Abstract

Multiple Drug Resistance (MDR) is acquired by bacteria, viruses, fungi, parasites and malignant tumours at interaction with antibiotics/medicines of old or new generation. Here is presented an up-date of MDR reported on bacteria, viruses, fungi, parasites and tumors, in this last field with emphasis on ophthalmology and neurology/neurosurgery. Multidrug resistant organisms exhibit in vitro resistance to one or more antimicrobial agents. One cause is the increasing use and misuse of antibiotics on humans and animals. Whereas particular bacteria are naturally resistant to some antibiotics, MDR occurs in other cases by accumulation of resistant plasmids and/or of genes, each gene determining resistance to a specific agent. The action of efflux pumps able to pump out more than one drug type is also a possible mechanism involved in MDR. In general, MDR is the most important “process” by which tumors acquire resistance to drugs during chemotherapy. Bacterial resistance to antibiotics used in ophthalmology has been reported since more than 10 years showing that several bacteria resistant to antibiotics were found in isolates from ocular infections. In neuroscience, development of new therapies to treat brain infections is more difficult. The most important cause of failure in developing new drugs for treating brain diseases is the existence and action of blood brain barrier (BBB). Brain tumors have usually poor prognosis and due to BBB, drug delivery to brain tumors is difficult. Some studies mention that BBB is involved in drug restriction to different brain neoplasias. The chapter concludes about the need to improve the arsenal conceived to overcome MDR acquired by different biological targets.