In vitro and in vivo-release of nitroglycerin from a new transdermal therapeutic system

Feasibility of an Ambulance-Based Stroke Trial, and Safety of Glyceryl Trinitrate in Ultra-Acute Stroke

Background and Purpose—

The practicalities of doing ambulance-based trials where paramedics perform all aspects of a clinical trial involving patients with ultra-acute stroke have not been assessed.

Methods—

We performed a randomized controlled trial with screening, consent, randomization, and treatment performed by paramedics prior to hospitalization. Patients with probable ultra-acute stroke (<4 hours) and systolic blood pressure (SBP) >140 mm Hg were randomized to transdermal glyceryl trinitrate (GTN; 5 mg/24 hours) or none (blinding under gauze dressing) for 7 days with the first dose given by paramedics. The primary outcome was SBP at 2 hours.

Results—

Of a planned 80 patients, 41 (25 GTN, 16 no GTN) were enrolled >22 months with median age [interquartile range] 79 [16] years; men 22 (54%); SBP 168 [46]; final diagnosis: stroke 33 (80%) and transient ischemic attack 3 (7%). Time to randomization was 55 [75] minutes. After treatment with GTN versus no GTN, SBP at 2 hours was 153 [31] versus 174 [27] mm Hg, respectively, with difference −18 [30] mm Hg ( P =0.030). GTN improved functional outcome with a shift in the modified Rankin Scale by 1 [3] point ( P =0.040). The rates of death, 4 (16%) versus 6 (38%; P =0.15), and serious adverse events, 14 (56%) versus 10 (63%; P =0.75), did not differ between GTN and no GTN.

Conclusions—

Paramedics can successfully enroll patients with ultra-acute stroke into an ambulance-based trial. GTN reduces SBP at 2 hours and seems to be safe in ultra-acute stroke. A larger trial is needed to assess whether GTN improves functional outcome.

Clinical Trial Registration—

URL: http://www.controlled-trials.com/ISRCTN66434824/66434824 . Unique identifier: 66434824.

Interindividual variation in transdermal and oral drug deliveries

It is generally assumed that the topical absorption of drugs is subject to more interindividual variation than the oral absorption of drugs. To date, we are unaware of any clinical studies or meta-analyses that compare the interindividual variation of transdermal and oral drug deliveries for a large number of medications. In this research article, the absorption data for 10 medications that can be used as an oral medication or a transdermal patch were compiled, and from the collected data, the interindividual variance was calculated for topical and oral absorption as an overall average and by drug. This research article also briefly reviews the pharmacokinetics and pharmacodynamics of transdermal and oral drug absorption. Our results indicate that there is considerable interindividual variation in topical and oral absorption for the 10 medications investigated. Yet, surprisingly, the calculated overall mean and median coefficient of variation (CV) for topical and oral absorption were comparable (within 10% of each other). Therefore, the interindividual variation in topical and oral absorption may not be as divergent as assumed previously. In a drug-by-drug comparison, certain medications demonstrated considerably more variation when absorbed orally versus topically and vice versa. It is unclear why certain drugs had less variation in absorption when delivered topically versus orally (or vice versa). However, patterns in drug molecular weight (MW) or octanol partition coefficient (log K(OCT) ) could not totally explain these findings. In our analysis, the previously reported correlation between MW or log K(OCT) and interindividual variation in absorption could only be replicated when plotting the topical absorption CV and MW. What became clear from our analysis is that the drug itself is an important variable when considering which route of delivery (oral or topical) will provide the least amount of interindividual variation. Our study had many limitations because of study design, which may have affected our calculations and conclusions. Further experimentation is needed to support and reveal the basic science of skin or drug chemistry that can further explain these findings.

The Effect of Transdermal Glyceryl Trinitrate on 24 h Ambulatory Blood Pressure in Acute/Subacute Stroke

Background

High blood pressure is a common complication in acute stroke and is associated with a poor outcome.

Aims

This study assesses the effects of transdermal glyceryl trinitrate on 24 h ambulatory blood pressure in patients with recent stroke.

