[Enhanced bioavailability of digoxin by gamma-cyclodextrin complexation: evaluation for sublingual and oral administrations in humans]

The inclusion complex of digoxin with gamma-cyclodextrin was prepared in a molar ratio of 1:4, and evaluated for sublingual and oral administrations in humans. In the dissolution tests of digoxin tablets, the increase in dissolution rate and decrease in acid hydrolysis were attained by gamma-cyclodextrin complexation. The serum levels of digoxin after sublingual and oral administrations to human healthy volunteers in the form of complex tablets were higher than the digoxin alone, particularly in the case of the sublingual form of gamma-cyclodextrin complex. The present data suggested that the sublingual administration of the rapid dissolving form of gamma-cyclodextrin complex may be useful for improving the bioavailability of digoxin due to the prevention of acid hydrolysis in stomach and the enhancement of drug absorption rate.

Some pharmaceutical properties of 3-hydroxypropyl- and 2,3-dihydroxypropyl-beta-cyclodextrins and their solubilizing and stabilizing abilities

3-Hydroxypropyl- and 2,3-dihydroxypropyl-beta-cyclodextrins (3-HP- and DHP-beta-CyDs) with different degrees of substitution (D.S.) were prepared and their pharmaceutical properties were investigated. The aqueous solubility of 3-HP- and DHP-beta-CyDs was much higher than that of the parent beta-CyD and the dissolution of DHP-beta-CyD in water was endothermic. The acid- and alpha-amylase-catalyzed hydrolysis rates of 3-HP- and DHP-beta-CyDs were slower than those of the parent beta-CyD. The hemolytic activity (human erythrocytes) and local irritancy (rabbit muscle) of DHP-beta-CyD were considerably less than those of natural, methylated or other hydroxyalkylated beta-CyDs, and decreased with increasing D.S. The ability of the hydroxyalkylated beta-CyDs to remove cholesterol and proteins from human erythrocytes decreased with increasing D.S., and correlated well with their hemolytic activity. 3-HP-beta-CyD was a more effective solubilizer for poorly water-soluble drugs than the parent beta-CyD, and its stabilizing effect on chemically instable drugs was higher than that of the parent beta-CyD. The above data suggest a considerable pharmaceutical potential of 3-HP- and DHP-beta-CyDs as parenteral carriers.

An attempt to reduce the photosensitizing potential of chlorpromazine with the simultaneous use of beta- and dimethyl-beta-cyclodextrins in guinea pigs

The effects of topically applied beta-cyclodextrin (beta-CyD) and heptakis(2,6-di-O-methyl)-beta-cyclodextrin (DM-beta-CyD) on photoallergic contact dermatitis due to chlorpromazine hydrochloride (CPZ) were investigated using the photomaximization technique in guinea pigs. From the gross and histological observations, the photosensitizing potential of CPZ with the simultaneous topical use of beta-CyDs was significantly lower than that of CPZ alone. The alleviating efficacy of DM-beta-CyD was greater than that of beta-CyD. beta-CyDs suppressed the penetration of CPZ into the skin through the formation of poorly skin-permeable complexes. In addition, beta-CyDs inhibited (a) the photoinduced free radicals derived from CPZ in the isolated dry skin and (b) the in vitro photochemical binding of CPZ to bovine serum albumin. These observations suggest that beta-CyDs suppress the photochemical reactions between CPZ and biological macromolecules present in the skin, resulting in the failure to form a photoantigen. The present results indicate that DM-beta-CyD is particularly effective in alleviating photoallergic contact dermatitis due to CPZ.

Amorphous water-soluble cyclodextrin derivatives: 2-hydroxyethyl, 3-hydroxypropyl, 2-hydroxyisobutyl, and carboxamidomethyl derivatives of beta-cyclodextrin

The pharmaceutical usefulness of natural, crystalline cyclodextrins can be improved by chemical conversions into water-soluble, amorphous mixtures of their derivatives. Reaction of beta-cyclodextrin with 2-chloroethanol, 3-chloropropanol, isobutylene oxide, or iodoacetamide yielded the title compounds. Distributions of the substitution degree were close to symmetrical and relatively narrow. The average substitution degrees increased with the amount of alkylating reagent used in the preparation. The number of components (half-width of distribution) increased with increasing average substitution degree. Further, distributions of the substitution degree were measured in glucose derivatives after hydrolysis of 2-hydroxyethyl, 2-hydroxypropyl, and 2-hydroxyisobutyl-beta-cyclodextrin. The results show an uneven distribution of substituents around the cyclodextrins, suggesting that growth of oligoglycol side chains and/or clustering of substituents on one glucose residue occurs.

