Medium-chain Glycerides Research Articles

Formulation and physical characterization of water-in-oil microemulsions containing long- versus medium-chain glycerides

Stable self-emulsifying water-in-oil (w/o) microemulsions of extremely small particle size (5–30 nm) and consisting of an oil, a blend of a low and high HLB surfactants and an aqueous phase, have been developed using commercially available and pharmaceutically acceptable components. Their formation was monitored by the corresponding pseudo-ternary phase diagram. The oil phase contained long- or medium-chain triglycerides, and mono-/diglycerides or sorbitan esters (low HLB surfactants). Polysorbate 80 (Tween 80) was used as a high HLB surfactant. Microemulsions were readily prepared by admixing appropriate quantities of the various components with gentle hand-mixing or stirring to ensure thorough mixing. In the case of microemulsions incorporating long-chain glycerides and/or sorbitan esters, high temperature (40–60°C) was used to reduce viscosity and solubilize all components during the formation of microemulsions. Limited levels of aqueous phase (< 10%, w/w) can be solubilized within w/o microemulsions incorporating long-chain glycerides and/or sorbitan esters. Microemulsions containing medium-chain glycerides (mono-/di-/triglycerides) can be formulated at ambient temperature and can solubilize aqueous phase up to 40% (w/w). The conductance, viscosity, refractive index, density and mean particle diameter of a typical w/o microemulsion incorporating medium-chain glycerides (Captex 355/Capmul MCM/Tween 80/saline, 65/22/10/3, % w/w), were: 0.540 μmhos/cm, 56.7 cP, 1.449, 0.9677, and 15.2 ± 4.1 nm (polydispersity of 0.153), respectively. The corresponding values of a w/o microemulsion incorporating long-chain triglycerides and monoglycerides (Soybean oil/Arlacel 186/Tween 80/saline, 65/22/10/3, % w/w) were: 0.177 μmhos/cm, 125.1 cP, 1.471, 0.9010, and 10.3 ± 2.5 nm (polydispersity of 0.114), respectively. Several water-soluble molecules/peptides of different molecular size and charge have been formulated in these w/o microemulsions at pharmacological relevant levels. These systems are discussed in terms of their drug delivery potential.

Stabilization and intestinal absorption of human calcitonin

The effect of different excipients and/or surface active compounds on the stability of human calcitonin in aqueous solution was studied. Calcitonin solution was partially stabilized with dilute acetic acid (0.01% (w/v) or higher), and among many tested surfactants, only lauryl sulfate proved to be a very efficient long-term stabilizer (1 year or more). Concentration dependency studies indicated that lauryl sulfate micelles were necessary to achieve long-term stabilization of human calcitonin in solution. Another liquid formulation was developed that also stabilized human calcitonin over a long period of time (3 months or more). Calcitonin was dissolved in polar, nontoxic, nonaqueous solvents, such as propylene glycol or polyethylene glycol 200 and this solution was emulsified in an oil phase composed of medium-chain glycerides. Medium and long-term stabilized formulations of human calcitonin were then studied for intestinal absorption via the duodenum and colon in rats. Using aqueous formulations containing 1% sodium dodecyl sulfate or 6.6% dodecyl maltoside as the enhancer, bioavailability values greater than 10% were achieved by intracolonic route of administration, demonstrating that the colon is better suited for calcitonin delivery and absorption. Pharmacodynamic responses and time profiles obtained were significant and comparable to those observed for intramuscular injection of human calcitonin.

Water-in-oil microemulsions containing medium-chain fatty acids/salts: formulation and intestinal absorption enhancement evaluation.

