Reverse iontophoretic monitoring in premature neonates: feasibility and potential

Synergistic Strategies of Biomolecular Transport Technologies in Transdermal Healthcare Systems

Transdermal healthcare systems have gained significant attention for their painless and convenient drug administration, as well as their ability to detect biomarkers promptly. However, the skin barrier limits the candidates of biomolecules that can be transported, and reliance on simple diffusion poses a bottleneck for personalized diagnosis and treatment. Consequently, recent advancements in transdermal transport technologies have evolved toward active methods based on external energy sources. Multiple combinations of these technologies have also shown promise for increasing therapeutic effectiveness and diagnostic accuracy as delivery efficiency is maximized. Furthermore, wearable healthcare platforms are being developed in diverse aspects for patient convenience, safety, and on-demand treatment. Herein, a comprehensive overview of active transdermal delivery technologies is provided, highlighting the combination-based diagnostics, therapeutics, and theragnostics, along with the latest trends in platform advancements. This offers insights into the potential applications of next-generation wearable transdermal medical devices for personalized autonomous healthcare.

Reverse iontophoresis with the development of flexible electronics: A review

Skin-centric diagnosis techniques, such as epidermal physiological parameter monitoring, have developed rapidly in recent years. The analysis of interstitial fluid (ISF), a body liquid with abundant physiological information, is a promising method to obtain health status because ISF is easily assessed by implanted or percutaneous measurements. Reverse iontophoresis extracts ISF by applying an electric field onto the skin, and it is a promising method to noninvasively obtain ISF, which, in turn, enables noninvasive epidermal physiological parameter monitoring. However, the development of reverse iontophoresis was relatively slow around the 2010s due to the rigidity and low biocompatibility of the applied devices. With the rapid development of flexible electronic technology in recent years, new progress has been made in the field of reverse iontophoresis, especially in the field of blood glucose monitoring and drug monitoring. This review summarizes the recent advances and discusses the challenges and opportunities of reverse iontophoresis.

Non-Invasive Extraction of Gabapentin for Therapeutic Drug Monitoring by Reverse Iontophoresis: Effect of pH, Ionic Strength, and Polyethylene Glycol 400 in the Receiving Medium

Background:

Monitoring of plasma concentrations is a necessity for narrow therapeutic index potent drugs. Development of non-invasive methods can save the patients from the trauma of needles and hence is considered as a research priority.

Introduction:

Gabapentin, an anti-epileptic drug requires therapeutic monitoring because of its narrow therapeutic index. The objective of the study was to develop a suitable method for the non-invasive extraction of gabapentin for the same.

Methods:

Transdermal reverse iontophoresis was performed using pig ear skin as a barrier membrane. Three compartment iontophoretic cells were used for the extraction study. Extractions were carried out under low intensity electric field (current intensity- 0.5 mA/cm2, electrical field approximately 5 V). The donor compartment was charged with aqueous gabapentin (10 µg/ml in phosphate buffer of pH 7.4). For studying the effect of receiving vehicle (pH, ionic strength, and enhancer) on the extraction efficiency of gabapentin, the two receiver chambers were charged with media having varying concentration of these factors. Drug content was determined by HPLC.

Results:

Compared to other pHs, cumulative extraction of gabapentin at pH 5 was significantly higher at both anode and cathode (p<0.001). At low ionic strength, extraction of gabapentin increased linearly with the increase in concentration of ions up to a certain value but at very high ionic strength the pattern reversed. Similar results were obtained with enhancer (polyethylene glycol 400). Extraction increased with increase in polyethylene glycol 400 up to 3% and then decreased.

Conclusion:

Extraction flux can be optimized by manipulation of the receiver media.

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.

Transdermal reverse iontophoresis: A novel technique for therapeutic drug monitoring

Application of transdermal reverse iontophoresis for diagnostic purpose is a relatively new concept but its short span of research is full of ups and downs. In early nineties, when the idea was floated, it received a dubious welcome by the scientific community. Yet to the disbelief of many, 2001 saw the launching of GlucoWatch® G2 Biographer, the first device that could measure the blood sugar level noninvasively. Unfortunately, the device failed to match the expectation and was withdrawn in 2007. However, the concept stayed on. Research on reverse iontophoresis has diversified in many fields. Numerous in vitro and in vivo experiments confirmed the prospect of reverse iontophoresis as a noninvasive tool in therapeutic drug monitoring and clinical chemistry. This review provides an overview about the recent developments in reverse iontophoresis in the field of therapeutic drug monitoring.