Utilization of diethyl-beta-cyclodextrin as a sustained-release carrier for isosorbide dinitrate

Heptakis(2,6-di-O-ethyl)-beta-cyclodextrin (2) was prepared and its physicochemical properties, such as aqueous solubility and surface activity, were compared with those of beta-cyclodextrin (1) and heptakis(2,6-di-O-methyl)-beta-cyclodextrin (3). A possible utility of 2 as a sustained-release drug carrier was examined using a water-soluble drug, isosorbide dinitrate. The dissolution and release rates of isosorbide dinitrate from capsule and tablet forms were significantly retarded by the complexation with 2. The sustained-release pattern of isosorbide dinitrate was produced for a long period after the oral administration of a single dose of capsule or tablet containing the 2 complex to rats. The results indicated that 2 may serve as a hydrophobic drug carrier for sustained-release of isosorbide dinitrate.

gamma-Cyclodextrin:testosterone complex suitable for sublingual administration

A crystalline complex of testosterone with gamma-cyclodextrin was evaluated for solubility and dissolution rate. Whereas these parameters were at least an order of magnitude lower than those of testosterone complexes with amorphous derivatives of cyclodextrins, the properties of the crystalline complex enabled the preparation of a suitable pharmaceutical form for the sublingual administration of hormone to humans. This is in contrast to the situation with similar beta-cyclodextrin complexes, in which such administration was ineffective. Sublingual administration of the gamma-cyclodextrin complex, as shown in previous work using amorphous complexes, avoided rapid first-pass loss of hormone and directed it effectively into the circulation; administration of the complex into the stomach resulted in much lower circulatory hormone levels.

Photoactivation mechanism of hyaluronidase by chlorpromazine

A pre-irradiated chlorpromazine (CPZ) in pH 7.2 and aqueous solutions activated hyaluronidase, and it showed the enzyme-activating action even after 7 days of irradiation. This indicates that the stable photoproducts of CPZ activated the enzyme. But promazine and CPZ-5-sulfoxide, which are photoproducts of CPZ, did not activate the enzyme in the presence and absence of UVA. The dimer and higher molecular weight (MW) products of CPZ that were obtained by treating the pre-irradiated CPZ solution with gel permeation chromatography showed the hyaluronidase by activating action without UVA. In addition, photoactivation of hyaluronidase by CPZ was inhibited by radical quenchers. This suggested that the photoproducts with enzyme-activating action were produced via some radicals. On the basis of these findings, a possible mechanism for photoactivation of hyaluronidase by CPZ was proposed.

Effects of beta- and gamma-cyclodextrins on the pharmacokinetic behavior of prednisolone after intravenous and intramuscular administrations to rabbits

The effects of beta- and gamma-cyclodextrins (CyDs) on the pharmacokinetic behavior of prednisolone after intravenous or intramuscular administration in rabbits were investigated. The serum levels of prednisolone after intravenous administration were little affected by the two CyD complexes. This might have been due to the rapid dissociation of the complexes in the large volume of body fluid. On the other hand, the serum levels of prednisolone after intramuscular administration of the CyD complexes in the form of a suspension to rabbits were significantly higher than those of the drug alone. In addition, the mean residence times of both CyD complexes were shorter than that of prednisolone alone. In contrast, there was little or no difference in pharmacokinetic parameters after intramuscular administration of the drug in the form of a solution except for Tmax between prednisolone and its CyD complexes. The enhanced rate of bioavailability of prednisolone after intramuscular administration in the form of a suspension may be due to the rapid dissolution of CyD complexes.

