Phenoxymethylpenicillin (penicillin V) !

An oral penicillin stable in stomach acid for streptococcal pharyngitis and preventing relapses of rheumatic fever.

Updated 2026-11-01

Class: Beta-lactams
Enzyme: Penicillin-binding proteins (bacterial transpeptidases)
ATC code: J01CE02
WHO Model List of Essential Medicines

Also called: penicillin V potassium

Penicillin-binding proteins (bacterial transpeptidases)Phenoxymethylpenicillin (penicillin V)

The figure shows E. coli PBP4 acylated by penicillin V, bonded to the active-site serine.

Target in 3D: Penicillin-binding proteins (bacterial transpeptidases). PDB structure 2EX9 (RCSB PDB, public domain). View the structure at RCSB PDB

Mechanism of action

Penicillin V shares penicillin G's core and spectrum, but its phenoxymethyl side chain makes it resistant to stomach acid, so it is given by mouth. It acylates the PBPs of streptococci and other susceptible gram-positives and stops wall synthesis. Penicillinases destroy it and it barely acts on gram-negatives.

Withstands stomach acid and is absorbed
Acylates streptococcal PBPs
Peptidoglycan cross-linking stops
The streptococcus lyses

Pharmacokinetics

Absorption: Oral; absorption varies between people and some patients absorb too little.
Distribution: High protein binding.
Elimination: Rapid, in the urine.

Indications

Group A streptococcal pharyngitis and tonsillitis. Streptococcal pharyngitis →
Preventing relapses of rheumatic fever or chorea (continuous prophylaxis). Rheumatic heart disease →
Mild skin and respiratory infections due to susceptible streptococci or pneumococci.

Adverse effects

Common

Nausea, vomiting, diarrhoea, epigastric pain
Black hairy tongue
Rash, hives

Contraindications

History of a hypersensitivity reaction to any penicillin

Key interactions

Tetracyclines and chloramphenicol: Bacteriostatic drugs can antagonise the bactericidal effect.
Probenecid: Reduces tubular secretion: higher and longer-lasting β-lactam levels.

What is monitored

Clinical response and adherence in prophylaxis

Administration and safety

Oral; it may be given with meals, although levels are slightly higher on an empty stomach.
It does not replace parenteral penicillin in serious infections.
Do not confuse penicillin V with penicillin G (parenteral).

Nursing care

Before the first dose: ask about allergy to penicillins, cephalosporins and other β-lactams, and what the reaction was.
Stress completing the pharyngitis course: it prevents rheumatic fever.
In continuous prophylaxis, review adherence at each visit.
Teach the patient to report watery or bloody diarrhoea, even weeks after the course ends.

Pregnancy and breastfeeding

Penicillins are widely used in pregnancy without a known rise in birth defects.

Test yourself

Think of the answer, then tap the question to see it.

What advantage does penicillin V have over penicillin G?

It is stable in stomach acid, so it can be given by mouth.

Why is it important to finish treatment of streptococcal pharyngitis?

To eradicate group A streptococcus and prevent rheumatic fever.

Which intramuscular alternative is used for secondary prophylaxis of rheumatic fever?

Benzathine benzylpenicillin, which avoids relying on daily oral doses.

Add to my cards (3)

← Back to the class: Beta-lactams

Educational content on how drugs work; not a prescribing guide and no substitute for a health professional's advice. No doses are given.

Sources: Penicillin V Potassium: MedlinePlus Drug Information (MedlinePlus (U.S. National Library of Medicine), 2026); DailyMed - PENICILLIN V POTASSIUM tablet, film coated (DailyMed (U.S. National Library of Medicine), 2026); RCSB PDB - 2EX9: Crystal structure of penicillin binding protein 4 (dacB) from Escherichia coli, complexed with penicillin-V (RCSB Protein Data Bank, 2026); Farmacología básica y clínica (Katzung), cap. 43 (McGraw Hill, 2025).

Spotted a mistake?We are always improving for the community. Tell us what is wrong and our team will review it.Report a mistake

Representative model, for educational purposes only.