Application of the minimal trauma tissue biopsy to transdermal clinical pharmacokinetic studies

Preclinical pharmacokinetic investigation of the bioavailability and skin distribution of HY-072808 ointment, a novel drug candidate for the treatment of atopic dermatitis, in minipigs by a newly LC-MS/MS method

HY-072808 is a novel phosphodiesterase 4 inhibitor clinically used for topical atopic dermatitis treatment. Cytochrome P450 enzymes are involved in transforming it into major metabolite ZZ-24. An efficient UPLC-MS/MS method was established to detect HY-072808 and ZZ-24 in plasma and skin tissues of minipigs.One-step protein precipitation was performed with acetonitrile. Subsequently, elution was served with a methanol and water gradient containing 0.1% formic acid for 3.5 min. The plasma and skin tissue concentrations of HY-072808 and ZZ-24 showed good linearity from 0.200 to 200 ng/mL.The experimental minipigs exhibited low systemic exposure and bioavailability of 3.1-7.6% after transdermal application of 1-4% HY-072808 ointment. Multiple topical administrations over seven consecutive days showed a minor accumulation in systemic exposure, with accumulation factors of 2.3 and 4.0 for HY-072808 and ZZ-24, respectively.The distribution of HY-072808 ointment among different cortical layers in minipigs was studied for the first time. Following transdermal application of 2% HY-072808 ointment, the concentration in plasma and skin tissues in the order of epidermis > dermis > subcutaneous tissue ≈ subcutaneous muscle ≈ plasma; at 48 h after the administration, the epidermis and dermis still had a high concentration of the drug.

Reverse Iontophoresis: Noninvasive Assessment of Topical Drug Bioavailability

Assessing drug disposition in the skin after the application of a topical formulation is difficult. It is hypothesized that reverse iontophoresis (RI), which can extract charged/polar molecules for monitoring purposes, may provide a noninvasive approach for the assessment of local drug bioavailability. The passive and RI extraction of salicylic acid (SA) and nicotine (NIC) from porcine skin in vitro was assessed after a simple solution of the former and a transdermal patch of the latter had been applied for 24 and 8 h, respectively. Immediately after this "passive skin loading", the amount of drug in the stratum corneum (SC) and "viable" tissue (VT) was measured either (a) after tape-stripping and subsequent solvent extraction of both skin layers or (b) following RI extraction over 4 h. Parallel experiments were then performed in vivo in healthy volunteers; in this case, the VT was not sampled and the skin loading period for NIC was only 4 h. RI extraction of both drugs was significantly higher (in vitro and in vivo) than that achieved passively, and the cumulative RI extraction profiles as a function of time were mathematically analyzed using a straightforward compartmental model. Best-fit estimates of drug amounts in the SC and VT (ASC,0 and AVT,0, respectively) at the end of "loading" and two first-order rate constants describing transfer between the model compartments were then determined. The in vitro predictions of ASC,0 and AVT,0 were in excellent agreement with the experimental results, as was the value of the former in vivo. The rate constants derived from the in vitro and in vivo results were also similar. In summary, the results provide proof-of-concept that the RI method has the potential to noninvasively assess relevant metrics of drug bioavailability in the skin.

OFM-recirculation and OFM-suction: advanced in-vivo open flow microperfusion (OFM) methods for direct and absolute quantification of albumin in interstitial fluid

OBJECTIVE

To implement OFM-recirculation and OFM-suction capable of direct and absolute in-vivo quantification of albumin in the ISF of pigs.

APPROACH

OFM-recirculation and OFM-suction were used to collect ISF in-vivo in pigs and lymph was collected from the same pigs after OFM sampling. Blood was collected before and after OFM sampling, plasma was isolated and mean albumin plasma concentrations per pig were used to yield albumin ISF-to-plasma ratios. We characterized the quality of the collected undiluted ISF via (1) stable albumin ISF-to-plasma ratio in OFM-recirculation and in OFM-suction samples, (2) comparison of albumin ISF-to-plasma ratios from OFM-recirculation and OFM-suction and (3) comparison of normalized albumin concentrations in the ISF and lymph.

MAIN RESULTS

Both advanced OFM methods were successfully implemented and albumin was quantified from the collected ISF samples. OFM-recirculation reached stable albumin ISF-to-plasma ratios after 20 recirculation cycles. Absolute ISF albumin concentrations were 11.2 mg ml^-1 (OFM-recirculation) and 14.2 mg ml^-1 (OFM-suction). Albumin ISF-to-plasma ratios were 0.39 ± 0.04 (OFM -recirculation) and 0.47 ± 0.1 (OFM-suction).

