14C-Pipemidic acid was administered to male dd mice weighing about 20 g at a single oral dose of 0.5 mg (5.5 μCi) per body, and its distribution was examined by periodic macro-autoradiography followed by a so-called tissue scanning method, in which optical densities of macro-autoradiograms were scanned with a computerized auto-scanning microscope photometer. The results obtained were as follows.
1. 14C-Pipemidic acid administered orally showed good distribution to various tissues except for the central nervous system such as cerebrum, cerebellum and spinal cord, and its concentrations were extremely high in kidneys (medulla>cortex) and liver followed by parotid, myocardium, skin, skeletal muscle, etc. The concentrations in lung and spleen were as high as those in blood.
2. The concentrations of 14C-pipemidic acid in the foetuse were as high as those in placenta, i. e. maternal blood.
3. 14C-Pipemidic acid was rapidly distributed in high concentrations to an acute inflammatory area with cell infiltration in the experimental pyelonephritic mouse kidney, and remained there evidently 4 hours later. However, its distribution to a necrotic area of the kidney was found to be low.
4. In macro-autoradiograms prepared later than 4 hours after administration of 14C-pipemidic acid, darkend areas were found restrictedly in the peritoneal cavity, especially in liver and the inside of intestinal tracts, suggesting the presence of the enteric-hepatic circulation of the drug. Remains of 14C-pipemidic acid in mucous membranes corresponding to glandular stomach were also observed 24 hours after administration.
5. 14C-Pipemidic acid showed an affinity for bones and cartilages, and remained there at high concentrations even 6 hours later. However, it disappeared almost completely from those osteochondral tissues in macro-autoradiograms prepared 24 hours after single oral administration.
