Pneumonia

Pneumonia is the most common cause of death from infectious diseases worldwide. The most frequent pathogens responsible for community-acquired pneumonia (CAP) in adults include Streptococcus pneumoniae, Haemophilus influenzae, Mycoplasma pneumoniae, and Chlamydia species. Less common pathogens such as Legionella species, Staphylococcus aureus, and enteric gram-negative bacilli often produce more severe disease.

Common pathogens causing pneumonia in hospitalized patients or residents of long-term care facilities include: Staphylococcus aureus, aerobic enteric gram-negative bacilli, Pseudomonas aeruginosa, and mixed aerobic–anaerobic organisms.

Diagnosis of Pneumonia

Clinical manifestations of pneumonia may include:

• Cough

• Sputum production

• Shortness of breath

• Chest pain

• Fever

• Fatigue

• Sweating

• Headache

• Nausea

• Muscle pain

• Occasionally abdominal pain or diarrhea

Treatment

Depending on severity, a patient with pneumonia may receive outpatient treatment, be hospitalized in a general infectious diseases ward, or require ICU admission. Treatment varies accordingly.

1. Outpatient Management

A. Patients without comorbidities and no recent antibiotic use (past 3 months):

• A newer macrolide such as azithromycin, or

• Doxycycline

B. Patients without comorbidities but with recent antibiotic use:

• A respiratory fluoroquinolone alone, or

• A newer macrolide (e.g., azithromycin) plus a beta-lactam (e.g., amoxicillin-clavulanate)

2. Summary of Outpatient Regimens

3. Patients with Comorbidities (diabetes, renal failure, heart failure, cancer) Requiring Hospitalization

A. No recent antibiotic therapy:

• Newer macrolide + an injectable beta-lactam, or

• Respiratory fluoroquinolone

B. Recent antibiotic therapy:

• If recently treated with a fluoroquinolone → macrolide + beta-lactam

• If recently treated with a macrolide → respiratory fluoroquinolone

4. ICU Patients

A. Pseudomonas infection not suspected:

• Newer macrolide (azithromycin) + injectable beta-lactam, or

• Respiratory fluoroquinolone

B. Pseudomonas not suspected, but patient has beta-lactam allergy:

• Respiratory fluoroquinolone + clindamycin

C. Suspected Pseudomonas infection (e.g., CF patients or immunocompromised):

• Anti-pseudomonal beta-lactam (imipenem or meropenem) + ciprofloxacin

• Anti-pseudomonal beta-lactam + a respiratory fluoroquinolone or a newer macrolide

D. Suspected Pseudomonas infection + beta-lactam allergy:

• Aztreonam + aminoglycoside + respiratory fluoroquinolone

5. Healthcare-Associated Pneumonia (HCAP)

• Anti-pseudomonal beta-lactam + ciprofloxacin or levofloxacin

• Anti-pseudomonal beta-lactam + aminoglycoside + respiratory fluoroquinolone with a newer macrolide + vancomycin or linezolid for possible MRSA

What Is Drug Allergy?

Drug allergy—also called drug hypersensitivity—is an immune-mediated reaction in which the drug is mistakenly identified as a harmful invader. The immune system, instead of fighting disease, reacts abnormally to the medication.

Symptoms of a drug-allergic reaction may include:

• Skin rashes, redness, hives

• Itching

• Swelling

• In severe cases: difficulty breathing, low blood pressure, and even death

Important:
A drug allergy is not the same as a drug side effect.
Side effects can occur in anyone, whereas allergic reactions occur only in a small subset of people.

Drug allergies are classified into several types, each with distinct manifestations.

Immediate (Rapid) Drug Allergy

This is the most serious form and occurs shortly after taking the medication, often even if the drug was previously tolerated.

Symptoms include:

• Hives (raised, red, itchy lesions)

• Itching

• Flushing

• Swelling of the face, hands, feet, or throat

• Throat tightness, hoarseness, wheezing, breathing difficulty

• Nausea, vomiting, abdominal pain

• Lightheadedness

This type of reaction can progress to anaphylaxis, a life-threatening systemic response.

Delayed Drug Allergy

Much more common and significantly less dangerous.
Occurs days after starting the medication, usually limited to the skin.

Symptoms include:

• Mild skin rashes (with or without itching)

• Lesions that appear and remain stable without progression

Emergency Warning Signs

Seek immediate medical help if any of the following occur:

• Severe shortness of breath or wheezing

• Chest pain or tightness

• Fainting

• Swelling of the face, hands, tongue, or throat

Contact your doctor if you develop:

• Hives, severe restlessness

• Severe abdominal pain, vomiting, high fever

• Painful skin, blistering, or burning of eyes, mouth, vagina, or other mucous membranes

Penicillin Allergy

Penicillin is a common cause of anaphylaxis.
About 10% of people report reactions, but many are not true allergies.

What is Penicillin?

Penicillin is a widely used beta-lactam antibiotic family including:

• Nafcillin

• Oxacillin

• Dicloxacillin

• Ampicillin

• Amoxicillin

• Carbenicillin

• Ticarcillin

• Piperacillin

Anyone allergic to one member may react to others.

Pseudo-allergic symptoms such as abdominal pain, nausea, or diarrhea are not true allergies.

True allergic reactions to penicillin include:

• Hives

• Itchy rash appearing within hours

• Wheezing

• Swelling of throat, face, or skin

Note: Mild flat rashes appearing days after starting the drug are usually not significant and do not necessarily prevent future use.

Approximately 1–5% of people experience true allergic reactions to penicillin.

Anaphylaxis

Anaphylaxis is a severe allergic reaction characterized by:

• Marked hypotension

• Breathing difficulty

• Abdominal pain

• Swelling of throat and tongue

• Vomiting and diarrhea

Fortunately, it is rare.

Penicillin Skin Testing

One of the most reliable methods to predict penicillin allergy.

A positive result means the patient should avoid penicillin.

Allergy to Other Antibiotics

There are no standardized skin tests for most antibiotics.
Reported allergies are often based solely on patient history and may include many false positives, unnecessarily limiting treatment options.

Cephalosporins

These are widely used antibiotics structurally similar to penicillins.
Patients allergic to penicillin may react to cephalosporins—especially first and second generations such as:

• Cephalothin

• Cephalexin

• Cefadroxil

• Cefazolin

This cross-reactivity is due to similar side chains.
Second and third-generation cephalosporins carry a much lower risk.

Key Points

1. A history of penicillin allergy should not automatically prevent the use of cephalosporins.

2. Allergy to one specific cephalosporin does not rule out others.

3. Many drug allergies result from self-medication or improper drug use.

Important Notice

If a patient has a history of severe reactions such as anaphylaxis and now requires a drug with possible cross-reactivity, they must be evaluated by an allergy specialist