Generic and additional names: para-aminosalicylic acid; PAS

CAS name: 4-Amino-2-hydroxybenzoic acid

CAS registry #: 65-49-6

Molecular formula: C₇H₇NO₃

Molecular weight: 153.14

Intellectual property rights: Generic, marketed 1946

Brand names: PASER (Jacobus); Rezipas (Bristol-Myers Squibb)

Derivatives: Schiff-base analogs of PAS with improved activity have been reported¹

Solubility: One gram dissolves in about 500 ml water, in 21 ml alcohol. Slightly soluble in ether. Practically insoluble in benzene. Soluble in dilute nitric acid or dilute sodium hydroxide [Merck Index].

Polarity: Log P 1.012 [DrugBank]

Acidity/basicity: pKa 3.25; pH of 0.1% aq solution: 3.5 [Merck Index].

Melting point: 150.5ºC [DrugBank]

Formulation and optimal human dosage: Tablet 500 mg, dose is 8–12 g daily in 2–3 doses. Peloquin et al.² describe the advantages of twice daily dosing with granules as opposed to once daily dosing.