Methods

One hundred and seven patients with acute ischaemic or haemorrhagic stroke were included. The patients had been enrolled in one of two trials of transdermal glyceryl trinitrate (5 mg daily) or placebo/control, and underwent 24 h ambulatory blood pressure monitoring (56 glyceryl trinitrate, 51 control). Ambulatory blood pressure data were analysed using area under the curve for the entire 24 h, and day and night periods. Nocturnal dipping was defined as a decline in systolic blood pressure >10%. Comparisons of blood pressure between groups were performed by analysis of covariance (ANCOVA) with adjustments for trial and baseline measure.

Results

In comparison with control, glyceryl trinitrate significantly lowered 24 h blood pressure (systolic blood pressure/ diastolic blood pressure 9·4/4·8 mmHg, P < 0·001/0·001, n = 104), daytime blood pressure (8·7/4·2, P < 0·001/ < 0·001, n = 103) and night-time blood pressure (6·9/1·7, P = 0·008/0·458, n = 86). Only 86 patients (glyceryl trinitrate 45, placebo/control 41) had sufficient night blood pressure measurements to assign dipping status; 28 were dippers (12 glyceryl trinitrate, 16 control) and 58 were nondippers (33 glyceryl trinitrate, 25 control); glyceryl trinitrate significantly lowered systolic but not diastolic blood pressure in both dippers and nondippers. Treatment with glyceryl trinitrate increased the daytime heart rate (4·8 beats/min) but not the night-time heart rate. Patients whose blood pressure did not dip at night had a worse functional outcome at three-months.

Conclusions

Transdermal glyceryl trinitrate (5 mg) significantly lowered 24 h blood pressure by 9/5 mmHg (equivalent to a 6% reduction) in both dipping and nondipping patients with acute/subacute stroke. This reduction in blood pressure is clinically relevant and is unlikely to be excessive.

Transdermal drug pharmacokinetics in man: Interindividual variability and partial prediction

A database of human dermatopharmacokinetic parameters of 12 transdermal patches is established. The effect of system design, application site, and metabolism on pharmacokinetic data is discussed, and interindividual variability of data and its possible sources evaluated. Using multiple regression analysis, two equations based on drugs physicochemical characteristics are suggested for partial prediction of peak plasma concentration (C(max)) after patch application. Patch application presumably decreases variance as rub-off, wash and exfoliation steps are diminished. The results showed that interindividual variation, in terms of coefficient of variation (CV) of C(max), is inversely correlated with drugs molecular weight and lipophilicity in the range of 200<MW<400 and 1.6<logK(oct)<4.3. Multiple regression analysis of C(max) against physichochemical parameters demonstrated the prominent contribution of hydrogen bonding acceptability of the molecules on their maximal plasma concentration after patch administration. The findings suggest that the serum concentration profile for transdermal therapeutic systems (TTS) is a net result of the system performance, drug absorption and elimination. Thus, the variability in serum concentration is a function of variability of each process involved. This should be noted in explanation of effect of molecular features of drugs on their plasma concentration profile.

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.

Pharmacodynamic and pharmacokinetic evaluation of a new transdermal delivery system with a time-dependent release of glyceryl trinitrate

The pharmacokinetics of glyceryl trinitrate (GTN) and its main metabolites as well as the hemodynamic effects of a new transdermal delivery system (TDS) were investigated in ten healthy male volunteers using a single blind, placebo-controlled study design with an application period of active drug of 4 successive days. The adhesive-type matrix system contains 20-mg GTN and released about 75% in a time-dependent manner. The plasma concentrations of GTN and its metabolites 1-2- and 1-3 glyceryl dinitrate reflected the time-dependent release with higher plasma concentrations during the first 12 hours than during the second 12 hours. Continuous administration of the TDS, which released 15 mg GTN/day, caused an accumulation of GTN in the plasma (about 70% greater AUC at the fourth day in comparison with the first day). The total effect per dose on the a/b-ratio of the digital pulse (height of the peak of the systolic wave divided by height of the peak of the dicrotic wave) and the reflex tachycardia were diminished by about 50% and 37%, respectively, at the fourth treatment day. The effect on systolic blood pressure measured under orthostatic conditions was blunted already 8 hours after the first application. The effect of sublingually administered GTN on digital pulse was attenuated during administration and also 1 hour after removal of the last TDS. The effect was restored 8 to 12 hours after removal of the TDS. Thus, the discontinuous release of GTN from the new system does not prevent the decline of hemodynamic efficacy during continuous therapy.

