GI absorption of beta-lactam antibiotics. III: Kinetic evidence for in situ absorption of ionized species of monobasic penicillins and cefazolin from the rat small intestine and structure-absorption rate relationships

J Pharm Sci. 1979 Jul;68(7):812-6. doi: 10.1002/jps.2600680706.


Absorption rates of monobasic beta-lactam antibiotics were measured as a function of lumen solution pH between 4 and 9 by utilizing the rat intestinal recirculating method in situ. Between pH 6.5 and 9, the absorption rate constants of ionized antibiotics were almost identical; but, at pH 4, the unionized species were highly absorbed, depending on their lipophilicity through the GI membrane lipoidal barrier. The structure-absorption rate relationship was established with the unstirred layer model.

MeSH terms

  • Animals
  • Biotransformation
  • Cefazolin / metabolism*
  • Cephalosporins / metabolism*
  • Hydrogen-Ion Concentration
  • Intestinal Absorption*
  • Intestine, Small / metabolism*
  • Kinetics
  • Male
  • Penicillins / metabolism*
  • Rats
  • Structure-Activity Relationship


  • Cephalosporins
  • Penicillins
  • Cefazolin