On the anomalous sorption behaviour of chlorhexidine with poly(2-hydroxyethyl methacrylate)

Effect of dentin etching and chlorhexidine application on metalloproteinase-mediated collagen degradation

Dentin matrix metalloproteinases (MMPs) are involved in the degradation of collagen in resin-dentin interfaces. This study evaluated whether collagen degradation can be prevented by chlorhexidine digluconate (CHX) after different dentin demineralization procedures. The demineralization of human dentin was performed with phosphoric acid (PA), EDTA or acidic monomers (Clearfil SE Bond and Xeno V). Specimens were stored (for 24 h, or for 1 or 3 wk) in the presence or absence of CHX. In half of the groups, active MMP-2 was incorporated into the storage solution. At the end of each storage period, the C-terminal telopeptide (ICTP) concentration (which indicates the amount of collagen degradation) was measured in the storage solution. Collagen degradation was higher in PA- and EDTA-demineralized dentin. Chlorhexidine digluconate reduced collagen degradation in these groups only for 24 h. When dentin was demineralized with Clearfil SE Bond or Xeno V, collagen degradation was reduced by up to 30%, but the addition of exogenous MMP-2 significantly increased collagen degradation. In self-etchant-treated dentin, the inhibitory effect of CHX on MMPs lasted for up to 3 wk. Treating dentin with EDTA, PA or self-etching agents produces enough demineralization to permit cleavage of the exposed collagen. Monomer infiltration may exert protection on demineralized collagen, probably through immobilization of MMPs. The partial inhibitory action of CHX on MMP activity produced by self-etching adhesives was prolonged compared with the short-acting PA- or EDTA-treated dentin.

Interaction Characteristics and Thermodynamic Behaviour of Gatifloxacin by Aluminium Hydroxide

The interaction pattern of gatifloxacin was temperature-dependent Langmuir isotherm, and the Langmuir coefficients increased as the temperature was raised. The perturbation experiment conducted on this system showed that the nature of interaction was irreversible. The enthalpy change is a positive value, indicating the existence of increased activation energy as the temperature is raised. The entropy value, 24.21 e.u. obtained in this system, indicated that the hydration shells of the ions were rather tightly bound. Intestinal permeation study also revealed the decreased bioavailability of gatifloxacin relatively to the presence of aluminium hydroxide. The strong adsorption of gatifloxacin by aluminium hydroxide is due to formation of complexes with cations of aluminium hydroxide through carboxyl and carbonyl groups of gatifloxacin.

Corneal Staining and Subjective Symptoms With Multipurpose Solutions as a Function of Time

PURPOSE

Short-term changes in corneal staining and ocular symptoms were assessed at defined intervals to evaluate combinations of three soft lenses and four multipurpose solutions.

METHODS

A series of pilot studies were conducted over 11 months using a double-masked, randomized, crossover design. Asymptomatic, adapted, daily-wear soft lens users wore group II or IV soft hydrophilic or silicone hydrogel lenses for a maximum period each day. Before wear, new lenses were soaked overnight in one of four multipurpose solutions: Alcon OPTI-FREE Express MPDS, Bausch & Lomb ReNu MultiPlus Multipurpose Solution, CIBA Vision SOLO-Care PLUS Multipurpose Solution, or AMO Complete MoisturePLUS. Subjects rated comfort and ocular symptoms. Corneal staining type and area were evaluated at baseline and after lens removal.

RESULTS

Significantly increased extent of corneal staining, defined as the proportion of corneal zones showing staining of grade 1 or more severe, was observed at 1 and 2 hours when subjects wore group II lenses soaked in the polyhexamethylene biguanide-based systems. Significantly increased extent of staining was observed at 2 hours when subjects used silicone hydrogel lenses soaked in regimen 4. When subjects used regimen 1 and wore group II lenses, only a minimal staining response was observed at 1 and 2 hours of wear. Significant symptoms were not correlated with extent of staining.

CONCLUSIONS

This study design is a promising tool that can discriminate between the performance of different soft lens and multipurpose solution combinations rapidly using small patient samples. With some lens-care product combinations, corneal appearance may vary according to the time of day the patient is examined.

Studies on adsorption characteristics and mechanism of adsorption of chlorhexidine mainly by carbon black

The extent of adsorption of chlorhexidine to carbon black and sanitary cotton was determined by measuring the amounts of chlorhexidine adsorbed to carbon black or sanitary cotton from the chlorhexidine solution containing specific amount of carbon black or sanitary cotton. As another comparative antiseptic example of adsorption phenomena, adsorption of acrinol to sanitary cotton was also studied. The specific surface area of carbon black was measured by the BET method of adsorption isotherm. The pattern of adsorption of chlorhexidine to carbon black was temperature-dependent Langmuir isotherms, and the amounts adsorbed increased as the temperature was raised. Since chlorhexidine, whose pKa's are 2.2 and 10.3, is considered to exist in aqueous solution as the di-cation, an ion-ion interaction should be formed between protonated biguanide and anionic portions of carbon black or sanitary cotton. The chlorophenyl and hexane moieties interact with hydrophobic portions of carbon black or sanitary cotton. The perturbation experiment conducted on this interaction system showed that the nature of interaction was irreversible. The enthalpy change calculated from Langmuir constants was small, indicating the existence of ion-ion interaction. The entropy values, 27.4 to 28.2 e.u. obtained in this system, suggested that the hydration shells of the ions were rather tightly bound. The area occupied by a chlorhexidine molecule, 548 (A)(2), was twice greater than the projection area, 276 (A)(2), suggesting that chlorhexidine was adsorbed in such a way that each molecule is sufficiently well spaced.