Transdermal Absorption: A Unique Opportunity por Constant Delivery of Nitroglycerin

Comparative bioavailability of metoprolol tartrate after oral and transdermal administration in healthy male volunteers

BACKGROUND AND OBJECTIVE

Transdermal drug delivery systems (TDDSs) of metoprolol tartrate have been previously prepared and evaluated in vitro and in vivo in an animal model. This study compares the bioavailability of metoprolol tartrate from a TDDS with that from a conventional marketed tablet in healthy human volunteers.

METHODS

This was an open-label, balanced randomised, two-treatment, two-period crossover study with a washout period of 1 week. Volunteers were randomised (by means of a SAS software-generated randomisation schedule) to have a TDDS applied to their chest for 48 hours or to receive a 100 mg conventional marketed tablet of metoprolol tartrate in period I. In period II, the volunteers received the other dosage form. Blood samples were collected through an indwelling cannula placed in the forearm vein of each subject. Metoprolol tartrate concentrations were quantified in plasma samples by a validated high-performance liquid chromatography method.

RESULTS

A 3-fold improvement in bioavailability was observed with the TDDS form over oral therapy as shown by the extent of absorption indicated by the mean area under the concentration-time curve from time zero to time t values for tablets (451.98 ng x h/mL) and TDDS (1552.66 ng x h/mL). Although the maximum plasma concentration was higher for the tablet form than the TDDS (77.67 +/- 23.33 vs 51.16 +/- 16.61 ng/mL), the variable absorption profile, which is a characteristic feature of oral therapy, was quite evident. Plasma metoprolol tartrate concentrations plummeted to therapeutically ineffective concentrations as early as 8 hours following oral administration.

CONCLUSION

The TDDS developed in our laboratory produced therapeutically effective plasma concentrations for up to 48 hours, with a minimum of 26.09 ng/mL and a maximum of 76.70 ng/mL, which is in good agreement with the therapeutic range (20-100 ng/mL) of metoprolol tartrate. It could be concluded that the TDDS meets the intended goal of 2-day management of hypertension with application of a single patch, obviating the inconvenience of frequent administration and thus improving patient compliance.

Improved efficacy and tolerability of retinoic acid in acne vulgaris: a new topical formulation with cyclodextrin complex psi

OBJECTIVES

Retinoic acid (RA) has long been used, both topically and systemically, for disorders of keratinization, acne and related disorders. In the present study, the efficacy and tolerability of topical RA prepared as a cyclodextrin beta complex (beta-CD) is investigated in 66 acne vulgaris patients.

METHODS

This randomized, double-blind, placebo-controlled study compares nightly topical application of RA/beta-CD complex hydrogel formulation (0.025%), RA/beta-CD complex in moisturizing base (0.025%), hydrogel base, moisturizer base or a commercial RA gel (0.05%) in acne vulgaris patients. Improvement of acne was assessed using a 5-point improvement scale and by measuring sebum and moisture content of the skin using an SM 810 sebumeter/corneometer.

RESULTS

After 3 months of treatment, mean scores of acne improvement on the 5-point scale were 4 with the RA/beta-CD complex hydrogel formulation, 4.1 with the RA/beta-CD complex in moisturizing base, 1.2 with hydrogel placebo base, 1.1 with moisturizer placebo base and 3 with the commercial RA product. All patients treated with the commercial product experienced local side-effects. One patient discontinued due to severe irritation. None of the patients treated with the RA/beta-CD complex in the moisturizing base and hydrogel formulation experienced significant local irritation, although the sebum content of the skin decreased after application of the RA/beta-CD preparations. This change was not significant compared to controls. The moisture content of the skin was better preserved in the group treated with the RA/beta-CD complex in the moisturizing base.

CONCLUSION

The topical RA/beta-CD complex, in hydrogel and moisturizing base, was more effective than the twice concentrated commercial RA product. There were few topical side-effects with this new formulation, which increases patient compliance. Topical RA/beta-CD (0.025% RA) did not significantly reduce sebum secretion but may help to preserve optimum epidermal moisture content with the proper base formulation. This is the first study in the literature reporting efficacy and tolerability of the topical RA/beta-CD complex in acne vulgaris. We conclude that the topical RA/beta-CD complex displays an improved efficacy and tolerability profile and is an effective treatment alternative for acne vulgaris.

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.

