Head-to-head clinical analysis & difference comparison: details on mechanism of action, dosing, half-life, interactions, and maternal-fetal safety.
SODIUM P.A.S. vs INH
Clinician-reviewed, head-to-head comparison of mechanism, dosing, pharmacokinetics, and safety profiles.
Last clinically reviewed: July 2026 · OpiCalc Medical Review Team
Sodium P. A. S. (para-aminosalicylate) inhibits folic acid synthesis in Mycobacterium tuberculosis by competing with para-aminobenzoic acid, thereby suppressing bacterial growth.
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 as part of a multi-drug regimen (FDA-approved),Off-label: treatment of inflammatory bowel disease (ulcerative colitis, Crohn's disease) and other mycobacterial infections
First-line treatment and prophylaxis of tuberculosis (TB) caused by Mycobacterium tuberculosis
4 g orally three times daily (total 12 g/day). For intravenous administration, 4 g (10 m L of 40% solution) diluted in 250 m L of 5% dextrose or normal saline infused over 2-3 hours three times daily.
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.
0.5–1 hour (normal renal function); prolonged to ≥10 hours in renal impairment (requires 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.
Hepatic acetylation via N-acetyltransferase (NAT2); undergoes conjugation with glycine and glucuronic acid.
Primarily hepatic via N-acetyltransferase 2 (NAT2); also metabolized by cytochrome P450 (CYP2E1) to hepatotoxic metabolites.
Primarily renal (80-90% as unchanged drug) via glomerular filtration and tubular secretion; biliary/fecal ≤10%.
Renal: 75-95% as unchanged drug and metabolites (including acetylisoniazid, isonicotinic acid). Biliary/fecal: minor (<5%).
50–60% bound to serum albumin.
0-10% (low binding; primarily albumin).
0.2–0.4 L/kg (suggests low tissue penetration, primarily extracellular).
0.6-0.8 L/kg (distributes into total body water, including cerebrospinal fluid and tuberculous cavities).
Oral: ~80–90%. IV: 100%.
Oral: ~90%. Intramuscular: ~100%.
GFR 30-50 m L/min: administer every 12 hours. GFR 10-30 m L/min: administer every 24 hours. GFR <10 m L/min: administer every 48 hours or avoid use.
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 Class A: no adjustment. Child-Pugh Class B: reduce dose by 50%. Child-Pugh Class C: avoid use due to risk of hepatotoxicity.
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.
Children: 150-300 mg/kg/day orally in 3-4 divided doses, maximum 12 g/day. Intravenous: 150-300 mg/kg/day in divided doses every 6-8 hours.
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 (e.g., 4 g orally twice daily) and titrate based on renal function. Monitor for electrolyte disturbances and hepatotoxicity.
No specific dose adjustment required, but monitor for hepatotoxicity and peripheral neuropathy, especially in patients with comorbidities or polypharmacy.
No FDA black box warning.
Severe and sometimes fatal hepatitis (especially in patients >35 years, daily alcohol users, and those with pre-existing liver disease); monitor hepatic function closely.
Hepatotoxicity, including hepatic necrosis and jaundice,Hypersensitivity reactions (drug rash, fever, eosinophilia),Gastrointestinal intolerance (nausea, vomiting, diarrhea),Renal impairment may require dose adjustment,Monitor liver function tests, blood counts, and renal function
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 para-aminosalicylate or any component,Severe hepatic impairment,Severe renal impairment (Cr Cl < 30 m L/min)
Acute liver disease,History of INH-induced hepatotoxicity,Previous severe adverse reaction (e.g., drug fever, arthritis)
Take with food to minimize gastrointestinal irritation. Avoid alcohol due to hepatotoxicity risk. No significant food-drug interactions except for potential interference with vitamin B12 absorption; consider monitoring B12 levels with prolonged use.
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.
PAS is not associated with major congenital malformations. First trimester: no significant increase in defect risk. Second/third trimester: may increase risk of maternal hemolysis in G6PD deficiency; no direct fetal toxicity reported. Limited human data.
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.
PAS enters breast milk in low concentrations; M/P ratio unknown. Considered compatible with breastfeeding by American Academy of Pediatrics, but monitor infant for gastrointestinal disturbances or allergic reactions.
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.
Pregnancy may decrease serum concentrations due to increased renal clearance. Monitor therapeutic levels if available; consider increasing dose if subtherapeutic. No standard dose adjustment, but individual titration based on clinical response and serum levels recommended.
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 P. A. S. (para-aminosalicylic acid) is a second-line antitubercular agent used in combination therapy for multidrug-resistant tuberculosis (MDR-TB). Administer with food to reduce gastrointestinal irritation. Monitor liver function tests due to hepatotoxicity risk. May cause hypothyroidism; monitor thyroid function. Avoid in patients with severe renal impairment (Cr Cl <30 m L/min).
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 with food to reduce stomach upset.,Complete full course of therapy as prescribed, even if you feel better.,Report any signs of liver problems: yellowing of skin/eyes, dark urine, severe nausea/vomiting.,May cause hypothyroidism; report fatigue, weight gain, or cold intolerance.,Avoid alcohol due to increased risk of liver damage.
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 SODIUM P.A.S. vs INH, answered by our medical review team.
SODIUM P.A.S. is a Antitubercular Agent that works by Sodium P. A. S. (para-aminosalicylate) inhibits folic acid synthesis in Mycobacterium tuberculosis by competing with para-aminobenzoic acid, thereby suppressing bacterial growth.. 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 SODIUM P.A.S. 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 SODIUM P.A.S. is: 4 g orally three times daily (total 12 g/day). For intravenous administration, 4 g (10 m L of 40% solution) diluted in 250 m L of 5% dextrose or normal saline infused over 2-3 hours three times daily.. 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 SODIUM P.A.S. 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. SODIUM P.A.S. is classified as Category C. PAS is not associated with major congenital malformations. First trimester: no significant increase in defect risk. Second/third trimester: may increase risk of maternal hemolysis . 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.