Penicillin V
Pronunciation: pen-ih-SILL-in vee.
- Generic name
- phenoxymethylpenicillin (penicillin V potassium)
- Drug class
- Penicillin-class antibiotic (narrow-spectrum, beta-lactamase-sensitive)
- Form
- Tablet or oral solution/powder for oral solution, strength and exact product country-specific
- Route
- Oral
- Legal status
- Prescription-only antibiotic
Availability and supply rules vary by country
Trade names by country:
Australia: · Full directory
What phenoxymethylpenicillin (penicillin V potassium) is and how it works
Penicillin V is an oral, narrow-spectrum penicillin antibiotic active against certain penicillin-sensitive bacteria, particularly streptococci and some staphylococci and pneumococci. It is not active against bacteria that produce the penicillinase enzyme, and it does not treat viral infections such as colds or flu. (1) (2) (4)
Penicillin V is used for mild to moderately severe bacterial infections and for long-term prevention of rheumatic fever recurrence and certain other conditions. Exact approved uses, dosing, and course length are set by the prescriber and local product label; the oral route is not relied on for severe or life-threatening infection.
Mechanism of action: how phenoxymethylpenicillin (penicillin V potassium) works
Penicillin V exerts a bactericidal effect against susceptible, actively multiplying penicillin-sensitive organisms by inhibiting bacterial cell-wall (mucopeptide) biosynthesis. It has high in vitro activity against non-penicillinase-producing staphylococci, streptococci, and pneumococci but is inactivated by penicillinase-producing organisms. (1) (4)
What phenoxymethylpenicillin (penicillin V potassium) is used for
Streptococcal infections, including throat infections
Penicillin V is used for streptococcal infections such as pharyngitis (sore throat) and tonsillitis. Treatment must run for a sufficient course (commonly around 10 days in the United States label) to reduce the risk of complications such as rheumatic fever, even if symptoms improve earlier. (1) (2) (3)
Mild to moderate pneumococcal and other respiratory, ear, and skin infections
Country labels describe use for milder pneumococcal respiratory-tract infections and staphylococcal infections of the respiratory tract, skin, and soft tissue caused by susceptible organisms. Severe pneumonia and similarly severe infections are excluded from oral penicillin V treatment in the acute stage. (1) (3)
Long-term prevention (prophylaxis)
Penicillin V is used long-term to help prevent recurrence of rheumatic fever after an initial episode, and in some countries to reduce infection risk in people with conditions such as sickle cell disease or after spleen removal. Prophylactic use and dosing are set by the prescriber and are not a general infection-prevention product. (1) (3)
Dental and Vincent's infections
Some labels include Vincent's infection of the mouth and throat, and dental practice guidance in some countries includes penicillin V for certain dental infections. Exact indication wording is country- and product-specific. (1) (3)
Before taking phenoxymethylpenicillin (penicillin V potassium)
Do not take / not appropriate for
- Do not take penicillin V if you have had a previous hypersensitivity (allergic) reaction to any penicillin. This is stated as a contraindication in the United States label. (all products) (1) (4)
- Do not rely on oral penicillin V for severe pneumonia, empyema, bacteraemia, pericarditis, meningitis, or arthritis in the acute stage, or in patients with severe illness, persistent vomiting, or conditions that impair swallowing or gut absorption. (all indications) (1) (4)
Tell your clinician about
- Any previous allergic reaction to penicillin, cephalosporins, or any other medicine, because cross-reactivity between penicillins and cephalosporins has occurred.
- Asthma or a history of multiple drug allergies, which may increase the risk or severity of a hypersensitivity reaction.
- Kidney problems, including severely impaired renal function.
- Pregnancy, plans for pregnancy, or breastfeeding.
- Every other medicine, including methotrexate, anticoagulants (warfarin-type medicines), oral contraceptives, other antibiotics, and typhoid vaccine.
How to take phenoxymethylpenicillin (penicillin V potassium)
- Take penicillin V exactly as prescribed, spacing doses evenly through the day as directed (commonly every 6 to 8 hours, or twice daily for prevention).
- Complete the full prescribed course even if you feel better before it is finished; stopping early can allow the infection to return and contributes to antibiotic resistance.
- Some product labels advise taking it on an empty stomach (for example, 30 minutes before food or at least 2 hours after eating) because food can reduce absorption; follow the instructions on your own product's leaflet.
- Swallow tablets whole; use the measuring device supplied with liquid products rather than a household spoon.
- Do not change the dose, frequency, or duration yourself, and do not share this medicine with anyone else.
Procedures and treatment changes
Tell the treating team before surgery, procedures, or any medicine change. Do not alter treatment without the responsible clinician. (1) (2) (3) (4) (5)
Missed dose
Take the missed dose as soon as you remember, unless it is almost time for the next dose, in which case skip the missed dose and continue the regular schedule. Do not take two doses together to make up for a missed one. If you are unsure, ask your pharmacist or prescriber.
