Study guide
10.4 Antimicrobial Use and Infection in the Immunosuppressed
ABIM Neurocritical Care Subspecialty Certification Exam
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1 Introduction & Exam Overview
1.1 Current Exam Facts 1.2 Eligibility, Practice Pathway, and the IM Training Route 1.3 Format, Scoring, Pearson VUE, and Score Reports 1.4 How to Use This Independent Study Guide
2 ICU Neurologic Exam, Cerebral Physiology, and CSF
2.1 Neurological Examination in the ICU 2.2 Cerebral Physiology, ICP, CBF, and Autoregulation 2.3 CSF Physiology
3 Core Neuropharmacology
3.1 Osmotic Agents 3.2 Anti-Seizure Drugs 3.3 Anesthetics, Sedatives, Analgesia, and Paralytics 3.4 Antihypertensives, Vasopressors, and Inotropes
4 Reperfusion Drugs, Airway, and Ventilation
4.1 Thrombolytics, Anticoagulants, and Antiplatelets 4.2 Reversal of Anticoagulation After Acute Hemorrhage 4.3 Airway Management and Tracheostomy 4.4 Mechanical Ventilation
5 Hemodynamics and Shock
5.1 Hemodynamic Monitoring 5.2 IABP, Temporary VADs, LVAD, and ECMO 5.3 Diagnosis and Management of Shock
6 Nutrition, Temperature, and ICU Prophylaxis
6.1 Nutrition (01.J) 6.2 Temperature Control (01.K) 6.3 ICU Prophylaxis, Delirium, and Early Mobility (01.L)
7 General Trauma
7.1 Emergency Evaluation of Polytrauma, Chest, and Abdominal Trauma 7.2 Long-Bone Fractures and Fat Embolism 7.3 Burns, Electrical Injury, and Hanging/Strangulation
8 Pulmonary Critical Care
8.1 Pulmonary Physiology and ARDS (01.N.1–2) 8.2 PE, Pneumonia, and Pulmonary Edema (01.N.3, 7–8) 8.3 COPD, Asthma, PAH, and Bronchoscopy Basics (01.N.4–6, 9)
9 Cardiovascular Critical Care
9.1 Cardiovascular Physiology, Stress Cardiomyopathy, ACS, and Valves 9.2 Arrhythmias and Pacing 9.3 Acute Aortic Dissection and Cardiac Ultrasound
10 Renal and Infectious Disease
10.1 AKI, RRT, and Renal Drug Dosing 10.2 Acid-Base and Electrolyte Disorders 10.3 Severe Sepsis, Septic Shock, and Infective Endocarditis 10.4 Antimicrobial Use and Infection in the Immunosuppressed
11 Endocrine and Salt-Water Disorders
11.1 Pituitary Apoplexy, DI, and Panhypopituitarism (01.R.1–4) 11.2 SIADH and Cerebral Salt Wasting (01.R.5–6) 11.3 Thyrotoxicosis, Myxedema, Adrenal Crisis, and Dysglycemia (01.R.7–9)
12 Gastrointestinal Critical Care
12.1 GI Physiology, Acute Abdomen, Bleed, Ileus, and Perforation (01.S.1–5) 12.2 Mesenteric Ischemia and Abdominal Compartment Syndrome (01.S.6–7) 12.3 Fulminant Liver Failure, Cirrhosis Decompensation, and Hepatic Dosing (01.S.8–10)
13 Hematologic Disorders
13.1 Anemia, Transfusion, Thrombocytopenia, Coagulopathy, and DIC (01.T.1–4) 13.2 VTE in the Neuro ICU (01.T.5) 13.3 Chemo/Immune, SCT, CAR-T, Sickle Cell, and TMA (01.T.6–10)
14 Neuroimaging
14.1 CT of Brain and Spine 14.2 MRI and CT/MR Perfusion 14.3 Noninvasive Angiography and Catheter Angiography
15 EEG, EMG, and CSF Analysis
15.1 EEG, Standard and Processed (02.B) 15.2 Basic EMG Interpretation (02.G) 15.3 CSF Analysis (02.H)
16 ICP, TCD, and Multimodality Monitoring
16.1 ICP Monitoring (02.C) 16.2 Transcranial Doppler (02.D) 16.3 Brain-Tissue Oxygen and Multimodality Monitoring (02.E–F)