Effect of antioxidants and anti-irritants on the stability, skin irritation and penetration capacity of captopril gel

The effects of antioxidants and chelating agent on the stability of captopril in aqueous and semisolid were determined in this study. Then the influence of the combination of additives including antioxidants, anti-irritants and penetration enhancer on stability, skin irritation and penetration capacity of captopril in semisolid dosage form was investigated. In the stability study, the degradation of captopril followed the first-order kinetic. The chelating agent EDTA showed a potent stability effect and obviously increased the shelf-life up to 14-fold that of control gel. The anti-irritants such as clobetasol and diphenhydramine had potent inhibition irritation activity and the effect was not retarded by the addition of EDTA. Moreover, the captopril gel containing penetration enhancer, anti-irritants and chelating agent had a higher penetration capacity and the minimum therapeutic concentration could be obtained by applying about 13.24 cm(2) of administered area, indicating that the formulation can possibly be developed for a transdermal drug delivery system.

Open questions on bioequivalence: some problems and some solutions

This paper focuses on some specific situations where bioequivalence requires careful attention and tailored protocols in order to overcome intrinsic difficulties either marginally covered or fully neglected by operating guidelines. Some problems congregate with serious difficulties, namely high variability, very poorly absorbed drugs and endogenous substances with their own baseline. With endogenous substances, the dilemma faced is whether to subtract baseline from post-dose values in assessing bioequivalence. Either approach has intrinsic problems and is somewhat puzzling. In an attempt to resolve other existing problems, the most appropriate approach should be selected on a case-by-case basis, ensuring that the adopted procedure does not conflict with operating guidelines and scientific literature on the matter. Problematic cases include the management of trials with a predominant active metabolite, the absence of a reliable analytical bioassay, the availability of various strengths of the same drug on the market, a wide acceptability titre range, the management of studies on topical drugs that are devoid of systemic activity, the management of drugs that cannot be given for ethical reasons to healthy subjects or that may cause adverse events, especially when a steady state design is required. The parallel group study design appears to be more appropriate than the cross-over or the individual bioequivalence design in assessing drugs with a long half-life. Some pharmacokinetic and statistical analysis-related issues are also discussed such as the sequence/period interaction sometimes encountered in these trials, which, in the absence of the carry-over effect, does not bias the bioequivalence results and the need to process data with non-compartmental pharmacokinetic analysis.

Development of a new silicon-based transdermal system. I. Study of silicone elastomers and effect of liquid ingredients

The polarities of four elastomers made of silicon oligomers of different viscosities were investigated by measuring the uptake of swelled solvent in different polarity solvents after 24, 48, and 72 hr of treatment. The solvent uptake provides a good characterization for the polarity of the inside of the matrix. On the basis of the results the oligomers were divided into two groups. The same method has been used for the investigation of the change of the inner polarity of samples containing various amounts of polar and apolar liquid ingredients. It was shown that the polarity of the inside of the matrix is related to the swelling properties. The ingredients used changed the matrix framework, which was also influenced by the type of oligomers. The solvent uptake shows large dependence on the timing of the measurement. Measurements carried out after 48 hr of polymer production showed constant solvent uptakes, indicating that the final structure of the polymer was formed.

Injectable microcapsules prepared with biodegradable poly(alpha-hydroxy) acids for prolonged release of drugs

In this paper, microencapsulation techniques for the preparation of drug-containing monolithic microcapsules for prolonged release using biodegradable poly(alpha-hydroxy) acids, such as polylactic acid, poly(lactide-co-glycolide) and copoly(lactic/glycolic) acid are reviewed. Phase separation, solvent evaporation, and spray drying procedures are discussed. In order to achieve controlled-release formulations of highly water-soluble drugs that are entrapped efficiently, various manufacturing techniques and procedures have been developed. Degradation of poly(alpha-hydroxy) acids is altered by the copolymer ratio and molecular weight of the polymer used to make microcapsules and the amounts of released microencapsulated drugs correlate almost linearly with polymer degradation, indicating that controlled-release formulations, which release drugs over different times, can be prepared using suitable poly(alpha-hydroxy) acids with different degradation rates.

