Recent developments of collagen-based materials for medical applications and drug delivery systems

In this review, an attempt was made to summarize some of the recent developments in the application of collagen as a biomaterial and in drug delivery systems. The main applications covered include: collagen for burn/wound cover dressings; osteogenic and bone filling materials; antithrombogenic surfaces; and immobilization of therapeutic enzymes. Recently, collagen used as a carrier for drug delivery has attracted many researchers throughout the world. The use of collagen for various drug delivery systems has also been reviewed in this article. Collagen-based drug delivery systems include: injectable microspheres based on gelatin (degraded form of collagen); implantable collagen-synthetic polymer hydrogels; interpenetrating networks of collagen; and synthetic polymers collagen membranes for ophthalmic delivery. Recent efforts to use collagen-liposomal composites for controlled drug delivery, as well as collagen as controlling membranes for transdermal delivery, were also reviewed. In this review, the main emphasis was on the work done in our laboratory.     

Transdermal therapeutic methods

Percutaneous absorption has now been largely demonstrated and is defined as the passage of a molecule applied to the skin from the external environment to the blood. This phenomenon takes place in two main steps: penetration and actual absorption. Percutaneous absorption avoids the first-pass effect to which orally and rectally administered molecules are submitted, although these molecules can be metabolized in the skin, but to a much lesser degree that by hepatic metabolism. Transdermal devices present many advantage compared to forms administered by other routes: improved patient compliance, easy self-administration, prolonged plasma plateau levels. However, it depends on the skin type and, in the case of allergic reactions, other classical forms designed for the cutaneous route, such as ointments or gels. There are two types of transdermal device: so-called matricial forms, which are semi-solid or solid preparations in which the active ingredient(s) can be dispersed or dissolved; reservoir systems, in which one of the walls is a membrane, placed directly on the skin. In the case of the nitroglycerin, plasma curves are essentially identical regardless of the type of device used. The active ingredients currently available on the market in the form of transdermal devices are scopolamine, nitroglycerin, 17-beta-oestradiol, nicotine, and, for the future, forms containing fentanyl, timolol, ephedrine ... are currently being developed.     

Pharmacokinetics of testosterone in hypogonadal men after transdermal delivery: influence of dose

To assess the pharmacokinetics of testosterone after application of one, two, or three testosterone transdermal delivery systems to hypogonadal patients, 12 hypogonadal men (mean age 46.6 +/- 10.5 years) were enrolled in an open-label, randomized, crossover study. Each application period comprised 4 days: a 2-day washout period with no exogenous testosterone therapy followed by 2 days of therapy with one, two, or three transdermal systems applied daily to the patient's back. On day 4 of each period, serial blood samples were collected for determination of total and non-sex hormone binding globulin (non-SHBG) bound serum testosterone concentrations. Serum concentrations of testosterone were determined using validated radioimmunoassay methods. Residual testosterone analysis of used transdermal systems was used to estimate testosterone delivery through the skin. In general, serum concentrations of testosterone rose in accordance with an increase in dose. Using a strict bioequivalence approach to dose proportionality, the increases in area under the concentration-time curve (AUC) and morning concentrations were proportional to the increase in dose from two to three transdermal systems, but somewhat less than proportional with an increase from one to two transdermal systems. Results from the non-SHBG bound serum testosterone concentrations closely paralleled those of total serum testosterone. Use of three transdermal systems yielded serum concentrations of testosterone that tended to be above the upper limit of the normal range. The AUC and cumulative release of testosterone were linearly related to the number of applied systems. If necessary, the standard recommended dose of two testosterone transdermal delivery systems can be modified to accommodate interindividual differences in testosterone requirements of hypogonadal men.     

Nicotine delivery kinetics and abuse liability.

It is well established that nicotine meets all criteria of a highly addictive drug. However, as recognized by the US surgeon general, the nicotine delivery system itself is an important determinant of the toxic and addictive effects engendered by nicotine use. Therefore, altering the form of nicotine dosing may allow for selective therapeutic action in efforts to develop safer and less addictive nicotine replacement therapies. While it is the case that initial tobacco use often escalates to compulsive use accompanied by tolerance and physical dependence, this is not usually observed with nicotine replacement therapies. These observations are consistent with laboratory data indicating that (1) nicotine polacrilex and transdermal systems deliver nicotine more slowly and at lower dose levels than tobacco-based forms, and (2) human data suggesting that the abuse liability of these systems is substantially lower than that of the tobacco-based nicotine delivery system. Because the drug dosage form can be systematically manipulated and evaluated, further research in developing alternative nicotine delivery forms may hold substantial promise in the treatment of tobacco dependence. Psychological research methods can play an important part in their evaluation. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Squamoid eccrine ductal carcinoma

A wide range of drugs are capable of being administered as transdermal drug delivery systems (TDDS). Despite their advantages, these systems are known to have adverse effects. This report describes localised skin reactions with reference to a burn-like lesion on the shoulder of a patient caused by a testosterone TDDS. Patients should be advised of the potential adverse effects of these systems and also of suitable application sites, avoiding areas liable to prolonged pressure.     

