Category: Formulation and Quality
Purpose: Utility of in vitro flux measurements in formulation development and bioequivalence prediction have been explored in a number of recent studies [1 - 3] The benefits of such measurements are based on the fact that they capture the complex interplay between effects of formulation ingredients on solubility, dissolution rate and permeability of an active pharmaceutical ingredient (API). This work extends usage of flux values for predictive biopharmaceutics modelling, namely by using them as input parameter for calculation of maximum absorbable dose (MAD) or fraction of the API absorbed (Fa) from an oral dosage form. This study explores a feasibility of using flux measurements through gastro-intestinal tract (GIT) mimicking artificial membrane to predict MAD and Fa values in biopharmaceutics modelling for BCS Class 2 drugs.
Methods: Several commercially available drug products of Itraconazole (ITZ), Telmisartan (TMS), Albendazole (ABZ) and Carbamazepine (CBZ) were used for the study. Flux measurements were performed using BioFLUX™ instruments (Pion Inc.). In this apparatus all formulations were introduced to the donor compartments containing 200 mL of simulated gastric fluid (SGF). After 30 min of dissolution assay the SGF medium was transformed into 250 mL of FaSSIF and absorption chamber containing 16 mL of absorption sink buffer (ASB, Pion Inc) was introduced to allow permeation of the drug. For fed condition studies FeSSIF was used with no conversion step. The donor and acceptor chambers were separated by a filter-supported artificial lipophilic membrane (Double-Sink™ PAMPA model, Pion Inc. ) with area 3.7 cm2. The concentration of API was monitored in the acceptor and in the donor (when possible) compartments by fiber optic dip probes connected to the Rainbow® instrument (Pion Inc.). Flux was calculated based on the slope of the concentration – time profiles in the acceptor (µg mL-1 min-1) and multiplying this value by a ratio of the volume in the acceptor divided by the membrane area (mL cm-2). All measurements were performed at 37 ºC. A modelling approach was based on the extended framework described elsewhere .
Results: An initial flux of ITZ from Sporanox® capsules (100 mg dose) was measured to be 0.42 µg min-1 cm-2 in FeSSIF while flux from the HP-b-CD based Sporanox® solution of ITZ was twice of that value. Using the described model the predicted fraction absorbed for ITZ was estimated to be 32% for Sporanox capsules while ~ 65% for the solution that was in a good agreement with reported value of 85%  for absorption of ITZ solution. It was estimated that 40 mg dose of both the brand name TMS (initial flux 0.80 µg min-1 cm-2) and the generic forms of TMS (initial flux 0.67 µg min-1cm-2) a 100% absorption would be expected while 90% Fa was reported in humans . ABZ precipitated upon media transformation from SGF to FaSSIF, however it seemed to create a colloidal phase and stayed at concentration of ~ 30 µg/mL while its crystalline solubility in FaSSIF was only 0.5 µg/mL. The flux of ABZ was changing from 0.16 µg min-1 cm-2 immediately after transformation to 0.05 µg min-1 cm-2 after 5 hours of experiment. Considering Fluxmax MAD for ABZ was estimated to be 11 mg or 5.5% of 200 mg dose. For CBZ estimations for Fa were 68% for 200 mg IR dose and 42% for 400 mg IR dose while human absorption for these doses were reported to be 100% and 75% respectively.
Conclusion: The feasibility study demonstrated that flux values measured under the biorelevant conditions could be used as input parameters for biopharmaceutics modelling and simulations. The flux measurements capture the influence of formulations on all key physicochemical parameters affecting oral absorption. A follow up investigation is setup to validate and augment this approach by comparing predicted Fa based on in vitro flux results to the reported in vivo Fa values for a larger set of drugs.
Enikő Borbás– Budapest University of Technology and Economics, Budapest, Budapest, Hungary
Oksana Tsinman– Pion Inc., Billerica, Massachusetts
Bálint Sinkó– Manager, Technology Development, Pion Inc., Billerica, Massachusetts