The infections that generate the 2am page, across all three pathogen classes, plus the rare-but-lethal presentations where recognition — not the antibiotic itself — is the rate-limiting step. Companion file covers board-tested outpatient/floor presentations.
Source usually presumed before it's proven; empiric coverage broadened deliberately, de-escalation planned from the first order.
| Infection | Empiric Abx | Abx Rationale | Symptom Profile | Clinical Result Profile | Notes |
|---|---|---|---|---|---|
| Sepsis / Septic Shocksource unknown | Piperacillin-tazobactam + vancomycin± antifungal if high-risk (recent surgery, TPN, prolonged ICU) | Broadest reasonable single-pass coverage (Gram-positive incl. MRSA, Gram-negative incl. Pseudomonas, anaerobes) while source is being localized — narrow within 48–72h on culture data. | Fever/hypothermia, tachycardia, tachypnea, altered mentation, hypotension unresponsive to fluid. | Lactate elevated, blood cultures x2 before abx if it doesn't delay therapy, qSOFA/SOFA scoring. | Antibiotics within 1 hour of recognition; 30mL/kg crystalloid bolus; source control identified in parallel. |
| Severe CAPICU-level | Ceftriaxone + macrolide or fluoroquinolone+ vancomycin/linezolid if MRSA risk (post-influenza, cavitary) | Combination covers typical + atypical pathogens simultaneously; ICU-level disease no longer permits narrow empiric guessing before culture return. | Respiratory failure or septic shock from pneumonia; one major or ≥3 minor IDSA/ATS severity criteria. | CXR: multilobar infiltrates; hypoxemia, elevated procalcitonin, positive urinary pneumococcal/Legionella antigen if available. | Consider MRSA/Pseudomonas coverage in structural lung disease, recent hospitalization, or post-influenza necrotizing pneumonia. |
| HAP / VAP | Cefepime/pip-tazo/meropenem + vancomycin± second anti-pseudomonal agent if high resistance risk | Hospital-acquired flora skews toward MDR Gram-negatives (Pseudomonas, resistant Enterobacterales) and MRSA — outpatient CAP regimens are inadequate. | New/worsening infiltrate + fever, purulent secretions, leukocytosis, worsening oxygenation ≥48h after admission or on a ventilator. | CXR/CT new infiltrate; respiratory culture (endotracheal aspirate or BAL) to guide de-escalation. | Base regimen on unit-specific antibiogram; de-escalate aggressively once cultures return. |
| Aspiration Pneumonia | Ampicillin-sulbactamAlt: clindamycin (PCN-allergic) | Oropharyngeal flora includes anaerobes and mixed Gram-positive/negative organisms; anaerobic coverage is the key addition versus standard CAP. | Witnessed aspiration event or risk factors (altered LOC, dysphagia, seizure) with subsequent fever, cough, foul-smelling sputum. | CXR: infiltrate in dependent lung segments (right lower lobe most common, supine → posterior segments). | Routine anaerobic coverage of chemical pneumonitis alone (no true infection) is often unnecessary and overused. |
| Urosepsiscomplicated UTI | Ceftriaxone or pip-tazo (if resistant flora risk) | IV therapy with reliable Gram-negative and renal-tract penetration; broaden for prior resistant organisms, indwelling catheter, or recent instrumentation. | Fever, flank pain, hemodynamic instability layered on lower-tract symptoms; may present as delirium in elderly without classic symptoms. | UA with pyuria/bacteriuria, blood cultures, lactate; renal ultrasound/CT if obstruction suspected. | Obstructing stone with infected urine = urologic emergency — needs decompression, not just antibiotics. |
| Intra-abdominal Infectionperforation / abscess | Piperacillin-tazobactamAlt: ceftriaxone + metronidazole | Polymicrobial source (enteric Gram-negatives + anaerobes) requires combined or single broad-spectrum agent with both aerobic and anaerobic activity. | Diffuse or localized abdominal pain, fever, rebound/guarding, distension. | CT abdomen/pelvis: free air, abscess, fat stranding; leukocytosis, lactate elevation with ischemia. | Source control (drainage/surgery) is the primary intervention — antibiotics alone will not cure an undrained abscess. |
