• Metabolism: Not metabolized Route of Elimination: They are concentrated by the liver in the bile and excreted in the urine and feces at high concentrations in a biologically active form. Half Life: 6-12 hours
• Uses/Sources: Used to treat bacterial infections such as Rocky Mountain spotted fever, typhus fever, tick fevers, Q fever, rickettsialpox and Brill-Zinsser disease. May be used to treat infections caused by Chlamydiae spp., B. burgdorferi (Lyme disease), and upper respiratory infections caused by typical (S. pneumoniae, H. influenzae, and M. catarrhalis) and atypical organisms (C. pneumoniae, M. pneumoniae, L. pneumophila). May also be used to treat acne. Tetracycline may be an alternative drug for people who are allergic to penicillin.
• Health Effects: Side effects from normal doses of tetracyclines are relatively minimal, but of particular note is phototoxicity. Tetracylclines increase the risk of sunburn under exposure to light from the sun or other sources. Tetracyclines may also cause stomach or bowel upsets, and, on rare occasions, allergic reactions. Very rarely, severe headache and vision problems may be signs of dangerous secondary intracranial hypertension, also known as pseudotumor cerebri. Tetracyclines are teratogens and cause tooth discolouration and poor tooth mineralization in the fetus as they develop in infancy. Symptoms of tetracycline overdose include anorexia, nausea, diarrhea, glossitis, dysphagia, enterocolitis and inflammatory lesions, skin reactions such as maculopapular and erythematous rashes, exfoliative dermatitis, photosensitivity, hypersensitivity reactions such as urticaria, angioneurotic oedema, anaphylaxis, anaphyl-actoid purpura, pericarditis, and exacerbation of systemic lupus erythematosus, benign intracranial hypertension in adults disappearing on discontinuation of the medicine, haematologic abnormalities such as haemolytic anaemia, thrombocytopenia, neutropenia, and eosinophilia.
• Treatment: Drug therapy is discontinued immediately; exchange transfusion may be required to remove the drug. Sometimes, phenobarbital (UGT induction) is used.
• Route of Exposure: Bioavailability is less than 40% when administered via intramuscular injection, 100% intravenously, and 60-80% orally (fasting adults). Food and/or milk reduce GI absorption of oral preparations of tetracycline by 50% or more.

• Carcinogenicity: No indication of carcinogenicity to humans (not listed by IARC).
• Toxicity: LD50=808mg/kg (orally in mice)

Tetracyclines target the 28S small subunit of the mitochondrial ribosome thereby deactivation mitochondrial protein synthesis. As a result tetracyclines are cytotoxic to the most metabolically active cells or tissues including the heart, liver, thymus and bone-marrow. (A7823). The likely target of most tetracyclines is the 12S rRNA molecule in the mitochondrial ribosome, which is analogous to the 16S rRNA in bacterial ribosomes.