SIGNIFICANCE

Knowledge of the ISF protein content is of major importance when assessing PK/PD effects, especially of highly protein bound drugs. Up to now, only blood albumin values have been available to determine the degree of protein binding in several tissues. OFM-recirculation and OFM-suction allow direct, absolute quantification of albumin in ISF for the first time and enable investigation of the degree of protein binding of a drug directly in its target tissue.

Methods for evaluating penetration of drug into the skin: A review

BACKGROUND

Skin being the largest organ of the human body plays a very important role in the permeation and penetration of the drug. In addition, the transdermal drug delivery system (TDDS) plays a major role in managing dermal infections and attaining sustained plasma drug concentration. Thus, evaluation of percutaneous penetration of the drug through the skin is important in developing TDDS for human use.

MATERIAL AND METHODS

Various techniques are used for getting the desired drug penetration, permeation, and absorption through the skin in managing these dermal disorders. The development of novel pharmaceutical dosage forms for dermal use is much explored in the current era. However, it is very important to evaluate these methods to determine the bioequivalence and risk of these topically applied drugs, which ultimately penetrate and are absorbed through the skin.

RESULTS

Currently, numerous skin permeation models are being developed and persuasively used in studying dermatopharmacokinetic (DPK) profile and various models have been developed, to evaluate the TDD which include ex vivo human skin, ex vivo animal skin, and artificial or reconstructed skin models.

CONCLUSION

This review discusses the general physiology of the skin, the physiochemical characteristics affecting particle penetration, understand the models used for human skin permeation studies and understanding their advantages, and disadvantages.

Liquid chromatography method to assay tretinoin in skin layers: validation and application in skin penetration/retention studies

A liquid chromatography (LC) method for the quantification of tretinoin (TTN) in different matrices (adhesive tape, cotton and porcine skin layers, stratum corneum, viable epidermis, and dermis) was validated and applied in in vitro porcine skin penetration/retention studies. This study proposes, for the first time, a method for assaying TTN in separated porcine skin layers (stratum corneum, viable epidermis, and dermis). The skin studies were carried out using tape stripping and cutaneous retention techniques. The procedures for the extraction of TTN from dermatological formulations (creams and gels) and biological and non-biological matrices used with the tape stripping and retention techniques were also evaluated. The LC method consisted of a mobile phase composed of a mixture of methanol, water, and glacial acetic acid (85:15:1, v/v); a C18 column used as the stationary phase; a flow rate of 1.0 mL min⁻¹; an injection volume of 100 μL; and TTN detection at 342 nm. The method was linear in the range of 0.05–15.00 μg mL⁻¹ (r = 0.9999), and it was precise and accurate. The limit of detection (LOD) and limit of quantification (LOQ) were 0.0165 μg mL⁻¹ and 0.0495 μg mL⁻¹, respectively. TTN was extracted from different matrices, showing good precision [relative standard deviation (RSD) of <5%] and accuracy (89.4–113.9%). This method was successfully applied in the evaluation of TTN skin retention/permeation from dermatological formulations (cream and gel). A higher penetration of TTN through the skin was achieved with the gel rather than the cream, showing the influence of the dosage form. Therefore, the developed method can easily be applied in porcine skin penetration/retention studies of dermatological formulations containing TTN, and it is able to discriminate the behaviours of the different formulations.

Quantification of uptake and clearance of acyclovir in skin layers

BACKGROUND

Quantification of drug uptake and clearance in the skin layers could provide better insight into the skin kinetics of dermatological formulations aimed for deeper skin tissues. This study assessed the skin kinetics of acyclovir in different skin layers following topical application on the abdominal region of Wistar rats.

METHODS

In vivo skin pharmacokinetics parameters were determined by two different protocols such as post drug load assessment and subsequent drug load assessment following topical application of 500 mg of cream formulation containing 5% (w/w) of acyclovir.

RESULTS

Topical application of acyclovir exhibited concentration gradient between the skin layers (stratum corneum > viable epidermis > dermis) which were inconsistent over the time-course of the study. The rate and extent of drug reaching target site (basal epidermis) was relatively low. The drug uptake and clearance profiles were found to be distinct in all the three skin layers suggesting no drug concentration correlation (P<0.05) between skin layers. Drug concentration in the viable epidermis continued to increase even after termination of therapy (Tmax=4 h) and then declined rapidly. The availability of acyclovir in the target was comparatively low (approximately 0.4% of the applied dose) although an order of magnitude higher percentage was determined in the stratum corneum.

CONCLUSIONS

The data observed in this study demonstrates low skin uptake and rapid clearance of acyclovir in the target site. Further, the methodology employed can be useful for studying other topical antiviral agents as well as for optimizing formulations for drugs (such as acyclovir) that may enhance their efficacy.