| Necrotizing Fasciitis | Vancomycin + pip-tazo + clindamycinSurgical Emergency | Broad coverage for polymicrobial/mixed disease plus clindamycin specifically to suppress exotoxin production (protein synthesis inhibition, not just bacterial killing). | Pain out of proportion to exam, rapidly spreading erythema, crepitus, bullae, systemic toxicity. | CT/plain film may show soft tissue gas; markedly elevated CK, LRINEC score; definitive diagnosis is surgical exploration. | Emergent surgical debridement is the definitive treatment — antibiotics alone are not curative. |
| Febrile Neutropenia | Cefepime or pip-tazo monotherapy+ vancomycin if line infection/skin-soft tissue signs, instability | Pseudomonas coverage is non-negotiable given rapid, fulminant course in the neutropenic host; monotherapy preferred unless specific risk factors argue for additions. | Fever (single temp ≥38.3°C or ≥38°C x1h) with ANC <500 in a chemotherapy/hematologic malignancy patient. | Blood cultures from all lines and peripheral, CBC with differential, CXR. | Antibiotics within 1 hour is a hard quality metric here — do not wait for source to declare itself. |
| Adult Bacterial MeningitisICU / immunocompromised | Vancomycin + ceftriaxone + ampicillin+ dexamethasone | Ampicillin added over the standard adult regimen to cover Listeria in age >50 or immunocompromised hosts; steroid given with/before first antibiotic dose. | Fever, headache, nuchal rigidity, altered mentation; may be blunted in elderly/immunocompromised. | LP: neutrophilic pleocytosis, low glucose, high protein, elevated opening pressure; CT before LP if focal deficit, papilledema, or altered mentation. | Do not delay antibiotics for imaging — draw blood cultures and start empiric therapy immediately if LP delayed. |
| Infective Endocarditisacute, native valve | Vancomycin + ceftriaxoneProsthetic valve: add gentamicin + rifampin | Empiric coverage for S. aureus (incl. MRSA), streptococci, and enterococci pending blood culture speciation; narrow once organism/sensitivities return. | Fever, new murmur, embolic phenomena (Janeway lesions, Osler nodes, Roth spots, splinter hemorrhages). | Blood cultures x3 from separate sites before antibiotics; echocardiogram (TTE → TEE) for vegetation; Duke criteria. | IVDU history strongly suggests right-sided (tricuspid) S. aureus endocarditis with septic pulmonary emboli. |
| CLABSI | Vancomycin + cefepime (or pip-tazo) | Coverage for coagulase-negative staph/MRSA (most common) plus Gram-negatives, since line infections can seed systemically before organism is known. | Fever, chills, hemodynamic instability in a patient with a central line, without another identified source. | Paired blood cultures (peripheral + through-line) with differential time to positivity; culture line tip if removed. | Line removal is generally required for S. aureus, Candida, or persistent bacteremia despite therapy. |
| Diabetic Foot Infectionmoderate–severe | Piperacillin-tazobactam (± vancomycin if MRSA risk) | Chronic wounds are typically polymicrobial (Gram-positive, Gram-negative, anaerobes); broad coverage warranted once infection extends beyond superficial skin. | Wound with purulence plus ≥2 signs of inflammation; deep/large ulcers with systemic signs in severe disease. | Probe-to-bone test, plain films/MRI for osteomyelitis, wound culture (deep tissue preferred over surface swab). | Osteomyelitis changes duration of therapy significantly — image early if bone is a concern. |
| Toxic Shock Syndromestaphylococcal / streptococcal | Vancomycin (or oxacillin) + clindamycin | Clindamycin suppresses toxin (TSST-1/exotoxin) synthesis via protein synthesis inhibition independent of bacterial killing — critical adjunct beyond the beta-lactam/glycopeptide alone. | High fever, diffuse macular erythroderma, hypotension, multi-organ involvement; desquamation 1–2wk later. | Clinical diagnosis (CDC criteria); blood cultures often negative in staphylococcal TSS (toxin-mediated, low bacteremia). | Identify and remove the source (retained tampon, wound packing, abscess) — source control is essential. |
Fungal disease that behaves like an ICU emergency: neutropenic, transplant, and DKA hosts where the antifungal has to start before speciation.
