TETRACYCLIN

CLASSIFICATION OF BROAD SPECTRUM ANTIBIOTIC:
  • Short acting:
  1. Tetracycline
  2. Oxytetracycline
  • Intermediate acting
  1. Demeclocyclin
  2. Lymecyclin
  • Long acting
  1. Doxycyclin
  2. Minocyclin
MECHANISM OF ACTION:
  • They are mainly bacteriostatic. 
  • Act by binding to 30 S ribosome of susceptible organism which interferes with attachment of t-RNA to acceptor site of mRNA. 
  • Due to this peptide chain fails to grow and thus protein synthesis is inhibited
  • Carrier involved in the active transport of tetracyclines is absent in host mammalian cells.
  • They also do not bind to mammalian 40 S or 60 S ribosomal units. 
  • Thus, the protein synthesizing apparatus of host cell is less susceptible to tetracyclines.
  • Due to these, tetracyclines are selectively toxic to the microbes and not to the host
RESISTANCE:
  • Develops by 4 main mechanisms:
  1. ↓ cell permeability of drug 
  2. ↑ drug efflux from bacterial cell 
  3. Ribosomal protection 
  4. Enzymatic inactivation of drug 
  • Incomplete cross resistance seen among different members of this group. 
  • Partial cross resistance exists between tetracyclines and chloramphenicol.
PHARMACOKINETICS:
  • Variably absorbed from the GIT . 
  • Food ↓ absorption of all tetracyclines except doxycycline & minocycline. 
  • Tetracyclines have “chelating property”; form complexes with dairy products (milk, curd), Ca++, Mg++, Al+++(antacids), Fe++ (iron preparations)
  • These decrease bioavailability of tetracyclines so co administration should be best avoided. 
  • Rate of newly synthesized osteoid mineralization can be best estimated by Tetracycline 
  • Tetracycline ointment for mass prophylaxis 0.1%
USES:
  • As First Choice Drugs: 
  1. Venereal diseases like Chlamydial non-specific urethritis, Lymphogranuloma venereum and Granuloma Inguinale.
  2. Atypical pneumonia (Mycoplasmal and Chlamydial), Psittacosis, Relapsing fever. 
  3. Rhinoscleromatosis 
  4. Trachoma 
  5. Cholera (limit stool volume), Brucellosis, Plague (bubonic & pneumonic), Lyme disease 
  6. Rickettsial infections( typhus, Q fever etc)
  • Second Choice Drugs:
  1. To penincillin for anthrax, tetanus, Listeria and Leptospirosis 
  2. Ceftriaxone/azithromycin for gonorrhoea. 
  3. To ceftriaxone in syphilis for penicillin allergic patients.
  4. To Streptomycin for Tularemia 
  5. To ceftriaxone/azithromycin for chancroid 
  • Miscellaneous Other Uses:
  1. UTI where organism tests sensitive. 
  2. Community acquired pneumonia where a more selective agent cant be used. 
  3. Amoebiasis along with metronidazole. 
  4. As adjuvant to quinine or artesunate in chloroquine resistant P. falciparum malaria.
  5. Acne (P. acnes is sensitive to tetracyclines). 
  6. H. pylori induced peptic ulcer where these are used as adjuvants. 
  7. Prophylaxis of traveller’s diarrhea 24
ADVERSE EFFECT:
  • Oral administration can cause N,V,D epigastric burning, stomatitis. 
  • Chronic use can cause fungal esophagitis. 
  • If given after first trimester of pregnancy or in children below 10 yrs, staining of both permanent and deciduous teeth & retardation of bone growth may occur. 
  • Hepatotoxicity may occur rarely, esp. in pregnant women 
  • Tetracyclines are known to have teratogenic effects. 
  • Consumption of Tetracycline during pregnancy may cause dental enamel dysplasia and bony deformities in the child.
  • Tetracycline injection causes palsy of radial nerve
  • Tetracycline causes Pseudotumour cerebri 
Exam Question
  • Tetracyclines are known to have teratogenic effects. 
  • Tetracyclines inhibits protein synthesis by binding to 30S ribosomal subunit, and prevents the attachment of aminoacyl tRNA to the mRNA – ribosome complex.
  • Tetracycline is the drug of choice for chemoprophylaxis of cholera.
  • Drug of choice in rhinoscleromatosis is Tetracycline 
  • Fatty change in liver is seen with use of Tetracycline
  • Rate of newly synthesized osteoid mineralization can be best estimated by Tetracycline 
  • Tetracycline injection causes palsy of radial nerve
  • Tetracycline causes Pseudotumour cerebri 
  • Treatment of granuloma inguinale is Tetracycline 
  • The drug of choice for chemoprophylaxis in contacts of a patient of penumonic plague is Tetracycline 
  • Drug of choice of trachoma is Tetracycline 
  • Tetracycline ointment for mass prophylaxis 0.1%
  • Drug of choice for lymphogranuloma venerum is Tetracycline
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