The effects of revised operational dose quantities on the response characteristics of a beta/gamma personal dosemeter

The International Commission on Radiation Units and Measurements is considering revising the definitions of the operational dose quantities used for personal monitoring. This paper investigates the impacts of the proposed changes on the Public Health England two-element β/γ personal thermoluminescence dosemeter (TLD), in terms of its energy and angle dependences of responses for both skin and whole-body dose assessments. In general, the photon response of the skin element would be unaffected by the proposal, though technical issues may arise during calibration. For body photon doses, the current TLD design still produces acceptable response characteristics in some circumstances, but in general it will need to be redesigned to better match the requirements of the new operational quantity; to that end, a simple adaption is demonstrated that might provide a partial solution. For electron/beta exposures, matching the combined responses of both the body and skin elements to the dose quantities may be more challenging. The performance criteria against which dosemeters are judged may also need to be revised to reflect the proposed change.

INTERNATIONAL COMPARISON EXERCISE ON NEUTRON SPECTRA UNFOLDING IN BONNER SPHERES SPECTROMETRY: PROBLEM DESCRIPTION AND PRELIMINARY ANALYSIS

This article describes the purpose, the proposed problems and the reference solutions of an international comparison on neutron spectra unfolding in Bonner spheres spectrometry, organised within the activities of EURADOS working group 6: computational dosimetry. The exercise considered four realistic situations: a medical accelerator, a workplace field, an irradiation room and a skyshine scenario. Although a detailed analysis of the submitted solutions is under preparation, the preliminary discussion of some physical aspects of the problem, e.g. the changes in the unfolding results due to the perturbation of the neutron field by the Bonner spheres, is presented.

THE RESPONSE OF THE PHE NEUTRON PERSONAL DOSEMETER IN TERMS OF THE PROPOSED ICRU PERSONAL DOSE EQUIVALENT

The ICRU is considering amending the definition of the operational quantity for personnel monitoring. The present work investigates the impact of the proposed change on the PHE neutron personal dosemeter, which utilizes electrochemically etched PADC and is currently optimized in terms of Hp(10). The energy-dependent dose response characteristics of the dosemeter, and its performance in realistic workplace neutron fields, are calculated and compared for both the current and proposed dose quantities, for both frontal and rotationally isotropic fields. Adoption of the proposed quantity would make the dosemeter more sensitive to normally incident neutrons, but it would require some modification to ensure that it is able to meet the recommendations of the current ISO standard at all energies and its directional dependence of response would be poorer. The implications of this are discussed.

The effects of a revised operational dose quantity on the response characteristics of neutron survey instruments

The ICRU is considering revising the definition of ambient dose equivalent. This paper investigates the impacts of the proposed change on four designs of neutron survey instrument, the GNU, HSREM, LB6411 and Studsvik 2202D, in terms of their respective energy dependences of response and their performances in realistic workplace fields. In some circumstances the current designs of instrument still produce acceptable characteristics, but in general they may need to be re-optimized to better match the requirements of the new operational quantity; to that end, a simple retrofit solution for the GNU is demonstrated. The performance criteria against which instruments are judged may also need to be revised to reflect the proposed change.

THE PHE FORTUITOUS DOSIMETRY CAPABILITY BASED ON OPTICALLY STIMULATED LUMINESCENCE OF MOBILE PHONES

The Public Health England fortuitous dosimetry capability is reviewed, with particular attention focussed on the derivation of its energy and fading corrections, the Monte Carlo techniques used to generate the calibration factors between phone and body doses, and the procedures set in place to facilitate a reliable and effective service.

USE OF A SIMPLE THERMALISED NEUTRON FIELD FOR QUALITY ACCEPTANCE OF WHOLE BODY TLDS

The individual monitoring service of Public Health England (PHE) uses Harshaw™ whole-body and extremity thermoluminescent dosemeters (TLDs) with high-sensitivity lithium fluoride LiF:Mg,Cu,P, together with Harshaw 8800™ automated readers. The neutron-insensitive, (6)Li-depleted variety of TLD material is used by PHE because the service provides separate neutron and photon dosemeters. The neutron dosemeters are not sensitive to photons and vice versa Since insensitivity to neutrons is a supply requirement for TLDs, there is a need to test every new (annual) consignment for this. Because it is thermal neutrons that produce a response in (6)Li TLDs, a thermal field is needed. To this end, PHE has adopted the simple approach of sandwiching the TLDs between two ISO water-filled slab phantoms. In this arrangement, the fast neutrons from an Am-Be source are effectively thermalised. Details of the method are given, together with the results of supporting MCNP calculations and some typical results.