Water-in-oil (w/o) microemulsions have been developed which, in addition to non-ionic medium-chain glycerides, incorporate ionic lipids, primarily medium-chain fatty acids, such as caprylic (C8) capric (C10) and lauric (C12) acids and their corresponding sodium salts. The absorption enhancing activity of w/o microemulsions incorporating these lipids was evaluated in the rat using Calcein (MW = 623) a water-soluble and poorly absorbed marker molecule. Phase diagrams were constructed where C8/C10 or C12 fatty acids were treated as lipophilic surfactants and their sodium salts as hydrophilic ones. The anesthetised rat model was employed to evaluate Calcein absorption upon a single intraduodenal administration from a solution and the various w/o microemulsions. A wide range of clear and transparent w/o microemulsions were obtained at ambient temperature either in liquid or solid form when a fixed blend of medium chain fatty acid/salt was titrated by a fixed ratio of the oil containing the oil-soluble mono- and diglycerides and deionized water or physiological saline. Upon intraduodenal administration in the anesthetised rat, the absorption of Calcein was improved from about 2% in aqueous solution up to about 37% in w/o microemulsions. Solid and liquid formulations were equally effective in improving bioavailability. The absorption enhancement activity of the fatty acids/salts followed the order C8 approximately C10 > C12. Absorption enhancement of Calcein was significantly reduced in the absence or presence of low levels of C8/C10 mono-/diglycerides. These results further support the use of medium-chain glycerides and fatty acids/salts in microemulsion formulations to improve intestinal absorption of water-soluble compounds.

Site-specific drug delivery and penetration enhancement in the gastrointestinal tract

New types of biodegradable and pH-sensitive hydrogels were synthesized by the crosslinking of polymeric precursors. They contained both acidic comonomer and enzymatically degradable azoaromatic crosslinks. Such hydrogels are suitable for colon-specific drug delivery. In the low pH range of the stomach, the swelling of the gel is low and the drug is protected against digestion by enzymes. In the small intestine, the swelling increases. Upon arrival in the colon, a degree of swelling is reached that makes the crosslinks accessible to azoreductase activity. The gel is degraded and drug released. The hydrogels were characterized by the network structure (i.e., content of crosslinks, unreacted pendent groups, and cycles), the equilibrium and dynamic swelling as a function of pH, modulus of elasticity, and in vitro/in vivo degradation. The results indicated that the hydrogel network structure strongly depends on the reaction conditions such as polymer concentration, and the ratio of the reactive groups during the crosslinking reaction. The swelling and mechanical properties of hydrogels can be controlled by the modification of polymer backbone structure and/or the crosslinking density. Depending on the network structure, the degradation of hydrogels followed either a surface erosion or a bulk-degradation-like process. In vivo degradation rate of hydrogels was three to five times faster than that in vitro. The effect of a penetration enhancer, CapMul MCM (a medium chain glyceride), on physiological properties of rabbit intestinal epithelium was investigated in vitro using the Ussing chamber technique. It was shown that CapMul MCM affected tissue ion transport, permeability, and morphology in a concentration- and time-dependent manner. It was found that with minimal epithelial disruption and moderate change in ion transport in the colon, the increase in marker molecule permeabilities ranged between 7 and 25 times depending upon their molecular weight.

Effect of medium-chain glycerides on physiological properties of rabbit intestinal epithelium in vitro.

Medium chain glycerides (MCGs) have been reported to enhance intestinal absorption of hydrophilic drugs. However, the mechanisms involved in absorption enhancement are not well understood. The effects of MCGs (CapMul MCM) on physiological properties of rabbit ileum and distal colon, including active ion transport, transepithelial resistance (Rt) and passive permeability, have been investigated in vitro. CapMul MCM inhibited active ion transport (measured as a decrease in short-circuit current, Isc) in both intestinal segments in a concentration-dependent manner. The inhibition of Isc was rapidly reversible (within 100 min) upon removal of CapMul MCM. The data indicate that CapMul MCM preferentially affected ion transport by villus cells in the ileum and surface cells in the distal colon. Ion transport in crypt cells in both segments was not significantly altered. Rt of the ileum was not significantly affected by 5% CapMul MCM, while mannitol transport was 6 fold enhanced. Treatment of distal colon with 1% CapMul MCM reduced Rt by 95%, while mannitol transport was 100 fold enhanced. In a parallel experiment, mucosal(m)-to-serosal(s) transport of cephalexin, a beta-lactam antibiotic, in the ileum was about 40% reduced in the presence of 5% CapMul MCM, whereas transport in the s-to-m direction was 2.5 fold enhanced. Treatment of the distal colon with 1% CapMul MCM resulted in 25 fold enhancement of cephalexin transport in either direction. These results suggest that absorption enhancement by MCGs results from an increased permeability of the intestine confined to the villus or surface epithelium.

Formulation and intestinal absorption enhancement evaluation of water-in-oil microemulsions incorporating medium-chain glycerides.

