The aim of this study was to develop
hydrophobic ionic drug polymer
complexes in order to provide sustained drug release from self-emulsifying
drug delivery systems (SEDDS). Captopril (CTL) was used as an anionic
model drug to form ionic complexes with the cationic polymers Eudragit
RS, RL, and E. Complexes of polymer to CTL charge ratio 1:1, 2:1,
and 4:1 were incorporated in two SEDDS, namely FA which was 40% Kolliphor
RH 40, 20% Kolliphor EL, and 40% castor oil and FB, which was 40%
Kolliphor RH 40, 30% glycerol, 15% Kolliphor EL, and 15% castor oil.
Blank and complex loaded SEDDS were characterized regarding their
droplet size, polydispersity index (PDI), and zeta potential. Resazurin
assay was performed on Caco-2 cells to evaluate the biocompatibility
of SEDDS. Release of CTL from SEDDS was determined in release medium
containing 0.2 mg/mL of 5,5′-dithiobis(2-nitrobenzoic
acid) (DNTB) allowing quantification of free drug released into solution
via a thiol/disulfide exchange reaction between CTL and DNTB forming
a yellow dye. The droplet size of SEDDS FA and SEDDS FB were in the
range of 100 ± 20 nm and 40 ± 10 nm, respectively, with
a PDI < 0.5. The zeta potential of SEDDS FA and SEDDS FB increased
after the incorporation of complexes. Cell viability remained above
80% after incubation with SEDDS FA and SEDDS FB in a concentration
of 1% and 3% for 4 h. Without any polymer, CTL was entirely released
from both SEDDS within seconds. In contrast, the higher the cationic
lipophilic polymer to CTL ratio in SEDDS, the more sustained was the
release of CTL. Among the polymers which were evaluated, Eudragit
RL provided the most sustained release. SEDDS FA containing Eudragit
RL and CTL in a ratio of 1:1 released 64.78 ± 8.28% of CTL, whereas
SEDDS FB containing the same complex showed a release of 91.85 ±
1.17% within 1 h. Due to the formation of lipophilic ionic polymer
complexes a sustained drug release from oily droplets formed by SEDDS
can be achieved. Taking into account that drugs are otherwise instantly
released from SEDDS, results of this study might open the door for
numerous additional applications of SEDDS for which a sustained drug
release is essential.