Effect of hydroxypropyl-beta-cyclodextrin-complexation and pH on solubility of camptothecin

Int J Pharm. 2004 Oct 13;284(1-2):61-8. doi: 10.1016/j.ijpharm.2004.07.014.


The influence of both pH and complexation by hydroxypropyl-beta-cyclodextrin (HP-beta-CD) on the overall solubility of camptothecin (CPT) was studied, with particular focus on the equilibrium between its lactone- and carboxylate-form. Phase solubility studies at therapeutically relevant pH values (pH 5.5-7.0) and physiologically acceptable HP-beta-CD-concentrations (0-25% (w/v)) were performed, and amounts of solubilized CPT quantified by HPLC. The solubility of CPT increased with both increasing pH and HP-beta-CD-concentration. The apparent complexation constant (KC) decreased with increasing pH (245 M(-1) at pH 5.5; 184 M(-1) at pH 7.0). The lactone-carboxylate equivalence point shifted from a pH value of 6.8-7.0 and 7.1 with 0, 10 and 25% HP-beta-CD, respectively. The lactone-carboxylate-ratios from the equilibrium study were applied to the phase-solubility data, and the lactone- and carboxylate concentrations at 0, 10 and 25% HP-beta-CD calculated. Separate complexation constants (KC) for the carboxylate-CPT and lactone-CPT could thus be derived, and found to be 113 +/- 7 and 260 +/- 18 M(-1), respectively. This allows the prediction of amounts of both lactone- and carboxylate-CPT solubilized at any HP-beta-CD concentration and pH-combination.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • 2-Hydroxypropyl-beta-cyclodextrin
  • Camptothecin / chemistry*
  • Camptothecin / pharmacokinetics
  • Hydrogen-Ion Concentration
  • Solubility / drug effects
  • beta-Cyclodextrins / chemistry*
  • beta-Cyclodextrins / pharmacokinetics


  • beta-Cyclodextrins
  • 2-Hydroxypropyl-beta-cyclodextrin
  • Camptothecin