Chitosan: a unique polysaccharide for drug delivery

The aim of this review is to give an insight into the many potential applications of chitosan as a pharmaceutical drug carrier. The first part of this review concerns the principal uses of chitosan as an excipient in oral formulations (particularly as a direct tableting agent) and as a vehicle for parenteral drug delivery devices. The use of chitosan to manufacture sustained-release systems deliverable by other routes (nasal, ophthalmic, transdermal, and implantable devices) is discussed in the second part.     

Mathematical modelling of the release of drug from porous, nonswelling transdermal drug-delivery devices

A general model is presented for the release of drug from porous nonswelling, transdermal drug-delivery devices and it is shown to reduce to previously proposed models in suitable limits. The processes which govern the release of drug are considered to be diffusion of dissolved drug and dissolution of dispersed drug, both in the body of the device and in the device pores, and transfer of drug between the two domains. In the classical limit of large dissolution rates, the problem reduces to one of the moving-boundary type, and solution of this problem in the case where the initial drug loading is much greater than the drug solubility in the device yields expressions for the flux of drug to a perfect sink (modelling in vitro conditions). It is shown that behaviour greatly differing from the classical first-order drug delivery (alpha t 1/2) may be exhibited, depending upon the parameter regime. In some situations the dissolution rates may not be so large and solutions of the general model are derived in the case where the dispersed drug is considered to be undepleted and the diffusivity in the solvent-filled pores is much larger than in the body of the delivery device. Numerical studies are undertaken, and the coupling of delivery device and skin-diffusion models (in order to model the complete transdermal drug-delivery process) is also considered.     

Selective serotonin-reuptake inhibitors in pregnancy and lactation

We explore the effects on the developing fetus and neonate of selective serotonin-reuptake inhibitors (SSRIs) during pregnancy and lactation, reviewing the relevant animal and human studies published in English from 1976 to the present. Medline was used to search the terms SSRI, fluoxetine, pregnancy, lactation, and teratogenesis. Animal studies were inconclusive: some found that fetal exposure to high doses of fluoxetine produced no congenital anomalies, while others linked the drug to abnormalities such as craniofacial malformations, alterations in serotonergic neurotransmitter systems, birth-related hematomas, and inhibition of the milk-ejection reflex. Human investigations indicated no relationship between in utero exposure to fluoxetine and teratogenic effects, although data are limited, and none have been collected regarding behavioral teratogenesis. However, we found a suggestion of an increased rate of miscarriage, an association with infants large for gestational age, one reported case of perinatal toxicity, and one case of an infant who was colicky while receiving breast milk from a mother taking fluoxetine. Based on these data, controlled prospective studies of exposure to SSRIs during pregnancy and lactation are needed, as is long-term evaluation for behavioral teratogenesis and enduring cognitive effects. Data are lacking on drug levels in breast milk and neonatal serum. Neonatal toxicity and the effect of SSRIs on labor and delivery, the mother-infant interaction, and lactation also merit further study. Clinically, a conservative approach is encouraged, minimizing the use of SSRIs in pregnancy, avoiding such drugs during the first trimester, tapering them prior to delivery, and discouraging breast-feeding during their use.     

Augmentation of transdermal drug penetration

Transdermal drug delivery is an alternative to conventional routes of administration. It is limited due to the low permeability of the skin. Iontophoresis (application of low intensity current) and electroporation (application of high voltage pulses) increase drug delivery by several orders of magnitude. The mechanisms and the parameters controlling drug transport as well as safety issues have been studied. New therapeutic applications for the delivery of drugs, peptides and nucleic acids, have been developed.     

