Transdermal delivery of theophylline to premature infants using a hydrogel disc system

Serum theophylline after multiple dosing with transdermal gels in cats

OBJECTIVES

Our objectives were, first, to determine if therapeutic serum theophylline concentrations could be achieved using long-term, once-daily dosing of transdermal theophylline and, secondarily, to evaluate the difference between two transdermal theophylline formulations.

METHODS

Seven healthy cats, 1-10 years of age, were evaluated in a two-way, randomized, double-blinded, crossover study. Participants received transdermal theophylline at 15 mg/kg for 21 days in either pluronic lecithin organogel (PLO) or Lipoderm formulation. On day 22, blood was collected 2, 6, 14 and 24 h after dosing. After a 14 day washout period, blood was collected to verify non-detectible theophylline concentrations. The alternate formulation was administered for 21 days, and sampling was repeated. Serum theophylline concentrations were determined using an automated immunoassay. Serum concentrations were compared between formulations using a two-way random-measures ANOVA and over time within a formulation using a repeated-measures ANOVA.

RESULTS

Therapeutic serum theophylline concentrations were achieved for 2/7 cats in each group. Of 56 serum theophylline measurements obtained, only seven (13%) were within the therapeutic range. No significant difference was detected in drug concentrations achieved by the transdermal formulations at any time point. In addition, no significant difference in serum theophylline concentrations was noted between time points for PLO ( P = 0.751) or Lipoderm ( P = 0.107).

CONCLUSIONS AND RELEVANCE

Once-daily transdermal dosing of theophylline does not reliably achieve therapeutic concentrations. Individual cats may achieve therapeutic concentrations. No significant difference was noted between PLO and Lipoderm formulations. Therefore, transdermal theophylline formulations should not be considered as a first-line therapy in feline asthma patients.

Pharmacology related to paediatric anaesthesia

A child is not a mini adult. They differ from adults in terms of weight, shape, anatomical size and major body systems such as cardiovascular and respiratory as well as psychologically. Each organ system is immature in paediatric age group and their growth and development can dramatically affect the pharmacokinetics of different drugs. Children differ in every way from an adult thus mandating to have a basic knowledge of the pharmacokinetic and pharmacodynamic principles in paediatric population to prevent under dosing or toxicity of drugs. This review article aims to simplify the basic principles of pharmacokinetics and pharmacodynamics in paediatric population. It also highlights physiological and pharmacological differences between adults and paediatric age. We performed a PUBMED search for English language articles using keywords including pharmacology, child, paediatric anaesthesia. We also hand searched references from relevant review articles and text book chapters. We have also discussed drug interaction in anaesthesia, pharmacology pertaining to neuromuscular junction and effects of anaesthesia over the developing brain.

Potential of iontophoresis as a drug delivery method for midazolam in pediatrics

Drug delivery to the neonatal and premature pediatric populations is very challenging. This research assessed the potential of delivering midazolam by transdermal iontophoresis as an alternative strategy in pediatric therapy. In vitro experiments used intact and tape-stripped porcine skin as models for the skin barrier function of full-term and premature newborns, respectively. Midazolam transdermal transport was significantly enhanced by applying higher currents, increasing the formulation pH, and optimizing the drug's mole fraction in the vehicle. When the skin barrier was decreased to half of its baseline competence, the passive permeation of midazolam increased by approximately 60-fold; and complete stratum corneum removal led to an additional 20-fold enhancement in permeation. Iontophoresis retained control of the drug transport trough partially compromised skin. However, a very high passive contribution undermined the iontophoretic control when the barrier was fully compromised. Overall, midazolam delivery could be rate-controlled by iontophoresis in most circumstances, and therapeutically useful fluxes could be achieved.

Effective use of transdermal drug delivery in children

Transdermal administration offers a non-invasive and convenient method for paediatric drug delivery. The competent skin barrier function in term infants and older children limits both water loss and the percutaneous entry of chemicals including drugs; but the smaller doses required by children eases the attainment of therapeutic concentrations. Transdermal patches used in paediatrics include fentanyl, buprenorphine, clonidine, scopolamine, methylphenidate, oestrogens, nicotine and tulobuterol. Some patches have paediatric labelling supported by clinical trials whereas others are used unlicensed. Innovative drug delivery methods, such as microneedles and sonophoresis are being tested for their safety and efficacy; needleless injectors are primarily used to administer growth hormone; and two iontophoretic devices were approved for paediatrics. In contrast, the immature and rapidly evolving skin barrier function in premature neonates represents a significant formulation challenge. Unfortunately, this population group suffers from an absence of approved transdermal formulations, a shortcoming exacerbated by the significant risk of excessive drug exposure via the incompletely formed skin barrier.

