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If you have ever sat up at night with a sick child who got well after an injection of antibiotics, you probably appreciate the power of modern treatment of infectious disease. In the 1940's, when antibiotics first became generally available, they were considered to be miracle drugs. Before the introduction of antibiotics, something as simple as stepping on a nail or cutting your hand on broken glass could quickly result in death. After the introduction of antibiotics, infections that had killed millions of people in the prime of life became manageable, sometimes with just few injections of a few tablets of the right antibiotic.
Modern antibiotics are not entirely beneficial, or free of side effects.
By the 1980's, however, antibiotics had begun to be regarded as something of a mixed blessing. Some people were allergic to antibiotics. There had been thousands of deaths (out hundreds of millions of treatments) due to allergic reactions to antibiotics. Moreover, bacteria began to be able to "outsmart" antibiotics. By chance, some bacteria would have genetics that enabled them to resist the effects of medications. They could pass these genes to other bacteria without having to reproduce themselves, making them also resistant to the drug. The more often an antibiotic is used, the more bacteria that are resistant to it, making many medications less and less useful as time goes by. Because many antibiotics are used not just to treat diseases in people but also to help livestock gain weight, antibiotic resistance is becoming a worldwide problem.
Antibiotic resistance is one of the biggest threats to global health, food security, and development today. It can affect anyone, of any age, in any country: a growing number of infections – such as pneumonia, tuberculosis, and gonorrhoea – are becoming harder to treat as the antibiotics used to treat them become less effective.
The answer to the question "How long does it take antibiotics to work?" is always longer than it takes to start feeling better.
It may take 24 hours or less to start feeling better when the doctor has prescribed the right antibiotic for your illness. It may take longer if the doctor has made an ill-advised choice. Most antibiotics get demonstrable results in less than 48 hours. However, the antibiotic still has more work to do even after you start feeling better.
Symptoms begin to subside when a majority of bacteria have been killed. However, a few stronger bacteria may hang on even after most others have died. It is important to kill those bacteria, too, because stopping antibiotic treatment too soon will allow them to multiply unchecked. An infection may "rebound" a few days after symptoms subside, and because the new infection is caused by stronger, meaner, nastier bacteria, it will take longer to get back under control. If this process is repeated often enough, there will eventually be a strain of bacteria that cannot be controlled by antibiotics at all. That is precisely what has been happening with countless antibiotics used to treat dozens of infections all over the world.