4-Aminosalicylic acid

4-Aminosalicylic acid (PAS) is an antibacterial drug used chiefly as a second-line treatment for tuberculosis. It inhibits folate synthesis in susceptible mycobacteria.

Folate synthesis: The pathway by which cells produce folates needed for nucleotide synthesis and other reactions. PAS interferes with this pathway in susceptible mycobacteria.
Tuberculosis: An infectious disease caused mainly by Mycobacterium tuberculosis, usually affecting the lungs. This is the disease for which PAS is chiefly used.
Jörgen Lehmann: A Swedish physician who introduced para-aminosalicylic acid as a tuberculosis treatment in the 1940s. Lehmann helped establish PAS as an effective antituberculosis drug.
Antimicrobial resistance: The ability of microorganisms to survive exposure to drugs that would normally inhibit or kill them. Resistance to tuberculosis drugs creates the need for reserve agents such as PAS.
Dihydropteroate synthase: A bacterial enzyme that joins p-aminobenzoate to a pteridine precursor during folate synthesis. PAS competes with p-aminobenzoate at this folate-pathway step.
Drug-resistant tuberculosis: Tuberculosis caused by bacteria resistant to one or more antituberculosis drugs. PAS is reserved mainly for regimens treating resistant disease.
Streptomycin: An antibiotic discovered in 1943 and used as an early treatment for tuberculosis. Early clinical studies tested PAS alongside streptomycin to improve tuberculosis treatment.
Para-aminosalicylic acid resistance: Reduced susceptibility to PAS arising through changes in bacterial folate metabolism and drug handling. Resistance can undermine PAS activity and constrain its use in combination regimens.
Para-aminobenzoic acid: An aromatic compound used by bacteria as a precursor in folate synthesis. PAS resembles this natural substrate and can substitute for it in the pathway.
Multidrug-resistant tuberculosis: Tuberculosis resistant to at least isoniazid and rifampicin. PAS may be included when standard first-line drugs cannot form an effective regimen.

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4-Aminobenzoic acidCompared with: This related aromatic acid has a distinct therapeutic use and an extra hydroxyl substituent.