At a time when we are worried about antibiotic misuse, clinicians must be as diligent in administering them only when necessary. To do so, they would need to base their decision on five fundamental criteria: efficacy, appropriateness, affordability, convenience of use, and side effect avoidance. If they fail to do any one of these, then the patient will be at risk of receiving no benefit from his or her medication or suffering from some undesirable effect. Antibiotics can save lives by clearing up infections that other treatments could not. However, overuse of these medicines leads to the development of drug-resistant bacteria, which are harder for antibiotics to kill. This creates a need for new drugs that are more effective against these resistant organisms. There are many factors that go into deciding what medications to prescribe for an individual patient. For example, physicians may choose an antibiotic because it is recommended by their hospital's formulary or approved by the U.S. Food and Drug Administration. They may also choose an antibiotic because there are few or no alternative therapies available (for example, if all else fails, patients with bacterial pneumonia will still require treatment with antibiotics). Physicians may select an antibiotic based on their own experience with similar cases or simply because it is easy to obtain. Some medications are more effective than others in treating certain illnesses; for example, first-line antibiotics work better when used early in the course of illness before the disease has had a chance to develop complications.