Aminohippuric acid

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Clinical data
SynonymsPAH, PAHA, Aminohippurate, 4-Aminohippuric acid , N-(4-Aminobenzoyl)glycine, para-Aminohippurate
ATC code
CAS Number
PubChem CID
E number{{#property:P628}}
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Chemical and physical data
Molar mass194.19 g/mol
3D model (JSmol)

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]


Aminohippuric acid or para-aminohippuric acid (PAH), a derivative of hippuric acid, is a diagnostic agent useful in medical tests involving the kidney used in the measurement of renal plasma flow. It is an amide derivative of the amino acid glycine and para-aminobenzoic acid that is not naturally found in humans; it needs to be IV infused before use diagnostically.



PAH is useful for the measurement of renal plasma flow because it is secreted primarily by the renal tubules; only 20-30% is filtered by the glomerulus.[1] PAH is freely filtered from plasma in the glomerulus and not reabsorbed by the tubules, similar to inulin. PAH differs from inulin in that the fraction of PAH that bypasses the glomerulus and enters the nephron's tubular cells (via the peritubular capillaries) is completely secreted. Thus, through the above two mechanisms, PAH is completely filtered from the plasma reaching the nephron. For this reason, renal clearance of PAH is useful in calculation of renal plasma flow (RPF), which empirically is (1 − hematocrit) × renal blood flow. The clearance of PAH, however, is reflective only of RPF to portions of the kidney that deal with urine formation, and thus underestimates actual RPF by about 10%.[2]

The renal extraction ratio of PAH in a normal individual is approximately 0.92.[3]


Aminohippuric acid is often used as the sodium salt sodium para-aminohippurate. During World War II, para-aminohippurate was given along with penicillin in order to prolong the time penicillin circulated in the blood. Because both penicillin and para-aminohippurate compete for the same transporter in the kidney, administering para-aminohippurate with penicillin decreased the clearance of penicillin from the body by the kidney, providing better antibacterial therapy. Transporters found in the kidney eliminate organic anions and cations from the blood by moving substances, in this case, drug metabolites, from blood into urine.


In vultures, the NSAID diclofenac, which is extraordinarily toxic to vultures, interferes with the renal transport of uric acid via the PAH channel.[4]

pKa = 3.83

See also


  1. Phillips, R. A.; P. B. Hamilton (1948-02-29). "Effect of 20,60 and 120 minutes of renal ischemia on glomerular and tubular function" (PDF). Am J Physiol. 152 (3): 523–30. ISSN 0002-9513. PMID 18863150. Retrieved 2008-03-20.
  2. Costanzo, Linda. Physiology, 4th Edition. Philadelphia: Lippincott Williams and Wilkins, 2007. Page 156-160.
  3. Reubi, François C. (1953-04-29). "Glomerular filtration rate, renal blood flow and blood viscosity during and after diabetic coma". Circ. Res. 1 (5): 410–3. ISSN 0009-7330. PMID 13082682. Retrieved 2008-03-19.
  4. Naidoo V, Swan GE (August 2008). "Diclofenac toxicity in Gyps vulture is associated with decreased uric acid excretion and not renal portal vasoconstriction". Comp. Biochem. Physiol. C Toxicol. Pharmacol. 149 (3): 269–74. doi:10.1016/j.cbpc.2008.07.014. PMID 18727958.

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