What are the Most Common Uses for Penicillin?

Mary McMahon

Penicillin is an umbrella term for a large family of antibiotics doctors can prescribe to treat infections caused by bacteria. These antibiotics are broad spectrum, working against a variety of organisms, and they are the drug of choice in many infections because their toxicity is low, and they can be highly effective. Some patients have penicillin allergies and sometimes bacteria have resistance to the antibiotic, in which case the patient must take a different medication.

Penicillin may be used to treat an ear infection.
Penicillin may be used to treat an ear infection.

These antibiotics were originally derived from fungi in the genus Penicillium and they work by killing bacteria so they cannot continue causing infection. Penicillin is famous for being among the first antibiotics people successfully developed for medical use, and it made a significant breakthrough in fighting infectious disease during the Second World War. Today, penicillins are available for a number of different kinds of infections, if a doctor believes a patient is a good candidate for treatment with drugs in this class.

Like other antibiotics, penicillin can cause some patients to experience side effects.
Like other antibiotics, penicillin can cause some patients to experience side effects.

Ear, respiratory, and intestinal infections with a variety of bacteria can respond to penicillin therapy. In patients with these infections, a doctor may prescribe an antibiotic first to see if it works, only requesting a culture if the patient does not respond to the treatment. Endocarditis and periodontal infections are also common uses for this drug, and patients with gonorrhea can receive treatment with this medication. Doctors may prescribe the drug for other uses, depending on the specifics of a patient's case and the doctor's experience and prescribing preferences.

A doctor may prescribe an antibiotic first to see if it works, only requesting a culture if the patient does not respond to the treatment.
A doctor may prescribe an antibiotic first to see if it works, only requesting a culture if the patient does not respond to the treatment.

Only bacterial infections can be treated with this medication. Viral and fungal infections will not respond, nor will underlying inflammation without any bacteria present. If a doctor is not sure about what is causing an infection, it may be necessary to take a sample for culture to learn more about the situation. Patients should also make sure their doctors are aware of any history of adverse reactions to medication, as allergies to penicillin could be a concern in some patients.

Penicillin is the only antibiotic that can be tested for a drug allergy as of the year 2010.
Penicillin is the only antibiotic that can be tested for a drug allergy as of the year 2010.

Doctors can give patients oral tablets or injections of penicillin, depending on how fast they need the medication to act. Antibiotic resistance is a prescribing concern. Patients who do not finish their medications can contribute to the development of resistance and over time, this can make it harder to treat bacterial infections because antibiotics will be less useful. When a doctor writes a prescription, it is important to complete treatment and attend a follow-up appointment to make sure the infection is completely gone.

Penicillin is derived from the penicillium mold.
Penicillin is derived from the penicillium mold.

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Discussion Comments


In my experience, most doctors do a culture if they suspect an infection is going on. They might start a patient on a round of penicillin, and wait to see if the culture shows an infection. Then if there is no infection present, the patient is told to stop taking the penicillin or other antibiotic.

Different doctors have different philosophies about treating infections. Some seem to prefer starting the drugs and waiting to see if the patient improves. And if they don't, then doing a culture. I like the other way better.


The discovery of penicillin was really a medical miracle. To think that so many people died of bacterial infections before it was discovered. During World War II, and for so many years after, it saved the lives of many soldiers and people back home.

I think that it is not used as often these days because of it has become somewhat resistant to bacteria, and many people are allergic to it.

Both of my daughters took penicillin for strep throat infection. After the second time of taking it, they both showed allergic reactions - their lips and mouths swelled up. Fortunately, other antibiotics have been discovered, so there is another one available to take.


@SZapper - I'm allergic to penicillin too! However, I discovered by accident that there are a lot of antibiotics that are related to penicillin, even if they aren't labeled penicillin on the bottle.

