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Compared with most other cephalosporins, which antibiotics are associated with a higher incidence of a particularly dangerous adverse response for some patients?
Which antimicrobial drug or drug class is most likely chelated by calcium in milk, leading to reduced oral bioavailability when taken together?
Which drug is the preferred agent for therapy of antibiotic-associated pseudomembranous colitis caused by C. difficile infection?
How does amoxicillin differ from ampicillin?
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Which drug should be avoided in a patient with severe penicillin allergy due to potential cross-reactivity?
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A patient on antimicrobial therapy develops cough, dyspnea, pulmonary infiltrates, neutropenia, bleeding tendencies, and paresthesias. Which of the following is the most likely cause of these symptoms?
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What is the mechanism by which sulfamethoxazole (SMZ) and trimethoprim (TMP) combination exerts its effects against Pneumocystis carinii?
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What is the unique unwanted side effect of Ticarcillin among all penicillins?
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Which antibiotic is most likely responsible for the patient becoming flushed while receiving a prophylactic dose before heart valve surgery?
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What is the most likely cause of antibiotic-associated pseudomembranous colitis?
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What is the main reason for including ethambutol in the treatment of a patient with active tuberculosis alongside isoniazid?
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Why is the first-year house officer's choice of gentamicin doomed to fail in treating a severe infection caused by anaerobic bacteria?
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In patients with hepatic coma or portal-systemic encephalopathy, which antibiotic is the antibiotic of choice to decrease the production and absorption of ammonia from the gastrointestinal tract?
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In treating vancomycin-resistant enterococcal infection, which antibiotic is most likely associated with a clinical picture of significant spike in blood pressure, leading to a pounding headache and bone marrow suppression?
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Which antibiotic commonly used to treat tuberculosis induces some of the microsomal cytochrome P450 enzymes in the liver?
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Which quinolone is the most effective choice against Pseudomonas aeruginosa?
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In a patient with an anaphylactoid reaction to oral penicillin and cephalosporin, which antibiotic would be the best choice for treating the infection with the least risk of cross-reactivity and an allergic response?
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Study Notes
Anti-Infectives
Antibacterials
- Antibacterials include antimicrobials, antivirals, antifungals, and antiparasitics
- Examples of antibacterials:
- Antibacterials: Penicillins, Cephalosporins, Macrolides, Aminoglycosides, Tetracyclines, Sulfonamides, Fluoroquinolones
- Antimycobacterials: Isoniazid
- Antivirals: Acyclovir, Zidovudine
- Antifungals: Amphotericin B, Fluconazole
- Antiprotozoals: Metronidazole, Pentamidine
Antibiotic-Associated Adverse Effects
- Examples of antibiotic-associated adverse effects:
- Allergic reactions: Penicillins, Cephalosporins
- Nephrotoxicity: Aminoglycosides, Cephalosporins
- Hepatotoxicity: Tetracyclines
- Pseudomembranous colitis: Clindamycin
- Ototoxicity: Aminoglycosides
- Bone marrow suppression: Chloramphenicol
Mechanisms of Antibacterial Action
- Inhibition of cell wall synthesis: Penicillins, Cephalosporins
- Inhibition of protein synthesis: Tetracyclines, Aminoglycosides
- Inhibition of DNA replication: Fluoroquinolones
- Inhibition of folic acid synthesis: Sulfonamides
- Disruption of cell membrane: Polymyxins
Drug Interactions
- Examples of drug interactions:
- Induction of hepatic microsomal enzymes: Rifampin
- Inhibition of protein synthesis: Tetracyclines
- Displacement of other drugs from plasma protein-binding sites: Cephalosporins
Specific Antibiotics
Penicillins
- Examples of penicillins:
- Narrow-spectrum: Penicillin G, Penicillin V
- Broad-spectrum: Ampicillin, Amoxicillin
- Penicillinase-resistant: Methicillin, Nafcillin
- Antipseudomonal: Piperacillin, Ticarcillin
Cephalosporins
- Examples of cephalosporins:
- First-generation: Cephalexin, Cephalothin
- Second-generation: Cefaclor, Cefuroxime
- Third-generation: Cefotaxime, Ceftazidime
- Fourth-generation: Cefepime, Cefpirome
Aminoglycosides
- Examples of aminoglycosides:
- Gentamicin, Tobramycin, Amikacin
- Streptomycin
Macrolides
- Examples of macrolides:
- Erythromycin, Clarithromycin, Azithromycin
Fluoroquinolones
- Examples of fluoroquinolones:
- Ciprofloxacin, Ofloxacin, Levofloxacin
Tetracyclines
- Examples of tetracyclines:
- Tetracycline, Doxycycline, Minocycline
Sulfonamides
- Examples of sulfonamides:
- Sulfamethoxazole, Trimethoprim-sulfamethoxazole
Antivirals
- Examples of antivirals:
- Acyclovir, Zidovudine, Didanosine
Antifungals
- Examples of antifungals:
- Amphotericin B, Fluconazole, Itraconazole
Antiprotozoals
- Examples of antiprotozoals:
- Metronidazole, Pentamidine### Aminoglycosides
- In the perioperative setting, having an aminoglycoside "on board" may increase the risk of prolonged response to neuromuscular blockers.
- Aminoglycosides are effective against Rickettsia, Mycoplasma, and Chlamydia infections, and are also used to treat acne vulgaris lesions.
Isoniazid (INH)
- INH is used to treat tuberculosis (TB) as part of a multidrug regimen.
- Vitamin B6 is given prophylactically to prevent some adverse effects of INH therapy.
Rifampin
- Rifampin is used to treat tuberculosis (TB) and may induce the metabolism of theophylline, leading to loss of asthma control and onset of asthma signs and symptoms.
- Rifampin may also reduce the efficacy of oral contraceptives.
Antibiotics for Specific Infections
- Legionella: Erythromycin or azithromycin are the drugs of choice.
- Mycobacterium tuberculosis: Streptomycin is often used in combination with other antibiotics.
- Pseudomonas and Enterobacter species: Clavulanic acid, sulbactam, or tazobactam are added to some penicillin combination products to inhibit β-lactamase-producing bacteria.
- Anaerobic bacteria: Gentamicin is not effective against anaerobes because it requires oxygen to be active.
- Vancomycin-resistant enterococcal infections: Linezolid may be used to treat these infections.
Other Antibiotics
- Tetracycline is effective against Rickettsia, Mycoplasma, and Chlamydia infections, as well as acne vulgaris lesions.
- Rifampin is associated with the fewest problems with resistance or typical aminoglycoside-induced adverse effects among the aminoglycosides.
- Clavulanic acid, sulbactam, or tazobactam are added to some penicillin combination products to inhibit β-lactamase-producing bacteria.
- Neomycin may be used to decrease the production and absorption of ammonia from the gastrointestinal tract in patients with hepatic coma.
Drug Interactions
- Rifampin may induce the metabolism of oral contraceptives, reducing their efficacy.
- Rifampin may also induce the metabolism of theophylline, leading to loss of asthma control and onset of asthma signs and symptoms.
- Gentamicin is not effective against anaerobes because it requires oxygen to be active.
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