Glucose monitoring in neonates: need for accurate and non-invasive methods

Neonatal hypoglycaemia can lead to devastating consequences. Thus, constant, accurate and safe glucose monitoring is imperative in neonatal care. However, point-of-care (POC) devices for glucose testing currently used for neonates were originally designed for adults and do not address issues specific to neonates. This review will address currently available monitoring options and describe new methodologies for non-invasive glucose monitoring in newborns.

Performance of transdermal therapeutic systems: Effects of biological factors

Transdermal drug delivery (TDD) is a technique that is used to deliver a drug into the systemic circulation across the skin. This mechanism of drug delivery route has many advantages, including steady drug plasma concentrations, improved patient compliance, elimination of hepatic first pass, and degradation in the gastrointestinal tract. Over the last 30 years, many transdermal products have been launched in the market. Despite the inherent advantages of TDD and the growing list of transdermal products, one of the major drawbacks to TDD is the occurrence of inter- and intraindividual variation in the absorption of the drug across the skin. A majority of these variations are caused by biological factors, such as gender, age, ethnicity, and skin hydration and metabolism. These factors affect the integrity and the barrier qualities of the skin, which subsequently result in the variation in the amount of drug absorbed. The main objective of this review article is to provide a concise commentary on the biological factors that contribute to the variation in transdermal permeation of drugs across human skin and the available transdermal therapeutic systems that may reduce the variations caused by biological factors.

Factors and Mechanisms for Pharmacokinetic Differences between Pediatric Population and Adults

Many physiologic differences between children and adults may result in age-related changes in pharmacokinetics and pharmacodynamics. Factors such as gastric pH and emptying time, intestinal transit time, immaturity of secretion and activity of bile and pancreatic fluid among other factors determine the oral bioavailability of pediatric and adult populations. Anatomical, physiological and biochemical characteristics in children also affect the bioavailability of other routes of administration. Key factors explaining differences in drug distribution between the pediatric population and adults are membrane permeability, plasma protein binding and total body water. As far as drug metabolism is concerned, important differences have been found in the pediatric population compared with adults both for phase I and phase II metabolic enzymes. Immaturity of glomerular filtration, renal tubular secretion and tubular reabsorption at birth and their maturation determine the different excretion of drugs in the pediatric population compared to adults.

Development of an in vitro model for premature neonatal skin: Biophysical characterization using transepidermal water loss

The objective was to develop an in vitro model for the developing skin of the premature neonate. Barriers of different levels of efficiency were produced by differentially tape-stripping the stratum corneum (SC) from the skin of excised porcine ears, and were characterized by measurements of transepidermal water loss (TEWL). In this way, it was possible to express the recorded TEWL as a function of percentage SC thickness (F) generating the following relationship: TEWL = 2.7 + 41.exp [- 0.028.F]. These data were then compared to previously published in vivo measurements of TEWL obtained from a population of premature neonates at various post-conceptional ages (PCA). The latter conformed to a remarkably parallel relationship to that found in vitro with the porcine skin model, namely TEWL = 3.3 + 41.exp [-0.026.(PCA-160)]. It can be suggested, therefore, that the empirically adjusted PCA (i.e., PCA-160) correlates closely with the developing thickness of the neonate's SC. The corollary is that porcine skin, in vitro, tape-stripped to a particular level, can provide a barrier corresponding to a specific degree of neonate maturation and can serve, hence, as a useful tool with which to explore whether transdermal drug delivery in this unique patient population may be beneficial.

Transdermal Xenobiotics in Newborn Skin

Newborn infants are regularly exposed to a wide variety of topical agents, including treatments for rashes, antimicrobial agents, solvents, and skin barriers or moisturizers. Premature and hospitalized infants are also exposed to topical iodine for antisepsis and to topical analgesic agents. The fact that most of these agents have not been specifically evaluated for use in infants has recently been recognized as a major public health concern. The epidermis of preterm infants is not fully developed, constituting an incomplete barrier to systemic absorption of topical agents. Thus, substances applied to the skin can have adverse systemic effects. Povidone-iodine and steroid creams have been associated with thyroid and hypothalamic-pituitary axis suppression, respectively, in premature infants. Application of topical EMLA (Eutectic Mixture of Local Anesthetics) for analgesia has been implicated in methemoglobinemia in premature infants. Exposure to natural latex in gloves and medical equipment may sensitize infants, leading to the development of airway hyperreactivity and other allergic manifestations. Therefore, it is advisable to limit skin exposure of premature infants to xenobiotics. Further work is required to define safe doses of common agents. In addition, transdermal administration of systemic medications, including methylxanthines, may be practical in premature infants.

The epidermal barrier

A mature epidermis is an effective barrier which prevents dehydration from the loss of body water, poisoning from the absorption of noxious substances, and systemic infection from invading surface microorganisms. The epidermal barrier resides within the most superficial layer of the skin, the stratum corneum. In utero the fetus has no need for a skin barrier, so the stratum corneum does not start to develop until around 24 weeks' gestation. After 24 weeks there is a steady increase in the number of epidermal cell layers and in epidermal thickness, although it is not until around 34 weeks' gestation that a well-defined stratum corneum has completely developed. A weak epidermal barrier is, therefore, present is very preterm infants (<30 weeks' gestation) during the first 2-3 weeks of life and if the skin is damaged by trauma or disease.