Hydrogel-Forming Microneedle Arrays Allow Detection of Drugs and Glucose In Vivo: Potential for Use in Diagnosis and Therapeutic Drug Monitoring

We describe, for the first time the use of hydrogel-forming microneedle (MN) arrays for minimally-invasive extraction and quantification of drug substances and glucose from skin in vitro and in vivo. MN prepared from aqueous blends of hydrolysed poly(methyl-vinylether-co-maleic anhydride) (11.1% w/w) and poly(ethyleneglycol) 10,000 daltons (5.6% w/w) and crosslinked by esterification swelled upon skin insertion by uptake of fluid. Post-removal, theophylline and caffeine were extracted from MN and determined using HPLC, with glucose quantified using a proprietary kit. In vitro studies using excised neonatal porcine skin bathed on the underside by physiologically-relevant analyte concentrations showed rapid (5 min) analyte uptake. For example, mean concentrations of 0.16 μg/mL and 0.85 μg/mL, respectively, were detected for the lowest (5 μg/mL) and highest (35 μg/mL) Franz cell concentrations of theophylline after 5 min insertion. A mean concentration of 0.10 μg/mL was obtained by extraction of MN inserted for 5 min into skin bathed with 5 μg/mL caffeine, while the mean concentration obtained by extraction of MN inserted into skin bathed with 15 μg/mL caffeine was 0.33 μg/mL. The mean detected glucose concentration after 5 min insertion into skin bathed with 4 mmol/L was 19.46 nmol/L. The highest theophylline concentration detected following extraction from a hydrogel-forming MN inserted for 1 h into the skin of a rat dosed orally with 10 mg/kg was of 0.363 μg/mL, whilst a maximum concentration of 0.063 μg/mL was detected following extraction from a MN inserted for 1 h into the skin of a rat dosed with 5 mg/kg theophylline. In human volunteers, the highest mean concentration of caffeine detected using MN was 91.31 μg/mL over the period from 1 to 2 h post-consumption of 100 mg Proplus^® tablets. The highest mean blood glucose level was 7.89 nmol/L detected 1 h following ingestion of 75 g of glucose, while the highest mean glucose concentration extracted from MN was 4.29 nmol/L, detected after 3 hours skin insertion in human volunteers. Whilst not directly correlated, concentrations extracted from MN were clearly indicative of trends in blood in both rats and human volunteers. This work strongly illustrates the potential of hydrogel-forming MN in minimally-invasive patient monitoring and diagnosis. Further studies are now ongoing to reduce clinical insertion times and develop mathematical algorithms enabling determination of blood levels directly from MN measurements.

Microneedle-mediated minimally invasive patient monitoring

BACKGROUND

The emerging field of microneedle-based minimally invasive patient monitoring and diagnosis is reviewed. Microneedle arrays consist of rows of micron-scale projections attached to a solid support. They have been widely investigated for transdermal drug and vaccine delivery applications since the late 1990s. However, researchers and clinicians have recently realized the great potential of microneedles for extraction of skin interstitial fluid and, less commonly, blood, for enhanced monitoring of patient health.

METHODS

We reviewed the journal and patent literature, and summarized the findings and provided technical insights and critical analysis.

RESULTS

We describe the basic concepts in detail and extensively review the work performed to date.

CONCLUSIONS

It is our view that microneedles will have an important role to play in clinical management of patients and will ultimately improve therapeutic outcomes for people worldwide.

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.

Determination of zeta-potential and tortuosity in rat organotypic hippocampal cultures from electroosmotic velocity measurements under feedback control

Extracellular translational motion in the brain is generally considered to be governed by diffusion and tortuosity. However, the brain as a whole has a significant zeta-potential, thus translational motion is also governed by electrokinetic effects under a naturally occurring or applied electric field. We have previously measured zeta-potential and tortuosity in intact brain tissue; however, the method was tedious. In this work, we use a four-electrode potentiostat to control the potential difference between two microreference electrodes in the tissue, creating a constant electric field. Additionally, some alterations have been made to simplify our previous procedure. The method entails simultaneously injecting two 70 kDa dextran conjugated fluorophores into rat organotypic hippocampal cultures and observing their mobility using fluorescence microscopy. We further present two methods of data analysis: regression and two-probe analysis. Statistical comparisons are made between the previous and current methods as well as between the two data analysis methods. In comparison to the previous method, the current, simpler method with data analysis by regression gives statistically indistinguishable mean values of zeta-potential and tortuosity, with a similar variability for zeta-potential, -21.3 +/- 2.8 mV, and a larger variability for the tortuosity, 1.98 +/- 0.12. On the other hand, we find that the current method combined with the two-probe analysis produces accurate and more precise results, with a zeta-potential of -22.8 +/- 0.8 mV and a tortuosity of 2.24 +/- 0.10.

