Antibacterial therapy for pneumonia: what drugs are used?

Pneumonia can have various causes. Antibiotics are indicated when a bacterial cause is suspected or when there is a high risk of bacterial complications, while in the case of viral pneumonia without signs of bacterial overgrowth, antiviral and supportive measures are the priority. The decision on antibacterial therapy is based on clinical presentation, severity, examination data, and the epidemiological context. The minimum reasonable duration of treatment for community-acquired pneumonia in adults is at least 5 days, once clinical stability has been achieved. [1]

The key principle today is early initiation of empirical therapy when bacterial pneumonia is clinically suspected, followed by clarification based on laboratory and microbiological data, and mandatory de-escalation in the absence of risk factors for resistant pathogens. This approach improves survival while simultaneously reducing the pressure on resistance. [2]

Drugs are selected based on the infection site and risk factors: community-acquired, hospital-acquired, or ventilator-associated, the presence of comorbidities, previous antibacterial therapy, contact with healthcare providers, and local resistance data. The presence of risk factors for resistant pathogens requires expanded initial coverage, but does not negate the principle of subsequent de-escalation. [3]

High fever, dyspnea, tachycardia, decreased oxygen saturation, altered consciousness, hypotension, and involvement of multiple lung lobes are signs of severe progression, requiring hospitalization, oxygen, and parenteral antibiotics. European guidelines for severe community-acquired pneumonia emphasize the timely initiation of combination therapy and close monitoring. [4]

Antibiotics do not replace supportive care: oxygen therapy, fluid resuscitation as indicated, fever control, thrombosis prophylaxis, and nutritional support. Diagnosis clarification and pathogen identification continue in parallel with treatment. [5]

Table 1. Where we start with antibiotics when pneumonia is suspected

Situation	Action
Community-acquired bacterial pneumonia in an adult	Immediate empirical treatment, then de-escalation
Severe community-acquired pneumonia	Combination therapy and hospitalization
Viral pneumonia without signs of bacterial complication	Etiotropic antiviral therapy according to indications and observation
Nosocomial or ventilator-associated pneumonia	Broad starting coverage taking into account risk factors and local antibiogram
[6]

Etiology and classification: from "home" to "hospital"

Community-acquired pneumonia in adults is most often caused by pneumococci, Haemophilus influenzae, atypical pathogens such as mycoplasma and chlamydia pneumoniae, and, less commonly, Legionella. The risk of resistant strains increases in people with underlying medical conditions, recent antibiotic use, and in the elderly. This determines the choice of initial regimen. [7]

Hospital-acquired and ventilator-associated pneumonia are most often associated with gram-negative bacteria, including Pseudomonas aeruginosa, and methicillin-resistant Staphylococcus aureus. Local antibiograms and individual risk factors must be considered when selecting a dressing. [8]

Severe community-acquired pneumonia is classified as a separate clinical and tactical group with a higher mortality rate: international European recommendations offer clear algorithms for the initiation of combination therapy and intensive monitoring. [9]

For children, the spectrum of pathogens and the choice of antibiotics differ: pneumococcus has priority and the dose-dependent effect of amoxicillin plays a high role; atypical pathogens are significant in schoolchildren and adolescents. [10]

Finally, during viral epidemics, rapid diagnosis of the influenza virus and other respiratory viruses is important, since confirmed influenza in adults is an indication for the early administration of antiviral drugs, and antibiotics are only used if there is certainty of a bacterial complication. [11]

Table 2. Who we expect more often under different scenarios

Scenario	Possible pathogens	Practical tip
Outpatient, no severity	Pneumococcus, Haemophilus influenzae, Mycoplasma, Chlamydia pneumoniae	Cover typical and atypical cases according to indications
Outpatient, severe	Pneumococcus, Legionella, Staphylococcus	Combination with a macrolide or respiratory fluoroquinolone
Nosocomial and ventilator-associated	Gram-negative, Pseudomonas aeruginosa, methicillin-resistant Staphylococcus aureus	Initial broad coverage of risks and antibiograms
[12]

Adults, outpatient treatment: first-line regimens

For mild community-acquired pneumonia without comorbidities or resistance risk factors, amoxicillin at an appropriate dose remains the first-line treatment. Doxycycline is an alternative, especially if an atypical etiology is suspected. Macrolides are acceptable as monotherapy only in cases where local pneumococcal resistance to macrolides is low. The minimum course duration is 5 days until stability is achieved. [13]

For patients with comorbidities or recent antibiotic use, amoxicillin with clavulanic acid plus a macrolide or doxycycline, or monotherapy with a respiratory fluoroquinolone, is recommended unless contraindicated. The advantage of the combination regimen is coverage of both typical and atypical pathogens with a moderate risk of resistance selection. [14]

It is important to immediately discuss a de-escalation plan and follow-up contact timeframes. If progress is good, repeat imaging is not routinely required. If there is no improvement within 48-72 hours, the diagnosis, adherence, and pathogen susceptibility are reviewed. [15]

