The antibiotics used to treat pneumonia depend on where you caught the infection, how severe it is, and which type of bacteria is most likely causing it. For most adults with community-acquired pneumonia who are otherwise healthy, amoxicillin (1 g three times daily) or doxycycline (100 mg twice daily) is the standard first-line treatment. But the picture gets more complex when atypical bacteria, drug-resistant organisms, or hospital settings are involved.
First-Line Antibiotics for Adults
If you’re a generally healthy adult without chronic conditions like heart disease, diabetes, or lung disease, your doctor will likely start with one of two options: amoxicillin or doxycycline. These target the most common culprit behind bacterial pneumonia, a bacterium called Streptococcus pneumoniae, along with other typical respiratory bacteria. American Thoracic Society and Infectious Diseases Society of America guidelines consider amoxicillin the stronger recommendation of the two, with doxycycline as a solid alternative.
If you do have chronic health conditions or have recently taken antibiotics, treatment usually steps up to a combination approach. This typically means pairing amoxicillin with a macrolide antibiotic like azithromycin, or using a respiratory fluoroquinolone on its own. The goal is to cover a broader range of bacteria, including atypical organisms that standard amoxicillin won’t touch.
Treatment for Atypical Pneumonia
Not all pneumonia is caused by the usual suspects. Bacteria like Mycoplasma pneumoniae, which causes “walking pneumonia,” lack a cell wall entirely. That makes them inherently resistant to penicillin-type antibiotics like amoxicillin, which work by breaking down bacterial cell walls. If your doctor suspects atypical pneumonia, the antibiotic class changes completely.
Macrolide antibiotics (azithromycin, clarithromycin) are considered the treatment of choice for Mycoplasma infections in both children and adults. Doxycycline is an option for older children and adults. Fluoroquinolones are reserved for adults. The CDC specifically notes that tetracyclines and fluoroquinolones shouldn’t be prescribed for young children under normal circumstances.
There’s a complication worth knowing about: resistance to macrolides among Streptococcus pneumoniae has become substantial. A large global analysis found that 66% of tested S. pneumoniae strains were resistant to azithromycin and nearly 62% were resistant to clarithromycin. This doesn’t mean macrolides are useless, but it helps explain why your doctor might choose a different class or combine antibiotics, especially if your symptoms aren’t improving.
Antibiotics for Children
Amoxicillin is the go-to antibiotic for childhood pneumonia across British, European, WHO, and most international guidelines. Dosing is weight-based, typically ranging from 40 to 80 mg/kg per day for children aged one to five, divided into two or three daily doses. For severe infections, doses can go significantly higher, up to 200 mg/kg per day.
Treatment length has been shifting shorter in recent years. The traditional recommendation was 7 to 10 days, but a systematic review of outpatient children in high-income countries found that 3 to 5 days was equally effective and safe for children six months and older. Updated guidelines in several countries now reflect this shorter course, though your child’s doctor may extend treatment if symptoms aren’t resolving or lab results suggest a more stubborn infection.
Hospital-Acquired Pneumonia
Pneumonia caught in a hospital setting is a different challenge. The bacteria involved tend to be tougher, more drug-resistant organisms like Pseudomonas and MRSA (methicillin-resistant Staphylococcus aureus). Guidelines from the Infectious Diseases Society of America recommend that initial treatment cover S. aureus, Pseudomonas, and other gram-negative bacteria. This means broader-spectrum antibiotics, often given intravenously.
MRSA-specific coverage isn’t always necessary. Current recommendations suggest adding an MRSA-active antibiotic only when specific risk factors are present, when more than 10 to 20% of staph isolates in that hospital unit are methicillin-resistant, or when local resistance data isn’t available. The emphasis is on using hospital antibiogram data to avoid unnecessary antibiotic exposure, which can drive further resistance.
If You Have a Penicillin Allergy
A documented penicillin or cephalosporin allergy changes the playbook. Hospitalized pneumonia patients with these allergies are about 50% more likely to receive fluoroquinolones compared to patients without allergies (23% vs. 14% in one large study). They’re also more than twice as likely to receive fourth-generation cephalosporins, which have a lower cross-reactivity risk than earlier generations.
If you’ve been told you’re allergic to penicillin, it’s worth discussing allergy testing with your doctor. Many people labeled with a penicillin allergy in childhood can actually tolerate the drug safely. Confirming or ruling out the allergy can open up more effective, narrower-spectrum treatment options.
IV to Oral: What Happens in the Hospital
If you’re hospitalized for pneumonia, you’ll typically start on intravenous antibiotics. Once you’re clinically stable, meaning your fever has broken, your breathing has improved, and you’re able to eat and drink, guidelines strongly recommend switching to oral antibiotics. This transition can happen within a few days for many patients and is an important step toward going home. Both the American Thoracic Society and IDSA antimicrobial stewardship guidelines endorse making this switch as soon as stability criteria are met.
How Long Treatment Lasts
For uncomplicated community-acquired pneumonia in adults, a typical antibiotic course runs 5 to 7 days. The key factor isn’t hitting a specific number of days but rather clinical stability: being fever-free, eating normally, and showing improving symptoms. For children, the trend is moving toward shorter courses of 3 to 5 days when the infection is straightforward. Hospital-acquired or complicated pneumonia generally requires longer treatment, sometimes two weeks or more depending on the organism involved and how quickly you respond.
Common Side Effects by Antibiotic Class
Every antibiotic class used for pneumonia comes with potential side effects. Knowing what to expect can help you distinguish a normal drug reaction from something that needs attention.
Penicillins (amoxicillin): The most common issues are digestive. Nausea, diarrhea, bloating, and stomach pain affect roughly 0.1 to 1% of patients. Skin rashes and hives can occur. True anaphylaxis is extremely rare, affecting fewer than 2 in 100,000 people.
Macrolides (azithromycin, clarithromycin): Stomach pain, diarrhea, nausea, and vomiting are the most frequent complaints. More concerning but less common are irregular heart rhythms, particularly in people with a pre-existing heart rhythm condition. Hearing changes, though rare, can occur and may not be reversible.
Fluoroquinolones (levofloxacin, moxifloxacin): These carry a broader side effect profile. Digestive issues and headaches are common. More serious risks include tendon inflammation and rupture (especially in people over 60 or those taking corticosteroids), persistent nerve pain or numbness, and confusion or psychiatric disturbances. Because of these risks, fluoroquinolones are generally reserved for situations where safer options aren’t suitable.
Cephalosporins: Rashes affect 1 to 2% of patients, and digestive side effects are more common with newer generations (up to 15%) compared to older ones (around 2.5%). Headaches and dizziness occur in 1 to 2% of patients.
All of these antibiotic classes carry some risk of C. difficile infection, a secondary gut infection caused by disruption of normal intestinal bacteria. Third-generation cephalosporins and erythromycin carry the highest relative risk, while azithromycin and moxifloxacin carry the lowest among their respective classes.