When you’re sick with a bacterial infection, your doctor doesn’t just hand you any antibiotic. They pick one based on what’s causing the illness, your medical history, and how your body reacts to drugs. Erythromycin has been around since the 1950s, but it’s not the first name you hear today. You’re more likely to hear about amoxicillin, azithromycin, or doxycycline. So why does erythromycin still matter? And when is it actually the best choice?
What is erythromycin, really?
Erythromycin is a macrolide antibiotic that works by stopping bacteria from making proteins they need to grow and multiply. Also known as Erythromycin base, it was first isolated from a soil bacterium called Streptomyces erythraeus in 1952. It’s not new, but it’s still used because it’s effective against certain stubborn bugs that other antibiotics miss.
Unlike penicillin-based drugs, erythromycin doesn’t attack the cell wall. Instead, it targets the bacterial ribosome - the tiny machine that builds proteins. This makes it useful for people allergic to penicillin. About 10% of people have penicillin allergies, and for them, erythromycin is often the go-to alternative.
It comes in tablets, capsules, liquid, and even eye ointment. Doctors prescribe it for things like strep throat, whooping cough, pneumonia caused by Mycoplasma, and skin infections like cellulitis. It’s also used to treat acne in teens and young adults, especially when topical treatments fail.
How does erythromycin compare to azithromycin?
Azithromycin - sold as Zithromax or Z-Pak - is the modern cousin of erythromycin. Both are macrolides, but azithromycin was developed later to fix some of erythromycin’s biggest problems: stomach upset and frequent dosing.
Here’s how they stack up:
| Feature | Erythromycin | Azithromycin |
|---|---|---|
| Dosing frequency | 2-4 times daily | Once daily |
| Treatment length | 7-14 days | 3-5 days (often) |
| Stomach side effects | High - nausea, cramps, diarrhea | Moderate - less frequent and milder |
| Drug interactions | Many - affects liver enzymes | Fewer - better tolerated with other meds |
| Blood concentration | Shorter half-life | Long half-life - stays in body longer |
For most people, azithromycin wins on convenience. A five-day course of Z-Pak is easier to stick to than taking erythromycin four times a day. But azithromycin isn’t always better. For certain infections like Legionnaires’ disease or some types of chlamydia, erythromycin is still preferred because it’s been proven to work better over time.
How does it compare to amoxicillin?
Amoxicillin is the most common antibiotic prescribed in Australia and the U.S. It’s cheap, effective, and safe for kids. But it’s useless if you’re allergic to penicillin. That’s where erythromycin steps in.
Amoxicillin kills bacteria by breaking down their cell walls. It works great for ear infections, sinus infections, and strep throat - if the bacteria are sensitive to it. But resistance is growing. In some areas, over 30% of strep throat cases are now resistant to amoxicillin.
Erythromycin doesn’t face the same resistance patterns. In fact, in places where penicillin resistance is high, erythromycin is often the first alternative. It’s also used for respiratory infections in babies who can’t take amoxicillin due to allergies.
But here’s the catch: erythromycin doesn’t work as well as amoxicillin for some common infections. If you have a middle ear infection or a urinary tract infection caused by E. coli, amoxicillin will clear it faster and with fewer side effects.
What about doxycycline or clarithromycin?
Doxycycline is a tetracycline antibiotic. It’s used for acne, Lyme disease, and some types of pneumonia. It’s not a macrolide, so it works differently. It’s often chosen for tick-borne illnesses or when a patient needs something that works against both bacteria and some parasites.
Clarithromycin is another macrolide, similar to azithromycin. It’s stronger against H. pylori (the stomach bacteria that causes ulcers) and is often paired with other drugs in triple therapy. But like erythromycin, it can cause nausea and interact with blood thinners or cholesterol meds.
So why not always pick clarithromycin or azithromycin? Because cost and availability matter. Erythromycin is one of the cheapest antibiotics on the market - often under $10 for a full course in Australia. In rural clinics or low-resource settings, that makes a big difference.
Who should take erythromycin?
Erythromycin isn’t for everyone. But it’s the right choice in specific cases:
- You’re allergic to penicillin or amoxicillin
- You have a respiratory infection caused by Mycoplasma pneumoniae or Chlamydia pneumoniae
- You’re pregnant and need an antibiotic - erythromycin is considered safe in pregnancy
- You have acne that hasn’t responded to topical treatments
- You’re in a region where bacterial resistance to other antibiotics is high
It’s also used in hospitals for patients who can’t swallow pills - it’s available as an IV form. And in newborns, it’s given to prevent eye infections after birth.
What are the downsides?
Erythromycin isn’t perfect. The biggest problem? Your stomach. Up to 30% of people taking it get nausea, vomiting, or cramps. Taking it with food helps a little, but not always. Some people just can’t tolerate it.