We developed self-emulsifying water-in-oil (w/o) microemulsions incorporating medium-chain glycerides and measured their conductance, viscosity, refractive index and particle size. Formulation of Calcein (a water-soluble marker molecule, MW = 623), or SK&F 106760 (a water-soluble RGD peptide, MW = 634) in a w/o microemulsion having a composition of Captex 355/Capmul MCM/Tween 80/Aqueous (65/22/10/3, % w/w), resulted in significant bioavailability enhancement in rats relative to their aqueous formulations. Upon intraduodenal administration the bioavailability was enhanced from 2% for Calcein in isotonic Tris, pH 7.4 to 45% in the microemulsion and from 0.5% for SK&F 106760 in physiological saline to 27% in the microemulsion formulation. The microemulsion did not induce gross changes in GI mucosa at a dosing volume of 3.3 ml/kg. These results suggest that water-in-oil microemulsion systems may be utilized for enhancement of intestinal drug absorption.

Production of medium‐chain glycerides by immobilized lipase in a solvent‐free system

AbstractEnzymatic synthesis of medium‐ chain glycerides (MCGs) was studied by using capric acid (decanoic acid) and glycerol as substrates for immobilized lipase (LipozymeTM) without any solvents or surfactants. Quantitative analysis of the reaction mixture was conducted by using highperformance liquid chromatography (HPLC), which enabled the exact tracing of the capric glyceride synthesis. Oleic acid was also used for comparison. The esterification activity of Lipozyme was determined at 40°C in an open batch reactor; the activities were 400 and 200 units/g for the capric glyceride and oleic glyceride synthesis, respectively. Maximum initial reaction rate was obtained at 50°C for capric and 60°C for oleic glyceride synthesis. The time course of the capric glyceride synthesis was compared in terms of different molar ratios, from which we infer that this enzyme is 1,3‐ specific, but not absolute, in this esterification reaction. The final conversion was greatly influenced by the methods used to remove water, among which the cold trap method resulted in a noticeable improvement.

Effect of Medium-Chain Glycerides on the Intestinal Absorption of phenol red: Studies on Mechanisms of the Promoting Effect

To elucidate the mechanisms of the promoting action of medium-chain glyceride (MCG) on the intestinal absorption of phenol red (PR), the effect of different MCG dose levels on PR absorption, the absorption kinetics of MCG itself, and the mucosal reduced glutathione (GSH) levels were investigated to determine whether or not they are related to the promoting action of MCG. The absorption of PR was found to be enhanced with an increase in MCG dose (as an emulsion in the range 0.5–4.0%). Urinary excretion of PR was reduced by absorbed MCG components, which also resulted in an increase in the AUC. Moment analysis of plasma PR concentrations after intraintestinal administration revealed a shorter mean absorption time (MAT) for the emulsion formulation than for the control. The mucosal GSH level was lowered by the administration of the MCG emulsion (2–10%) into the intestinal lumen. Pretreatment with a 4% MCG emulsion decreased GSH levels to one-half of the control. In these cases, the level of mucosal GSH seemed to remain constant to the end of the experiment after it had decreased during the initial period. On the other hand, results from the in situ loop or recirculation study showed that enhancement of PR absorption appeared in the earlier period and then gradually decreased. The time course of the PR absorption rate, estimated from plasma concentration data, was similar to that of the MCG absorption rate. These results suggest that the promotion of intestinal absorption is related to the absorption kinetics of MCG itself, but not directly to the level of mucosal GSH.

Effect of medium-chain glycerides on the membrane transport of D-glucose and sulfanilic acid in the intestinal brush-border membrane vesicles.

To clarify the influence of medium-chain glycerides (MCG) on a biological membrane, we investigated the membrane transport of D-glucose and sulfanilic acid in the brush-border membrane (BBM) vesicles pretreated with MCG. The size distribution of the BBM vesicles determined by electron microscopic observation was not significantly different between the vesicles incorporated with MCG and those of the control. However, the amount of D-glucose taken up by the vesicles at an equilibrated stage (30 min) was significantly decreased in the MCG-treated ones based on unit content of protein. Based on these results we estimated the membrane transport of D-glucose and sulfanilic acid in consideration of vesiculation or filter-capturing efficiency in MCG-treated vesicles. The rates of Na+ gradient-independent D-glucose transport and sulfanilic acid transport were significantly greater in MCG-treated vesicles than in the control. On the other hand, the magnitude of overshooting effect in Na+ gradient-dependent uptake of D-glucose in MCG-treated vesicles was maintained similar to the control. Comparison of kinetic parameters for active D-glucose transport at different concentrations indicated that Km and Vmax were not significantly different between MCG-treated and the control vesicles. These results indicated that passive diffusion of D-glucose and sulfanilic acid was significantly increased but Na(+)-glucose cotransporter was not significantly changed by the incorporation of MCG in the intestinal BBM vesicles.

