Haemodynamic effects of glyceryl trinitrate following repeated application of a transdermal delivery system with a phasic release profile

Low-amplitude pulses to the circulation through periodic acceleration induces endothelial-dependent vasodilatation

Low-amplitude pulses to the vasculature increase pulsatile shear stress to the endothelium. This activates endothelial nitric oxide (NO) synthase (eNOS) to promote NO release and endothelial-dependent vasodilatation. Descent of the dicrotic notch on the arterial pulse waveform and a-to-b ratio (a/b; where a is the height of the pulse amplitude and b is the height of the dicrotic notch above the end-diastolic level) reflects vasodilator (increased a/b) and vasoconstrictor effects (decreased a/b) due to NO level change. Periodic acceleration (pG(z)) (motion of the supine body head to foot on a platform) provides systemic additional pulsatile shear stress. The purpose of this study was to determine whether or not pG(z) applied to rats produced endothelial-dependent vasodilatation and increased NO production, and whether the latter was regulated by the Akt/phosphatidylinositol 3-kinase (PI3K) pathway. Male rats were anesthetized and instrumented, and pG(z) was applied. Sodium nitroprusside, N(G)-nitro-l-arginine methyl ester (l-NAME), and wortmannin (WM; to block Akt/PI3K pathway) were administered to compare changes in a/b and mean aortic pressure. Descent of the dicrotic notch occurred within 2 s of initiating pG(z). Dose-dependent increase of a/b and decrease of mean aortic pressure took place with SNP. l-NAME produced a dose-dependent rise in mean aortic pressure and decrease of a/b, which was blunted with pG(z). In the presence of WM, pG(z) did not decrease aortic pressure or increase a/b. WM also abolished the pG(z) blunting effect on blood pressure and a/b of l-NAME-treated animals. eNOS expression was increased in aortic tissue after pG(z). This study indicates that addition of low-amplitude pulses to circulation through pG(z) produces endothelial-dependent vasodilatation due to increased NO in rats, which is mediated via activation of eNOS, in part, by the Akt/PI3K pathway.

Nitric oxide is released into circulation with whole-body, periodic acceleration

STUDY OBJECTIVE

To determine if comfortably applied, whole-body, periodic acceleration releases significant amounts of nitric oxide (NO) into the circulation of healthy subjects and patients with inflammatory diseases.

MATERIALS

Fourteen healthy adults and 40 adult patients with inflammatory diseases underwent single 45-min trials of whole-body, periodic acceleration with a new "passive exercise" device, while an ECG and a digital pulse wave were obtained with a photoelectric-plethysmograph sensor.

METHODS

The position of the dicrotic notch from the pulse waveform was computed from the amplitude of the pulse divided by the height of the dicrotic notch above the end-diastolic level (a/b ratio). Increase of the a/b ratio reflects the vasodilator action of NO that causes downward movement of the dicrotic notch in the diastolic limb of the digital pulse, thereby elevating the a/b ratio.

RESULTS

Application of whole-body, periodic acceleration was well tolerated in all participants, and all completed the 45-min treatment. The peak value of the a/b ratio markedly rose during periodic acceleration and returned to baseline during a 5-min recovery period in all healthy subjects and patients with inflammatory diseases.

CONCLUSIONS

Whole-body, periodic acceleration increased pulsatile shear stress to the endothelium leading to vasodilatation and a fall in the dicrotic notch, consistent with increased NO bioactivity in every healthy adult and adult patient with inflammatory disease so treated. Therefore, passive exercise using whole-body, periodic acceleration produces an important benefit that occurs with active exercise.

Optimisation of treatment by applying programmable rate-controlled drug delivery technology

A number of programmable rate-controlled drug delivery technologies have been developed during the last two decades with the aim of regulating the rate of drug delivery, sustaining the duration of therapeutic action and/or targeting the delivery of drug to a specific tissue. As a result, several therapeutically beneficial outcomes can be achieved, such as: (i) controlled delivery of a therapeutic dose at a desirable rate of delivery; (ii) maintenance of drug concentrations within an optimal therapeutic range for prolonged duration of treatment; (iii) maximisation of efficacy-dose relationship; (iv) reduction of adverse effects; (v) minimisation of the need for frequent dose intake; and (vi) enhancement of patient compliance. The treatment of illness can thus be optimised. To gain a better understanding of how to optimise the treatment of illnesses by applying programmable rate-controlled drug delivery technologies, this article reviews the scientific concepts and technical principles behind the development of various programmable rate-controlled drug delivery systems that have been marketed or are under active development. Finally, the roles of these technologies in optimising therapeutic outcomes in nine therapeutic areas are discussed.

