Classification
of Antibiotics Commonly Used in
Clinical Practice
(I)
β-lactam
1.Penicillins
-Natural penicillins, such as penicillin G, mainly act on Gram-positive bacteria, and have high antibacterial activity against hemolytic streptococcus, streptococcus pneumoniae, and staphylococci that do not produce penicillinase. It is the first choice for the treatment of group A hemolytic streptococcal pharyngitis, tonsillitis, scarlet fever, cellulitis, etc., and is also an important treatment for Streptococcus pneumoniae pneumonia. However, it has a narrow antibacterial spectrum and is easily destroyed by gastric acid and β-lactamase.
-Semisynthetic penicillin: Amoxicillin is one of the representatives. It has a broad antibacterial spectrum and good antibacterial effect on some Gram-negative bacteria. It can be absorbed orally. It can be used for respiratory tract, genitourinary tract, skin and soft tissue infections, especially for children with otitis media and sinusitis.
2. Cephalosporins
-First-generation cephalosporins, such as cefradine, have a strong effect on Gram-positive bacteria and a weak effect on Gram-negative bacteria. They are mainly used to treat upper and lower respiratory tract infections, skin and soft tissue infections caused by methicillin-sensitive staphylococci, hemolytic streptococci and Streptococcus pneumoniae.
-Second-generation cephalosporins: The activity of cefuroxime against Gram-positive bacteria is similar to or slightly worse than that of the first-generation cephalosporins. The antibacterial activity against Gram-negative bacteria is significantly enhanced. It also has antibacterial activity against some anaerobic bacteria. It can be used to treat pneumonia, biliary tract infection and bacteremia caused by sensitive bacteria.
-Third-generation cephalosporins: Ceftriaxone has strong antibacterial activity against Gram-negative bacteria, but its effect on Gram-positive bacteria is not as good as that of the first and second generations. It is highly stable to beta-lactamase and can penetrate the blood-brain barrier. It is often used for severe Gram-negative bacilli infection, especially for multi-drug-resistant bacteria infection and hospital-acquired infection. Such as meningitis, septicemia, etc.
-Fourth-generation cephalosporins: Cefepime and others are highly effective against both Gram-positive and Gram-negative bacteria, are more stable against beta-lactamases, and can be used to treat severe infections caused by Gram-negative bacilli resistant to third-generation cephalosporins.
(II) Macrolides
Erythromycin and azithromycin are commonly used drugs. These drugs have strong antibacterial activity against Gram-positive bacteria, Gram-negative cocci, anaerobic bacteria, Legionella, Mycoplasma, Chlamydia and so on. The antibacterial spectrum of azithromycin is similar to that of erythromycin, but azithromycin has the advantages of high tissue concentration, long half-life and good oral absorption. Macrolides are often used to treat community-acquired pneumonia, especially pneumonia caused by atypical pathogens such as Mycoplasma pneumoniae and Chlamydia pneumoniae, as well as pertussis and Campylobacter jejuni enteritis.
(III) Aminoglycosides
Gentamicin and amikacin are representatives of this kind. They mainly have strong antibacterial activity against aerobic gram-negative bacilli, such as Escherichia coli, Klebsiella, Enterobacter and so on. However, these drugs have ototoxicity (including vestibular dysfunction and hearing loss) and nephrotoxicity, which require close monitoring of renal function and hearing changes in clinical use. It is usually used for severe gram-negative bacilli infection or in combination with other antimicrobial agents for the treatment of multidrug-resistant bacterial infections.
(4) Quinolones
Levofloxacin and moxifloxacin are commonly used quinolones in clinic. They have good antibacterial activity against Gram-negative bacteria, and also have certain effect on Gram-positive bacteria, anaerobic bacteria, mycoplasma, chlamydia and so on. Quinolones are widely used in urinary tract infection, intestinal tract infection, respiratory tract infection and other infectious diseases. However, it is generally not used in children and pregnant women because it may affect cartilage development.
(5) Glycopeptides
Vancomycin and norvancomycin belong to glycopeptides. They have a strong bactericidal effect on Gram-positive bacteria, especially on drug-resistant bacteria such as methicillin-resistant Staphylococcus aureus (MRSA) and methicillin-resistant Staphylococcus epidermidis (MRSE). It is mainly used to treat severe Gram-positive bacterial infections, such as septicemia and endocarditis, but these drugs have certain nephrotoxicity and ototoxicity, so they should be used with caution.
(VI) Nitroimidazoles
Metronidazole and tinidazole are representative drugs. They have strong antibacterial activity against anaerobic bacteria and are widely used in the treatment of oral, abdominal, pelvic and other infections caused by anaerobic bacteria.