Effect of several enhancers on the skin permeation of water-soluble drugs.

Since the percutaneous absorption rates of water-soluble drugs are low in general, an enhancing system is needed when using the skin as an administration site for the drugs. We have investigated the effect of various penetration enhancers on the in vitro and in vivo percutaneous absorptions of catecholamine analogs, i.e. levodopa (LD), dopamine hydrochloride (DPH) and isoproterenol hydrochloride (IPH), as model water-soluble drugs. It was found that medium-chain glycerides (Sefsol 318) markedly enhanced the in vitro permeation of the drugs through excised hairless rat skin among the enhancers tested in the present experiments; the permeation rates with 5% Sefsol 318 in water were about 65, 34 and 53 times higher than the corresponding control (without enhancer) for LD, DPH and IPH, respectively. In addition, the in vivo percutaneous absorption experiments showed that the blood levels of these drugs after application of aqueous gels containing 5% Sefsol 318 on rat skin were higher than those in the absence of enhancer. Drug levels in the liver and kidney were also higher than without Sefsol 318. Percutaneous administration of DPH with Sefsol 318 to hairless rats resulted in lower diastolic blood pressure and a slightly higher heart rate with as compared to administration without the enhancer. These results suggest that Sefsol 318 is a potential candidate to enhance the transdermal absorption of water-soluble drugs.

Rectal absorption enhancement of des-enkephalin-gamma-endorphin (DE gamma E) by medium-chain glycerides and EDTA in conscious rats.

The stability of the neuroleptic peptide des-enkephalin-gamma-endorphin (DE gamma E; Org 5878) in the rectal lumen and the rectal bioavailability of DE gamma E were investigated in conscious rats. Furthermore, the influence of peptidase inhibition, peptidase saturation, and absorption enhancement on DE gamma E bioavailability were evaluated. Na2EDTA (0.25%, w/v) prolonged the degradation half-life of DE gamma E in the ligated colon from 33 +/- 7 to 93 +/- 45 min. Without adjuvant, tritium-labeled DE gamma E was absorbed from the rat rectum to a very low extent (0-4%). After administration of an excess of unlabeled DE gamma E or with Na2EDTA, comparable results were obtained. The medium-chain glyceride preparation MGK markedly enhanced the rectal DE gamma E bioavailability, up to 8-20%, which was further increased to 10-44% by coadministration of Na2EDTA. No substantial influence of varying the rectal delivery rate was observed. The results suggest that absorption enhancement and enzyme inhibition both are essential for effective increase of rectal peptide bioavailability.

Enhancement of membrane permeability to a poorly absorbed drug by medium-chain glycerides: effect of medium-chain glycerides on the release of phenol red from egg phosphatidylcholine liposomes.

The influence of medium-chain glyceride (MCG) on the membrane permeability was investigated. Liposomes with a basal composition of egg phosphatidylcholine : cholestero=4 : 1 were used to examine the effect of MCG and its components on the release of phenol red (PR) through the liposomal membrane by the dynamic dialysis method. With increase of MCG content in the membrane, the release of PR was enhanced. Among MCG components tested, dicaprylglyceride and tricaprylglyceride enhanced the release. When MCG emulsion was added to the control liposome suspension, PR was released more rapidly than from liposome without addition of MCG emulsion. To investigate the mechanism of the enhancement of membrane permeability, the effect of temperature on the release of PR was examined. The activation energies calculated from the slope of Arrhenius plots did not change significantly with the addition of MCG, so that it was unclear whether the change of membrane permeability could be correlated with the membrane fluidity.

Enhanced membrane permeability to phenol red by medium-chain glycerides: studies on the membrane permeability and microviscosity.

