Head-to-head clinical analysis & difference comparison: details on mechanism of action, dosing, half-life, interactions, and maternal-fetal safety.
P.A.S. SODIUM vs INH
Clinician-reviewed, head-to-head comparison of mechanism, dosing, pharmacokinetics, and safety profiles.
Last clinically reviewed: July 2026 · OpiCalc Medical Review Team
P. A. S. (p-aminosalicylic acid) sodium is a bacteriostatic agent that competitively inhibits the synthesis of folic acid in Mycobacterium tuberculosis by antagonizing the incorporation of p-aminobenzoic acid (PABA) into dihydrofolate. It is selective for mycobacterial folate synthase.
INH inhibits Inh A, an enoyl-acyl carrier protein reductase involved in mycolic acid synthesis, essential for the mycobacterial cell wall. It also disrupts NAD and NADH metabolism via the Kat G-activated isonicotinoyl-NAD adduct.
Treatment of tuberculosis (TB) in combination with other antituberculosis agents, particularly in multidrug-resistant TB (FDA-approved).,Off-label: Used as a second-line agent in atypical mycobacterial infections and in Crohn's disease (though not FDA-approved for these indications).
First-line treatment and prophylaxis of tuberculosis (TB) caused by Mycobacterium tuberculosis
Oral: 4 g three times daily (total daily dose 12 g); IV: 12 g daily in 2-4 divided doses.
300 mg orally once daily (or 15 mg/kg orally once daily, up to 300 mg total) for active tuberculosis; for latent tuberculosis, 300 mg orally once daily or 900 mg orally twice weekly under directly observed therapy.
1 hour (normal renal function); prolonged to 5-7 hours in anuria or severe renal impairment; clinical context: requires frequent dosing or renal dose adjustment
Fast acetylators: 0.5-1.5 hours; slow acetylators: 2-4 hours. Clinically, slow acetylators have higher risk of peripheral neuropathy and hepatotoxicity.
Primarily metabolized by hepatic acetylation via N-acetyltransferase (NAT); minor pathways include glycine conjugation and renal excretion of unchanged drug.
Primarily hepatic via N-acetyltransferase 2 (NAT2); also metabolized by cytochrome P450 (CYP2E1) to hepatotoxic metabolites.
Renal (80% as active drug and metabolites, primarily acetylated form); fecal (minor; <10%)
Renal: 75-95% as unchanged drug and metabolites (including acetylisoniazid, isonicotinic acid). Biliary/fecal: minor (<5%).
50-60% (primarily to albumin)
0-10% (low binding; primarily albumin).
0.5-0.6 L/kg (indicates distribution into total body water, with some tissue binding)
0.6-0.8 L/kg (distributes into total body water, including cerebrospinal fluid and tuberculous cavities).
Oral: approximately 90% (well absorbed from GI tract)
Oral: ~90%. Intramuscular: ~100%.
Cr Cl <50 m L/min: reduce dose by 50%; Cr Cl <10 m L/min: avoid use or reduce to 25% of normal dose.
In patients with GFR < 30 m L/min, reduce dose to 200 mg daily or 300 mg three times weekly. For GFR 30-50 m L/min, no adjustment necessary. For GFR < 10 m L/min, consider 150 mg daily or 300 mg twice weekly.
Child-Pugh A: no adjustment; Child-Pugh B: reduce dose by 50%; Child-Pugh C: avoid use.
In Child-Pugh class A, no adjustment. In Child-Pugh class B, reduce dose to 200 mg daily. In Child-Pugh class C, use 150 mg daily or avoid if severe hepatic impairment.
Oral: 200-300 mg/kg/day in 3-4 divided doses, maximum 12 g/day.
10-15 mg/kg orally once daily (max 300 mg) for active tuberculosis; for latent tuberculosis, 10-15 mg/kg orally once daily (max 300 mg) or 20-40 mg/kg orally twice weekly (max 900 mg per dose).
