Urinary Excretion Ratio Research Articles

Analysis of Pharmacokinetic Data Provided in Japanese Package Inserts and Interview Forms Focusing on Urinary Excretion of Pharmacologically Active Species

In optimizing oral pharmacotherapy for patients with renal failure, information on actual urinary excretion ratio of the unchanged drug, which is obtained by dividing a urinary excretion ratio by a bioavailability after oral dose, is quite helpful. In addition, urinary excretion ratio of the active species is sometimes equally important where metabolites have a pharmacological potency. In the present study, we conducted a survey of Japanese package inserts and interview forms of drugs, which is being prescribed at the University of Tokyo Hospital, on pharmacokinetic data that enables an estimation of actual urinary excretion ratio. The total urinary excretion of a drug was documented in 70.1% of package inserts and 84.5% of interview forms, respectively. The total urinary excretion is often measured by radioactivity and thus includes its metabolites and degradation products. However, inclusion of degradation products/metabolites was described explicitly for 43.7% and 66.2%, and the absolute fraction of the unchanged drug or degradation product/metabolite was given only for 29.0% and 48.9% in package inserts and interview forms, respectively. The pharmacological activity of metabolite(s) was documented for 19.8% and 54.3%, and the oral bioavailability was described only for 5.7% and 30.6% in respective documents. For some drugs, the time period for the urine collection was too short to evaluate the urinary excretion ratio. With regard to 65 drugs (38.7%), more detailed information on urinary excretion was found in published books, but not provided in the package inserts or interview forms. It is hoped that more distinct and sufficient descriptions on the urinary excretion and bioavailability will be associated to the package inserts and the interview forms in future, for safe and efficient use of prescription drugs.

Evaluation of the Drug Interaction Potential of Aplaviroc, a Novel Human Immunodeficiency Virus Entry Inhibitor, Using a Modified Cooperstown 5 + 1 Cocktail

Aplaviroc is a novel CCR5 antagonist, a class of compounds under investigation as viral entry inhibitors for the treatment of human immunodeficiency virus infection. A modified Cooperstown 5+1 cocktail was used to assess the drug interaction potential of aplaviroc. Fifteen healthy subjects were administered single oral doses of caffeine (CYP1A2), warfarin (CYP2C9), omeprazole (CYP2C19), dextromethorphan (CYP2D6), and midazolam (CYP3A) alone (reference treatment) and during steady-state administration of aplaviroc (400 mg every 12 hours, test treatment). Metabolite-to-parent area under the plasma concentration versus time curve (AUC) ratios (paraxanthine/caffeine and 5-hydroxyomeprazole/omeprazole), oral clearance (S-warfarin), AUC (midazolam), and metabolite-to-parent urinary excretion ratio (dextrorphan/dextromethorphan) were determined. The test-to-reference treatment ratios (geometric mean ratio and 90% confidence interval) were caffeine, 1.06 (0.97-1.17); S-warfarin, 0.93 (0.76-1.15); omeprazole, 1.07 (0.98-1.16); dextromethorphan, 1.17 (0.97-1.42); midazolam, 1.30 (1.04-1.63). No significant inhibition of CYP1A2, CYP2C9, CYP2C19, or CYP2D6 enzyme activity was observed. Mild inhibition of CYP3A isozymes should not preclude the use of concomitant CYP3A substrates in future clinical studies with aplaviroc.

AUTOINDUCTION OF MKC-963 [(R)-1-(1-CYCLOHEXYLETHYLAMINO)-4-PHENYLPHTHALAZINE] METABOLISM IN HEALTHY VOLUNTEERS AND ITS RETROSPECTIVE EVALUATION USING PRIMARY HUMAN HEPATOCYTES AND CDNA-EXPRESSED ENZYMES

