Skip to content
ClinCalc Pro
Menu
Calculators Drugs Pathways AI Dx Donate Get the App
Antimycobacterial (Anti-tuberculosis Agent) Pregnancy: Not recommended during pregnancy or in women of childbearing potential not using contraception — there are no or limited data in pregnant women and animal studies have shown some reproductive toxicity; it should be given to a pregnant woman only if clearly needed. Should not be used during breast-feeding, as para-aminosalicylic acid is excreted in human milk and there is insufficient information on effects in newborns/infants. There is no evidence available on the effect on fertility.

Aminosalicylic Acid (Para-aminosalicylic acid, PAS)

Brand names: Granupas

Aminosalicylic acid (para-aminosalicylic acid, PAS) is a second-line antituberculous agent used in combination regimens for drug-resistant tuberculosis.

Adult dose

Dose: Tuberculosis, in combination therapy — adults: 4 g (one sachet) three times per day; the recommended schedule is 4 g every 8 hours
Route: Oral. The contents of the sachet should be added to a glass of orange or tomato juice; the granules will not dissolve, but swirling the juice in the glass will help re-suspend them if they sink, and the drink should be taken at once, with any granules left at the bottom of the glass swallowed immediately by adding a small quantity of liquid. The granules should not be crushed or chewed, as this impairs the gastro-resistant coating
Frequency: Three times per day, every 8 hours. May be taken with food
Max: 12 g daily — the SPC states 'Maximum daily dose is 12 g.' This is the ceiling for the same oral tuberculosis regimen as the dose above (4 g three times a day is itself 12 g in 24 hours). No higher figure appears anywhere in the quoted posology
DURATION: 'Usual duration of treatment is 24 months.' DESENSITIZATION, verbatim: 'Desensitization can be accomplished by starting with 10 mg para-aminosalicylic acid (PAS) given as a single dose. The dosage is doubled every 2 days until reaching a total of 1 gram after which the dosage is divided to follow the regular schedule of administration. If a mild temperature rise or skin reaction develops, the increment is to be dropped back one level or the progression held for one cycle. Reactions are rare after a total dosage of 1.5 g.' Patients should be advised that the skeletons of the granules may be seen in the stools.

Paediatric dose

Dose: 150 mg/kg/day
Route: Oral. Smaller doses in children should be measured using the dosing spoon provided and given by sprinkling on apple sauce or yogurt; the medicinal product should be swallowed immediately after mixing whilst the granules are intact, and the granules should not be crushed or chewed
Frequency: Divided into two intakes per day
Max: The SPC states no separate paediatric ceiling; the adult maximum daily dose is 12 g
UNIT IS A DAILY TOTAL, NOT A PER-DOSE FIGURE — 150 mg/kg is the dose PER DAY and is then split into two intakes, so each individual intake is half of the daily total. Verbatim SPC paediatric population text: 'The optimal dose regimen in children is uncertain. Limited pharmacokinetic data suggest no substantial difference between adults and children. For infants, children and adolescents the dosage will be adapted to the patient's weight at 150 mg/kg per day, divided in two intakes. A dosing spoon is provided to measure small doses below 4 g for young children.' NEONATES: 'The safety and efficacy of para-aminosalicylic acid in neonates have not been established. No data are available.' Frequency, type and severity of adverse reactions in children are expected to be the same as in adults.

Dose adjustments

Renal

Contraindicated in severe renal disease — patients with severe renal impairment should not receive para-aminosalicylic acid, as they will accumulate the inactive acetyl metabolite. Given that the metabolites are largely excreted via glomerular filtration, caution is warranted in patients with mild to moderate renal impairment. The SPC gives no numerical dose reduction.

Hepatic

Should be used with caution in patients with hepatic impairment. The SPC gives no numerical dose reduction.

Dose independently re-sourced from UK Summary of Product Characteristics (SPC) via the eMC — clinician-reviewed. Always confirm against the product SmPC and your local formulary before prescribing.

Paediatric weight-based calculator

UNIT IS A DAILY TOTAL, NOT A PER-DOSE FIGURE — 150 mg/kg is the dose PER DAY and is then split into two intakes, so each individual intake is half of the daily total. Verbatim SPC paediatric population text: 'The optimal dose regimen in children is uncertain. Limited pharmacokinetic data suggest no substantial difference between adults and children. For infants, children and adolescents the dosage will be adapted to the patient's weight at 150 mg/kg per day, divided in two intakes. A dosing spoon is provided to measure small doses below 4 g for young children.' NEONATES: 'The safety and efficacy of para-aminosalicylic acid in neonates have not been established. No data are available.' Frequency, type and severity of adverse reactions in children are expected to be the same as in adults.