| Infection | Empiric Antifungal | Rationale | Symptom Profile | Clinical Result Profile | Notes |
|---|---|---|---|---|---|
| Candidemia / Invasive Candidiasisseptic ICU patient | Echinocandin (micafungin/caspofungin) | Fungicidal activity and coverage of azole-resistant species make it preferred first-line in the unstable ICU patient pending speciation. | Persistent fever/shock unresponsive to broad-spectrum antibacterial therapy in a line-bearing, post-op, or TPN-dependent ICU patient. | Blood cultures positive for Candida species; dilated fundoscopic exam to exclude endophthalmitis. | Source control (line removal/exchange) is essential; step down to fluconazole once susceptible and stable. |
| Invasive Pulmonary Aspergillosis | VoriconazoleAlt: isavuconazole (fewer interactions/QT effects) | Voriconazole is first-line per IDSA guidance for reliable Aspergillus activity and CNS penetration. | Fever, cough, hemoptysis, pleuritic chest pain in a neutropenic, transplant, or chronic-steroid ICU patient. | CT: halo sign or air-crescent sign; serum galactomannan (+); BAL galactomannan more sensitive than serum. | Mortality remains high even with treatment; early initiation on radiographic suspicion improves outcomes. |
| Mucormycosisrhino-orbital-cerebral | Liposomal amphotericin B (high-dose)+ Emergent Surgical Debridement | Amphotericin remains the most reliably active agent against Mucorales; azoles (fluconazole, voriconazole) have no activity — a critical distinction from Aspergillus. | Facial pain/swelling, black necrotic eschar on palate/nasal turbinates, proptosis, cranial nerve deficits in poorly-controlled DKA or profound neutropenia. | Biopsy: broad, non-septate, right-angle branching hyphae; CT/MRI shows sinus/orbital invasion. | Surgical debridement is co-equal with antifungal therapy — delay in either drives mortality. |
| Pneumocystis Pneumonia (PJP) | TMP-SMX (high-dose)+ corticosteroids if PaO2 <70 or elevated A-a gradient | TMP-SMX remains first-line with the best-evidenced outcomes; steroids blunt the inflammatory response to organism die-off that otherwise worsens hypoxemia. | Subacute dyspnea, dry cough, fever in AIDS (CD4 <200) or other profound immunosuppression. | CXR/CT: bilateral ground-glass infiltrates; elevated LDH; BAL silver stain or PCR for Pneumocystis jirovecii. | Steroids must start with or before the first antimicrobial dose in moderate-severe hypoxemia, not after. |
Viral disease severe enough to need ICU-level supportive care, with the narrow set of cases where an antiviral genuinely changes the outcome.
| Infection | Empiric Antiviral / Mgmt | Rationale | Symptom Profile | Clinical Result Profile | Notes |
|---|---|---|---|---|---|
| Severe Influenzaviral ARDS | Oseltamivir (IV peramivir if enteral route unusable)+ lung-protective ventilation | Antiviral therapy is indicated regardless of symptom-onset timing once hospitalized with severe disease; the IV formulation covers patients who can't absorb enterally. | Rapid progression to hypoxemic respiratory failure, bilateral infiltrates, hemodynamic instability during flu season/outbreak. | PCR respiratory panel (+) for influenza; CXR/CT bilateral ground-glass/consolidative infiltrates. | Watch for post-influenza necrotizing S. aureus (incl. MRSA) pneumonia — add empiric MRSA coverage if suspected. |
| HSV / VZV EncephalitisICU | IV Acyclovir (high-dose) — start empiricallyTreat Before Confirmation | Untreated mortality is extremely high, and the drug's toxicity profile is low enough to justify empiric use on suspicion alone — same principle as the outpatient/floor entry. | Fever, altered mentation, seizures, focal deficits; consider in any ICU patient with unexplained encephalopathy plus fever. | MRI temporal lobe changes (HSV); CSF PCR for HSV/VZV; EEG may show PLEDs in HSV. | Monitor renal function and hydration closely — acyclovir crystallizes in renal tubules at high doses. |
| Severe COVID-19pneumonia / ARDS | Remdesivir + dexamethasone± immunomodulator (tocilizumab/baricitinib) per severity | Remdesivir modestly reduces recovery time in hospitalized hypoxemic patients; dexamethasone reduces mortality specifically in patients requiring supplemental oxygen or ventilation by dampening the hyperinflammatory phase. | Progressive dyspnea, hypoxemia, bilateral infiltrates roughly 7–10 days into the illness course (inflammatory phase). | PCR (+) for SARS-CoV-2; CXR/CT bilateral peripheral ground-glass opacities; elevated CRP, ferritin, D-dimer. | Timing matters — steroids given early in the viral-replication phase (before hypoxemia) may worsen outcomes. |
| CMV Reactivationcritically ill / transplant ICU | Ganciclovir (or valganciclovir PO if tolerating enteral route) | Viral kinase-dependent activation targets actively replicating CMV; treatment is reserved for end-organ disease or high viral load in the immunosuppressed/transplant ICU population, not incidental low-level viremia. | Unexplained fever, worsening pulmonary status (pneumonitis), or GI bleeding/diarrhea (colitis) in a transplant or critically ill immunosuppressed patient. | CMV PCR viral load trending; tissue biopsy with immunohistochemistry for definitive end-organ disease diagnosis. | Ganciclovir causes significant myelosuppression — monitor counts closely, especially with other marrow-suppressive agents. |
Low pretest probability, high consequence for missing the window — including select bioterrorism-relevant pathogens where recognition, not the antibiotic itself, is the rate-limiting step.
