MSA 50MG/G OINTMENT

Indications

• Bacterial infections
• Urinary tract infections
• Respiratory tract infections
• Gastrointestinal infections
• Certain skin infections

Dosage

Children: Paediatric dosing of sulphanilamide must be referenced from the BNF for Children, as specific doses vary by age and weight.

Adults: For adults, the dosage of sulphanilamide should be determined based on the specific condition being treated. Refer to the BNF for exact dosing guidelines.

Mechanism of action

Sulphanilamide acts as a competitive inhibitor of the bacterial enzyme dihydropteroate synthetase. By mimicking para-aminobenzoic acid (PABA), it prevents the enzyme from synthesizing folic acid, which is essential for bacterial growth and replication. This inhibition of folic acid metabolism effectively stunts bacterial proliferation.

Pharmacodynamics

As a sulfonamide antibiotic, sulphanilamide exhibits bacteriostatic properties, inhibiting the growth of bacteria by blocking the incorporation of PABA into folic acid. Its activity is dependent on the bacterial sensitivity, which is consistent across sulfonamide derivatives. Resistance to one sulfonamide typically indicates resistance to others within the class. The drug is well-absorbed when administered orally, although parenteral forms can cause irritation due to their alkaline nature.

Pharmacokinetics

Sulphanilamide is absorbed well from the gastrointestinal tract, achieving high tissue distribution including pleural, peritoneal, synovial, and ocular fluids. Although its penetration into cerebrospinal fluid is significant, it is not commonly used for meningitis treatment. The drug's antibacterial effectiveness may be diminished in the presence of pus, which can inhibit its action.

Adverse effects

• Allergic reactions (e.g., skin rash, pruritus)
• Gastrointestinal disturbances (e.g., nausea, vomiting)
• Hematologic reactions (e.g., leukopenia, thrombocytopenia)
• Renal toxicity (e.g., crystalluria, nephritis)
• Hepatotoxicity (rare)

Interactions

• May enhance the effects of anticoagulants (e.g., warfarin)
• May decrease the efficacy of oral contraceptives
• Potential interaction with methotrexate, increasing toxicity
• Increased risk of adverse effects with other nephrotoxic agents

Precautions

• Use with caution in patients with renal impairment
• Monitor for signs of hypersensitivity reactions
• Consider alternative therapy in patients with G6PD deficiency
• Ensure adequate hydration to prevent crystalluria

Pregnancy

Use during pregnancy only if the potential benefit justifies the potential risk to the fetus. Category C.

Breast-feeding

Sulfanilamide is excreted in breast milk. Caution should be exercised when administering to nursing mothers.

Storage

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

Formulations

• Tablets
• Oral suspension
• Injectable formulations

Mechanism of action

Sulfanilamide is a competitive inhibitor of bacterial enzyme dihydropteroate synthetase. This enzyme normally uses para-aminobenzoic acid (PABA) for synthesizing the necessary folic acid. The inhibited reaction is normally necessary in these organisms for the synthesis of folic acid. Without it, bacteria cannot replicate. Sulfonamides are structural analogs and competitive antagonist of para-aminobenzoic acid ... and thus prevent normal bacterial utilization of para-aminobenzoic acid for the synthesis of folic acid (pteroylglutamic acid). ... More specifically, sulfonamides are competitive inhibitors of dihydropteroate synthase, the bacterial enzyme responsible for the incorporation of para-aminobenzoic acid into dihydropteroic acid, the immediate precursor of folic acid. /Sulfonamides/

Pharmacodynamics

Sulfanilamide is a sulfonamide antibiotic. The sulfonamides are synthetic bacteriostatic antibiotics with a wide spectrum against most gram-positive and many gram-negative organisms. However, many strains of an individual species may be resistant. Sulfonamides inhibit multiplication of bacteria by acting as competitive inhibitors of <i>p</i>-aminobenzoic acid in the folic acid metabolism cycle. Bacterial sensitivity is the same for the various sulfonamides, and resistance to one sulfonamide indicates resistance to all. Most sulfonamides are readily absorbed orally. However, parenteral administration is difficult, since the soluble sulfonamide salts are highly alkaline and irritating to the tissues. The sulfonamides are widely distributed throughout all tissues. High levels are achieved in pleural, peritoneal, synovial, and ocular fluids. Although these drugs are no longer used to treat meningitis, CSF levels are high in meningeal infections. Their antibacterial action is inhibited by pus.