BENZALIN

Indications

• Rheumatic fever prevention
• Syphilis treatment
• Streptococcal infections
• Bacterial endocarditis prophylaxis

Dosage

Children: For children, the recommended dose for rheumatic fever prophylaxis is 600,000 units for those weighing less than 27 kg, and 1.2 million units for those weighing 27 kg or more, administered every 3 to 4 weeks.

Adults: The usual adult dose for the treatment of syphilis is a single intramuscular injection of 2.4 million units. For rheumatic fever prophylaxis, the recommended dose is 1.2 million units every 3 to 4 weeks.

Mechanism of action

Benzathine exerts its antibacterial effect by inhibiting bacterial cell wall synthesis. It binds to penicillin-binding proteins (PBPs) within the bacterial cell wall, leading to cell lysis and death. This mechanism is effective against a wide range of gram-positive bacteria, particularly Streptococcus species.

Pharmacodynamics

The pharmacodynamics of benzathine penicillin involves the drug's ability to maintain therapeutic concentrations in the body for an extended period. The prolonged release from the injection site allows for sustained antibacterial activity, making it effective in treating infections such as rheumatic fever and syphilis. The drug is particularly effective against organisms that are sensitive to penicillin.

Pharmacokinetics

Benzathine is administered intramuscularly, where it is slowly absorbed into the bloodstream. The peak plasma concentrations occur within 12 to 24 hours after administration, with a half-life that can extend up to several days, depending on the dosage and individual patient factors. It is primarily excreted by the kidneys. Due to its long-acting nature, benzathine is suitable for single-dose treatment regimens in certain infections.

Contra-indications

• Hypersensitivity to benzathine or any component of the formulation
• Severe allergies to other penicillins or beta-lactam antibiotics

Adverse effects

• Allergic reactions, including anaphylaxis
• Rash
• Fever
• Angioedema
• Nausea
• Vomiting
• Diarrhea
• Superinfection with prolonged use

Interactions

• May have reduced efficacy when administered concurrently with bacteriostatic antibiotics such as tetracyclines
• Probenecid may increase the serum concentrations of benzathine

Precautions

• Use with caution in patients with a history of allergies or asthma
• Monitor for signs of anaphylaxis during and after administration
• Evaluate renal function in patients receiving high doses or prolonged therapy

Pregnancy

Benzathine is classified as category B. Animal studies have shown no harm; however, adequate and well-controlled studies in pregnant women are lacking.

Breast-feeding

Benzathine is excreted in breast milk. Caution is recommended when administering to breastfeeding mothers.

Storage

Store in a cool, dry place, away from light. Do not freeze.

Formulations

• Benzathine benzylpenicillin injection
• Benzathine penicillin G suspension

Indications

• Streptococcal infections
• Pneumococcal pneumonia
• Syphilis
• Meningitis
• Endocarditis
• Skin and soft tissue infections
• Bone and joint infections

Dosage

Children: Refer to specific guidelines for paediatric dosing; doses are generally based on weight and the type of infection being treated.

Adults: Refer to specific guidelines for dosing; typical adult doses vary based on infection type and severity.

Mechanism of action

Benzylpenicillin exerts its bactericidal effect by inhibiting bacterial cell wall synthesis. It binds to penicillin-binding proteins (PBPs) located inside the bacterial cell wall, leading to the inhibition of transpeptidation, which is essential for cross-linking peptidoglycan layers. This results in cell lysis and death of the bacteria.

Pharmacodynamics

Benzylpenicillin is effective against a range of bacteria, particularly those that are susceptible to penicillin. The drug's effectiveness is influenced by the bacterial growth phase, with maximal activity observed during the logarithmic growth phase. Its bactericidal action is concentration-dependent, meaning higher concentrations lead to faster bacterial killing. Resistance can occur through the production of beta-lactamase enzymes by certain bacteria, rendering the drug ineffective.

Pharmacokinetics

Benzylpenicillin is administered parenterally, as it is not absorbed well from the gastrointestinal tract. It distributes widely in body fluids and tissues, with significant concentrations achieved in the lungs, liver, kidneys, and heart. The drug is primarily eliminated through renal excretion, with a half-life of approximately 30 to 60 minutes. Dosage adjustments may be necessary in patients with renal impairment to avoid toxicity.

Contra-indications

• Hypersensitivity to benzylpenicillin or any penicillin antibiotic
• History of severe allergic reactions to beta-lactam antibiotics

Adverse effects

• Allergic reactions including anaphylaxis
• Rash
• Nausea
• Vomiting
• Diarrhea
• Seizures (in cases of high doses or renal impairment)
• Superinfection with resistant organisms

Interactions

• Probenecid may increase the levels of benzylpenicillin by inhibiting renal tubular secretion
• Other antibiotics may have antagonistic effects when used concurrently

Precautions

• Use with caution in patients with renal impairment
• Monitor for signs of allergic reaction
• Consider alternative therapy in patients with a history of penicillin allergy

Pregnancy

Benzylpenicillin is generally considered safe during pregnancy, but it should only be used if clearly needed.

Breast-feeding

Benzylpenicillin is excreted in breast milk in small amounts; it is usually considered safe for use during breastfeeding.

Storage

Store in a cool, dry place away from direct light. Reconstituted solutions should be used immediately or stored in a refrigerator and used within a specified timeframe as per product guidelines.

Formulations

• Injection: Benzylpenicillin sodium
• Injection: Benzylpenicillin potassium