To clarify the mechanism of the drug absorption enhancement by medium-chain glycerides (MCG), the changes in membrane permeability provoked by MCG were investigated with liposomal uptake experiments. Uptake of phenol red (PR) into liposomes increased with an increase in MCG content in the liposomal membrane, suggesting that PR absorption was enhanced in the "transcellular route." However, the apparent membranous microviscosity obtained in fluorescence depolarization studies tended to increase with the addition of MCG in both the hydrophobic core and the polar head regions of the liposomal membrane. Thus, an enhancement in membrane permeability caused by MCG was not accompanied by a decrease in the apparent membranous microviscosity.

Effect of medium chain glycerides on enteral and rectal absorption of beta-lactam and aminoglycoside antibiotics.

The rat enteral and rabbit rectal models were utilized to study the effect of Capmul (medium chain glycerides) on the absorption of a selection of beta-lactam and aminoglycoside antibiotics. All tested non-orally available beta-lactam antibiotics (cefamandole, cefotaxime, moxalactam, cefoxitin, mezlocillin, carumonam, penicillin G and amdinocillin) showed increased absorption enterally in rats and rectally in rabbits when formulated with Capmul. The orally available beta-lactam antibiotics, cephalexin and cephradine, were not enhanced in their enteral or rectal absorption by Capmul in the two model systems. Ampicillin absorption was enhanced rectally and enterally by Capmul. Rectal absorption of the aminoglycoside antibiotics, tobramycin and gentamycin, was enhanced by Capmul while enteral absorption was not.

Effect of medium-chain glycerides on the intestinal absorption and the hepatobiliary transport of Phenol red

The effects of medium-chain glyceride (MGK) on the intestinal absorption and the hepatobiliary transport of Phenol red (PR) were investigated in rats. The in situ recirculation experiment using the small intestine showed that disappearance of PR from the recirculated MGK emulsion at a lipid content of 4% was over 5 times greater than that from the buffer solution, although the effect diminished with the increase of the lipid content. On the contrary, in the everted sac experiments, mucosal to serosal transport of PR from MGK emulsion was reduced to about one half of the control, and the pretreatment with PR-free MGK emulsion could not enhance PR disappearance from the buffer solution recirculated successively. The effect of a polyoxyethylene derivative of castor oil (HCO-100) employed for emulsion preparation on the transport of PR was investigated by the everted sac experiments. The amount of PR transported was decreased with the increase of HCO-100 in the range of 0.1–2.0%. These results may suggest that other factors are related with the promoting effect except for the membrane permeability. When the absorption of MGK components was examined by in situ and in vitro studies, the disappearance of MGK components in the former was nearly twice of that in the latter. The inhibiting effect of MGK on the biliary excretion of PR was observed in the in situ recirculation study with MGK emulsion containing PR. The biliary excretion percent of PR was also significantly reduced by injecting the components of MGK into the mesenteric vein.

Effect of medium-chain glycerides (MGK) on the intestinal absorption and the hepatobiliary transport of bromthymol blue.

The effect of medium chain glyceride (MGK) emulsion on the intestinal absorption and the biliary excretion of bromthymol blue (BTB) was investigated in rats. Extensive tissue accumulation of BTB was reduced when BTB was administered with MGK emulsion formulation. HCO-100, an emulsifier, was also important for the decrease in the tissue accumulation of BTB. The ratios of absorption percent to tissue accumulation percent and to free fraction, not contained in the droplet of emulsion, in MGK emulsion were much greater than that of the control. Pretreatment with BTB-free emulsion reduced BTB absorption under the control, although tissue accumulation was not affected. The absorption appeared to decrease with increase in the time of pretreatment. The effect of leaving treatment after pretreatment on the absorption of BTB was also investigated. With the increase in leaving time after pretreatment, reduced absorption tended to resume to the level of control. The change in monocaprylate content from 54 to 60% in MGK made a difference in BTB absorption and it was suggested that monocaprylate content in MGK was one of the significant factors of MGK emulsion on drug absorption. Bile recovery study was simultaneously carried out with an in situ recirculation experiment. The recovery of BTB into bile tended to decrease. The ratio of recovery percent of BTB into bile to the absorption percent of BTB also decreased extensively, which is possibly another effect of MGK on drug disposition.

