P.A.S. SODIUM
Clinical safety rating
cautionComprehensive clinical and safety monograph for P.A.S. SODIUM (P.A.S. SODIUM).
Comprehensive clinical and safety monograph for P.A.S. SODIUM (P.A.S. SODIUM).
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).
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.
| Metabolism | Primarily metabolized by hepatic acetylation via N-acetyltransferase (NAT); minor pathways include glycine conjugation and renal excretion of unchanged drug. |
| Excretion | Renal (80% as active drug and metabolites, primarily acetylated form); fecal (minor; <10%) |
| Half-life | 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 |
| Protein binding | 50-60% (primarily to albumin) |
| Volume of Distribution | 0.5-0.6 L/kg (indicates distribution into total body water, with some tissue binding) |
| Bioavailability | Oral: approximately 90% (well absorbed from GI tract) |
| Onset of Action | Oral: 1-2 hours; IV: immediate |
| Duration of Action | 4-6 hours (oral); clinical notes: peak serum concentration at 1-2 hours, drug-free interval needed to reduce toxicity |
| Molecular Weight | 154.12 (as sodium salt) |
Oral: 4 g three times daily (total daily dose 12 g); IV: 12 g daily in 2-4 divided doses.
| Dosage form | POWDER |
| Renal impairment | CrCl <50 mL/min: reduce dose by 50%; CrCl <10 mL/min: avoid use or reduce to 25% of normal dose. |
| Liver impairment | Child-Pugh A: no adjustment; Child-Pugh B: reduce dose by 50%; Child-Pugh C: avoid use. |
| Pediatric use | Oral: 200-300 mg/kg/day in 3-4 divided doses, maximum 12 g/day. |
| Geriatric use | Start at lower end of dosing range; monitor renal function and adjust based on CrCl; typical initial dose 4 g twice daily. |
| 1st trimester | Avoid due to potential teratogenicity; use only if clearly needed. |
| 2nd trimester | Use with caution; monitor for hepatotoxicity and ototoxicity. |
| 3rd trimester | Use with caution; risk of kernicterus in neonate if given near term. |
Clinical note
Comprehensive clinical and safety monograph for P.A.S. SODIUM (P.A.S. SODIUM).
| Placental transfer | Crosses placenta; fetal concentrations may approach maternal levels. |
| Breastfeeding | Excreted into breast milk in low concentrations; generally considered compatible with breastfeeding, but monitor infant for drowsiness, diarrhea, or rash. |
| Lactation Rating | L2 (Probably Compatible) |
| Teratogenic Risk | 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. |
| Fetal Monitoring | Monitor hepatic function (AST, ALT), renal function (serum creatinine, BUN), and CBC with differential monthly. Assess for hypersensitivity reactions and gastrointestinal intolerance. Fetal growth ultrasound if prolonged use. |
| Fertility Effects | No known effects on fertility in humans; animal studies not sufficiently reported. |
■ FDA Black Box Warning
None explicitly stated in current FDA labeling; however, caution is advised in hepatic impairment due to risk of hepatitis.
| Serious Effects |
Hypersensitivity to PAS or any componentSevere renal diseaseSevere hepatic disease
| Precautions | 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. |
| Food/Dietary | 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. |
| Clinical Pearls | 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. |
| Patient Advice | 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. |
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