17 Brain Death and Bedside Procedures
17.1 Brain Death Prerequisites and Clinical Exam (02.I) 17.2 Apnea Testing and Ancillary Studies (02.I) 17.3 Vascular Access, Thoracic Echo, and Lung Ultrasound (02.J–L)
18 Coma, Anoxia, and Intracranial Hypertension
18.1 Coma and Other States of Altered Consciousness (03.A) 18.2 Global Anoxia-Ischemia and Post-Resuscitation Encephalopathy (03.A.1) 18.3 Toxidromes, ICU Delirium, and Hypertensive Encephalopathy (03.A.2–4) 18.4 Intracranial Hypertension as a Disease State (03.B)
19 Acute Ischemic Stroke
19.1 IV Reperfusion Therapy (03.C.3) 19.2 Mechanical Thrombectomy Windows and Imaging Selection (03.C.3) 19.3 Malignant Hemispheric Infarction and Basilar Artery Occlusion (03.C.1–2)
20 Intraparenchymal Hemorrhage
20.1 Intracerebral Hematoma (03.D.1) 20.2 Cerebellar Hematoma (03.D.2) 20.3 Intraventricular Hemorrhage (03.D.3)
21 SAH, CVST, and Spinal Cord Infarction
21.1 Aneurysmal Subarachnoid Hemorrhage (03.E.1) 21.2 Non-Aneurysmal SAH (03.E.2) 21.3 Cerebral Venous Sinus Thrombosis (03.F) 21.4 Spinal Cord Infarction (03.G)
22 Vascular Anomalies and Traumatic Brain Injury
22.1 Unruptured Aneurysm, Cavernoma, AVM, and Dural AVF (03.H) 22.2 Diffuse Axonal Injury and Cerebral Contusions (03.I.1–2) 22.3 Epidural Hematoma, Subdural Hematoma, and Penetrating Injury (03.I.3–4, 7) 22.4 Arterial Dissection and Carotid-Cavernous Fistula (03.I.5–6)
23 Spine, Hydrocephalus, and CNS Infection
23.1 Spinal Cord Injury, Central Cord, and Neurogenic Shock (03.J) 23.2 Unstable Spine Fractures (03.K) 23.3 Hydrocephalus and CSF Diversion (03.L) 23.4 Acute CNS Infections (03.M)
24 Seizures and Neuromuscular Emergencies
24.1 Status Epilepticus and Seizures (03.N) 24.2 Guillain-Barré Syndrome (03.O.1) 24.3 Myasthenic Crisis (03.O.2) 24.4 Motor Neuron Disease, Acute Myopathies, Rhabdomyolysis, and CINM (03.O.3–6)
25 Inflammatory Disease, Neuro-Oncology, and Special Populations
25.1 Fulminant Demyelinating Diseases (03.P) 25.2 Autoimmune Encephalitis and Acute Autonomic Hyperactivity (03.Q–R) 25.3 Neuro-Oncology and Treatment Complications (03.S) 25.4 Pregnancy/Post-Partum, Post-Transplant, and Pediatric Patients (03.T–U)
26 Neurosurgical and Perioperative Complications
26.1 Postoperative Seizures, Hemorrhage, Ischemia, and Hyperperfusion (04.A, C, D, H) 26.2 Infection, CSF Leak, and Pneumocephalus (04.B, E, F) 26.3 Complications of EVD and Lumbar Drain (04.G, I)
27 Ethics, Prognostication, and Organ Donation
27.1 Communication, Decision-Makers, Advance Directives, and DNR (05.A, B, G) 27.2 Uncertainties of Prognostication and the Self-Fulfilling Prophecy (05.C) 27.3 Palliative Care, Withdrawal, Withholding, and Futility (05.D–F) 27.4 Donation After Cardiac Death and Care of the Organ Donor (05.H–I)
10.4 Antimicrobial Use and Infection in the Immunosuppressed
Key Takeaways Explain This Topic AI
Stewardship in the neuro ICU means cultures that do not delay needed drugs, meningitis-range dosing, de-escalation when identities return, and stopping extra coverage that never reached CSF.
