Developing whole cell standards for the microbiome field

BACKGROUND

Effective standardisation of the microbiome field is essential to facilitate global translational research and increase the reproducibility of microbiome studies. In this study, we describe the development and validation of a whole cell reference reagent specific to the gut microbiome by the UK National Institute for Biological Standards and Control. We also provide and test a two-step reporting framework to allow microbiome researchers to quickly and accurately validate choices of DNA extraction, sequencing, and bioinformatic pipelines.

RESULTS

Using 20 strains that are commonly found in the gut, we developed a whole cell reference reagent (WC-Gut RR) for the evaluation of the DNA extraction protocols commonly used in microbiome pipelines. DNA was first analysed using the physicochemical measures of yield, integrity, and purity, which demonstrated kits widely differed in the quality of the DNA they produced. Importantly, the combination of the WC-Gut RR and the three physicochemical measures allowed us to differentiate clearly between kit performance. We next assessed the ability of WC-Gut RR to evaluate kit performance in the reconstitution of accurate taxonomic profiles. We applied a four-measure framework consisting of Sensitivity, false-positive relative abundance (FPRA), Diversity, and Similarity as previously described for DNA reagents. Using the WC-Gut RR and these four measures, we could reliably identify the DNA extraction kits' biases when using with both 16S rRNA sequencing and shotgun sequencing. Moreover, when combining this with complementary DNA standards, we could estimate the relative bias contributions of DNA extraction kits vs bioinformatic analysis. Finally, we assessed WC-Gut RR alongside other commercially available reagents. The analysis here clearly demonstrates that reagents of lower complexity, not composed of anaerobic and hard-to-lyse strains from the gut, can artificially inflate the performance of microbiome DNA extraction kits and bioinformatic pipelines.

CONCLUSIONS

We produced a complex whole cell reagent that is specific for the gut microbiome and can be used to evaluate and benchmark DNA extractions in microbiome studies. Used alongside a DNA standard, the NIBSC DNA-Gut-Mix RR helps estimating where biases occur in microbiome pipelines. In the future, we aim to establish minimum thresholds for data quality through an interlaboratory collaborative study. Video Abstract.

Urban waste no replacement for natural foods—Marabou storks in Botswana

We compared diets of marabou storks Leptoptilos crumenifer foraging from urban landfills and natural areas in northern Botswana using stable isotope analyses and inductively coupled plasma mass spectrometry on moulted feathers. There were significant differences in the diet of marabous foraging from natural areas compared to urban waste sites, reflected by lower δ13C and less enriched δ15N concentrations in those feeding at landfills, suggesting a shift in trophic niche. Feathers from birds foraging at landfills also had significantly higher concentrations of chromium, lead, nickel, and zinc and lower levels of cadmium and potassium than feathers sampled from natural areas. We also analysed marabou regurgitant (42 kg, naturally expelled indigestible food resources) from the Kasane landfill site. More than half was plastic, with single regurgitants weighing up to 125 g. Urban waste stored in open air landfills is altering some marabou diets, affecting their natural trophic niche, resulting in the consumption (and regurgitation) of large amounts of plastic, and exposing marabou to potentially chronic levels of trace metals. Despite the marabou’s apparent resilience to this behavioural shift, it could have long-term effects on the population of the marabou stork, particularly considering Botswana has some of the few regular marabou breeding colonies in southern Africa.

Fibrinogen protects neutrophils from the cytotoxic effects of histones and delays neutrophil extracellular trap formation induced by ionomycin

Neutrophils are pivotal players in immune defence which includes a process of release of histones and DNA as neutrophil extracellular traps (NETs). Histones, while toxic to invading pathogens, also kill host cells, including neutrophils. Bacteria have evolved mechanisms to escape neutrophils, including the secretion of leucocidins (e.g. ionomycin). Live cell video microscopy showed how fibrinogen and fibrin influence NETosis and neutrophil responses to extracellular histones. Histones were rapidly lethal to neutrophils after binding to cells, but formation of fibrinogen/fibrin-histone aggregates prevented cell death. Histone cytotoxicity was also reduced by citrullination by peptidyl arginine deiminase 4, or digestion by serine proteases. Ionomycin and phorbol 12-myristate 13 acetate (PMA) are used to trigger NETosis. Fibrinogen was responsible for a second distinct mechanism of neutrophil protection after treatment with ionomycin. Fibrinogen clustered on the surface of ionomycin-stimulated neutrophils to delay NETosis; and blocking the β integrin receptor, α_Mβ_2, abolished fibrinogen protection. Fibrinogen did not bind to or protect neutrophils stimulated with PMA. Fibrinogen is an acute phase protein that will protect exposed cells from damaging circulating histones or leucocidins; but fibrinogen depletion/consumption, as in trauma or sepsis will reduce protection. It is necessary to consider the role of fibrinogen in NETosis.

Investigating the impact of M1 protein from Group A Streptococcus on fibrin clot formation, structure and fibrinolytic potential

Background: Fibrin formation is an essential part of innate immunity, sealing off infections to limit bacterial spreading.The surface-anchored M1 protein is a major virulence determinant of Group A streptococcus (GAS). During early infection M1 is cleaved from the cell surface by SpeB, a streptococcal protease regulated by CovR/S. M1 forms a supramolecular complex with fibrinogen however the impact on fibrin formation is not known.

Methods: The effects of recombinant M1 (rM1) were assessed in fibrin clots made from plasma or purified fibrinogen incubated with thrombin, by confocal microscopy and scanning electron microscopy. Clotting and lysis profiles (with plasminogen activators and plasminogen) were investigated kinetically using thromboelastography (ROTEM).

Results: rM1 (0.47-60 μg/ml) increased clotting rates to produce heterogeneous clots with irregular fibre bundles and compacted fibrin. Formation of the protective fibrin biofilm was also disrupted by rM1. Furthermore, mechanical strength of fibrin clots was reduced with increasing rM1 concentrations and was undetectable above 15.5 μg/ml. Purified and plasma clots formed with rM1 were more susceptible to lysis by plasmin, with a 1.4 – 2-fold reduction in lysis times.

Conclusions: At sites of GAS infection, cleaved M1 may bind to fibrinogen generating fibrin clots which: lack the protective film at the clot surface; are mechanically weaker; and are less resistant to lysis by plasmin. GAS strains of M1-type are commonly associated with invasive infections; the impact of M1 on fibrin structure could contribute to the severity of GAS infection by compromising the fibrin barrier that limits bacterial proliferation and migration.