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

The haemodynamic effects and plasma concentrations of glyceryl trinitrate (GTN) and its dinitrate metabolites were investigated in 8 healthy male volunteers during 5 days of application of a new transdermal delivery system (TDS) with time-dependent release characteristics, which were considered to prevent or to diminish development of nitrate tolerance. On the first and fifth day of administration the following haemodynamic parameters were determined: digital pulse ratio of height of systolic peak to height of dicrotic wave (i.e. a/b-ratio), heart rate and systolic blood pressure under orthostatic conditions. Peak plasma concentrations of GTN were 139 and 155 pg.ml-1 on the first and fifth day of treatment, and the corresponding trough concentrations (i.e. 24 h after administration) were 52.5 and 36.6 pg.ml-1, respectively. Compared to placebo, the area under the effect curve of the a/b-ratio of the digital pulse was increased on the first (25.6%) and fifth day (13%). A significant increase of heart rate and a decrease of systolic blood pressure were seen only on the first day of treatment. The haemodynamic effects of sublingual GTN 0.8 mg were reduced by 69% (a/b-ratio) and 52% (standing heart rate) on the fifth day compared to the pretreatment values. Thus, the phasic release of GTN from the new TDS can be demonstrated by the time course of the plasma concentrations of GTN and its metabolites. Nevertheless, following repeated administration the hemodynamic effects are blunted.

New developments in drug delivery systems

The rate-controlled drug delivery systems outlined above have been steadily introduced into the biomedical community since the middle of the 1970s. It is the author's belief that many more of the conventional drug delivery systems which we have been using for many decades will be gradually replaced, in coming years, by these high-tech-based rate-controlled drug delivery systems.

Swelling of PHEMA based membranes in ethanol and their nitroglycerin permeabilities

The aim of this study is to prepare PHEMA based polymeric membranes for a transdermal delivery system, which includes a skin permeation enhancer (i.e. ethanol) for nitroglycerin. Membranes were prepared by bulk polymerization of HEMA monomer. Polymerization was achieved in the presence of EGDMA, as the cross-linker, and AIBN as the initiator. MMA was used as a comonomer to improve the mechanical properties and to adjust the permeabilities of the resulting membranes. Water was also included in the polymerization mixture to control the matrix structure. Membranes with different chemical and physical structures were prepared. Swelling behaviour of these matrices in ethanol were observed. Nitroglycerin diffusion through swollen membranes (in ethanol) were investigated. It was obtained that the relative amounts of ingredients (i.e., HEMA, MMA, EGDMA and water) in the casting solutions affect both the equilibrium swelling values and the permeabilities. By increasing the water content and by decreasing the amounts of MMA and EGDMA both parameters can be increased. AIBN does not affect these parameters significantly.

Transdermal delivery of narcotic analgesics: comparative permeabilities of narcotic analgesics through human cadaver skin

