Tetracyclines

Administered PO (most common), IV (fewer side effects), IM (rare, painful), topically (eyes only).

Original broad-spectrum antibiotic with activity against gram-positive and gram-negative bacteria; species of Chlamydia, Rickettsia, and Mycoplasma (in adults); some protozoa. One of few agents active against organisms without cell walls. Resistance is increasing worldwide.

Secondary uses: Alternative drugs in the treatment of syphilis, treatment of respiratory infections caused by susceptible organisms, prophylaxis against infection in chronic bronchitis, treatment of leptospirosis, and in the treatment of acne.

Selective uses:

• Tetracycline for treatment of GI ulcers caused by Helicobacter pylori

• Doxycycline for Lyme disease, prevention of malaria, and treatment of amebiasis

• Minocycline for meningococcal carriers

• Demeclocycline for management of pts with ADH-secreting tumors

Usage in USA is about 20 million doses per y.

IV tetracycline frequently leads to thrombophlebitis, lessens efficacy of oral contraceptives.

Decrease dose with age.

Decrease dose in those with poor renal/hepatic function, because tetracycline accumulates in such pts and can lead to hepatic toxicity (instead, in pts with renal dysfunction, use doxycycline, which has an unchanged elimination half-life in such pts).

Barbiturates may lower the half-life β ; tetracycline will increase cone of digoxin or warfarin. Pts may exhibit GI distress, even Clostridium difficile colitis.

Tetracycline (especially first-generation) is absorbed poorly if given within 3 h of divalent or trivalent cations (Ca ²⁺ , Al ³⁺ , Mg ²⁺ , Fe ²⁺ , Bi ³⁺ ).

Possibility of tetracycline-resistant bacterial enteritis as well as GI distress limits the oral doses of these antibiotics.

Doxycycline should be administered only PO or IV.