Higher mass meningococcal group C-tetanus toxoid vaccines conjugated with carbodiimide correlate with greater immunogenicity

To examine the link between meningococcal C (MenC) vaccine size and immunogenic response, a panel of MenC glycoconjugate vaccines were prepared differing in chain length, molar mass and hydrodynamic volume. The preparations consisted of different lengths of MenC polysaccharide (PS) covalently linked to monomeric purified tetanus toxoid (TT) carrier protein using the coupling reagent ethylcarbodiimide hydrochloride (EDC). Size exclusion chromatography with multi-angle light scattering (SEC-MALS) and viscometry analysis confirmed that the panel of MenC-TT conjugates spanned masses of 191,500 to 2,348,000 g/mol, and hydrodynamic radii ranging from 12.1 to 47.9 nm. The two largest conjugates were elliptical in shape, whereas the two smallest conjugates were more spherical. The larger conjugates appeared to fit a model described by multiple TTs with cross-linked PS, typical of lattice-like networks described previously for TT conjugates, while the smaller conjugates were found to fit a monomeric or dimeric TT configuration. The effect of vaccine conjugate size on immune responses was determined using a two-dose murine immunization. The two larger panel vaccine conjugates produced higher anti-MenC IgG1 and IgG2b titres after the second dose. Larger vaccine conjugate size also stimulated greater T-cell proliferative responses in an in vitro recall assay, although cytokines indicative of a T-helper response were not measurable. In conclusion, larger MenC-TT conjugates up to 2,348,000 g/mol produced by EDC chemistry correlate with greater humoral and cellular murine immune responses. These observations suggest that conjugate size can be an important modulator of immune response.

Human iPSC-Derived Neural Crest Stem Cells Exhibit Low Immunogenicity

Recent clinical trials are evaluating induced pluripotent stem cells (iPSCs) as a cellular therapy in the field of regenerative medicine. The widespread clinical utility of iPSCs is expected to be realized using allogeneic cells that have undergone thorough safety evaluations, including assessment of their immunogenicity. IPSC-derived neural crest stem cells (NCSCs) have significant potential in regenerative medicine; however, their application in cellular therapy has not been widely studied to date, and no reports on their potential immunogenicity have been published so far. In this study, we have assessed the expression of immune-related antigens in iPSC-NCSCs, including human leukocyte antigen (HLA) class I and II and co-stimulatory molecules. To investigate functional immunogenicity, we used iPSC-NCSCs as stimulator cells in a one-way mixed lymphocyte reaction. In these experiments, iPSC-NCSCs did not stimulate detectable proliferation of CD3⁺ and CD3⁺CD8⁺ T cells or induce cytokine production. We show that this was not a result of any immunosuppressive features of iPSC-NCSCs, but rather more consistent with their non-immunogenic molecular phenotype. These results are encouraging for the potential future use of iPSC-NCSCs as a cellular therapy.

A phase 1b clinical trial of the CD40-activating antibody CP-870,893 in combination with cisplatin and pemetrexed in malignant pleural mesothelioma

BACKGROUND

Data from murine models suggest that CD40 activation may synergize with cytotoxic chemotherapy. We aimed to determine the maximum tolerated dose (MTD) and toxicity profile and to explore immunological biomarkers of the CD40-activating antibody CP-870,893 with cisplatin and pemetrexed in patients with malignant pleural mesothelioma (MPM).

PATIENTS AND METHODS

Eligible patients had confirmed MPM, ECOG performance status 0-1, and measurable disease. Patients received cisplatin 75 mg/m(2) and pemetrexed 500 mg/m(2) on day 1 and CP-870,893 on day 8 of a 21-day cycle for maximum 6 cycles with up to 6 subsequent cycles single-agent CP-870,893. Immune cell subset changes were examined weekly by flow cytometry.

RESULTS

Fifteen patients were treated at three dose levels. The MTD of CP-870,893 was 0.15 mg/kg, and was exceeded at 0.2 mg/kg with one grade 4 splenic infarction and one grade 3 confusion and hyponatraemia. Cytokine release syndrome (CRS) occurred in most patients (80%) following CP-870,893. Haematological toxicities were consistent with cisplatin and pemetrexed chemotherapy. Six partial responses (40%) and 9 stable disease (53%) as best response were observed. The median overall survival was 16.5 months; the median progression-free survival was 6.3 months. Three patients survived beyond 30 months. CD19+ B cells decreased over 6 cycles of chemoimmunotherapy (P < 0.001) with a concomitant increase in the proportion of CD27+ memory B cells (P < 0.001) and activated CD86+CD27+ memory B cells (P < 0.001), as an immunopharmacodynamic marker of CD40 activation.

CONCLUSIONS

CP-870,893 with cisplatin and pemetrexed is safe and tolerable at 0.15 mg/kg, although most patients experience CRS. While objective response rates are similar to chemotherapy alone, three patients achieved long-term survival.

AUSTRALIA NEW ZEALAND CLINICAL TRIALS REGISTRY NUMBER

ACTRN12609000294257.

Quality control of oblique incidence optical coatings based on normal incidence measurement data

We demonstrate selection of reliable approaches for post-production characterization of oblique incidence multilayer optical coatings. The approaches include choice of input information, selection of adequate coating model, corresponding numerical characterization algorithm, and verification of the results. Applications of the approaches are illustrated with post-production characterization of oblique incidence edge filter, oblique incidence beam splitter and oblique incidence 43-layer quarter-wave mirror.

Ca²⁺ and calpain control membrane expansion during the rapid cell spreading of neutrophils

Following adherence of neutrophils to the endothelium, neutrophils undergo a major morphological change that is a necessary prelude to their extravasation. We show here that this shape change is triggered by an elevation of cytosolic inositol (1,4,5)-trisphosphate (IP3), to provoke physiological Ca(2+) influx through a store-operated mechanism. This transition from a spherical to 'flattened' neutrophil morphology is rapid (∼100 seconds) and is accompanied by an apparent rapid expansion of the area of the plasma membrane. However, no new membrane is added into the plasma membrane. Pharmacological inhibition of calpain-activation, which is triggered by Ca(2+) influx during neutrophil spreading, prevents normal cell flattening. In calpain-suppressed cells, an aberrant form of cell spreading can occur where an uncoordinated and localised expansion of the plasma membrane is evident. These data show that rapid neutrophil spreading is triggered by Ca(2+) influx, which causes activation of calpain and release of furled plasma membrane to allow its apparent 'expansion'.

