PHENOXYMETHYL 125MG/5ML ORAL SOLUTION

Indications

• Bacterial infections
• Pneumonia
• Streptococcal infections
• Syphilis
• Meningitis
• Endocarditis
• Skin infections

Dosage

Children: Refer to the BNF for Children for specific dosing recommendations based on the type of penicillin and indication.

Adults: Refer to the BNF for specific dosing recommendations based on the type of penicillin and indication.

Mechanism of action

Penicillin targets penicillin-binding proteins (PBPs) located inside the bacterial cell wall. By binding to these proteins, penicillin disrupts the transpeptidation process, which is essential for cell wall structural integrity. This results in weakened cell walls, causing osmotic instability and ultimately leading to cell lysis and death.

Pharmacodynamics

Penicillin exhibits bactericidal activity, meaning that it kills bacteria rather than merely inhibiting their growth. Its effectiveness is generally dependent on the growth phase of the bacteria, as it is most active against actively dividing cells. The spectrum of activity varies among different penicillins, with some being more effective against specific bacterial strains.

Pharmacokinetics

Penicillin is primarily absorbed in the gastrointestinal tract, with its bioavailability varying depending on the specific type of penicillin. It is primarily excreted by the kidneys, with a half-life that typically ranges from 30 minutes to 2 hours, depending on the formulation. Dosage adjustments may be necessary in patients with renal impairment to prevent accumulation and toxicity.

Contra-indications

• History of hypersensitivity to penicillins
• Severe allergic reactions to beta-lactam antibiotics

Adverse effects

• Allergic reactions such as rash, urticaria, and anaphylaxis
• Gastrointestinal disturbances including nausea, vomiting, and diarrhea
• Superinfection due to alteration of normal flora
• Hematologic reactions such as leukopenia, thrombocytopenia

Interactions

• valproate+penicillins: Severe (increases risk of adverse effects)
• allopurinol+penicillins: Unknown (increases risk of skin rash)
• leflunomide+penicillins: Unknown (increases exposure)
• nitisinone+penicillins: Unknown (increases exposure)
• penicillins+phenindione: Unknown (increases risk of bleeding events)
• teriflunomide+penicillins: Unknown (increases exposure)

Precautions

• Use with caution in patients with renal impairment
• Monitor for signs of allergic reactions
• Consider alternative therapy in patients with a history of severe allergies

Pregnancy

Penicillins are generally considered safe to use during pregnancy; however, consult local guidelines and assess benefits versus risks.

Breast-feeding

Penicillins are excreted in breast milk in small amounts; generally considered safe, but monitor infant for possible effects.

Storage

Store in a cool, dry place away from direct sunlight. Keep out of reach of children.

Formulations

• Oral tablets
• Oral suspension
• Intravenous injection
• Intramuscular injection

Indications

• Bacterial pharyngitis
• Tonsillitis
• Skin infections
• Dental abscesses
• Pneumonia caused by susceptible organisms

Dosage

Children: For children, the usual dosage of phenoxymethylpenicillin is based on the child's weight

Adults: The usual adult dosage for phenoxymethylpenicillin is 250 mg to 500 mg taken orally three to four times a day, depending on the severity of the infection. Dosage should be adjusted based on clinical response and renal function.

Mechanism of action

Phenoxymethylpenicillin exerts its antibacterial effect by inhibiting bacterial cell wall synthesis. It binds to penicillin-binding proteins (PBPs) located inside the bacterial cell wall, preventing the cross-linking of peptidoglycan layers, which is essential for maintaining cell wall integrity. This leads to cell lysis and death, particularly in actively dividing bacteria.

Pharmacodynamics

The pharmacodynamic profile of phenoxymethylpenicillin indicates that it is time-dependent in its bactericidal activity. The efficacy of this antibiotic is related to the time that the plasma concentration remains above the minimum inhibitory concentration (MIC) for the target organism. It is especially effective against streptococci and some staphylococci, but it has limited efficacy against gram-negative bacteria due to its inability to penetrate their outer membranes.

Pharmacokinetics

Phenoxymethylpenicillin is well absorbed from the gastrointestinal tract, with peak plasma concentrations occurring approximately 1-2 hours after oral administration. It is distributed widely throughout body tissues and fluids, but its penetration into the central nervous system is limited. Approximately 60-80% of the drug is protein-bound. The elimination half-life is about 0.5 to 1 hour, with renal excretion being the primary route of elimination, largely as unchanged drug.

Contra-indications

• History of hypersensitivity to penicillins
• Severe renal impairment (use with caution)

Adverse effects

• Allergic reactions including anaphylaxis
• Rash
• Nausea
• Diarrhea
• Clostridium difficile-associated diarrhea

Interactions

• May reduce the effectiveness of oral contraceptives
• Probenecid may increase the plasma concentration of phenoxymethylpenicillin

Precautions

• Monitor for signs of allergic reactions in patients with a history of penicillin allergy
• Use with caution in patients with renal impairment
• Ensure adequate hydration in patients receiving high doses

Pregnancy

Considered safe for use during pregnancy, but should be used only if clearly needed.

Breast-feeding

Excreted in breast milk in small amounts; generally considered safe.

Storage

Store in a cool, dry place away from direct sunlight. Keep out of reach of children.

Formulations

• Oral suspension
• Tablets
• Injectable form