Ceftriaxone and cefepime (and meropenem) are used for meningitis because they reach CSF; piperacillin-tazobactam is not a meningitis drug.
Empiric community bacterial meningitis is vancomycin plus a third-generation cephalosporin pending cultures; add ampicillin when Listeria risk is present, and add acyclovir when HSV encephalitis is plausible.
Neutropenia, high-dose steroids, transplant, and CAR-T reopen aspergillus, Pneumocystis, CMV, and cryptococcus; prophylaxis and early antigen or PCR testing beat late cover-everything cocktails.
Cefepime neurotoxicity—myoclonus, encephalopathy, nonconvulsive status—clusters with unadjusted doses in AKI; obtain EEG and stop cefepime rather than stacking more antiseizure drugs around an ongoing toxin.
Last updated: September 2026
An antibiotic that never reaches CSF is theater. This independent ExamFinch section covers stewardship in a unit full of EVDs, blood–brain barrier (BBB) penetration, empiric community meningitis (vancomycin plus a third-generation cephalosporin), HSV acyclovir , opportunistic infection in neutropenia , steroids , transplant , and chimeric antigen receptor T-cell (CAR-T) therapy, and how cefepime neurotoxicity mimics nonconvulsive status epilepticus (NCSE) . Infectious Diseases Society of America ( IDSA ) bacterial meningitis and 2017 healthcare-associated ventriculitis documents are the named dosing logic; this chapter teaches that logic for the exam rather than reprinting those PDFs.
Stewardship that still respects a dying brain
Stewardship is not delayed care. It is:
- Right source (CSF, blood, urine, lungs, hardware) without a 45-minute treasure hunt in shock
- Right dose for the compartment (meningitis grams, not pneumonia grams)
- De-escalation when the organism and MIC return
- Duration that matches the disease (ventriculitis is not a 3-day cystitis)
Stopping drugs that cannot do the job you assigned (piperacillin-tazobactam for meningitis; linezolid as a lone pneumococcal meningitis drug without expert backup)
Every extra day of meropenem selects resistant Gram-negatives and Clostridioides difficile . Every underdose of ceftriaxone in meningitis selects dead patients. Those are both stewardship failures.
BBB penetration: who actually treats meningitis
Inflamed meninges open the barrier somewhat; you still need agents with a track record in CSF.
Agent CSF usefulness in meningitis Exam use
Ceftriaxone or cefotaxime Reliable for susceptible pneumococcus and meningococcus at meningitis doses ( ceftriaxone 2 g IV every 12 hours in adults) Community Gram-positive/negative coverage backbone
Cefepime Reaches CSF; anti-pseudomonal Healthcare ventriculitis; 2 g IV every 8 hours typical adult meningitis dosing
Ceftazidime CSF-active anti-pseudomonal Alternative to cefepime for healthcare Gram-negatives
Meropenem CSF-active carbapenem Healthcare ventriculitis, ESBL, or penicillin-allergic pathways; 2 g IV every 8 hours often used for CNS infection
Vancomycin Variable, concentration-dependent; never monotherapy for pneumococcus Add for resistant pneumococcus until MIC is known; trough commonly 15–20 µg/mL if intermittently dosed
- Ampicillin Needs high, frequent dosing ( 2 g IV every 4 hours ) Listeria
- Piperacillin-tazobactam Unreliable CSF levels Hospital pneumonia or belly— not meningitis
- Aminoglycosides Poor CSF after IV dosing Sometimes adjunct or intraventricular in selected Gram-negatives
- Acyclovir Reaches CSF HSV/VZV
The classic wrong answer is “broaden to piperacillin-tazobactam” when an EVD patient spikes a fever. You have broadened the abdomen and abandoned the ventricle.