Ca2+ activation of cytosolic calpain induces the transition from apoptosis to necrosis in neutrophils with externalized phosphatidylserine

Physiologically, apoptotic neutrophils are ingested before they undergo necrosis. However, failure of ingestion will lead to necrosis of neutrophils and the unregulated release of neutrophil-derived pathogenic molecules, such as protease and hydrolases. Understanding the mechanism of postapoptotic necrosis is thus clearly important. Here, we monitored the apoptotic-to-necrotic transition in individual-aged human neutrophils in vitro by imaging fluorescent probes for externalized PS, cytosolic Ca(2+), and membrane integrity. This showed that prenecrotic-aged neutrophils with externalized PS had a significantly elevated cytosolic-free Ca(2+) level. A further unregulated Ca(2+) influx into PS-externalized neutrophils always preceded the necrotic transition. Ca(2+) elevation was not simply a consequence of aging, as PS externalization was not uniform in similarly aged neutrophil populations. PS-externalized neutrophils could be induced to undergo necrosis experimentally by simply elevating cytosolic Ca(2+) further with ionomycin. This effect was observed only in neutrophils that had externalized PS, and was independent of the time after their isolation from blood (i.e., in vitro age). As pharmacological inhibition of calpain-1 inhibition significantly reduced this CAIN, it was concluded that the apoptotic-to-necrotic transition was a consequence of uncontrolled calpain activation that resulted from Ca(2+) overload in PS-externalized neutrophils.

Optical characterization and reverse engineering based on multiangle spectroscopy

We perform characterization of thin films and reverse engineering of multilayer coatings on the basis of multiangle spectral photometric data provided by a new advanced spectrophotometer accessory. Experimental samples of single thin films and multilayer coatings are produced by magnetron sputtering and electron-beam evaporation. Reflectance and transmittance data at two polarization states are measured at incidence angles from 7 to 40 deg. We demonstrate that multiangle reflectance and transmittance data provide reliable characterization and reverse-engineering results.

Semiautomatic volume of interest drawing for 18F-FDG image analysis—method and preliminary results

PURPOSE

Functional imaging of cancer adds important information to the conventional measurements in monitoring response. Serial (18)F-fluorodeoxyglucose (FDG) positron emission tomography (PET), which indicates changes in glucose metabolism in tumours, shows great promise for this. However, there is a need for a method to quantitate alterations in uptake of FDG, which accounts for changes in tumour volume and intensity of FDG uptake. Selection of regions or volumes [ROI or volumes of interest (VOI)] by hand drawing, or simple thresholding, suffers from operator-dependent drawbacks.

MATERIALS AND METHODS

We present a simple, robust VOI growing method for this application. The method requires a single seed point within the visualised tumour and another in relevant normal tissue. The drawn tumour VOI is insensitive to the operator inconsistency and is, thus, a suitable basis for comparative measurements. The method is validated using a software phantom. We demonstrate the use of the method in the assessment of tumour response in 31 patients receiving chemotherapy for various carcinomas.

RESULTS

Valid assessment of tumour response could be made 2-4 weeks after starting chemotherapy, giving information for clinical decision making which would otherwise have taken 9-12 weeks. Survival was predicted from FDG-PET 2-4 weeks after starting chemotherapy (p = 0.04) and after 9-12 weeks FDG-PET gave a better prediction of survival (p = 0.002) than CT or MRI (p = 0.015).

CONCLUSIONS

FDG-PET using this method of analysis has potential as a routine tool for optimising use of chemotherapy and improving its cost effectiveness. It also has potential for increasing the accuracy of response assessment in clinical trials of novel therapies.

Radiolabelling of glycosylated MFE-23::CPG2 fusion protein (MFECP1) with 99mTc for quantitation of tumour antibody-enzyme localisation in antibody-directed enzyme pro-drug therapy (ADEPT)

MFECP1 is a glycosylated recombinant fusion protein composed of MFE-23, a high-affinity anti-carcinoembryonic antigen (CEA) single chain Fv (scFv), fused to the enzyme carboxypeptidase G2 (CPG2), and has been constructed for use in antibody-directed enzyme pro-drug therapy (ADEPT). Radiolabelling of glycosylated MFECP1 with technetium-99m was developed for the purpose of determining tumour localisation of MFECP1 in a phase I ADEPT clinical study. The method used was 99mTc-carbonyl [99mTc(H2O)3(CO)3]+ (abbreviated to TcCO) mediated labelling of 99mTc to the hexahistidine (His) tag of MFECP1. MFECP1 fusion protein was labelled with TcCO under a variety of conditions, and this was shown to be a relatively simple and robust method. Tissue biodistribution was assessed in a CEA-expressing LS174T (human colon carcinoma) nude mouse xenograft model. Tissues were taken at 1, 4 and 6 h for assessment of distribution of radioactivity and for measurement of CPG2 enzyme levels. The amount of radioactivity retained by the tumour proved to be an accurate estimation of actual measured enzyme activity, indicating that this radiolabelling method does not appear to damage the antibody-antigen binding or the enzyme activity of MFECP1. However, correlation between CPG2 enzyme activity and measured radioactivity in liver, spleen and kidney was poor, indicating retention of radioactivity in non-tumour sites but loss of enzyme activity. The high retention of technetium radioisotope in normal tissues may limit the clinical applicability of this radiolabelling method for MFECP1; however, these results suggest that this technique does have applicability for measuring the biodistribution of His-tagged recombinant proteins.

A phase I trial of antibody directed enzyme prodrug therapy (ADEPT) in patients with advanced colorectal carcinoma or other CEA producing tumours

Antibody-directed enzyme prodrug therapy is a targeted therapy in which a prodrug is activated selectively at the tumour site by an enzyme, which has been targeted to the tumour by an antibody (antibody-enzyme conjugate). Previous clinical trials have shown evidence of tumour response, however, the activated drug had a long half-life, which resulted in dose-limiting myelosuppression. Also, the targeting system, although giving high tumour to blood ratios of antibody-enzyme conjugate (10 000 : 1) required administration of a clearing antibody in addition to the antibody-enzyme conjugate. The purpose of this current study therefore was to attempt tumour targeting of the antibody-enzyme conjugate without the clearing antibody, and to investigate a new prodrug (bis-iodo phenol mustard, ZD2767P) whose activated form is highly potent and has a short half-life. Twenty-seven patients were treated with antibody-directed enzyme prodrug therapy using A5CP antibody-enzyme conjugate and ZD2767P prodrug, in a dose-escalating phase I trial. The maximum tolerated dose of ZD2767P was reached at 15.5 mg m(-2)x three administrations with a serum carboxypeptidase G2 level of 0.05 U ml(-1). Myelosuppression limited dose escalation. Other toxicities were mild. Patients' quality of life was not adversely affected during the trial as assessed by the measures used. There were no clinical or radiological responses seen in the study, but three patients had stable disease at day 56. Human anti-mouse antibody and human anti-carboxypeptidase G2 antibody were produced in response to the antibody enzyme conjugate (A5CP). The antibody-enzyme conjugate localisation data (carboxypeptidase G2 enzyme levels by HPLC on tumour and normal tissue samples, and gamma camera analysis of I-131 radiolabelled conjugate) are consistent with inadequate tumour localisation (median tumour: normal tissue ratios of antibody-enzyme conjugate of less than 1). A clearance system is therefore desirable with this antibody-enzyme conjugate or a more efficient targeting system is required. ZD2767P was shown to clear rapidly from the circulation and activated drug was not measurable in the blood. ZD2767P has potential for use in future antibody-directed enzyme prodrug therapy systems.

