domains on IgG with a dimer of IFN-α2b-DDD2, and subsequent formation of disulfide bonds (locking) between DDD2 and AD2. The 255-kDa conjugates, which were purified by Protein A, were readily detected by size-exclusion HPLC and non-reducing SDS-PAGE, and retained the biological functions of IFN-α2b in vitro. The IgG-IFN-α2b constructs exhibited potent anti-viral activity in vitro, with specific activities approaching that of recombinant human IFN-α2b. Additionally, the constructs all showed highly potent in vitro cytotoxicity against Burkitt lymphoma cell lines. Notably, the CD20-targeted IFN-α2b construct (20-2b) was 30-fold more potent than a control, non-targeting IgG-IFN-α2b. The enhanced cytotoxicity of 20-2b was not reproduced when non-targeting IgG-IFN-α2b was used in combination with veltuzumab, suggesting that IFN-α2b must be physically linked to achieve maximal potency. IgG-IFN-α2b fusion proteins, including 20-2b, induced significantly more potent ADCC compared to their parental MAbs. The targeting properties of 20-2b were comparable to veltuzumab, and its serum half-life was significantly longer than PEG-INTRON and PEGASYS. In the human Daudi xenograft model, 20-2b showed superior anti-tumor efficacy compared to both veltuzumab and other IgG-IFN-α2 agents. The median survival time (MST) for mice treated with single-dose 170 ng 20-2b was 101.5 days, whereas those treated with an equivalent dose of veltuzumab and untreated mice survived 39 and 28 days, respectively (P<0.0005). Lower 20-2b doses of 80, 17 and 8 ng resulted in MST of 97.5, 56.5 and 48 days, respectively, with the lowest dose still significantly better than the highest dose of veltuzumab (P=0.0434). Using a single 170-ng dose, a CD22-targeting IFN-α2b (22-2b) also increased MST significantly to 47 days (P =0.0119), while a non-targeting IgG-IFN-α2b (734-2b) did not.CONCLUSIONS: The DNL method provided an IFN-α2-targeting mAb fusion protein that showed improved anti-tumor efficacy over the mAb by itself, based on improved pharmacokinetics, ADCC, and tumor targeting, as well as reduced systemic toxicity. Thus, DNL provides a modular approach to efficiently tether cytokines to targeting antibodies, resulting in higher in vivo potency than the original cytokines or mAbs.

Asymmetric dimethylarginine, oxidative stress, and vascular nitric oxide synthase in essential hypertension

We reported impaired endothelium-derived relaxation factor/nitric oxide (EDRF/NO) responses and constitutive nitric oxide synthase (cNOS) activity in subcutaneous vessels dissected from patients with essential hypertension (n = 9) compared with normal controls (n = 10). We now test the hypothesis that the patients in this study have increased circulating levels of the cNOS inhibitor, asymmetric dimethylarginine (ADMA), or the lipid peroxidation product of linoleic acid, 13-hydroxyoctadecadienoic acid (HODE), which is a marker of reactive oxygen species. Patients had significantly (P < 0.001) elevated (means +/- SD) plasma levels of ADMA (P(ADMA), 766 +/- 217 vs. 393 +/- 57 nmol/l) and symmetric dimethylarginine (P(SDMA): 644 +/- 140 vs. 399 +/- 70 nmol/l) but similar levels of L-arginine accompanied by significantly (P < 0.015) increased rates of renal ADMA excretion (21 +/- 9 vs. 14 +/- 5 nmol/mumol creatinine) and decreased rates of renal ADMA clearance (18 +/- 3 vs. 28 +/- 5 ml/min). They had significantly increased plasma levels of HODE (P(HODE): 309 +/- 30 vs. 226 +/- 24 nmol/l) and renal HODE excretion (433 +/- 93 vs. 299 +/- 67 nmol/micromol creatinine). For the combined group of normal and hypertensive subjects, the individual values for plasma levels of ADMA and HODE were both significantly (P < 0.001) and inversely correlated with microvascular EDRF/NO and positively correlated with mean blood pressure. In conclusion, elevated levels of ADMA and oxidative stress in a group of hypertensive patients could contribute to the associated microvascular endothelial dysfunction and elevated blood pressure.

