Intercalation of atorvastatin and valsartan into Mg-Al layered double hydroxide host using a restacking procedure
Abstract
Anionic drugs very poorly soluble in water, namely antidyslipidemic atorvastatin and antihypertensive valsartan were intercalated into Mg-Al LDH host using a restacking procedure, when the drugs, dissolved in ethanol, were added to aqueous dispersion of LDH nanosheets, prepared by direct coprecipitation of Mg and Al nitrates in excess of aqueous ammonia solution under nitrogen. Despite the large size of intercalated molecules, the products with high drug loading were obtained; the content 75.8 wt% of atorvastatin and 43.7 wt% of valsartan corresponded to 100 and 60% of the LDH anion exchange capacity, respectively.
A marked increase in d003 basal spacing from 0.876 to 3.808 and 2.068 nm observed in powder XRD patterns of the LDH intercalated with atorvastatin and valsartan, respectively, confirmed the intercalation of both drugs into the LDH interlayer. The computational modeling applying the force field methods was used to calculate the most probable arrangement of the interlayer components at the atomic scale through energy minimization.
The final models showed good agreement between the calculated and experimentally determined d003 basal spacing values. Results of the molecular modeling confirmed weak electrostatic interactions between LDH layers and terminal carboxyl groups in the drug molecules, together with bonding between the valsartan tetrazole rings and the LDH layers.
Such interactions accompanied by deprotonation of carboxyl groups and tetrazole rings in the intercalated products were indicated by the FTIR and NMR measurements. The intercalation of drugs into LDH host slightly affected their back-release in aqueous media.
In the phosphate buffer, slower atorvastatin release from the intercalated product compared to the sample containing atorvastatin calcium salt was observed, whereas enhanced valsartan release from the intercalated sample was found in the diluted HCl. The measured release profiles corresponded to the pseudo-second-order kinetics, indicating an intraparticle diffusion as the rate-limiting step.