It also interferes with how your liver processes other drugs. If you’re on statins, blood thinners like warfarin, or certain anti-anxiety meds, erythromycin can cause dangerous buildups in your system. Always tell your doctor what else you’re taking.
And yes, it can cause rare but serious heart rhythm problems - especially in older adults or those with existing heart conditions. That’s why doctors avoid it in people with long QT syndrome.
When should you avoid erythromycin?
Don’t take erythromycin if:
- You’ve had liver problems from it before
- You’re taking medications like simvastatin, lovastatin, or colchicine (risk of muscle damage)
- You have myasthenia gravis - it can worsen muscle weakness
- You’re allergic to other macrolides like clarithromycin or azithromycin
And if you’ve had diarrhea after taking antibiotics before - especially if it was watery or bloody - talk to your doctor. Erythromycin can trigger C. diff infection, just like other antibiotics.
What’s the bottom line?
There’s no single "best" antibiotic. It depends on what’s making you sick, your allergies, your age, your other medications, and even where you live. Erythromycin isn’t the first choice anymore - but it’s still in the toolbox for a reason.
If you’re allergic to penicillin, erythromycin might be your safest bet. If you’re treating a specific infection like whooping cough or certain types of pneumonia, it’s still the gold standard. And if cost is a factor, it’s one of the most affordable options.
But if you’re just looking for a quick fix for a sinus infection or strep throat, azithromycin or amoxicillin will likely work better - and be easier on your stomach.
Never pick your own antibiotic. Always get tested and follow your doctor’s advice. Antibiotics aren’t candy. Misuse leads to resistance, and that hurts everyone.
Is erythromycin still used today?
Yes, erythromycin is still used, but more selectively. It’s commonly prescribed for people allergic to penicillin, for certain respiratory infections like whooping cough and Mycoplasma pneumonia, and for acne. It’s also used in newborns to prevent eye infections. While newer antibiotics like azithromycin are more convenient, erythromycin remains important where cost, allergies, or specific infection types make it the best option.
Can I take erythromycin if I’m allergic to penicillin?
Yes, erythromycin is a safe alternative for people with penicillin allergies because it belongs to a different antibiotic class (macrolide). It doesn’t contain any penicillin-related compounds. However, always tell your doctor about any drug allergies before starting a new antibiotic, as cross-reactions can rarely occur with other macrolides like clarithromycin.
Does erythromycin cause stomach problems?
Yes, stomach upset is the most common side effect. Up to 30% of people experience nausea, vomiting, abdominal cramps, or diarrhea. Taking it with food can help reduce this, but it doesn’t always work. If side effects are severe, your doctor may switch you to azithromycin, which is better tolerated. Never stop antibiotics without talking to your doctor, even if you feel sick.
How long does it take for erythromycin to work?
Most people start feeling better within 2-3 days, but it’s important to finish the full course - usually 7 to 14 days. Stopping early can allow surviving bacteria to become resistant. For skin infections or acne, it may take several weeks to see full results. Always follow your doctor’s instructions on duration.
Can erythromycin be used during pregnancy?
Yes, erythromycin is considered safe during pregnancy and is often used to treat infections like chlamydia or group B strep in pregnant women. It doesn’t cross the placenta in harmful amounts and has been used for decades without evidence of birth defects. However, always consult your doctor before taking any medication while pregnant.
Is erythromycin effective against viral infections like colds or flu?
No, erythromycin does not work against viruses. Colds, flu, most sore throats, and bronchitis are caused by viruses - not bacteria. Taking erythromycin for these illnesses won’t help you feel better and increases your risk of antibiotic resistance. Only take antibiotics when a bacterial infection is confirmed by a doctor.
What should I avoid while taking erythromycin?
Avoid alcohol - it can worsen stomach upset. Also avoid taking it with certain medications like statins (simvastatin, lovastatin), blood thinners (warfarin), and some anti-anxiety drugs, as it can cause dangerous interactions. Grapefruit juice can also increase side effects. Always check with your pharmacist before combining erythromycin with other drugs or supplements.
If you’ve been prescribed erythromycin, keep the full course handy. Don’t skip doses. Track your symptoms. And if you feel worse after a few days, call your doctor. Antibiotics are powerful tools - but only when used correctly.
2 Responses
Man, I’ve been on erythromycin twice-once for pneumonia, once for acne. The stomach stuff? Brutal. I’d take a Z-Pak any day, but I get why docs still reach for it. Like, if you’re allergic to penicillin and broke, it’s literally the only affordable option. Still, I wish pharma would make a better macrolide that doesn’t turn your gut into a warzone.
Look, I get the nostalgia for erythromycin, but come on. It’s 2025. Azithromycin’s cheaper now, easier to take, and doesn’t make you want to vomit into a trash can. If your doc still prescribes this like it’s 1987, they’re either lazy or stuck in the Stone Age. Just sayin’.