Blood concentration refers to the steady-state concentration of a drug in human blood. The so-called steady-state blood concentration refers to the blood concentration when the amount of absorption and excretion of the organism reach the equilibrium state after regular drug administration. The doctor can monitor the blood concentration to develop an individualized drug delivery plan, which has the following benefits compared to the empirical drug use in the past: 1. Adjusting the dose according to the blood concentration gives full play to the therapeutic effect of antiepileptic drugs, greatly improves the single drug control rate of epilepsy, and avoids unreasonable combination drug use. 2.Monitoring the blood concentration not only can timely detect the toxic reaction caused by drug overdose, but also can provide scientific basis for judging the degree of poisoning and adjusting the drug regimen. 3.Shorten the time of figuring out the drug dosage and make a reasonable drug administration plan for patients. 4.To monitor the blood concentration of the drug for patients with special pharmacokinetics (such as infants and children, maternal, elderly and hepatic and renal insufficiency) to develop their own characteristics of the drug regimen. 5. Non-compliance with medical advice is one of the main reasons for drug therapy failure, and physicians can understand patients’ compliance through the objective value of blood concentration. Not all patients need to be monitored at all times, otherwise it will cause unnecessary financial burden to the patient. Generally speaking, blood concentration testing is necessary in the following cases: 1. At present, it is considered necessary to monitor only those drugs whose blood concentration is closely related to the drug effect and whose effective blood concentration range is narrow, such as carbamazepine, phenytoin sodium and phenobarbital. Especially phenytoin sodium, its therapeutic dose and poisoning dose are close to each other, the low dose cannot control the seizure, and the high dose is prone to poisoning, so its blood concentration should be measured at the initial dose and before each dose adjustment. The blood concentration of sodium valproate fluctuates greatly, and there is no good correlation between its blood concentration and therapeutic effect, so the measurement is not very meaningful. 2. Due to individual differences, even the efficacy of the same drug may vary for different patients. When the drug dose has reached the conventional dose and still cannot control the seizure, the blood concentration should be measured first to clarify whether it has reached the effective blood concentration. 3. If there is no significant change in seizures after the first dose or increase in dose, the blood concentration must be known before adjusting the dose. It should be measured after 5 half-lives after the first dose or increased dose. When two or more antiepileptic drugs are used in combination, the measurement of blood concentration can help to understand the nature and extent of drug interactions, so as to judge the therapeutic effect of each drug. The blood concentration should be monitored when the patient with epilepsy has liver, kidney or gastrointestinal diseases or when other drugs are added, which may have an effect on the metabolism and elimination of the antiepileptic drugs being taken. 6. Blood concentration should be measured as soon as ataxia, mental abnormality or cognitive impairment occurs during treatment, and the dose should be adjusted promptly if the drug concentration is found to be higher than the upper limit of normal. The blood specimen is best collected in the morning before the first dose, when the measured concentration reflects the trough concentration of the drug, i.e. the lowest effective level of the drug in the body. Patients should not take medication in the early morning of the day of blood collection, and carry the medication with them to be taken in time after blood sampling. At the same time, the patient’s age, weight, gender, liver and kidney function and medication consumption should be taken into account in order to make a correct assessment of the blood concentration. It should be emphasized that although the monitoring of blood drug concentration is of great importance, as a clinician, you should not only pay attention to the value of blood drug concentration and ignore the analysis of the actual clinical situation. The effective blood concentration is a relative concept that only provides a reference for clinical treatment, and physicians must pay attention to the individual differences in drug metabolism. If a patient’s seizures are fully controlled, but his or her blood concentration is below the effective range of decline, there is no need to increase the dose at this time. Conversely, if a toxic reaction occurs when a patient’s blood concentration is in the effective range, the dose of the drug taken should be reduced immediately.