When I was in high school a doctor treated me for a sinus infection with an antibiotic called cefzil. I developed a reaction-my joints swelled up and I broke out into hives. After my doctor did a little more research, it turns out people who are allergic to penicillin are likely to be allergic to cefzil also! Now I make it a point to do serious research before I take any antibiotic- you can't always rely on the doctor to do it unfortunately!


@lonelygod - I'm allergic to penicillin too! Luckily for me, I (or should I say my parents) discovered my allergy when I was very young. Apparently I had some really horrible side effects, but I don't remember a thing!

Normally when you have a penicillin allergy the doctor will prescribe you with azithromycin. Unfortunately, when I was a teenager I developed an allergy to that too! Needless to say, I try really hard not to get sick. There are some antibiotics I can take, but they are usually much more expensive than penicillin.


My sister experienced an extreme side effect while taking penicillin. She didn’t know it until weeks later, though.

The informational packet that came with the drug said that it could make birth control pills less effective. She had to take it for ten days, and her first anniversary was coming up in five. She decided to take her chances.

She first noticed something was wrong when her period didn’t arrive on schedule. The pills made its arrival easy to predict, and she was more than a week late. She went to her doctor and found out that she was pregnant.


I remember being a bit confused when my doctor prescribed penicillin to treat my strep throat. I thought that it was the basis for all other antibiotics, and I did not know it could be sold in pure form.

After reading this, I now know that it is a broad category that includes many antibiotics. However, the name on the pill bottle simply said “penicillin.”

It seemed to work at first, but I think that I was getting better because of the steroids he prescribed along with it. After I finished taking the steroids, the sore throat returned, and I had to take a different type of antibiotic.


@Sara007 - I know of one famous case. I stumbled across it recently while looking for information on penicillin, which my doctor had just prescribed to treat my ear infection.

Hitler’s life was saved by penicillin after he got injured during an assassination attempt. A bomb had gone off near him, and his doctor treated him with penicillin.

America had penicillin at the time, and in a roundabout way, they helped heal Hitler, though not intentionally. They had been supplying neutral countries with it, and somehow Nazi medics had gotten their hands on some.


My kids are doing a research project on the discovery of penicillin, as well as the history of penicillin. I must say that is article has been really helpful on providing us some great background about this wonder drug.

It really makes me sad to think about how many people suffered and died from very common bacterial infections prior to the invention of penicillin. I wonder how many people in poorer nations still go untreated for the same things?

Also, does anyone know of any famous cases of a person being saved by penicillin. I think having one case study would make my kid's project even better.


If your doctor gives you penicillin for a bacterial infection like strep throat be very careful. Some of the penicillin side effects can be very unpleasant, and my doctor told me that penicillin is one of the most common drugs that people are allergic too.

I was prescribed penicillin a few weeks ago and it ended up giving me a terrible rash and it made me itch like crazy. I went right back to my doctor and got switched to something different. The only thing that helped my rash go down was a lot of antihistamines and cool showers. I was just glad I didn't stop breathing like some people do with a penicillin allergy.


@KoiwiGal - It's a real issue and one that I don't think most doctors are helping. Even when they know an infection is viral, they will often prescribe antibiotics, in order to make the patient happy.

Fortunately, at the moment there are other options if people can't have penicilin or if the bacteria is found to be resistant to it.

But, if people keep going down this path, prescribing it at the drop of a hat, or even pumping it into animals so they can be kept in unnatural conditions without getting sick, we are soon going to be in real trouble.

The world isn't prepared for a full onslaught of resistant bacteria. I just hope we don't have to find out what it is like.


Penicillin has to have been one of the greatest discoveries of the last few hundred years. I'm not sure anything else has saved so many lives, or even just improved the health of them. Before they discovered penicillin, it was just standard practice to lop off a limb if it was badly injured, even before gangrene set in, just because you couldn't take the chance.

The scary thing is, now penicillin is much less potent than it used to be, because we've used it so much the bacteria have started to become resistant. I hope we manage to discover a better way of killing off bugs before we really need it.

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