Prescribing antibiotics for confirmed influenza without signs of a bacterial complication does not improve outcomes and increases the risk of adverse reactions. Therefore, antiviral therapy and observation are the priority. The exception is the appearance of signs of a bacterial superinfection. [16]

Consider drug interactions and the risk of prolonging the ECG interval for macrolides and fluoroquinolones, especially in the elderly and with polypharmacy. Choosing a beta-lactam with a macrolide is often safer. [17]

Table 3. Outpatient regimens for adults

Clinical situation	Recommended options	Duration at stability
No concomitant diseases	Amoxicillin; or doxycycline; macrolide if local resistance is low	At least 5 days
With concomitant diseases	Amoxicillin with clavulanic acid plus a macrolide or doxycycline; or a respiratory fluoroquinolone	At least 5 days
Confirmed influenza without bacterial signs	Antiviral therapy, without antibiotics	According to antiviral recommendations
[18]

Adults, hospital: mild and severe community-acquired pneumonia

For hospitalizations without signs of severity, beta-lactam with a macrolide or monotherapy with a respiratory fluoroquinolone are recommended. The addition of a macrolide to beta-lactam improves outcomes due to coverage of atypical pathogens and immunomodulation. Transition to oral therapy is performed when stable, maintaining a total duration of at least 5 days. [19]

For severe community-acquired pneumonia, international European guidelines recommend combination therapy: beta-lactam plus a macrolide or beta-lactam plus a respiratory fluoroquinolone. In intensive care units, this regimen is initiated immediately after collecting biopsy specimens for culture. [20]

For methicillin-resistant staphylococci, linezolid or vancomycin is added; for Pseudomonas aeruginosa, an antipseudomonal beta-lactam is added, with subsequent de-escalation based on the results. The decision is based on the colonization history, recent hospitalization, and local resistance data. [21]

The duration of hospitalization is similar to that of outpatient treatment: the goal is to achieve stability and the absence of uncontrolled lesions. Prolongation of the course is warranted in the case of abscesses, significant pleural effusions, or slow stabilization. Routine systemic glucocorticosteroids are not indicated for community-acquired pneumonia without shock. [22]

The use of procalcitonin is reasonable to support the decision to de-escalate and discontinue therapy in severely ill patients, but should not delay the initiation of empirical antibiotics when there is a high clinical suspicion of bacterial pneumonia.[23]

Table 4. Inpatient regimens for adults

Scenario	Basic options	What to add in case of risks
Hospitalization, no severity	Beta-lactam plus macrolide; or respiratory fluoroquinolone	-
Severe out-of-hospital	Beta-lactam plus macrolide; or beta-lactam plus respiratory fluoroquinolone	Linezolid or vancomycin for methicillin-resistant staphylococci; antipseudomonal beta-lactam for Pseudomonas aeruginosa risk
[24]

Hospital-acquired and ventilator-associated pneumonia: how to start correctly

For hospital-acquired and ventilator-associated pneumonia, initial therapy depends on individual resistance risks and local antibiogram data. It is recommended to cover probable pathogens with a broad initial regimen, followed by de-escalation after 48-72 hours and obtaining microbiological results. Standard options include antipseudomonal beta-lactams; if there is a risk of methicillin-resistant staphylococci, the addition of linezolid or vancomycin. [25]

The duration of therapy for uncomplicated hospital-acquired and ventilator-associated pneumonia is usually 7-8 days with good progression. Longer courses are justified in cases of slow clinical stabilization, abscess, pleural empyema, or infections caused by non-fermentative gram-negative bacteria, or in cases of complicated lesions. [26]

Procalcitonin can be used as part of a antibiotic stewardship program to help guide early de-escalation in stable patients on long-term ventilation, but the biomarker does not replace clinical and culture data.[27]

Early switching to monotherapy after detection of susceptibility is safe and reduces toxicity if the patient does not have signs of severe sepsis and a susceptible pathogen is identified. This is one tool for containing resistance. [28]

Close communication with the laboratory and daily review of antibiotic indications are essential. Each additional day of unnecessary treatment increases the risk of adverse effects and colonization with resistant strains. [29]

Table 5. Nosocomial and ventilator-associated pneumonia

Step	The essence	Comment
Start	Extensive empirical coverage of risks and antibiograms	Add antistaph agent if appropriate risks exist
Review at 48-72 hours	De-escalation to a narrow spectrum based on results	Transition to oral route when stable
Duration	Usually 7-8 days with stability	Longer in case of complications
[30]

Children: doses, duration, atypical pathogens

In children with mild community-acquired pneumonia, high-dose amoxicillin remains the first-line treatment, as it overcomes the reduced susceptibility of pneumococci. The typical range is approximately 90 milligrams per kilogram of body weight per day, divided into 2-3 doses, taking into account the maximum daily dose according to the instructions. [31]

If an atypical etiology is suspected in schoolchildren and adolescents, a macrolide is added. The duration of treatment in uncomplicated cases is usually 5-7 days, provided the patient is stable. Dosage and drug selection are adjusted based on age, weight, and epidemiological factors. [32]

