Amoxicillin vs Penicillin

Listen to the article instead of reading through it.


For patients with bacterial infections, certain antibiotics that inhibit the growth of bacteria can help in alleviating symptoms and eradicating the infection. Amoxicillin and Penicillin are two such drugs that are prescribed for bacterial infections. They each impact different types of bacteria but both have bactericidal effects in patients with a variety of illnesses caused by susceptible strains of bacteria. Amoxicillin is a broad-spectrum penicillin antibiotic affecting many different types of gram-positive and gram-negative organisms while Penicillin, on the other hand, is more narrowly spectrum-focused primarily targeting gram-positive cocci like Streptococcus and Staphylococcus species. Both medications work by interfering with cell wall synthesis during bacterial replication which ultimately leads to their demise.

What is Amoxicillin?

Amoxicillin (also known by its brand name Amoxil) was a significant development upon the first class of antibiotic drugs known as penicillins. Amoxicillin was approved by the FDA in 1972 and is often prescribed for infections caused by bacteria, such as tonsillitis, bronchitis, pneumonia, and infections of the ear, nose or throat. Similar to Penicillin, it targets bacteria cells but is more adept at fighting off a wider range of organisms. This makes amoxicillin a broader spectrum antibiotic compared to penicillin. It inhibits bacterial cell wall synthesis during active multiplication resulting in bactericidal activity against susceptible organisms. Like all antibiotics however, both medications can cause side effects like diarrhea and nausea with amoxicillin possibly causing skin rashes more frequently than penicillin.

What conditions is Amoxicillin approved to treat?

Amoxicillin is approved for the treatment of various bacterial infections, including:

  • Ear infections, also known as otitis media
  • Streptococcal pharyngitis (strep throat)
  • Pneumonia
  • Skin infections
  • Urinary tract Infections It can also be used in combination with other medications to treat stomach ulcers caused by H. pylori infection.

How does Amoxicillin help with these illnesses?

Amoxicillin works to combat bacterial infections by inhibiting the formation of bacterial cell walls, which is essential for their growth and survival. It does this by binding to certain proteins within bacteria, preventing them from forming a strong and intact cell wall. Without a solid cell wall, bacteria become vulnerable and can easily burst or degrade. Penicillin operates in a similar way but has a narrower spectrum of activity compared to amoxicillin. This means that while both can be used against several types of bacteria, amoxicillin is effective against more varieties than penicillin. In addition, some people may have developed resistance or allergies to penicillins making amoxicillin a better choice for these individuals as it tends not to cause allergic reactions as often.

What is Penicillin?

Penicillin is a name covering a group of antibiotics derived from Penicillium fungi, including penicillin G (intravenous use), penicillin V (oral use), procaine penicillin, and benzathine penicillin. Discovered in 1928 by Alexander Fleming, it was the first antibiotic to be widely used and has saved countless lives since its introduction. Penicillins work by inhibiting the synthesis of bacterial cell walls which eventually leads to their death.

Penicillins are effective against gram-positive bacteria like Staphylococcus aureus and Streptococcus pneumoniae but less effective against gram-negative bacteria due to their outer membrane that can block drug penetration. Side effects are infrequent but may include nausea, diarrhea, and skin rash or hives if allergic reaction occurs.

Its distinct mechanism means that there's no direct impact on human cells because these do not have cell walls; therefore side effect profile is different compared to other classes of drugs. For those who cannot tolerate typical antibiotics or with specific infections resistant to them, Penicillins remain an important alternative.

What conditions is Penicillin approved to treat?

Penicillin is a well-known antibiotic that has been utilized for decades to treat a wide range of bacterial infections. Approved uses of penicillin include:

  • Streptococcal infections (including strep throat and scarlet fever)
  • Pneumococcal infections
  • Certain staphylococcal infections
  • Syphilis and other sexually transmitted diseases It's an effective treatment option for many patients, although some people may be allergic or resistant to this form of medication.

How does Penicillin help with these illnesses?

Penicillin is a type of antibiotic that plays a crucial role in combating bacterial infections by inhibiting the synthesis of the bacteria's cell wall, leading to its death. It has been heavily involved in fighting various types of infections since its discovery and remains an important tool for medical professionals. Amoxicillin, on the other hand, is actually a derivative of penicillin and works similarly but with some added benefits such as better absorption when taken orally and effectiveness against a wider range of bacteria. However, due to increasing resistance among certain bacteria strains towards penicillins including amoxicillin, it sometimes falls short compared to newer antibiotics. But despite this challenge, Penicillin still holds significant importance in healthcare because it continues to be effective for many patients suffering from susceptible bacterial infections.

How effective are both Amoxicillin and Penicillin?

