Head-to-head clinical analysis & difference comparison: details on mechanism of action, dosing, half-life, interactions, and maternal-fetal safety.
INH vs PASER
Clinician-reviewed, head-to-head comparison of mechanism, dosing, pharmacokinetics, and safety profiles.
Last clinically reviewed: July 2026 · OpiCalc Medical Review Team
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.
Inhibits cell wall synthesis in Mycobacterium tuberculosis by blocking mycolic acid synthesis. Also acts as a competitive inhibitor of folate synthesis.
First-line treatment and prophylaxis of tuberculosis (TB) caused by Mycobacterium tuberculosis
Treatment of tuberculosis in combination with other antituberculosis drugs,Off-label: None
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.
4 g (8 capsules of 500 mg) orally every 8 hours, taken with food or an acidic beverage (e.g., orange juice) to enhance absorption.
Fast acetylators: 0.5-1.5 hours; slow acetylators: 2-4 hours. Clinically, slow acetylators have higher risk of peripheral neuropathy and hepatotoxicity.
Terminal elimination half-life is 1.5 to 2.5 hours in patients with normal renal function. In anuria or severe renal impairment (Cr Cl <10 m L/min), half-life may extend to 8-12 hours. Clinical context: Accumulation occurs with renal failure, requiring dose adjustment.
Primarily hepatic via N-acetyltransferase 2 (NAT2); also metabolized by cytochrome P450 (CYP2E1) to hepatotoxic metabolites.
Hepatic via N-acetyltransferase (polymorphic acetylation); major metabolite is acetyl-PAS.
Renal: 75-95% as unchanged drug and metabolites (including acetylisoniazid, isonicotinic acid). Biliary/fecal: minor (<5%).
Renal excretion accounts for approximately 80% of the administered dose, with about 60-70% as unchanged drug and 10-20% as metabolites (primarily acetylated). The remainder is excreted via feces (approximately 10-15%) and minor biliary elimination. Renal clearance is highly dependent on glomerular filtration rate.
0-10% (low binding; primarily albumin).
Protein binding is approximately 10-15%, primarily to albumin. Binding is low, nonlinear, and saturable at high concentrations.
0.6-0.8 L/kg (distributes into total body water, including cerebrospinal fluid and tuberculous cavities).
Volume of distribution is 0.5-0.7 L/kg, indicating distribution into total body water. Clinical meaning: Moderate distribution suggests penetration into well-perfused tissues but limited CNS penetration unless inflamed.
Oral: ~90%. Intramuscular: ~100%.
Oral bioavailability is approximately 70-80% (range 60-90%). Food decreases the rate and extent of absorption, with AUC reduction of about 20-40%.
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.
Contraindicated in severe renal impairment (Cr Cl <30 m L/min). For Cr Cl 30-50 m L/min: reduce dose to 4 g orally every 12 hours; monitor serum concentrations. Use with caution in moderate impairment.
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.
No specific dose adjustment guidelines for Child-Pugh classification. Use with caution in severe hepatic impairment due to potential hepatotoxicity; monitor liver function tests.
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).
Not recommended for children (safety and efficacy not established).
No specific dose adjustment required, but monitor for hepatotoxicity and peripheral neuropathy, especially in patients with comorbidities or polypharmacy.
Lower initial doses may be considered due to age-related decline in renal function. Monitor renal function and serum concentrations closely.
Severe and sometimes fatal hepatitis (especially in patients >35 years, daily alcohol users, and those with pre-existing liver disease); monitor hepatic function closely.
None
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)
May cause hypothyroidism, hepatitis, and crystalluria. Use with caution in patients with renal impairment or glucose-6-phosphate dehydrogenase deficiency.
Acute liver disease,History of INH-induced hepatotoxicity,Previous severe adverse reaction (e.g., drug fever, arthritis)
Hypersensitivity to para-aminosalicylic acid or any component; severe renal impairment.
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.
Take with food to reduce gastrointestinal irritation. Avoid high-fat meals as they may delay absorption. Avoid alcohol.
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.
PASER (aminosalicylic acid) is classified FDA pregnancy category C. First trimester: Limited human data; animal studies show no teratogenicity but some fetal toxicity at high doses. Second and third trimesters: No known major malformations; risks may include gastrointestinal intolerance in mother. Advised use only if clearly needed.
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.
Excreted into breast milk in small amounts. M/P ratio unknown. Considered compatible with breastfeeding by American Academy of Pediatrics; monitor infant for diarrhea or rash.
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.
No dosing adjustment required for pregnancy. Pharmacokinetic changes in pregnancy (increased clearance) not significant for PASER; standard adult dose of 4 g twice daily is recommended.
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.
PASER (aminosalicylic acid) is a second-line antitubercular agent that inhibits folic acid synthesis. Administer with food to reduce GI upset; avoid concurrent use with salicylates due to additive GI irritation. Monitor for hepatotoxicity and hypersensitivity reactions. Drug levels should be monitored in patients with renal impairment.
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.
Take this medication with food to minimize stomach upset.,Do not crush or chew the tablets; swallow them whole.,Complete the full course of therapy even if you feel better.,Report any signs of liver problems (yellowing of skin/eyes, dark urine) or allergic reactions (rash, fever) immediately.,Avoid alcohol during treatment.,Store at room temperature away from moisture and heat.
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 INH vs PASER, answered by our medical review team.
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.. PASER is a Antitubercular Agent that works by Inhibits cell wall synthesis in Mycobacterium tuberculosis by blocking mycolic acid synthesis. Also acts as a competitive inhibitor of folate synthesis.. They differ in pharmacokinetic profiles, FDA-approved indications, and side effect profiles.
Potency comparisons between INH and PASER 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 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.. The standard adult dose of PASER is: 4 g (8 capsules of 500 mg) orally every 8 hours, taken with food or an acidic beverage (e.g., orange juice) to enhance absorption.. 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 INH and PASER 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. 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. PASER is classified as Category C. PASER (aminosalicylic acid) is classified FDA pregnancy category C. First trimester: Limited human data; animal studies show no teratogenicity but some fetal toxicity at high doses. Always consult a maternal-fetal medicine specialist before taking either drug during pregnancy or lactation.