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Antimycobacterial (Anti-tuberculosis Agent)

Aminosalicylic Acid (Para-aminosalicylic acid, PAS)

Brand names: Granupas

Adult dose

Dose: 8–12 g/day in 2–3 divided doses (usually 4 g sachets 2–3 times daily)
Route: Oral (granules dissolved in water, juice, or sprinkled on food)
Frequency: 2–3 times daily with meals

Clinical pearls

  • Used for drug-resistant TB (MDR-TB and XDR-TB) as part of combination regimens
  • Group C drug in WHO TB treatment classification for MDR-TB (2022 update)
  • Granupas granules are enteric-coated — sprinkle on acidic foods (yoghurt, juice) to improve tolerability
  • Do NOT use hot foods/drinks to dissolve (destroys the coating)
  • Manage GI side effects with dose titration and administration with food
  • Monitor thyroid function (hypothyroidism is common with prolonged use — treat with levothyroxine if needed)

Contraindications

  • Severe renal impairment
  • Glucose-6-phosphate dehydrogenase (G6PD) deficiency (haemolysis risk)
  • Hypersensitivity to salicylates

Side effects

  • Gastrointestinal: nausea, vomiting, diarrhoea, abdominal pain (very common)
  • Hypersensitivity reactions (fever, rash, hepatitis) — can be severe
  • Hypothyroidism (inhibits thyroid hormone synthesis with prolonged use)
  • Haemolytic anaemia (G6PD deficiency)
  • Malabsorption of vitamin B12 and folate

Interactions

  • Rifampicin — PAS delays absorption of rifampicin; separate administration by 8–12 hours
  • Isoniazid — PAS may increase isoniazid toxicity
  • Digoxin — reduced digoxin absorption
  • Warfarin — PAS may enhance anticoagulant effect
  • Probenecid — reduces renal elimination of PAS

Monitoring

  • LFTs monthly
  • Thyroid function (TSH) every 3–6 months
  • Haemoglobin and reticulocytes (haemolysis)
  • Vitamin B12 and folate levels
  • Clinical response (sputum cultures, imaging)

Reference: BNF; NICE NG33 (Tuberculosis, 2016 updated 2023); WHO MDR-TB Guidelines (2022); BSAC/PHE TB guidelines; https://bnf.nice.org.uk/drugs/aminosalicylic-acid/. Verify against your local formulary and the latest BNF before prescribing.

Related

Curated clinical cross-links plus same-class fallbacks.

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