Antibiotics

Amoxicillin

Rapid Review

  • Mechanism of Action: Beta-lactam antibiotic; inhibits bacterial cell wall synthesis.
  • Indications: Typically used for otitis media, strep pharyngitis, sinusitis, and community acquired pneumonia. 
  • Contraindications: allergy to class/drug
  • Dosage: General: 500 – 1000 mg q12h x 10 days 
  • Half-Life: 30 – 90 minutes
  • Adverse Reactions: Common reactions: nausea, vomiting, diarrhea, rash. Serious reactions: anaphylaxis, SJS/TEN, hypersensitivity vasculitis.
  • Special Considerations: N/A

Pearls

  • High-dose amoxicillin (90mg/kg/day) is required when treating pediatric patients with community-acquired pneumonia, sinusitis, or otitis media
  • Amoxicillin can cause a skin rash if mistakenly given to patients with mononucleosis (Epstein-Barr virus) instead of strep pharyngitis.
Video Credit: JJ Medicine

Azithromycin

Rapid Review

  • Mechanism of Action: Macrolide antibiotic; 
  • Indications: community-acquired pneumonia, sinusitis, pharyngitis, COPD exacerbations, and genital infections.
  • Contraindications: allergy/hypersensitivity to macrolides
  • Dosage: Typically a tapered dose of 500 mg PO on day 1, then 250 mg PO x 4 days). Often a single 1-2 gram dose for sexually transmitted infections.
  • Half-life: 68 hours
  • Adverse Reactions: vomiting, diarrhea, headache, vision changes. May also cause prolonged QT or hepatic necrosis.
  • Special Considerations: None

Pearls

  • Azithromycin has fallen out of favor for the treatment of Chlamydia trachomatis due to low cure rates and increased resistance. Doxycycline is a better choice, unless the patient is pregnant.
  • Use caution, as there is a small increased risk of arrhythmias and sudden cardiac death in patients > 65 and/or those with cardiovascular disease.
Video Credit: Medicosis Perfectionales

Cephalexin

Rapid Review

Pearls

Deep Dive

Cefazolin

Rapid Review

  • Mechanism of Action: 1st generation cephalosporin; inhibits cell wall mucopeptide synthesis.
  • Indications: Frequently used for cellulitis, osteomyelitis, and intra-abdominal infections. May also be used for surgical prophylaxis.
  • Contraindications: allergy to class/drug
  • Dosage: generally 500-1000 mg IM/IV q6-8hrs.
  • Half-life: 1.8 hours
  • Adverse Reactions: GI effects (nausea/vomiting/diarrhea). Hypersensitivity reactions.
  • Special Considerations: N/A

Pearls

  • A penicillin allergy is highly unlikely to cause an adverse reaction with cefazolin administration, as cefazolin does not share an R1 side chain with any beta-lactam antibiotics.
  • Since cefazolin is excreted through the kidneys, the dose should be adjusted based on creatinine clearance of the patient. 
Video Credit: MED CRAM

Cefepime

Rapid Review

  • Mechanism of Action: 4th-generation cephalosporin antibiotic; inhibits cell wall mucopeptide synthesis.
  • Indications: empiric treatment for severe infections (sepsis, bacteriemia, multi-drug resistant infections, hospital-acquired pneumonia)
  • Contraindications: allergy to class/drug
  • Dosage: Generally 1-2 g IV/IM q12 hours
  • Half-life: 2-19 hours (depending on dose/route)
  • Adverse Reactions: GI effects (nausea/vomiting/diarrhea). Hypersensitivity reactions.

Pearls

  • Cefipime has the same broad spectrum activity as ceftriaxone, but with added pseudomonas coverage. However, it still does not cover MRSA like 5th generation cephalosporins.
  • Cefipime is associated with some delayed hypersensitivity reactions, including steven-johnson syndrome and acute generalized exanthematous pustulosis

Deep Dive

Video Credit: MED CRAM

Cefotaxime

Rapid Review

  • Mechanism of Action: 3rd-generation cephalosporin antibiotic; inhibits bacterial wall synthesis
  • Indications: Commonly used to treat intra-abdominal infections, meningitis, gonorrhea, and pneumonia.
  • Contraindications: allergy/hypersensitivity to drug class
  • Dosage: generally 1-2 g IV/IM q6-12 hrs
  • Half-life: 1-2 hrs
  • Adverse Reactions: local reaction to injection site, GI effects, hypersensitivity

Pearls

  • Cefotaxime has comparable activity to ceftriaxone, though may be favorable in terms of reducing rates of Clostridium difficile infections.
  • Although it has broad antimicrobial activity, it still does not cover MRSA or Pseudomonas. 
Video Credit: MED CRAM

