Give me dosage regimens and treatment guidelines for Pneumonia

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Pneumonia: Dosage Regimens and Treatment Guidelines

This guide covers Community-Acquired Pneumonia (CAP), Hospital-Acquired / Ventilator-Associated Pneumonia (HAP/VAP), Pneumocystis Pneumonia (PCP), and special pathogens. Based on ATS/IDSA guidelines and multiple major textbooks.

1. Severity Assessment Before Treatment

CURB-65 Score (Practical Bedside Tool)

Criterion	Points
Confusion (new-onset)	1
Urea > 19 mg/dL (7 mmol/L)	1
Respiratory rate >= 30/min	1
Blood pressure < 90 systolic or <= 60 diastolic	1
65 years or older	1

Score 0-1: Outpatient treatment likely safe (low mortality)
Score 2: Consider inpatient admission
Score >= 3: ICU-level care warranted; score >3 suggests intermediate or intensive care unit admission

The Pneumonia Severity Index (PSI) uses 20 variables; scores <=90 points (classes I-III) support outpatient management. Scores >130 warrant ICU consideration.

2. Community-Acquired Pneumonia (CAP)

Antibiotics should be started as soon as CAP is diagnosed, ideally within 4 hours of hospital arrival, as delays increase mortality. Therapy should be narrowed once a microbiologic etiology is confirmed.

Outpatient Regimens

No comorbidities, no MRSA/Pseudomonas risk:

Drug	Dose	Duration
Amoxicillin	1000 mg PO q8h	>= 5 days
Doxycycline	100 mg PO q12h	>= 5 days
Azithromycin	500 mg PO day 1, then 250 mg qday days 2-5	5 days

With comorbidities (chronic heart/lung/liver/renal disease, diabetes, alcoholism, malignancy, asplenia):

Combination therapy - choose one beta-lactam PLUS one atypical agent:

Beta-lactam (choose one)	Dose
Amoxicillin/clavulanate	875/125 mg PO q12h
Cefpodoxime	200 mg PO q12h
Cefuroxime	500 mg PO q12h

PLUS doxycycline 100 mg PO q12h OR azithromycin

OR Monotherapy with a respiratory fluoroquinolone:

Levofloxacin 750 mg PO qday
Moxifloxacin 400 mg PO qday

Inpatient Non-Severe CAP

Regimen	Agents
Beta-lactam + macrolide	Ampicillin-sulbactam 1.5-3 g IV q6h, OR ceftriaxone 1-2 g IV qday, OR cefotaxime 1-2 g IV q8h, OR ceftaroline 600 mg IV q12h PLUS azithromycin
Monotherapy	Levofloxacin or moxifloxacin (respiratory fluoroquinolone)

Note: In clinically stable patients, 3 days of IV beta-lactam therapy may be sufficient without oral step-down.

Inpatient Severe CAP (ICU Admission)

Dual therapy is mandatory:

Beta-lactam PLUS macrolide
Beta-lactam PLUS fluoroquinolone

Duration: Minimum 5 days for most; 7 days if MRSA or Pseudomonas suspected.

CAP with Special Resistance Risks

Prior MRSA Isolation / High-Risk MRSA

Add one of:

Drug	Dose
Vancomycin	15 mg/kg IV q12h (adjusted for renal function/levels)
Linezolid	600 mg IV/PO q12h

A rapid nasal MRSA PCR test can help guide decision - negative PCR has high negative predictive value.

Prior Pseudomonas Isolation / High-Risk P. aeruginosa

Add one of (anti-pseudomonal beta-lactam):

Drug	Dose
Piperacillin-tazobactam	4.5 g IV q6h
Cefepime	2 g IV q8h
Ceftazidime	2 g IV q8h
Imipenem	500 mg IV q6h
Meropenem	1 g IV q8h
Aztreonam	2 g IV q8h

3. Hospital-Acquired Pneumonia (HAP) and Ventilator-Associated Pneumonia (VAP)

Common MDR pathogens: MRSA, Pseudomonas aeruginosa, gram-negative bacilli (Klebsiella, Acinetobacter, Enterobacteriaceae).

Risk Factors for MDR Organisms

Category	Risk Factors
MDR VAP	Prior IV antibiotics within 90 days; septic shock at VAP onset; ARDS preceding VAP; >=5 days in hospital before VAP; acute renal replacement therapy
MDR HAP	Prior IV antibiotics within 90 days
MRSA VAP/HAP	See local antibiogram (>10-20% prevalence = cover empirically)

Empiric Therapy for HAP/VAP

Risk Category	Recommended Regimen
Not high mortality risk; low MRSA risk	Piperacillin-tazobactam OR Cefepime OR Imipenem/Meropenem OR Levofloxacin (monotherapy)
Not high mortality risk; MRSA risk present	Above anti-pseudomonal beta-lactam/FQ PLUS Vancomycin or Linezolid
High mortality risk (septic shock / mechanical ventilation)	Anti-pseudomonal agent from 2 different classes PLUS Vancomycin or Linezolid

If local gram-negative resistance >10% or rates unknown: use 2 anti-pseudomonal agents from different classes
MSSA confirmed: De-escalate to oxacillin, nafcillin, or cefazolin
MRSA confirmed: Vancomycin or linezolid
Avoid aminoglycosides as monotherapy (poor lung penetration, nephrotoxicity/ototoxicity risk)
Acinetobacter: Ampicillin-sulbactam or carbapenem (imipenem/meropenem; ertapenem has no Pseudomonas coverage)
De-escalate to monotherapy once septic shock resolves and cultures are available