Creatinine and pseudouridine in plasma and urine from Brahman-cross steers fed a low, medium or high plane of nutrition

Metabolic state as influenced by growth rate may influence meat toughness and can be estimated from metabolites excreted in urine. Urine collection over 24 h requires animals to be constrained in metabolism crates for many days. Single blood sampling to estimate metabolites in plasma would be less stressful on animals than collecting 24 h urine excretion. This study investigated the hypothesis that the plasma concentrations of pseudouridine and creatinine were representative of those found in 24 h urine excretions in steers fed different quality diets. Eleven Brahman-cross steers were fed a high ( n = 3), medium ( n = 4) or low ( n = 4) quality hay diet for three weeks. Steers were catheterized and housed in metabolism crates for 6 days. Urine was collected every 24 h and total volume sub-sampled for analyses of creatinine and pseudouridine. Jugular blood was collected from each steer every 3 h from 07:30 to 16:30 h. Plasma was separated from red blood cells by centrifugation and frozen for creatinine and pseudouridine analyses. No time of day effect was apparent for pseudouridine or creatinine so daily means were used to test for effect of diet and to relate to urinary concentrations. Nutritional restriction halted live weight gain but had no effect on urinary or plasma pseudouridine, suggesting that diet did not affect tRNA turnover. Increased plasma creatinine concentrations and reduced urinary creatinine concentration in steers experiencing nutritional restriction indicated that their renal clearance rate decreased. As a result, the ratio of plasma pseudouridine to creatinine concentration was not directly proportional to that of 24 h urinary excretion.

Influence of Burns on Pharmacokinetics and Pharmacodynamics of Drugs Used in the Care of Burn Patients

The pharmacokinetics and pharmacodynamics of drugs are significantly altered in the burn patient, and the burn patient population shows wide inter- and intraindividual variation in drug handling. Burn injury evolves in two phases. The first phase corresponds to the burn shock, which occurs during the first 48 hours after thermal injury. In this phase, hypovolaemia, oedema, hypoalbuminaemia and a low glomerular filtration rate are observed, which result in a slower rate of drug distribution and lower renal clearance. The second phase (beyond 48 hours after injury) is a hyperdynamic state with high blood flow in the kidneys and liver, an increased alpha1-acid-glycoprotein level and loss of the drug with exudate leakage. As a result, protein binding, drug distribution and clearance may be altered. Because of the alteration in these variables, wide intraindividual variation of pharmacokinetic parameters occurs depending upon the time since thermal injury and fluid resuscitation. Interindividual variations may be correlated with the percentage of the body surface area that is burnt, creatinine clearance, albuminaemia or the alpha1-acid-glycoprotein level. A number of important variations in pharmacodynamic parameters have been described, but their mechanisms are poorly understood. From a practical point of view, for the subpopulation of burn patients who eliminate drugs extremely rapidly, higher doses and/or shorter dosing intervals are required to avoid treatment inefficacy. Drug concentration measurements help to take into account interindividual variability. However, adaptation of doses based on Bayesian methods is frequently not possible because the distribution of pharmacokinetic parameters is poorly characterized in this population. Methods based only on individual data or on a surrogate marker for efficacy may be used to optimize the dosing regimen in this population.

Prediction of Ammonia Emission from Dairy Cattle Manure Based on Milk Urea Nitrogen: Relation of Milk Urea Nitrogen to Urine Urea Nitrogen Excretion

The objectives of this study were to assess the relationship between urinary urea N (UUN) excretion (g/d) and milk urea N (MUN; mg/dL) and to test whether the relationship was affected by stage of lactation and the dietary crude protein (CP) content. Twelve lactating multiparous Holstein cows were randomly selected and blocked into 3 groups of 4 cows intended to represent early [123±26 d in milk (DIM); mean±standard deviation], mid (175±3 DIM), and late (221±12 DIM) lactation stages. Cows within each stage of lactation were randomly assigned to a treatment sequence within a split-plot Latin square balanced for carryover effects. Stage of lactation formed the main plots (squares) and dietary CP levels (15, 17, 19, and 21% of diet dry matter) formed the subplots. Graded amounts of urea were added to the basal total mixed ration to linearly increase dietary CP content while maintaining similar concentrations of all other nutrients among treatments. The experimental periods lasted 7 d, with d 1 to 6 used for adjustment to diets and d 7 used for total collection of urine as well as milk and blood sample collection. Dry matter intake and yields of milk, fat, protein, and lactose declined progressively with lactation stage and were unaffected by dietary CP content. Milk and plasma urea-N as well as UUN concentration and excretion increased in response to dietary CP content. Milk and urine urea-N concentration rose at increasing and decreasing rates, respectively, as a function of plasma urea-N. The renal urea-N clearance rate differed among lactation stages and dietary CP contents. The relationship between UUN excretion and MUN differed among lactation stages and diverged from linearity for cows in early and late lactation. However, these differences were restricted to very high MUN concentrations. Milk urea N may be a useful tool to predict the UUN excretion and ultimately NH3 emission from dairy cattle manure.

