Bacterial Infections

Which antibiotic classes are preferred first-line for asymptomatic bacteriuria in pregnant individuals, and which class must be completely avoided?

• Preferred: Beta-lactams, such as amoxicillin ± clavulanate or an oral cephalosporin (e.g., cephalexin).

• Avoided: Quinolones must be avoided due to the risks of cartilage toxicity and arthropathies.

What are the preferred first-line antibiotic regimens for a 1st episode of CDI?

• Fidaxomicin (FDX) 200 mg PO BID × 10 days.

• Vancomycin (VAN) 125 mg PO QID × 10 days.

• (Note: Metronidazole 500 mg PO TID × 10 days is only an option if non-severe AND preferred treatments are unavailable).

How does the management of a 2nd CDI episode (1st recurrence) differ depending on what was used for the initial episode?

• If FDX was used first: Use a VAN prolonged pulse/tapered course.

• If VAN was used first: Use FDX 200 mg PO BID × 10 days OR a VAN prolonged pulse/tapered course.

What is the first-line drug of choice, route, and dosing duration for early latent vs. late latent/tertiary Syphilis?

• Early Latent (< 1 year duration): Penicillin G benzathine (Bicillin L-A) 2.4 million units IM × 1 dose.

• Late Latent (> 1 year or unknown duration): Penicillin G benzathine (Bicillin L-A) 2.4 million units IM weekly × 3 weeks.

What is the first-line treatment regimen for uncomplicated Gonorrhea, and what must be added if a chlamydia co-infection has not been excluded?

• Weight < 150 kg: Ceftriaxone 500 mg IM × 1.

• Weight ≥ 150 kg: Ceftriaxone 1 gram IM × 1.

• Chlamydia not excluded: Add oral doxycycline 100 mg PO BID × 7 days.

What are the first-line treatment differences for Chlamydia between non-pregnant and pregnant patients?

• Non-pregnant: Doxycycline 100 mg PO BID × 7 days.

• Pregnant: Azithromycin 1 gram PO × 1 dose.

What is the drug of choice for Trichomoniasis, and how does the dosing strategy change based on biological sex?

• Drug: Metronidazole.

• Females: 500 mg PO BID × 7 days.

• Males: 2 grams PO × 1 dose.

What is the general pre-operative timing rule for administering standard IV antibiotics like cefazolin or cefuroxime?

Infuse the antibiotic within 60 minutes before the first surgical incision.

What is the pre-operative timing rule if a quinolone or vancomycin is used for surgical prophylaxis?

Start the infusion 120 minutes before the first surgical incision.

When should additional intra-operative doses of antibiotics be administered?

For longer surgeries (e.g., > 4 hours) or if there is major blood loss.

What are the preferred antibiotics for most surgeries to prevent MSSA and streptococcal infections, and what is an alternative for patients with a beta-lactam allergy?

• Preferred: Cefazolin (1st gen cephalosporin) or cefuroxime (2nd gen cephalosporin).

• Beta-lactam allergy alternative: Clindamycin (or Vancomycin).

What extra coverage is required for prophylaxis in gastrointestinal surgeries, and what preferred regimens satisfy this?

• Coverage needed: Skin flora plus broad gram-negative and anaerobic organisms.

• Preferred Regimens: Cefazolin + metronidazole, cefotetan, cefoxitin, or ampicillin/sulbactam.

Why is IV dexamethasone given in acute bacterial meningitis, and when must it be administered?

It is given to prevent neurological complications (e.g., hearing loss) and death from pneumococcal meningitis. It must be administered 15–20 minutes prior to or with the first antibiotic dose.

What is the empiric antibiotic regimen for meningitis in Neonates (< 1 month)?

Ampicillin (for Listeria coverage) + Ceftazidime or cefepime ± Gentamicin.

What is the empiric antibiotic regimen for meningitis in patients aged 1 month to 50 years?

Ceftriaxone + Vancomycin (Vancomycin is added for double coverage of S. pneumoniae).

What is the empiric antibiotic regimen for meningitis in patients age > 50 years or immunocompromised?

Ampicillin (for Listeria coverage) + Ceftriaxone + Vancomycin.

