When selecting an appropriate animal model for predicting efficacy of a drug, it is important to match the etiology of the disease state as closely as possible to the human condition. However, many human dermatological conditions, such as rosacea, acne, and psoriasis, do not occur in other species, and are therefore difficult to model at the preclinical stage. Instead, indirect approaches are used to address specific physiological processes associated with such disorders, including inflammation, orthokeratosis, angiogenesis, and immunologic response. New treatments under development are often compared to existing products for their efficacy toward these processes.
Animal models for dermal wound healing are much more established and are described in detail in FDA’s “Guidance for Industry: Chronic Cutaneous Ulcer and Burn Wounds – Developing Products for Treatment” (June 2006). Minipigs are increasingly becoming the species of choice for evaluating wound healing due to their similarity to humans with regard to skin structure and healing properties. A key trait of minipigs is that their skin heals by granulation and re-epithelialization, similar to humans, whereas other species heal by contraction. Wounds can be simulated in animals to match the target clinical state in terms of type (chronic ulcer or burn), depth (full or partial thickness), and size (percent of total body surface area). Procedures for wounding, wound care, and bandaging must be optimized for each test article formulation and animal model. Study design elements such as randomization of wound treatments and timing of exams and observations are also critical to accurately evaluate a test article’s healing properties.