Most of the isolates obtained produce known antibiotics, but when a new antibiotic is discovered, it is produced in sufficient amounts for structural analyses and then tested for toxicity and therapeutic activity in animals. Unfortunately, most new antibiotics fail these tests. However, a few prove to be medically useful and go on to be produced commercially. The time and costs in developing a new antibiotic, from discovery to clinical usage, average 15 years and 1 billion ($US). This includes many phases of clinical trials, which alone can take several years to complete, analyze, and submit for United States Food and Drug Administration (FDA) approval.