Ampicillin belongs to the penicillin class of antibacterial drugs, it is easy to cause allergies, so before use, skin testing should be conducted, the following is the configuration of the skin test steps: take 0.5 grams of each bottle of ampicillin and add saline to 2 ml, the concentration of the solution obtained at this time is 250mg/mL. then take 0.1 ml, add 0.9 ml of saline to 1 ml, the concentration of the solution obtained is 25mg/mL. then take 0.1 ml of the solution, add 0.5 ml of saline to 1 ml, the concentration of the solution obtained is 2.5mg/mL. Then take 0.1ml of the solution and add 0.5ml of saline to 1ml to get a concentration of 2.5mg/mL. Then take 0.1ml and add 0.9ml of saline to 1ml to get 0.25mg/mL of ampicillin skin test solution. Take 0.1ml from it, which is 25ug of ampicillin to do intradermal test, and observe for 20 minutes to judge the result.