Background: Pharmacokinetics is defined as a mechanism or set of mechanisms by which the body interacts with the substances administered during the entire duration of drug exposure. The components of pharmacokinetics are absorption, distribution, metabolism, and excretion. All patients suffering from life-threatening illnesses must receive care in an intensive care unit. In this unit, it is not only necessary to have equipment that can provide comprehensive care to the patient, but also to have staff trained to act in any clinical environment.Methodology: A systematic review was carried out through various databases from January 2014 to February 2022; The search and selection of articles was carried out in indexed journals in English. Results:The understanding of the pharmacokinetics in the critical patient is of vital importance, being the pillar of this understanding the patient and providing adequate care and management. The cornerstones of intensive care management are the optimization of the patient's physiology, the provision of advanced organ support, and the identification and treatment of underlying disease processes. In antibiotic therapy it is necessary to optimize the dosage and improve the route of administration. Table 1 reports the main pharmacokinetic changes. Conclusion:This review offers up-to-date and detailed information on the pharmacokinetics in critically ill patients with the aim of providing "personalized" care depending on the patient's physiological state.