Antimicrobials are a potent defence against bacteria and other pathogens, but they have one weakness: if used to excess, their power fails. Overuse and inappropriate use of antimicrobials is a key factor contributing to infectious diseases becoming unresponsive to these drugs. Ongoing inappropriate use of antimicrobials assists microbes to evolve increased resistance. When an antibiotic is no longer effective, others must be developed to deal with the new resistant forms of the disease. This increases costs and the new drugs may have harsher side effects.
Reduced effectiveness of these drugs costs lives, especially in developing countries.
Drug misuse places a heavy burden across the population, with a disproportionate impact on vulnerable communities, such as aged-care residents and people in rural and remote areas. In the Third World, antibiotics are a treated as a cure-all, and are mostly available without prescription.
Antibiotics either kill bacteria (bactericidal) or stop them from multiplying, without necessarily killing them (bacteriostatic). Doctors and veterinarians are prescribing antibiotics against nonbacterial organisms, notably viruses that cause the common cold, for which the drugs are not effective.
The greatest volume of antibiotics are administered through feed to domestic animals. They then make their way into human food and resistant bacteria into the human food chain. Hospital and household sewage adds substantial quantities of antibiotics into the environment. Bacteria exposed to antibiotics in sewage sludge, or water, have an opportunity to develop resistance. Repeated exposure of bacteria to drugs can result in the development of resistant strains. These resistant bacteria can then spread throughout the population. Thus, treatment for some diseases is now more difficult and expensive.
The overuse of antibiotics, such as penicillin and tetracycline, has dramatically reduced their effectiveness. For example, one type of penicillin, 100% effective in the 1940s against the common Staphylococcus aureus bacterium (MRSA), is now only 10% effective. The new drug needed to successfully treat Staphylococcus aureus bacterium is 10 times as expensive as the original penicillin.
Up to 75% of antibiotic prescriptions each year in the USA are for colds, bronchitis and other acute respiratory infections, mostly caused by viruses. Streptococcus bacteria cause about 10% of sore throat cases in adults; sinusitis is sometimes caused by bacteria; for the rest, antibiotic treatment of upper-respiratory infections is almost always inappropriate.
The report Antimicrobial prescribing practice in Australian hospitals: Results of the 2017 Hospital National Antimicrobial Prescribing Survey (2018) found that around one-third of antibiotic prescriptions have been assessed as non-compliant with treatment guidelines and one in four have been deemed inappropriate. It claimed that up to 50% of the antibiotics prescribed could be eliminated through more appropriate prescribing practices. Curbing antibiotic prescriptions for respiratory infections such as sinusitis, bronchitis and other, non-specific infections can reduce the prevalence of antibiotic-resistant bacteria.