Relationships between the in vitro permeation rates of select narcotic analgesics through human skin and their physicochemical properties were investigated by following the permeation kinetics of six representative compounds in small diffusion cells. The relative permeability coefficients of three phenylpiperidine analogues, meperidine, fentanyl, and sufentanil, all measured on a single piece of skin, were 3.7 x 10(-3), 5.6 x 10(-3), and 1.2 x 10(-2) cm/hr, respectively. Using membranes from the same skin section, the permeability coefficients of three opioid alkaloids, morphine, codeine, and hydromorphone, were considerably lower, at 9.3 x 10(-6), 4.9 x 10(-5), and 1.4 x 10(-5) cm/hr, respectively. The high permeability coefficients of the former compounds are due to their highly lipophilic nature as reflected in high octanol/water partition coefficients and low solubility parameters. Generally, the permeability coefficients of the narcotics increase as the lipophilicity increases. When viewed in literature perspective, the data suggest that aqueous tissue control of transport is approached in the case of the phenylpiperidine analogues, all of which have Koctanol/water values greater than 40. Permeability coefficients of fentanyl and sufentanil were also determined as a function of pH over the pH range 7.4 to 9.4, in this instance with membranes prepared from additional samples of skin. The permeability coefficients of each drug varied less than threefold over the pH range, a behavior consistent with the highly hydrophobic natures of the compounds. The low permeability coefficients of morphine, codeine, and hydromorphone coupled with their low potencies make these drugs poor transdermal candidates. It appears that fentanyl and sufentanil can be successfully transdermally delivered.

Comparative clinical trial of the tolerability, patient acceptability and efficacy of two transdermal glyceryl trinitrate patches ('Deponit' 5 and 'Transiderm-Nitro' 5) in patients with angina pectoris

A randomized two-period crossover trial was carried out to compare the efficacy, tolerability and patient acceptability of two transdermal ('patch') formulations of glyceryl trinitrate. 'Deponit' 5 and 'Transiderm-Nitro' 5, both designed to deliver 5 mg glyceryl trinitrate in 24 hours. All patients were treated for 4 weeks with each of the formulations, changed once per day. Forty-seven patients entered the trial and all completed both phases of treatment. Both drugs resulted in highly significant mean reductions in angina attack frequency, the reduction being significantly greater with 'Deponit'. Similarly, mean sublingual glyceryl trinitrate consumption was also reduced; again, the greater reduction with 'Deponit' was significant. In terms of effectiveness, 'Deponit' was preferred to 'Transiderm-Nitro' by 19 patients, whilst only 5 patients preferred 'Transiderm-Nitro' (p less than 0.01). In terms of ease of application, comfort, appearance and adhesion (assessed in relation to daytime, night-time, washing, bathing and exercising), there were no appreciable or significant differences between patients' assessments of the two forms. Neither treatment had any appreciable effect on heart rate or blood pressure. Both formulations were very well tolerated, with very few reported side-effects.

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.

Transdermal drug delivery and cutaneous metabolism

The delivery of drugs via the skin to achieve systemic therapeutic effect is currently under intense investigation. The skin offers unique advantages and limitations for drug input into the body. For example, while hepatic first pass may be circumvented, the excellent barrier function of the stratum corneum (the thin outermost layer of skin) precludes, at present, all but the most potent drugs from this route of administration. Examples of approved transdermally delivered drugs are scopolamine, nitroglycerin, clonidine and estradiol. The delivery systems which have been formulated for these agents have been designed to provide essentially zero-order input kinetics for between 1 and 7 days. The impact of cutaneous metabolism on transdermal drug delivery has not yet been evaluated rigorously. Limited in vivo data for nitroglycerin suggest a cutaneous first pass effect of between 10 and 20%. More work has been directed towards the use of topical prodrugs and the design of molecules better able to transport across the stratum corneum and then undergo local enzymatic activation. Further research in this area will require a more specific quantitative understanding of the metabolic capabilities of human skin in vivo.

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.

The bioavailability of dermatological and other topically administered drugs

The literature addressing determination of the bioavailability of dermatological and other topically administered drugs has been reviewed. The various methods employed, their advantages and drawbacks, have been identified and evaluated. The state of the art and the success of topical bioavailability assessment are discussed in the light of the information presented. It is concluded that, although current methodology ensures the responsible use of topical medicaments, the techniques are, on the whole, quantitatively inadequate. A number of recommendations are proposed as possible improvements to the approaches now undertaken, and specific measurements for drugs in different therapeutic categories are suggested. The ultimate objective of this survey is to catalyze the establishment of straightforward, objective, quantitative, and reproducible methods to evaluate topical bioavailability and to reduce significantly, thereby, the incidence of bioinequivalence and pharmacological inactivity observed following drug dosing to the skin.