| Infection | Empiric Abx | Abx Rationale | Symptom Profile | Clinical Result Profile | Notes |
|---|---|---|---|---|---|
| Anthraxcutaneous | Ciprofloxacin or doxycycline | B. anthracis remains fluoroquinolone/tetracycline-sensitive; oral therapy sufficient for localized cutaneous disease without systemic toxicity. | Painless papule → vesicle → black eschar with surrounding non-pitting edema; history of animal hide/wool/livestock exposure. | Gram stain/culture of lesion: large Gram-positive boxcar-shaped rods; PCR confirmatory. | Do not debride the eschar — it typically resolves with antibiotics alone; systemic spread is the real risk. |
| Anthraxinhalational / systemic | Ciprofloxacin (or levofloxacin) + linezolid + a third agent — multi-drug IVAdd antitoxin (raxibacumab/obiltoxaximab) if available | Systemic disease requires bactericidal + protein-synthesis-inhibiting combination to both kill the organism and halt ongoing toxin production; antitoxin neutralizes circulating lethal/edema toxin the antibiotics can't touch. | Biphasic: flu-like prodrome → abrupt respiratory failure, mediastinal widening, shock. GI form: severe abdominal pain, bloody diarrhea after contaminated meat. | CXR/CT: widened mediastinum (hemorrhagic mediastinitis), pleural effusions; blood cultures, PCR. | Report to Public Health Suspected bioterrorism exposure — near-uniform fatality without early recognition and treatment. |
| Plaguebubonic | Streptomycin (or gentamicin)Alt: doxycycline, fluoroquinolone | Aminoglycosides remain first-line for Y. pestis given rapid bactericidal activity needed to outpace the organism's fulminant course. | Sudden fever, chills, and an intensely painful, swollen lymph node (bubo) — history of flea bite/rodent exposure (Southwestern US, endemic regions). | Gram stain of bubo aspirate: bipolar "safety-pin" staining Gram-negative coccobacillus; culture/PCR/serology confirms. | Untreated bubonic plague can progress to secondary septicemic or pneumonic plague — treat empirically on suspicion. |
| Plaguepneumonic | Streptomycin/gentamicin or fluoroquinolone IV | Same rationale as bubonic form, but pneumonic disease is uniformly and rapidly fatal without treatment and is the only form transmissible person-to-person via respiratory droplets. | Fulminant pneumonia: fever, cough, hemoptysis, respiratory failure within 1–2 days of exposure. | Sputum Gram stain/culture: bipolar-staining Gram-negative rod; CXR shows rapidly progressive consolidation. | Droplet Isolation Only form transmissible human-to-human — implement droplet precautions immediately, notify public health. |
| Botulism | Botulinum antitoxin — antibiotics are not primary treatment | Disease is toxin-mediated, not infection-mediated; antitoxin neutralizes circulating unbound toxin. Aminoglycosides are specifically avoided — they potentiate neuromuscular blockade. | Descending, symmetric flaccid paralysis: diplopia, dysarthria, dysphagia progressing to respiratory failure; afebrile, no sensory deficit. | Clinical diagnosis; toxin assay (mouse bioassay or PCR) of serum/stool/food source; EMG shows characteristic incremental response. | Avoid Aminoglycosides Infant botulism (honey exposure) uses human botulism immune globulin, not equine antitoxin. |
| Tularemia | Streptomycin (or gentamicin)Alt: doxycycline, ciprofloxacin for milder disease | Francisella tularensis is an intracellular organism requiring an agent with good intracellular penetration and bactericidal activity for severe/systemic disease. | Ulceroglandular form: painful skin ulcer + tender regional lymphadenopathy after tick/rabbit/deer-fly exposure; can also present as pneumonic or typhoidal illness. | Serology (most common confirmatory method); culture is hazardous to lab personnel — notify lab of suspicion. | Classic exposure: skinning/handling rabbits or other wild game; consider in hunters/trappers. |