Clinical pharmacokinetics of nitrates

The pharmacokinetics of organic nitrates are discussed with emphasis on the possible clinical relevance. For glyceryl trinitrate, the measurement of plasma concentrations is very difficult. Its pharmacokinetics are unusual, with a very rapid disappearance from plasma, and large intraindividual and interindividual variations. After oral administration, there seems to be a very extensive first-pass hepatic extraction and the plasma concentrations are often below the detection limit; after sublingual administration, glyceryl trinitrate appears in plasma. With transdermal glyceryl trinitrate controlled-release systems, plasma concentrations of glyceryl trinitrate can be maintained over 24 hours, although with fluctuations and important intraindividual and interindividual variability. After administration of glyceryl trinitrate via different routes, glyceryl dinitrates and mononitrates are present in plasma. The pharmacokinetics of isosorbide dinitrate are somewhat easier to understand. The substance disappears less rapidly from the plasma than does glyceryl trinitrate. After oral administration, there is also a hepatic first-pass extraction; the plasma concentrations can be prolonged by administering slow-release products. Sublingual administration leads to higher plasma concentrations than oral administration. Isosorbide dinitrate is metabolized in the organism to isosorbide 5-mononitrate and isosorbide 2-mononitrate, which both have vasodilator activity: after administration of isosorbide dinitrate, the mononitrates, and mainly the 5-mononitrate, reach very high concentrations in plasma. Isosorbide 5-mononitrate has been studied in its own right as an antianginal agent: it is completely absorbed after oral administration; it has a half-life of around 4 hours, and oral standard and controlled-release formulations have been extensively studied.(ABSTRACT TRUNCATED AT 250 WORDS)

Pharmacokinetics and haemodynamic effects of ISDN following different dosage forms and routes of administration

The pharmacokinetics and haemodynamic effects of isosorbide dinitrate (ISDN) have been investigated following administration of single doses as a sublingual (SL) spray (2.5 mg), sublingual tablet (5 mg) and peroral tablet (10 mg) in a randomised, placebo-controlled double-blind cross-over trial in 16 healthy volunteers. After the sublingual spray Cmax was higher (39.0 ng.ml-1) and tmax was shorter (3.9 min) than after the sublingual (22.8 ng.ml-1 and 13.8 min) and peroral (16.9 ng.ml-1 and 25.6 min) tablets. The AUC of ISDN did not differ following any of the three formulations (1031; 879; 997 ng.ml-1.min, for the spray, SL tablet and PO-tablet, respectively). Mononitrate metabolites of ISDN (IS-2-MN and IS-5-MN) and total nitrates in plasma increased in proportion to the administered dose. This indicates that the fraction of the dose absorbed was the same for all the formulations but that the extent of first-pass metabolism increased in the order sublingual spray < sublingual tablet < peroral tablet. Thus, compared to the spray, the relative bioavailability of ISDN was 48% and 28% from the sublingual and peroral tablets, respectively. The haemodynamic effects were quantified using the a/b ratio of the finger pulse wave and the systolic blood pressure and heart rate under orthostatic conditions.(ABSTRACT TRUNCATED AT 250 WORDS)

Comparison of the effects of two different galenical preparations of glyceryl trinitrate on pulmonary artery pressure and on the finger pulse curve

The time course and the magnitude of the effect of glyceryl trinitrate (GTN) on central venous (pulmonary artery diastolic pressure-PAPd) and peripheral arterial (a/b-ratio of the finger pulse wave) haemodynamics were compared in a randomized double-blind cross-over study in 12 patients suffering from congestive heart failure (NYHA II-III) with elevated PAPd at rest (> or = 15 mmHg). The data were obtained in a bioavailability study of two sprays of glyceryl trinitrate, which differed in their galenical characteristics and in the dose of GTN (0.4 mg vs. 0.8 mg). Following sublingual administration of each spray, PAPd, a/b-ratio and the plasma concentrations of GTN and its metabolites were measured up to 30 min. The relative bioavailability of GTN of the test preparation was estimated to be 157%, 161% and 147%, when calculated from the plasma concentration-time data or the integrated effect of GTN on a/b-ratio or PAPd, respectively. The mean time courses of the decrease in PAPd and the increase in the a/b-ratio of the finger pulse curve were mirror images. Thus, there was a strong correlation between the mean values of PAPd and a/b-ratio following the administration of glyceryl trinitrate. Since the slope of the relationship differed considerably between the patients, the magnitude of effect of GTN on PAPd in the individual patient could not be predicted from the changes in a/b-ratio.