Noninvasive ultrasonic glucose sensing with large pigs (approximately 200 pounds) using a lightweight cymbal transducer array and biosensors

BACKGROUND

To prevent complications in diabetes, the proper management of blood glucose levels is essential. Since conventional glucose meters require pricking fingers or other areas of the skin, a noninvasive method for monitoring blood glucose levels is desired. Using a lightweight cymbal transducer array, this study was conducted to noninvasively determine the glucose levels of pigs having a similar size to humans.

METHOD

In vivo experiments using eight pigs (approximately 200 pounds) were performed in five groups. A cymbal array with four biosensors was attached to the axillary area of the pig. The array was operated at 20 kHz at special peak-temporal peak intensity (I(sptp)) equal to 50 or 100 mW/cm(2) for 5, 10, or 20 minutes. After the ultrasound exposure, glucose concentrations of the interstitial fluid were determined using biosensors. For comparison, glucose levels of blood samples collected from the ear vein were measured by a commercial glucose meter.

RESULT

In comparison, glucose levels determined by a cymbal array and biosensor system were close to those measured by a glucose meter. After a 20-minute ultrasound exposure at I(sptp) = 100 mW/cm(2), the average glucose level determined by the ultrasound system was 175 +/- 7 mg/dl, which is close to 166 +/- 5 mg/dl measured by the glucose meter.

CONCLUSION

Results indicate the feasibility of using a cymbal array for noninvasive glucose sensing on pigs having a similar size to humans. Further studies on the ultrasound conditions, such as frequency, intensity, and exposure time, will be continued for effective glucose sensing.

Determination of zeta-potential in rat organotypic hippocampal cultures

zeta-potentials of entities such as cells and synaptosomes have been determined, but zeta of brain tissue has never been measured. Electroosmotic flow, and the resulting transport of neuroactive substances, would result from naturally occurring and experimentally or clinically induced electric fields if zeta is significant. We have developed a simple method for determining zeta in tissue. An electric field applied across a rat organotypic hippocampal slice culture (OHSC) drives fluorescent molecules through the tissue by both electroosmotic flow and electrophoresis. Fluorescence microscopy is used to determine each molecule's velocity. Independently, capillary electrophoresis is used to measure the molecules' electrophoretic mobilities. The experiment yields zeta-potential and average tissue tortuosity. The zeta-potential of OHSCs is -22 +/- 2 mV, and the average tortuosity is 1.83 +/- 0.06. In a refined experiment, zeta-potential is measured in various subregions. The zeta-potentials of the CA1 stratum pyramidale, CA3 stratum pyramidal, and dentate gyrus are -25.1 +/- 1.6 mV, -20.3 +/- 1.7 mV, and -25.4 +/- 1.0 mV, respectively. Simple dimensional arguments show that electroosmotic flow is potentially as important as diffusion in molecular transport.

Correlation between plasma and urinary caffeine levels in preterm infants

BACKGROUND

We hypothesize that urine levels might be reliable to assess the therapeutic range of caffeine.

OBJECTIVES

We correlated plasma and urinary levels of caffeine in preterm infants treated with this drug for apnea of prematurity.

METHODS

Infants (n=56) were given a loading dose of caffeine citrate (10 mg/kg, per os) and 24 h later a maintenance dose (2 mg/kg, per os, once a day). Plasma and urinary levels of caffeine were determined 24 h after the loading dose (before administration of the maintenance dose) and then weekly.

RESULTS

Plasma and urinary levels correlate at all examined ages: 29 weeks (r=0.92, P<0.001), 30 weeks (r=0.97, P<0.001), 31 weeks (r=0.82, P<0.001), 32 weeks (r=0.92, P<0.001), 33 weeks (r=0.87, P<0.001), 34 weeks (r=0.81, P<0.001).

CONCLUSION

Urinary levels of caffeine might be a useful means to assess therapeutic ranges.

