Penicillin is one of the most important drugs ever discovered. It was discovered in 1928 by Alexander Fleming, Professor of Bacteriology at St. Mary's Hospital in London. Penicillin is derived from Penicillium fungi.
Penicillin V potassium (Phenoxymethylpenicillin) is the phenoxymethyl analog of penicillin G. It combines acid stability with immediate solubility and rapid absorption.
Penicillin V is used to treat:
- Upper and lower respiratory tract infections (tonsillitis, pharyngitis)
- Middle ear infections
- Scarlet fever
- Skin infections
- Prophylaxis of rheumatic fever
- Ulcerative gingivitis
The most common side effects are nausea, vomiting, epigastric distress, diarrhea, and black hairy tongue.
Efficacy for Streptococcal Pharyngitis
Streptococcal pharyngitis (strep throat) is one of the most common bacterial infections in children 5 to 15 years of age. Streptococcal pharyngitis is caused by Group A β-hemolytic streptococcus (GAS, Streptococcus pyogenes). Streptococcus pyogenesis is the most common bacterial cause of acute pharyngitis.
Distinguishing features of Strep throat:
- Sudden onset of sore throat and other symptoms
- Severe pain on swallowing
- Inflammation of pharynx and tonsils
- Patchy discrete exudates
- Tender, enlarged cervical nodes
- Aged 5-15 years
Penicillin is recommended as a first-line choice for the treatment of uncomplicated Streptococcal pharyngitis by Infectious Diseases Society of America (IDSA)8 and American Academy of Pediatrics (AAP)12. Penicillin has long-standing proven efficacy, and Streptococcus pyogenesis resistant to penicillin have not been documented.
Penicillin cure rate for strep throat is about 80-90%3.
Head-to-head comparisons between penicillin and other antibiotics provide important data on relative efficacy and safety of different treatments:
- Amoxicillin may be slightly more effective than penicillin for the treatment of tonsillopharyngitis4.
- Clarithromycin is equally effective as penicillin V in the treatment of streptococcal tonsillopharyngitis3.
- Azithromycin and penicillin have similar high efficacy, but provides lower rate of eradication of the Group A β-hemolytic Streptococci from the throat 5, 10.
- Cefdinir is slightly better than penicillin for streptococcal pharyngitis6, 9. Both antibiotics provide high cure rates.
Dosage for Streptococcal pharyngitis
- Children: 250 mg 2-3 times per day for 10 days.
- Adults: 250 mg 3-4 times for 10 days; or, alternatively, 500 mg 2 times per day for 10 days.
Intramuscular benzathine penicillin G may be prescribed for patients unlikely to complete a full 10-day course of oral penicillin V.
- Very effective antibiotic for the treatment of streptococcal pharyngitis. Penicillin is the recommended antibiotic of choice by IDSA8 and AAP12 for the treatment of streptococcal pharyngitis.
- Prevents the occurrence of acute rheumatic fever.
- Shortens the duration of the illness.
- Narrow antimicrobial spectrum. In fact, Penicillin V is a treatment for streptococcal pharyngitis with the narrowest antimicrobial spectrum.
- Impressive safety profile.
- May be given with meals. Penicillin V potassium has the distinct advantage over penicillin G in being resistant to inactivation by gastric acid.
- Safe in pregnancy -- Pregnancy risk factor B.
- Cost: penicillin is very inexpensive.
- Allergic reactions - the risk is approximately 1 to 2%. The hypersensitivity reactions reported are skin eruptions (maculopapular to exfoliative dermatitis), urticaria and other serum-sicknesslike reactions, laryngeal edema, and anaphylaxis. If an allergic reaction occurs, the medicine should be discontinued and the appropriate therapy instituted. According to the recent study, female sex appears to be a risk factor for penicillin allergy 2.
- Frequent dosage regimen - short duration of action.
Penicillin treatment failure
When after completing antibiotic therapy a patient redevelops symptoms of strep throat, with the infection confirmed by laboratory tests, this patients has either relapse or reinfection.
Possible reasons of treatment failure:
- Insufficient doses
- Poor compliance
- Inactivation of penicillin by beta-lactamases produced by oropharyngeal flora.
Note: No penicillin-resistant strains of Group A β-hemolytic Streptococci have ever been identified11.
Alternatives to Penicillin for streptococcal pharyngitis
- Amoxicillin, amoxicillin-clavulanate potassium (Augmentin)
- Cephalosporins: cephalexin, cefadroxil
- Macrolides: erythromycn, azithromycin
Difference between "Penicillin G", "Penicillin V", and "Penicillin VK"
The first forms of penicillin were a mixture of different natural penicillins that were designated by letters. These individual penicillins contained a common nucleus and differed only in their side chain, or "R-group".