MKC-963, (R)-1-(1-cyclohexylethylamino)-4-phenylphthalazine, a potent inhibitor of platelet aggregation, was synthesized and used in clinical trials in the 1990s. In the process of clinical study, it was found that urinary excretion ratios for 6beta-hydroxycortisol and free cortisol increased significantly in parallel with decreases in the plasma concentrations of MKC-963 after repeated oral administration of the compound to healthy volunteers. These findings suggested that MKC-963 caused autoinduction (defined as the ability of a drug to induce enzymes that enhance its own metabolism, resulting in dispositional tolerance) in humans, and clinical studies using the compound were stopped. This experience prompted us to reevaluate the effects of this compound on CYP3A4 using primary human hepatocytes and cDNA-expressed human cytochrome P450 (P450) enzymes to determine whether the autoinduction of MKC-963 metabolism in humans could have been predicted if these in vitro systems had been used for the evaluation of MKC-963 in the preclinical study. The results of in vitro study showed that MKC-963 increased CYP3A4 mRNA expression level and activity of testosterone 6beta-hydroxylation to extents similar to those observed with rifampicin in primary human hepatocytes. In addition, approximately 90% of the MKC-963 metabolism in human liver microsomes was estimated to be attributable to CYP3A4. These in vitro findings are in good agreement with the results of clinical study, suggesting that studies using human hepatocytes and cDNA-expressed human P450s are useful for assessing the autoinductive nature of compounds under development before starting clinical studies.

The pharmacokinetics of escitalopram in patients with hepatic impairment

The effect of hepatic impairment on the pharmacokinetics of escitalopram was determined by means of nonlinear mixed effect modeling, considering both the Child-Pugh classification (and its components) and cytochrome P450 2C19 (CYP2C19) activity. Twenty-four subjects were grouped according to their Child-Pugh score as healthy, with mild hepatic impairment or with moderate hepatic impairment. The subjects were administered a single oral dose of escitalopram 20 mg, and blood was sampled up to 168 hours after dosage. The serum concentration of escitalopram was determined and the pharmacokinetics assessed by nonlinear mixed effect modeling. The CYP2C19 activity was measured from the urinary excretion ratio of S/R-mephenytoin. All subjects tolerated the treatment well, and no serious adverse events were reported. Predicted mean area under the curve from zero to infinity (AUC(inf)) values were 51% and 69% higher for patients with mild and moderate hepatic impairment (Child-Pugh classification), respectively, compared with healthy subjects. The best-fitting model showed an influence of CYP2C19 activity on clearance and body weight on the volume of distribution for escitalopram. CYP2C19 activity is a better predictor of escitalopram clearance than is Child-Pugh classification.

Telithromycin, but not montelukast, increases the plasma concentrations and effects of the cytochrome P450 3A4 and 2C8 substrate repaglinide

The antidiabetic repaglinide is metabolized by cytochrome P450 (CYP) 2C8 and CYP3A4. Telithromycin, an antimicrobial agent, inhibits CYP3A4 in vitro and in vivo. Montelukast, an antiasthmatic drug, is a potent inhibitor of CYP2C8 in vitro. We studied the effects of telithromycin, montelukast, and the combination of telithromycin and montelukast on the pharmacokinetics and pharmacodynamics of repaglinide. In a randomized 4-phase crossover study, 12 healthy volunteers received 800 mg telithromycin, 10 mg montelukast, both telithromycin and montelukast, or placebo once daily for 3 days. On day 3, they ingested a single 0.25-mg dose of repaglinide. Plasma and urine concentrations of repaglinide and its metabolites M1, M2, and M4, as well as blood glucose concentrations, were measured for 12 hours. Telithromycin alone raised the mean peak plasma repaglinide concentration to 138% (range, 91%-209%; P = .006) and the total area under the plasma concentration-time curve from 0 hours to infinity [AUC0-infinity] of repaglinide to 177% (range, 125%-257%; P < .001) of control (placebo). Telithromycin reduced the AUC0-infinity ratio of the metabolite M1 to repaglinide by 68% (P < .001) and the urinary excretion ratio of M1 to repaglinide by 77% (P = .001). In contrast to previous estimates based on in vitro CYP2C8 inhibition data, montelukast had no significant effect on the pharmacokinetics of repaglinide or its metabolites and did not significantly alter the effect of telithromycin on repaglinide pharmacokinetics. Telithromycin, unlike montelukast, lowered the maximum blood glucose concentration (P = .002) and mean blood glucose concentration from 0 to 3 hours (P = .008) after repaglinide intake, as compared with placebo. Telithromycin increases the plasma concentrations and blood glucose-lowering effect of repaglinide by inhibiting its CYP3A4-catalyzed biotransformation and may increase the risk of hypoglycemia. Unexpectedly, montelukast has no significant effect on repaglinide pharmacokinetics, suggesting that it does not significantly inhibit CYP2C8 in vivo. The low free fraction of montelukast in plasma may explain the lack of effect on CYP2C8 in vivo, despite the low in vitro inhibition constant, highlighting the importance of incorporating plasma protein binding to interaction predictions.