Empiric community meningitis pending cultures
Adult community bacterial meningitis empiric therapy remains vancomycin plus a third-generation cephalosporin (ceftriaxone or cefotaxime) until pneumococcal susceptibility is known. Add ampicillin if the patient is older than about 50 years or immunocompromised ( Listeria ). Give dexamethasone just before or with the first antibacterial dose when pneumococcus is likely, then stop steroids if a different organism is identified. Do not withhold the first antibacterial hour to wait for LP if LP will be delayed by CT; draw blood cultures and treat, then sample CSF as soon as it is safe.
Healthcare-associated ventriculitis and meningitis (IDSA 2017): vancomycin plus cefepime, ceftazidime, or meropenem , chosen with local Gram-negative resistance in mind. Intraventricular antibiotics are a second-line adjunct when CSF is not clearing, not the opening move in every cloudy EVD.
HSV: acyclovir while the PCR is pending
Fever, altered mental status, seizures, temporal-lobe imaging, or a hemorrhagic CSF profile can be herpes simplex virus (HSV) encephalitis. Start acyclovir 10 mg/kg ideal body weight IV every 8 hours as soon as that phenotype is on the list. Reduce the interval or dose in AKI; acyclovir crystal nephropathy is a real reason creatinine climbs if the patient is volume-down. Stop acyclovir if a sensitive CSF PCR is negative and the story has moved on; do not run 21 days “just in case” without a diagnosis. VZV gets the same drug at similar intravenous doses when shingles plus vasculitis or encephalitis is the concern.
Opportunistic infection: four host stories
Think in hosts, not in random fungus names.
Host Window What to worry about First moves
Neutropenia (especially prolonged, after chemotherapy) Days of ANC <500/µL Bacterial Gram-negatives including Pseudomonas ; Candida ; Aspergillus as days stack Fever plus neutropenia protocols; chest CT if respiratory symptoms; galactomannan/beta-D-glucan as adjuncts
High-dose steroids (brain tumor, vasculitis, spinal cord protocols) Weeks Pneumocystis jirovecii (PCP) , aspergillus, Cryptococcus , Listeria , nocardia, HSV/VZV PCP prophylaxis with trimethoprim-sulfamethoxazole when steroids are high and prolonged; cryptococcal antigen if headache or encephalopathy
Solid-organ or allogeneic transplant Calendar of immune suppression CMV , PCP, aspergillus, cryptococcus, later JC virus CMV PCR when leukopenia or colitis or retinitis; continue PCP prophylaxis
CAR-T Neutropenic phase, then steroids/tocilizumab for CRS/ICANS Bacterial sepsis, CMV, aspergillus, PCP if prophylaxis lapses Do not attribute every encephalopathy to ICANS without considering infection and cefepime
Aspergillus loves prolonged neutropenia, steroids, and transplant lungs and sinuses. A new nodule, halo sign, or invasive sinus disease is a CT and antifungal decision, not a “watch overnight.” Voriconazole or other mold-active therapy is a named treatment family; check drug interactions with antiseizure meds (phenytoin induces azole metabolism; voriconazole can raise other levels).
PCP presents with hypoxia out of proportion to the chest film, elevated A-a gradient, and sometimes a normal auscultation. Steroid-taper periods are classic. Treatment is high-dose trimethoprim-sulfamethoxazole; add steroids when hypoxemia is significant, following HIV-era logic that is often extended to non-HIV immunocompromised hosts. Prophylaxis is easier than a 14-day ICU stay.