What is the standard first-line antibiotic treatment and specific dosing for AOM?

High-dose Amoxicillin (90 mg/kg/day in 2 divided doses) or Amoxicillin/clavulanate (90 mg/kg/day of amoxicillin with 6.4 mg/kg/day of clavulanate in 2 divided doses).

What are the recommended alternative treatments for AOM if a child has a mild/non-severe penicillin allergy?

A second- or third-generation cephalosporin is recommended due to low cross-reactivity:

• Cefdinir (14 mg/kg/day in 1 or 2 doses)

• Cefuroxime (30 mg/kg/day in 2 divided doses)

• Cefpodoxime (10 mg/kg/day in 2 divided doses)

• Ceftriaxone (50 mg/kg IM daily for 1 or 3 days)

What is the standard duration of oral antibiotic treatment for AOM based on age?

• Age < 2 years: 10 days

• Ages 2–5 years: 7 days

• Ages ≥ 6 years: 5–7 days

What is the drug class of choice for treating Pertussis (whooping cough), and why is it used?

Macrolides (azithromycin or clarithromycin). They are highly effective at eradicating Bordetella pertussis and preventing transmission to vulnerable populations.

What are the preferred empiric outpatient regimens for a Healthy CAP patient (no comorbidities)?

• Amoxicillin high-dose (1 gram TID), OR

• Doxycycline, OR

• Macrolide (azithromycin or clarithromycin), but only if local pneumococcal resistance is < 25%.

What are the preferred empiric regimens for a non-severe inpatient CAP admission to a general medicine unit?

• A Beta-lactam + macrolide or doxycycline (Preferred beta-lactams: ceftriaxone, ceftaroline, or ampicillin/sulbactam).

• OR Respiratory quinolone monotherapy.

What is the preferred empiric regimen for severe inpatient CAP (ICU admission), and what should be avoided?

• Preferred: Beta-lactam + macrolide, OR Beta-lactam + respiratory quinolone.

• Avoid: Do not use quinolone monotherapy.

Which Latent TB treatment regimen is explicitly contraindicated in pregnant patients due to unknown fetal risk?

INH and rifapentine once weekly for 12 weeks via directly observed therapy (DOT) or self-administered.

What Latent TB regimen options are available for non-pregnant adults, and which is preferred in HIV-positive patients?

• Options: INH + rifapentine weekly x 12 weeks, INH + rifampin daily x 3 months, or Rifampin 600 mg daily x 4 months.

• Preferred for HIV-positive: INH 300 mg daily for 6 or 9 months (9 months is recommended if taking antiretroviral therapy to minimize drug interaction risks).

What is the standard preferred regimen and duration for treating Active Tuberculosis?

Treatment is divided into two phases for a total duration of 6 months:

• Intensive Phase: 4 drugs (Rifampin + Isoniazid + Pyrazinamide + Ethambutol) for 2 months.

• Continuation Phase: 2 drugs (Isoniazid + Rifampin) for 4 months.

What is a major contraindication and a notable, harmless side effect of Rifampin?

• Contraindication: Do not use with protease inhibitors.

• Side Effect: Orange-red discoloration of body secretions (saliva, urine, sweat, tears), which can permanently stain contact lenses and clothing.

What is the Boxed Warning for Isoniazid, and how is its primary neurological warning managed?

• Boxed Warning: Severe and fatal hepatitis.

• Management: To prevent INH-associated peripheral neuropathy, administer pyridoxine (vitamin B6) 25–50 mg PO daily, especially if predisposed (e.g., HIV, diabetes, pregnancy, malnutrition).

What are the key contraindications for Pyrazinamide and Ethambutol, respectively?

• Pyrazinamide: Contraindicated in acute gout and severe hepatic damage (due to side effects of hyperuricemia and increased LFTs).

• Ethambutol: Contraindicated in optic neuritis (requires monitoring for dose-related visual acuity and color changes).

How does renal impairment alter the dosing schedule for Pyrazinamide and Ethambutol?

The dosing interval must be extended for both drugs if clearance drops below specific thresholds:

• Pyrazinamide: Extend interval if CrCl < 30 mL/min.

• Ethambutol: Extend interval if CrCl < 50 mL/min.

