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Penicillin V

( Phenoxymethyl Penicillin , Penicillin V Potassium )

Pronunciation: PEN-i-SIL-in
Class: Natural penicillin

Trade Names

Penicillin V Potassium
- Tablets, oral 250 mg
- Tablets, oral 500 mg
- Powder for oral solution 125 mg per 5 mL
- Powder for oral solution 250 mg per 5 mL


Inhibits mucopeptide synthesis of bacterial cell wall.



Widely distributed to most body fluids and tissues; highest levels are found in kidneys, with a lesser amount in the liver, skin, and intestines. Also penetrates CSF. Protein binding is 80%.


Excreted rapidly; however, recovery of the drug from the urine indicates that only approximately 25% of the dose given is absorbed.

Special Populations

Renal Function Impairment

Excretion is considerably delayed.

Hepatic Function Impairment

Pharmacokinetic information not available.


In neonates and young infants, excretion is considerably delayed.

Indications and Usage

Bacterial endocarditis

Prophylaxis against bacterial endocarditis.


For the treatment of mild to moderate severe infections of the oropharynx (Vincent gingivitis and pharyngitis).

Pneumococcal infections

For the treatment of mild to moderately severe infections of the respiratory tract.

Rheumatic fever and/or chorea

For the prevention of recurrence following rheumatic fever and/or chorea.

Streptococcal infections (without bacteremia)

For the treatment of mild to moderate infections of the upper respiratory tract, scarlet fever, and mild erysipelas. Streptococci in groups A, C, G, H, L, and M are very sensitive to penicillin. Other groups, including group D ( Enterococcus ), are resistant.

Staphylococcal infections (penicillin G sensitive)

For the treatment of mild infections of the skin and soft tissues.


Hypersensitivity to penicillins.

Dosage and Administration

Dosage may vary with site of infection and organism being treated.

Fusospirochetosis (Vincent infection) of the oropharynx
Adults and Children 12 y and older

PO 250 to 500 mg every 6 to 8 h.

Pneumococcal infections
Adults and Children 12 y and older

PO 250 to 500 mg every 6 h until the patient has been afebrile for at least 2 days.

Prevention of rheumatic fever/chorea
Adults and Children 12 y and older

PO 125 to 250 mg twice daily on a continuing basis.

Prophylaxis against bacterial endocarditis
Adults and Children 12 y and older

PO 2 g (1 g for patients less than 27 kg) 1 h before the procedure, then 1 g (500 mg for patients less than 27 kg) 6 h later.

Staphylococcal infections
Adults and Children 12 y and older

PO 250 to 500 mg every 6 to 8 h.

Streptococcal infections
Adults and Children 12 y and older

PO 125 to 250 mg every 6 to 8 h for 10 days.

General Advice

  • May be given with meals; however, blood levels are slightly higher when the drug is given on an empty stomach.
  • Shake the oral solution well before measuring each dose.


Store between 59° and 86°F. After reconstitution, solution must be stored in a refrigerator. Discard any unused solution after 14 days.

Drug Interactions

Anticoagulants (oral and heparin)

May increase bleeding risks of anticoagulant by prolonging bleeding time. In some situations, warfarin plasma concentrations and anticoagulant effects may be decreased. Monitor coagulation status and adjust the anticoagulant dose as needed.

Contraceptives, hormonal

May reduce efficacy of oral contraceptives. Use nonhormonal methods of birth control during coadministration.


Serum concentrations and pharmacologic effects of methotrexate may be increased by penicillins. Toxicity may occur. Close clinical and methotrexate concentration monitoring is warranted.


Increases penicillin serum concentration.


May impair bactericidal effects of penicillin V. Avoid coadministration.

Laboratory Test Interactions

May cause false-positive results with copper sulfate tests (Benedict test, Fehling test, or Clinitest tablets); enzyme-based tests (eg, Clinistix , Tes-Tape ) are not affected.

Adverse Reactions


Diarrhea or bloody diarrhea; epigastric distress; nausea; vomiting.


Hypersensitivity reactions (eg, anaphylaxis, death, laryngeal edema, skin eruptions [maculopapular to exfoliative dermatitis], urticaria).


Black, “hairy” tongue; eosinophilia; fever.



Category B .


Excreted in breast milk.


Reactions range from mild to life-threatening. Administer with caution to cephalosporin-sensitive patients because of possible cross-reactivity.

Renal Function

Use with caution.

Special Risk Patients

Severe pneumonia, empyema, bacteremia, pericarditis, meningitis, and arthritis should not be treated with penicillin V during the acute stage. Use caution in patients with histories of significant allergies and/or asthma.


May result in bacterial or fungal overgrowth of nonsusceptible organisms, including fungi.

Clostridium difficile –associated diarrhea

Mild diarrhea to fatal colitis may occur.


The powder for solution contains phenylalanine 4.5 mg per 5 mL.



None well documented.

Patient Information

  • Instruct patients to finish the course of therapy even if they are feeling better.
  • Counsel patients to use antibacterial drugs, including penicillin, only to treat bacterial infections. Antibacterial drugs do not treat viral infections (eg, the common cold).
  • Inform patients that diarrhea is a common problem caused by antibiotics, which usually ends when the antibiotic is discontinued. Sometimes after starting treatment with antibiotics, patients can develop watery and bloody stools (with or without stomach cramps and fever), even as late as 2 or more months after having taken the last dose of the antibiotic. If this occurs, advise patients to contact their health care provider as soon as possible.
  • Advise women using oral contraceptives to use a nonhormonal form of contraceptive while taking penicillin.
  • Inform patients of signs of hypersensitivity (eg, skin rash, itching, hives, shortness of breath, wheezing) and other side effects, such as black tongue, sore throat, nausea, vomiting, severe diarrhea, fever, swollen joints, and instruct patients to notify health care provider should they occur.
  • Instruct patients to notify their health care provider if there is no improvement in symptoms of infection.
  • Advise patients to notify their health care provider of signs of superinfection (eg, black, “hairy” tongue; vaginitis).

Further information

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.