A New Class of Dimeric α-Interferons (IFN-α) Made by the Dock and Lock (DNL) Method for Improved Cancer Therapy.

Background: IFN-α2 is indicated for the therapy of hairy cell leukemia, chronic myelogenous leukemia, follicular lymphoma, and malignant melanoma. As is the case for most cytokines, the pharmacokinetic (PK) properties of IFN-α2 are critical for dosing and efficacy. In vivo, the protein is quickly degraded, diffuses widely throughout the body, and has a rapid rate of renal clearance. Pegylation of IFN-α2 significantly increases the serum half-life and reduces renal clearance, thus enhancing its efficacy. However, established pegylation of IFN-α2 results in a mixture of positional isomers and reduced in vitro activity, as known for PEGASYS (Roche) and PEG-INTRON (Schering-Plough).Methods: To improve the PK properties and the potency, the DNL method (Rossi et al. Proc. Natl. Acad. Sci. USA, 2006,103:6841) was used to generate novel agents having two copies of IFN-α2b conjugated to polyethylene glycol (PEG).Results: A fusion protein (DDD2-IFN-α2b) composed of IFN-α2b with a dimerization-and-docking domain (DDD2) and a six-His tag was expressed both in myeloma cells and in E. coli. Two PEG-based modules, each composed of a fluorescent molecule, an anchor domain (AD) and either a 20-kDa PEG (IMP362) or a 30-kDa PEG (IMP413), were synthesized. Combining DDD2-IFN-α2b and IMP362 or IMP413 under redox conditions resulted in the desirable DNL conjugates consisting of two copies of IFN-α2b and one PEG linked site-specifically via the DDD and AD interaction. The cytotoxic activity of DDD2-IFN-α2b on Daudi lymphoma cells was similar to that of commercially available recombinant IFN-α2 (rhIFN-α2). The purity and identity of the two DNL conjugates (α2b-413 and α2b-362) were demonstrated by SDS-PAGE, immunoblotting, and fluorescence imaging. Both also showed potent cytotoxic activity on Daudi cells in vitro and superior PK properties to PEG-INTRON. For example, the mean blood residence times for α2b-362 (10.3 h) and α2b-413 (21.7 h) were significantly longer than those of rhIFN-α2 (0.7 h) and PEG-INTRON (5.1 h). Initial studies in mice bearing Daudi xenografts showed a significant therapeutic advantage over PEG-INTRON for both α2b-362 and α2b-413. Animals given 14,000 IU of PEG-INTRON had a median survival (MS) of 32 days compared to 21 days for saline control, whereas those receiving α2b-362 at 14,000 IU, 7,000 IU and 3,500 IU resulted in MS of 45, 41 and 32 days, respectively. More remarkably, α2b-413 was the most effective, achieving MS of 46, >53, and >53 days with 3,500 IU, 7,000 IU and 14,000 IU, respectively, all statistically significant improvements (P< 0.0028) compared to PEG-INTRON given at each equivalent activity.Conclusions: The DNL method provides a novel pegylation strategy for generating a dimeric IFN-α2b that is linked site-specifically to a single PEG at the predetermined location. Since the resulting conjugates exhibit improved PK and efficacy in a Burkitt lymphoma model, they may represent a new class of interferons for use in cancer and infectious disease therapy.

Measurement of renal blood flow in human subjects using the ultrasound velocity profiling technique.

To (1) assess the accuracy of the ultrasound velocity profiling (USVP) technique of renal blood flow (RBF) measurement in normal subjects and (2) compare renal blood flow measurements obtained using USVP and renal clearance rate in patients with renal diseases. First, we calculated unilateral renal blood flow (unil-RBF) using USVP and the clearance rate of para-aminohippuric acid (CPAH) simultaneously in six healthy male subjects. We then compared unil-RBFUSVP and unil-RBFPAH in nine patients with chronic glomerulonephritis (CGN). In the first study, the limits of agreement in a Bland-Altman plot ranged from -325.3 to 32.0 ml/min per 1.48 m(2). The mean bias was -146.7 ml/min per 1.48 m(2). Subdivision for values of unil-RBFUSVP by flow showed small discrepancies in values above 280 ml/min per 1.48 m(2): mean bias, -98.2 ml/min per 1.48 m(2); limits of agreement, -223.3 to 26.8 ml/min per 1.48 m(2). The three patients in the second study had immunoglobulin A (IgA) nephropathy, in whom unil-RBFPAH was estimated as being markedly lower than unil-RBFUSVP, contrary to the primary result. Despite its consistent negative bias, USVP may be a reliable method of quantifying renal blood flow noninvasively when measured values exceed 280 ml/min per 1.48 m(2). We assumed that the p-aminohippurate extraction rate (EPAH) was profoundly impaired in the three patients with IgA nephropathy.

