Phenoxypen

Phenoxypen and Phenoxypen potassium are indicated in the treatment of mild to moderately severe infections associated with micro-organisms whose susceptibility to penicillin is within the range of serum levels attained with the dosage form.

Phenoxypen is indicated for prophylaxis against:

- Pneumococcol infection (e.g. in asplenia and in patients with sickle cell disease).

Note: Severe empyema, bacteraemia, pericarditis, meningitis and arthritis should not be treated with Penicillin V during the acute phase.

Consideration should be given to official guidance on the appropriate use of antibacterial agents.

The following infections will usually respond to adequate doses:

Streptococcal infections (without bacteraemia): 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 sensitive to penicillin: mild infections of the skin and soft tissues. Fusospirochaetosis (Vincent's gingivitis and pharyngitis): mild to moderately severe infections of the oropharynx usually respond to therapy with oral penicillin.

Prophylactic use: prophylaxis with oral penicillin has proved effective in preventing recurrence of rheumatic fever and chorea.

Patients with a past history of rheumatic fever receiving continuous prophylaxis may harbour penicillin-resistant organisms. In these patients, the use of another prophylactic agent should be considered.

Note: oral penicillin should not be used as adjunctive prophylaxis for genito - urinary instrumentation or surgery, lower intestinal tract surgery, sigmoidoscopy and child birth.

Posology

Phenoxypen 125 mg/5ml Oral Solution should be given in divided doses (4 times a day) and preferably half an hour before meals or at least three hours after a meal.

The following dosage schedule applies to Phenoxypen 125 mg/5ml Oral Solution:

Method of Administration

For oral administration only

Patients with Renal Impairment

Reduce dose if renal function is markedly impaired.

To avoid late complications (rheumatic fever), infections with β-haemolytic streptococci should be treated for 10 days.

Phenoxypen is contraindicated in patients known to be hypersensitive to Penicillin and should be used with caution in patients with known histories of allergy.

Penicillin should be used with caution in individuals with histories of significant allergies and/or asthma.

All degrees of hypersensitivity, including fatal anaphylaxis, have been observed with oral penicillin. These reactions are more likely to occur in individuals with a history of sensitivity to penicillins, cephalosporins and other allergens. Enquiries should be made for such a history before therapy is begun. If any allergic reaction occurs, the drug should be discontinued and the patient treated with the usual agents (e.g. adrenaline and other pressor amines, antihistamines and corticosteroids).

Oral therapy should not be relied upon for patients with severe illness, or with nausea, vomiting, gastric dilation, achalasia or intestinal hypermotility. Occasionally patients do not absorb therapeutic amounts of orally administered penicillin.

Administer with caution in the presence of markedly impaired renal function, as safe dosage may be lower than the usually recommended doses.

Streptococcal infections should be treated for a minimum of 10 days, and post therapy cultures should be performed to confirm the eradication of the organisms.

Prolonged use of antibiotics may promote the over growth of non-susceptible organisms, including fungi. If super infection occurs, appropriate measures should be taken.

Sucrose:

This product contains sucrose. Patients with rare hereditary problems of fructose intolerance, glucose-galactose malabsorption or sucrase-isomaltase insufficiency should not take this medicine. Contains 2.80g of sucrose per 5ml dose. To be taken into consideration by patients with diabetes mellitus. May be harmful to the teeth.

E110 & E124:

This product contains Ponceau 4R (E124) and Sunset yellow (E110) which may cause allergic reactions.

None known

The most common reactions to oral penicillin are gastrointestinal effects and hypersensitivity reactions. Although hypersensitivity reactions have been reported much less frequently after oral than after parenteral therapy, it should be remembered that all forms of hypersensitivity, including fatal anaphylaxis have been observed with oral penicillin.

Blood and lymphatic disorders:

There have been very rare (<1/10,000) reports of changes in blood counts, including, thrombocytopenia, neutropenia, leucopenia, eosinophilia and haemolytic anaemia. Coagulation disorders (including prolongation of bleeding time and defective platelet function) have also been reported.

Gastrointestinal disorders:

Nausea, vomiting, abdominal pain, diarrhoea are common (>1/100 to <1/10). Sore mouth and black hairy tongue (discolouration of tongue) has been reported rarely (>1/10,000 to <1/1,000).

Hepatobiliary diorders:

Hepatitis and cholestatic jaundice have been reported very rarely (<1/10,000).

Immune disorders:

Allergic reactions may commonly occur (>1/100 to <1/10) and typically manifest as skin reactions (See Skin and subcutaneous disorders). Severe allergic reactions causing angioedema, laryngeal oedema and anaphylaxis have been reported rarely (>1/10,000 to <1/1,000).

Serum sickness-like reactions are characterised by fever, chills, arthralgia and oedema.

