A brief history of gamma scintigraphy.

Gamma scintigraphy involves the radiolabeling of inhaled drug formulations, followed by in vivo imaging of deposition in two dimensions. This permits whole lung deposition to be quantified as mass of drug or percentage of the dose, and regional deposition patterns to be assessed. Gamma scintigraphy is the method by which the majority of inhaled drug deposition data have been obtained, and scintigraphic studies have become viewed as milestone assessments in the development of new pulmonary drug products. Lung deposition data are used to show "proof of concept" in vivo for these products, and act as a bridge between in vitro laboratory testing and a clinical trials program. Gamma scintigraphy is likely to remain the method of choice for assessing inhaled drug deposition for some time to come.

Deposition and pharmacokinetics of an HFA formulation of triamcinolone acetonide delivered by pressurized metered dose inhaler.

Novel formulations of asthma drugs contained in pressurized metered dose inhalers (pMDIs) are being developed containing hydrofluoroalkane (HFA) propellants. The objectives of this study were to assess the deposition in the lungs and oropharynx of triamcinolone acetonide (TAA; Azmacort, Aventis Pharma, Collegeville, PA) delivered by pMDI formulated with HFA-134a, together with the pharmacokinetic profile of TAA, and to determine the extent to which the Azmacort spacer improves targeting of TAA to the lungs. The deposition of TAA, labelled with 99mTc, was assessed by gamma scintigraphy in 10 patients with mild to moderate asthma (mean forced expiratory volume in one second [FEV1] 76% predicted), who received in randomized order three delivered (ex-device) doses of 75 microg TAA via pMDI coupled to an Azmacort spacer (TAA-spacer), and three delivered doses of 230 microg TAA via the same device, but with the spacer removed (TAA-no spacer). Mean lung deposition expressed as mass of drug was similar for each regimen (TAA-no spacer 175 microg; TAA-spacer 188 microg), but when expressed as percentage delivered dose, lung deposition was higher for TAA-spacer (53.8%) versus TAA-no spacer (26.0%), indicating superior drug targeting for TAA-spacer. The spacer reduced oropharyngeal deposition. The pharmacokinetic data showed higher plasma levels of drug for TAA-no spacer, resulting from higher oropharyngeal deposition. "Pharmacoscintigraphic" data showed proof of concept for a novel HFA delivery system for an inhaled corticosteroid based on pulmonary targeting of drug.

A comparison of the lung deposition of budesonide from Easyhaler, Turbuhaler and pMDI plus spacer in asthmatic patients.

Inhaled corticosteroids in pressurized metered does inhalers (pMDIs) are often delivered via a large volume spacer device, but these are bulky and inconvenient. Dry powder inhalers (DPIs) provide a highly portable and convenient propellant-free alternative to pMDIs for asthma maintenance therapy However, each DPI could have unique in vivo delivery characteristcs. In order to quantify the total and regional lung deposition of budesonide (200 microg) from (a) Easyhaler, (b) Turbuhaler and (c) pMDI plus Nebuhaler 750 ml spacer, a three-way randomized cross-over study was carried out in 12 mild to moderate asthmatic patients. Deposition was quantified by the imaging technique of gamma scintigraphy Optimal inhalation techniques were used throughout. Mean (SD) whole lung deposition (% metered dose) was similar for Easyhaler [18.5 (7.8) %] and Turbuhaler [21.8 (8.2) %], but was significantly higher for pMDI plus Nebuhaler [44.1 (10.0) %, P < 0.01]. The regional distribution patterns in the lungs were predominantly central for all three devices. Nebuhaler reduced oropharyngeal deposition significantly compared with the two DPIs. Easyhaler showed comparable deposition to Turbuhaler and hence drugs delivered by Easyhaler would be expected to have a similar clinical effect to those delivered by Turbuhaler in asthma maintenance therapy.

Scintigraphic evaluation of lung deposition with a novel inhaler device.

A gamma-scintigraphic study was carried out in 13 healthy individuals to compare the lung deposition of budesonide from a novel multidose dry powder inhaler (MDPI; Novolizer) with that from the Pulmicort Turbuhaler, and to assess the degree of flow rate dependence of the Novolizer. Median whole lung depositions for the Novolizer at peak inhaled flow rates of 90, 60 and 45 l/min were 32.0, 25.4 and 19.9% of the metered dose, respectively, compared with 21.4% for the Turbuhaler (peak inhaled flow rate 60 l/min). Patterns of regional lung deposition were similar for all four regimens. These data provided proof of concept in vivo for the novel MDPI device, and demonstrated that it delivers drug to the lungs efficiently. The deposition data enabled drug doses to be used in subsequent clinical trials comparing the Novolizer with the Turbuhaler to be predicted with confidence.

