What to Know About Penicillin VK (Penicillin V Potassium)

An Antibiotic Drug Used to Treat Bacterial Infection.

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Penicillin VK (penicillin V potassium), also sold under the brand name, Beepen VK, is an antibiotic drug used to treat bacterial infection. It’s often indicated for a range of diseases, including scarlet fever, respiratory infections, as well as those of the ear, nose, throat, gums, or mouth.

This pill can also be used preventatively to prevent rheumatic fever following strep throat or scarlet fever, a very dangerous condition that can lead to inflammation of the heart valves among other symptoms.

Like other antibiotics, penicillin VK works by directly targeting and killing bacteria in the body. If you’ve been prescribed this medication, it’s essential to understand as much as you can about how to safely use it.

Pharmacist dispensing penicillin VK
  Tom Werner / DigitalVision / Getty Images


Penicillin VK takes on a host of bacterial infections, but, importantly, this drug doesn’t work on viral diseases such as the common cold, influenza (the flu), and others. Primarily, it targets and kills three different types of bacteria: Streptococcus, the pneumococcus (Streptococcus pneumoniae), and many Staphylococcus strains.

Depending on the site of infection, infection by these pathogens can cause an array of diseases. As such, you’ll see penicillin VK prescribed for:

  • Pneumonia: When this potentially very critical infection of one or both lungs is caused by pneumococcus bacteria, penicillin VK is among the treatment options. 
  • Scarlet fever: Caused by a type of streptococcus, this disease characterized by rashes, sore throat, headache, and chills among other symptoms. It usually affects children ages 5 to 15.
  • Strep throat/throat infection: Infection of the throat by streptococcal bacteria—as well as some others—can lead to sore throat and other symptoms.   
  • Ear and nose infections: Depending on the strain of bacteria at play, many ear and nose infections are treated with penicillin VK.
  • Gum infection: Penicillin VK may also be used to take on the gum infection, fusospirochetosis (commonly known as “trench mouth”).
  • Skin infection: More mild skin infections by staphylococcal bacteria can be treated with this drug.

Off-Label Uses

Alongside the above condition, penicillin VK has several off-label uses. This means that, while not directly indicated for use by the FDA, healthcare providers may prescribe this drug to help with other conditions based on significant bodies of evidence. These are quite numerous and include:

  • Actinomycosis: This rare bacterial infection affects the skin and soft tissues, leading to pain, inflammation, and, in serious cases, infection of the blood. Penicillin VK may be employed to combat this condition, following initial treatments of other antibiotics and/or surgery.
  • Anthrax: For this aggressive skin infection, Penicillin VK may be considered among the treatment approaches.
  • Animal bite wounds: Animal bites, which can lead to infection, can be treated with a combination of Penicillin VK and another antibiotic, dicloxacillin.
  • Prosthetic joint infection: Penicillin VK may be used for cases of infection of prosthetic joints, such as replaced knees, ankles, or hips, when other antibiotics aren’t expected to work.
  • Cutaneous erysipeloid: This skin infection often resolves on its own; however, Penicillin VK may be administered to combat it.
  • Infection due to stem cell transplant: Complications can occur when stem cells (undifferentiated cells) are harvested from the bone marrow to take on leukemia, a dangerous blood cancer. This can lead to chronic graft versus host disease (GVHD), which can be treated with penicillin VK. 
  • Chronic group A Streptococcus: Some people become chronic carriers of group A Streptococcus, a major cause of strep throat. Pencillin VK may be considered a treatment option for this condition.

