Renal or hepatic failure implies the need adjust the dosage of antibiotics that are eliminated in active form through the kidneys or metabolized through the liver. In the first case, the dose should be reduced by 30% for each level of renal impairment (moderate and severe). In hepatic failure, there is no general rule, and the specific information provided for each antibiotic should be used. Hemodialysis clears antibiotics with a low molecular weight, and a reduced protein binding and distribution volume. Thus, the dose should be administered immediately after the session or a supplementary dose should be provided. When the most intensive extrarenal clearance techniques are used, the presence of a high volume of distribution is the only guarantee that the antibiotic will not be eliminated.