1. Clinical Overview
Sodium aminosalicylate is an anti-tuberculosis drug, specifically a second-line agent used in the treatment of multidrug-resistant tuberculosis (MDR-TB). It is a bacteriostatic agent that acts as a competitive antagonist of para-aminobenzoic acid (PABA) in the folate synthesis pathway of Mycobacterium tuberculosis. It is almost exclusively used as part of a combination regimen to prevent resistance.
| Onset | Duration | Bioavailability |
|---|---|---|
| Not well characterized; therapeutic effect is delayed and depends on bacterial growth cycle. | Approximately 8-12 hours, necessitating multiple daily doses. | Approximately 80-90% from the gastrointestinal tract. |
2. Mechanism of Action
Sodium aminosalicylate is a structural analog of para-aminobenzoic acid (PABA). It competitively inhibits the bacterial enzyme dihydropteroate synthase (DHPS). This inhibition blocks the incorporation of PABA into dihydrofolic acid, a precursor of folic acid. Since Mycobacterium tuberculosis cannot utilize preformed folic acid from the host, this disruption of folate synthesis leads to bacteriostatic inhibition of mycobacterial growth and replication.
3. Indications & Uses
- Multidrug-Resistant Tuberculosis (MDR-TB)
- Extensively Drug-Resistant Tuberculosis (XDR-TB) as part of a regimen
4. Dosage & Administration
Adult Dosage: 8-12 grams per day, administered in 2-3 divided doses. The 800mg tablet strength typically requires 10-15 tablets daily (e.g., 4g every 8 hours). Dose is weight-based: 200-300 mg/kg/day, not to exceed 12g/day.
Administration: Administer with or immediately after meals to minimize gastric irritation. Tablets should be swallowed whole with a full glass of water. Do not crush or chew. Doses should be evenly spaced. Can be dispersed in fruit juice or yogurt if swallowing multiple tablets is difficult, but must be consumed immediately.
5. Side Effects
Common side effects may include:
- Nausea
- Vomiting
- Diarrhea
- Abdominal pain
- Anorexia
- Hypersalivation
- Metallic taste
6. Drug Interactions
| Drug | Effect | Severity |
|---|---|---|
| Rifampicin | May decrease serum levels of sodium aminosalicylate due to increased hepatic metabolism. | Moderate |
| Isoniazid | Concurrent use may increase risk of hepatotoxicity. PAS may increase INH levels. | Moderate |
| Digoxin | PAS may reduce digoxin absorption from the GI tract, decreasing its efficacy. | Moderate |
| Vitamin B12 | PAS can impair absorption of vitamin B12, potentially leading to deficiency and megaloblastic anemia. | Moderate |
| Warfarin | May potentiate the anticoagulant effect by displacing warfarin from protein binding sites and affecting vitamin K metabolism. | Major |
| Methotrexate | Increased risk of hematological toxicity due to synergistic folate antagonism. | Major |
| Probenecid | May decrease renal excretion of PAS, increasing risk of toxicity. | Moderate |
7. Patient Counselling
- DO take with food to reduce stomach upset.
- DO take the exact number of tablets as prescribed, even if it is many.
- DO space your doses evenly throughout the day.
- DO drink plenty of fluids (2-3 liters daily) to prevent kidney problems.
- DO inform all your doctors and dentists you are taking this medicine.
- DO store in a cool, dry place away from light.
- DON'T stop taking this medicine without consulting your doctor, even if you feel better.
- DON'T crush, chew, or break the tablets unless advised by your doctor/pharmacist.
- DON'T take antacids at the same time as this medicine. Separate by at least 2 hours.
8. Toxicology & Storage
Overdose: Severe nausea, vomiting, diarrhea, abdominal pain, electrolyte imbalance (hypernatremia, hypokalemia), metabolic acidosis, crystalluria leading to renal damage (hematuria, oliguria), possible hepatotoxicity, and CNS effects like dizziness or tinnitus.
Storage: Store below 30°C, in a cool, dry place, protected from light and moisture. Keep the container tightly closed. Keep out of reach of children. Do not use after the expiry date printed on the pack.