Before Taking

Before penicillin VK is indicated, healthcare providers need to see evidence of infection by Streptococcus, pneumococcus, and many forms of the staphylococcal bacteria (as noted above). This typically involves both an assessment of any symptoms, as well as a number of other tests, including:

  • Culture: This involves taking samples of urine, blood, or saliva (and occasionally other tissues), and essentially allowing any bacteria to grow in specialized broth or agar plates. This allows the lab professionals to identify the specific strain and to decide which antibiotic would work best.
  • Stains and microscopy: By taking a tissue or fluid sample, placing it on a slide, staining it, and examining under a microscope, lab professionals detect bacterial strains. Staphylococcus and Streptococcus can be identified by their purple color when Gram stained, as well as their size and shape.
  • Darkfield and fluorescent microscopy: This approach uses ultraviolet (UV) light to assess specimens through a microscope. Bacteria are viewed against a dark background, with the light coming from the side rather than the back of the slide. This will primarily detect or rule out certain tuberculosis strains.
  • Antigen detection: Known for its rapidity, antigen detection involves testing bodily fluids such as urine, spinal fluid, or saliva taken via throat swab. These samples are tested using a specialized kit, and, when employed on material from a throat swab, this approach can detect certain forms of Streptococcus, among others.

Essential in all of this is that the healthcare providers are able to figure out the exact strain of bacteria at play. This way, they can devise the best possible intervention.

Precautions and Contraindications

As with any medication, Penicillin VK may not be the best choice for certain populations and may also interact poorly with other prescribed or over-the-counter medications, vitamins, or supplements.

Make sure to let your healthcare provider know as much as you can about what you’re taking; while some substances pose minor risks when taken alongside this antibiotic, others may be contraindicated outright.

Prior to starting a Penicillin VK course, your healthcare provider will need to consider several factors:

  • Allergic reaction: Notably, some people are allergic to penicillin VK, which can lead to a severe and occasionally even fatal reaction, in which sudden inflammation obstructs airways. The risk of this increases if patients have other allergies. If you’re having trouble breathing while on this drug, contact emergency medical help.
  • Asthma: In light of the above allergic reaction, patients with asthma may require an alternative approach.
  • Renal (kidney) impairment: Since the kidneys play an essential role in processing drugs in the bloodstream, patients experiencing kidney problems—up to and including kidney failure—may not be the best candidates for this therapy.
  • Seizures: Some people with a history of seizures may be at increased risk while on this drug; it’s important to let your healthcare provider know if this is your case.
  • Other allergies: Those who are allergic to some other antibiotics or food dyes might also require a different or modified approach. See below for more about adverse drug interactions.
  • Pregnancy: Penicillin VK is known to be able to cross the placenta. While it may generally be considered safe for treating some conditions, healthcare providers may be cautious about prescribing this drug. If you become pregnant while on your course, let your provider know immediately.
  • Age: While this antibiotic is safe for patients of all ages, certain derivatives may lead to increased risk of adverse reactions in infants. Specifically, Penicillin VK formulated using benzyl alcohol can lead to “gasping syndrome” (difficulty breathing), which can be fatal if untreated.

Other Penicillins

Penicillin has a long history; having been first identified for its antibiotic capability by Dr. Alexander Fleming in 1928, an initial form was hailed as a “miracle drug” during World War II. In the intervening years, pharmacists have been able to create many derivatives of this drug. These include drugs of several classes:

  • Aminopenicillin: This type, known to have the broadest effect, includes several types of amoxicillin drugs, sold under the brand names Amoxicot, Moxatag Pro, and Moxillin, among others. Ampicillin is another of this type and appears in the market as Principen, Totacillin-N or Omnipen-N.  
  • Antipseudomonal penicillin: This class, usually prescribed for certain more aggressive infections, includes Geocillin (carbenicillin), Pipracil (piperacillin), and Ticar (ticarcillin).
  • Beta-lactamase inhibitor: This type disrupts the activity of beta-lactamase, a destructive byproduct of certain bacteria. It’s rarely prescribed on its own but will be an adjunct to other treatments. Examples are Augmentin Pro (amoxicillin/clavulanate), Unasyn Pro (ampicillin/sulbactam), and Zosyn Pro (piperacillin/tazobactam).
  • Natural penicillin: Naturally occurring penicillins are used to prevent the spread of infections and actually include Penicillin VK. Other common types include Bicillin L-A (penicillin G benzathine), Bicillin C-R (penicillin G benzathine/procaine penicillin), and Isoject Permapen (penicillin G benzathine), among others.
  • Penicillinase resistant penicillins: Prescribed for strains of bacteria that are resistant to other types of penicillin, this class includes Bactocill (oxacillin), Dycil or Dynapen (dicloxacillin), as well as Unipen (nafcillin).