CALIBRATION OF THERMOLUMINESCENCE AND FILM DOSEMETERS FOR SKIN DOSES FROM HIGH-ACTIVITY MICROPARTICLES

The use of EXT-RAD™ extremity TLDs and radiochromic film to measure doses from primarily beta-emitting microparticles is discussed. Specific calibration techniques have been developed, using both Monte Carlo modelling and experiments. Results for a (90)Sr/(90)Y microparticle are presented to illustrate the general techniques and to demonstrate reasonable agreement between the dosimetry methods.

Development of a retrospective/fortuitous accident dosimetry service based on OSL of mobile phones

Work is presented on the development of a retrospective/fortuitous accident dosimetry service using optically stimulated luminescence of resistors found in mobile phones to determine the doses of radiation to members of the public following a radiological accident or terrorist incident. The system is described and discussed in terms of its likely accuracy in a real incident.

Dynamic laryngeal narrowing during exercise: a mechanism for generating intrinsic PEEP in COPD?

INTRODUCTION

Patients with COPD commonly exhibit pursed-lip breathing during exercise, a strategy that, by increasing intrinsic positive end-expiratory pressure, may optimise lung mechanics and exercise tolerance. A similar role for laryngeal narrowing in modulating exercise airways resistance and the respiratory cycle volume-time course is postulated, yet remains unstudied in COPD. The aim of this study was to assess the characteristics of laryngeal narrowing and its role in exercise intolerance and dynamic hyperinflation in COPD.

METHODS

We studied 19 patients (n=8 mild-moderate; n=11 severe COPD) and healthy age and sex matched controls (n=11). Baseline physiological characteristics and clinical status were assessed prior to an incremental maximal cardiopulmonary exercise test with continuous laryngoscopy. Laryngeal narrowing measures were calculated at the glottic and supra-glottic aperture at rest and peak exercise.

RESULTS

At rest, expiratory laryngeal narrowing was pronounced at the glottic level in patients and related to FEV1 in the whole cohort (r=-0.71, p<0.001) and patients alone (r=-0.53, p=0.018). During exercise, glottic narrowing was inversely related to peak ventilation in all subjects (r=-0.55, p=0.0015) and patients (r=-0.71, p<0.001) and peak exercise tidal volume (r=-0.58, p=0.0062 and r=-0.55, p=0.0076, respectively). Exercise glottic narrowing was also inversely related to peak oxygen uptake (% predicted) in all subjects (r=-0.65, p<0.001) and patients considered alone (r=-0.58, p=0.014). Exercise inspiratory duty cycle was related to exercise glottic narrowing for all subjects (r=-0.69, p<0.001) and patients (r=-0.62, p<0.001).

CONCLUSIONS

Dynamic laryngeal narrowing during expiration is prevalent in patients with COPD and is related to disease severity, respiratory duty cycle and exercise capacity.

Measurements with the new PHE neutron survey instrument

A novel design of survey instrument has been developed to accurately estimate ambient dose equivalent from neutrons with energies in the range from thermal to 20 MeV. The device features moderating and attenuating layers to ease measurement of fast and intermediate energy neutrons, combined with guides that channel low-energy neutrons to the single, central detector. A prototype of this device has been constructed and exposed to a set of calibration fields: the resulting measured responses are presented and discussed here, and compared against Monte Carlo data. A simple simulated workplace neutron field has also been developed to test the device.

Monte Carlo modelling of 90Sr/90Y and 85Kr beta fields for Hp(3) measurements

In support of research aimed at developing a thermoluminescence dosemeter capable of accurately measuring ionising radiation doses to the lens of the eye, Monte Carlo modelling of a standard beta exposure set-up has been performed. It was found that electrons with an energy distribution corresponding to the beta emission spectrum from (85)Kr deposit negligible doses at a depth of 3 mm in tissue, but doses from (90)Sr/(90)Y are significant; free in air and fluence-to-Hp(3,θ°) and -Hp(0.07,θ°) conversion coefficient data were found for this field for exposures at 0°, 30° and 60° angles of incidence, and the response characteristics of the new eye dosemeter were evaluated. It was shown that the results were not affected greatly by the shape of the calibration phantom. However, it was demonstrated that the presence of intermediating air and beam flattening filters hardens the energy distribution of the field at the point of test, relative to a raw (90)Sr/(90)Y source, and this impacts dose depositions.

Type testing of a head band dosemeter for measuring eye lens dose in terms of H(P)(3)

A new head band dosemeter, for the measurement of eye lens dose in terms of Hp(3), has been type tested by Public Health England's Centre for Radiation, Environmental and Chemical Hazards [formerly part of the UK Health Protection Agency (HPA)]. The type tests were based on the International Standard ISO 12794, drawing also upon earlier work at HPA. The results show that, unlike many existing dosemeters, the new head band dosemeter correctly measures Hp(3) for beta radiations as well as photons.