Effects of Tangshenling Mixture and benazepril on rats with diabetic nephropathy and its mechanism

To investigate the effects of Tangshenling Mixture (TSLM) and benazepril on rats with diabetic nephropathy (DN) and its mechanism. Diabetic nephropathy was induced in rats by intraperitoneal injection of streptozotocin. Fifty-eight rats with DN were randomly divided into four groups: untreated group, TSLM-treated group, TSLM plus benazepril-treated group and benazepril-treated group. Another seven normal rats were included in normal control group. Then, rats in each group were accordingly given normal saline, TSLM, TSLM plus benazepril and benazepril orally for six weeks respectively. Blood and urine biochemical indexes, plasma atrial natriuretic factor (ANF), pathomorphology of renal tissue, transforming growth factor beta1 (TGF-beta1) and glucose transporter 1 (GLUT1) mRNAs in renal tissue were observed. Both TSLM and benazepril could decrease urinary albumin excretion rates, creatinine clearance and ratio of kidney weight to body weight of the rats with DN as well as reduce the pathological damages of the renal tissues. TSLM could reduce the level of plasma ANF and the expression of GLUT1 mRNA, but had no significant effect on the expression of TGF-beta1 mRNA. Benazepril could reduce the expression of TGF-beta1 mRNA, but had no significant effect on plasma ANF and the expression of GLUT1 mRNA. TSLM can reduce the pathological damages of renal tissues in rats with early-stage DN, and its mechanism may relate to decreasing the level of plasma ANF and the expression of GLUT1 mRNA which is different from that of benazepril. It seems that TSLM has synergetic effect with benazepril.

Genotoxicity and Potential Carcinogenicity of 2,4,6-Trinitrotoluene: Structural and Toxicological Considerations

Environmental contamination with 2,4,6-TNT (trinitrotoluene) represents a worldwide problem. Concern for carcinogenicity can be derived from chemically related compounds, especially the dinitrotoluenes. In the metabolism of TNT, the reductive routes are preponderant. The main urinary metabolites of TNT are 4-amino-2,6-dinitrotoluene and 2-amino-4,6-dinitrotoluene. In humans exposed to TNT, the formation of hemoglobin adducts of the amino-dinitrotoluenes is in general concordance with the ratio of urinary excretion. The variations in quantities of excreted metabolites among the different occupational cohorts studied are likely explained by the different routes of exposure to TNT, including dermal uptake. Most studies show that urinary excretion of the amino-dinitrotoluenes (4-amino-dinitrotoluene plus 2-amino-dinitrotoluene) in a range of 1 to 10 mg L(-1) (5-50 microM) are not uncommon--for instance in persons employed with the disposal of military waste. Trinitotoluene is mutagenic in Salmonella typhimurium strains TA98 and TA100, with and without exogenous metabolic activation. Mutagenic activity has been found in urine from workers who were occupationally exposed to TNT. An unpublished 2-year study was reported in 1984 by the IIT Research Institute, Chicago, IL. Fischer 344 rats were fed diets containing 0.4, 2.0, 10, or 50 mg/kg TNT per day. In the urinary bladder, hyperplasia (12 of 47 animals p < .01) and carcinoma (11 of 47 animals, p < .05) were observed at significant levels in high-dose (50 mg kg(-1)) females and in one or two females, respectively, at 10 mg kg(-1). Taking all the available evidence together, the appropriate precautions should be taken.

