How long between each dose needs to be determined by the elimination half-life of the drug. For example, penicillin every 6 to 12 hours and lidocaine every two hours. The elimination half-life of a drug is the time it takes for the plasma drug concentration to fall by half. The length of the period can reflect the rate of drug elimination in the body. The interval between administrations can be determined from the half-life, and the usual administration time is about one half-life. If the half-life is too short, the toxicity is small, you can increase the dose and make the drug interval longer than the half-life, so that you can avoid giving too often, but also in the two intervals between the administration of high blood concentration. For example, penicillin has a half-life of only 1 hour, but large doses are usually given every 6 to 12 hours. For example, the half-life of commonly used anti-heart rate common tardive dyskinesia drugs: lidocaine is 2 hours, propranolol is 3 to 4 hours, and quinidine is 5 to 7 hours. However, the specific time of medication, but also under the guidance of the physician to determine, do not unauthorized use of drugs.