A Few Antibiotics to Know

Beta-lactams

Our gold-standard class of antibiotics that are extremely effective and very well tolerated

Amoxicillin (PO) and ampicillin (IV) are great against most streptococci, and a few Gram-negatives
Cloxacillin (and oxacillin and others) is great against methicillin-sensitive Staphylococcus aureus (MSSA)
Amoxicillin-clavulanic acid (PO) is broad-spectrum, and works against most Gram-positives and Gram-negatives, as well as some anaerobes
Piperacillin-tazobactam (IV) adds even better anaerobic coverage, as well as anti-pseudomonal activity

Cephalexin (PO) and cefazolin (IV) are first-generation cephalosporins that are fantastic against most Gram-positives, including streptococci and MSSA, as well as many non-resistant Gram-negatives
Ceftriaxone (IV) is worse for Staph. aureus, but maintains excellent streptococcal coverage and improves the Gram-negative coverage significantly
Ceftazidime (IV) is like ceftriaxone but adds anti-pseudomonal activity

Ertapenem (IV) covers essentially everything except MRSA and some very resistant Gram-negatives
Meropenem (IV) adds anti-pseudomonal activity

Broad-spectrum and great oral bioavailability (PO ~= IV), but low barrier to resistance and many side effects
Levofloxacin (PO/IV) and moxifloxacin (PO/IV) cover Gram-positives that includes staph. aureus and Gram-negatives
Ciprofloxacin (PO/IV) has less good Gram-positive coverage but better Gram-negative coverage, including anti-pseudomonal activity

Vancomycin (IV) and daptomycin (IV) work only against Gram-positives, and are reserved for resistant infections such as methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin-resistant Enterococcus (VRE)
- Vancomycin has renal toxicity and possibly ototoxicity
- Daptomycin doesn't work for pneumonia (inactivated by surfactant)
Vancomycin (PO) is not absorbed, and is used only for Clostridium difficile-associated diarrhea
Linezolid (PO/IV) is another antibiotic that treats only Gram-positives, including MRSA

Tobramycin (IV) and gentamicin (IV) are reserved for very resistant Gram-negative infections, and have side effects of renal toxicity and ototoxicity

Septra (TMP-SMX) (PO/IV) has good Gram-negative coverage, including many resistant Gram-negatives, as well as MRSA coverage
Azithromycin (PO) is used for community-acquired pneumonia, covering Strep. pneumoniae and atypicals like Chlamydia, Mycoplasma, and Legionella
Clindamycin (PO/IV) is used for Gram-positives (including MRSA) and oral anaerobes, as well as streptococcal toxic shock syndrome
Doxycycline (PO) is used for weird infections, but also includes MRSA coverage
Metronidazole (PO/IV) treats gut anaerobes and C. difficile