Penicillin G (benzylpenicillin) is the most potent natural penicillin. It is inactivated by gastric acid and so it is administrated parenterally only. Penicillin G is available as sodium and potassium salts, as a less soluble procaine salt, and as an even less soluble benzathine salt.
Penicillin V (phenoxymethylpenicillin) is more acid stable and can be administered orally. Penicillin V is less active than penicillin G against N. meningitidis, N. gonorrhoeae, and H. influenzae, though their spectrum is similar.
Penicillin V potassium is the potassium salt of penicillin V. It is usually referred as Penicillin VK, where "V" means vesco or vescor, and "K" means potassium.
- Elimination half-life: 0.5 to 1 hr.
- Metabolism: Hepatic biotransformation is 55%.
- Excretion: Mainly renal (20% to 40% as unchanged).
Mechanism of action
Penicillin V exerts a bactericidal action against sensitive microorganisms during the stage of active multiplication. It acts through the inhibition of biosynthesis of cell-wall mucopeptide. It is not active against the penicillinase-producing bacteria, which include many strains of staphylococci.
Penicillin exerts high in vitro activity against staphylococci (except penicillinase-producing strains), streptococci (groups A, C, G, H, L and M), and pneumococci. Other organisms sensitive in vitro to penicillin V are Corynebacterium diphtheriae, Bacillus anthracis, Clostridia, Actinomyces bovis, Streptobacillus moniliformis, Listeria monocytogenes, Leptospira, and Neisseria gonorrhoeae. Treponema pallidum is extremely sensitive.
- 1. U.S. FDA. Penicillin
- 2. 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
- 3. Takker U, Dzyublyk O, Busman T, Notario G. Comparison of 5 days of extended-release clarithromycin versus 10 days of penicillin V for the treatment of streptococcal pharyngitis/tonsillitis: results of a multicenter, double-blind, randomized study in adolescent and adult patients. Curr Med Res Opin. 2003;19(5):421-9. PubMed
- 4. Curtin-Wirt C, Casey JR, Murray PC, et al. Efficacy of penicillin vs. amoxicillin in children with group A beta hemolytic streptococcal tonsillopharyngitis. Clin Pediatr (Phila). 2003 Apr;42(3):219-25. PubMed
- 5. Schaad UB, Kellerhals P, Altwegg M; Swiss Pharyngitis Study Group. Azithromycin versus penicillin V for treatment of acute group A streptococcal pharyngitis. Pediatr Infect Dis J. 2002 Apr;21(4):304-8. PubMed
- 6. Nemeth MA, McCarty J, Gooch WM, Henry D, Keyserling CH, Tack KJ. Comparison of cefdinir and penicillin for the treatment of streptococcal pharyngitis. Cefdinir Pharyngitis Study Group. Clin Ther. 1999 Nov;21(11):1873-81. PubMed
- 7. Otolaryngology : Basic Science and Clinical Review. Thomas R Van de Water
- 8. Stanford T. Shulman, Alan L. Bisno, Herbert W. Clegg, Michael A. Gerber, Edward L. Kaplan, Grace Lee, Judith M. Martin, Chris Van Beneden. Clinical Practice Guideline for the Diagnosis and Management of Group A Streptococcal Pharyngitis: 2012 Update by the Infectious Diseases Society of America. PDF
- 9. Nemeth MA, Gooch WM, Hedrick J, Slosberg E, Keyserling CH, Tack KJ. Comparison of cefdinir and penicillin for the treatment of pediatric streptococcal pharyngitis. Clin Ther. 1999 Sep;21(9):1525-32. PubMed
- 10. Schaad UB, Heynen G. Evaluation of the efficacy, safety and toleration of azithromycin vs. penicillin V in the treatment of acute streptococcal pharyngitis in children: results of a multicenter, open comparative study. Pediatr Infect Dis J. 1996 Sep;15(9):791-5. PubMed
- 11. Sarah S. Long, MD, Larry K. Pickering, MD and Charles G. Prober. Principles and Practice of Pediatric Infectious Diseases, 4th ed. New York, USA: 2012. pp. 203-205.
- 12. American Academy of Pediatrics. Group A streptococcal infections. In: Pickering L. Red Book: Report of the Committee on Infectious Diseases. Elk Grove Villiage, IL, American Academy of Pediatrics, 2009, pp. 616–628