Variations in Porphobilinogen and 5-Aminolevulinic Acid Concentrations in Plasma and Urine from Asymptomatic Carriers of the Acute Intermittent Porphyria Gene with Increased Porphyrin Precursor Excretion

The heme precursors porphobilinogen (PBG) and 5-aminolevulinic acid (ALA) accumulate during overt crises of acute intermittent porphyria (AIP), and high excretion of these metabolites often continues in the asymptomatic phase. We measured concentrations of PBG and ALA and investigated the correlation between these metabolites in plasma and urine in 10 asymptomatic AIP carriers with high excretion and in 5 healthy individuals. We quantified plasma concentrations with an HPLC-mass spectrometric method and urine concentrations with ion-exchange chromatography. The mean (SD) plasma concentrations of PBG and ALA in the AIP carriers were 3.1 (1.0) and 1.7 (0.7) micromol/L, respectively. The mean 8-h urinary excretion amounts of PBG and ALA in the AIP carriers were 102 (25) and 56 (18) micromol, respectively, whereas the corresponding values for healthy individuals were 2.9 (0.7) and 9.3 (1.2) micromol. The correlations between PBG and ALA values in plasma and urine of the AIP carriers were 0.678 and 0.856, respectively. The mean PBG/ALA ratio was approximately 2.0 in both plasma and urine for the AIP carriers and 0.3 in urine for the healthy individuals. The renal clearance rates for PBG and ALA were 71 (15) and 70 (13) mL/min, respectively. The described HPLC-mass spectrometric method enabled characterization of variations in plasma PBG and ALA in AIP carriers during an 8-h period. The renal clearances were similar for both metabolites. This method could be used to monitor AIP patients during treatment.

Serum, urinary, and salivary nitric oxide in rheumatoid arthritis: complexities of interpreting nitric oxide measures

Nitric oxide (NO) may play important roles in rheumatoid arthritis (RA). RA is an inflammatory disease involving joints and other systems including salivary glands. To assess NO production in RA patients, we compared levels of serum, urine, and salivary nitrite and nitrate (NOx) in patients with RA and normal subjects, and we examined the relationships of these measures to disease activity. Serum, urine, and NOx levels as well as renal creatinine, NOx clearance and fractional excretion rates were compared in 25 RA patients and 20 age- and gender-matched healthy controls. Subjects were hospitalized for 3 days and placed on a NOxrestricted diet. NOx was assayed using nitrate reductase and the Griess reagent. RA activity was assessed using standard clinical and laboratory measures. While consuming a restricted diet for 3 days to eliminate the effects of oral intake of NOx, 24 hour urinary NOx excretion decreased in both RA patients and healthy controls. Urine NOx levels at all time points were not significantly different between RA patients and normal subjects. Serum NOx levels also decreased during the 3 days of NOx restriction, but RA patients had higher serum NOx levels at all time points compared with the control group. Likewise, serum NOx/creatinine ratios were higher in RA patients than in controls. Although basal salivary flow rate and tear flow were lower in RA patients, salivary NOx levels did not differ between normal and RA subjects. While renal creatinine clearance was not different between the two groups, we found that RA patients had lower renal NOx clearance and lower renal NOx fractional excretion. After correction of p values for multiple comparisons, there were no significant relationships for the RA group between measures of disease activity and the urinary NOx, serum NOx, or urinary NOx clearance. Despite interest in the use of NO as a marker of disease activity, alterations in renal NOx clearance and fractional excretion in RA make it difficult to assess in vivo NO production even with strict dietary restriction of NOx intake.