Generally speaking, this antibiotic is administered in pill form and are to be taken one hour before or two hours after meals. Specific dosages of Penicillin VK depend on the condition being treated. The guidelines for adults are as follows:

  • Pharyngitis: For streptococcal throat infections, 500 milligram (mg) doses two to three times a day for 10 days. Alternately, 250 mg doses four times a day for the same period of time may also be prescribed. 
  • Rheumatic fever: For more stubborn or recurrent cases, Penicillin VK may be administered in 250 mg doses twice a day. The duration of treatment will depend on the progression of the illness.
  • Fusospirochetosis: For this gum infection, 250 to 500 mg doses every six to eight hours are recommended until there’s a resolution of symptoms.
  • Erysipelas: This skin infection is treated with 500 mg doses four times a day; however, there’s significant evidence that smaller doses of 125 to 250 mg every six to eight hours may be effective.
  • Animal bite: An off-label use, 500 mg doses four times a day are recommended.
  • Pneumococcal prophylaxis in stem cell transplant: Infections and complications following stem cell therapy are treated with 250 to 500 mg doses, twice a day.
  • Actinomycosis: An off-label use of Penicillin VK in taking on this condition is to supplement intravenous administration of penicillin G with two to four grams (2,000 to 4,000 mg) doses every six hours. 
  • Chronic streptococcus: If deemed necessary, chronic streptococcus carriers may be prescribed 500 mg doses, four times a day, for 10 days.  
  • Anthrax: If anthrax is contracted via inhalation, the recommended dosage is 500 mg every six hours for 42 to 60 days.
  • Prosthetic joint infection: An off-label use of Penicillin VK, 500 mg doses two to four times a day may be recommended.
  • Streptococcal skin infection: In these cases, 250 to 500 mg doses are recommended every six hours.

Keep in mind that these are manufacturer recommended guidelines; as such, doublecheck your specific prescription and talk to your healthcare provider to ensure you’re taking the right dosage for you.


The activity of antibiotics can also vary based on age; what works well for an adult or a senior person might be too much for an infant or child. As such, therapeutic effect is seen in typically smaller doses, and ingestion of more than 2,000 mg in a day is not recommended for this population.

What sorts of dosage modifications can you expect for younger patients? Here’s a quick breakdown:

  • Pneumonia/Streptococcus infection: Infants, children, and adolescents should take 50 to 75 mg per kilogram (kg) of body weight (one kilogram is approximately 2.2 pounds) in four divided doses a day.   
  • Pneumococcal infection prophylaxis, sickle cell anemia: To prevent the spread of pneumococcal bacteria in those who have the genetic disorder sickle cell anemia, infants and children below three should be given 125 mg doses twice a day. Those older than three can take 250 mg, twice a day.
  • Pharyngitis: To prevent respiratory infections from developing into rheumatic fever, children that weigh less than 25 kg (approximately 59.5 lbs) take 250 mg doses two to three times a day for 10 days.
  • Rheumatic fever: As with adults, Penicillin VK may be administered in 250 mg doses twice a day for pediatric patients. The duration of treatment will depend on the progression of the illness.
  • Fusospirochetosis: Mild to moderate cases of this gum infection in children 12 or younger and adolescents are treated with 250 to 500 mg doses every six to eight hours.
  • Anthrax: Anthrax acquired via inhalation is treated with 50 to 75 mg/kg of divided doses every six to eight hours for 60 days.  
  • Chronic streptococcus: If deemed necessary, child and adolescent carriers of type A streptococcus should take 50 mg/kg a day in divided doses in combination with rifampin for 10 days.
  • Pneumococcal prophylaxis with chronic host versus graft disease: Problems with blood infection following stem cell transplant are treated with 125 mg a day for those aged two months to three years; 250 mg a day for children, and up to 500 mg a day for adolescents.  

