Intestinal Bile Secretion Promotes Drug Absorption from Lipid Colloidal Phases via Induction of Supersaturation

Toward an improved understanding of the precipitation behavior of weakly basic drugs from oral lipid-based formulations

The aim of the present study was to analyze the impact of lipid-based formulation (LBF) dispersion and digestion on the precipitation behavior of weakly basic drugs. Loratadine and carvedilol were formulated in a range of LBFs and drug solubilization was analyzed under simulated dispersive and digestive conditions (fasted state). The extent of supersaturation and drug precipitation as well as the solid-state properties and redissolution behavior of precipitated drugs were assessed. X-ray powder diffraction indicated that carvedilol precipitated in a crystalline form upon dispersion, but interestingly, this drug gave an amorphous precipitate during lipolysis. In contrast, loratadine precipitated as crystalline material during both formulation dispersion and digestion. No influence of the formulation composition on the type of precipitation was observed. These results suggested that in vitro conditions (dispersive versus digestive) largely influenced the solid-state properties of precipitating weak bases. Solid-state characterization of precipitated drugs under different experimental conditions should be routinely performed in formulation screening to better understand the biopharmaceutical behavior of LBFs. Hence, these findings are of high practical importance for the pharmaceutical development and in vitro assessment of LBFs using weakly basic drugs.

In vitro-in vivo correlation of the effect of supersaturation on the intestinal absorption of BCS Class 2 drugs

The aim of this study was to establish an in vitro method for evaluating the effect of supersaturation on oral absorption of poorly water-soluble drugs in vivo. Albendazole, dipyridamole, gefitinib, and ketoconazole were used as model drugs. Supersaturation of each drug was induced by diluting its stock solution by fasted state simulated intestinal fluid (FaSSIF) (solvent-shift method), then dissolution and precipitation profile of the drug was observed in vitro. The crystalline form of the precipitate was checked by differential scanning calorimetry (DSC). For comparison, control suspension was prepared by suspending a drug powder directly into FaSSIF (powder-suspending method). In vivo intestinal absorption of the drug was observed in rats by determined the plasma concentration after intraduodenal administration of drug suspensions. For all drugs, suspensions prepared by solvent-shift method showed significantly higher dissolved concentration in vitro than that prepared by powder-suspending method, clearly indicated the induction of supersaturation. DSC analysis revealed that crystalline form of the precipitate profoundly affects the extent and the duration of supersaturation. A rat in vivo study confirmed that the supersaturation of these drugs increased the fraction absorbed from the intestine, which corresponded well to the in vitro dissolution and precipitation profile of drugs except for ketoconazole. For ketoconazole, an in vivo absorption study was performed in rats pretreated with 1-aminobenzotriazole, a potent inhibitor of CYP mediated metabolism. CYP inhibition study suggested that the high luminal concentration of ketoconazole caused by supersaturation saturated the metabolic enzymes and further increased the systemic exposure of the absorbed drug. The additional effects of supersaturation on the absorption of ketoconazole are consistent with previous studies in humans under differing gastric pH conditions. In conclusion, effects of supersaturation on the intestinal absorption of poorly water-soluble drugs could be predicted from in vitro dissolution and a precipitation study. However if supersaturation affects the pharmacokinetic profiles of drugs, such as a first-pass metabolism, a combination with in vivo study should be required to evaluate its impact on oral bioavailability.

Solid self-nanoemulsifying drug delivery system (S-SNEDDS) for oral delivery of glimepiride: development and antidiabetic activity in albino rabbits

CONTEXT

This study presents novel self-nanoemulsifying drug delivery system potential of oral delivering which leads poorly aqueous soluble drug glimepiride.

OBJECTIVE

The objective of this study was to prepare solid self-nanoemulsifying drug delivery system (S-SNEDDS) for the improved oral delivery of glimepiride and to evaluate its therapeutic efficacy in albino rabbits.

RESULTS AND DISCUSSION

The droplet size analyses revealed a droplet size of less than 200 nm. The solid state characterization of S-SNEDDS by scanning electron microscopy (SEM), X-ray powder diffraction and differential scanning calorimetry (DSC) revealed the absence of crystalline glimepiride in the S-SNEDDS. The in vitro dissolution studies revealed that the significant improvement in glimepiride release characteristics. The effect of S-SNEDDS on therapeutic efficacy of glimepride was assessed in albino rabbits by monitoring blood glucose levels and compared with free drug suspension, L-SNEDDS. The S-SNEDDS showed significant (p < 0.05) increase in in vitro drug release and therapeutic efficacy as compared with free drug.

CONCLUSION

This study demonstrated that S-SNEDDS is a promising novel drug delivery system of glimepride to enhance oral delivery.

Excipient foods: designing food matrices that improve the oral bioavailability of pharmaceuticals and nutraceuticals

The oral bioavailability of many lipophilic bioactive agents (pharmaceuticals and nutraceuticals) is limited due to various physicochemical and physiological processes. Excipient foods can be designed to improve the oral bioavailability of these bioactive agents.

Toward the establishment of standardized in vitro tests for lipid-based formulations, part 3: understanding supersaturation versus precipitation potential during the in vitro digestion of type I, II, IIIA, IIIB and IV lipid-based formulations

PURPOSE

Recent studies have shown that digestion of lipid-based formulations (LBFs) can stimulate both supersaturation and precipitation. The current study has evaluated the drug, formulation and dose-dependence of the supersaturation - precipitation balance for a range of LBFs.

METHODS

Type I, II, IIIA/B LBFs containing medium-chain (MC) or long-chain (LC) lipids, and lipid-free Type IV LBF incorporating different doses of fenofibrate or tolfenamic acid were digested in vitro in a simulated intestinal medium. The degree of supersaturation was assessed through comparison of drug concentrations in aqueous digestion phases (APDIGEST) during LBF digestion and the equilibrium drug solubility in the same phases.

RESULTS

Increasing fenofibrate or tolfenamic acid drug loads (i.e., dose) had negligible effects on LC LBF performance during digestion, but promoted drug crystallization (confirmed by XRPD) from MC and Type IV LBF. Drug crystallization was only evident in instances when the calculated maximum supersaturation ratio (SR(M)) was >3. This threshold SR(M) value was remarkably consistent across all LBF and was also consistent with previous studies with danazol.

CONCLUSIONS

The maximum supersaturation ratio (SR(M)) provides an indication of the supersaturation 'pressure' exerted by formulation digestion and is strongly predictive of the likelihood of drug precipitation in vitro. This may also prove effective in discriminating the in vivo performance of LBFs.