Use of minipig skin biopsy model as an innovative tool to design topical formulation to achieve desired pharmacokinetics in humans

In vitro cadaver skin permeation studies are often conducted to characterize the permeation profile of compounds for dermal delivery. However, its utility could be limited in the case of topical products because of lack of reliable prediction of in vivo skin kinetics. In this paper, the use of in vivo skin biopsy data to guide topical formulation development is described. A formulation was developed by compounding MK-0873, a phosphodiesterase 4 (PDE4) inhibitor, into a commercially available cream base. The cream was characterized by skin pharmacokinetic studies in minipigs, which demonstrated that MK-0873 concentrations in the epidermis and dermis were substantially higher than the IC80 for human whole blood PDE4 inhibition of ∼200 nM, suggesting that cream should provide sufficient skin exposure to assess clinical efficacy. In toxicological studies, after 1 month repeat application in minipigs minor dermal irritation and minimal systemic exposure were observed. Based on these preclinical data, the cream formulation was chosen for single rising dose clinical studies, where plasma levels of MK-0873 were mostly below the LOQ, whereas skin biopsy concentrations ranged from 6.5 to 25.1 μM. These data suggested that minipig skin biopsy model can be a valuable tool to assess performance of topical formulations and guide formulation development.

In vivo methods for the assessment of topical drug bioavailability

This paper reviews some current methods for the in vivo assessment of local cutaneous bioavailability in humans after topical drug application. After an introduction discussing the importance of local drug bioavailability assessment and the limitations of model-based predictions, the focus turns to the relevance of experimental studies. The available techniques are then reviewed in detail, with particular emphasis on the tape stripping and microdialysis methodologies. Other less developed techniques, including the skin biopsy, suction blister, follicle removal and confocal Raman spectroscopy techniques are also described.

Dermatopharmacokinetic prediction of topical drug bioavailability in vivo

The overall goal of this study was to explore the potential of using stratum corneum (SC) tape-stripping, post-application of a topical drug formulation, to derive dermatopharmacokinetic parameters describing the rate and extent of delivery into the skin. Ibuprofen was administered in 75:25 v/v propylene glycol-water to the ventral forearms of human volunteers for periods ranging between 15 and 180 minutes. Subsequently, SC was tape-stripped, quantified gravimetrically, and extracted for drug analysis. Together with concomitant transepidermal water loss measurements, SC concentration-depth profiles of the drug were reproducibly determined and fitted mathematically. The SC-vehicle partition coefficient (K) and a first-order rate constant related to ibuprofen diffusivity in the membrane (D/L2, where L=SC thickness) were derived from data-fitting and characterized the extent and rate of drug absorption across the skin. Integration of the concentration profiles yielded the total drug amount in the SC at the end of the application period. Using K and D/L2 obtained from the 30-minute exposure, it was possible to predict ibuprofen uptake as a function of time into the SC. Prediction and experiment agreed satisfactorily suggesting that objective and quantitative information, with which to characterize topical drug bioavailability, can be obtained from this approach.

Microdialysis

Microdialysis is a probe-based sampling method, which, if linked to analytical devices, allows for the measurement of drug concentration profiles in selected tissues. During the last two decades, microdialysis has become increasingly popular for preclinical and clinical pharmacokinetic studies. The advantage of in vivo microdialysis over traditional methods relates to its ability to continuously sample the unbound drug fraction in the interstitial space fluid (ISF). This is of particular importance because the ISF may be regarded as the actual target compartment for many drugs, e.g. antimicrobial agents or other drugs mediating their action through surface receptors. In contrast, plasma concentrations are increasingly recognised as inadequately predicting tissue drug concentrations and therapeutic success in many patient populations. Thus, the minimally invasive microdialysis technique has evolved into an important tool for the direct assessment of drug concentrations at the site of drug delivery in virtually all tissues. In particular, concentrations of transdermally applied drugs, neurotransmitters, antibacterials, cytotoxic agents, hormones, large molecules such as cytokines and proteins, and many other compounds were described by means of microdialysis. The combined use of microdialysis with non-invasive imaging methods such as positron emission tomography and single photon emission tomography opened the window to exactly explore and describe the fate and pharmacokinetics of a drug in the body. Linking pharmacokinetic data from the ISF to pharmacodynamic information appears to be a straightforward approach to predicting drug action and therapeutic success, and may be used for decision making for adequate drug administration and dosing regimens. Hence, microdialysis is nowadays used in clinical studies to test new drug candidates that are in the pharmaceutical industry drug development pipeline.