Small-bowel permeability in collagenous colitis

Objective. Collagenous colitis (CC) is a chronic inflammatory bowel disease that affects the colon. However, some patients with CC present with accompanying pathologic small-bowel manifestations such as coeliac disease, defects in bile acid absorption and histopathologic changes in small-intestinal biopsies, indicating that CC is a pan-intestinal disease. In small-intestinal disease, the intestinal barrier function may be impaired, and the permeability of the small intestine altered. The purpose of this research was to study small-bowel function in patients with CC as expressed by intestinal permeability. Material andmethods. Ten patients with CC and chronic diarrhoea participated in the study. Coeliac disease was excluded by small-bowel biopsy and/or serology. Intestinal permeability was assessed as urinary excretion (ratios) 2, 4 and 6 h after ingestion of 14C-labelled mannitol (14C-mannitol) and 99mTc-labelled diethylenetriamine-pentaacetic acid (99mTc-DTPA). Data were compared with the results from healthy controls. Results. No difference was found between groups in urinary excretion of 14C-mannitol and 99mTc-DTPA after 2, 4 or 6 h, respectively. Likewise, no significant differences in the 99mTc-DTPA/14C-mannitol ratios between patients and controls were detected after 2 h: 0.030 (0.008–0.130) versus 0.020 (0.007–0.030), p=0.19, after 4 h: 0.040 (0.009–0.180) versus 0.020 (0.008–0.040), p=0.14 or after 6 h: 0.040 (0.012–0.180) versus 0.020 (0.010–0.040), p=0.17. Conclusions. No alterations in intestinal permeability in patients with CC could be demonstrated. Impairment of the integrity of the mucosa of the small bowel and the presence of a general dysfunction of the small intestine in patients with CC seem unlikely.

Increased gut permeability after multiple trauma.

Gut permeability was studied in multiply injured patients with respect to the development of multiple organ failure (MOF). Two groups were defined according to MOF score (threshold 10 points) as to whether MOF developed (group 1; n = 11, four deaths) or did not (group 2; n = 21, no death). Gut permeability was determined from the ratio of urinary excretion of enterally administered lactulose and mannitol. Serum elastase concentrations were also determined. Mean(s.e.m.) gut permeability was abnormal during the entire study (day 1: group 1--5.1(2.1) versus group 2--10.6(4.1) (P not significant; P < 0.001 versus normal volunteers, 0.56(0.24)). An increase on days 3 and 5 correlated with serum elastase levels only in patients in group 1 (rs = 0.71, P < 0.01). Severe injury leads to increased intestinal permeability, which is related to a systemic inflammatory response.

Comparative Efficacy and Safety of Low-dose Fluticasone Propionate and Montelukast in Children with Persistent Asthma

To evaluate efficacy, safety, health outcomes, and cost-effectiveness of fluticasone propionate (FP) versus montelukast (MON) in 342 children (6 to 12 years of age) with persistent asthma. Randomized, double-blind, 12-week study of treatment with FP inhalation powder 50 mug twice daily or MON chewable 5 mg once daily for 12 weeks. Compared with MON, FP significantly increased mean percent change from baseline FEV1 (forced expiratory volume in 1 second) (P=.002), morning PEF (peak expiratory flow) (P=.004), evening PEF (P=.020), and percent rescue-free days (P=.002) at end point, and it significantly reduced nighttime symptom scores (P <.001) and mean total (P=.018), and nighttime (P <.001) albuterol use. Withdrawals from the study were more frequent with MON (21%) than with FP (13%). Adverse events (69% vs 71%) and mean end point to baseline 12-hour urinary cortisol excretion ratios were similar. Parents and physicians were more satisfied with FP treatment than with MON (P=.006 and P=.016, respectively, at Week 12). Mean total daily asthma-related cost per patient in the FP group was approximately one-third of that in the MON group ($1.25 vs $3.49). FP was significantly more effective than MON in improving pulmonary function, asthma symptoms, and rescue albuterol use. Both therapies had similar safety profiles. Parent- and physician-reported satisfaction ratings were higher with FP treatment, and asthma-related costs were lower.

