[Serum concentration of glyceryl trinitrate (GTN) in transdermal application of GTN dressings of various origins]

Animal models for percutaneous absorption

Animal models are important tools to predict human in vivo percutaneous absorption/penetration. Monkey, pig, rat, rabbit, guinea pig, hairless rodents, such as hairless rat, hairless mouse, hairless guinea pig and hairless dog, are among the most used animals for this purpose. Each animal model has its own advantages and weakness or limitation. To better correlate animal data with human skin absorption, we need to be familiar with each animal model's characteristics as well as experimental method and condition. We reviewed the original papers published after 1993 that described permeability of both animal skin and human skin. It showed that monkey, pig and hairless guinea pig are more predictive of human skin absorption/penetration and common laboratory animals, such as rat, rabbit, guinea pig, generally overestimate human skin absorption/penetration.

Nitrates: why and how should they be used today? Current status of the clinical usefulness of nitroglycerin, isosorbide dinitrate and isosorbide-5-mononitrate

Nitrates are highly effective both in terminating acute attacks of angina pectoris and in the prophylaxis of symptomatic and asymptomatic myocardial ischemia. Preload reduction by venodilatation is the prevailing mechanism of nitrates in patients with chronic stable angina and is the unique feature distinguishing them from beta and calcium-channel blockers. Nitrates dilate coronary arteries not only in pre- and poststenotic vessels, but also in eccentric lesions. In patients with endothelial dysfunction, nitrates seem to be the physiological substitute for endothelium-derived relaxing factor. During the past decade, however, there has been substantial evidence of a clinically relevant loss of the anti-ischemic effects ("nitrate tolerance"). Many studies with oral dosing of isosorbide dinitrate or isosorbide-5-mononitrate at least three times daily have proven nitrate tolerance in patients with coronary artery disease and/or congestive heart failure. Complete loss of anti-ischemic effects after repetitive, continuous patch attachments has also been found. As we first showed in 1983, intermittent therapy with once-daily ingestion of high-dose sustained-release isosorbide dinitrate was successful in preventing the development of tolerance. Similarly, tolerance to isosorbide-5-mononitrate also does not develop when it is ingested once daily. It is now generally accepted that a daily low-nitrate interval is required to prevent tolerance development. Although the minimal patch-free interval required to prevent tolerance needs further investigation, a 12-h patch-free interval should prevent tolerance in most patients. The prolonged duration of action of once-daily high-dosage administration of sustained-release formulations, the improved patient compliance with a single daily administration, and the increased likelihood of maximal anti-ischemic effects are important reasons for recommending high single daily doses of isosorbide dinitrate or isosorbide-5-mononitrate.

Efficacy of a new transdermal nitroglycerin patch (Deponit 10) for stable angina pectoris

In this double-blind randomized placebo-controlled crossover study, the antianginal and anti-ischemic effect of a new transdermal system, releasing 10 mg of nitroglycerin (NTG) over 24 hours, was assessed in 19 outpatients with stable exercise-induced angina pectoris. The trial consisted of a 3-day washout: a 1-week period with verum or placebo patch followed by a second 1-week period with the other patch. During the study only sublingual NTG was allowed, and its consumption and the number of attacks recorded. Treadmill exercise tests were performed at the end of washout before patch application (baseline test) and 3 and 24 hours, respectively, after each period of 7 days of application of 1 patch daily. Systolic blood pressure and heart rate did not vary significantly at rest in the 17 patients who completed the trial. Angina was reduced 31.3% and NTG consumption 34.3% (p less than 0.01) during the week with Deponit 10 as compared with placebo. Exercise duration increased 29 and 16.1% (p less than 0.001 and p less than 0.1, respectively) at 3 and 24 hours with a verum patch as compared with placebo. ST-segment depression at comparable loads decreased 69 and 40.5% (p less than 0.01) at 3 and 24 hours, respectively, after application of Deponit. Onset of angina was delayed and maximal heart rate-blood pressure product significantly increased at 3 and 24 hours of treatment. It is concluded that Deponit 10 patch is effective in reducing anginal attacks and in increasing exercise capacity up to 24 hours after application.

Clinical pharmacokinetics of glyceryl trinitrate following the use of systemic and topical preparations

Glyceryl trinitrate has been used for more than a century for the treatment of angina pectoris and, more recently, for the treatment of congestive heart failure. The introduction of transdermal delivery systems has renewed the controversy regarding the efficacy of the drug, mainly in the light of the development of tolerance. With concentrations of the order of 1 microgram/L or less, the measurement of glyceryl trinitrate in plasma is not easy: gas chromatography with electron capture detection has been used widely but recently gas chromatography-mass spectrometry has provided satisfactory results. Assay problems are most likely to be responsible for some of the unexpected results reported. Further factors which may confound the results of the study of plasma concentrations are the rapid metabolism of glyceryl trinitrate in blood in vitro, adsorption to containers and infusion sets, and the uptake and/or metabolism in vessel walls. From the intravenous infusion data, the large interindividual variability in plasma concentrations of glyceryl trinitrate is apparent. The plasma half-life is about 2 to 3 minutes; plasma clearance values reported vary from 216 to 3270 L/h, indicating extensive non-hepatic metabolism. With transdermal administration, mainly with the transdermal controlled delivery systems, plasma concentrations of glyceryl trinitrate appear to be maintained for up to 24 hours, with large interindividual variations. Despite the ability to maintain, for example with the transdermal delivery systems, relatively constant concentrations of glyceryl trinitrate, it has not been possible to find a relationship between plasma concentrations and pharmacological or clinical effects. This is in part due to the attenuation of the effects with time; from the available data it is clear that this attenuation occurs at a pharmacodynamic level (reflex adaptation and tolerance) and not at the pharmacokinetic level.

Various administration forms of nitrates and their possibilities

This article reviews the development and pharmacokinetics of a number of new dosage formulations (e.g. transdermal patches and buccal tablets) and new active substances (e.g. isosorbide 5-mononitrate) which have recently been introduced to overcome some of the problems inherent in conventional formulations of organic nitrates.