Doses and risks from uranium are not increased significantly by interactions with natural background photon radiation

The impact of depleted uranium (DU) on human health has been the subject of much conjecture. Both the chemical and radiological aspects of its behaviour in the human body have previously been investigated in detail, with the radiological impact being assumed to be linked to the alpha decay of uranium. More recently, it has been proposed that the accumulation in tissue of high-Z materials, such as DU, may give rise to enhanced local energy deposition in the presence of natural background photon radiation due to the high photoelectric interaction cross sections of high-Z atoms. It is speculated that, in addition to producing short-range photoelectrons, these events will be followed by intense Auger and Coster-Kronig electron emission, thereby causing levels of cell damage that are unaccounted for in conventional models of radiological risk. In this study, the physical and biological bases of these claims are investigated. The potential magnitudes of any effect are evaluated and discussed, and compared with the risks from other radiological or chemical hazards. Monte Carlo calculations are performed to estimate likely energy depositions due to the presence of uranium in human tissues in photon fields: whole body doses, organ doses in anthropomorphic phantoms and nano-/micro-dosimetric scenarios are each considered. The proposal is shown generally to be based on sound physics, but overall the impact on human health is expected to be negligible.

Individual monitoring for external radiation at accelerator facilities

Individual monitoring at accelerator facilities is discussed, within the framework set out by the International Commission on Radiological Protection and with reference to the implementation of the recommendations of that body within the European Basic Safety Standards. Legislation in other parts of the world may differ, but a worldwide perspective on this subject would be too exhaustive. The fields at accelerator facilities are contrasted in terms of particle type and energy with those encountered at more conventional sites within the nuclear fuel cycle, medical applications and general industry. The implications for individual monitoring are discussed in relation to the dose quantities for these accelerator fields and also with respect to the personal dosemeters options.

A Monte Carlo analysis of possible cell dose enhancement effects by uranium microparticles in photon fields

Uranium microparticles (radii: 50 nm-1.25 μm) were modelled surrounded by tissue and exposed to natural background radiation, in order to investigate potential dose enhancements from photon interactions. Generally, the results depended on the microparticle size. For a 0.5 μm radius microparticle in an isotropic field, it was found that the combined photon/electron doses deposited in 1 and 10 μm radii shells around it were raised by factors of ∼3.8 and ∼1.1, respectively; for a typical background photon fluence rate, these would correspond to increased energy depositions of a few 10s and a few 100s of eV y(-1), which are far less than the likely deposition rate resulting from the radioactive decay of a (238)U microparticle. The health hazard from uranium microparticle interactions with background photons was concluded to be negligible.

Analysis of the CONRAD computational problems expressing only stochastic uncertainties: neutrons and protons

Within the scope of CONRAD (A Coordinated Action for Radiation Dosimetry) Work Package 4 on Computational Dosimetry jointly collaborated with the other research actions on internal dosimetry, complex mixed radiation fields at workplaces and medical staff dosimetry. Besides these collaborative actions, WP4 promoted an international comparison on eight problems with their associated experimental data. A first set of three problems, the results of which are herewith summarised, dealt only with the expression of the stochastic uncertainties of the results: the analysis of the response function of a proton recoil telescope detector, the study of a Bonner sphere neutron spectrometer and the analysis of the neutron spectrum and dosimetric quantity H(p)(10) in a thermal neutron facility operated by IRSN Cadarache (the SIGMA facility). A second paper will summarise the results of the other five problems which dealt with the full uncertainty budget estimate. A third paper will present the results of a comparison on in vivo measurements of the (241)Am bone-seeker nuclide distributed in the knee. All the detailed papers will be presented in the WP4 Final Workshop Proceedings.

The MCNP-4C2 design of a two element photon/electron dosemeter that uses magnesium/copper/phosphorus doped lithium fluoride

The Health Protection Agency is changing from using detectors made from 7LiF:Mg,Ti in its photon/electron personal dosemeters, to 7LiF:Mg,Cu,P. Specifically, the Harshaw TLD-700H card is to be adopted. As a consequence of this change, the dosemeter holder is also being modified not only to accommodate the shape of the new card, but also to optimize the photon and electron response characteristics of the device. This redesign process was achieved using MCNP-4C2 and the kerma approximation, electron range/energy tables with additional electron transport calculations, and experimental validation, with different potential filters compared; the optimum filter studied was a polytetrafluoroethylene disc of diameter 18 mm and thickness 4.3 mm. Calculated relative response characteristics at different angles of incidence and energies between 16 and 6174 keV are presented for this new dosemeter configuration and compared with measured type-test results. A new estimate for the energy-dependent relative light conversion efficiency appropriate to the 7LiF:Mg,Cu,P was also derived for determining the correct dosemeter response.

