Penicillin VK (Pen-Vee K)

Penicillin in Brief
  • Generic name: Penicillin VK (Penicillin V Potassium, Phenoxymethyl Penicillin)
  • Brand names: Beepen VK, Betapen-VK, V-Cillin K, Pen-Vee K, Robicillin VK, Veetids
  • Therapeutic class: Antibiotic
  • Pharmacologic class: Natural penicillin
  • FDA Approved: January 13, 1958
  • Pregnancy Category: B
  • Originally discovered: London, UK USA

Based on "Antibiotic and Chemotherapy"
written by Roger G. Finch


Penicillin V potassium (Phenoxymethylpenicillin) is the potassium salt of penicillin V. This chemically improved form combines acid stability with immediate solubility and rapid absorption.

Penicillin V potassium exerts high in vitro activity against staphylococci (except penicillinase-producing strains), streptococci (groups A, C, G, H, L and M), and pneumococci.


Penicillin History

The discovery of penicillin has often been described as a miracle drug, and that is exactly what it was.

Do you know who invented penicillin? Originally it was noticed by a French medical student, Ernest Duchesne, in 1896. Penicillin was re-discovered by bacteriologist Alexander Fleming working at St. Mary's Hospital in London in 1928 10. He observed that a plate culture of Staphylococcus had been contaminated by a blue-green mold and that colonies of bacteria adjacent to the mold were being dissolved. Curious, Alexander Fleming grew the mold in a pure culture and found that it produced a substance that killed a number of disease-causing bacteria. Naming the substance penicillin, Dr. Fleming in 1929 published the results of his investigations, noting that his discovery might have therapeutic value if it could be produced in quantity.

What is penicillin used for

FDA approved uses:

  • Streptococcal infections (without bacteremia) - mild to moderate infections of the upper respiratory tract, scarlet fever, and mild erysipelas.
  • Pneumococcal infections - mild to moderately severe infections of the respiratory tract.
  • Staphylococcal infections (penicillin G-sensitive) - mild infections of the skin and soft tissues, including skin sepsis.
  • Fusospirochetosis (Vincent's gingivitis and pharyngitis) - mild to moderately severe infections of the oropharynx usually respond to therapy with oral penicillin.
  • Prevention of recurrence following rheumatic fever and/or chorea: Prophylaxis with oral penicillin on a continuing basis has proven effective in preventing recurrence of these conditions.

Only mild to moderate infections are treated with oral penicillin. Patients with more severe infections can be given penicillin by injection. Penicillin V is not recommended for the treatment of gonorrhea, syphilis, or leptospirosis.

Off-label & Investigational uses:

  • Prophylactic treatment of sickle cell anemia in children4
  • Anaerobic infections5-6
  • Lyme disease (erythema migrans)7
    Lyme disease is caused when an Ixodes tick passes on the germ known as "Borrelia burgdorferi," while sucking blood from its victim. Most people who get Lyme disease will show a rounded red rash at the place the tick bit them within a month. Some never develop a rash, while others develop multiple spots. The rash is called erythema migrans (formerly erythema chronicum migrans).
  • Endocarditis8-9
  • Cat bites 11


Penicillin VK "pros" and "cons"


  • May be taken with meals - resistant to inactivation by gastric acid.
  • Bactericidal against sensitive bacteria.
  • Relatively non-toxic
  • Excellent tissue penetration
  • Relatively inexpensive in comparison with other antibiotics.
  • Pregnancy category B. Penicillin is considered safe during pregnancy.
  • Less likely to induce antimicrobial resistance than broad spectrum antibiotics.
  • Very effective treatment for streptococcal pharyngitis1.


  • Frequent dosage regimen. Because of its short half-life, penicillin must be administered at short intervals, usually every 6 hours.
  • Penicillin allergy (hypersensitivity) - about 10% of population has allergy. All degrees of hypersensitivity, including fatal anaphylaxis, have been reported with penicillin.
  • Unpalatable suspension. Many children dislike the taste of penicillin suspension. In one study 2 it was the least palatable of 14 commonly prescribed antibiotic suspensions.
  • Narrow antibacterial spectrum.
  • Penicillin V is somewhat less potent than Penicillin G (benzylpenicillin) and is not used for serious infections because absorption can be unpredictable and plasma concentrations variable.
  • Lacks stability to β-lactamase.
  • May alter test results for urine.

Mode of action

Penicillin exerts a bactericidal action and acts during the period of bacterial multiplication, inhibiting the biosynthesis of the mucopeptide of the cell wall.

Time to clear out of the system

Penicillin VK half-life is 0.5 to 1 hour. So it takes about 5 hours to clear out of the system.

Further reading


  • 1. Altamimi S, Khalil A, Khalaiwi KA, Milner RA, Pusic MV, Al Othman MA. Cochrane Database Syst Rev. 2012 Aug 15;8. PubMed
  • 2. Ruff ME, Schotik DA, Bass JW, Vincent JM. Taste of antimicrobial drug suspensions. Pediatr Infect Dis J 1991; 10: 3033.
  • 3. Park MA, Matesic D, Markus PJ, Li JT. Female sex as a risk factor for penicillin allergy. Ann Allergy Asthma Immunol. 2007 Jul;99(1):54-8. PubMed
  • 4. Fonseca PB, Braga JA, Machado AM, Brandileone MC, Farhat CK. Nasopharyngeal colonization by Streptococcus pneumoniae in children with sickle cell disease receiving prophylactic penicillin. J Pediatr (Rio J). 2005 Mar-Apr;81(2):149-54. PubMed
  • 5. Busch DF, Kureshi LA, Sutter VL, Finegold SM. Susceptibility of respiratory tract anaerobes to orally administered penicillins and cephalosporins. Antimicrob Agents Chemother. 1976 Oct;10(4):713-20.
  • 6. Head TW, Bentley KC, Millar EP, deVries JA. Penicillin V in eliminating anaerobes from postextraction bacteremias. Oral Surg Oral Med Oral Pathol. 1984 Aug;58(2):152-5. PubMed
  • 7. Bennet L, Danell S, Berglund J Clinical outcome of erythema migrans after treatment with phenoxymethyl penicillin. Scand J Infect Dis. 2003;35(2):129-31. PubMed
  • 8. Pujadas R, Escriva E, Jane J, Galera MC, Fava P, Garau J, Mirelis B. Efficacy of orally administered penicillin V for prophylaxis of experimentally induced streptococcal endocarditis. Antimicrob Agents Chemother. 1987 Oct;31(10):1474-7.
  • 9. Josefsson K, Magni L, Nord CE. High dose phenoxymethylpenicillin for preventing endocarditis. Scand J Infect Dis. 1982;14(2):131-3.
  • 10. Hare R. New light on the history of penicillin. Med History 1982 Jan;26(1):1-24. PubMed
  • 11. Yaqub S, Bjørnholt JV, Hellum KB, Steinbakk M, Enger AE. Bite wound infections. Tidsskr Nor Laegeforen. 2004 Dec 16;124(24):3194-6. PubMed

Published: June 16, 2008
Last updated: January 26, 2017

Interesting facts
Penicillin VK facts
  • Female sex appears to be a risk factor for penicillin allergy3.
  • Penicillin V potassium has the distinct advantage over penicillin G in being resistant to inactivation by gastric acid.

More Facts
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