infections
Overview of Antibiotics
Selecting an Antibiotic
Each antibiotic is effective only against certain types of bacteria. In selecting an antibiotic to treat a person with an infection, doctors evaluate which bacteria are likely to be the cause. For example, some infections are caused only by certain types of bacteria. Sometimes one antibiotic is predictably effective against all of the bacteria that are most likely to be causing an infection and so further testing may not be needed. If infections may be caused by many different types of bacteria or by bacteria that are not predictably susceptible to antibiotics, a laboratory is asked to Diagnosis of Infectious Disease from samples of blood, urine, or tissue taken from the person ( see Antibiotics that are effective in the laboratory do not necessarily work in an infected person. The effectiveness of the treatment depends on How well the drug is absorbed into the bloodstream (for Oral route ) How much of the drug reaches the sites of infection in the body (see Drug Distribution ) How quickly the body eliminates the drug (see Drug Elimination ) These factors may vary from person to person, depending on other drugs being taken, other disorders present, and the person’s age. In selecting an antibiotic, doctors also consider the following: The nature and seriousness of the infection The status of the person's immune system (how well it can help the drug fight the infection) The drug’s possible side effects The possibility of allergies or other serious reactions to the drug The cost of the drug Doctors also consider how hard it may be for people to take antibiotics for the entire time prescribed and complete the full course of treatment. People may find it more difficult to complete treatment if the drug must be taken very often or only at specific times (such as before meals, during meals, or after meals). Combinations of antibiotics may be needed to treat the following: Severe infections, particularly during the first days when the bacteria's susceptibility to antibiotics is not known Certain infections caused by bacteria that rapidly develop resistance to a single antibiotic Infections caused by more than one type of bacteria if each type is susceptible to a different antibiotic 