Protection against the photosensitized skin irritancy of chlorpromazine by cyclodextrin complexation

The efficacy of three types of cyclodextrins (CyDs) to reduce skin irritation in guinea pigs caused by photoirradiated chlorpromazine (CPZ) was in the order of beta-greater than gamma-much greater than alpha-CyD, depending upon the magnitude of the stability constant of the CPZ-CyD complexes. The inhibitory effects of CyDs may be attributable to the alteration in the photochemical reactivity of CPZ through inclusion complexation. By the photoirradiation of CPZ in the presence of CyDs, promazine, which is less toxic than CPZ, was produced and the yield decreased in the order of beta-greater than gamma-much greater than alpha-CyD. These results clearly indicate that beta-CyD complexation is particularly useful to reduce the CPZ-photosensitized damage to skin.

Improvement of dissolution and suppository release characteristics of flurbiprofen by inclusion complexation with heptakis(2,6-di-O-methyl)-beta-cyclodextrin

The inclusion behavior of methylated beta-cyclodextrins, heptakis(2,6-di-O-methyl)-beta-cyclodextrin and heptakis-(2,3,6-tri-O-methyl)-beta-cyclodextrin in solution and the solid state was compared with that of natural beta-cyclodextrin using an anti-inflammatory drug, flurbiprofen, as a guest molecule. Stability constants were determined by the solubility method at various temperatures, and the thermodynamic parameters were calculated for inclusion complex formation in aqueous solution. The solid complexes were obtained in a molar ratio of 1:1, and their dissolution behavior and release from suppository bases were examined. The data suggest that the inclusion mode of the complex with 3 is somewhat different from that of the complexes with 1 and 2. From a practical point of view, 2 seems to be particularly useful for improving the pharmaceutical properties of flurbiprofen in various dosage forms.

Improvement in the percutaneous absorption of beclomethasone dipropionate by gamma-cyclodextrin complexation

Inclusion complex formation of beclomethasone dipropionate (BMDP) with gamma-cyclodextrin (gamma-CyD) in water and in solid state was assessed by solubility analysis and X-ray diffractometry. The solid complex of BMDP with gamma-CyD in a molar ratio of 1:2 was prepared and its in-vitro release behaviour was investigated using an ointment release simulator. The release of BMDP from hydrophilic ointment was significantly improved by the gamma-CyD complexation. Permeation and uptake studies indicated that the enhanced release of BMDP from the ointment may be due to the faster dissolution and the lower binding affinity of the complex in the ointment base. The vasoconstrictor activity of BMDP in man was found to be increased by gamma-CyD complexation, suggesting an improvement in the percutaneous absorption of BMDP.

Effects of penicillins on binding of phenytoin to plasma proteins in vitro and in vivo

Effects of penicillins on the binding of phenytoin to plasma proteins were examined in vitro and in vivo. The results from in vitro studies showed that the penicillins including oxacillin and dicloxacillin were effective in displacing phenytoin from its binding sites. In vivo, the total phenytoin concentration in serum decreased during penicillin administration, while the free phenytoin concentration increased. As a result, penicillins caused a significant increase in the apparent volume of distribution and in the total body clearance of phenytoin. These results can be explained on the basis of the displacement of phenytoin from its plasma protein binding site by penicillins.

Inclusion complexation of prostaglandin F2 alpha with gamma-cyclodextrin in solution and solid phases

A solid complex of prostaglandin F2 alpha (dinoprost) with gamma-cyclodextrin in a molar ratio of 1:1 was obtained on the basis of the BS-type phase solubility diagram. The mode of interaction in the solid state was studied by powder X-ray diffractometry, thermal analysis, and carbon-13 cross polarization/magic angle spinning nuclear magnetic resonance (13C-CP/MAS-NMR) spectrometry. The X-ray diffraction and NMR data suggested that prostaglandin F2 alpha is included in the cylindrical channels formed by coaxial alignment of gamma-cyclodextrin molecules to give a channel type structure. Dissolution and thermal behaviors of the prostaglandin F2 alpha-gamma-cyclodextrin complex were examined and compared with the drug itself. The result indicated that the gamma-cyclodextrin complex may have great utility as a rapidly dissolving form of prostaglandin F2 alpha with improved thermal stability.