Antibiotics should only be administered after microbiological specimens are taken, except in emergencies. Most antibiotics are removed from the body via the kidneys. Renal failure may cause the accumulation of a drug, or its metabolites. This is a particular problem with glycopeptides and aminoglycosides where toxic levels are associated with severe and permanent side effects such as ototoxicity and renal impairment. Organisms resistant to multiple antibiotics such as methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin-resistant enterococci (VRE) have emerged in healthcare environments and have proved difficult to control in many countries. Prophylaxis is recommended where a bacteraemia is expected, and the resultant infection may result in significant morbidity or mortality. The commonly used antibiotics on intensive care unit are: beta-lactams, carbapenems, aminoglycosides, glycopeptides, quinolones, macrolides, rifampicin, oxazolidinone and nitroimidazoles. The three major classes of anti-fungal drug are: azoles, polyenes, and echinocandins.