Newborn percutaneous absorption: hazards and therapeutic uses

THE SKIN ACTS AS A VITAL BARRIER between an individual and the environment by limiting water loss and by protecting against the entry of harmful substances. Various material can pass through the skin barrier, a process called percutaneous absorption. Although the skin’s permeability can lead to harmful effects, it can be beneficial in making the skin a possible route for the delivery of therapeutic drugs. Differences between adult and neonatal skin, especially preterm skin, expose the neonate to a greater potential for percutaneous absorption.1 Neonatal nurses need to be familiar with the characteristics of newborn skin, principles for maintaining skin integrity, and the risks and benefits of percutaneous absorption.

Neonatal skin and skin care

Infant skin differs from adult skin in several ways. These important differences place infants at increased risk for fluid electrolyte imbalance, thermal instability, skin damage, percutaneous infection, and percutaneous toxicity from topically applied agents. This article includes a review of skin development, as well as the details of current skin care practices in the neonatal nursery. A better understanding of the principles of infant skin care and a more uniform approach to skin care in the neonatal nursery can minimize risks and costs to this special population of patients.

Topical treatment of erectile dysfunction: randomised double blind placebo controlled trial of cream containing aminophylline, isosorbide dinitrate, and co-dergocrine mesylate

OBJECTIVE

To examine the effectiveness in treating impotence to topically applied cream containing three vasodilators--aminophylline, isosorbide dinitrate, and co-dergocrine mesylate--which act by different mechanisms.

DESIGN

Randomised double blinded placebo controlled crossover trial over two weeks.

SUBJECTS

36 men with erectile dysfunction randomly allocated to two equal groups.

INTERVENTIONS

Active cream containing aminophylline 3%, isosorbide dinitrate 0.25%, and co-dergocrine mesylate 0.05% for one week and placebo for another.

MAIN OUTCOME MEASURES

Patients' reported experience of penile responses and side effects of treatment in questionnaires. Penile tumescence and arterial flow in the laboratory.

RESULTS

21 patients reported full erection and satisfactory intercourse with the active cream. Three men reported full erection and satisfactory intercourse with either cream. The active cream was more effective in psychogenic than organic impotence (eight out of nine men with psychogenic impotence achieved a full erection upsilon four out of eight with neurogenic impotence and two out of seven with arterial insufficiency). No major side effects were reported. In the laboratory the active cream increased penile arterial flow (0.19 (SD 0.08) m/s upsilon 0.02 (0.15) m/s with placebo) and induced tumescence in 24 patients.

CONCLUSIONS

Topical treatment with a cream containing three different vasodilators might be considered before intracavernous injection of vasoactive agents, particularly in psychogenic impotence.

An in vitro study of diamorphine permeation through premature human neonatal skin

The permeation kinetics of diamorphine through human premature neonatal cadaver skin over a range of gestational ages between 24 and 36 weeks was investigated using small diffusion cells. A strong inverse correlation was noted between the apparent permeability coefficient and the gestational age of the skin (P < 0.01; n = 26). The calculated apparent permeability coefficients decreased with gestational age from 6.0 x 10(-2) cm.hr-1 at 24 weeks' gestation to 5.2 x 10(-6) cm.hr-1 at 36 weeks' gestation. The amount of diamorphine remaining bound within the skin at the end of the in vitro experiments did not change significantly with gestational age of the skin. Diamorphine was subject to degradation over the course of the in vitro experiments to produce significant amounts of 6-monoacetylmorphine and evidence is presented to suggest that this was due to residual skin esterase activity. It is calculated that the steady-state flux rate of diamorphine through neonatal skin observed in these experiments would be sufficient to obtain a therapeutic plasma concentration of morphine assuming a 2-cm2 area for application and a delivery rate of 15 micrograms hr-1 kg-1. However, the prolonged half-life of morphine in the premature neonate would result in a delay of some hours before the attainment of this level.

Percutaneous absorption and age. Implications for therapy

Human skin changes dramatically with increasing age. Morphological, physiological, and biochemical changes within the tissue have been investigated and documented. Considerable interest in transdermal drug delivery to produce systemic effect has occurred in recent years. However, it is not known whether the penetration barrier of aged skin changes. Morphological and physiological changes in aged skin may affect the percutaneous absorption of compounds and thus their potential for localised, as well as systemic, efficacy. This article reviews the published literature on skin aging changes from adulthood to old age, collates these changes with clinical implications pertinent to the practising dermatologist, reviews the existing data supporting a change in the barrier function of human skin with increasing age, and comments on the relevance of conclusions previous investigators have drawn from their studies.