Improvement of bioavailability of poorly absorbed drugs. II. Effect of medium chain glyceride base on the intestinal absorption of cefmetazole sodium in rats and dogs.

The effect of medium chain glyceride (MCG) on the intestinal absorption of cefmetazole sodium (CMZ) was investigated in rats and dogs. In rats, MCG containing glyceryl mono-, di- and tri-caprylate enhanced the intestinal absorption of CMZ after intraduodenal administration, though the promoting effect of MCG was less than that after rectal administration. The promoting effect of MCG was found to be mainly due to glycerylmonocaprylate and dependent on the dosage of MCG. The plasma CMZ levels after intraduodenal administration as MCG solution tended to be slightly higher than those observed after administration as MCG emulsion, though the differences were found to be statistically insignificant. Moreover, the intestinal absorption of CMZ after intraduodenal administration as MCG emulsion was decreased significantly by increasing the amount of water in the emulsion. The promoting effect of MCG in dogs was more clearly demonstrated in the lower intestine than in the upper intestine. Furthermore, the oral bioavailability of pharmaceutical formulations of CMZ was also investigated in dogs. When enteric coated capsules filled with MCG solution were administered to dogs, the bioavailability of CMZ was enhanced significantly.

Improvement of bioavailability of poorly absorbed drugs. IV. Mechanism of the promoting effect of medium chain glyceride on the rectal absorption of water soluble drugs.

The mechanisms of the promoting effect of medium chain glyceride (MCG) containing glyceryl mono-, di- and tri-caprylate on rectal absorption of water soluble drugs were investigated. It was found that the solubility behavior of the drugs in mucosal fluids on the surface of the membrane are critical factor for the enhanced rectal absorption. Moreover, the drugs to be readily absorbed from MCG base may be ones of low partition coefficients to MCG phase as well as high solubility in water. And it was found that MCG can't be absorbed from the rectum, different from oral administration, suggesting an interaction of MCG with absorption membrane, rather than the carrier effect of MCG itself. Furthermore, from the results in the pretreatment experiments and additional administration of MCG alone, it was suggested that the interactions of MCG with the membrane components, as well as the induction of biological or physiological changes, may be at least partly responsible for the promoting effect of MCG.

Improvement of bioavailability of poorly absorbed drugs. III. Oral acute toxicity and local irritation of medium chain glyceride.

Oral acute toxicity of medium chain glyceride (MCG) was studied in mice and rats. In mice and rats, clinical signs such as irregular respiration, laxity of movement, staggering gait and loss of righting reflex appeared after single oral administration of MCG at a relatively large dose. The LD50 values determined in male and female mice were 26.9 and 28.5 ml/kg, and in male and female rats were 27.4 and 26.7 ml/kg, respectively. In order to evaluate the biological safety of MCG suppository of cefmetazole sodium (CMZ), its local irritation on the mucous membrane was studied. Primary eye irritation of MCG suppository of CMZ was studied in rabbits. Although mild irritation was seen in conjunctivae, no remarkable changes were observed in cornea and iris. Furthermore, primary effect of MCG suppository of CMZ on the rectal mucous membrane was studied macro- and microscopically. It was observed that remarkable histological changes of rectal mucous membrane by MCG suppository of CMZ were not observed in all animals used.

Improvement of bioavailability of poorly absorbed drugs. V. Effect of surfactants on the promoting effect of medium chain glyceride for the rectal absorption of beta-lactam antibiotics in rats and dogs.

The promoting effects of medium chain glyceride (MCG) on the rectal absorption of beta-lactam antibiotics were compared among various experimental animals (such as rats, rabbits and dogs). The plasma levels of cefmetazole (CMZ) after rectal administration, when MCG was used as the vehicle, significantly increased in all animals, but the bioavailability of CMZ was greatly varied among the animal species; the bioavailability of CMZ in dogs was apparently less than those in other animals (rats = rabbits greater than dogs). However, in dogs, the promoting effect of MCG on the rectal absorption of CMZ increased by addition of nonionic surfactants such as ether-type (Brij 30 and Brij 35) and ester type (Nikkol MYL-10). And the promoting effect of surfactants in the MCG vehicle is not always correlated with blood hemolysis, suggesting contribution of other physicochemical or biological factors.