BCIDP cheat sheet

Gram-positive cocci in clusters = Staphylococcus; in pairs/chains = Streptococcus; in pairs with lancet shape = Streptococcus pneumoniae.

Gram-negative diplococci in PMNs = Neisseria; oxidase-positive = N. gonorrhoeae or N. meningitidis.

Obligate anaerobes lack catalase and superoxide dismutase; growth requires anaerobic transport and culture.

Biofilm formation (e.g., Staphylococcus epidermidis on devices, Pseudomonas aeruginosa in CF) increases tolerance to antibiotics and host defenses.

Endotoxin = lipopolysaccharide (LPS) in Gram-negative outer membrane; triggers TLR4 and cytokine storm.

Exotoxins (e.g., toxic shock syndrome toxin-1, diphtheria toxin, tetanus toxin) are proteins; toxoids can be used for vaccination.

Opsonization by IgG and C3b enhances phagocytosis; encapsulated organisms (S. pneumoniae, H. influenzae type b, N. meningitidis) require opsonizing antibody.

Neutropenia (<500 cells/µL) is the major risk factor for invasive bacterial and fungal infections; T-cell defects predispose to intracellular pathogens (e.g., Pneumocystis, Mycobacteria).

Time-dependent killing (e.g., beta-lactams, vancomycin) correlates with fT>MIC; goal is to maximize duration of free drug above MIC.

Concentration-dependent killing (e.g., aminoglycosides, daptomycin) correlates with Cmax/MIC or AUC/MIC; goal is high peak.

AUC/MIC is the best predictor for vancomycin efficacy (target AUC24 400–600 mg·h/L for serious MRSA infection).

Half-life (t1/2) = 0.693 × Vd / CL; steady state reached after ~4–5 half-lives.

Loading dose = Vd × target concentration; maintenance dose = CL × target concentration × dosing interval.

Protein binding reduces free drug available for activity; only free drug is pharmacologically active.

Post-antibiotic effect (PAE) is prolonged for aminoglycosides, fluoroquinolones, and daptomycin; minimal for beta-lactams against Gram-negatives.

Beta-lactam mechanism: acylation of penicillin-binding proteins (PBPs) → inhibited cell wall cross-linking; resistance via beta-lactamase, altered PBP, or efflux.

Core stewardship strategies: prospective audit and feedback, formulary restriction/preauthorization, de-escalation, dose optimization, and IV-to-PO conversion.

Antibiotic time-out: reassess indication, dose, duration, and need for de-escalation at 48–72 hours.

Hand hygiene is the single most effective intervention to prevent healthcare-associated infections.

Contact precautions for MRSA, VRE, C. difficile, and multidrug-resistant Gram-negatives; droplet for influenza, pertussis, meningococcus; airborne for TB, measles, varicella.

Antimicrobial resistance mechanisms: enzymatic inactivation, target modification, decreased permeability, efflux pumps, and biofilm formation.

Clostridioides difficile infection: avoid unnecessary antibiotics, use soap and water (alcohol does not kill spores), and isolate with contact precautions.

Surgical prophylaxis: administer within 60 minutes before incision; redose intraoperatively based on drug half-life and blood loss.

Stewardship metrics: days of therapy (DOT) per 1000 patient-days, defined daily dose (DDD), antibiotic utilization, and C. difficile rates.

Community-acquired pneumonia (CAP): assess severity (CURB-65 or PSI); empiric therapy covers S. pneumoniae, H. influenzae, and atypicals.

Sepsis: obtain cultures before antibiotics, give broad-spectrum antibiotics within 1 hour of recognition, and provide 30 mL/kg crystalloid for hypotension or lactate ≥4 mmol/L.

Infective endocarditis: obtain ≥3 blood culture sets before antibiotics; empiric therapy for native valve covers staphylococci, streptococci, and enterococci.

Meningitis: empiric therapy includes vancomycin plus a third-generation cephalosporin; add ampicillin if Listeria risk (age >50, immunocompromised).

Urinary tract infection: uncomplicated cystitis first-line = nitrofurantoin, TMP-SMX, or fosfomycin; avoid fluoroquinolones when alternatives exist.

Intra-abdominal infection: source control is essential; empiric coverage for Gram-negatives and anaerobes (e.g., piperacillin-tazobactam or ceftriaxone plus metronidazole).

Skin and soft tissue infection: purulent (abscess) → incision and drainage; non-purulent → beta-lactam; MRSA coverage if risk factors.

Candidemia: echinocandin first-line; remove central venous catheters and obtain follow-up blood cultures until clearance.

Renal dosing: adjust for CrCl <50 mL/min; use Cockcroft-Gault for drug dosing, not eGFR from CKD-EPI.

Aminoglycosides and vancomycin require dose adjustment in renal impairment and therapeutic drug monitoring.

Pregnancy: avoid fluoroquinolones, tetracyclines, and aminoglycosides; beta-lactams and macrolides are generally preferred.

Pediatric dosing: use weight-based dosing (mg/kg); neonates have immature renal and hepatic clearance requiring extended intervals.

Obesity: use adjusted body weight for aminoglycosides; vancomycin loading dose should be based on actual body weight.

Cystic fibrosis: increased Vd and CL for many antibiotics; higher doses may be needed (e.g., beta-lactams, aminoglycosides).

Hemodialysis: vancomycin and aminoglycosides are removed; dose after dialysis or supplement based on levels.

Hepatic impairment: reduce dosing for drugs with hepatic metabolism (e.g., metronidazole, rifampin, voriconazole); monitor LFTs.

MIC = lowest concentration of antimicrobial that inhibits visible growth; MBC = lowest concentration that kills ≥99.9% of inoculum.

CLSI breakpoints categorize as susceptible (S), intermediate (I), or resistant (R); EUCAST breakpoints may differ.

Beta-lactamase testing: nitrocefin-based tests detect penicillinase; ESBL confirmation by clavulanate synergy.

MRSA detection: cefoxitin disk diffusion or oxacillin MIC; mecA gene PCR is definitive.

Vancomycin TDM: target AUC24 400–600 mg·h/L for serious MRSA; trough-only monitoring is less accurate.

Aminoglycoside TDM: monitor peak (efficacy) and trough (toxicity); target trough <1 mg/L for gentamicin/tobramycin.

Procalcitonin may support antibiotic discontinuation in respiratory infections; not a standalone diagnostic test.

Blood cultures: obtain before antibiotics, 2–3 sets from separate sites; incubation for 5 days is standard.

Beta-lactam allergy: cross-reactivity between penicillins and cephalosporins is low (<2%); direct oral challenge may be used for low-risk patients.

Fluoroquinolones: risk of tendinopathy, QT prolongation, aortic aneurysm, and CNS effects; avoid in myasthenia gravis.

Aminoglycosides: nephrotoxicity and ototoxicity; monitor levels and renal function.

Vancomycin: infusion-related reaction (flushing) can be mitigated by slowing infusion; nephrotoxicity risk increases with high troughs and concomitant nephrotoxins.

Linezolid: myelosuppression (thrombocytopenia), serotonin syndrome with serotonergic drugs, and peripheral neuropathy with prolonged use.

Rifampin: potent CYP450 inducer; reduces levels of warfarin, oral contraceptives, and many antifungals.

Macrolides and azoles: QT prolongation; avoid with other QT-prolonging drugs.

Regulatory: FDA-approved labeling, REMS programs (e.g., for some antifungals), and antimicrobial stewardship standards (Joint Commission, CMS).