4. Pneumocystis Pneumonia (PCP) - HIV/Immunocompromised Patients

(From Goldman-Cecil Medicine)

Mild PCP (PaO2 >= 70 mmHg or A-a gradient < 35 mmHg)

Preference	Drug	Route	Dose
Preferred	TMP-SMX	PO	2 DS tablets (160/800 mg) TID
Alternative	Trimethoprim + Dapsone	PO	TMP 5 mg/kg TID + Dapsone 100 mg qday
Alternative	Clindamycin + Primaquine	PO	Clindamycin 450 mg qday or 600 mg TID + Primaquine 30 mg (base) qday
Alternative	Atovaquone	PO	750 mg BID with food

Test for G6PD deficiency before using dapsone or primaquine.

Moderate-to-Severe PCP (PaO2 < 70 mmHg or A-a gradient >= 35 mmHg)

Preference	Drug	Route	Dose
Preferred	TMP-SMX	IV	TMP 5 mg/kg q8h + SMX 25 mg/kg q8h (= TMP 15 mg/kg/day + SMX 75 mg/kg/day); may switch to oral when improving
Alternative	Pentamidine	IV	3-4 mg/kg qday (infuse over >60 min)
Alternative	Clindamycin + Primaquine	IV/PO	Clindamycin 600 mg q6h or 900 mg q8h IV; Primaquine 30 mg (base) qday PO

Adjuvant Corticosteroids (Moderate-to-Severe, PaO2 < 70 mmHg)

Start within 72 hours (efficacy not demonstrated if started later):

Drug	Route	Dose/Schedule
Prednisone	PO	40 mg BID days 1-5; 40 mg qday days 6-10; 20 mg qday days 11-21
Methylprednisolone	IV	30 mg BID days 1-5; 30 mg qday days 6-10; 15 mg qday days 11-21

5. Newer/Reserve Antibiotics for Pneumonia

(From Fishman's Pulmonary Diseases)

Drug	Class	Coverage	Dose
Omadacycline	Aminocycline	MRSA, DRSP, atypicals	100 mg IV once daily
Lefamulin	Pleuromutilin	MRSA, MSSA, VRE, DRSP, Legionella, Mycoplasma, Chlamydia	450 mg PO q12h x 5 days
Delafloxacin	Non-fluorinated quinolone	MRSA, Enterococcus, Mycoplasma, Legionella	300 mg IV q12h, then 450 mg PO q12h x 5-10 days
Nemonoxacin	Novel quinolone	Gram-positive, gram-negative, atypicals, MRSA, VRE	500 mg once daily x 7 days
Telavancin	Lipoglycopeptide	Gram-positive including MRSA/VRE	10 mg/kg q24h
Ceftobiprole	5th-gen cephalosporin	MSSA, H. influenzae, K. pneumoniae, P. aeruginosa	600 mg PO BID

Key considerations:

Lefamulin and fluoroquinolones are contraindicated in prolonged QT interval
Lefamulin is also contraindicated in moderate-to-severe liver disease
Fluoroquinolones carry risk of C. difficile, tendinopathy, peripheral neuropathy, and QT prolongation

6. Aspiration Pneumonia

Common organisms: Oral anaerobes (Prevotella, Peptostreptococcus, Fusobacterium, Bacteroides, Actinomyces), MRSA, Klebsiella.

Routine anaerobic coverage (e.g., clindamycin) is not recommended unless lung abscess or empyema is suspected
Empiric regimens otherwise follow CAP or HAP guidelines based on setting

7. Duration of Therapy Summary

Setting	Duration
Outpatient CAP (uncomplicated)	5 days
Inpatient non-severe CAP (stable)	3-5 days IV, then oral if clinically stable
Inpatient severe CAP	Minimum 5 days
Suspected MRSA or Pseudomonas	7 days
HAP/VAP	Based on clinical response; de-escalate once culture data available
PCP (mild)	21 days total
PCP (moderate-severe)	21 days total

8. Adjunctive and Supportive Measures

Corticosteroids in CAP: Not recommended routinely; reserved for refractory septic shock (hydrocortisone 200 mg for 4-8 days may be considered)
Thoracentesis: Perform on pleural effusions (analyze pH, cell count, Gram stain, culture, protein, LDH); drain empyemas
Influenza co-infection: Add antiviral therapy (oseltamivir) plus antibiotics for bacterial co-infection; treat all hospitalized influenza-positive patients regardless of symptom duration
SARS-CoV-2: Do NOT give antibiotics unless bacterial co-infection is suspected; use antivirals/antibody treatments in high-risk patients
Procalcitonin: Professional societies recommend against using procalcitonin alone to decide whether to start antibiotics
De-escalation: Always narrow therapy once culture/susceptibility data are available

Sources: The Washington Manual of Medical Therapeutics; Goldman-Cecil Medicine; Fishman's Pulmonary Diseases and Disorders; Current Surgical Therapy 14e - based on ATS/IDSA 2019 CAP Guidelines and IDSA/ATS 2016 HAP/VAP Guidelines.

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