Which oral anticoagulants are explicitly contraindicated with rifampin?

Apixaban, rivaroxaban, edoxaban, and dabigatran.

What is the preferred empiric antibiotic regimen for Staphylococci (MSSA vs. MRSA) in IE, and what is added if a prosthetic valve is present?

• MSSA: Nafcillin or cefazolin.

• MRSA: Vancomycin.

• Prosthetic Valve Present: Add gentamicin and rifampin to either regimen.

What finding in an ascitic fluid sample confirms a diagnosis of Spontaneous Bacterial Peritonitis (SBP), and what is the preferred empiric treatment?

• Diagnostic criteria: PMNs (polymorphonuclear leukocytes) ≥ 250 cells/mm³ collected via paracentesis.

• Empiric treatment: Ceftriaxone for 5–7 days.

If an intra-abdominal infection regimen lacks coverage against anaerobes (like Bacteroides fragilis), what specific antibiotic must be added?

Metronidazole

What are the preferred empiric outpatient/inpatient regimens for community-acquired, low-risk (mild-to-moderate)intra-abdominal infections to cover PEK, anaerobes, and streptococci?

• Ertapenem monotherapy

• Moxifloxacin monotherapy

• (Cefuroxime or Ceftriaxone) + Metronidazole

• (Ciprofloxacin or Levofloxacin) + Metronidazole

What is the clinical presentation of Impetigo, and how is it treated based on the extent of the lesions?

• Presentation: Blister-like rash anywhere on the face/limbs that dries and forms honey-colored crusts.

• Limited, localized lesions: Topical antibiotic, typically mupirocin.

• Numerous, extensive lesions: Oral Cephalexin 250–500 mg PO QID or Dicloxacillin 250–500 mg PO QID.

What non-pharmacologic management is recommended for large furuncles/carbuncles, and what oral empiric antibiotics should be selected to cover CA-MRSA?

• Management: Incision & drainage (I&D).

• Antibiotics: SMX/TMP DS 1–2 tablets PO BID, OR Doxycycline 100 mg PO BID.

What are the typical bacterial pathogens and empirical oral antibiotic options for mild, non-purulent Cellulitis?

• Pathogens: Streptococci (including S. pyogenes) and S. aureus.

• First-line options: Cephalexin 500 mg PO QID or Dicloxacillin 500 mg PO QID.

• Beta-lactam allergy option: Clindamycin 300 mg PO QID.

What is the standard duration of treatment for mild cellulitis?

5 days (treatment should be extended longer if there is no clinical improvement within 5 days).

What oral empirical antibiotics can be selected for a mild purulent abscess to ensure CA-MRSA coverage?

• SMX/TMP DS 1–2 tablets PO BID

• Doxycycline 100 mg PO BID

• Minocycline 200 mg PO × 1, then 100 mg PO BID

• Clindamycin 300 mg PO QID

• Linezolid 600 mg PO BID

What IV antibiotic options are preferred for a severe purulent SSTI, and what is the target trough level if vancomycin is chosen?

• Options: Vancomycin, Daptomycin, or Linezolid.

• Vancomycin target trough: 10–15 mcg/mL.

What is the empiric antibiotic regimen for necrotizing fasciitis, and why is clindamycin explicitly added?

• Regimen: Vancomycin or daptomycin PLUS a broad-spectrum beta-lactam (such as piperacillin/tazobactam or meropenem) PLUS clindamycin.

• Role of Clindamycin: It is added specifically to suppress streptococcal toxin production.

What empiric IV antibiotic options provide coverage for a DFI when no MRSA or Pseudomonas coverage is required?

Ampicillin/sulbactam, Ertapenem, Ceftriaxone, or Levofloxacin/Moxifloxacin.

What are the top first-line oral drugs of choice and their specific durations for Acute Uncomplicated Cystitis?

• Nitrofurantoin (Macrodid): 100 mg PO BID × 5 days (Contraindicated if CrCl < 60 mL/min).

• SMX/TMP DS: 1 tablet PO BID × 3 days (Avoid if sulfa allergy or local E. coli resistance ≥ 20%).

• Fosfomycin: 3 grams PO × 1 dose.