Human lung deposition data: the bridge between in vitro and clinical evaluations for inhaled drug products?

Regulatory dossiers for new inhaled drug products generally contain in vitro data, which assess delivered dose and particle size distribution, together with clinical efficacy and safety data. Human lung deposition data may be generated using radionuclide imaging techniques or appropriate pharmacokinetic methods, and can act as a 'bridge' via which a seamless transition can be made between in vitro testing in the laboratory and efficacy/safety testing in the clinic. By enabling informed decisions to be made about the evaluation of new devices or formulations in man, lung deposition data permit a long and expensive clinical trials programme to be commenced with much greater certainty of a successful outcome. Human lung deposition data should be considered for supplementing the information required for regulatory dossiers.

Scintigraphic comparison of budesonide deposition from two dry powder inhalers.

Chlorofluorocarbons (CFCs), used in metered dose inhalers (MDIs), have been identified as being deleterious to the environment leading to a ban on their production. Dry powder inhalers (DPIs) are a widely used alternative to MDIs. One disadvantage of DPIs is that in vivo lung deposition can be influenced by the patient's inspiratory flow rate. The ASTA Medica multi-dose dry powder inhaler (AM-MDPI) has been designed to offer low resistance on inhalation, so that asthmatic patients can achieve inhaled flow rates of approximately 90 L x min(-1). The aim of the study was to evaluate the in vivo deposition of budesonide from the AM-MDPI at different flow rates and to compare this with delivery from a Turbuhaler DPI at a high flow rate. The study was a scintigraphic, randomized, crossover study in which 13 healthy volunteers inhaled a single 200 microg dose of radiolabelled budesonide on four separate occasions with a minimum 44-h washout period between dosings. At the lowest flow rate of 54 L x min(-1), comparable to that for the Turbuhaler (58 L x min(-1)), a similar percentage of the metered dose was delivered to the lung (AM-MDPI median 19.9%; Turbuhaler median 21.4%). At high flow rate (peak inspiratory flow rate 99 L x min(-1)) the AM-MDPI delivered significantly more drug to the lung (median 32.1% of metered dose) than at 65 L x min(-1) or 54 L x min(-1) (median 25.0% and 19.9% of metered dose, respectively), thus demonstrating flow rate dependence. The pattern of regional lung deposition from the AM-MDPI was similar for all three inhalation manoeuvres. It was concluded that the ASTA Medica multi-dose dry powder inhaler achieves at least as much deposition of budesonide in the lungs as a Turbuhaler when used at similar inspiratory flow rates.

Regional lung deposition of a technetium 99m-labeled formulation of mometasone furoate administered by hydrofluoroalkane 227 metered-dose inhaler.

BACKGROUND: A new inhaled suspension formulation of mometasone furoate (MF), a potent corticosteroid with minimal systemic availability, has been developed for the treatment of asthma. This formulation is delivered by metered-dose inhaler (MDI) using the nonchlorofluorocarbon propellant hydrofluoroalkane 227 (HFA-227). OBJECTIVE: The primary goal of this study was to determine the respiratory tract deposition of this formulation of MF. A secondary objective was to measure plasma concentrations of MF and a putative metabolite, 6-X-OH MF, to determine the systemic exposure to corticosteroid. METHODS: This was a single-dose, open-label study in which 200 microg of technetium 99m (99mTc)-radiolabeled MF was administered to patients with asthma. Gamma scintigraphy was used to quantify lung, oropharyngeal, stomach, and MDI mouthpiece deposition patterns of MF. RESULTS: Eleven patients, aged 21 to 47 years, with a history of asthma were enrolled in and completed the study. The mean (+/- SD) whole lung deposition of MF was 13.9%+/-5.7% of the metered (ex-valve) dose. The central lung zone received 5.3%+/-2.8% of the dose; the intermediate zone received 4.7%+/-1.9%; and peripheral lung deposition was 4.0%+/-1.5%. The mean (+/- SD) ratio of peripheral to central lung deposition was 0.8+/-0.2. Oropharyngeal deposition was 79.1%+/-8.7% of the ex-valve dose, with 6.3%+/-7.8% deposited on the MDI mouthpiece and 0.7%+/-0.5% exhaled. The majority of plasma samples taken for analysis of MF and 6-13-OH MF concentrations were below the limit of quantification (50 pg/mL) in all patients after inhalation of 200 microg 99mTc-labeled ME CONCLUSION: The lung deposition of MF when administered via HFA-227 MDI is comparable to the 10 to 20% lung deposition seen with other corticosteroid suspension for- mulations administered by MDI that have demonstrated effectiveness in the treatment of asthma.