Overdose
A single extra dose is unlikely to cause serious harm, but taking much more than prescribed can cause nausea, vomiting, and diarrhoea, and in people with impaired kidney function may require blood-level monitoring. If an overdose is suspected, contact a doctor, pharmacist, or poison-control/emergency service promptly and take the medicine packet with you; do not wait for symptoms to appear. (3) (4)
Side effects
Most people tolerate penicillin V well. Serious and occasionally fatal hypersensitivity (anaphylactic) reactions have been reported with penicillin therapy and can occur even without a prior reaction to penicillin.
Nausea, vomiting, or stomach discomfort
What to notice: Mild stomach upset, indigestion, or epigastric discomfort, occurring in roughly 1 in 10 people.
What to do: Stick to simple, non-spicy meals and take with water; contact a clinician if severe or persistent. (1) (3)
Diarrhoea
What to notice: Loose stools during treatment.
What to do: Stay hydrated. Severe diarrhoea lasting more than 24 hours, or diarrhoea with fever and blood or mucus, needs prompt medical assessment (see serious warnings). (1) (3)
Black, hairy tongue
What to notice: A harmless but visible tongue discoloration and texture change that can occur with penicillin therapy.
What to do: Usually resolves after the course; mention it to a clinician or pharmacist if concerned. (1)
Mild allergic-type skin reaction
What to notice: Mild rash, itching, or hives without breathing difficulty or facial/throat swelling.
What to do: Contact a clinician or pharmacist promptly; do not continue the course without medical advice. (3)
Antibiotic-associated diarrhoea (possible colitis)
What to notice: Severe or persistent watery or bloody diarrhoea with stomach pain and fever, which can begin during treatment or up to about two months after it ends.
What to do: Seek prompt medical assessment; do not self-treat with anti-diarrhoeal medicines without advice. (1) (3)
Serious warnings
Anaphylaxis and other serious hypersensitivity reactions — emergency
Symptoms: Sudden swelling of the lips, mouth, throat, or tongue; breathing very fast or struggling to breathe; wheezing; throat tightness or difficulty swallowing; skin, lips, or tongue turning blue, grey, or pale; sudden confusion, drowsiness, or dizziness; fainting or collapse.
Action: This is a medical emergency. Call emergency services immediately. Serious anaphylactic reactions require immediate treatment with epinephrine (adrenaline), oxygen, and other emergency measures given by medical staff. Reactions are more likely in people with a previous penicillin or multi-drug allergy history but can occur without warning. (1) (4) (3)
Clostridioides difficile-associated diarrhoea (antibiotic-associated colitis) — high caution
Symptoms: Severe, persistent, or bloody diarrhoea with abdominal pain and fever, which can range from mild to a life-threatening colitis and may appear up to roughly two months after the course ends.
Action: Contact a clinician promptly for assessment; this can occur with nearly any antibacterial agent, including penicillin V. (1) (3)
Serious blood disorders (rare) — high caution
Symptoms: Unusual bruising or bleeding, sore throat with fever, or unusual tiredness or pallor, which can reflect rare reactions such as haemolytic anaemia, leukopenia, or thrombocytopenia.
Action: Seek prompt medical assessment if these symptoms occur during or shortly after treatment. (1)
Interactions
| Medicine or test | Effect | Action |
|---|---|---|
| Probenecid | Delays elimination of penicillin V, increasing and prolonging its blood levels. | Only a prescriber should combine these; dose or monitoring adjustments may be needed. (4) |
| Methotrexate | Penicillin V can reduce methotrexate excretion, increasing the risk of methotrexate toxicity. | Tell the prescriber if methotrexate is being taken; closer monitoring may be required. (4) |
| Warfarin and other anticoagulants (coumarins, phenindione) | INR (blood-clotting test results) may be altered during penicillin V therapy. | Anticoagulant monitoring may need to be increased during and after the course; tell the prescriber. (4) |
| Bacteriostatic antibiotics (e.g., tetracyclines, erythromycin, chloramphenicol, sulfonamides) | May theoretically reduce the bactericidal effectiveness of penicillin V. | Combination antibiotic choices should be made by the prescribing clinician. (4) |
| Oral typhoid vaccine | Antibacterial agents, including penicillin V, can inactivate live oral typhoid vaccine. | Tell the prescriber or pharmacist about planned vaccinations; timing may need to be adjusted. (4) |
| Combined hormonal contraceptives | Severe or persistent diarrhoea or vomiting during penicillin V treatment may reduce contraceptive pill effectiveness. | Use additional contraceptive precautions as advised on the contraceptive product leaflet if significant diarrhoea or vomiting occurs. (3) (4) |
Pregnancy, breastfeeding, kidney/liver function, age
Pregnancy and breastfeeding
Penicillin V has a long history of clinical use in pregnancy without evidence of teratogenic effect, and most pregnant and breastfeeding people can take it when prescribed. Small amounts pass into breast milk; tell the prescriber if breastfeeding so they can weigh the individual benefit and any risk of infant bowel-flora disturbance or allergic sensitisation. (4) (3)
Children
Penicillin V is used in children with age- and weight-appropriate dosing set by the prescriber. Use only the exact product and dose prescribed for the child; do not use an adult product or share doses between family members. (3) (1)
Kidney impairment
People with significantly reduced kidney function may need dose adjustment or blood-level monitoring because elimination of penicillin V is slower. Tell the prescriber about any known kidney problems. (4)
Asthma or multiple allergies
People with asthma or a history of several drug allergies may be more likely to have a hypersensitivity reaction to penicillin V; tell the prescriber before starting. (3) (1)
Monitoring
Before starting
- Confirm the exact infection or preventive indication, the organism where known, and any previous penicillin or cephalosporin allergy.