Hospitalization is indicated for severe respiratory failure, malnutrition, ineffective outpatient therapy, and the presence of concomitant conditions. Parenteral beta-lactams are initiated in the hospital, with subsequent transition to oral forms based on clinical findings. [33]

Antibiotics are not prescribed if purely viral pneumonia is suspected without signs of bacterial addition; if influenza is confirmed in children, early antiviral therapy and observation are indicated. [34]

Parents are informed of the importance of adherence and the criteria for immediate referral: worsening shortness of breath, recurrence of fever, refusal to drink, drowsiness, and cyanosis. This reduces the risk of complications and rehospitalization. [35]

Table 6. Pediatric landmarks

Situation	Drug and dosage	Duration
Mild community-acquired pneumonia	Amoxicillin about 90 mg per kg per day in 2-3 doses	5-7 days
Suspected atypical etiology	Add macrolide based on age and weight	Around the clinic
Inpatient	Parenteral beta-lactam with transition to oral	According to the clinic and stability
[36]

Duration, transition to oral administration, de-escalation

In adults with community-acquired pneumonia, most regimens can be completed within 5 days once stability is achieved: normalization of temperature, pulse, and respiration, adequate oxygen saturation, normal consciousness, and stable blood pressure. Extending the course is justified in the event of complications or slow stabilization. [37]

The transition to oral therapy occurs when the patient is eating and drinking, the temperature has subsided, there are no signs of sepsis, and the selected antibiotic has an equivalent oral form. This shortens hospitalization without worsening outcomes. [38]

De-escalation is mandatory after culture and resistance test results are available, and even earlier if negative predictors of highly resistant pathogens are present. This is a central element of antibiotic stewardship. [39]

Procalcitonin and other biomarkers can be used as auxiliary arguments for termination of therapy in stable patients, but clinical picture and dynamics remain primary. [40]

Repeat chest imaging is not routinely needed in patients with a good clinical response; it is performed in cases of atypical presentation, in older smokers, and in patients with persistent symptoms. Local guidelines describe groups for follow-up imaging. [41]

Table 7. Duration and criteria of clinical stability in adults

Parameter	Landmark for completion
Body temperature	No fever for approximately 48 hours
Pulse and respiration	Within safe limits for the patient
Oxygen saturation	Acceptable in air or stable with minimal support
Consciousness, pressure	No delirium, stable blood pressure
Foci and complications	There are no signs of an uncontrolled outbreak
[42]

Special groups and safety: pregnancy, allergies, heart and kidneys

During pregnancy, beta-lactams and macrolides are preferred for community-acquired pneumonia, as indicated; fluoroquinolones are avoided. Doses and duration are individualized; in severe cases, treatment is managed jointly by an obstetrician and a pulmonologist. [43]

For a true beta-lactam allergy, options include respiratory fluoroquinolones in adults or a combination of alternative antibiotics based on the pathogen and risks. It is important to double-check the medical history, as many "allergies" turn out to be intolerances rather than immune reactions. [44]

Renal and hepatic impairment require dosage adjustments. In cases of polypharmacy, interactions are assessed: macrolides and fluoroquinolones can prolong the ECG interval, increasing the risk of arrhythmia, especially in the elderly. A combination of a beta-lactam plus a macrolide with monitoring is often preferred. [45]

Antibiotics for hospital-acquired and ventilator-associated pneumonia vary in their side effects and nephrotoxicity. A broad-spectrum approach is recommended only until results are obtained, and then coverage should be narrowed. This reduces toxicity and curbs resistance. [46]

Influenza and pneumococcal vaccination in adults and children significantly reduces the risk of severe forms of the disease and hospitalizations. Prevention complements, and does not replace, appropriate antibacterial therapy for the disease. [47]

Table 8. Quick solutions in special situations

Situation	What to prefer	What to avoid
Pregnancy	Beta-lactams, macrolides as indicated	Fluoroquinolones
True beta-lactam allergy	Alternative regimens or fluoroquinolone in adults	Unauthorized discontinuation of therapy
Old age, cardiac risk	Caution with macrolides and fluoroquinolones, monitoring	Ignoring interactions
Renal failure	Dose adjustment	Standard doses without clearance calculation
Nosocomial pneumonia	Wide start with de-escalation	Long-term "extensive" treatment without the need
[48]

A short reminder

1. Start promptly, choose a regimen based on the location of infection and risks, and plan for de-escalation from day one. At least 5 days for stable adults with community-acquired pneumonia. [49]
2. In hospital, do not prolong combination therapy in severe cases. Then narrow the coverage as soon as possible based on the results. [50]
3. In children, the priority is amoxicillin in high doses, macrolide according to indications. [51]
4. Biomarkers help to complete, but not initiate, treatment. Clinical and dynamic characteristics are primary. [52]
5. Treat viral flu with antiviral drugs, and antibiotics only if there is a bacterial complication. [53]