CMV is a transplant and CAR-T virus: fever, marrow suppression, pneumonitis, colitis, retinitis, and occasionally encephalitis. Plasma PCR plus tissue or quantitative CSF PCR when the CNS is involved. Ganciclovir or valganciclovir are the usual first agents; marrow toxicity matters in a patient who is already neutropenic.
Cryptococcus is steroids, transplant, and sometimes unexplained subacute meningitis with high opening pressure. Serum and CSF cryptococcal antigen, India ink as a historical adjunct, and careful pressure management (repeat LPs) are the exam cluster. Amphotericin plus flucytosine induction is the severe-disease backbone; fluconazole consolidates. A positive antigen in an immunocompromised headache is not “colonization.”
CAR-T cytokine release syndrome (CRS) and immune effector cell-associated neurotoxicity syndrome (ICANS) are not infections, but their treatment (tocilizumab, high-dose steroids) plus neutropenia creates an infection hole. Work up fever. Keep PCP prophylaxis on the list. Do not skip HSV prophylaxis in profoundly lymphopenic patients when local protocols call for it.
Cefepime neurotoxicity versus nonconvulsive status epilepticus
Cefepime is a workhorse for healthcare ventriculitis and febrile neutropenia. It is also a GABA-A antagonist in toxic concentrations. Risk explodes when AKI is under-dosed (the patient still gets 2 g every 8 hours on a creatinine of 3.5 mg/dL without CRRT) or when the drug accumulates in an oliguric patient overnight. Clinical picture: progressive encephalopathy, aphasia, myoclonus, agitation, or coma, often without a convincing new fever source. EEG may show triphasic waves, stimulus-induced patterns, or true NCSE .
The exam move is not “add a third antiseizure drug and continue cefepime because the wound needs it.” The move is:
EEG to characterize NCSE versus toxic encephalopathy
Stop cefepime (or immediately reduce to a renal-adjusted dose if you have no alternative and the EEG is not seizing)
Switch Gram-negative coverage to an agent the team can justify (ceftazidime, meropenem, aztreonam) based on allergies and microbiology
Treat definite NCSE with the status pathway (benzodiazepine, then a second agent) while removing the toxin
Cefepime toxicity and NCSE can coexist: the drug lowers the seizure threshold. Dialysis can clear cefepime if the patient already needs RRT. Other beta-lactams (including high-dose penicillin and some carbapenems) can cause similar encephalopathy, but cefepime is the one written into neuro ICU items over and over.
Differentiate from other encephalopathies: ICANS after CAR-T, HSV, cryptococcus, cefepime, and nonconvulsive seizures can look identical at the door. Time course (drug started 3 days ago; CAR-T infusion 5 days ago; transplant month 2) plus EEG plus a focused PCR/antigen panel is how you avoid treating only one of them.
Dosing reminders that show up as options
Load vancomycin and beta-lactams in sepsis even if GFR is low; then adjust.
On CRRT, meropenem and cefepime are cleared—do not use once-daily ESRD meningitis underdosing while the filter runs (see 10.1).
Acyclovir is dosed on ideal body weight to limit nephrotoxicity in obesity.
Trimethoprim-sulfamethoxazole for PCP is dosed on the trimethoprim component (commonly 5 mg/kg IV every 6–8 hours in severe disease) and interacts with phenytoin and warfarin.
Exam traps
Piperacillin-tazobactam for EVD infection. Ceftriaxone 1 g daily for bacterial meningitis. Forgetting vancomycin until the pneumococcal MIC returns resistant. Forgetting ampicillin in a 72-year-old. Stopping acyclovir before the HSV PCR is sent. Blaming ICANS for every CAR-T encephalopathy without EEG or infection labs. Continuing full-dose cefepime through anuria while treating “new seizures” with three anticonvulsants. Calling cryptococcal antigen colonization in a steroid-dependent patient with high opening pressure.