Health science: clinical use of anti-infective drugs

 Anti-infective drugs, as the name suggests, are mainly used in infectious diseases, i.e., infections due to pathogens with varying degrees of contagiousness, epidemiology, endemicity and seasonality, and also include immunologic features, and the clinical manifestations of infectious diseases ultimately depend on the outcome of the interactions between microorganisms, the host, and the environment.
Antiinfective drugs are mainly antimicrobials, which are absorbed into the blood circulation after administration by different routes. The degree and speed of absorption varies among different antibacterial drugs, generally 1~2 hours after oral administration and 0.5~1 hour after intramuscular injection, the drugs are absorbed into the blood to reach the peak blood concentration. Oral absorption of complete drugs are cephradine, cefaclor, amoxicillin, clindamycin, rifampicin, doxycycline, cotrimoxazole (SMZ + TMP, cotrimoxazole), metronidazole, levofloxacin, gatifloxacin and moxifloxacin, etc., the above drugs can be absorbed by more than 80% to 90% of the administered amount after oral intake; tetracyclines, except for doxycycline, the absorption of which is generally lower than 60% to 70% of the administered amount; the absorption of the tetracyclines is generally lower than 60% to 70% of the administered amount; the absorption of the tetracyclines is generally lower than 60% to 70% of the administered amount after oral intake. 60% ~ 70%; most penicillins can be destroyed by gastric acid (penicillin V exception), oral ampicillin, benzoxicillin only absorbed 30% ~ 40% of the amount of drug; aminoglycosides, cephalosporin injection, polymyxin, vancomycin, amphotericin B oral absorption of the amount of drug is very little, about 0.5% ~ 3.0%. Due to the differences in the absorption process of various types of drugs, in the treatment of mild and moderate infections, the antimicrobial drugs that are sensitive to the pathogenic bacteria and easy to be absorbed orally can be chosen, but in the treatment of critical infections, static injection or intravenous drip is preferred in order to avoid the influence of various factors on the absorption of the drugs when they are taken or injected into the muscle.
  Drugs that enter the blood circulation are rapidly distributed to tissues and body fluids to reach the site of infection. Generally speaking, the concentration is higher in tissues with rich blood supply, such as liver, kidney and lung tissues, and lower in tissues with poor blood supply, such as brain, bone and prostate, etc. Physiological barriers exist in some areas, such as the existence of blood-brain barrier, so that the cerebrospinal fluid concentration of most of the drugs is low, and the distribution characteristics of different antimicrobial drugs are also different, such as: clindamycin, some varieties of fluoroquinolones can reach the effective therapeutic concentration in bone tissue, fluoroquinolones can reach the effective therapeutic concentration of fluoroquinolone, and the concentration of fluoroquinolone can reach the effective therapeutic concentration of fluoroquinolone in bone tissue. The concentration of fluoroquinolones, erythromycin, tetracycline, etc. can reach the effective concentration in prostate fluid and tissues, chloramphenicol, sulfadiazine, isoniazid, flucytosine, etc. can reach the concentration of cerebrospinal fluid in cerebrospinal fluid in meningitis, and the concentration can reach the concentration of 50-100% of the blood drug concentration, and so on.
  The sterilization mode of antibacterial drugs in the body can be divided into the following types: ① concentration-dependent: the higher the concentration of the drug, the higher the bactericidal activity and bactericidal rate. This kind of drug mostly has a longer post antibiotic effect (PAE). Aminoglycosides, fluoroquinolones, metronidazole, amphotericin B, etc. belong to this type. Such drugs can usually be given once a day (except for severe infections). ② time-dependent: antimicrobial drug concentration in the pathogenic bacteria within the MIC of 4 to 5 times, the bactericidal effect is related to the concentration, but more than the concentration range, the bactericidal rate of saturation, the bactericidal effect of the drug and the concentration of the drug is more than the MIC of the pathogenic bacteria for the length of time. Penicillins, cephalosporins, carbapenems and other β-lactams are such drugs. The main PK/PD index is AUC0-24/MIC. azithromycin, clarithromycin, tetracyclines, vancomycin and other glycopeptides, clindamycin and other drugs belong to this type.