Synthesis and transdermal permeation-enhancing activity of ketone, amide, and alkane analogs of Transkarbam 12

Transkarbam 12 (5-(dodecyloxycarbonyl)pentylammonium-5-(dodecyloxycarbonyl)pentylcarbamate, T12) is a highly active transdermal permeation enhancer. In this study, ketone, amide, and alkane analogs of T12 have been synthesized and evaluated for their permeation-enhancing activity using porcine skin and theophylline as a model drug. Replacement of ester by methylene and ketone, respectively, led to a significant decrease of activity. Amide analogs displayed lower activity in 60% propylene glycol and were comparable to T12 in isopropyl myristate. An intramolecular H-bond between ester and ammonium-carbamate group was suggested to be important for the permeation-enhancing activity of T12.

Electroporation and transcutaneous extraction (ETE) for pharmacokinetic studies of drugs

The therapeutic activity and toxicity of drugs often depends on the accumulation of drugs in the peripheral anatomical compartment rather than the central compartment. In the routine practice of therapeutic drug monitoring (TDM) and pharmacokinetic studies, drug concentration determined by intermittent blood sampling is used as a surrogate for calculating the drug concentration in the peripheral compartment tissues. Microdialysis, a relatively less invasive procedure, has been used for estimation of free drug levels in dermal, subcutaneous and muscle tissues. Transcutaneous extraction of drugs from the dermal tissue is a good noninvasive alternative to phlebotomy and microdialysis. This requires a technique, which can facilitate the extraction of significant and reproducible amounts of drugs from the dermal extracellular fluid (ECF) within a short sampling duration. In the present work, we assessed the feasibility of electroporation and transcutaneous extraction (ETE) method for determining the time course of drugs in dermal ECF, using salicylic acid (SA) as a test drug. Electroporation protocol was optimized based on the in vitro diffusion studies of salicylic acid across rat skin. The concentration-time profile of total SA was determined in rats after a single i.v. bolus administration. The in vivo permeability coefficient (P(in vivo)) of rat skin was determined under steady state plasma concentration of drug created by i.v. bolus followed by constant rate infusion of SA. The pharmacokinetic parameters of the drug were determined using a two-compartment pharmacokinetic model. The theoretical predicted time course of free SA in the dermal ECF after a single i.v. bolus administration was calculated using standard formulae. The concentration of free SA determined by ETE is in good agreement with that calculated using two-compartment pharmacokinetic model. This study thus provides a credible evidence for the validity of ETE technique for determining the concentration of SA in the dermal ECF.

Transdermal reverse iontophoresis of valproate: a noninvasive method for therapeutic drug monitoring

PURPOSE

The objectives of this work were (a) to explore the potential of transdermal reverse iontophoresis for therapeutic drug monitoring and (b) to develop an "internal standard" calibration procedure so as to render the technique completely noninvasive.

METHODS

A series of in vitro iontophoresis experiments was performed in which the subdermal concentration of sodium valproate was varied from 21 microM to 1 mM. Glutamic acid was also introduced into the subdermal donor at a fixed concentration to act as an "internal standard" for the calibration method.

RESULTS

Both valproate and glutamate anions were recovered, as expected, at the anodal receptor chamber. The iontophoretic extraction flux of valproate was linearly correlated with the subdermal concentration. Glutamate flux was constant. It follows that the ratio of extracted fluxes (valproate/glutamate) was directly dependent upon (a) the subdermal valproate concentration and (b) the subdermal concentration ratio (valproate/glutamate), offering a means, thereby, to a completely noninvasive methodology.

CONCLUSIONS

This work demonstrates the potential of reverse iontophoresis for noninvasive therapeutic monitoring. The simultaneous quantification of the analyte of interest and of an "internal standard" renders the withdrawal of a blood sample unnecessary.

Reverse iontophoresis for non-invasive transdermal monitoring

Iontophoresis is the application of a small electric current to enhance the transport of both charged and polar, neutral compounds across the skin. Manipulation of either the total charge delivered and/or certain electrode formulation parameters allows control of electromigration and electroosmosis, the two principal mechanisms of transdermal iontophoresis. While the approach has been mainly used for transdermal drug delivery, 'reverse iontophoresis', by which substances are extracted to the skin surface, has recently been the subject of considerable effort. Glucose monitoring has been extensively studied and other applications, including therapeutic drug monitoring, are contributing to the development of the technique. An internal standard calibration procedure may ultimately render this novel monitoring technique completely non-invasive.