Improved characterisation of the HPA PADC neutron personal dosemeter

The fast neutron energy dependence of response of the HPA PADC neutron personal dosemeter has been measured from 144 keV to 19 MeV using monoenergetic neutron fields. Below 144 keV the relative energy and angle dependence of response have been determined using MCNP-4C2. New data from the SIGMA field at Cadarache, France, have been used to determine the appropriate scaling factor for the calculated response to thermal and intermediate energy neutrons. These newly determined response characteristics of the dosemeter are discussed with respect to its performance in the EVIDOS workplace field irradiations.

Neutron area survey instrument measurements in the EVIDOS project

Neutron survey instruments have been exposed at all the measurement locations used in the EVIDOS project. These results have an important impact in the interpretation of the results from the project, since operationally the survey instrument will be used for an initial assessment of and routine monitoring of the ambient dose equivalent dose rate. Additionally, since the response of these instruments is in some cases very well characterised, their systematic deviations from the reference quantities provide an important verification of the determination of those quantities.

Achievements in workplace neutron dosimetry in the last decade: lessons learned from the EVIDOS project

The availability of active neutron personal dosemeters has made real time monitoring of neutron doses possible. This has obvious benefits, but is only of any real assistance if the dose assessments made are of sufficient accuracy and reliability. Preliminary assessments of the performance of active neutron dosemeters can be made in calibration facilities, but these can never replicate the conditions under which the dosemeter is used in the workplace. Consequently, it is necessary to assess their performance in the workplace, which requires the field in the workplace to be fully characterised in terms of the energy and direction dependence of the fluence. This paper presents an overview of developments in workplace neutron dosimetry but concentrates on the outcomes of the EVIDOS project, which has made significant advances in the characterisation of workplace fields and the analysis of dosemeter responses in those fields.

Pitfalls and modelling inconsistencies in computational radiation dosimetry: lessons learnt from the QUADOS intercomparison. Part II: Photons, electrons and protons

'QUADOS', a concerted action of the European Commission, has promoted an intercomparison aimed at evaluating the use of computational codes for dosimetry in radiation protection and medical physics. This intercomparison was open to all users of radiation transport codes. Eight problems were selected for their relevance to the radiation dosimetry community, five of which involved photon and proton transport. This paper focuses on a discussion of lessons learned from the participation in solving the photon and charged particle problems. The lessons learned from the participation in solving the neutron problems are presented in a companion paper (in this issue).

Pitfalls and modelling inconsistencies in computational radiation dosimetry: lessons learnt from the QUADOS intercomparison. Part I: Neutrons and uncertainties

The QUADOS EU cost shared action conducted an intercomparison on the usage of numerical methods in radiation protection and dosimetry. The eight problems proposed were intended to test the usage of Monte Carlo and deterministic methods by assessing the accuracy with which the codes are applied and also the methods used to evaluate uncertainty in the answer gained through these methods. The overall objective was to spread good practice through the community and give users information on how to assess the uncertainties associated with their calculated results.

Modelling of neutron survey instrument performance and experimental validation of those calculated response data

Three moderator-type neutron survey instruments have been modelled for energy and angle dependence of the response, in greater detail than before. These response data have been verified by comparison with published experimental measurements and measurements made specifically for this project. Influences on the instrument response have also been investigated. These have included its mode-of-use and perturbations caused by variations in the instrument manufacture. The implications of these new response data have been assessed by an extensive programme of folding the responses with workplace energy distributions.

QUADOS intercomparison: a summary of photon and charged particle problems

QUADOS, a Concerted Action of the European Commission, has promoted an intercomparison aimed at evaluating the use of computational codes for dosimetry in radiation protection and medical physics. This intercomparison was open to all users of radiation transport codes. Eight problems were selected for their relevance to the radiation dosimetry community, five of which involved photon and proton transport. This paper focuses on the analysis of the photon and charged particle problems. The neutron problems were presented in a paper at the NEUDOS9 conference.

Intercomparison on the usage of computational codes in radiation dosimetry

'QUADOS', a Concerted Action of the European Commission, has run an intercomparison aimed at evaluating the use of computational codes for dosimetry in radiation protection and medical physics. This intercomparison was open to all users of Monte Carlo, analytic and semi-analytic codes or deterministic methods. Its main aim was to provide a snapshot of the methods and codes currently in use. It also intended to furnish information on the methods used to assess the reliability of computational results and disseminate 'good practice' throughout the radiation dosimetry community. Eight problems were selected for their relevance to the radiation dosimetry community, three of which involve neutron transport. This paper focuses on the analysis of the neutron problems.

