Zar FA et al: A comparison of vancomycin and metronidazole for the treatment of Clostridium difficile-associated diarrhea. Clin Infect Dis 2007;45:302.
An intravenous third-generation cephalosporin (ceftriaxone or cefotaxime) with adequate penetration into inflamed meninges that is active against the common bacteria that cause community-acquired pneumonia and meningitis (pneumococcus, meningococcus, Haemophilus) should be ordered. Vancomycin also should be administered until culture and sensitivity results are available in case the patient is infected with a resistant pneumococcus. Although the patient has a history of rash to amoxicillin, the presentation was not consistent with an anaphylactic reaction. The ami-nopenicillins are frequently associated with rashes that are not caused by Type I hypersensitivity. In this instance, cross-reactivity with a cephalosporin is unlikely—particularly with a third-generation drug—and the patient presents with life-threatening illness necessitating appropriate and proven antibiotic coverage.
Tetracyclines, Macrolides, Clindamycin, Chloramphenicol, Streptogramins, & Oxazolidinones
Camille E. Beauduy, PharmD, & Lisa G. Winston, MD motion tenderness is present. A first-catch urine specimen is obtained for chlamydia and gonorrhea nucleic acid amplifi-cation testing. A urine pregnancy test is also ordered as the patient reports she “missed her last period.” Pending these results, the decision is made to treat her presumptively for chlamydial cervicitis. What are two potential treatment options for her possible chlamydial infection? How does her potential pregnancy affect the treatment decision? A 22-year-old woman presents to her college medical clinic complaining of a 2-week history of vaginal discharge. She denies any fever or abdominal pain but does report vaginal bleeding after sexual intercourse. When questioned about her sexual activity, she reports having vaginal intercourse, at times unprotected, with two men in the last 6 months. A pelvic examination is performed and is positive for muco-purulent discharge from the endocervical canal. No cervical
The drugs described in this chapter inhibit bacterial protein synthesis by binding to and interfering with ribosomes. Most are bacteriostatic, but a few are bactericidal against certain organisms. Tetracycline and macrolide resistance is common. Except for tigecycline and the streptogramins, these antibiotics may be administered orally.
All of the tetracyclines have the basic structure shown at right: *There is no OH at position 6 on methacycline and doxycycline.
Free tetracyclines are crystalline amphoteric substances of low solubility. They are available as hydrochlorides, which are more soluble. Such solutions are acidic and fairly stable. Tetracyclines chelate divalent metal ions, which can interfere with their absorption and activity. Tigecycline is a glycylcycline and a semisynthetic derivative of minocycline.
Mechanism of Action & Antimicrobial Activity
Tetracyclines are broad-spectrum bacteriostatic antibiotics that inhibit protein synthesis. Tetracyclines enter microorganisms in part by passive diffusion and in part by an energy-dependent process of active transport. Susceptible organisms concentrate the drug intracellularly. Once inside the cell, tetracyclines bind reversibly to the 30S subunit of the bacterial ribosome, blocking the binding of aminoacyl-tRNA to the acceptor site on the mRNA-ribosome complex (Figure 44–1). This prevents addition of amino acids to the growing peptide.