Both amoxicillin and penicillin are antibiotics that belong to the penicillin class, with a long history of use in treating bacterial infections. They were approved by the FDA several decades apart - Penicillin was discovered in 1928 and amoxicillin was made available in the early 1970s. Both drugs work by inhibiting bacterial cell wall synthesis; however, their effectiveness can vary based on the type of bacteria being treated.

Amoxicillin is often preferred over penicillin due to its broader spectrum of activity against both gram-positive and some gram-negative organisms. It's also more bioavailable, meaning it gets absorbed better after oral administration compared with penicillin which requires intravenous administration for systemic effects.

A study published in 2009 comparing these two antibiotics showed similar efficacy between them when used for preventing dental infection post-surgery; yet it noted amoxicilln had better patient compliance because of less frequent dosing.

While both medications have well-established safety profiles, allergic reactions remain a significant concern associated with this class of drug. If an individual has a known allergy to one medication within this category (like having a reaction to either amoxicllin or penicllin), they will likely react similarly to any other member of this group as well.

In summary, while both drugs are effective at fighting off many types of bacteria causing various common infections like strep throat or ear infections, doctors might lean towards prescribing Amoxcilllin due its wider range action and easy-to-use oral form.

abstract image of a researcher studying a bottle of drug.

At what dose is Amoxicillin typically prescribed?

Oral dosages of Amoxicillin range from 250–500 mg every 8 hours, or 500–875 mg every 12 hours depending on the severity and type of infection. For children under the age of three months, dosage is based on body weight and given every 12 hours. In either population, dosage can be adjusted according to the response seen after a few days. The maximum adult dosage that should not be exceeded in any case is around 4 grams per day (g/day). Penicillin V oral dose ranges between 125–500mg taken every six to eight hours for adults, while children's doses are calculated by their weight ranging from 25-50mg/kg per day divided into four doses; adjustments may also be made based on therapeutic response but do not exceed recommended daily limits.

Find Top Clinical Trials

Choose from over 30,000 active clinical trials.

At what dose is Penicillin typically prescribed?

Penicillin treatment usually begins at a dosage of 250-500 mg every 6-8 hours. The dose can then be increased to 1 g every four to six hours, depending on the severity of the infection. For severe infections or those caused by less sensitive organisms, maximum dosage is up to 4 g daily in divided doses and should not exceed this amount. If there's no response or improvement after a few days of treatment with the initial dose, it may be necessary to increase the dose or switch antibiotics under your doctor's guidance. Penicillin should always be taken with a full glass of water on an empty stomach (1 hour before meals and 2 hours after) for optimal absorption.

What are the most common side effects for Amoxicillin?

Common side effects of both amoxicillin and penicillin can include:

  • Nausea, vomiting or diarrhea
  • Abdominal pain or discomfort
  • Skin rash (in the form of hives or other types)
  • Headache
  • Oral thrush (yeast infection in the mouth with white patches and soreness)
  • Vaginal yeast infection (itchiness, burning, unusual discharge)
  • Allergic reaction symptoms like difficulty breathing; swelling of your face, lips, tongue, or throat

Less common but more serious side effects can also occur. Always seek medical assistance if you experience any adverse reactions when taking these antibiotics.

abstract image of a patient experiencing side effect

Are there any potential serious side effects for Amoxicillin?

While both amoxicillin and penicillin are generally safe antibiotics, they can sometimes lead to serious side effects in rare cases. These may include:

  • An allergic reaction which could cause difficulty breathing, swelling of your face or throat, a severe skin rash with blistering and peeling
  • Easy bruising or bleeding (nosebleeds, bleeding gums), purple or red pinpoint spots under your skin
  • Yellowed eyes, dark colored urine indicating liver issues
  • Severe stomach pain, diarrhea that is watery or bloody indicating intestinal problems
  • Unusually weak or tired feeling; confusion; trouble speaking or understanding speech - these could indicate neurological complications
  • A fast heart rate, shortness of breath - signs that the antibiotic might be affecting your heart
  • Muscle weakness twitches

If you experience any of these symptoms while taking either medication it's important to seek medical attention immediately. However remember that such severe reactions are rare: most people take these medications without experiencing any major issues.

What are the most common side effects for Penicillin?

Common side effects of penicillin can include:

  • Mild diarrhea
  • Nausea and vomiting
  • Stomach pain or cramps
  • White patches in the mouth or throat (oral thrush)
  • Headache, dizziness
  • Swelling, itching, rash (signs of an allergic reaction) It's important to note that while Penicillin is a commonly prescribed antibiotic, it does have potential for serious allergic reactions in some individuals. Should any unusual symptoms occur while taking Penicillin like difficulty breathing or swelling around the face/lips/tongue/throat, medical attention should be sought immediately.