Angle dependence of response characteristics of neutron survey instruments

Neutron area survey instruments are designed to have an approximately isotropic response. In practice, the response cannot be perfectly isotropic for instruments that do not have spherical symmetry, and for all instruments it is modified by the inclusion of batteries, electronics, handles, etc. This affects the ability of the survey instrument to measure accurately an isotropic dose equivalent quantity. Measurements of the angle dependence of response for four of the most commonly used designs of survey instrument (Harwell 0949, Mark 7 NRM, NM2 and Studsvik 2202D) have been performed in a low-scatter room using radionuclide and monoenergetic neutron sources. The Monte Carlo code MCNP has been used to model the responses and to investigate their sensitivity to the polyethylene density, counting gas pressure and other manufacturing tolerances. Preliminary modelling results are presented here.

Practical implications of neutron survey instrument performance

Improvements have been made to the Monte Carlo modelling used to calculate the response of the neutron survey instruments most commonly used in the UK, for neutron energies up to 20 MeV. The improved modelling of the devices includes the electronics and battery pack, allowing better calculations of both the energy and angle dependence of response. These data are used to calculate the response of the instruments in rotationally and fully isotropic, as well as unidirectional fields. Experimental measurements with radionuclide sources and monoenergetic neutron fields have been, and continue to be made, to test the calculated response characteristics. The enhancements to the calculations have involved simulation of the sensitivity of the response to variations in instrument manufacture, and will include the influence of the user and floor during measurements. The practical implications of the energy and angle dependence of response, variations in manufacture, and the influence of the user are assessed by folding the response characteristics with workplace energy and direction distributions.

The use of passive personal neutron dosemeters to determine the neutron dose equivalent component of radiation fields in spacecraft

For the altitude range and inclination of the International Space Station (ISS), secondary neutrons can be a major contributor to dose equivalent inside a spacecraft. The exact proportion is very dependent on the amount of shielding of the primary galactic cosmic radiation and trapped particles, but is likely to lie in the range of 10-50%. Personal neutron dosemeters of simple design, processed using simple techniques developed for personal dosimetry, may be used to estimate this neutron component.

High energy neutron response characteristics of a passive survey instrument for the determination of cosmic radiation fields in aircraft

A passive survey instrument has been developed for the determination of cosmic radiation fields in aircraft. The instrument contains 30 TLDs and 36 PADC etched track detectors in order to obtain the required precision and an isotropic response. Two active electronic personal dosemeters are included to record the time profile of the field intensity. The instrument is robust and reliable, and is particularly useful to verify values of route doses based on calculations. The energy of the neutron component of the field to be determined extends to over 500 MeV, but with the majority of the dose equivalent below 200 MeV. The results are reported of measurements at Uppsala University and Physikalisch-Technische Bundesanstalt of the response characteristics of the instrument to quasi-monoenergetic neutrons in the energy range 60 to 180 MeV and for monoenergetic neutrons of energy from 70 keV to 14.7 MeV.

The measurement using passive dosemeters of the neutron component of aircraft crew dose

The cosmic radiation field at aviation altitudes can be measured with simple passive detectors. The non-neutron component may be measured by means of thermoluminescence dosimetry or other techniques, and the neutron component may be measured using poly allyl diglycol carbonate (PADC) dosemeters as described in this paper. Effective dose from neutron radiation becomes the larger component for altitudes above about 10 km, in general. The dominance is more pronounced for higher latitudes. The neutron energies range up to the maximum of the incident protons, that is many GeV. However the majority of the dose is contributed by neutrons of a few hundred MeV and less, with two maxima in the fluence spectrum, one between 1 and 10 MeV and the other between 50 and 150 MeV. We have used PADC dosemeters, electrochemically etched, to estimate the neutron component of effective dose. Up to 50 dosemeters are used in a single measurement to obtain an estimate of sufficient precision for total neutron effective doses of 50 microSv and less. The neutron fluence response characteristics of the dosemeter have been measured up to 70 MeV. These are extrapolated up to 180 MeV. This extrapolation is validated, partially, by a comparison of measured and predicted readings in the CERN reference field. From the dosemeter readings for exposure on board aircraft, neutron fluence may be estimated assuming an isotropic radiation field and the estimated neutron fluence spectrum. The neutron fluence may then be converted to effective dose using published values of conversion coefficients with the same assumptions of isotropy and known fluence spectrum. For the measurement results reported here, the calculated spectrum for the CERN concrete shielded field is used.

