Improvement of the oral bioavailability of digitalis glycosides by cyclodextrin complexation

Inclusion complexes of the digitalis glycosides digitoxin, digoxin, and methyl digoxin with three cyclodextrins (alpha-, beta-, gamma-homologues) in water and in the solid state were studied by a solubility method, IR and 1H-NMR spectroscopy, and X-ray diffractometry. Solid complexes (in a molar ratio of 1:4) of the digitalis glycosides with gamma-cyclodextrin were prepared and their in vivo absorption examined. The rapidly dissolving form of the gamma-cyclodextrin complex significantly increased plasma levels of digoxin (approximately 5.4-fold) after oral administration to dogs.

Reduction in the local tissue toxicity of chlorpromazine by beta-cyclodextrin complexation

Effect of beta-cyclodextrin (beta-CyD) on the local tissue toxicity of chlorpromazine (CPZ) was investigated following the intramuscular injection to rabbits. From the gross and histological examinations, beta-CyD was found to alleviate the muscular tissue damage produced by CPZ on M. vastus lateralis in rabbits. The protective effect of beta-CyD may be ascribed to the decrease in affinity of CPZ to the tissue membrane through inclusion complexation. The present data suggest that beta-CyD complexation is particularly useful to reduce the local toxicity of phenothiazine neuroleptics without altering the pharmacological efficacy.

Protective mechanism of beta-cyclodextrin for the hemolysis induced with phenothiazine neuroleptics in vitro

beta-Cyclodextrin (beta-CyD) was found to protect the human erythrocytes from the hemolysis induced with ten phenothiazine neuroleptics in isotonic solution. The hemolytic activities of the phenothiazine-beta-CyD systems appeared to depend upon the free phenothiazine concentration, suggesting that the complexed form of phenothiazines is essentially inactive to cause hemolysis. The binding abilities and surface activities of the complexed form of phenothiazines were much smaller than those of free phenothiazines. These results indicate that the protective effect of beta-CyD may be due to the decrease in the effective hemolytic concentration of phenothiazines by inclusion complexation rather than the stabilizing effect of beta-CyD on the erythrocyte membrane.

Improvement of oral bioavailability of prednisolone by beta-cyclodextrin complexation in humans

Inclusion complex of prednisolone with beta-cyclodextrin (beta-CyD) in 1:2 molar ratio was prepared and its dissolution, membrane permeation and oral absorption behaviors were examined. The rates of dissolution and permeation through a cellophane membrane in water were significantly increased by beta-CyD complexation. A crossover bioavailability study was performed using human subjects with lower doses of prednisolone tablets, where the plasma levels of the drug were determined by radioimmunoassay. The enhanced bioavailability of prednisolone by beta-CyD complexation suggested the possibility of smaller doses and fewer side effects in prednisolone therapy.

Enhanced oral bioavailability of antiinflammatory drug flurbiprofen in rabbits by tri-O-methyl-beta-cyclodextrin complexation

Inclusion complex of antiinflammatory drug flurbiprofen with tri-O-methyl-beta-cyclodextrin in 1:1 molar ratio was prepared, and its dissolution and absorption characteristics were compared with those of flurbiprofen. The apparent dissolution rate of flurbiprofen in water was significantly increased by the inclusion complexation. The serum level of flurbiprofen following the oral administration of the complex to rabbits was higher than that of the drug alone. The enhanced bioavailability of flurbiprofen suggests the possible utility of tri-O-methyl-beta-cyclodextrin in pharmaceutical formulation.

Effect of cyclodextrins on the acid hydrolysis of digoxin

The effects of three cyclodextrins (alpha-, beta-, gamma-CyD) on the acid hydrolysis of digoxin were examined. From the high performance liquid chromatographic tracing of each of the four components (digoxin, bisdigitoxoside, monodigitoxoside, digoxigenin) in reaction mixtures, the individual rate constants (K1-K6) were determined by analogue computer simulation. The hydrolysis was suppressed by CyDs in the order of beta-great than gamma-greater than alpha-greater than-CyD, where beta-CyD inhibited the appearance rates of digoxigenin (k3, K5, and K6) significantly. In the dissolution study of digoxin tablets, the increase in dissolution rate and decrease in acid hydrolysis were attained by inclusion complexation. The data are presented suggesting that CyDs are useful for improving the oral bioavailability of digoxin.

