Effect of beta-cyclodextrin on the degradation rate of cinnarizine in aqueous solution

[Formulation Studies and Application of Their Experimental Techniques to Drug Discoveries]

In my first experience as a researcher, I isolated and performed structural predictions of the novel compounds, cis- and trans-palythenic acids, from Noctiluca milialis. I then worked for a pharmaceutical company in a research laboratory of pharmaceutics. I examined an inclusion complex of cinnarizine with β-cyclodextrin, and found that the inclusion complex did not improve the oral bioavailability of cinnarizine. However, the bioavailability of the inclusion complex after its oral administration was improved by a competing agent. This was the first study to show the potential of a competing agent to improve bioavailability. I subsequently joined a laboratory performing drug discovery research and used experimental techniques from pre-formulation studies. A screening system of solubility for drug design and discovery was constructed to increase the solubilities of compounds synthesized in the laboratory. This screening system contributed to the discovery of a phosphodiesterase type 5 inhibitor with sufficient solubility. As a visiting lecturer at a university, I prepared amoxicillin intragastric buoyant sustained-release tablets for the eradication of Helicobacter pylori and applied cinnarizine as a competing agent. I established a laboratory of pharmaceutics at a university in Tochigi. To develop an enema with fluticasone propionate for ulcerative colitis, I investigated its physicochemical properties and methods to improve its solubility. After moving to another university in Kagawa, I developed a method to reduce the amount of drugs remaining on the surfaces of a pestle and mortar following the grinding of tablets, and new cleaning agents for an automatic dividing packaging machine were discovered.

Effects of cyclodextrins on the chemical stability of drugs

Cyclodextrins (CDs) are enabling pharmaceutical excipients that can enhance both solubility and stability of wide variety of drugs in aqueous solutions through formation of drug/CD inclusion complexes where apolar moieties of the drug molecules are located inside the CD cavity. In properly designed pharmaceutical formulations CDs will improve physiochemical properties of lipophilic drugs without affecting their intrinsic ability to permeate biological membranes. Here the effect of CD complexes on the chemical stability of drugs is reviewed. Numerous studies shown that in aqueous solutions CD complexation can hamper hydrolysis, oxidation, photodegradation, isomerization and enzyme catalyzed degradation of dissolved drugs. However, some drugs, such as β-lactam antibiotics, can under certain conditions undergo CD catalyzed degradation in aqueous solutions. Also, some drugs that are stabilized by CDs in aqueous solutions are destabilized by the same CDs in solid dosage forms. Thus, the effects of CDs on drug stability have to be tested and verified in the final drug formulation and under the recommended storage conditions.

Structural effects on the binding of amine drugs with the diphenylmethyl functionality to cyclodextrins. I. A microcalorimetric study

Solution calorimetry has been employed to evaluate the stability constants and enthalpy changes associated with complex formation between alpha-, beta, or gamma-cyclodextrin (CD) and a group of amine compounds having the diphenylmethyl functionality. Data from thermal titrations of the compounds were analyzed using nonlinear least squares. The standard free energy decrease accompanying the formation of inclusion complexes is generally due to a negative standard enthalpy change (delta H degrees). The standard entropy change (delta S degrees) was negative, except in the case of complexes formed with gamma-CD. Of the 13 compounds studied, only 2 formed complexes with 1:2 (compound:beta-CD) stoichiometry, terfenadine . HCl and cinnarizine . 2HCl. All the others formed 1:1 complexes. The structural effect on the stability constants, thermodynamics, and inclusion geometry was explored by relating the calorimetric results to the chemical structures of the guest molecules and the cavity sizes of the CD molecules. The results suggest that one of the phenyl groups of the diphenylmethyl functionality resides in the CD cavity and is in van der Waals contact with the inside wall of the CD cavity. In the case of alpha- and beta-CDs, van der Waals interaction dominates in the stabilization. On the other hand, the interaction between these compounds and gamma-CD is largely entropically driven. Adiphenine . HCl forms a more stable complex with beta-CD than proadifen . HCl, suggesting that hydrogen bonding to the carbonyl oxygen by the hydroxyl group on the rim of the CD ring can influence the strength of the binding interaction.