Measurement of the critical DNA lesions produced by antibody-directed enzyme prodrug therapy (ADEPT) in vitro, in vivo and in clinical material

An antibody-directed enzyme prodrug therapy (ADEPT) system against CEA-positive tumours is currently in phase I clinical trials. It consists of a prodrug, 4-[N,N-bis(2-iodoethyl) amino] phenoxycarbonyl L -glutamic acid (ZD2767P) and a conjugate of the F(ab')(2) anti-CEA antibody A5B7 and the bacterial enzyme carboxypeptidase G2 (CPG2). ZD2767P is converted by antibody-targeted CPG2 into an active bifunctional alkylating drug (ZD2767) at the tumour site. The IC(50) value of the prodrug against the human colorectal tumour LS174T cell line was 55 +/- 9 microM following a 1 h exposure. In contrast, co-incubation of ZD2767P with CPG2 resulted in 229-fold increase in activity. Using a modified comet assay, DNA interstrand cross links (ISC) were detected within 1 h of ZD2767P + CPG2 treatment and were repaired by 24 h. A clear dose-response was seen between the level of ISC, growth inhibition and ZD2767 concentration. Administration of a therapeutic dose of ZD2767P 72 h after the F(ab')(2) A5B7 conjugate to mice bearing LS147T xenografts resulted in extensive ISC in the tumour after 1 h; repair was seen at 24 h. Tumour biopsies and peripheral lymphocytes were studied in 5 patients on the ADEPT phase I clinical trial. In 4 patients no ISC were detected. These patients also demonstrated poor localization of conjugate and no tumour response was seen. However a significant level of ISC was detected in one tumour biopsy, which also showed evidence of conjugate localization and clinical response. These studies demonstrate the application of the comet assay in the measurement of ISC in vitro and in clinical material and confirm that activation of ZD2767P results in the formation of DNA crosslinks.

Critical pathways: not just for patients anymore

Hospital managers initiate a nurse orientation program modeled after critical pathways. The structure allows them to assess nurses' competency while providing experience.

A double-blind, placebo-controlled trial of two dose ranges of nefazodone in the treatment of depressed outpatients

BACKGROUND

Nefazodone hydrochloride, a 5-HT2 receptor antagonist that selectively inhibits serotonin reuptake, was evaluated in a double-blind, dose-finding study of novel design, involving 240 patients with major depression.

METHOD

Patients were randomly assigned to three treatment groups and received either placebo (2-6 capsules per day), a lower-dose range of nefazodone (50-300 mg/day), or a higher-dose range of nefazodone (100-600 mg/day) for 6 weeks.

RESULTS

At the end of treatment, the Hamilton Rating Scale for Depression and the clinician- and patient-rated Inventory for Depressive Symptomatology scores showed significant improvement (p < or = .05) for patients receiving higher-dose range nefazodone (mean = 392 mg/day) compared with placebo treatment. The percentage of responders (at least "much improved" on the Clinical Global Impressions-Improvement scale) in the higher-dose range nefazodone group (58%) was significantly greater (p < or = .05) than in the placebo group (39%). The treatment group receiving nefazodone in the lower-dose range was not differentiated in clinical response from placebo controls. The rate of discontinuation for adverse experience (14%) was similar for patients treated with higher-dose range nefazodone and placebo.

CONCLUSION

The findings of this study indicate that nefazodone is an effective and well-tolerated antidepressant drug, with a recommended therapeutic dose range of 100 to 600 mg/day and a starting dose of 100 mg b.i.d.

Receptors for angiotensins I and II: their relevance to renal haemodynamics, blood pressure control and hind-limb blood flow

The well established differential pulmonary handling of angiotensins I and II indicates the possibility that vascular receptors for the deca- and octa-peptides do not necessarily involve common sites in the renal vasculature either. Experimental findings involving haemodynamic changes within the kidney in anaesthetised and conscious sheep, with utilization of the angiotensins, and also of noradrenaline, are briefly presented; the implications of the intra-renal water and creatinine transfers are discussed, especially as they concern the possible location of angiotensin receptors in the renal blood vessels. Other aspects of the relationships between the peptides are also taken into account particularly with regard to a postulated angiotensin I [NaCl] dependent peritubular capillary antidiuretic action, angiotensin converting enzyme inhibition, Goldblatt clamp induced hypertension and blood flow through the hind-limbs.

Initial and steady state pharmacokinetics of cilazapril in congestive cardiac failure

Twenty one patients with NYHA class II-III congestive heart failure received single ascending doses of 0.5, 1.25 and 2.5 mg cilazapril daily followed by the minimum effective dose for six weeks. Fifteen patients completed the study, but the data from only 11 were sufficiently complete for kinetic evaluation. The pharmacokinetics of the metabolite, cilazaprilat, after a single dose of 0.5 mg cilazapril were similar to previous observations in healthy volunteers at identical dosage. Repeat administration, however, led to greater accumulation than previously observed in volunteers at the higher dosages of 1.25 or 5 mg given for 8 days. Seven patients experienced adverse events. Four were severe, leading to withdrawal of the patients from the study, but only one event was related to cilazapril. Of the other three, one suffered a myocardial infarction and subsequently died due to worsening congestive heart failure. One other patient was withdrawn with two adverse events probably related to cilazapril. No other deaths occurred amongst the study population, and there were no significant abnormalities in haematology or blood chemistry.

Clinical pharmacology of cilazapril

In clinical pharmacology studies, cilazapril, after its bioactivation to cilazaprilat, was characterised as a potent, reversible angiotensin converting enzyme (ACE) inhibitor with a terminal half-life of 30 to 50 hours, which is consistent with saturable binding to ACE. Despite the arterial vasodilatation, only slight increases in heart rate occurred during cilazapril administration. Cilazapril had no acute effect on cardiovascular reflexes, and increased effective renal plasma flow slightly. Glomerular filtration rate remained unaltered. A close positive correlation was found between the cilazaprilat plasma concentration and degree of ACE inhibition. The potency of cilazaprit, defined as the concentration of cilazaprilat causing 50% inhibition of ACE, was approximately 1 microgram/L plasma. In short term studies in patients with hypertension, it appeared that more than 90% inhibition of plasma ACE was needed to obtain blood pressure reduction. Results of various dose-response studies established the indirect relationship between dose, the plasma concentration of the drug, and the blood pressure response, and identified the dose producing the maximal effect to be 5mg. Cilazapril inhibited ACE for a relatively long period which was extended in patients with severe chronic renal impairment or hepatic failure. In these patients a reduction of the dose and/or less frequent administration is recommended. There was no clinically relevant interaction of cilazapril with food, furosemide (frusemide), digoxin or coumarins. The effects of hydrochlorothiazide on sodium and chloride excretion were potentiated by cilazapril, and an additive effect of propranolol and nitrendipine on the blood pressure response to cilazapril was observed. An interaction with indomethacin and cilazapril might occur, potentially reducing the blood pressure-lowering effect of cilazapril. In general, cilazapril was well tolerated.

