The absence of an intestinal absorption sink is a significant weakness of standard in vitro lipolysis methods, potentially leading to poor prediction of in vivo performance and an overestimation of drug precipitation. In addition, the majority of the described lipolysis methods only attempt to simulate intestinal conditions, thus overlooking any supersaturation or precipitation of ionizable drugs as they transition from the acidic gastric environment to the more neutral conditions of the intestine. The aim of this study was to develop a novel lipolysis method incorporating a two-stage gastric-to-intestinal transition and an absorptive compartment to reliably predict in vivo performance of lipid-based formulations (LBFs). Drug absorption was mimicked by in situ quantification of drug partitioning into a decanol layer. The method was used to characterize LBFs from four studies described in the literature, involving three model drugs (i.e., nilotinib, fenofibrate, and danazol) where in vivo bioavailability data have previously been reported. The results from the novel biphasic lipolysis method were compared to those of the standard pH-stat method in terms of reliability for predicting the in vivo performance. For three of the studies, the novel biphasic lipolysis method more reliably predicted the in vivo bioavailability compared to the standard pH-stat method. In contrast, the standard pH-stat method was found to produce more predictive results for one study involving a series of LBFs composed of the soybean oil, glyceryl monolinoleate (Maisine CC), Kolliphor EL, and ethanol. This result was surprising and could reflect that increasing concentrations of ethanol (as a cosolvent) in the formulations may have resulted in greater partitioning of the drug into the decanol absorptive compartment. In addition to the improved predictivity for most of the investigated systems, this biphasic lipolysis method also uses in situ analysis and avoids timeand resource-intensive sample analysis steps, thereby facilitating a higher throughput capacity and biorelevant approach for characterization of LBFs.
The concept of using
precipitation inhibitors (PIs) to sustain
supersaturation is well established for amorphous formulations but
less in the case of lipid-based formulations (LBF). This study applied
a systematic
in silico
–
in vitro
–
in vivo
approach to assess the merits of
incorporating PIs in supersaturated LBFs (sLBF) using the model drug
venetoclax. sLBFs containing hydroxypropyl methylcellulose (HPMC),
hydroxypropyl methylcellulose acetate succinate (HPMCAS), polyvinylpyrrolidone
(PVP), PVP-
co
-vinyl acetate (PVP/VA), Pluronic F108,
and Eudragit EPO were assessed
in silico
calculating
a drug–excipient mixing enthalpy,
in vitro
using a PI solvent shift test, and finally, bioavailability was
assessed
in vivo
in landrace pigs. The estimation
of pure interaction enthalpies of the drug and the excipient was deemed
useful in determining the most promising PIs for venetoclax. The sLBF
alone (i.e., no PI present) displayed a high initial drug concentration
in the aqueous phase during
in vitro
screening. sLBF
with Pluronic F108 displayed the highest venetoclax concentration
in the aqueous phase and sLBF with Eudragit EPO the lowest.
In vivo
, the sLBF alone showed the highest bioavailability
of 26.3 ± 14.2%. Interestingly, a trend toward a decreasing bioavailability
was observed for sLBF containing PIs, with PVP/VA being significantly
lower compared to sLBF alone. In conclusion, the ability of a sLBF
to generate supersaturated concentrations of venetoclax
in
vitro
was translated into increased absorption
in
vivo
. While
in silico
and
in vitro
PI screening suggested benefits in terms of prolonged supersaturation,
the addition of a PI did not increase
in vivo
bioavailability.
The findings of this study are of particular relevance to pre-clinical
drug development, where the high
in vivo
exposure
of venetoclax was achieved using a sLBF approach, and despite the
perceived risk of drug precipitation from a sLBF, including a PI may
not be merited in all cases.
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