Serum concentrations of para-aminosalicylic acid (PAS) produced by various forms of PAS.

Para-aminosalicylic acid (PAS) is now generally accepted as an effective antibacterial agent in the treatment of certain forms of tuberculosis when administered alone or in combination with one of the streptomycins. However, there remains a great deal of uncertainty as to the best method of administering the drug. Both the free acid and the sodium salt of PAS have been given in various dosage forms in an effort to diminish the symptoms of gastro-intestinal irritation which the drug produces. We have given the free acid as compressed uncoated tablets, entenic-coated tablets, entenic-coated granules, capsules, and as powder mixed with food or suspended in a liquid such as milk. The sodium salt has been given as a solution in water mixed with various fruit juices. Although an occasional patient preferred one of the forms of the free acid, most patients have been able to take larger daily doses of PAS as a solution of the sodium salt. This is In agreement with the reports of most clinical investigators. However, it is obvious that the total daily dose is of less importance than the concentration of PAS that is present in the blood serum after administration of each of these forms of the drug. In 1949 Lehmann’ advised against the use of the sodium salt of PAS stating, “We have generally used the PAS acid in the granules and not the sodium salt. The reason for not using the sodium salt is that it is very soluble in water, rapidly absorbed in the intestinal canal, and rapidly excreted by the kidneys. The blood level will therefore not be as high as one might except from the relatively large dose. The PAS acid is only soluble in 0.4 per cent in water and is not absorbed in the intestinal canal before neutralization by the intestinal juice.” More recently he2 has written, “Whether PAS should be used routinely as an acid enteric coated