Pharmacokinetics of cilazapril during repeated oral dosing in healthy young volunteers

The pharmacokinetics of cilazapril and its active metabolite cilazaprilat in plasma were investigated in an open study of 13 healthy male volunteers, aged 18 to 43 years. One capsule containing 2.5 mg cilazapril was administered to each volunteer daily for 8 days. Plasma samples were obtained after the first and eighth doses. Concentrations of cilazapril, cilazaprilat and activities of angiotensin converting enzyme (ACE) were measured by radioenzymatic methods. For cilazapril, the values of apparent plasma clearance (about 15 l/h) and volume of distribution (around 28 l) were sufficiently high to suggest that significant pre-systemic hydrolysis to cilazaprilat occurred. There were no significant changes in these values after repeated dosing. There were small, but statistically significant, increases in mean peak concentrations, mean areas under concentration-time curves and mean trough concentrations from the first to the eighth dose. A steady state was achieved after eight doses with an accumulation of 20-30%. The mean effective half-life was approximately 9 h. Despite the accumulation of cilazaprilat in plasma, there were no significant differences in plasma ACE inhibition from the first to the eighth dose.

Clinical pharmacology of cilazapril

In clinical pharmacology studies cilazapril, after its bioactivation to cilazaprilat, was characterized as a potent, reversible angiotensin-converting enzyme (ACE) inhibitor with a terminal half-life of 30 to 50 hours consistent with saturable binding to ACE. Despite the arterial vasodilation, only slight increases in heart rate were found. Cilazapril had no acute effect on cardiovascular reflexes. Cilazapril increased effective renal plasma flow slightly. Glomerular filtration rate remained unaltered. A close and steep correlation between cilazaprilat plasma concentration and ACE inhibition was found. The potency of cilazaprilat, defined as the concentration of cilazaprilat causing 50 percent ACE inhibition, was approximately 1 ng/ml plasma. In short-term studies in hypertensive patients, it appeared that more than 90 percent of plasma ACE inhibition is needed to obtain blood pressure reduction. The result of various dose-response studies established the indirect relationship between dose, plasma concentration of the drug, and the blood pressure response and identified the dose producing maximal effect (i.e., 5 mg). Cilazapril had relatively long-lasting effects on ACE inhibition. In patients with severe chronic renal impairment or hepatic failure, the duration of ACE inhibition of cilazapril was prolonged. In these patients a reduction of the dose and/or less frequent dosing is recommended. There was no clinically relevant interaction of cilazapril with food or furosemide. The effects of hydrochlorothiazide on sodium and chloride excretion were potentiated by cilazapril. An additive effect of propranolol and nitrendipine on the blood pressure response to cilazapril was observed. An interaction with nonsteroidal anti-inflammatory drugs and cilazapril might occur, potentially reducing the blood pressure lowering effect. In general cilazapril was well tolerated.

A pharmacokinetic study of cilazapril in patients with congestive heart failure

1. The pharmacokinetics of cilazapril and the inhibition of angiotensin converting enzyme (ACE) were investigated in 10 patients with congestive heart failure, NYHA class II-III, receiving diuretics with or without digoxin. 2. Patients received 0.5 mg and 1 mg cilazapril on the first 2 days, followed by 0.5 mg or 1 mg daily for the next 8 weeks, in a single-blind study. Plasma cilazaprilat concentrations and plasma ACE activities were measured by radioenzymatic methods up to 24 h after the first and last doses. 3. After the initial 0.5 mg dose of cilazapril, a mean maximum plasma concentration of cilazaprilat of 6.8 ng ml-1 was observed at 2.3 h. Concentrations declined up to 8 h with a mean half-life of 5.8 h, followed by slower decrease to 24 h. Total clearance, based on data to 24 h, was estimated at 8.5 l h-1, with three-fold inter-individual variation. Mean maximum plasma ACE inhibition was 87%, decreasing to 65% at 24 h. 4. In the multiple dose phase of the study, four patients received cilazapril 0.5 mg daily, and six patients 1 mg daily. Cilazapril accumulation for the 0.5 mg group averaged 77%, but steady state concentrations for the 1 mg group were less than double those of the 0.5 mg group. ACE inhibition profiles at steady state were similar for both groups, and they differed from first dose data only in a somewhat lower inhibition at 24 h. 5. Historical comparison of the first-dose data with those for healthy young volunteers at identical dosage revealed only minor differences in kinetic parameters.(ABSTRACT TRUNCATED AT 250 WORDS)

The pharmacokinetics and bioavailability of cilazapril in normal man

1. The pharmacokinetics of cilazapril and its active metabolite, cilazaprilat, were investigated in a three-part crossover study in 12 healthy male volunteers aged 19-38 years, excluding one subject who withdrew from the study. 2. Single 2.5 mg oral doses of cilazapril, and equivalent oral and intravenous doses of cilazaprilat were administered as aqueous solutions to the fasted subjects. There was an interval of 1 week between treatments. Concentrations of cilazapril and cilazaprilat in plasma and urine, and activities of angiotensin converting enzyme (ACE) in plasma were measured by radioenzymatic methods. 3. After 10 min infusion of cilazaprilat, the mean plasma concentration was 194 ng ml-1, and ACE inhibition was almost 100%. The decline in concentrations was polyphasic, with mean half-lives for the periods 1-4 h and 24-168 h of 0.90 and 46 h, respectively. Between 4 and 24 h the decline was non-linear, and ACE inhibition decreased from 91% to 67%. Urinary recovery of cilazaprilat averaged 91% of dose. 4. After oral cilazapril, the parent drug was rapidly absorbed and rapidly eliminated, with a mean maximum plasma concentration of 82 ng ml-1 at 0.83 h and a single elimination half-life of 1.3 h. Cilazaprilat peaked at 36 ng ml-1 about 1.7 h after dosing and the decline in concentrations was biphasic, with half-lives of 1.8 h and 45 h. After oral cilazaprilat, plasma concentrations were considerably lower, and the peak later (2.2 h). 5. Urinary recovery data indicated an absolute bioavailability for cilazaprilat of 57% (range 45-75%) from oral cilazapril, but only 19% (range 8-40%) from oral cilazaprilat.(ABSTRACT TRUNCATED AT 250 WORDS)