Ciprofloxacin

Rapid Review

  • Mechanism of Action: Fluoroquinoline antibiotic; inhibits DNA gyrase
  • Indications: Commonly used for diverticulitis, colitis, and urinary tract infections.
  • Contraindications: allergy to class/drug, administration with tizanidine
  • Dosage: Generally 250-750mg PO q12h or 200-400mg IV q12hrs.
  • Half-life: 4 hours
  • Adverse Reactions: GI effects (nausea/vomiting/diarrhea), tendon rupture

Pearls

  • Although ciprofloxacin can cover a multitude of infections, it should not be used for cystitis, pneumonia, or gonorrhea due to increasing bacterial resistance. 
  • Like other fluoroquinolones, there are several potential adverse reactions from usage, including tendon ruptures, increased risk of aortic dissection/aneurysm, dysrhthmias, and Clostridioides difficile infection. Avoid this class of medication when possible. 
Video Credit: Medical Animations

Ceftriaxone

Rapid Review

  • Mechanism of Action: 3rd generation cephalosporin with broad-spectrum gram-negative activity. Inhibits cell wall synthesis
  • Indications: Bacterial meningitis, gonorrhea, pelvic inflammatory disease, joint infection
  • Contraindications: Allergy to class/drug, age < 1 month
  • Dosage
    • Generally 1-2 grams IM/IV q24hrs
    • Gonorrhea: 500 mg IM (single dose)
  • Half-life: 5.8 – 8.7hrs
  • Adverse Reactions: Anaphylaxis, bronchospasm, SJS, diarrhea, eosinophilia

Pearls

  • Many guidelines give a dose range of “1-2 grams”. When in doubt, use the higher dosage. Ceftriaxone has an excellent safety profile.
  • Do NOT give ceftriaxone simultaneously with any calcium-containing products (including lactated ringers”. This can cause a life-threatening precipitation, especially in neonates.
Video Credit: USMLE Pass

Clindamycin

Rapid Review

  • Mechanism of Action: Lincosamide antibiotic; bacteriostatic/bactericidial 
  • Indications: odontogenic infections, MRSA, necrotizing soft tissue infections
  • Contraindications: allergy to class/drug; ulcerative colitis
  • Dosage: generally 150-450mg PO q6 hrs; 1200-2700mg/day IV/IM q6-12 hrs
  • Half-life: 2.5-3 hours
  • Adverse Reactions: GI effects (nausea/vomiting/diarrhea), pruritus, thrombocytopenia.
  • Special Considerations: clindamycin should be used rarely due to high risk of clostridium difficile associated diarrhea.

Pearls

  • Clindamycin is unique in that it covers for both MRSA and anaerobes, making it very useful in head/neck and soft tissue infections. It also helps decrease toxin production, making it a good adjunct for necrotizing infections. 
  • Clindamycin has some of the highest rates of Clostridioides difficile infections compared to other antibiotics. Avoid using the antibiotic if comparable alternatives are available. 
Video Credit: Medical Animations

Doxycycline

Rapid Review

  • Mechanism of Action: Tetracycline; inhibits bacterial protein synthesis after specific ribosomal binding
  • Indications: Community-acquired pneumonia, cellulitis, bacterial sinusitis, chlamydia/gonorrhea, PID, lyme disease
  • Contraindications: Allergy to drug/class, pregnancy, Age < 8 years old (due to teeth staining, although short courses are permissible)
  • Dosage: Generally 100mg PO/IV daily or q12 hours x 7 days
  • Onset: Peak concentration after 2-4 hours
  • Duration: Half life of 18 hours
  • Adverse Reactions: Headache, nausea, dyspepsia, tooth discoloration (controversial), C. Diff diarrhea
  • Special Considerations: None

Pearls

  • Doxycycline is notorious for increasing photosensitivity of the skin. Advise patients to wear sunscreen or limit sun exposure throughout the course of the treatment. 
  • Although doxycycline is commonly used for abscesses given it’s MRSA coverage, it has poor activity against Streptococcus species. Add an additional agent (ex. cephalexin) if cellulitis is suspected.
Video Credit: Pharmacist Conversations

Gentamicin

Rapid Review

  • Mechanism of Action: Aminoglycoside; bactericidal antibiotic with broad coverage against aerobic gram-negative bacteria, including Pseudomonas. Binds to the 16s rRNA at the 30s ribosomal subunit, disrupting mRNA translation.
  • Indications: PID, sepsis, meningitis, endocarditis, blepharitis
  • Contraindications: Allergy to drug/class
  • Dosage: Generally 5-7 mg/kg IV q24 hours
  • Onset: Reaches peak concentrations after 30-90 minutes
  • Duration: 2-3 hours
  • Adverse Reactions: Ototoxicity, renal toxicity, abnormal LFTs, rashes 

