The realisation that new chemical entities under development as drug candidates fail in three of four cases in clinical trials, together with increased costs and increased demands of reducing preclinical animal experiments, have promoted concepts for improvement of early screening procedures in humans. Positron emission tomography (PET) is a non-invasive imaging technology, which makes it possible to determine drug distribution and concentration in vivo in man with the drug labelled with a positron-emitting radionuclide that does not change the biochemical properties. Recently, developments in the field of rapid synthesis of organic compounds labelled with positron-emitting radionuclides have allowed a substantial number of new drug candidates to be labelled and potentially used as probes in PET studies. Together, these factors led to the logical conclusion that early PET studies, performed with very low drug doses-PET-microdosing-could be included in the drug development process as one means for selection or rejection of compounds based on performance in vivo in man. Another important option of PET, to evaluate drug interaction with a target, utilising a PET tracer specific for this target, necessitates a more rapid development of such PET methodology and validations in humans. Since only very low amounts of drugs are used in PET-microdosing studies, the safety requirements should be reduced relative to the safety requirements needed for therapeutic doses. In the following, a methodological scrutinising of the concept is presented. A complete pre-clinical package including limited toxicity assessment is proposed as a base for the regulatory framework of the PET-microdosing concept.
1. The systemic effects of inhaled fluticasone propionate (FP), administered via Diskhaler, on the hypothalamo‐pituitary‐adrenal (HPA) axis were assessed primarily by measuring plasma cortisol at frequent intervals for 20 h after drug administration. 2. FP showed a dose‐ related suppression of plasma cortisol measured as area under the plasma cortisol vs time curve (AUC 0‐20). The cortisol suppression (expressed as % fall from placebo) was 8, 19, and 28% for single doses of 250 micrograms FP, 500 micrograms FP and 1000 micrograms FP, respectively. A single dose of budesonide, 800 micrograms (via Turbuhaler), resulted in a 16% cortisol suppression. The cortisol suppression for all three single doses of FP, and for the single dose of budesonide, was statistically significantly different from placebo. 3. Repeated dosing of FP (1000 micrograms twice daily for 3.5 days) resulted in a more marked plasma cortisol suppression; a fall of 65% from placebo (AUC FP 1000 mg twice daily vs AUC placebo, P < 0.001). 4. In a well‐controlled study in healthy volunteers, inhaled FP, in therapeutic doses, was shown to exhibit systemic effects which appear to be more pronounced after repeated dosing.
Intrasubject variation in bioavailability (rate and extent) and disposition of furosemide 40 mg was investigated using a repeated, randomized, double-blind cross-over study in 8 healthy subjects. Two generic tablet formulations (Lasix and Furix) and intravenous furosemide were compared on 6 separate days. Extensive intrasubject variability after oral administration was observed in AUC, mean absorption time (MAT) and urinary excretion. The variability (error variance) within the dosage forms was as large as that between the two generics. These variations most probably depended on the absorption process, since the repeated i.v. doses showed only marginal intrasubject variability. Absolute bioavailability was 56% for Lasix and 55% for Furix (AUC). The range was 20 to 84% between individuals and the maximal range within one individual was 20 to 61%. Confidence interval and Bayesian analysis showed a high probability of non-equivalence not only between but also within the generics when the separate cross-over experiments were analyzed (8 observations). When extending the analysis to 16 observations, bioequivalence was demonstrated for the two generic tablets. Rate of absorption, quantified as MAT, was 128 min for Lasix and 98 min for Furix (16 observations). Since MAT was significantly longer (p less than 0.001) than the mean residence time after the i.v. dose (57 min), absorption was evidently the rate-limiting step in the overall kinetics of oral furosemide. Intraindividual variation in absorption is a confounding factor in bioavailability studies of furosemide using limited numbers of subjects. This is important to consider when designing and evaluating bioavailability studies for drugs showing these variations.
Patients with symptoms of gastro-oesophageal re¯ux disease (GERD) are today routinely treated with drugs that have an inhibitory effect on acid production from the stomach. Community-based surveys in the UK and Scandinavia have revealed that 21±40% of people reported suffering from heartburn at some time during the 6±12 month survey period. 1±3 In the UK, about 25% of GERD patients seek medical advice for their symptoms. 4 The therapeutic effect of these drugs, when taken irregularly for the relief of acid-related discomforts, is related both to the onset and duration of action, i.e. how quickly and for how long the pH is raised in the stomach or the oesophagus. To obtain rapid symptom relief, rapid onset of action on gastric acidity after intake of the drug is very important. Formulations designed for rapid onset of action have been developed for the H 2 -receptor antagonists (ranitidine, famotidine, cimetidine). Several comparative clinical pharmacology (intragastric pH monitoring) studies have demonstrated a more rapid onset of action for these dosage forms in comparison to conventional dosage forms. 5±7 Fast onset of pH neutralization parallels fast relief of symptoms. 8,9 Comparative crossover studies comparing both SUMMARY Background: The therapeutic effect of drugs inhibiting acid production on acid-related discomforts is related to both the onset and duration of action of the drug. The effects on gastric pH by single oral doses of some acidinhibiting drugs were investigated by measuring daytime (morning to lunch) intragastric pH in healthy volunteers. Methods: This randomized, single-dose, 4-way crossover study included 15 healthy fasting subjects. Effervescent ranitidine tablets 150 and 300 mg, fast-dissolving famotidine tablets 20 mg and capsules of omeprazole 20 mg were administered. Measurements of intragastric pH were performed every 4 s for 10 min prior to drug administration and during the following 4 h. Results: The effervescent ranitidine tablets (150 or 300 mg) produced similar changes in intragastric pH:
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.