Pharmacokinetics of cilazapril in patients with renal failure

1. The pharmacokinetics of a single 1 mg dose of cilazapril were determined in six subjects with normal renal function and in 19 uraemic patients with various degrees of renal impairment. 2. Significant decreases in systolic and diastolic blood pressure were noted in all groups of subjects between 2 and 8 h after administration of 1 mg cilazapril. 3. There was a significant correlation between ACE inhibition at 24 h and creatinine clearance (CrCL). 4. For cilazapril, Cmax and tmax were independent of creatinine clearance. AUC(24) was inversely related to CrCL and apparent plasma clearance (CL/F) was directly related to CrCL. 5. For cilazaprilat, Cmax and tmax were related to creatinine clearance. AUC(24) was inversely related to CrCl and apparent plasma clearance (CL/F) was directly related to CrCL. 6. Dialysis clearance was approximately 2 l h-1 for cilazapril and for cilazaprilat. 7. The effects of renal impairment on cilazapril and cilazaprilat kinetics were similar to those observed for other inhibitors of angiotensin-converting enzyme such as captopril, enalapril and lisinopril. 8. It may be necessary to modify doses of cilazapril for the treatment of essential hypertension in uraemic patients. When creatinine clearance was below 15 ml min-1 cilazaprilat concentrations were increased, half-lives were prolonged and ACE inhibition remained above 90% for at least 24 h. A reduced dosage is indicated for these patients. 9. In patients requiring haemodialysis, maintenance doses of 0.5 mg given after each haemodialysis session are sufficient.

The pharmacokinetics and angiotensin converting enzyme inhibition dynamics of cilazapril in essential hypertension

1. In a double-blind, placebo controlled, crossover study 12 patients with essential hypertension received single doses of 5, 10 and 20 mg of cilazapril. 2. Peak plasma levels of cilazaprilat and the 24 h areas under curve were directly proportional to dose. 3. The elimination half-life during the first 8 h was about 1.7 h. 4. From 24 h onwards there was a prolonged terminal elimination phase with a half-life of about 40 h, and strict dose proportionality of plasma concentrations was not maintained. 5. The pharmacokinetics of cilazaprilat and the pharmacodynamics of plasma ACE inhibition were well described by a one compartment model with saturable binding to ACE. 6. The coefficients of the model which related to plasma ACE and its interaction with cilazaprilat were in good agreement with model independent observations. 7. The values for kinetic and dynamic parameters in hypertensive patients were comparable with those reported for healthy volunteers.

Kinetic investigations into the possible cause of low serum histidine in rheumatoid arthritis

To investigate the cause of low serum histidine in rheumatoid arthritis (RA) single oral and intravenous doses of L-histidine were administered to patients with active RA, and to an equal number of age and sex matched control subjects. In the first study 13 patients and their controls received a 100 mg kg-1 dose of L-histidine as an aqueous slurry. Significant differences were seen in body weight, predose baseline serum histidine concentration, Cmax, t1/2, and area under curve, AUC0-infinity. In a second study six patients and six controls each received a 50 mg kg-1 dose of L-histidine both orally and intravenously on two separate occasions. The patients with RA had a lower baseline serum histidine concentration, a lower volume of distribution, and a shorter plasma half life than the controls, but these differences were not statistically significant. No difference was seen in bioavailability or clearance. Low serum histidine in RA is unlikely to be due to malabsorption from the gut, uptake by abnormal gut flora, or increased metabolism.

Anther culture of Hordeum vulgare L.: a genetic study of microspore callus production and differentiation

The inheritance of the ability of barley anthers to produce microspore-derived callus in vitro was investigated. The genotypes selected were the two spring cultivars 'Dissa' (D) and 'Sabarlis' (S), the two F1 hybrids (DxS, SxD), the two backcross generations [Dx(DxS), Sx(DxS)], and an F2 generation derived from DxS. From a number of individuals of each generation, the first five spikes were harvested sequentially and after pre-treatment the anthers were removed and placed in culture. Cultures were scored for microspore callus production and plantlet differentiation. Although 'Dissa' gave a significantly higher level of callus production than 'Sabarlis', the overall frequencies of green and albino plant production were higher from 'Sabarlis'. There was no significant difference between reciprocal F1 hybrids. Analysis of variance revealed significant differences in response between the spikes sampled from the plants. This was the major source of variation in the experiment. Spike to spike variation also appeared to be a heritable character.

Effects of single doses of the converting enzyme inhibitor cilazapril in normal volunteers

The new converting enzyme inhibitor cilazapril, or RO 31-2848, was evaluated in 14 healthy male volunteers. In a pilot study in two subjects, the inhibiting capacity of single oral doses of 5 and 10 mg on the pressure and heart rate response to exogenous angiotensin I was assessed. Both doses reduced the blood pressure response to angiotensin I to 10% of control within 45 min and for the 4 h tested. In the main study, 12 volunteers each received two single oral doses of cilazapril at a 2-week interval, and plasma converting enzyme and renin activity, blood angiotensin I, plasma immunoreactive angiotensin II and aldosterone were measured serially. Single doses of 1.25, 2.5, 5, and 10 mg of cilazapril were tested in groups of six subjects each. All doses inhibited plasma converting enzyme activity by 90% for at least 8 h and induced the expected pattern of changes of the renin-angiotensin-aldosterone system. Only slight dose-dependent variations in the effect were observed. Basic heart rate and blood pressure were not altered by any of the doses, which all were well tolerated. These data suggest that cilazapril is a very potent and long-acting new converting enzyme inhibitor.

Pharmacokinetics of the converting enzyme inhibitor cilazapril in normal volunteers and the relationship to enzyme inhibition: development of a mathematical model

The pharmacokinetics of the new converting enzyme inhibitor cilazapril were investigated in 12 healthy male volunteers. Single oral doses of 1.25, 2.5, 5, and 10 mg of cilazapril were tested in groups of six subjects, each of whom received two different doses. A 2-week interval was allowed between treatments. Plasma levels of cilazaprilat, the active form of cilazapril, were measured for up to 3 days after drug administration. Peak plasma levels and 24-h areas under the curve (AUCs) were almost directly proportional to dose, and the elimination half-life (t1/2) during the first 8 h after dosing was 1.5 h. From 24 h on, there was a prolonged terminal phase with a t1/2 of approximately 50 h, and there was only slight dose-dependency during this phase. These data suggest that the pharmacokinetics of cilazapril are nonlinear. A physiologically realistic model based on saturable binding to converting enzyme was developed to account both for the drug kinetics and for the relationship of the kinetics to the dynamics of plasma converting enzyme inhibition. A number of conclusions relevant to the therapeutic application of cilazapril in hypertension are drawn from the data and from the pharmacokinetic-pharmacodynamic model.

