Abstract
Following oral administration BT-PABA is selectively cleaved by pancreatic chymotrypsin liberating PABA which is passively absorbed, conjugated and excreted in the urine. Recently we have proposed that PABA measured in plasma 90 min after oral BT-PABA is superior to a 6 hr urine collection for determining pancreatic function in CF pts. However, this test assumes that the PABA marker has similar distribution and elimination patterns in normal and CF subjects. Since various drugs have altered pharmacokinetic patterns in CF, we studied the disposition of PABA in plasma and urine following oral BT-PABA and equimolar free PABA. The study group included six controls (age 19-28 yrs) and 18 CF pts (13-38 yrs; 7 steatorrheic and 11 non-steatorrheic). Following oral free PABA, elimination T½ of PABA was significantly shorter in CF pts (58±21 min) as compared to controls (93.5±28) (P<0.005). This change in T½ could be correlated with lower PABA distribution volume (r=0.51, P<0.02). PABA clearance was comparable between CF and control. In CF, mean plasma PABA values after free PABA were reduced by 7% at 90 min, 18% at 120 min and 38% at 180 min. Therefore, lowered plasma PABA may accentuate differences between normal and CF subjects following BT-PABA. This defect is minimized by taking plasma samples at 90 min rather than 180 min. Alterations of PABA kinetics in CF pts should be considered when interpreting the BT-PABA test.
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Koren, G., Weizman, Z., Forstner, G. et al. PLASMA BENZOYL-TYROSYL-PABA TEST IN EVALUATING EXOCRINE PANCREATIC FUNCTION IN CF: A PHARMACOKINETIC APPROACH. Pediatr Res 18 (Suppl 4), 203 (1984). https://doi.org/10.1203/00006450-198404001-00660
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DOI: https://doi.org/10.1203/00006450-198404001-00660