Common variants of the beta and gamma subunits of the epithelial sodium channel and their relation to plasma renin and aldosterone levels in essential hypertension

BackgroundRare mutations of the epithelial sodium channel (ENaC) result in the monogenic hypertension form of Liddle's syndrome. We decided to screen for common variants in the ENaC βand γ subunits in patients with essential hypertension and to relate their occurrence to the activity of circulating renin-angiotensin-aldosterone system.MethodsInitially, DNA samples from 27 patients with low renin/low aldosterone hypertension were examined. The DNA variants were subsequently screened for in 347 patients with treatment-resistant hypertension, 175 male subjects with documented long-lasting normotension and 301 healthy Plasma renin and aldosterone levels were measured under baseline conditions and during postural and captopril challenge tests.ResultsTwo commonly occurring βENaC variants (G589S and a novel intronic i12-17CT substitution) and one novel γENaC variant (V546I) were detected. One of these variants occurred in a heterozygous form in 32 patients, a prevalence (9.2%) significantly higher than that in normotensive males (2.9%, p = 0.007) and blood donors (3.0%, p = 0.001). βENaC i12-17CT was significantly more prevalent in the hypertension group than in the two control groups combined (4.6% vs. 1.1%, p = 0.001). When expressed in Xenopus oocytes, neither of the two ENaC amino acid-changing variants showed a significant difference in activity compared with ENaC wild-type. No direct evidence for a mRNA splicing defect could be obtained for the βENaC intronic variant. The ratio of daily urinary potassium excretion to upright and mean (of supine and upright values) plasma renin activity was higher in variant allele carriers than in non-carriers (p = 0.034 and p = 0.048).ConclusionsAt least 9% of Finnish patients with hypertension admitted to a specialized center carry genetic variants of β and γENaC, a three times higher prevalence than in the normotensive individuals or in random healthy controls. Patients with the variant alleles showed an increased urinary potassium excretion rate in relation to their renin levels.

Clinical Pharmacokinetics of Imatinib

Imatinib is a potent and selective inhibitor of the protein tyrosine kinase Bcr-Abl, platelet-derived growth factor receptors (PDGFRalpha and PDGFRbeta) and KIT. Imatinib is approved for the treatment of chronic myeloid leukaemia (CML) and gastrointestinal stromal tumour (GIST), which have dysregulated activity of an imatinib-sensitive kinase as the underlying pathogenetic feature. Pharmacokinetic studies of imatinib in healthy volunteers and patients with CML, GIST and other cancers show that orally administered imatinib is well absorbed, and has an absolute bioavailability of 98% irrespective of oral dosage form (solution, capsule, tablet) or dosage strength (100 mg, 400 mg). Food has no relevant impact on the rate or extent of bioavailability. The terminal elimination half-life is approximately 18 hours. Imatinib plasma concentrations predictably increase by 2- to 3-fold when reaching steady state with 400mg once-daily administration, to 2.6 +/- 0.8 microg/mL at peak and 1.2 +/- 0.8 microg/mL at trough, exceeding the 0.5 microg/mL (1 micromol/L) concentrations needed for tyrosine kinase inhibition in vitro and leading to normalisation of haematological parameters in the large majority of patients with CML irrespective of baseline white blood cell count. Imatinib is approximately 95% bound to human plasma proteins, mainly albumin and alpha1-acid glycoprotein. The drug is eliminated predominantly via the bile in the form of metabolites, one of which (CGP 74588) shows comparable pharmacological activity to the parent drug. The faecal to urinary excretion ratio is approximately 5:1. Imatinib is metabolised mainly by the cytochrome P450 (CYP) 3A4 or CYP3A5 and can competitively inhibit the metabolism of drugs that are CYP3A4 or CYP3A5 substrates. Interactions may occur between imatinib and inhibitors or inducers of these enzymes, leading to changes in the plasma concentration of imatinib as well as coadministered drugs. Hepatic and renal dysfunction, and the presence of liver metastases, may result in more variable and increased exposure to the drug, although typically not necessitating dosage adjustment. Age (range 18-70 years), race, sex and bodyweight do not appreciably impact the pharmacokinetics of imatinib.

The SOD mimetic tempol ameliorates glomerular injury and reduces mitogen-activated protein kinase activity in Dahl salt-sensitive rats.

