Phenoxymethylpenicillin has a range of antimicrobial activity against Gram-positive bacteria that is similar to that of benzylpenicillin and a similar mode of action, but it is substantially less active than benzylpenicillin against Gram-negative bacteria.Phenoxymethylpenicillin is more acid-stable than benzylpenicillin, which allows it to be given orally. Phenoxymethylpenicillin is usually used only for the treatment of mild to moderate infections, and not for severe or deep-seated infections since absorption can be unpredictable. Except for the treatment or prevention of infection with Streptococcus pyogenes (which is uniformly sensitive to penicillin), therapy should be guided by bacteriological studies (including sensitivity tests) and by clinical response. People treated initially with parenteral benzylpenicillin may continue treatment with phenoxymethylpenicillin by mouth once a satisfactory response has been obtained.It is not active against beta-lactamase-producing bacteria, which include many strains of Staphylococci. Adverse effects
Phenoxymethylpenicillin is usually well tolerated but may occasionally cause transient nausea, vomiting, epigastric distress, diarrhea, constipation, acidic smell to urine and black hairy tongue. A previous hypersensitivity reaction to any penicillin is a contraindication. Mechanism of action
The mechanism of phenoxymethylpenicillin is identical to that of all other penicillins. It exerts a bactericidal action against penicillin-sensitive microorganisms during the stage of active multiplication. It acts by inhibiting the biosynthesis of cell-wall peptidoglycan. Compendial status
British Pharmacopoeia

History
The Austrian pharmaceutical company, Biochemie, was founded in Kundl in July 1946 at the site of a derelict brewery, at the suggestion of a French officer, Michel Rambaud (a chemist), who was able to obtain a small amount of Penicillium start culture from France.
Contamination of the fermentation tanks was a persistent problem and in 1951, the company biologist, Ernst Brandl, attempted to solve this by adding phenoxyethanol to the tanks as an anti-bacterial disinfectant. This resulted unexpectedly in an increase in penicillin production: but, the penicillin produced was not benzylpenicillin, but phenoxymethylpenicillin. Phenoxyethanol was fermented to phenoxyacetic acid in the tanks, which was then incorporated into penicillin via biosynthesis. Importantly, Brandl realised that phenoxymethylpenicillin is not destroyed by stomach acid and can therefore be given by mouth. Phenoxymethyl penicillin was originally discovered by Eli Lilly in 1948 as part of their efforts to study penicillin precursors, but was not further exploited, and there is no evidence that Lilly understood the significance of their discovery at the time. : 119–121 Biochemie is now part of Sandoz. Names
There were four named penicillins at the time penicillin V was discovered (penicillins I, II, III, IV), however, Penicillin V was named "V" for Vertraulich (confidential);: 121  it was not named for the Roman numeral "5". Penicillin VK is the potassium salt of penicillin V (K is the chemical symbol for potassium). References
External links
"Penicillin V". Drug Information Portal. U.S. National Library of Medicine.