Cyclodextrin-induced hemolysis and shape changes of human erythrocytes in vitro

Cyclodextrins (CyDs) at higher concentrations were found to cause hemolysis of human erythrocytes in the order of beta- greater than alpha- greater than gamma-CyD in isotonic solution. Biphasic effects of CyDs were observed for the osmotic and heat-induced hemolysis; i.e. the protection at relatively low CyD concentrations and stimulation at higher CyD concentrations. From the scanning electron microscopic observations, CyDs induced shape changes of membrane internalization type on erythrocytes. CyDs caused the release of cholesterol from erythrocyte membrane in the order of beta- greater than gamma- greater than alpha-CyD. These results clearly indicate that CyD-induced hemolysis is probably a secondary event resulting from the membrane disruption which elicited the removal of membrane components from erythrocytes.

Effects of cyclodextrins on chlorpromazine-induced haemolysis and central nervous system responses

Cyclodextrins (CyDs) protected the human erythrocytes from haemolysis induced with chlorpromazine (CPZ) in isotonic solution, depending upon the magnitude of the stability constant of CPZ-CyD complexes (beta-greater than-gamma-greater than alpha-CyD). From the observations of CPZ uptake into erythrocytes and changes in surface activity of CPZ, the protective effects of CyDs in vitro appeared to be due to the decrease in effective haemolytic concentration of CPZ through inclusion complex formation rather than the direct interaction of CyDs with the erythrocyte membrane. The effect of beta-CyD on some central nervous system (c.n.s.) actions of CPZ in rats was also investigated to see if there were any advantages in the use of beta-CyD complexes given by injection. The results suggest that beta-CyD does not after the time-course or magnitude of the effects of CPZ on the c.n.s.

Enhanced bioavailability of digoxin by gamma-cyclodextrin complexation

Inclusion complex of digoxin with gamma-cyclodextrin (gamma-CyD) in 1:4 molar ratio was prepared, and its dissolution and absorption behaviors were compared with those of digoxin alone. The dissolution rate of digoxin in water was found to be markedly increased by gamma-CyD complexation. Bioavailability of digoxin following the oral administration of gamma-CyD complex to dogs was 5.4 times as much as that of digoxin alone. The present data did indicate improvement of dissolution and absorption characteristics of digoxin by inclusion complexation, suggesting the decrease in dose in oral digoxin therapy.

Protective effects of cyclodextrins on drug-induced hemolysis in vitro

beta-Cyclodextrin (beta-CyD) significantly protected the human erythrocytes from hemolysis and shape changes induced with chlorpromazine and flufenamic acid in isotonic solution. A good correlation between the stability constants of inclusion complexes (beta- greater than gamma- greater than alpha-CyD) and the inhibitory effects on drug-induced hemolysis was found. From the observations of drug uptake into erythrocytes and changes in surface tension, the protective effects of CyDs appeared to be due to the decrease in effective concentration of drug through inclusion complexation rather than the direct interaction of CyDs with erythrocyte membrane.

Improvements of dissolution characteristics and chemical stability of 16,16-dimethyl-trans-delta 2-prostaglandin E1 methyl ester by cyclodextrin complexation

Inclusion complexation of 16,16-dimethyl-trans-delta 2-prostaglandin E1 methyl ester (I), which is effective in early pregnancy termination, with cyclodextrins in water was ascertained by a solubility study. A solid complex of I-beta-cyclodextrin in a 1:2 molar ratio was obtained, and its dissolution behavior and chemical stability were examined. The results indicated that the complex may have great utility as a rapidly dissolving form of I with prolonged storage time.

Utilization of cyclodextrin complexation for separation of E, A, and B prostaglandins by ion-exchange liquid chromatography

Application of cyclodextrin complexation to the separation of E-, A-, and B-type prostaglandins by ion-exchange liquid chromatography is demonstrated. The addition of alpha-or beta-cyclodextrin into the mobile phase on an anion-exchange support decreased the retention times of the prostaglandins significantly because of soluble complex formation. Chromatographic separation behavior is discussed on the basis of the stability of the inclusion complex. A rapid and sensitive method for the separation and quantification of the prostaglandins, using beta-cyclodextrin in the mobile phase, is described.