Choosing the Appropriate Antibiotic

CHOOSING ANTIBIOTICS

There are some general guidelines that can be used in determining the appropriate antibiotic.

Penicillins act against gram- positive and

gram- negative bacilli. The gram- positive bacilli are Bacillus anthracis, Clostridium perfringens, or Clostridium tetani. There are many penicillinase-resistant penicillins, and these agents are oxacillin, nafcillin, and dicloxacillin. Its spectrum of activity is for methicillin- sensitive Staphylococcus aureus (MSSA). It is active against most streptococci but has no gram- negative or anaerobic activity. 

The β- lactam and β- lactamase inhibitor combinations are commonly used. They have a good anaerobic activity and increased activity against β- lactamase- producing organisms such as MSSA. It is not active against methicillin- resistant Staphylococcus aureus (MRSA) or penicillin-resistant Streptococcus pneumoniae.

Сephalosporins are mostly used. Cefepime is very active against Pseudomonas aeruginosa, has an improved gram- positive activity toward Staphylococcus aureus and pneumococci, is less likely to induce β- lactamase of Enterobacter species, and has very good CNS penetration.

The fluoroquinolones include ciprofloxacin and levofloxacin. These drugs have an excellent tissue penetration with high enteric absorption. It is most active against aerobic gram- negative bacteria including the Enterobacteriaceae and active against Pseudomonas aeruginosa. It is not reliable against streptococci such as Streptococcus pneumoniae.


Vancomycin is the drug of choice for multipleresistant gram- positive organisms. Vancomycin has significant toxicity that includes infusionrelated pruritus and erythematous rash involving face, neck, and upper body, producing a “red man” syndrome.

Linezolid has excellent tissue- distribution but has significant adverse effects that include thrombocytopenia, anemia, and long- term peripheral. It is primarily used to treat MRSA and VRE.

Tigecycline is a new agent derived from minocycline and is active against many gram- positive, gram- negative, aerobic, and atypical species. It is very important to note that it is inactive against Pseudomonas aeruginosa.

READ ALSO: Cephalosporin antibiotics, classification and using.



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