| MeningococcemiaWaterhouse-Friderichsen | Ceftriaxone (empiric, immediately)+ hydrocortisone if adrenal hemorrhage/shock | N. meningitidis progresses from petechiae to purpura fulminans within hours; immediate ceftriaxone reduces mortality dramatically, and stress-dose steroids address adrenal hemorrhage-driven shock. | Fever, rapidly spreading petechial/purpuric rash, hypotension, DIC; can progress to full circulatory collapse within hours. | Blood cultures (do not delay treatment to obtain); adrenal hemorrhage on CT in Waterhouse-Friderichsen; DIC labs (low platelets, elevated INR/PTT, low fibrinogen). | Treat Before Confirmation Give antibiotics on clinical suspicion — do not wait for LP or culture results. |
| Rocky Mountain Spotted Fever | Doxycycline — start empirically, at any age | Doxycycline is the only agent proven to reduce mortality; delay while awaiting serology (often negative early) significantly worsens outcomes — this overrides usual pediatric tetracycline avoidance. | Fever, headache, myalgias, followed by a maculopapular rash starting on wrists/ankles and spreading centripetally to palms/soles. | Serology often negative in the first week (retrospective diagnosis); low platelets, low sodium, elevated LFTs are supportive clues. | Rash may be absent or atypical early — treat empirically based on exposure history and clinical suspicion alone. |
| LeptospirosisWeil's disease | Doxycycline (mild) or penicillin G / ceftriaxone (severe) | Both drug classes remain reliably active against Leptospira; severity dictates the switch from oral tetracycline to IV beta-lactam coverage. | Biphasic illness: fever, myalgias, conjunctival suffusion → severe form (Weil's disease) with jaundice, renal failure, hemorrhage after freshwater/animal urine exposure. | Serology (MAT) confirmatory but slow; elevated bilirubin with only mildly elevated transaminases (distinguishes from viral hepatitis), elevated CK, renal dysfunction. | Consider in returning travelers with fever after freshwater exposure (rafting, flooding) in endemic regions. |
| Rabiespost-exposure prophylaxis | Rabies immune globulin + vaccine series — not an antibiotic; prevention only | Immune globulin provides immediate passive antibody at the wound site while active vaccination builds durable immunity before the long incubation period ends — once symptoms begin, disease is essentially uniformly fatal. | Once symptomatic: agitation, hydrophobia, hypersalivation, autonomic instability progressing to paralysis and death. | Diagnosis (if symptomatic) via saliva PCR, skin biopsy (nuchal), or serology — pre-symptomatic PEP decision is clinical/exposure-based, not lab-based. | Prevention Is the Treatment PEP decision hinges on animal type, provocation, and local rabies prevalence — infiltrate immune globulin directly into and around the wound. |
| Viral Hemorrhagic FeverEbola / Marburg | Supportive care ± investigational monoclonal antibodies (Ebola) — no antibiotic role | These are viral, not bacterial, pathogens; management is aggressive supportive care (fluid/electrolyte repletion) plus, for Ebola specifically, monoclonal antibody therapy where available. | Fever, severe malaise, GI symptoms progressing to hemorrhagic manifestations (bleeding gums, petechiae, GI bleeding) in a patient with relevant travel/exposure history. | PCR confirmatory (send to reference lab under strict biosafety protocol); marked thrombocytopenia, elevated transaminases, coagulopathy. | Isolate + Notify Public Health Immediately Strict isolation (PPE, negative pressure) before any further workup — this is a diagnosis made by travel history first. |