Measurements of the high energy neutron component of cosmic radiation fields in aircraft using etched track dosemeters

Measurements of the complex cosmic radiation field in aircraft at altitude are made with a passive survey meter comprising routine-use thermoluminescent detectors and etched track detectors. The energy dependence of response of the etched track detectors used to determine the neutron component has been characterized, partly, up to a neutron energy of 180 MeV. The neutron detectors are routinely calibrated in the CERN/EC Reference Field. The 15% determination level for total dose equivalent is 100 microSv. The evidence is that the passive survey meter provides a reliable determination of route dose.

The NRPB PADC neutron personal dosimetry service

The UK National Radiological Protection Board has been operating a successful contract neutron personal dosimetry service based on poly-allyl diglycol carbonate (PADC, also known by the trade name CR-39) since 1986, covering about 1500 workers and serving major nuclear sites in the UK and abroad. In that time approximately 100,000 dosemeters have been issued. Since the service was launched, a number of aspects have undergone evolution and it is therefore worthwhile to give an updated summary of how the service operates and performs today. The description covers the choice of plastic and of etching technique, the design of the dosemeter, the features of the automated image analysis, and the characteristics of the control software. Also described are the approaches to calibration and traceability and to compensation for energy and angle dependence, with particular mention of the ability of the service to estimate the quantity Hp(10) in accordance with the requirements of the European Council Directive 96/29/Euratom.

Disposition of inhaled 1,1,1,2-tetrafluoroethane (HFA134A) in healthy subjects and in patients with chronic airflow limitation. Measurement by 18F-labeling and whole-body gamma-counting

HFA134a (1,1,1,2-tetrafluoroethane) is a nonozone-depleting candidate to replace the chlorofluorocarbons used as propellants in metered-dose inhalers (MDIs) for pharmaceuticals that are widely used in the treatment of respiratory tract disease. As a means for ensuring the safety of such a compound for human use, it is necessary to establish that there is no excessive or unexpected accumulation in the body and in selected regions. A sensitive whole-body gamma-counting technique has been used with 18F-labeled HFA134a to measure the whole-body and regional absorption, distribution, and retention of HFA134a after administration in humans by single-breath inhalation. In seven healthy subjects, labeled HFA134a was rapidly eliminated by ventilation during the first few minutes, with an average of 9.6% of the radioactivity retained in the body at 5 min. This radioactivity cleared with an apparent terminal half-life of 1.5-4.2 hr to leave, on average, < 1% of the administered dose (< 750 micrograms, approximately 0.2 microCi) retained in the body at 5.8 hr. Disposition of radioactivity was independent of the position of label. Thus, there was no evidence of any significant degradative metabolism. On average, only 0.0056% of the administered dose appeared in the urine within the first 2 hr. Later samples contained no significant radioactivity. Inhaled HFA134a first distributed to all regions of the body and then cleared without evident accumulation in any specific region.(ABSTRACT TRUNCATED AT 250 WORDS)

The minimal metabolism of inhaled 1,1,1,2-tetrafluoroethane to trifluoroacetic acid in man as determined by high sensitivity 19F nuclear magnetic resonance spectroscopy of urine samples

In this work, oxidative metabolism of the new propellant, 1,1,1,2-tetrafluoroethane to trifluoroacetic acid in man is shown to be minimal. Alternative propellants and refrigerants are under development to replace the currently used chlorofluorocarbons which lead to stratospheric ozone depletion. One potentially useful replacement is the hydrofluorocarbon, 1,1,1,2-tetrafluoroethane (HFA-134a). Before it can be used, however, particularly as a propellant in an aerosol pharmaceutical formulation whereby the compound is in effect dosed to people, it is important that the safety of this compound is established. As a part of this safety evaluation it is necessary to understand the metabolism of HFA-134a. In this work the production of the potential oxidative metabolite of HFA-134a, trifluoroacetic acid (TFA) has been studied in human urine following inhalation dosing with HFA-134a. The concentrations of TFA in urine have been measured using a highly sensitive 19F nuclear magnetic resonance procedure with a limit of detection of 10 ng ml-1 based on an acquisition time of only 2.25 h per sample. TFA is the only fluorinated species observed in the urine samples and only at very low levels, indicating that the oxidative route of metabolism can occur in vivo in man, but this metabolism is minimal in terms of percentage of administered dose.