II. Principles
for the Use of Antibiotics
(1) Use
after definite diagnosis of bacterial infection A detailed history, physical examination, and necessary laboratory tests, including bacterial cultures and susceptibility tests, should be performed as much as possible before
the use of antimicrobial agents. Antimicrobial agents should be used only when bacterial infection is confirmed or highly suspected. For example, for patients with fever, if it is caused by viral infection (such as common cold, which is mostly caused by rhinovirus), the use of antibiotics is ineffective. For bacterial culture, samples should be collected correctly according to the site of infection, such as blood samples for blood infection and sputum samples for lung infection, so as to improve the positive rate and accuracy of culture.
(2) Selection of
appropriate antibiotics
1. Select
according to the type of pathogenic bacteria and the results of drug sensitivity.
When the results of pathogenic bacteria and drug sensitivity are obtained, sensitive antibiotics should be given priority. For example, if drug sensitivity results show that Streptococcus pneumoniae is sensitive to penicillin, penicillin can be used in the treatment of Streptococcus pneumoniae pneumonia. However, when the pathogenic bacteria are not clear or the results of drug sensitivity are not reported, empirical medication can be used according to the site of infection and the patient’s condition. For example, for community-acquired pneumonia, macrolides or penicillins can be used for young adults without underlying disease; for the elderly or those with underlying disease, respiratory quinolones or second-generation cephalosporins can be used.
2. Consider the distribution
of drugs at the site of infection
Different antibacterial agents have different distribution in the body. For example, in case of brain infection, drugs that can penetrate the blood-brain barrier should be selected. Ceftriaxone and sulfadiazine can reach effective concentration in cerebrospinal fluid. For bone tissue infection, clindamycin and lincomycin have higher concentration in bone tissue. Urinary tract infections can choose drugs that are mainly excreted by the kidney and have high concentrations in the urine, such as nitrofurantoin and quinolones.
3. Combined with individual factors
of patients Factors such as
patient’s age, liver and kidney function, and history of allergy also affect the choice of antimicrobial agents. For children, drugs that affect the growth and development of children should be avoided, such as aminoglycosides and quinolones (except for special circumstances); for the elderly, the liver and kidney function decreases, and the ability of drug metabolism and excretion decreases, the dosage should be adjusted appropriately to avoid the use of nephrotoxic drugs or reduce the dosage. For patients with allergic history, such as those allergic to penicillin, penicillins and cephalosporins with possible cross-allergic reactions should be avoided (careful evaluation is required before use).
(3) Correct dosage and course of treatment
1. Reasonable
dosage The dosage of
antibiotics should be determined according to the drug instructions, patient weight, age, severity of infection and other factors. Too low dose may lead to ineffective treatment, bacteria can not be effectively eliminated, and may induce the emergence of drug-resistant bacteria; too high dose may increase the risk of adverse reactions. For example, when using gentamicin, excessive dosage can aggravate ototoxicity and nephrotoxicity.
2. Sufficient
course of treatment The course of
treatment should be determined according to the type and condition of the infection. In general, for acute infections, such as acute cystitis, antimicrobial agents are used for 3-7 days; for more severe infections such as pneumonia, the course of treatment may take 7-14 days or longer. For severe systemic infections such as sepsis, the course of treatment may last for several weeks. However, the course of treatment should not be too long, otherwise it will increase the chance of drug-resistant bacteria and the incidence of adverse drug reactions.
(4) There should be a basis
for combined use of drugs.
1. Indications
for combined medication If the infection can be controlled by
a single antibiotic, the combination of antibiotics should be avoided as far as possible. Combination of drugs is mainly used for the following conditions: one is severe infection, such as septicemia, infective endocarditis, etc., and a single drug may not be able to effectively control the disease; the other is mixed infection, such as abdominal infection, which is often accompanied by mixed infection of aerobic and anaerobic bacteria, and anti-aerobic and anti-anaerobic drugs can be used in combination; Third, for serious infections with unknown pathogenic bacteria, a combination regimen with a wide range of coverage can be selected according to the possible pathogenic bacteria; fourth, long-term drug use is prone to drug resistance, such as the treatment of tuberculosis, the use of combination drugs to reduce the occurrence of drug resistance.
2. Choose the appropriate combination regimen
. Drug combinations with synergistic or additive effects
should be selected to avoid antagonistic effects. For example, the combination of beta-lactams and aminoglycosides has a synergistic effect on some gram-negative bacilli infections, while the combination of chloramphenicol and penicillin may have an antagonistic effect because chloramphenicol inhibits the bactericidal effect of penicillin. At the same time, attention should be paid to the adverse reactions of drugs when combined with drugs, so as to avoid increasing the severity or incidence of adverse reactions due to combined use.
In a word, the clinical use of antibiotics should strictly follow the principles of use, select and use antibiotics reasonably, in order to improve the therapeutic effect and reduce the occurrence of drug-resistant bacteria and adverse drug reactions.