Repeated administration of the converting enzyme inhibitor cilazapril to normal volunteers

Cilazapril 1.25 and 5.0 mg p.o. q.d. was administered in double-blind fashion to two groups of six normal volunteers on 8 consecutive days. Blood pressure, heart rate, and plasma converting enzyme activity were measured each day prior to drug administration and up to 72 h after the last dose. Plasma renin activity, blood angiotensin I, plasma angiotensin II, and aldosterone as well as plasma cilazaprilat levels were determined on the first and the last day of active treatment at times 0, 4, and 24 h. The drug was very well tolerated by all volunteers. At 4 h postdrug, plasma converting enzyme activity was reduced in dose-dependent fashion on the first and the eighth day; plasma cilazaprilat levels were also clearly dose dependent. Nevertheless, 24 h postdrug cilazaprilat levels were similar on the first and last day of drug administration, and plasma converting enzyme activity was also stable throughout the 8 days. The various components of the renin-angiotensin system responded in the usual fashion. These results provide strong evidence that cilazapril is a very potent and highly effective converting enzyme inhibitor. Doses well below 5 mg/day will probably suffice for therapeutic efficacy. These data also confirm the hypothesis formulated in the preceding article, i.e., that there is no accumulation of the drug with repeated administration despite its long pharmacological half-life (t1/2).

Pharmacokinetics of tenoxicam after oral administration in healthy human subjects of various single doses

Single oral dose pharmacokinetics of tenoxicam in the dose range intended for therapeutic application of the drug have been defined in healthy human subjects. Twelve male volunteers were given, in random fashion, oral administration of 10, 20 or 40 mg of tenoxicam. Plasma drug levels were determined by a standard HPLC method with U.V. detection. Model-independent analysis showed the clearance, elimination half-life and apparent volume of distribution to be independent of dose with mean values of 0.096 L/h, 76 h and 9.2 L respectively. Interindividual variation was six-fold and individual variation less than two-fold. Similar values for kinetic parameters were obtained by model-dependent methods. The pharmacokinetics of oral tenoxicam were linear in the 10-40 mg dose range and the single dose data predict five-fold accumulation for once daily administration.

Pharmacodynamic and pharmacokinetic studies on bufuralol in man

Observations were made in eight subjects who exercised before and at 1, 2, 4, 6, 8 and 24 h after the double-blind oral administration of placebo, bufuralol 7.5, 15, 30, 60 and 120 mg and propranolol 40 and 160 mg. The exercise heart rate remained constant after placebo. Bufuralol 7.5 mg and propranolol 40 mg reduced exercise heart rate up to 6 and 8 h respectively after dosing but bufuralol 15, 30, 60 and 120 mg and propranolol 160 mg were still active at 24 h. The lowest exercise heart rate occurred at 2 h after all active treatments. Bufuralol 60 and 120 mg produced similar reduction in exercise tachycardia as propranolol 40 mg but less than propranolol 160 mg. Plasma levels of bufuralol and its two major metabolites were measured. The peak plasma concentrations of bufuralol occurred at 1.5 h after 7.5 mg and at 2 h after the other doses of bufuralol. In six subjects the plasma elimination half-life of bufuralol was 2.61 +/- 0.18 h and in the other three subjects 4.85 +/- 0.35 h. There was a corresponding longer time to peak concentration and plasma elimination half-life of the two metabolites in these three subjects. These findings show that bufuralol is a potent beta-adrenoceptor antagonist with partial agonist activity. It has a long duration of action and there is bimodal metabolism of the drug in man.

Pharmacokinetics of single and multiple doses of flusoxolol (Ro 31-1411) in healthy subjects

Flusoxolol (Ro 31-1411) is the pharmacologically active optical isomer of Ro 31-1118, a potent cardioselective beta-adrenoceptor antagonist with partial agonist activity. It was given to 6 healthy volunteers in a single dose, 40 mg, and then in multiple doses, 40 mg daily for 8 days. Plasma concentration data were best described by a linear two-compartment pharmacokinetic model with first order absorption, and the results confirmed linear kinetics. Pharmacokinetic data for flusoxolol were comparable to those for the racemate Ro 31-1118.

The effects of food and of antacid on the single oral dose pharmacokinetics of tenoxicam

A single oral dose (40 mg) of tenoxicam (Ro12-0068) was administered to six normal male volunteers pre- and post-prandially and to a further six volunteers with and without antacid to determine the effect of food and and of antacid on absorption. The rate of absorption was slower with post-prandial than with pre-prandial administration, resulting in a significantly later time for peak plasma drug levels (4.1 h compared to 1.3 h). No effect was evident on the extent of absorption or other pharmacokinetic parameters. Similarly, the rate of absorption was significantly slower after concurrent antacid than without antacid (t1/2 0.47 h compared to 0.18 h) resulting in a later peak time (4.7 h compared to 2.3 h) and significantly lower peak level (4.2 micrograms X ml-1 compared to 5.1 micrograms X ml-1) of parent drug in plasma. Again, no effect was evident on the extent of absorption or other pharmacokinetic parameters. It is concluded that food and antacids both tend to reduce the rate of absorption of tenoxicam, but that the extent of absorption is essentially unchanged. The influence on the overall kinetic profile is relatively minor, and thus unlikely to affect the therapeutic response.