Metabolic fate and disposition of 1,1,1,2-tetrafluoroethane (HFC134a) in rat following a single exposure by inhalation

1. The metabolic fate and disposition of [U-14C]-1,1,1,2-tetrafluoroethane ([U-14C]-HFC134a) has been determined in the male and female rat following a 1 h single exposure by inhalation to atmospheres of 10,000 ppm. 2. Of the inhaled dose, approx. 1% was recovered in urine, faeces and expired air postexposure indicating that absorption of this fluorocarbon across the lung is poor. Of this 1%, approx, two-thirds were exhaled within 1 h of the cessation of exposure as unchanged HFC134a. The remaining radioactivity was exhaled as [14C]-carbon dioxide or excreted in urine and faeces as trifluoroacetic acid. 3. Carbon dioxide was the major metabolite of HFC134a accounting for 0.22 and 0.27% of the inhaled dose in the male and female rat, respectively. Urinary excretion accounted for 0.09% of the dose and faecal excretion 0.04% of the dose by both sexes. 4. Total metabolism measured as the sum of the radioactivities in urine, faeces and as carbon dioxide amounted to 0.34 and 0.40% of the inhaled dose in male and female, respectively. 5. There were no major sex differences in the rates, routes or amounts of radiolabel excreted. Analysis of a range of tissues at 5 days postexposure showed a relatively uniform distribution of radioactivity. There was no evidence for a specific uptake of HFC134a or a metabolite into any organ or tissue analysed, including fat.

Preclinical studies on the anti-migraine drug, sumatriptan

Sumatriptan is believed to constrict selectively the cranial vessels that are distended and inflamed during migraine. The action is mediated by activation of a 5-HT1 receptor subtype which has been shown in animals to be localized in cranial vessels. Further studies to elaborate sumatriptan's precise clinical mode of action have focused on the human meningeal circulation and should lead to a better understanding of the pathogenesis of migraine. Administering [14C]sumatriptan, drug-related material was shown to be well absorbed. Following absorption there was some first-pass metabolism resulting in oral bioavailabilities of 37, 58 and 23% in rat, dog and rabbit, respectively. In all species, circulating sumatriptan was cleared rapidly by metabolic and renal clearance with a half-life of 1-2 h. The indoleacetic acid metabolite is the primary metabolic product; however, rats, mice and rabbits also N-demethylate the methylaminosulphonylmethyl side-chain. The passage of sumatriptan and its metabolites across the blood-brain barrier appeared to be very limited, although some drug could be detected in the cerebrospinal fluid after administration of high intravenous doses. Safety studies in various animal species showed that sumatriptan produced few adverse pharmacodynamic effects when administered acutely, except at high doses, although it was less well tolerated in dogs. No findings of toxicological significance were observed in rats and dogs after chronic dosing for 1 year or more.(ABSTRACT TRUNCATED AT 250 WORDS)

The clinical pharmacology, pharmacokinetics and metabolism of sumatriptan

Clinical pharmacology studies were undertaken in young healthy volunteers, in a small number of elderly subjects and in migraine subjects during and between attacks. Absorption after subcutaneous and oral administration was rapid. Bioavailability was nearly 100% after subcutaneous administration and averaged 14% after oral administration. Elimination was predominantly by metabolism to a non-active indoleacetic acid analogue. The plasma half-lives of sumatriptan and the metabolite were about 2 h. Pharmacokinetic and pharmacodynamic variables were similar in all groups studied and were not altered by the presence of food, alcohol, dihydroergotamine or prophylactic migraine treatments. Sumatriptan produced a number of minor adverse events, but had no clinically significant effect on routine haematological or biochemical investigations using the intravenous, subcutaneous or oral routes. Transient rises in blood pressure were observed which were no greater than those that would be anticipated during moderate exercise. The physician-administered subcutaneous injection resulted in transient stinging at the site of injection in many subjects; administration using the auto-injector was better tolerated.

Determination of albuterol concentrations in human plasma using solid-phase extraction and high-performance liquid chromatography with fluorescence detection

A fast, simple, and accurate method for determining albuterol concentrations in human plasma has been developed and validated for use in routine clinical analyses. This method involves a solid-phase extraction procedure using silica cartridges and normal-phase high-performance liquid chromatography with fluorescence detection. Regression analysis showed the method was linear over the standard curve range 1-16 ng ml-1. The percent recovery for albuterol and the internal standard, bamethane, at 5 ng ml-1 was found to be greater than 90%. The newly developed method has been applied in the analysis of plasma samples from patients and healthy volunteers.

Automated extraction of drugs from biological fluids

An automated continuous flow liquid-liquid extraction procedure is described for the separation of the H2-antagonist loxtidine from plasma samples containing two metabolites which interfere in the radioimmunoassay of the drug. The extraction of the bronchodilator salbutamol was studied using the DuPont Prep I automated liquid solid extraction apparatus, with a 12 cartridge capacity, and a vacuum extraction box designed in this laboratory to hold 30 Sep-pak C-18 (Waters Associates) cartridges. Twenty-four plasma samples per hour can be automatically processed with the Prep I. Although the vacuum box is not fully automated 45 plasma samples per hour can be processed. The Prep I can only be used with DuPont XAD, strong cation and anion exchange cartridges. Cartridges containing alumina, silica, florisil, cation and anion exchange resins and reverse phase packings can all be used with the vacuum extraction box. The latter costs only a fraction of the Prep I and therefore each analyst can have his own unit.