- Review kidney function, asthma history, pregnancy/breastfeeding status, and all other medicines including methotrexate, anticoagulants, and contraceptives.
- Select the exact product, strength, dosing interval, and course length appropriate to the indication and local label.
During treatment
- Complete the prescribed course length even after symptoms improve, particularly for streptococcal infections where under-treatment risks rheumatic fever.
- Reassess promptly for signs of hypersensitivity, severe diarrhoea, or lack of clinical improvement.
- For long-term prophylactic use, periodically reassess continued need and adherence with the prescriber.
Storage
Store tablets in the original container, out of sight and reach of children, following the temperature guidance on the product label. Reconstituted oral solutions typically have a limited shelf life once mixed and may need refrigeration; follow the exact instructions on your product's leaflet and discard any unused liquid after the stated period.
Study the drug class: Penicillins
Professional information
Clinician-facing context only. Use the current local indication, dosing table, renal-adjustment guidance, and antimicrobial-stewardship pathway.
United States
Indication: Streptococcal, pneumococcal, staphylococcal infections; rheumatic fever prophylaxis
Dose summary: No universal dose is displayed. The US label describes examples such as 125-250 mg every 6-8 hours for 10 days for streptococcal pharyngitis, 250-500 mg every 6 hours until afebrile for pneumococcal infection, and 125-250 mg twice daily for rheumatic fever prophylaxis; the exact regimen must follow current local prescribing information.
Renal context: Severe renal impairment may require dose or interval adjustment; individual assessment is required. (1)
United Kingdom
Indication: Mild to moderately severe penicillin-sensitive infections; rheumatic fever prophylaxis
Dose summary: UK SmPC examples include 250-500 mg every 6 hours in adults, weight/age-banded paediatric doses, and 250 mg twice daily for long-term rheumatic fever prophylaxis; administration is generally advised at least 30 minutes before food.
Renal context: Use with caution and consider dose reduction in markedly impaired renal function. (4)
Hepatic guidance
No specific hepatic dose adjustment is described in the reviewed labels; use local product information and clinical judgement.
Overdose note
Overdose management is supportive; blood-level monitoring may be advisable in patients with renal impairment. There is no published specific antidote. (1) (4)
Frequently asked questions
Is penicillin V the same as penicillin G or amoxicillin?
No. Penicillin V (phenoxymethylpenicillin) is an oral penicillin distinct from injectable penicillin G and from amoxicillin. They are not interchangeable without a prescriber's instruction. (1)
Can I stop taking penicillin V once I feel better?
No. Complete the full prescribed course, especially for streptococcal throat infections, because stopping early risks the infection returning and complications such as rheumatic fever, and contributes to antibiotic resistance. (2) (3)
What should I do if I think I am having an allergic reaction?
Mild rash or itching needs prompt medical advice and should not be ignored. Sudden swelling of the face, lips, or throat, breathing difficulty, or collapse is a medical emergency — call emergency services immediately. (3) (1)
Can I take penicillin V during pregnancy or while breastfeeding?
It has a long record of use in pregnancy and is generally considered compatible when prescribed, and small amounts pass into breast milk. Tell the prescriber so they can confirm it is appropriate for your situation. (4)
What is the mechanism of action of phenoxymethylpenicillin (penicillin V potassium)?
Penicillin V exerts a bactericidal effect against susceptible, actively multiplying penicillin-sensitive organisms by inhibiting bacterial cell-wall (mucopeptide) biosynthesis. It has high in vitro activity against non-penicillinase-producing staphylococci, streptococci, and pneumococci but is inactivated by penicillinase-producing organisms. (1) (4)
References
- DailyMed: Penicillin V Potassium tablet / powder for oral solution — prescribing informationDailyMed, U.S. National Library of Medicine (FDA-approved label) · United States · accessed 2026-07-26 · source 1
- MedlinePlus: Penicillin V PotassiumMedlinePlus, U.S. National Library of Medicine · United States · accessed 2026-07-26 · source 2
- NHS: Phenoxymethylpenicillin — antibiotic to treat infectionsNHS · United Kingdom · accessed 2026-07-26 · source 3
- UK Phenoxymethylpenicillin 500 mg Film-coated Tablets Summary of Product Characteristicselectronic Medicines Compendium (UK SmPC) · United Kingdom · accessed 2026-07-26 · source 4
- TGA ARTG: Phenoxymethylpenicillin (as potassium salt) 250mg/5ml powder for oral liquidTherapeutic Goods Administration (TGA), Australian Register of Therapeutic Goods · Australia · accessed 2026-07-26 · source 5
Brand names by country
Single-ingredient phenoxymethylpenicillin (penicillin V potassium) names are shown separately by country. Product availability, strengths, and supply rules can change; combination products are not included here.