Verify in a children's formulary

Contraindications

  • Hypersensitivity to the active substance or to any of the excipients
  • Severe renal disease — patients with severe renal impairment should not receive para-aminosalicylic acid

Side effects

  • Common: abdominal pain, vomiting, nausea, bloating, diarrhoea, soft stools
  • Common: giddiness, vestibular syndrome
  • Common: cutaneous hypersensitivity, skin rash
  • Uncommon: anorexia
  • Rare: hypothyroidism (very common in HIV co-infected patients, particularly with ethionamide/prothionamide)
  • Rare: malabsorption syndrome, peptic ulcer, gastrointestinal bleeding, jaundice, metallic taste
  • Rare: urticaria
  • Frequency unknown: hepatitis
  • Very rare: thrombocytopenia, purpura, leukopenia, anaemia, methaemoglobinaemia, agranulocytosis
  • Very rare: hypoglycaemia
  • Very rare: tendon pain, headache, visual abnormalities, peripheral neuropathy, dizziness
  • Very rare: crystalluria
  • Very rare: decreased prothrombin level, hepatocytolysis, increased blood alkaline phosphatase and transaminases, weight loss

Interactions

  • Vitamin B12 — absorption may be reduced, with clinically significant erythrocyte abnormalities developing after depletion; patients on therapy of more than one month should be considered for maintenance of vitamin B12
  • Digoxin — para-aminosalicylic acid may decrease gastrointestinal absorption of digoxin by inhibiting the absorption function of intestinal cells; serum digoxin levels should be monitored on concomitant therapy
  • Ethionamide — co-administration may intensify adverse reactions of para-aminosalicylic acid, mainly gastrointestinal effects including jaundice, hepatitis, nausea, vomiting, diarrhoea, abdominal pain or anorexia; ethionamide should be withdrawn if these effects are significant
  • Diphenylhydramine — decreases the gastrointestinal absorption of para-aminosalicylic acid and should not be administered concomitantly
  • Antiretrovirals — no interaction studies conducted in patients with HIV infection; given the metabolic pathway, no significant drug interaction is anticipated
  • No formal interaction studies have been performed; the above are drawn from the literature summary in the SPC

Monitoring

  • Monitor carefully during the first three months of therapy and discontinue immediately at the first sign of a rash, fever or other premonitory signs of intolerance
  • Hepatic toxicity — para-aminosalicylic acid may cause hepatitis; first symptoms usually appear within three months of starting therapy, most commonly a rash, followed by fever and much less frequently by anorexia, nausea or diarrhoea; treatment should be stopped immediately in this case
  • Thyroid function in HIV co-infected patients — before commencing treatment and regularly during treatment, in particular when co-administered with ethionamide/prothionamide
  • Serum digoxin levels in patients on concomitant digoxin
  • Vitamin B12 status in patients treated for more than one month

Clinical monograph

How it works

It is a bacteriostatic agent that inhibits folate synthesis in Mycobacterium tuberculosis, acting as an analogue in the folate pathway.

Prescribing in practice

  • Must only be used as part of an appropriate combination regimen for drug-resistant tuberculosis to prevent further resistance.
  • Gastrointestinal intolerance is common and may limit adherence.
  • It can cause hypothyroidism and hepatotoxicity, so thyroid and liver function should be monitored.

Monitoring

Monitor liver function and thyroid function, and review gastrointestinal tolerability during treatment.

Counselling the patient

  • Take with food to reduce stomach upset.
  • Report persistent vomiting, jaundice or symptoms of an underactive thyroid such as tiredness or weight gain.
  • Complete the full course as part of your tuberculosis regimen.

Evidence & guidelines

It is included among the agents for multidrug-resistant tuberculosis in World Health Organization and NICE-aligned treatment frameworks.

Reference: NICE NG33 (Tuberculosis, 2016 updated 2023); WHO MDR-TB Guidelines (2022); BSAC/PHE TB guidelines; Drug verified in RxNorm (NLM); confirm dosing against the manufacturer SPC (eMC). Verify against your local formulary and current prescribing references before prescribing. The structured dose values shown have been reviewed by a clinician. Monograph status: clinician-reviewed (2026-07-04).

Related

Curated clinical cross-links plus same-class fallbacks.

Calculators
Pathways