Evidence for an inhibitor of renal urate and PAH secretion in rabbit blood

Results of previous studies of urate secretion in isolated perfused S2 segments of the rabbit proximal tubule suggested that a bath of rabbit serum may inhibit urate transport in comparison to a synthetic medium. In the current study we tested for a urate transport inhibitor by determining the steady-state tissue-to-medium ratio (T/M) of [14C]urate in nonperfused S2 segments during incubation in synthetic medium (BSA-Burg) and commercial rabbit serum (RS-PF). With 80-120 microM urate in the bath the T/M ratio was 7.66 +/- 0.53 (n = 29) in BSA-Burg and 5.29 +/- 0.40 (n = 29) in RS-PF. RS-PF decreased the influx of urate into the cells but had no effect on urate efflux. Freshly drawn rabbit serum and plasma also inhibited urate accumulation, and the inhibition was reversible. p-Aminohippurate accumulation was inhibited by RS-PF, but tetraethylammonium bromide uptake was not. RS-PF inhibited transepithelial secretion of urate and PAH, but net fluid absorption was not decreased. The inhibitory material in rabbit serum could not be removed by extensive dialysis (14,000-dalton exclusion), by ultrafiltration (50,000-dalton exclusion), or by charcoal or ethanol extraction. Inhibitory activity was detected in both albumin and globulin fractions of rabbit serum. The relation between bath and intracellular urate concentrations of nonperfused tubules in rabbit serum was sigmoidal, whereas the relation in the BSA-Burg medium was more nearly hyperbolic. We conclude that organic anion transport in rabbit S2 segments is inhibited or suppressed by normal serum and suggest that urate secretion and excretion may be subject to allosteric modification by serum proteins.

Use of high-performance liquid chromatography-mass spectrometry for the study of the metabolism of ranitidine in man

High-performance liquid chromatography has been used for the qualitative analysis of metabolites and the quantitative analysis of ranitidine in the urine from subjects given oral and intravenous doses of ranitidine. Ranitidine, ranitidine-N-oxide, ranitidine-S-oxide and desmethylranitidine were identified in extracts of the urine obtained by the XAD-methanol procedure. A selected-ion monitoring technique, using [2H3]ranitidine as the internal standard, was used to determine ranitidine. A normal-phase system consisting of methanol-propan-2-ol-5 M ammonium acetate (50:50:1) was used, and because of this the volume of urine which could be injected on-column without deterioration of the chromatography was limited to 10 microliters. This limited the sensitivity of the method to 1.0 microgram of ranitidine per millilitre of urine.

Applications of high-voltage paper electrophoresis for the characterization of drug metabolites

1. The application of high-voltage paper electrophoresis (h.v.p.e.) to the identification of drug metabolites in urine and bile has been investigated. 2. The major urinary metabolite of [3H]salbutamol in man had an electrophoretic mobility indicative of a sulphate ester. 3. A metabolite of [14C]ranitidine present in rat bile was shown to contain an ionized group with a pKa corresponding to a carboxylic acid. 4. The electrophoretic mobility-pH profile of a metabolite of radiolabelled N"-cyano-N-[2-[5-(dimethylaminomethyl)-2-furanylmethylthio]ethyl]-N-methylguanidine (14C-AH 18801) excreted in dog urine suggested that oxidation of the tertiary amine group of the compound had occurred. 5. H.v.p.e. provided valuable information on the structure of both phases I and phase II metabolites at a stage when the material was insufficiently pure for identification by other techniques.

The use of on-line high-performance liquid chromatography-mass spectrometry for the identification of ranitidine and its metabolites in urine

1. Reverse and normal phase h.p.l.c. systems have been developed for separation ranitidine and three metabolites, desmethylranitidine, ranitidine-S-oxide and ranitidine-N-oxide. 2. These h.p.l.c. systems have been evaluated for characterization of ranitidine and metabolites using an h.p.l.c. coupled to a mass spectrometer with a moving belt interface. 3. Ranitidine and its metabolites were thermally degraded under the conditions required to evaporate the reverse phase eluent that contained 40% aq. 0.05 M ammonium acetate. 4. The normal phase eluent was evaporated in the interface at a lower temp. and satisfactory mass spectra were obtained from 1 microgram of ranitidine and each metabolite injected on to the h.p.l.c. column. 5. Normal phase h.p.l.c.-mass spectrometry has been used to identify ranitidine and three of its metabolites in rabbit and human urine obtained after oral administration of ranitidine.