Pearls

  • Gentamicin provides excellent coverage of gram negative bacteria, including Pseudomonas, however it typically requires a second agent (usually a beta-lactam) for severe infections.
  • Although not a concern for single dose administration in the ED, gentamicin levels must be monitored during admission to ensure adequate antimicrobial coverage and to minimize ototoxicity/nephrotoxicity.
Video Credit: Drug Talk

Levofloxacin

Rapid Review

  • Mechanism of Action: 3rd generation Fluoroquinolone; inhibits bacterial DNA synthesis. Broad spectrum antibiotic with good coverage against both gram positive and gram negative organisms.
  • Indications: Pneumonia (community or nosocomial), pyelonephritis, UTI, sinusitis, prostatitis.
  • Contraindications: QT prolongation, hypersensitivity, myasthenia gravis
  • Dosage:
    • Pyelonephritis: 250 mg PO daily X 10 days
    • Prostatitis: 500 mg PO X 28 days
    • Pneumonia: 750 mg PO/IV q24 hours X 7-14  days 
  • Half-life: 6-8 hours (27-35 hours in adults with renal impairment)
  • Adverse Reactions: Tendon rupture, photosensitivity, nausea, prolonged QT
  • Special Considerations: Has limited coverage against pseudomonas compared to ciprofloxacin
  • Levofloxacin is a fluoroquinolone antibiotic that is commonly used to treat pneumonia and COPD exacerbation

Pearls

  • Due to growing bacterial resistance to levofloxacin, it is not a first line choice for cystitis or gonorhea.
  • Like other fluoroquinolones, levofloxacin carries an increased risk of aortic dissection, tendinopathies, neurological reactions, and QT prolongation. This class of medications should be avoided, if possible. 
Video Credit: Medical Animations

Metronidazole

Rapid Review

  • Mechanism of Action: Nitroimidazole antibiotic/anti-protozoan. Inhibits protein synthesis by interacting with DNA. 
  • Indications: Intra-abdominal infections (colitis, diverticulitis), genital infections (pelvic inflammatory disease, bacterial vaginosis, trichomoniasis) C. difficile, amebiasis
  • Contraindications: Hypersensitivity, 1st trimester pregnancy
  • Dosage:
    • Intra-abdominal infections: 500 mg IV q8 hours
    • Genital infections (PID, BV, Trich): Generally 500 mg PO q12 hours X 7 days
  • Half-life: 8 hours
  • Adverse Reactions: Headache, vaginitis, nausea, confusion, neuropathy
  • Special Considerations: Patient should avoid alcohol consumption while on this medication and at least 2-3 days after last dose (creates a disulfiram-like effect)

Pearls

  • Metronidazole has historically been known to cause a disulfiram-like reaction with alcohol use, but the evidence behind this claim is limited.
  • Metronidazole has excellent activity against most anaerobes and is generally considered the gold standard. 
Video Credit: Medical Animations

Piperacillin-Tazobactam

Rapid Review

  • Mechanism of Action: Antipseudomonal penicillin. Piperacillin inhibits cell wall mucopeptide synthesis, tazobactam inhibits the beta lactamase enzyme to prevent bacteria from destroying the piperacillin.
  • Indications: Pneumonia, sepsis, pelvic inflammatory disease, intra-abdominal infections.
  • Contraindications: Hypersensitivity
  • Dosage: 
  • Half-life: 0.7-1.2 hours
  • Adverse Reactions: Anaphylaxis, SJS, nausea/vomiting, headache

Pearls

  • Piperacillin-tazobactam is a strong antibiotic with broad coverage against gram positives, gram negatives (including Pseudomonas), and anaerobes. However, it does not cover MRSA, which is why it is often paired with vancomycin. 
  • Treatment with piperacillin-tazobactam is associated with Clostridioides difficile-associated diarrhea and colitis. Use caution, especially in elderly patients or those with immunosuppression.
Video Credit: Drug Talk

Vancomycin

Rapid Review

  • Mechanism of Action: Glycopeptide antibiotic; inhibits cell wall synthesis, exhibiting a bactericidal action. Very potent against gram-positive bacteria. 
  • Indications: Sepsis, MRSA skin and soft tissue infections, endocarditis, meningitis, C difficile colitis
  • Contraindications: Allergy to class/drug
  • Dosage: Initial loading dose generally 15-20mg/kg IV. Maintenance dose is 500-1000 IV q12 hours.
  • Onset: Rapid
  • Duration: Half life of 4-6 hrs
  • Adverse Reactions: Hypotension (with rapid IV use), “red man syndrome”,  nausea
  • Special Considerations: None

Pearls

  • Vancomycin in it’s PO formulation is the drug of choice for Clostridium-difficile GI infections.
  • Vancomycin is the gold standard and first-line choice for MRSA infections. However, consultation with pharmacy for dosing is ideal, especially in patients with renal disease or extremes in age.
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