Bugs and Drugs

I have a long ways to go until I can say I feel comfortable with ID. But as a start...

Infectious
Penacillins need to be adjusted for renal deficiency (NO renal adjustment for NO ~nafcillin and oxacillin). These are time-dependent drugs, meaning the effect of the antibiotic will depend on how long the concentration in your body is above the MIC.

• Antistaph penicillins are: nafcillin, oxacillin, dicloxacillin
• DOC for enterococcus: aminopenicillins 
• Pip/tazo covers pseudomonas and acinetobacter but amp/sulbactam does not. 

Cephalosporins need to be adjusted for renal deficiency (except for ceftriaxone), and are time-dependent drugs as well. They are also bacteriocidal. As you move up in generation, you move up in gram negative coverage and down in gram positive coverage.

• First generation: cefazolin and cephalexin
• Second generation: cefoxitin (IV), cefuroxime (PO and good e. coli coverage)
• Third generation: cefpodoxime (PO), ceftriaxone (IV and no pseudomonas coverage), ceftazadime (IV and yes pseudomonas coverage)
• Fourth generation: cefepime (covers pseudomonas and acinetobacter)
• Fifth generation: ceftobiprole (covers MRSA*** and pseudomonas)

Vancomycin covers gram positive, and is DOC for MRSA. It's a 'cidal drug, and is renally eliminated. The loading dose is 15-25mg/kg actual body weight, and maintenance is determined with CrCl.

Carbapenems are 'cidal antibiotics as well.

• Ertapenem does not cover pseudomonas
• Imipenem (AKA Seizurpenem), meropenem, doripenem DO! 
• If a patient has a history of seizures and has poor kidney function, then don't give imipenem.

Aztreonam only covers Gram negative!!
Linezolid only covers Gram positive!! This includes VRE and MRSA, and oddly, its PO bioavailability is greater than its IV bioavailability. Oh, and don't give this drug with an SSRI.

Daptomycin is a 'cidal and concentration-dependent drug.

• Covers MRSA and VRE
• Doesn't work in lung infections like pneumonia, since pulmonary surfactants inactivate it. 

Polymyxins

• Usually reserved for multi drug resistant gram negatives 
• Examples polymyxin B and E

Macrolides cover atypicals

• Clarithromycin is good for H. pylori
• Azithromycin is good for pneumonia, including S. pneumonia 

Clindamycin is the biggest cause of drug-induced C.dif

Tetracyclines cover atypicals as well

• Atypicals = chlamydia, mycoplasma, and legionella 
• Demecocycline is best for SIADH (Syndrome of Inappropriate Secretion of Antidiuretic Hormone)
• Tigecycline does not cover pseudomonas 

Bactrim

• Covers gram positive and negative, MRSA. 
• There's 5x more sulfamethoxazole than trimethoprim in dosage forms 

Aminoglycosides

• Have a post antibiotic effect - it doesn't mean the drug will keep killing the bugs after the medication is stopped...what it means is that there won't be any more growth of the bug.
• Nephrotoxic side effects are reversible, but ototoxic side effects are irreversible. 

Metronidazole cover anaerobes!!

Fluoroquinolones are 'cidal

• Moxifloxacin and levofloxacin are respiratory quinolones, and do cover strep pneumonia. They don't cover pseudomonas.
• Ciprofloxacin is not a respiratory quinolone, doesn't cover strep pneumonia. It does cover pseudomonas.
• If the QTc > 500 when on these drugs, then action needs to be taken.

As a general rule, if an antibiotic works on the cell wall, then it's bacteriocidal. If it works on protein synthesis, then it's bacteriostatic. The exception is aminoglycosides - they work on protein synthesis, and are bacteriocidal! This was a very basic overview of antibiotics. I needed a basic review, since I feel like I forgot almost everything from second year ID, so my preceptor gave a presentation that he had prepared for a talk a while ago :).