It was shown recently that renal injury in Dahl salt-sensitive (DS) hypertensive rats is accompanied by mitogen-activated protein kinase (MAPK) activation. The present study was conducted to elucidate the contribution of reactive oxygen species to MAPK activities and renal injury in DS rats. DS rats were maintained on high salt (H; 8.0% NaCl; n = 7) or low salt (L; 0.3% NaCl; n = 6) diets; H + a superoxide dismutase mimetic, tempol (3 mmol/L in drinking water; n = 8); or H + hydralazine (0.5 mmol/L in drinking water; n = 8) for 4 wk. Mean BP (MBP) in DS/H and DS/L rats was 185 +/- 7 and 113 +/- 3 mmHg, respectively. DS/H rats showed a higher ratio of urinary protein excretion and creatinine (U(protein)V/U(cr)V; 20.3 +/- 1.1) and a higher cortical collagen content (22 +/- 1 micro g/mg) than in DS/L rats (2.4 +/- 0.1 and 13 +/- 1 micro g/mg, respectively). The expression of p22-phox and Nox-1, essential components of NAD(P)H oxidase, in renal cortical tissue was approximately threefold higher in DS/H rats than in DS/L rats. Increased activities of renal cortical MAPK, including extracellular signal-regulated kinases (ERK) 1/ERK2 and c-Jun NH(2)-terminal kinases (JNK) were also observed in DS/H rats by 7.0 +/- 0.7- and 4.3 +/- 0.2-fold, respectively. Tempol treatment significantly decreased MBP (128 +/- 3 mmHg), U(protein)V/U(cr)V (4.8 +/- 0.4), and cortical collagen content (14 +/- 1 micro g/mg) and normalized ERK1/ERK2 and JNK activities in DS/H rats. Histologically, tempol markedly ameliorated progressive sclerotic and proliferative glomerular changes in DS/H rats. Hydralazine-treated DS/H rats showed similar MBP (127 +/- 5 mmHg) to tempol-treated DS/H rats. Hydralazine also decreased U(protein)V/U(cr)V (16.2 +/- 1.5) and cortical collagen content (19 +/- 1 micro g/mg) in DS/H rats. However, these values were significantly higher than those of tempol-treated rats. Furthermore, although hydralazine significantly reduced JNK activity (-56 +/- 3%), ERK1/ERK2 activities were unaffected. These data suggest that reactive oxygen species, generated by NAD(P)H oxidase, contribute to the progression of renal injury through ERK1/ERK2 activation in DS/H hypertensive rats.

Effects of pentoxifylline administration on urinary N-acetyl-β-glucosaminidase excretion in type 2 diabetic patients: a short-term, prospective, randomized study

Background:Tubulointerstitial injury is a major feature of diabetic nephropathy and an important predictor of renal dysfunction. In 45 patients with type 2 diabetes mellitus (DM), we prospectively analyzed urinary excretion of N-acetyl-β-glucosaminidase (NAG), a marker of tubular renal damage; the potential relationship with urinary protein excretion; and effects of pentoxifylline (PTF) administration. Methods:Forty-five patients with type 2 DM initially were compared with 15 healthy controls matched for age and sex. After randomization, PTF (1,200 mg/d) was administered for 4 months to 30 patients and results were compared with data from a control group (n = 15). Results:Proteinuria and urinary NAG excretion were significantly greater in patients with DM with respect to healthy controls. Before PTF administration, baseline parameters were similar in both groups of patients with DM. At the end of the study, urinary protein excretion and NAG-creatinine ratios decreased in the active group from 920 ± 522 mg/d and 14.3 ± 16.9 U/g to 803 ± 523 mg/d (P < 0.001) and 10.5 ± 9.3 U/g (P < 0.05), respectively. Conversely, proteinuria and urinary NAG excretion did not change in the control group. Regression analysis showed that urinary NAG excretion was significantly associated with duration of DM (r = 0.61; P < 0.001) and proteinuria (r = 0.51; P < 0.001). Conclusion:Urinary NAG excretion is elevated in patients with type 2 DM compared with healthy individuals and increases as nephropathy progresses. PTF administration is effective in reducing proteinuria and urinary NAG excretion in these patients. These findings suggest that PTF may have beneficial effects on tubulointerstitial damage in diabetic kidney disease.