Role of nitric oxide in the development of corticotropin-induced hypertension in sheep

Excipients are often used in transdermal formulations to overcome the formidable barrier offered by the epidermis in order to achieve the target flux. In this study we describe the use of frequency-domain fluorescence spectroscopy to characterize the effect of two commonly used excipients, propyleneglycol monolaurate (PGML) and oleic acid on stratum corneum and in a silicone-based transdermal delivery system. Fluorescence lifetime and limiting anisotropy for the probe 1,6-diphenyl-1,3,5-hexatriene in isolated human epidermis were measured as a function of formulation treatment. The drop in lifetime ranged from 0.5 to 2.3 ns, indicative of an increased dielectric constant of the lipophilic barrier exposed to all formulations. This increase is due to increased partitioning of the polar excipients from the delivery system into the stratum corneum. The limiting anisotropy showed a drop of 0.1 in the case of the epidermis exposed to oleic acid formulation and not the PGML formulations, indicative of the different modes of action for these two excipients. The fluorescence data suggested fluidization of the silicone matrix by both oleic acid and PGML. The dynamic fluorescence measurements described in this study are a powerful way to screen formulations while gaining valuable mechanistic insight into the mode of flux enhancement in transdermal formulations.     

An explanation for the variation of the sonophoretic transdermal transport enhancement from drug to drug

Over the last few decades, application of therapeutic ultrasound (frequency between 1 and 3 MHz and intensity between 1 and 2 W/cm2) has been attempted to enhance transdermal transport of several drugs, a method referred to as sonophoresis. The sonophoretic enhancement of transdermal drug transport was found to vary significantly from drug to drug. In certain cases, ultrasound did not induce any enhancement of transdermal drug transport. This variation in the efficacy of sonophoresis has raised a controversy regarding its applicability as a transdermal delivery enhancer. The objective of this paper is to provide a summary of the literature data on sonophoresis and an explanation for the observed variation of the sonophoretic enhancement from drug to drug. This paper also presents an equation to qualitatively predict whether therapeutic ultrasound may enhance transdermal transport of a given drug based on knowledge of the drug passive skin permeability and octanol-water partition coefficient.     

Nutritional care of the patient with HIV/AIDS

Confluence in technologic advances in medical electronics, the availability of new intravenous pharmaceuticals, increasing sophistication of home care delivery systems and the economic motivations imposed by Diagnosis-Related Groups and capitated care payment mechanisms stimulated dramatic developments in intravenous delivery technologies, both for the hospital and the outpatient environment. Success in the use of these sophisticated drug delivery systems, however, depends on appropriate patient selection, optimal selection of a delivery alternative and careful patient monitoring for both desired therapeutic response, health delivery quality and patient safety.     

Defects generated in human stratum corneum specimens by ultrasound

Over the last two decades, ultrasound (US) has been applied to enhance transdermal drug delivery. This method is called sonophoresis. The physical mechanism of the enhancement is far from being fully understood. It has been shown in our study that 168-kHz continuous US of spatially averaged pressure amplitude of 1.9 x 10(5) Pa induced a new structural state and generated defects (entrapped air pockets) in human stratum corneum specimens. The dimensions of the defects were found to be about 20 microns, large enough to allow the transdermal passage of high-molecular-weight drug molecules that normally elude the unenhanced transdermal drug delivery.     

Microfabricated microneedles: a novel approach to transdermal drug delivery

Although modern biotechnology has produced extremely sophisticated and potent drugs, many of these compounds cannot be effectively delivered using current drug delivery techniques (e.g., pills and injections). Transdermal delivery is an attractive alternative, but it is limited by the extremely low permeability of skin. Because the primary barrier to transport is located in the upper 10-15 micron of skin and nerves are found only in deeper tissue, we used a reactive ion etching microfabrication technique to make arrays of microneedles long enough to cross the permeability barrier but not so long that they stimulate nerves, thereby potentially causing no pain. These microneedle arrays could be easily inserted into skin without breaking and were shown to increase permeability of human skin in vitro to a model drug, calcein, by up to 4 orders of magnitude. Limited tests on human subjects indicated that microneedles were reported as painless. This paper describes the first published study on the use of microfabricated microneedles to enhance drug delivery across skin.     

Testosterone pharmacokinetics after application of an investigational transdermal system in hypogonadal men

This open-label, randomized, placebo lead-in, three-treatment crossover study in 19 hypogonadal men (27-82 years of age) evaluated dose proportionality of serum testosterone concentrations with application of one or two investigational transdermal testosterone systems for application to the arm or torso. Testosterone in vivo kinetics profiles were determined using DeMonS, a recently developed numerical deconvolution method that estimates drug absorption at different time intervals and/or drug disposition model parameters. After application of the investigational transdermal systems, the mean serum testosterone, dihydrotestosterone, estradiol, and free testosterone concentrations were elevated to normal levels. Treatment allowed approximation of the normal circadian pattern of endogenous testosterone secretion, and the increase in serum testosterone concentrations was proportional to the surface area of systems applied. The investigational transdermal system provided effective testosterone replacement therapy as judged by pharmacokinetic parameters.     

