P.A.S. SODIUM
Clinical safety rating: caution
Comprehensive clinical and safety monograph for P.A.S. SODIUM (P.A.S. SODIUM).
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 |
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 | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
Comprehensive clinical and safety monograph for P.A.S. SODIUM (P.A.S. SODIUM).
| Breastfeeding | Excreted into breast milk in low amounts; M/P ratio not determined. Considered compatible with breastfeeding; monitor infant for diarrhea or rash. |
| 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 |
■ 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 p-aminosalicylic acid or any component.","Severe hepatic impairment.","Severe renal failure (unless dose-adjusted).","Contraindicated in patients with active peptic ulcer 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."] |
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| 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. |