How to Take and Store

Proper administration and safe storage of this drug, like all drugs, is essential for safety and crucial for treatment success. Here’s what you need to know about taking and handling Penicillin VK:

  • Take on an empty stomach: As noted above, ensure antibiotic efficacy by taking these pills with a glass of water one hour before or two hours after a meal.
  • Don’t double up on missed doses: The idea with antibiotic treatment is that you expose your body to the drug consistently for a period of time. If you miss a dose, simply take one when you remember. If it’s close to the next time you’re scheduled to take your next dose, just take that one and don’t ever double up.
  • Safe storage: Keep your pills in the original prescription bottle, tightly closed, and out of reach of children. Store tablets at room temperature, away from excessive heat or moisture (your bathroom cabinet may not be a good place). If you’ve been given a liquid solution, keep it refrigerated and don’t freeze it. 
  • Excess: If you’ve come to the end of your treatment—or if the healthcare provider has recommended you stop treatment—with tablets left over, dispose of them by taking them to your pharmacy for safe disposal. Don’t ever save antibiotics for a later date or offer them to anyone else.
  • Two weeks: Unless otherwise directed, it’s recommended that you safely dispose of any left-over antibiotic after 14 days.


If you or a loved one has accidentally taken a great deal of Penicillin VK, contact the Poison Control Center (1-800-222-1222) and your healthcare provider. If a person has collapsed, won’t wake up, is having difficulty breathing, or is experiencing seizures, treat this as a medical emergency and call 911.

Side Effects

As with most medications, there’s a chance that penicillin VK will lead to side effects. These can vary from the easily tolerated and common to those that are rare and life-threatening.


Some of the most common side effects include: 

  • Diarrhea
  • Nausea
  • Vomiting
  • Abdominal
  • Black, hairy tongue

If you’re struggling with these or they persist for extended periods of time, be sure to let your healthcare provider know.


More troubling and severe side effects require immediate medical attention. These include:

  • Rash
  • Hives
  • Itchiness
  • Hoarse voice
  • Wheezing
  • Difficulty swallowing or breathing
  • Swelling of the throat, tongue, or lips
  • Joint pain
  • A return of fever, sore throat, or other signs of infection
  • Severe diarrhea (watery or bloody stools)

Throughout the course of treatment, keep an eye on how you’re feeling and don’t hesitate to reach out for help.

Warnings and Interactions

Special care needs to be taken with Penicillin VK; like most medications, it can interact with other drugs, supplements, and vitamins you’re taking. Adverse reactions or diminished efficacy have been reported with the following:

  • Aminoglycosides (an antibiotic)
  • BCG (a tuberculosis vaccine)
  • Cholera vaccine
  • Typhoid vaccine
  • Dichlorphenamide (a treatment for paralysis)
  • Lactobacillus and estriol (a treatment to aid in menopause)
  • Vitamin K antagonists (drugs such as warfarin and others)
  • Methotrexate (a chemotherapy drug)
  • Mycophenolate (used after kidney transplants)
  • Tolvaptan (used in cases of heart failure or other conditions)
  • Nitisinone (a drug which slows the effect of hereditary kidney dysfunction)
  • Pretomanid (an antibiotic)
  • Probenecid (used to treat gout/uric acid build-up)
  • Sodium picosulfate (a laxative often used to prepare for colon surgery)
  • Teriflunomide (a multiple sclerosis treatment also known as Aubagio)
  • Tetracyclines (a class of antibiotics often used for acne)

As noted above, make sure you’re providing your healthcare provider with a complete and total list of what you’re taking. These drugs can either be affected by Penicillin VK, or themselves inhibit the function of this antibiotic.

The most adverse effect of Penicillin VK, clinically speaking, is severe allergic reaction, otherwise known as “anaphylactic shock.” This leads to a medical emergency, in which your airways become blocked. This is why your healthcare provider needs to have complete sense of any allergies you may have.

4 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. National Institutes of Health, US National Library of Medicine. Penicillin V potassium.

  2. Doron S, Gorbach S. Bacterial infections: overviewInternational Encyclopedia of Public Health.

  3. Coppoc GL. Penicillin derivatives. Purdue Research Foundation.

  4. US Food and Drug Administration. Penicillin VK: label.

By Mark Gurarie
Mark Gurarie is a freelance writer, editor, and adjunct lecturer of writing composition at George Washington University.