Heroin affects purine nucleotides catabolism in rats in vivo

To investigate the effect of heroin on purine nucleotides catabolism, a rat model of heroin administration and withdrawal was established. Concentrations of uric acid, creatinine, and urea nitrogen in plasma and ADA in plasma, brain, liver, and small intestine were tested. When two heroin administration groups were compared with the control group, the concentrations of plasma uric acid and ADA in plasma, brain, liver, and small intestine increased, whereas the plasma urea nitrogen concentrations in two heroin administration groups and the plasma creatinine concentration in the 3-day heroin administration group did not increase. It seemed that heroin exposure for a short time did not affect renal clearance rate notably. When two withdrawal groups were compared with two heroin administration groups, the concentrations of plasma uric acid and ADA in liver and small intestine decreased, but there was no significant reduction in ADA concentrations of the brain, while the plasma ADA concentrations in the two withdrawal groups were significantly higher than those of two heroin administration groups. When the two withdrawal groups were compared with the control group, there was no significant difference in the concentrations of plasma uric acid and ADA in liver and small intestine, while the concentrations of ADA in plasma and brain were still higher than those of the control group. The results imply that heroin administration may enhance the catabolism of purine nucleotides in the brain and other tissues by increased concentration of ADA and the effect may last for a long time in the brain.

Comparative inter-species pharmacokinetics of phenoxyacetic acid herbicides and related organic acidsEvidence that the dog is not a relevant species for evaluation of human health risk

Phenoxyacetic acids including 2,4-dichlorophenoxyacetic acid (2,4-D) and 4-chloro-2-methylphenoxyacetic acid (MCPA) are widely utilized organic acid herbicides that have undergone extensive toxicity and pharmacokinetic analyses. The dog is particularly susceptible to the toxicity of phenoxyacetic acids and related organic acids relative to other species. Active renal clearance mechanisms for organic acids are ubiquitous in mammalian species, and thus a likely mechanism responsible for the increased sensitivity of the dog to these agents is linked to a lower capacity to secrete organic acids from the kidney. Using published data describing the pharmacokinetics of phenoxyacetic and structurally related organic acids in a variety of species including humans, inter-species comparative pharmacokinetics were evaluated using allometic parameter scaling. For both 2,4-D and MCPA, the dog plasma half-life ( t 1/2 ) and renal clearance (Clr; mL/h) rates did not scale as a function of body weight across species; whereas for all other species evaluated, including humans, these pharmacokinetic parameters reasonably scaled. This exceptional response in the dog is clearly illustrated by comparing the plasma t 1/2 at comparable doses of 2,4-D and MCPA, across several species. At a dosage of 5 mg/kg, in dogs, the plasma t 1/2 for 2,4-D and MCPA were ∼92–106 and 63 h, respectively, which is substantially longer than in the rat (∼1 and 6 h, respectively) or in humans (12 and 11 h, respectively). This longer t 1/2 , and slower elimination in the dog, results in substantially higher body burdens of these organic acids, at comparable doses, relative to other species. Although these results indicate the important role of renal transport clearance mechanisms as determinants of the clearance and potential toxicity outcomes of phenoxyacetic acid herbicides across several species, other contributing mechanisms such as reabsorption from the renal tubules is highly likely. These findings suggest that for new structurally similar organic acids, a limited comparative species (rat versus dog) pharmacokinetic analysis early in the toxicology evaluation process may provide important insight into the relevance of the dog. In summary, the substantial difference between the pharmacokinetics of phenoxyacetic acids and related organic acids in dogs relative to other species, including humans, questions the relevance of using dog toxicity data for the extrapolation of human health risk.

Comparative inter-species pharmacokinetics of phenoxyacetic acid herbicides and related organic acidsEvidence that the dog is not a relevant species for evaluation of human health risk

Phenoxyacetic acids including 2,4-dichlorophenoxyacetic acid (2,4-D) and 4-chloro-2-methylphenoxyacetic acid (MCPA) are widely utilized organic acid herbicides that have undergone extensive toxicity and pharmacokinetic analyses. The dog is particularly susceptible to the toxicity of phenoxyacetic acids and related organic acids relative to other species. Active renal clearance mechanisms for organic acids are ubiquitous in mammalian species, and thus a likely mechanism responsible for the increased sensitivity of the dog to these agents is linked to a lower capacity to secrete organic acids from the kidney. Using published data describing the pharmacokinetics of phenoxyacetic and structurally related organic acids in a variety of species including humans, inter-species comparative pharmacokinetics were evaluated using allometic parameter scaling. For both 2,4-D and MCPA, the dog plasma half-life (t(1/2)) and renal clearance (Clr; mL/h) rates did not scale as a function of body weight across species; whereas for all other species evaluated, including humans, these pharmacokinetic parameters reasonably scaled. This exceptional response in the dog is clearly illustrated by comparing the plasma t(1/2) at comparable doses of 2,4-D and MCPA, across several species. At a dosage of 5mg/kg, in dogs, the plasma t(1/2) for 2,4-D and MCPA were approximately 92-106 and 63 h, respectively, which is substantially longer than in the rat (approximately 1 and 6 h, respectively) or in humans (12 and 11 h, respectively). This longer t(1/2), and slower elimination in the dog, results in substantially higher body burdens of these organic acids, at comparable doses, relative to other species. Although these results indicate the important role of renal transport clearance mechanisms as determinants of the clearance and potential toxicity outcomes of phenoxyacetic acid herbicides across several species, other contributing mechanisms such as reabsorption from the renal tubules is highly likely. These findings suggest that for new structurally similar organic acids, a limited comparative species (rat versus dog) pharmacokinetic analysis early in the toxicology evaluation process may provide important insight into the relevance of the dog. In summary, the substantial difference between the pharmacokinetics of phenoxyacetic acids and related organic acids in dogs relative to other species, including humans, questions the relevance of using dog toxicity data for the extrapolation of human health risk.

