Antimicrobial Pharmacology - NCLEX-PN

Fluoroquinolones (the most commonly prescribed of which is ciprofloxacin) carry a risk of all of the following adverse effects: sudden tendon rupture or tendonitis, hepatotoxicity or liver failure, seizures, and permanent peripheral neuropathy. Other adverse effects include C_lostridium difficile_ associated diarrhea, bone marrow suppression, Steven-Johnson's Syndrome, tremors, and psychosis. The majority of these adverse effects are seen in higher numbers in children and the elderly.

Tetracycline antibiotics are contraindicated in pregnant women and small children due to their tendency to irreversibly stain developing teeth. They can also affect fetal bone growth and so are pregnancy category D (known incidence and risk of fetal harm).

Of the antibiotics listed, amoxicillin is the only one considered safe in pregnancy. Doxycycline and gentamicin are both pregnancy category D (known to cause fetal harm). Levofloxacin is category C (fetal harm can not be ruled out).

All of the drugs listed frequently cause C_. difficile_ overgrowth and C_. difficile_ associated diarrhea except vancomycin, which is often used as a treatment for persistent C_. difficile_ infections.

Penicillins belong to a larger class of antibiotics known as beta-lactams. These antibiotics inhibit cell-wall synthesis and are exclusively used to treat Gram positive bacteria. They are not effective against Gram negative bacteria or fungi.

Fluoroquinolones are considered to be the treatment of choice for E . coli infections due to their effectiveness in relieving diarrhea and minimal serious adverse effects. Aminoglycosides and beta-lactam antibiotics may also be effective, as a second choice.

Gentamycin, an antibiotic and aminoglycoside, inhibits protein synthesis of gram-negative bacteria. It treats severe systemic infections. It may cause ototoxicity and nephrotoxicity, as well as anorexia, nausea, vomiting, and diarrhea. Diaphoresis is not a common side effect of gentamycin.

The correct answer is "inhibition of topoisomerase II," as this is the mechanism of action of fluoroquinolone antibiotics, such as levofloxacin.

The other choices are incorrect for the following reasons:

Blockage of tRNA-ribosome-mRNA complex binding is the mechanism of action of tetracycline antibiotics.

Disruption of mycolic acid synthesis is the mechanism of action of various anti-fungal agents.

Disruption of peptidoglycan cross-linkage is the mechanism of action of vancomycin.

Inhibition of peptidoglycan synthesis is the mechanism of action of beta-lactam antibiotics.

Acyclovir is converted to acyclovir-triphosphate and incorporated into the synthetic pathway for viral DNA as a guanosine molecule. The initial phosphorylation of acyclovir is carried out by viral thymidine kinase. Acyclovir has a higher affinity for viral thymidine kinase than mammalian thymidine kinase. Therefore, acyclovir is specifically effective in virally infected cells.

All of the drugs are antifungal agents but only flucytosine has been associated with bone marrow suppression and synergizes with other drugs which suppress bone marrow functions. Miconazole and ketoconazole may produce hepatotoxicity, gastro-intestinal upset and headaches. Amphotericin B may produce nephrotoxicity while itraconazole is associated with gastro-intestinal upset and rare liver dysfunction.

Amantadine only works after viral attachment to the cell, preventing viral uncoating. It is also believed to interfere with viral mRNA production. Amantadine is effective against influenza virus A.

All the listed agents are synthetic analogues, except interferon, which is a glycoprotein produced by many types of mammalian cells. It has been shown to be useful in treatment of hepatitis, papilloma viruses, hairy-cell leukemia and AIDS-related Kaposi's sarcoma. Idoxuridine, as its name implies, is a synthetic pyrimidine analog, which inhibits viral DNA polymerase. Zidovudine and zalcitabine are also synthetic pyrimidine analogs but they inhibit reverse transcriptase and act as chain terminators. Acyclovir is a synthetic purine analog which requires viral thymidine kinase to be converted to an active phosphorylated form, which then, inhibits viral DNA polymerase.

Loa loa is an extra-intestinal nematode, which may migrate to the CNS, causing encephalitis. Diethylcarbamazine is successful in treating Loa loa but will exacerbate the encephalitis unless steroids are used first to treat the symptoms of the encephalitis. Other side effects of diethylcarbamazine may be due to rapid death of nematodes and release of various toxic substances. Symptomatic treatment might be appropriate with a number of pharmacological classes, but most symptoms will resolve as the body is cleared of dead and dying nematodes.

Amantadine affects the central nervous system, producing mild, reversible disturbances. High dosages have been reported to induce seizures

Amoxicillin inhibits bacterial cell wall synthesis by interfering with the formation of cross-links between peptidoglycan polymer chains.

Macrolides, streptogramins, and clindamycin all work by inhibition of the 50S subunit of bacterial ribosomes. Tetracyclines have a similar mechanism of action, but instead affect the 30S unit of bacterial ribosomes.

Polymyxin antibiotics function by interfering with phospholipid function in bacterial cell membranes. After binding to lipopolysaccharide (LPS) in the outer membrane, polymyxins' hydrophobic tail causes damage to both the inner and outer membranes of Gram-negative bacteria.

Rifampin inhibits bacterial RNA synthesis by inhibiting RNA polymerase. This prevents the transcription of proteins within the bacterial cell, leading to cell death.

Hepatotoxicity and potential liver failure are the most serious potential adverse effects of rifampin use. Patients on this medication must establish baseline liver function tests and be monitored for liver damage. None of the other conditions listed are associated with rifampin use.