TETRACYCLINE
TETRACYCLINE
CLASSIFICATION:
- Short-acting:
- Tetracycline
- Oxytetracycline
- Intermediate-acting
- Demeclocycline
- Lymecycline
- Long-acting
- Doxycyclin
- Minocycline
MECHANISM OF ACTION:
- They are mainly bacteriostatic.
- Act by binding to 30 S ribosome of susceptible organism interfering with t-RNA attachment to mRNA acceptor site.
- Due to this peptide chain fails to grow & thus protein synthesis is inhibited
- Carrier involved in 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 protein-synthesizing apparatus of host cell is less susceptible to tetracyclines.
- Hence, are selectively toxic to microbes & not to host
PHARMACOKINETICS:
- Variably absorbed from GIT.
- Food ↓ absorption of all tetracyclines except doxycycline & minocycline.
- Have “chelating property”
- Form complexes with dairy products (milk, curd), Ca++, Mg++, Al+++(antacids), Fe++ (iron preparations)
- Hence decreases tetracyclines bioavailability.
- Thus, avoid coadministration.
- Rate of newly synthesized osteoid mineralization can be best estimated by Tetracycline.
- Ointment for mass prophylaxis 0.1%
USES:
As First Choice Drugs:
RESISTANCE:
- Venereal diseases like Chlamydial non-specific urethritis, Lymphogranuloma venereum and Granuloma Inguinale.
- Atypical pneumonia (Mycoplasmal and Chlamydial), Psittacosis, Relapsing fever.
- Rhinoscleromatosis
- Trachoma
- Cholera (limit stool volume), Brucellosis, Plague (bubonic & pneumonic), Lyme disease
- Rickettsial infections( typhus, Q fever etc)
Second Choice Drugs:
- To penicillin for anthrax, tetanus, Listeria & Leptospirosis.
- Ceftriaxone/azithromycin for gonorrhoea.
- To ceftriaxone in syphilis for penicillin-allergic patients.
- To Streptomycin for Tularemia.
- To ceftriaxone/azithromycin for chancroid.
- UTI where organism tests sensitive.
- Community-acquired pneumonia where a more selective agent can’t be used.
- Amoebiasis along with metronidazole.
- As adjuvant to quinine or artesunate in chloroquine resistant P. falciparum malaria.
- Acne (P. acnes sensitive to tetracyclines).
- H. pylori-induced peptic ulcer where these are used as adjuvants.
- Prophylaxis of traveller’s diarrhoea.
ADVERSE EFFECT:
- Oral administration causes nausea, vomiting, diarrhoea, epigastric burning & stomatitis.
- Chronic use can cause fungal esophagitis.
- Hepatotoxicity may occur rarely, esp. in pregnant women.
- Known to have teratogenic effects.
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- Tetracycline consumption during pregnancy causes dental enamel dysplasia & bony deformities in child.
- If given after first trimester of pregnancy or in children below 10 yrs, staining of both permanent & deciduous teeth & retardation of bone growth may occur.
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- Injection causes palsy of radial nerve
- Causes Pseudotumour cerebri.
RESISTANCE:
- Develops by 4 main mechanisms:
- ↓ cell permeability of drug
- ↑ drug efflux from bacterial cell
- Ribosomal protection
- Enzymatic inactivation of drug
- Incomplete cross resistance seen among different members of this group.
- Partial cross-resistance exists between tetracyclines and chloramphenicol.
Exam Important
- 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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