TY - JOUR

T1 - Thermodynamic investigation of the interaction between cyclodextrins and preservatives

T2 - Application and verification in a mathematical model to determine the needed preservative surplus in aqueous cyclodextrin formulations

AU - Holm, René

AU - Olesen, Niels Erik

AU - Alexandersen, Signe Dalgaard

AU - Dahlgaard, Birgitte N.

AU - Westh, Peter

AU - Mu, Huiling

PY - 2016

Y1 - 2016

N2 - Preservatives are inactivated when added to conserve aqueous cyclodextrin (CD) formulations due to complex formation between CDs and the preservative. To maintain the desired conservation effect the preservative needs to be added in apparent surplus to account for this inactivation. The purpose of the present work was to establish a mathematical model, which defines this surplus based upon knowledge of stability constants and the minimal concentration of preservation to inhibit bacterial growth. The stability constants of benzoic acid, methyl- and propyl-paraben with different frequently used βCDs were determined by isothermal titration calorimetry. Based upon this knowledge mathematical models were constructed to account for the equilibrium systems and to calculate the required concentration of the preservations, which was evaluated experimentally based upon the USP/Ph. Eur./JP monograph. The mathematical calculations were able to predict the needed concentration of preservation in the presence of CDs; it clearly demonstrated the usefulness of including all underlying chemical equilibria in a mathematical model, such that the formulation design can be based on quantitative arguments.

AB - Preservatives are inactivated when added to conserve aqueous cyclodextrin (CD) formulations due to complex formation between CDs and the preservative. To maintain the desired conservation effect the preservative needs to be added in apparent surplus to account for this inactivation. The purpose of the present work was to establish a mathematical model, which defines this surplus based upon knowledge of stability constants and the minimal concentration of preservation to inhibit bacterial growth. The stability constants of benzoic acid, methyl- and propyl-paraben with different frequently used βCDs were determined by isothermal titration calorimetry. Based upon this knowledge mathematical models were constructed to account for the equilibrium systems and to calculate the required concentration of the preservations, which was evaluated experimentally based upon the USP/Ph. Eur./JP monograph. The mathematical calculations were able to predict the needed concentration of preservation in the presence of CDs; it clearly demonstrated the usefulness of including all underlying chemical equilibria in a mathematical model, such that the formulation design can be based on quantitative arguments.

U2 - 10.1016/j.ejps.2015.09.011

DO - 10.1016/j.ejps.2015.09.011

M3 - Journal article

VL - 87

SP - 22

EP - 29

JO - European Journal of Pharmaceutical Sciences

JF - European Journal of Pharmaceutical Sciences

SN - 0928-0987

ER -