Table 1.
Pharmacokinetic properties of major antibiotic classes
| Antibiotic | Mechanism of Action | Targeted Microbes | Special Considerations |
|---|---|---|---|
| Penicillins (β-lactam) | BACTERICIDAL: Inhibit cell-wall synthesis, exposing unstable membranes, leading to cell lysis | Gram-positive, some gram-negative coverage | |
| β-Lactamase inhibitor (clavulanate, sulbactam, tazobactam) | Augment utility of β-lactam-ring–based antibiotics by inhibiting enzymatic breakdown | Extends spectrum of many penicillins to target resistant organisms and more gram-negative coverage | |
| Cephalosporins (β-lactam) | BACTERICIDAL: Inhibit cell-wall synthesis, exposing unstable membranes, leading to cell lysis, but less susceptible to β-lactamase | Some of the less commonly used inhibit vitamin K production and cause disulfiram-like reaction (eg, cefotetan) | |
| First generation (cephalexin, cefazolin) | Gram-positive cocci, gram-negative bacilli (Proteus, Escherichia coli, Klebsiella) | ||
| Second generation (cefaclor, cefuroxime, cefotetan, cefoxitin) | Gram-positive cocci, gram-negative cocci (Neisseria gonorrhoeae), gram-negative bacilli (Enterobacter, E coli, Haemophilus influenzae, Klebsiella, Proteus) | ||
| Third generation (cefdinir, cefixime, cefotaxime, cefpodoxime, ceftriaxone, ceftazidime) | Broader gram-negative coverage (Pseudomonas covered by ceftazidime) | Ceftriaxone is excreted in bile | |
| Fourth generation (cefepime) | Staphylococci, streptococci, and gram-negative bacilli (including Pseudomonas) | ||
| Fifth generation (ceftaroline) | Gram-positive cocci, gram-negative bacilli, MRSA (only SSTI) | ||
| Carbapenems (meropenem, imipenem, ertapenem, doripenem) | BACTERICIDAL: Inhibit cell-wall synthesis, exposing unstable membranes, leading to cell lysis, but less susceptible to β-lactamase | Penicillinase gram-positive and gram-negative organisms, anaerobes, and Pseudomonas | |
| Monobactams (aztreonam) | BACTERICIDAL: Inhibit cell-wall synthesis, exposing unstable membranes, leading to cell lysis but less susceptible to β-lactamase | Gram-negative only, including pseudomonas | Should be reserved for identified resistance; limit empiric use. |
| Vancomycin | BACTERICIDAL: Inhibit cell-wall synthesis, exposing unstable membranes, leading to cell lysis but less susceptible to β-lactamase | Gram-positive, including MRSA and enterococci | Oral use reserved for Clostridium difficile infection only Very broad coverage when combined with aminoglycoside Administer 1 g/h to prevent red man syndrome |
| Tetracyclines (doxycycline, minocycline) | BACTERIOSTATIC: Inhibit protein synthesis by reversibly binding ribosomes blocking tRNA | Gram-positive and some gram-negative; atypical or intracellular organisms (such as Chlamydia, Mycoplasma, and tick-borne disease) | Substantial bacterial resistance TERATOGENIC: causes discoloration and hypoplasia of bones and teeth, fetal hepatotoxicity |
| Aminoglycosides (amikacin, gentamicin, tobramycin, streptomycin) | BACTERICIDAL (based on concentration and dosing intervals): Inhibit protein synthesis by binding to ribosome subunit, preventing full ribosome assembly | Gram-negative (includes Pseudomonas) | Activity augmented when preceded by a penicillin |
| Macrolides (erythromycin, clarithromycin, azithromycin, telithromycin) | BACTERIOSTATIC: Inhibit protein synthesis by irreversibly binding ribosomes, preventing translocation | Atypical or intracellular organisms (such as Chlamydia, Legionella, Mycoplasma) | |
| Clindamycin | BACTERIOSTATIC: Inhibit protein synthesis by binding ribosomes, preventing translocation | Gram-positive (including MRSA), anaerobic bacteria | Most frequent culprit of C difficile infection Used for toxin-producing infections such as toxic shock syndrome |
| Linezolid | BACTERIOSTATIC: Inhibit protein synthesis by preventing full ribosome complex formation (bactericidal against certain organisms) | Gram-positive (MRSA, VRE, Listeria) | |
| Fluoroquinolones (levofloxacin, moxifloxacin, ciprofloxacin) | BACTERICIDAL (dose dependent): Inhibit DNA gyrase and topoisomerase, preventing DNA replication causing cell death, and blocks cell division by not allowing new DNA to segregate | Gram-negative (some Pseudomonas), gram-positive (no MRSA) and atypical organisms | TERATOGENIC: affects connective tissue development |
| Sulfonamides (trimethoprim-sulfamethoxazole) | BACTERIOSTATIC: Inhibit synthesis of bacterial folic acid preventing formation of essential cofactors | Gram-positive (MRSA), limited gram-negative | Severe hypersensitivities including SJS Can elicit hemolytic anemia in patients with G6PD |
| Metronidazole | BACTERICIDAL: forms unstable molecules within DNA | Anaerobic bacteria and protozoa | Biliary excretion allows it to be effective against C difficile |
Abbreviations: G6PD, glucose-6-phosphate dehydrogenase; MRSA, methicillin-resistant Staphylococcus aureus; SJS, Stevens-Johnson syndrome; VRE, vancomycin-resistant enterococci.