Infections and infestations:

Pseudomembranous colitis has rarely (>1/10,000 to <1/1,000) been reported.

Nervous system disorders:

Central nervous system toxicity including convulsions has been reported (especially with high doses or in severe renal impairment); paraesthesia may occur with prolonged use.

Neuropathy is an infrequent reaction and is usually associated with high doses of parenteral penicillin.

Renal and urinary disorders:

Interstitial nephritis has occurred in very rare cases (<1/10,000).

Nephropathy is an infrequent reaction and is usually associated with high doses of parenteral penicillin.

Skin and subcutaneous disorders

Urticarial, erythematous or mobilliform rash and pruritus occur commonly (>1/100 to <1/10), while exfoliative dermatitis occurs rarely (>1/10,000 to <1/1,000).

Reporting of suspected adverse reactions

Reporting suspected adverse reactions after authorisation of the medicinal product is important. It allows continued monitoring of the benefit/risk balance of the medicinal product. Healthcare professionals are asked to report any suspected adverse reactions via the yellow card scheme at www.mhra.gov.uk/yellowcard.

Symptoms: A large oral overdose of penicillin may cause nausea, vomiting, stomach pain, diarrhoea, and rarely, major motor seizures. If other symptoms are present, consider the possibility of an allergic reaction. Hyperkalaemia may result from overdosage, particularly for patients with renal insufficiency.

Management: No specific antidote is known. Symptomatic and supportive therapy is recommended. Activated charcoal with a cathartic, such as sorbitol may hasten drug elimination. Penicillin may be removed by haemodialysis.

ATC code: J01CE02

Phenoxypen is a beta-lactamase sensitive natural penicillin.

Mechanism of Action:

Phenoxypen acts through interference with the final stage of synthesis of the bacterial cell wall. The action depends on its ability to bind certain membrane-bound proteins, (penicillin-binding proteins or PBPs) that are located beneath the cell wall. These proteins are involved in maintaining cell wall structure, in cell wall synthesis and in cell division, and appear to possess transpeptidase and carboxypeptidase activity.

PK/PD relationship

The time above the minimum inhibitory concentration (T>MIC) is considered to be the major determinant of efficacy for Phenoxypen.

Mechanism(s) of Resistance:

Phenoxypen is inhibited by penicillinase and other beta-lactamases that are produced by certain micro-organisms. The incidence of beta-lactamase producing organisms is increasing.

Mechanisms of resistance

The two main mechanisms of resistance to Phenoxypen are:

- Inactivation by bacterial penicillinases and other beta-lactamases

- Alteration of PBPs, which reduce the affinity of the antibacterial agent for the target.

Impermeability of bacteria or efflux pump mechanisms may cause or contribute to bacterial resistance.

EUCAST clinical MIC breakpoints to separate susceptible (S) pathogens from resistant (R) pathogens (version 1.0 22.11.210) are:

The susceptibility of streptococci Groups A, C and G and S. pneumoniae to Phenoxypen is inferred from the susceptibility to benzylpenicillin.

Staphylococci: Most staphylococci are penicillinase-producers. Penicillinase-producing strains are resistant. The benzylpenicillin breakpoint (shown) will mostly, but not unequivocally, separate beta-lactamase producers from non-producers.

Streptococcus pneumoniae: For Phenoxypen, report S. pneumoniae with benzylpenicillin MICs above 0.06 mg/L resistant.

The prevalence of acquired resistance may vary geographically and with time for selected species and local information on resistance is desirable, particularly when treating severe infections. Expert advice should be sought as necessary when the local prevalence of resistance is such that the utility of the agent in at least some types of infection is questionable.

Absorption: Rapidly but incompletely absorbed after oral administration (about 60% of an oral dose is absorbed). Calcium and potassium salts are better absorbed than the free acid. Absorption appears to be reduced in patients with coeliac disease. Absorption appears to be more rapid in fasting than non-fasting subjects.

Blood concentration: after an oral dose of 125mg, peak serum concentrations of 200 to 700ng/ml are attained in 2 hours. After an oral dose of 500mg, peak serum concentrations reach 3 to 5micrograms/ml in 30 to 60 minutes.

Half-life: Biological half-life is about 30 minutes, increased to about 4 hours in severe renal impairment.

Distribution: Widely distributed throughout the body and enters pleural and ascitic fluids and also in cerebrospinal fluid when the meninges are inflamed; Phenoxypen crosses the placenta and is secreted in the milk; (protein binding 50 to 80% bound plasma proteins).

Metabolic reactions: Hydroxylation may occur

Excretion: 20% to 35% of an oral dose is excreted in the urine in 24 hours

Not applicable.

None known.

To reconstitute: Loosen powder, add 63ml water and shake well.

No special requirements for disposal.

Any unused medicinal product or waste material should be disposed of in accordance with local requirements.