Human pharmacokinetic and pharmacodynamic studies on Ro31-1118, a new beta-adrenoceptor antagonist

The pharmacokinetic and pharmacodynamic effects of Ro31-1118 were examined in groups of healthy volunteers. In three subjects given 10 mg of [14C]-Ro31-1118 orally, peak levels of radioactivity (84 +/- 5 ng/ml) were 16 times those of the parent drug (approximately 5 ng/ml). Very little parent drug was recovered in the urine, although recovery of total radioactivity was nearly 80% in the urine by day 5. In five subjects studied after both oral and intravenous administration of 20 mg Ro31-1118 the average bioavailability was 57% (range 41-73%). Following intravenous infusion the apparent volume of distribution for the five subjects averaged 590 1 (range 510-700 1). The elimination half-life averaged 18 h (range 17-26 h). In eight subjects who received 40, 80, 160 and 320 mg of Ro31-1118 orally there was a linear relationship between dose and plasma concentration (r = 0.999) and between dose and AUC (r = 0.996). Ro31-1118 had no effect on resting heart rate whereas atenolol reduced resting heart rate up to 6 h after all doses. The maximum reduction of an exercise tachycardia after Ro31-1118 (320 mg) was 23.13 +/- 0.7% and compared with atenolol (100 mg) was 28.2 +/- 1.25%. At 24 h the percentage reduction after Ro31-1118 was 21.5 +/- 1.7%, while after atenolol the percentage inhibition had decreased to 11.1 +/- 1.6%. In three subjects Ro31-1118 (160 mg) orally had no effect on resting heart rate, forearm blood flow and systolic blood pressure, while atenolol (50 mg) reduced all three parameters.(ABSTRACT TRUNCATED AT 250 WORDS)

Ro 31-1118, a new cardioselective beta-adrenoceptor antagonist. Pharmacokinetics and effects on heart rate and blood pressure in mild hypertensives

Five patients with mild hypertension were given single oral doses of Ro 31-1118 (10,20,40, and 80 mg) and placebo in a randomized, double-blind, within-patient study. Plasma concentrations of Ro 31-1118 and supine, standing, exercise, and post-exercise heart rates and blood pressures were measured before and at regular intervals after drug administration. The pharmacokinetic data were consistent with a one-compartment model with first-order absorption and a variable time lag. Peak plasma concentrations and area under curve were linearly related to dose, whereas time to peak concentration, half-time, clearance and apparent volume of distribution were dose-independent. There was a reduction in exercise and post-exercise heart rate of approximately 10% after 10 mg and 20 mg Ro 31-1118, and of approximately 15% after 40 mg and 80 mg. At all doses standing systolic blood pressure was reduced by approximately 5%. A similar fall was seen in exercise and post-exercise systolic blood pressures. There was no substantial effect of Ro 31-1118 on supine or standing heart rates nor on diastolic blood pressure. No adverse effects were reported. It is concluded that Ro 31-1118 has linear pharmacokinetics over the dose range 10-80 mg, and has a weak antihypertensive effect when administered in single doses to patients with mild hypertension.

ELSMOS--an extended least squares modelling system in FORTRAN IV for mini- or micro-computer implementation

A new program ELSMOS has been developed for curve fitting of pharmacokinetic and pharmacodynamic data. The form is sufficiently general, with user-defined model in a separate FORTRAN subroutine, to permit application in many other areas. The principal features are the use of a user-defined error model for statistically rigorous automatic weighting of data, and the containment of program size to a level that enables mini- or micro-computer implementation.

New potent inhibitors of angiotensin converting enzyme

Using an earlier model of the favoured orientation of binding functions of angiotensin converting enzyme (ACE) inhibitors, it has been possible to postulate a new, 7,6-bicyclic system, based on hexahydropyridazine, which might be expected to have high potency. Some members of this system which have been synthesised have been shown to be very active ACE inhibitors, in vitro and in vivo.

Kinetics and metabolism of (+)-, (-)- and (+/-)-bufuralol

Single oral doses of (+)-, (-)- and (+/-)-bufuralol were administered to a healthy volunteer to compare the disposition and metabolism of the individual isomers and the racemate. Plasma levels and area under plasma curve (AUC) of the active isomer, (-)-bufuralol, were higher than those of the (+)-isomer; plasma clearance was correspondingly lower. Intermediate values were found for the racemate. The elimination half-life of (-)-bufuralol was shorter than that of (+)-bufuralol, but similar to the racemate. Both isomers were cleared almost entirely by metabolism. The main metabolic pathway for (-)-bufuralol was aromatic hydroxylation, whereas the principal route for (+)-bufuralol was conjugation. Phenol metabolites in the systemic circulation were present mainly as conjugates. Both isomers also underwent aliphatic hydroxylation. This pathway was more favoured by the (+)-isomer, although plasma levels and AUC of the principal product, 2'-hydroxy-bufuralol, were almost identical for the two forms. Major differences in metabolic fate thus had relatively little effect on the disposition of pharmacologically active metabolites.

Influence of renal failure on the hepatic clearance of bufuralol in man

The beta-blocking agent bufuralol is subject to first-pass metabolism and is eliminated from the body almost entirely by biotransformation. Its major metabolite in plasma (1'-hydroxy-bufuralol) is biologically active and may contribute to the pharmacological effect of the drug. The effect of renal failure on the behavior of the parent compound and three of its metabolites was studied by comparing their kinetics in normal volunteers and in patients with severe renal insufficiency. Bufuralol was given orally to all subjects (20 mg); some of the healthy volunteers also received the drug intravenously (5 mg). Renal failure was found to be associated with a marked increase of the areas under the plasma concentration-time curves of the parent compound, whereas its halflife of elimination was not markedly influenced. The behavior of 1'-hydroxy-bufuralol was consistent with a decreased renal clearance. The behavior of bufuralol in patients with renal failure was analyzed using the clearance approach. From this analysis it appears that the presystemic biotransformation of bufuralol is decreased in renal failure and that changes in systemic clearance are compensated in our patients by modifications of the volume of distribution, resulting in little net change in the halflife of elimination.

[Role of metabolites in the relationship between pharmacokinetics and the effect of beta blockers. Studies on tolamolol and bufuralol]

Plasma concentrations of tolamolol and bufuralol (beta-blocking agents) were measured after oral and intravenous administration to healthy volunteers. The plasma levels of their main metabolite was also determined. Simultaneously, the effect of the drugs on the heart rate and blood pressure was monitored under various stimuli (isoproterenol, exercise or orthostatism) and Valsalva maneuver. When given orally, the two drugs are extensively metabolized by a hepatic first-pass effect. After reaching the systemic circulation, they are metabolized in the liver to hydroxylated derivatives with similar pharmacologic activity as the parent molecule. For tolamolol it is possible to demonstrate a good correlation between parent drug blood levels and the pharmacodynamic effect; this relation is less evident for bufuralol. The pharmacokinetic analysis of the behaviour of the two beta-blocking agents and their main metabolite makes it possible to explain this difference in part. The results of the present study emphasize the importance of measuring metabolites when dose-action relationships are investigated.

Determined of bufuralol and its metabolites in plasma by mass fragmentography and by gas chromatography with electron capture detection

A sensitive method for the simulataneous determination of bufuralol and its pharmacologically active metabolites in huamn plasma is described. The O-timethylsilyl,N-trifluoroacetyl derivatives are assayed by mass fragmentography. Sensitivity is 1 ng 76(-1) plasma for bufaralol and about 250 pg ml(-1) for the metabolites. An alternative procedure which uses gas chromatography with electron capture detection is also described. The sensitivity of this is about 10 ng ml(-1) plasma for all drug-related components.