Oxygen concentration and asexual development of Eimeria tenella in cell cultures

Cardiovascular diseases are the leading causes of death in the United States, with hypertension being amongst the most prevalent of the cardiovascular risk factors. Improvement of hypertension management has, in consequence, received much attention. Extensive pre- and post-marketing experience with the transdermal formulation of clonidine marketed in the USA in the mid-1980s has now been accumulated. Transdermal clonidine is effective as monotherapy in mild-moderate hypertension, and in combination with diuretics, calcium antagonists and ACE inhibitors in more resistant cases. It controls blood pressure throughout the 24-h circadian cycle. It is effective and generally well-tolerated in adolescents, the elderly, blacks, diabetics, and subjects with chronic renal insufficiency. It has been used perioperatively and for suppression of adrenergic symptoms in subjects withdrawing from addicting substances. In comparison with oral clonidine, transdermal clonidine reduces the incidence and severity of such symptomatic side-effects as dry mouth, drowsiness, and sexual dysfunction. Minor skin reactions occur at the site of application of the transdermal patch with moderate frequency. Adherence to transdermal clonidine therapy is high, and patients commonly prefer it to oral therapy. Transdermal administration of clonidine is a useful therapeutic advance in the long-term management of hypertension.     

Theoretical models for drug delivery to solid tumors

The effectiveness of anti-cancer drug therapies is often limited by the difficulty of achieving drug delivery throughout solid tumors. Mathematical models permit an analysis of the factors leading to inadequate drug delivery to tumors and can suggest strategies for improving delivery. An overview is given of key factors that influence drug delivery and the extent to which they have been incorporated into existing theoretical models. These factors include spatial gradients of drug concentration and other variables within tumors and other parts of the body, and the relative magnitudes of the time scales involved in drug transport, tumor cell kinetics, and host toxicity. Models for both systemic and regional delivery methods are considered, including intravenous, intraarterial, intraperitoneal, intrathecal, and intratumoral delivery. Strategies for improving delivery are discussed, including use of two-step therapies, hyperthermia, liposome encapsulation, and magnetic targeting. Until now, modeling has mainly developed in separate subfields of tumor growth and cell kill kinetics, compartmental modeling of the body, spatially distributed models for single tissues, radiation dose calculations, tumor oxygenation, tumor blood flow, and cellular pharmacokinetics. In the future, models that integrate these subfields should be developed.     

Transdermal clonidine in the prophylaxis of episodic cluster headache: an open study

Transdermal clonidine has recently been reported to be efficacious in the prophylaxis of cluster headache. A 2-week course of transdermal clonidine (5 mg the first week, 7.5 mg the second week) preceded by a 5-day run-in period, was administered to 16 patients with episodic cluster headache in an active cluster period. In 5 patients, the painful attacks disappeared after the seventh day of treatment. For the group as a whole, no significant variations in headache frequency, pain intensity, or attack duration were observed between the run-in period and the first and second weeks of treatment (ANOVA). Further studies are necessary to clarify the effectiveness of transdermal clonidine in the prophylaxis of episodic cluster headache.     

Effectiveness of the elcatonin transdermal system for the treatment of osteoporosis and the effect of the combination of elcatonin and active vitamin D3 in rat

The efficacy of percutaneous elcatonin (EC), a hypocalcemic peptide, in the treatment of experimental osteoporosis in rats was evaluated in vivo. Additionally, the effect of the combined use of EC and active vitamin D3 (1,25(OH)2D3) for the treatment was compared with those of three other groups: 1,25(OH)2D3 alone, estradiol plus 1,25(OH)2D3, and a placebo, and low calcium diet (low Ca). The EC transdermal system and the EC plus 1,25(OH)2D3 system, applied to the rat abdominal skin 6 times for 48 h, significantly increased the ash weight and calcium content of the tibia in the rats, compared with those of placebo group (p < 0.05). The EC systems also slightly lowered the alkaline phosphatase activity in plasma of the morbid rats, without a difference in the plasma calcium content. These EC systems were superior to the 1,25(OH)2D3 system and the estradiol plus 1,25(OH)2D3 system in improving osteoporotic parameters. Thus, the EC systems were concluded to be an efficient drug delivery system for Paget's disease and osteoporosis.     

Rodent malaria prophylaxis by transdermal delivery of primaquine

The efficacy of a new transdermal delivery system of primaquine in order to obtain causal prophylaxis against sporozoite-induced Plasmodium yoelii infection was evaluated. A single administration of a 1.0 cm2 transdermal delivery system containing 5.0 mg of primaquine was able to protect 100% of treated mice. This result suggests that the transdermal route may be a very interesting approach for malaria prophylaxis and should encourage further studies in order to determine the absolute bioavailability of the drug as well as its dose-effect relationship.