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1、Chapter 27 Tetracyclines and Chloramphenicol【Learning points】1.Tetracyclines 1.1 Classification of tetracycline drugs Natural tetracycline:tetracycline,terramycin,etc.Semi-synthetic tetracycline:doxycycline,minocycline(minocycline),etc.1.2 Antibacterial mechanism It is a quick-acting bacteriostatic
2、medicine.In the cytoplasm,the drug binds to the 30S subunit at the A site,preventing aminoacyl tRNA from entering the A site,inhibiting peptide chain extension and protein synthesis.It can also change the permeability of bacterial cell membrane,lead to the leakage of important substances such as nuc
3、leotides,and inhibit the replication of bacterial DNA.High concentrations also have a bactericidal effect.1.3 Antibacterial spectrum Broad-spectrum antimicrobial agents.The effect on G+bacteria was stronger than that on G-bacteria.It has good effect on mycoplasma pneumoniae,rickettsiae,chlamydia and
4、 so on.To pseudomonas aeruginosa,virus,fungus is invalid.1.4 Clinical application It has special effects on rickettsia,chlamydia,mycoplasma infection and some spirochetes infection.It can be the first choice.For infection caused by G+and G-bacteria,due to the increase of drug-resistant strains,it is
5、 currently only used as one of the first choice drugs for rabbit fever,brucellosis and cholera.It can treat intestinal amoebiasis(amebic dysentery).Among them,oxytetracycline is more effective in this class of drugs,but it is not effective for parenteral amoebiasis.With the increase of drug-resistan
6、t strains,tetracycline is no longer the first choice.Doxycycline is the drug of choice for this class of drugs.1.5 Adverse reactions Local irritation,double infection,affecting bone,tooth growth,other(allergic reactions,liver and kidney function damage),etc.1.6 Doxycycline Features:strong effect,qui
7、ck effect,long-term effect.Oral absorption is fast and complete,and is not easily affected by food.However,it is still affected by antacids or metal ions.Most drugs are excreted from the intestinal cavity.Most of the drugs in the intestine exist in an inactive binding type,rarely causing double infe
8、ction.Only a small amount of drug is excreted by the kidney.The amount of intestinal cavity excretion increases during renal failure,so renal failure can also be used.There is significant hepatointestinal circulation,T1/2 up to 14-22 hours.The antibacterial spectrum is comparable to tetracycline,and
9、 the antibacterial activity is 2-10 times stronger.It is the first choice of tetracycline drugs.It is especially suitable for those with kidney failure and bile duct infection.2.Chloramphenicol 2.1 Internal process The drug is well absorbed and widely distributed orally,and easily penetrates the blo
10、od-brain barrier.It binds to glucuronic acid in the liver and fails.Most of it is discharged from the kidney.2.2 Pharmacological effects Antibacterial mechanism The drug is reversibly bound to the peptide acyltransferase action site on the 50S subunit of the bacterial ribosome,preventing the reactio
11、n between the terminal carboxyl group of the peptide chain on the P position and the amino group of the amino acid tRNA on the A position,thus inhibiting the extension of the peptide chain and protein synthesis.Antibacterial spectrum The drug has a broad spectrum.It can inhibit the growth of bacteri
12、a at low concentration and has a bactericidal effect at high concentration.It has a strong effect on G-bacteria,especially on Typhoid fever,Haemophilus influenzae,and Neisseria meningitidis.It is effective against Rickettsia,Chlamydia trachomatis and Mycoplasma pneumoniae.The antibacterial effect on
13、 G+bacteria is not as good as penicillin and tetracycline.Clinical application a.Systemic application.The drug is generally not preferred,and can be used as a secondary drug for typhoid and paratyphoid fever caused by sensitive bacteria,severe brain infections caused by Haemophilus influenzae,and se
14、vere infections caused by Rickettsia.b.Local application.Treating superficial infections such as eyes and ears caused by sensitive bacteria.Adverse reactions a.Inhibiting bone marrow hematopoietic system Reversible inhibition.Hematopoietic dysfunction,blood cell reduction,which is related to the dose and course of treatment,can be restored after withdrawal.Irreversible inhibition.Aplastic anemia,which has nothing to do with the dose and duration of treatment,has a high mortality rate.b.Grey infant syndrome c.Others.Allergic reactions,optic neuritis,gastrointestinal reactions,etc