Inositol polyphosphate-mediated iron transport in Pseudomonas aeruginosa.

It has previously been shown that myo-inositol hexakisphosphate (myo-InsP6) mediates iron transport into Pseudomonas aeruginosa and overcomes iron-dependent growth inhibition. In this study, the iron transport properties of myo-inositol trisphosphate and tetrakisphosphate regio-isomers were studied. Pseudomonas aeruginosa accumulated iron (III) at similar rates whether complexed with myo-Ins(1,2,3)P3 or myo-InsP6. Iron accumulation from other compounds, notably D/L myo-Ins(1,2,4,5)P4 and another inositol trisphosphate regio-isomer, D-myo-Ins(1,4,5)P3, was dramatically increased. Iron transport profiles from myo-InsP6 into mutants lacking the outer membrane porins oprF, oprD and oprP were similar to the wild-type, indicating that these porins are not involved in the transport process. The rates of reduction of iron (III) to iron (II) complexed to any of the compounds by a Ps. aeruginosa cell lysate were similar, suggesting that a reductive mechanism is not the rate-determining step.

Synthesis and iron binding studies of myo-inositol 1,2,3-trisphosphate and (+/-)-myo-inositol 1,2-bisphosphate, and iron binding studies of all myo-inositol tetrakisphosphates.

The first syntheses of the natural products myo-inositol 1,2,3-trisphosphate and (+/-)-myo-inositol 1,2-bisphosphate are described. The protected key intermediates 4,5,6-tri-O-benzoyl-myo-inositol and (+/-)-3,4,5,6-tetra-O-benzyl-myo-inositol were phosphorylated with dibenzyl N,N-di-isopropylphosphoramidite in the presence of 1H-tetrazole and subsequent oxidation of the phosphite. The crystal structures of the synthetic intermediates (+/-)-1-O-(tert-butyldiphenylsilyl)-2,3,O-cyclohexylidene-myo-inos itol and (+/-)-4,5,6-tri-O-benzoyl-1-O-(tert-butyldiphenylsilyl)-2,3-O-cycl ohexylidene- myo-inositol are reported. myo-Inositol 1,2,3-trisphosphate, (+/-)-myo-inositol 1,2-bisphosphate, and all isomeric myo-inositol tetrakisphosphates were evaluated for their ability to alter HO. production in the iron-catalysed Haber-Weiss reaction. The results demonstrated that a 1,2,3-grouping of phosphates in myo-inositol was necessary for inhibition, also that (+/-)-myo-inositol 1,2-bisphosphate potentiated HO. production. myo-Inositol 1,2,3-trisphosphate resembled myo-inositol hexakisphosphate (phytic acid) in its ability to act as a siderophore by promoting iron-uptake into Pseudomonas aeruginosa.

The pyocin Sa receptor of Pseudomonas aeruginosa is associated with ferripyoverdin uptake.

We have used Tn5 mutagenesis to obtain a mutant resistant to pyocin Sa. When grown in iron-deficient succinate medium this mutant lacked an 85-kDa iron-regulated outer membrane protein (IROMP), and expression of a 75-kDa IROMP was increased compared with that in the parent strain. The mutant was deficient in pyoverdin biosynthesis and showed a 95% decrease in transport of ferripyoverdin purified from the parent strain, suggesting that the 85-kDa IROMP is the specific receptor for ferripyoverdin and pyocin Sa. The mutant compensated for the deficiency in pyoverdin biosynthesis and transport by exhibiting a fourfold increase in ferripyochelin transport. The low-level transport of ferripyoverdin in the Sa-resistant mutant, which extended to heterologous pyoverdins from other strains, suggests that Pseudomonas aeruginosa has a second ferripyoverdin uptake system of lower affinity and broader specificity.