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para-aminosalicylic acid

Para-aminobenzoic acid analogue · Antituberculosis

Para-aminobenzoic acid analogueAntituberculosis
CDSCO approved
EXCRETION
—
not curated
INTERACTIONS
—
none in our sources
PREGNANCY
—
not curated

Mechanism

Para-aminosalicylic acid (PAS) is a prodrug whose active products block M. tuberculosis growth downstream of dihydropteroate synthase (DHPS). It is a structural analogue of para-aminobenzoic acid (PABA).

Indications

multidrug-resistant tuberculosisResistant TB (used only when one of the tuberculocidal drugs or both static drugs cannot be used)

Dosing

Adult
Total daily dose of 12 g, divided into three equal portions and administered after meals.
Pediatric
150 to 300 mg/kg per day in three or four divided doses.
Renal adjustment
Dose must be reduced in renal dysfunction.

Pharmacokinetics

Half-life
~1 hour
Bioavailability
More than 90%
Protein binding
50% to 60%
Metabolism
N-acetylated in the liver to N-acetyl PAS
Excretion
Urine (>80%, more than 50% as acetylated compound)

Contraindications

  • glucose-6-phosphate dehydrogenase (g6pd) deficiency

Side effects

Common
gastrointestinal problems (10-30% incidence)skin eruptions (5-10% with hypersensitivity)fever (5-10% with hypersensitivity)eosinophilia (5-10% with hypersensitivity)hematological abnormalities (5-10% with hypersensitivity)AnorexiaNauseaEpigastric painRashesFeverMalaiseHypokalaemiaGoiterLiver dysfunction
Serious
  • hepatotoxicity (N-acetyl PAS is a potential hepatotoxin)
  • Blood dyscrasias (rarely)

Drug interactions

Isoniazid
Moderate
Textbook

Prolongs the half-life of isoniazid, potentially leading to increased isoniazid blood levels and enhanced effects or toxicity.

Monitor for isoniazid-related adverse effects; dose adjustment of isoniazid may be required.

Source: KDT 7e · p767

Related guidelines

Drug-resistant tuberculosis
RNTCP · Pulmonology · 2025
Pulmonary tuberculosis
RNTCP · Infectious Disease · 2023
Extrapulmonary tuberculosis
ICMR · Infectious Diseases · 2022
Benign prostatic hyperplasia
EAU · Urology · 2024
Latent tuberculosis infection
RNTCP · Infectious Disease · 2023

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Sources: KD Tripathi 7e, Goodman & Gilman 14e, Harrison 22e·Verified: 2026-05-10 · House clinical team