Evaluation of rat intestinal absorption data and correlation with human intestinal absorption

The absorption of 111 drug and drug-like compounds was evaluated from 111 references based on the ratio of urinary excretion of drugs following oral and intravenous administration to intact rats and biliary excretion of bile duct-cannulated rats. Ninety-eight drug compounds for which both human and rat absorption data were available were selected for correlation analysis between the human and rat absorption. The result shows that the extent of absorption in these two species is similar. For 94% of the drugs the absorption difference between humans and rats is less than 20% and for 98% of drugs the difference is less than 30%. There is only one drug for which human absorption is significantly different from rat absorption. The standard deviation is 11% between human and rat absorption. The linear relationship between human and rat absorption forced through the origin, as determined by least squares regression, is %Absorption (human)=0.997%Absorption (rat) ( n=98, SD=11). It is suggested that the absorption in rats could be used as an alternative method to human absorption in pre-clinical oral absorption studies.

Pioglitazone: effect on CYP3A4 activity.

Clinical studies demonstrate CYP3A4 enzyme induction with troglitazone, a thiazolidinedione derivative structurally related to pioglitazone. The objective of this prospective, open-label study conducted in healthy volunteers was to evaluate the influence of multiple-dose pioglitazone therapy on the urinary excretion ratio of 6-beta-hydroxycortisol to cortisol, an endogenous marker of CYP3A4 activity. Twelve subjects were given pioglitazone hydrochloride 45 mg daily for 14 days. Urine was collected over a 24-hour period before pioglitazone and after administration of the last tablet. Baseline and posttreatment CYP3A4 activity was assessed with the urinary 6-beta-hydroxycortisol/cortisol ratio. The mean +/- SD 6-beta-hydroxycortisol/cortisol ratios before and after treatment were 8.3 +/- 4.4 and 9.4 +/- 4.0, respectively (p = 0.29). The mean change from baseline was a nonsignificant 20.2%. Nine subjects had a small increase and 3 subjects had a reduction in the ratio. Using the ratio as a marker of CYP3A4 activity, the data support a lack of inductive effect on CYP3A4 by multiple-dose pioglitazone therapy. Thus, administration of pioglitazone should not result in clinically significant effects on the pharmacokinetics of other CYP3A4 substrates.

Use of an Oral/Intravenous Dual-Label Stable-Isotope Protocol to Determine Folic Acid Bioavailability from Fortified Cereal Grain Foods in Women

Folic acid fortification, mandatory in the United States, is currently being considered by the UK. The hypothesis that the matrix of some cereal-product vehicles may result in low fortificant bioavailability was tested using a dual oral/intravenous (i.v.) isotopic-label approach, which was evaluated concurrently. Fifteen women received 225 microg oral folate (capsules, fortified white bread and fortified branflakes), mainly as folic acid labeled with (13)C on 6 carbons of the benzoyl ring ((13)C(6)-PteGlu), followed by i.v. injection of 100 microg folic acid labeled with (2)H on 4 hydrogens of the glutamic acid group ((2)H(4)-PteGlu). The urinary excretion ratio (UER) in intact folate of the percentage of labeled oral dose excreted divided by the percentage of i.v. dose excreted was used as the primary index of absorption. The geometric mean (95% confidence interval) UER for folic acid capsules was 3.68 (1.90, 7.14) at 24 h and 2.18 (1.24, 3.83) at 48 h. Because these were significantly in excess of 1.0, indicative of 100% absorption of the oral dose, it was concluded that oral and i.v. labeled folic acid are handled differently by the body and that "absolute" absorption cannot be calculated. Compared with the 48-h UER for folic acid capsules, the "relative" 48-h UER for white bread and branflakes was 0.71 and 0.37, respectively, indicating that some cereal-based vehicles may inhibit absorption of fortificant. However, even the validity of this "relative" approach is questioned.

