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AMINOHIPPURATE SODIUM PAH
aminohippurate sodium injection, solution
----------AMINOHIPPURATE SODIUM “PAH”
Aminohippurate sodium1 is an agent to measure effective renal plasma flow (ERPF). It is the sodium salt of para-aminohippuric acid, commonly abbreviated “PAH”. It is water soluble, lipid-insoluble, and has a pKa of 3.83. The empirical formula of the anhydrous salt is C9H9N2NaO3 and its structural formula is:
It is provided as a sterile, non-preserved 20 percent aqueous solution for injection, with a pH of 6.7 to 7.6. Each 10 mL contains: Aminohippurate sodium 2 g. Inactive ingredients: Sodium hydroxide to adjust pH, water for injection, q.s.
PAH is filtered by the glomeruli and is actively secreted by the proximal tubules. At low plasma concentrations (1.0 to 2.0 mg/100 mL), an average of 90 percent of PAH is cleared by the kidneys from the renal blood stream in a single circulation. It is ideally suited for measurement of ERPF since it has a high clearance, is essentially nontoxic at the plasma concentrations reached with recommended doses, and its analytical determination is relatively simple and accurate.
PAH is also used to measure the functional capacity of the renal tubular secretory mechanism or transport maximum (TmPAH). This is accomplished by elevating the plasma concentration to levels (40-60 mg/100 mL) sufficient to saturate the maximal capacity of the tubular cells to secrete PAH.
Inulin clearance is generally measured during TmPAH determinations since glomerular filtration rate (GFR) must be known before calculations of secretory Tm measurements can be done (see DOSAGE AND ADMINISTRATION, Calculations).
INDICATIONS AND USAGE
Estimation of effective renal plasma flow.
Measurement of the functional capacity of the renal tubular secretory mechanism.
Intravenous solutions must be given with caution to patients with low cardiac reserve, since a rapid increase in plasma volume can precipitate congestive heart failure.
For measurement of ERPF, small doses of PAH are used. However, in research procedures to measure TmPAH, high plasma levels are required to saturate the capacity of the tubular cells. During these procedures, the intravenous administration of PAH solutions should be carried out slowly and with caution. The patient should be continuously observed for any adverse reactions.
Use caution when injecting this product into latex-sensitive individuals, since the vial stopper contains dry natural latex rubber that may cause allergic reactions.
Renal clearance measurements of PAH cannot be made with any significant accuracy in patients receiving sulfonamides, procaine, or thiazolesulfone. These compounds interfere with chemical color development essential to the analytical procedures.
Probenecid depresses tubular secretion of certain weak acids such as PAH. Therefore, patients receiving probenecid will have erroneously low ERPF and TmPAH values.
Carcinogenesis, Mutagenesis, Impairment of Fertility
Long-term studies in animals have not been done to evaluate any effects upon fertility or carcinogenic potential of PAH.
It is not known whether this drug is excreted in human milk. Because many drugs are excreted in human milk, caution should be exercised when PAH is administered to a nursing woman.
Hypersensitivity reactions including anaphylaxis, angioedema, urticaria, vasomotor disturbances, flushing, tingling, nausea, vomiting, and cramps may occur.
Patients may have a sensation of warmth or the desire to defecate or urinate during or shortly following initiation of infusion.
DOSAGE AND ADMINISTRATION
For intravenous use only
Clearance measurements using single injection techniques are generally inaccurate, particularly in the measurement of ERPF. For this reason, intravenous infusions at fixed rates are used to sustain the plasma PAH concentration at the desired level.
To measure ERPF, the concentration of PAH in the plasma should be maintained at 2 mg per 100 mL, which can be achieved with a priming dose of 6 to 10 mg/kg and an infusion dose of 10 to 24 mg/min.
As a research procedure for the measurement of TmPAH, the plasma level of PAH must be sufficient to saturate the capacity of the tubular secretory cells. Concentrations from 40 to 60 mg per 100 mL are usually necessary.
Parenteral drug products should be inspected visually for particulate matter and discoloration prior to use, whenever solution and container permit. NOTE: The normal color range for this product is a colorless to yellow/brown solution. The efficacy is not affected by color changes within this range.
Effective Renal Plasma Flow (ERPF)
The clearance of PAH, which is extracted almost completely from the plasma during its passage through the renal circulation, constitutes a measure of ERPF. Hence:
ERPF = UPAHV/PPAH
Where UPAH = concentration of PAH (mg/mL) in the urine
V = rate of urine excretion (mL/min), and
PPAH = plasma concentration of PAH (mg/mL).
UPAH = 8.0 mg/mL
V = 1.5 mL/min
PPAH = 0.02 mg/mL
ERPF = 8.0 x 1.5/0.02 = 600 mL/min
Based on PAH clearance studies, the normal values for ERPF are:
men 675 ± 150 mL/min
women 595 ± 125 mL/min
Maximum Tubular Secretory
aminohippurate sodium injection, solution
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|Labeler - Merck Sharp & Dohme Corp. (001317064)|
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Revised: 01/2011 Merck Sharp & Dohme Corp.
Reproduced with permission of U.S. National Library of Medicine
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