This will be a single center, open label, exploratory research study to evaluate the BE of already marketed formulations of acyclovir in dermal interstitial fluid (ISF) in healthy volunteers using dOFM. The study will be conducted at the Clinical Research Center at the Medical University Graz. dOFM represents the most reliable way to sample interstitial fluid from skin, since it provides diluted but otherwise unchanged dermal interstitial fluid. To assess BE and non-BE, we have designed the experiments in such a way that each subject can serve as its own control. Each subject will have two sets of BE and non-BE pairs in parallel. This study is designed to test dOFM, a new sampling method that allows measurement of skin penetration. Measurement of skin penetration enables the reduction of the impact of inter-subject variability and therefore decreases the number of subjects needed to achieve statistical significance.