Direct measurement of renal sympathetic nervous activity in high-fat diet-related hypertensive rats

The elevation of renal sympathetic nervous activity (SNA) is a possible cause of blood pressure (BP) elevation. Although a high-fat diet (FAT) often induces BP elevation in animals, the effect of FAT on renal SNA in animals is not consistent between studies. Thus, we compared the basal levels of efferent renal SNA and BP in FAT- or high-carbohydrate diet (CHO)-fed rats. Twenty-four male Sprague-Dawley rats were fed FAT (P/F/C=20/45/35% cal) or CHO (20/5/75) from 5 weeks of age. After 20–21 weeks of feeding, a 24-h urine sample was collected to measure sodium excretion. The next day, blood (0.2 ml) was withdrawn from a femoral artery, and basal efferent renal nerve discharges and mean arterial pressure (MAP) were recorded under anesthesia. Immediately after the experiment, abdominal (epididymal, perirenal and mesenteric) adipose tissues were dissected. Total abdominal fat weight was significantly greater in the FAT group than in the CHO group. The plasma level of leptin was significantly higher in the FAT group, but blood glucose and plasma insulin levels did not differ between the two groups. MAP and renal SNA were significantly higher in the FAT group. In addition, the ratio of urinary sodium excretion to dietary sodium intake was significantly lower in the FAT group than in the CHO group. The data suggest that the increased renal SNA may contribute to BP elevation in FAT-fed rats. The present study firstly demonstrated that renal SNA was elevated with FAT-related BP elevation.

Validity of Dual-Label Stable Isotopic Protocols and Urinary Excretion Ratios to Determine Folate Bioavailability from Food

We tested the hypothesis that some cereal-product vehicles may reduce fortificant bioavailability below 85% and examined the feasibility of using single dose, dual-label, non-saturation protocols for studying bioavailability based on urinary excretion ratios (UER; % oral 13C6 isotope dose excreted in intact folate/% i.v. 2H4 isotope dose excreted). Fifteen females received 225 micrograms oral folate (capsules, fortified bran flakes, and fortified white bread), mainly as 13C6-PteGlu, followed by i.v. injection of 100 micrograms 2H4-PteGlu. UERs were used as the primary index of absorption. Urinary folate was cleaved to p-aminobenzoylglutamic acid, dervivatized and determined by gas chromatography/mass spectroscopy (GC/MS). The UER mean (95%CI) for folic acid was 2.18 (1.2-3.8) at 48 hours and as these were greater than 1.0, it was concluded that oral and i.v. isotopes of folic acid are handled differently by the body. Compared to the 48 hour UER for folic acid, UERs for white bread and bran flakes were 0.71 and 0.37, respectively, thus indicating some matrix inhibition of absorption. Consideration should be given to the choice of cereal-based fortification vehicles in order to maximize bioavailability. Plasma enrichment of folate can be measured using LC/MSMS (liquid chromatography/mass spectroscopy-mass spectroscopy) but seems unfeasible with the GC/MS method.

Salivary and urinary excretion and plasma-saliva concentration ratios of isoniazid in the presence of Co-administered ciprofloxacin.

Salivary and urinary excretion and plasma-saliva concentration ratios of isoniazid (INH) in the absence and presence of ciprofloxacin (CP) were investigated in healthy female volunteers. Results obtained indicated an absorption form of interaction between INH and CP. This led to delay in gastric emptying and onset of absorption of INH in the upper part of the gastrointestinal tract, resulting in a corresponding delay in the onset of salivary and urinary excretion of the drugs. There was a 1-hour reduction in the time to attain peak saliva concentration of INH (tmax), an insignificant difference in peak saliva concentration (Cmax), and a significant (P = 0.05) increase in AUC(0-24h) of INH in the presence of CP. Cumulative amount of INH excreted in the urine increased approximately 38% in the presence of CP. The calculated plasma-saliva concentration ratios of INH were reduced in the presence of CP and were slightly lower than the experimental values. This indicates increased amount of the drug secreted into saliva in the presence of CP and possible buccal partitioning of the drug. Overall, results of the current study indicate that CP delayed the onset but not the extent of INH absorption. Therefore, concurrent administration of the two drugs was considered relatively safe, and the absorption interaction that may have occurred may not be of reasonable clinical consequence.