Dermal Absorption

The dermal absorption process helps to evaluate and understand the safety and efficacy of drug formulations. The main purpose of dermal absorption is to deliver drug effector molecules to the skin and circulation in the body. In vitro skin absorption testing provides information on the behavior of a test substance when applied to the skin surface. BOC Sciences has extensive experience in dermal absorption testing, and we offer in vitro dermal absorption studies to predict the dermal absorption potential of new compounds and evaluate skin permeability.

The skin is the largest organ in the human body, with a surface area of approximately 2 square meters in a healthy adult. Skin is a heterogeneous multilayered tissue whose main function is to protect the body from the external environment by acting as an effective barrier for the absorption of exogenous molecules. Topical and transdermal administration has shown significant advantages in clinical practice in targeting the site of action in vivo, which reduces systemic side effects. Controlled or prolonged drug delivery can also be achieved through skin administration, and this route could be explored as an alternative to the oral route. Currently, different methods have been proposed to evaluate the skin absorption of drugs to optimize the development of new formulations for skin delivery. In vitro assessment is an important tool for developing and screening formulations and predicting skin absorption in vivo. Skin in vitro absorption assays allow precise control of experimental variables with the simplest protocols. BOC Sciences provides in vitro skin penetration testing support for compounds designed to help pharmaceutical scientists select the most suitable specific research formulation.

• Diffusion Cell System

Diffusion cells are the most widely used experimental instruments for evaluating drug release and skin penetration from topical and transdermal drug delivery systems. The main purpose of these evaluations is to identify the main variables during formulation design that may alter the in vivo bioavailability of a drug. BOC Sciences' proprietary diffusion cell system evaluates different formulations such as gels, creams, ointments and patches. The assay employs a glass cylindrical tube, whose borders are closed on one side, with excised skin and an interior with stratum corneum. The formulation was placed in a cylindrical tube above the stratum corneum, dermal side immersed in receptor medium. Media samples were taken at various times for drug quantification.

Fig. 1. Vertical diffusion cell (Beverly: Wiley-Scrivener. 2017, 413-454).

• Tape-stripping Technique

The Tape-stripping technique was used in vitro to analyze drug penetration into the stratum corneum. The procedure can be applied in vivo using animal models or human volunteers. The technique has also been used to assess the potential toxicity of bioactive compounds absorbed by the stratum corneum. The Tape-stripping technique involves the sequential removal of the cellular layers of the stratum corneum by applying pieces of tape. Tape fragments were collected and solvents were used for drug extraction. The samples are stirred and centrifuged, and the drug is recovered in the supernatant. Validation studies were performed by using spiked tapes of known drug concentrations to determine recovery.

• Skin Retention Studies

Skin retention studies of active compounds can be assessed by directly measuring drug concentrations throughout the skin and in previously isolated skin layers or using reconstructed skin models. The skin layers can be separated using various techniques. For example, immerse the skin in hot water (60 °C) for 1 minute to separate the dermis from the epidermis. The experimental protocol is based on in vitro and in vivo assessment of skin penetration. These evaluations can be performed in vitro following skin penetration assays using diffusing cells. Drug quantification is performed by using selective and validated analytical methods. In general, HPLC is the commonly used analytical technique.

BOC Sciences offers a variety of skin samples, including rat skin, porcine skin, and human skin. Our ex vivo skin models include full-thickness skin, skin sections, isolated stratum corneum, or mucosa. In addition, we provide skin in vivo absorption services to support skin irritation, corrosion and sensitization risk assessment of drug candidates. If you are interested in our dermal absorption services, please contact us for more information.