Preparation of thermo-responsive membranes. II

Two types of liquid crystal (LC)-immobilized membranes were prepared by a soaking method and sandwich method to control the permeation of indomethacin, as a model drug, in response to local and systemic fever. Monooxyethylene trimethylolpropane tristearate (MTTS) was used as a model LC because it has a gel-liquid crystal phase transition temperature near the body temperature, 39-40 degrees C in phosphate buffered saline (pH 7.4). Two porous polypropylene (PP) membranes were soaked into 20% MTTS chloroform solution in the soaking method, and two PP membranes were poured with the melted MTTS and pressed in the sandwich method. Thermo-response efficacy of the soaked membrane was dependent upon the content of MTTS in MTTS membrane, and the MTTS content above the void volume of PP membrane (38%) was needed for high efficacy. On the other hand, the sandwich membrane exhibited higher thermo-response efficacy than the soaked membrane, because more LC was embedded in the pores of sandwich membrane than that of the soaked membrane. The sandwich membrane permeation of indomethacin was sharply controlled by temperature changes between 32 and 38 degrees C.

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.

Rate and extent of absorption of clonidine from a transdermal therapeutic system

The in-vivo performance of a clonidine transdermal therapeutic system (TTS 3.5 cm2, 2.5 mg) was assessed in 12 healthy normal volunteers. Particular attention was paid to the rate and extent of absorption of clonidine from the TTS dosage form by reference to a 2 h i.v. infusion of clonidine. The absolute bioavailability of clonidine from the TTS dosage form was found to be approximately 60% with clonidine being released from the TTS at a relatively reproducible and consistent rate of 4.32 micrograms h-1 over a 7-day period.

Antianginal effects of intravenous nitroglycerin over 24 hours

To determine the constancy of hemodynamic and antianginal effects of the constant infusion of intravenous nitroglycerin (NTG) and their relationship to infusion rate and plasma NTG concentration, we administered maximal tolerated doses of intravenous NTG (range 10 to 120 micrograms/min, mean = 52 +/- 33 micrograms/min) and placebo to 10 patients with chronic stable angina for 25 hr each in a randomized, double-blind fashion. Sublingual NTG (0.4 mg) was given at 24.5 hr of infusion as a positive control. Bicycle exercise time (NIH protocol), blood pressure, heart rate, exercise ST response, and venous plasma NTG were determined before and at 1, 4, 8, 24, and 24.5 hr. Plasma NTG was linearly related to infusion rate, reached a steady state within 15 min and was unchanged over 24 hr (mean = 5.5 +/- 1.2 ng/ml). Mean plasma NTG clearance was 9.3 liters/min. However, during dose titration, patients demonstrated different relationships between plasma NTG and hemodynamic effects, with widely varying slopes and intercepts. Intravenous NTG produced a sustained reduction in blood pressure and a rise in heart rate at rest, and a reduction in blood pressure during submaximal exercise at as late as 24 hr, associated with reduced submaximal ST segment abnormality. In contrast, exercise tolerance to onset of angina showed a marked initial increase on intravenous NTG but fell progressively and did not differ from that with placebo at 24 hr. Increased exercise tolerance was associated with an increase in maximal heart rate and double product (heart rate X blood pressure), suggesting that direct coronary vasodilation and/or reduced left ventricular volume were the principal determinants of increased exercise tolerance.(ABSTRACT TRUNCATED AT 250 WORDS)

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.

Pharmaceutical considerations of transdermal nitroglycerin delivery: the various approaches

When formulated as a sublingual or an oral sustained-release dosage form, nitroglycerin has certain shortcomings, i.e., decreased duration of antianginal action and extensive hepatic first-pass elimination, which limit its efficacy. The finding that administration of nitroglycerin in the form of topical ointment decreases the extent of hepatic first-pass elimination and increases the duration of therapeutic activity has pointed the way to the possibility of developing a more effective transdermal drug delivery device. Three such devices are the Nitrodisc , Nitro-Dur, and Transderm -Nitro systems. All three systems generate effective plasma drug levels within 30 minutes and maintain steady-state drug plasma levels as follows: the 16 cm2 Nitrodisc at 280.6 +/- 18.7 pg/ml for 32 hours; the 20 cm2 Nitro-Dur at 201.4 +/- 60.7 pg/ml for 24 hours; and the 20 cm2 Transderm -Nitro system at 209.8 +/- 22.8 pg/ml for 24 hours. In vitro studies show that the drug penetrates the skin with zero-order kinetics in all three systems, the rate for Nitrodisc being 20% greater than that of the other systems. When the daily nitroglycerin dose is calculated in terms of skin permeation rate and the device's surface area, the three transdermal systems become clinically interchangeable.