Pharmacokinetic and pharmacodynamic properties of eptifibatide in subjects with normal or impaired renal function

Backgroud: Previous studies of the glycoprotein IIb-IIIa inhibitor eptifibatide have included patients with moderate renal impairment (serum creatinine concentrations, 2.0–4.0 mg/dL). In these patients, adjustment of the standard infusion dose (2.0 μg/kg·min) to 1.0 μg/kg·min was recommended on empiric grounds because ∼50% of eptifibatide is cleared renally. Objective: The present study was designed to assess teh pharmacokinetic and pharmacodynamic properties of eptifibatide in subjects with various levels of creatinine clearance (CrCl), a parameter that is a more accurate indicator of renal function than serum creatinine concentration to determine the appropriate dose adjustment in patients with reduced renal function. A secondary objective was to determine the tolerability of eptifibatide when administered to patients with decreased renal function. Methods: This open-label study was concluded at 3 US sites experienced in conducting similar studies. Subjects with differing renal function (normal [group 1, CrCl > 80 mL/min], mild renal impairment [group 2, CrCl 51–80 mL/min], moderate renal impairment [group 3, CrCl 30–50 mL/min], or severe renal impairment [group 4, CrCl <30 mL/min]) received a 24-hour eptifibatide infusion of 2.0 μg/kg·min (groups 1, 2, and 3) or 1.0 μg/kg·min (group 4). The primary end point was the eptifibatide steady-state plasma concentration; the secondary end points included inhibition of platelet aggregation and eptifibatide clearance, terminal plasma half-life, and area under the plasma concentration-time curve. In addition to analyses performed for each group, pharmacokinetic models were estimated and eptifibatide clearance was related to CrCl as a continuous variable by linear regression. All adverse events were recorded, with particular attention to bleeding. Results: Thirty-one subjects (21 men, 10 women; mean age, 58.5 years [range, 44–73 years]; mean body weight, 81.6 kg [range, 51.5–105.1 kg]; mean height, 162.9 cm [range, 150–183 cm]) were included in the study. A strong correlation was found between eptifibatide clearance and CrCl. A tree-based analytic model indicated that the optimal discrete break point for the purpose of dose adjustment was a CrCl of 55.85 mL/min, which was rounded to 50 mL/min for practical clinical reasons. In patients with moderate or severe renal impairment (CrCl ≤ 50 mL/min), clearance rates and steady-state concentrations of eptifibatide were ∼50% lower and almost 2-fold higher, respectively, than in patients with normal renal function or mild renal impairment (CrCl > 50 mL/min). Inhibition of platelet aggregation exceeded the clinically significant threshold of 80% in all groups. Five subjects had a mild bleeding event and 4 subjects experienced mild to moderate nonbleeding events, 2 of which were considered drug-related by the investigator. None of the events required intervention. Conclusions: In this study, moderate to severe renal impairment was associated with an ∼50% reduction in total eptifibatide clearance and a corresponding doubling of plasma eptifibatide concentration. Based on these findings, in patients with moderately or severely impaired renal function (calculated CrCl ≤50 mL/min) who are scheduled for percutaneous coronary intervention or who have non-ST-segment elevation acute coronary syndromes, it is appropriate to reduce the infusion dose of eptifibatide by 50% (from 2 to 1 μg/kg·min). Because the bolus dose(s) is (are) used to establish the initial targeted plasma eptifibatide concentrations, which are independent of clearance, and given that the volume of distribution did not correlate with renal function, no adjustment of the bolus dose(s) is required.