Are there any potential serious side effects for Penicillin?

Penicillin, while generally well-tolerated and safe for most people, can occasionally lead to serious side effects. These may include:

  • A severe allergic reaction, characterized by hives; difficulty breathing; swelling of your face, lips, tongue or throat
  • Unusual changes in behavior or mood swings
  • Seizure (convulsions)
  • Diarrhea that is watery or bloody (this could even start months after you have finished taking penicillin)
  • Fever, swollen glands, rash or itching
  • Joint pain
  • General ill feeling

If any of these symptoms appear after using Penicillin it's important to stop the medication immediately and consult with a healthcare professional as soon as possible.

Contraindications for Amoxicillin and Penicillin?

Both Amoxicillin and Penicillin, like most antibiotics, may cause a variety of side effects in some individuals. If you notice symptoms such as hives, difficulty breathing or swallowing, swelling of your lips, face or tongue, severe diarrhea with blood or mucus or yellowing of your eyes/skin (jaundice), please seek immediate medical attention.

Neither amoxicillin nor penicillin should be taken if you are allergic to cephalosporins or other penicillins. Always inform your physician about any allergies to medications; this is crucial because people who are allergic to certain types of drugs may also react negatively to similar medications - for instance if you're allergic to amoxicillin there's a chance you might be allergic to penicillin too.

If you have liver disease, kidney disease or asthma consult with your doctor before taking either drug. It's also important that patients with mononucleosis avoid taking amoxicillin as it can lead to a rash.

It is worth noting that misuse of antibiotics like Amoxicilin and Penicilin can lead antibiotic resistance where the bacteria become immune making subsequent treatment difficult.

How much do Amoxicillin and Penicillin cost?

For the brand name versions of these drugs:

  • The price for 30 capsules of Amoxil (500 mg), which is a brand-name version of amoxicillin, averages around $15, working out to approximately $0.50/day.
  • The price for 28 tablets of Penicillin V Potassium (250 mg) is about $70, making it roughly $2.5/day.

Thus, if you are in the higher dosage range for Penicillin V (i.e., 1g per day or more), then branded Amoxil would be less expensive on a per-day treatment basis. However, cost should not be a primary consideration in determining which antibiotic is right for treating your infection.

In terms of generic options:

  • Generic amoxicillin is available starting from as low as $10 for 30 capsules (500mg each). Therefore, depending on your dose, this can work out to between about $.33 and $.67 per day.
  • Generic penicillin V potassium starts at around $40 for 28 tablets (250mg each), so daily costs could range from approximately $.71 to just over $1.42.

These prices can vary significantly based on factors such as insurance coverage and pharmacy location among others. Consequently it's always advisable to check with your local pharmacies before making any decisions based strictly on drug costs alone.

Popularity of Amoxicillin and Penicillin

Amoxicillin, in forms such as Amoxil and others, was estimated to have been prescribed to about 24.9 million people in the US in 2020. It accounted for nearly 20% of antibiotic prescriptions in outpatient settings. Amoxicillin is a broad-spectrum penicillin-like antibiotic that has consistently dominated its class due to its strong efficacy against a wide range of bacteria.

Penicillin V or phenoxymethylpenicillin, which includes brand versions like Pen-Vee K and Truxcillium among others, had fewer prescriptions compared to amoxicillin with an estimated number reaching just over 1 million people in the USA during the same year. The use of this drug accounts for roughly around 3% of total penicillin-related antibiotics prescribed across different healthcare settings. While it's less commonly used today than other newer drugs like amoxicillin due to resistance issues or spectrum coverage, it remains effective against specific organisms and conditions.


Both amoxicillin and penicillin have long-standing records of usage in treating bacterial infections, supported by numerous clinical studies indicating their effectiveness. These two antibiotics may sometimes be used together, but the decision to do so must be made carefully by a physician due to potential interactions. Their different mechanisms of action mean they're often prescribed under different circumstances: penicillin is primarily effective against gram-positive bacteria such as Streptococcus pneumoniae, while amoxicillin has a broader spectrum of activity including many gram-negative bacteria.

Amoxicillin and penicillin are both available as generic drugs, which can represent significant cost savings for patients paying out-of-pocket. The onset of effects might not be immediate following treatment commencement with either drug.

The side effect profiles are similar between these two antibiotics: most commonly reported side effects include diarrhea, nausea and skin rash. Allergic reactions can occur with both medications; however, amoxicillin’s broader spectrum means it is more likely to cause resistance if overused or misused than penicillins like Penicilin V or G. For both medications, patients should closely monitor their symptoms when starting treatment and seek medical help immediately if they notice any sign of an allergic reaction or worsening infection.