Start at lower end of dosing range; monitor renal function and adjust based on Cr Cl; typical initial dose 4 g twice daily.
No specific dose adjustment required, but monitor for hepatotoxicity and peripheral neuropathy, especially in patients with comorbidities or polypharmacy.
None explicitly stated in current FDA labeling; however, caution is advised in hepatic impairment due to risk of hepatitis.
Severe and sometimes fatal hepatitis (especially in patients >35 years, daily alcohol users, and those with pre-existing liver disease); monitor hepatic function closely.
May cause severe hypersensitivity reactions (e.g., fever, rash, lymphadenopathy).,Hepatic toxicity: risk of hepatitis, especially with prolonged use; monitor liver function.,Renal impairment: dose adjustment required in severe renal disease.,Gastrointestinal intolerance: nausea, vomiting, diarrhea common.,Development of resistance if used as monotherapy.,May induce hemolytic anemia in G6PD deficiency.
Hepatotoxicity (monitor LFTs, discontinue if signs of hepatitis),Peripheral neuropathy (pyridoxine prophylaxis recommended),CNS effects (seizures, psychosis; avoid in active CNS disease),Lupus-like syndrome,Drug interactions (e.g., carbamazepine, phenytoin)
Hypersensitivity to p-aminosalicylic acid or any component.,Severe hepatic impairment.,Severe renal failure (unless dose-adjusted).,Contraindicated in patients with active peptic ulcer disease.
Acute liver disease,History of INH-induced hepatotoxicity,Previous severe adverse reaction (e.g., drug fever, arthritis)
Take with food, especially acidic foods (e.g., applesauce, yogurt) to improve taste and reduce gastrointestinal irritation. Avoid alkaline foods (e.g., milk, antacids) as they may decrease absorption. Avoid alcohol due to increased risk of hepatotoxicity.
Foods high in tyramine (e.g., aged cheese, cured meats, soy products) may rarely cause hypertensive crisis in patients also taking MAOIs, though interaction is less significant with INH alone. High-fat meals may delay absorption, so avoid fatty foods near dosing time. No specific dietary restrictions beyond taking on empty stomach.
First trimester: No evidence of teratogenicity in human studies; limited animal data show no adverse effects. Second trimester: No specific risks identified. Third trimester: No known adverse fetal effects; use only if clearly needed.
INH (isoniazid) is not known to be a major teratogen. In first trimester, risk of malformations is not significantly increased. In second and third trimesters, there is a potential for hepatotoxicity and peripheral neuropathy, and possibly increased risk of neonatal hemorrhage due to vitamin K deficiency.
Excreted into breast milk in low amounts; M/P ratio not determined. Considered compatible with breastfeeding; monitor infant for diarrhea or rash.
INH is excreted into breast milk in low concentrations (M/P ratio approximately 1.6). Breastfeeding is generally considered safe, but monitor infant for signs of peripheral neuropathy or liver toxicity. The American Academy of Pediatrics considers INH compatible with breastfeeding.
No pharmacokinetic changes requiring dose adjustment in pregnancy; use standard dosing but monitor for hepatotoxicity, which may be increased.
No dose adjustment is routinely required for pregnancy. However, due to increased clearance (30-50% higher), some experts recommend monitoring serum INH levels and adjusting dose to maintain therapeutic levels. Pyridoxine supplementation (25-50 mg/day) is recommended to prevent peripheral neuropathy.
Sodium aminosalicylate (PAS sodium) is a second-line antituberculosis agent used in multidrug-resistant TB (MDR-TB). It is bacteriostatic against Mycobacterium tuberculosis by inhibiting folate synthesis. Must be administered with other antitubercular drugs to prevent resistance. Monitor for hepatotoxicity, hypersensitivity reactions (fever, rash, eosinophilia), and gastrointestinal intolerance. Can cause hypothyroidism; monitor thyroid function. Drug interactions: may increase phenytoin levels; avoid concurrent probenecid (increases PAS levels). PAS granules should be sprinkled on soft acidic food to reduce GI upset.
