A new application of lipid nanoemulsions as coating agent, providing zero-order hydrophilic drug release from tablets

Abstract

The objective of the present investigation was to evaluate potential of nanoemulsions as a coating material for the tablets. The nanoemulsion of size less than 100 nm was prepared using a simple and low-energy spontaneous emulsification method. Conventional tablets containing theophylline as a model hydrophilic drug were prepared. The theophylline tablets were coated with the nanoemulsion using a fluid bed coater. The effect of different levels of the nanoemulsion coating on the theophylline release was evaluated. The theophylline tablets containing different levels of the nanoemulsion coating could be successfully prepared. Interestingly, the coating of tablet with the nanoemulsion resulted in zero-order release of theophylline from the tablets. The noncoated theophylline tablets release the entire drug in less than 2 minutes, whereas nanoemulsion coating delayed the release of theophylline from tablets. This investigation establishes the proof of concept for the potential of nanoemulsions as a coating material for tablets.

Figure 1

Nanoemulsions formulated with low-energy spontaneous emulsification. Surfactant = Cremophor RH40 oil = Labrafil M1944CS. Hydrodynamic diameter (filled circles) and polydispersity index (open squared) are plotted against the surfactant/oil weight ratio (SOR).

Figure 2

Theophylline release profiles from tablets (A) for different levels of nanoemulsion coating: 2%, 5%, 6.5% and 7.8%, and without coating (noncoated tablets).

Figure 3

Theophylline release profiles from tablets (b) for different levels of nanoemulsion coating: 2%, 5.5%, 6%, and 7.6%, and without coating (noncoated tablets). The two graphs show the same results with different time scale, in order to emphasize the different release regimes arising for 2% and 5% (for which the frontiers between both are indicated by the arrows).

Figure 4

SEM micrographs of the tablets formulation (A). Observations performed on the tablet surface (top) and inside (bottom), for noncoated tablets and nanoemulsions coated (NE-coated).

Figure 5

SEM micrographs of the tablets formulation (B). Observations performed on the tablet surface (top) and inside (bottom), for noncoated tablets and nanoemulsions coated (NE-coated).

Figure 6

Interpretations of the drug release behaviors from Figure 3. Theophylline release from tablets (b), for different levels of nanoemulsion coating: 2%, 5.5%, 6%, and 7.6%, and noncoating tablets.