Medications administered to human organism undergo various subsequent pharmacokinetic processes. The drug must, first of all, be released from its formulation, i.e. tablet, capsule or suppository etc. Next, it is absorbed from various areas depending on the administration route – gastrointestinal tract when administered orally or rectally, subcutaneous or muscular tissue when given in form of tissue injection. Medications can be also absorbed through skin, and various types of mucous membrane other than in GI tract, e.g. in vagina or conjunctival sac of the eye. Volatile liquids, gasses and fine particles of solid bodies administered as aerosols or fine colloids can be absorbed by the lungs. Only drugs administered directly to circulatory system (intravenously, intra-arterially) are distributed instantaneously after administration, without release and absorption processes [1]. Both absorption as well as permeation of medications to tissues relies on transportation through various biological membranes. Such modes of transportation are: simple diffusion, convective transport, carrier mediated transport (facilitated diffusion and active transport), and pinocytosis. The essential role is played by simple diffusion and active transport. Simple diffusion is permeation of non-ionized and lipid-soluble particles through lipid membrane – the process is a movement down concentration gradient, is non-competitive and does not become saturated. Active transport is enabled by carrier system in cell membrane – the movement is against concentration gradient, is energy-dependent and its maximal speed is limited by number of carrier particles, it is competitively inhibited. Most of the processes described are determined in assumed physiological conditions [1].

One of the significant parameters capable of altering drugs efficacy is body temperature. In pharmacokinetics pertaining to physiological state, speed of processes is evaluated in normothermia (36–37°C) [1]. Hypothermia and hyperthermia may cause alterations in distribution, metabolism, and elimination processes of a drug, what in clinical practice translates into variation in response to administered drug, frequently a necessity to modify doses, and different profile of potential side effects. Majority of medications after reaching circulatory system become bound to blood proteins – protein-bound drug is inactive, does not become distributed, biotransformed, or excreted. In hypothermic patients binding to proteins may occur to a lower extent what implies a larger fraction of free drug i.e. available for receptors in target tissues [1, 2].