Administer on an empty stomach (1 hour before or 2 hours after meals) to maximize absorption. Monitor liver function tests (ALT, AST) at baseline and monthly during therapy. Pyridoxine (vitamin B6) 25-50 mg/day should be co-administered to prevent peripheral neuropathy. Hepatotoxicity risk increases with age, alcohol use, and concurrent use of other hepatotoxic drugs. Slow acetylators are more prone to toxicity. Patients with liver disease require careful monitoring and dose adjustment.
Take this medication exactly as prescribed, usually twice daily with food to reduce stomach upset.,Do not skip doses; complete the full course to prevent drug resistance.,Report any signs of liver problems: yellowing of skin/eyes, dark urine, severe abdominal pain.,Notify your doctor if you develop fever, rash, or unusual tiredness.,You may need regular blood tests to monitor thyroid and liver function.,Avoid alcohol while taking this medication.,Keep all appointments for TB treatment monitoring.
Take on an empty stomach with a full glass of water.,Do not drink alcohol while taking this medication due to increased risk of liver damage.,Report immediately any signs of liver problems: dark urine, yellowing of skin or eyes, persistent nausea, or abdominal pain.,Take vitamin B6 as prescribed to prevent numbness or tingling in hands and feet.,Complete full course of therapy even if you feel better to prevent resistance.,Avoid antacids within 1 hour of taking this medication as they may reduce absorption.
No interactions on record
No interactions on record
Explore head-to-head clinical comparisons of other medications in the same therapeutic classes.
Common clinical questions about P.A.S. SODIUM vs INH, answered by our medical review team.
P.A.S. SODIUM is a Antitubercular Agent that works by P. A. S. (p-aminosalicylic acid) sodium is a bacteriostatic agent that competitively inhibits the synthesis of folic acid in Mycobacterium tuberculosis by antagonizing the incorporation of p-aminobenzoic acid (PABA) into dihydrofolate. It is selective for mycobacterial folate synthase.. INH is a Antitubercular Agent that works by INH inhibits Inh A, an enoyl-acyl carrier protein reductase involved in mycolic acid synthesis, essential for the mycobacterial cell wall. It also disrupts NAD and NADH metabolism via the Kat G-activated isonicotinoyl-NAD adduct.. They differ in pharmacokinetic profiles, FDA-approved indications, and side effect profiles.
Potency comparisons between P.A.S. SODIUM and INH depend on the specific clinical indication. These are both Antitubercular Agent agents and are not directly interchangeable by dose. A physician or clinical pharmacist should guide any therapeutic switching decisions.
The standard adult dose of P.A.S. SODIUM is: Oral: 4 g three times daily (total daily dose 12 g); IV: 12 g daily in 2-4 divided doses.. The standard adult dose of INH is: 300 mg orally once daily (or 15 mg/kg orally once daily, up to 300 mg total) for active tuberculosis; for latent tuberculosis, 300 mg orally once daily or 900 mg orally twice weekly under directly observed therapy.. Dosing should always be individualized based on indication, renal and hepatic function, age, and other patient factors.
No direct drug-drug interaction has been formally documented between P.A.S. SODIUM and INH in current clinical databases. However, individual patient risk factors including other medications, organ function, and comorbidities should always be evaluated by a qualified healthcare provider.
The maternal-fetal safety profiles differ. P.A.S. SODIUM is classified as Category C. First trimester: No evidence of teratogenicity in human studies; limited animal data show no adverse effects. Second trimester: No specific risks identified. Third trimester: No kn. INH is classified as Category C. INH (isoniazid) is not known to be a major teratogen. In first trimester, risk of malformations is not significantly increased. In second and third trimesters, there is a potential. Always consult a maternal-fetal medicine specialist before taking either drug during pregnancy or lactation.