Developing a new medicine, including a new antibiotic, takes many years and has several stages. The first stage is discovery. Possible new drugs can be found in plants and in microorganisms. For example, penicillin comes from a mould. Chemicals can also be designed and made in a laboratory.
Next comes development of the chemical into a medicine that can be given safely. Then comes preclinical testing. The drug is tested on cells, tissues and live animals to check whether it is toxic and whether it works. This helps to check the safety of a drug before it is given to people.
Finally there is clinical testing on human volunteers. Low doses are used first to check the drug is safe, and then the best dose is found. In a double-blind trial, one group takes the drug and another group takes a placebo, which looks the same but has no drug in it. Neither the patients nor the doctors know who has which, so the results are not biased.