Alejandro Pérez-Pitarch (1,2,3), Laura Higueras (1,2), Isabel Lozoya-Agulló (1,2,4), Virginia Merino (1,2), Amparo Nácher (1,2), Matilde Merino-Sanjuán (1,2)
(1) Department of Pharmacy and Pharmaceutical Technology and Parasitology. University of Valencia, Valencia, Spain (2) Molecular Recognition and Technological Development Institute. Mixed Unit Polytechnic University of Valencia and University of Valencia, Spain. (3) Pharmacy department. University Clinical Hospital of Valencia. Valencia. Spain. (4) Department of Pharmacokinetics and Pharmaceutical Technology. Miguel Hernandez University. Alicante. Spain
Objectives: The influence of undernutrition on the intestinal absorption of gefitinib, a tyrosine kinase inhibitor, has not been previously evaluated. The main objective of the present study was to investigate the impact of nutritional status on gefitinib intestinal absorption in well- and undernourished rats.
Methods: Absorption studies for gefitinib were performed in male Wistar rats in accordance with the 2010/63/EU directive of 22 September 2010 regarding the protection of animals used for scientific experimentation. In order to provoke adequate protein energy malnutrition, the malnutrition protocol developed by Merino-Sanjuán et al. was employed (1). Assayed gefitinib concentrations were 8 μg/mL and 40 μg/mL in free solutions. Additionally, a gefitinib solution (40 μg/mL) with sodium azide (6500 μg/mL) – a metabolic inhibitor – was assayed. All solutions were buffered to pH 5.0 by addition of 1% (V/V) Sørensen phosphate buffer solution. Drug solutions (5 mL at 37°C) were introduced into the proximal and distal isolated intestinal segments. Samples of 200 µL were collected every 5 minutes up to a period of 30 minutes and gefitinib concentrations were determined chromatographically using an HPLC equiped with a UV detector (330 nm) and C18 column. Mobile phase consisted of acetonitrile/water acidified with trifluoroacetic acid (0.1%, pH = 2.5) (55:45). Thereafter, pharmacokinetic models were developed through non-linear mixed effects modelling using the NONMEM software, version 7.3 (2) to describe the intestinal lumen concentration-time profiles.
Results: Data was best described by a Weibull model (3-5), as described by the following equation:
dL/dt= -(α·L/β)·(t·α) β-1
where L represents drug concentration in intestinal lumen. The scaling factor α (hours-1) is proportional to the slope of the disappearance kinetics, and the shape factor β (dimensionless) determines the curvature of the disappearance kinetics.
A correction fraction (fr) was included in the final model to account for the fraction of initial concentration available for absorption from the intestinal lumen to the enterocyte (6). The final model considered an fr parameter for the 40 µg/mL gefitinib solution (fr40 < 1) but not for 8 µg/mL gefitinib solution (fr8 = 1). Statistically significant differences were not found for model parameters and between intestinal segments. On the other hand, parameter fr40 proved to be 19% higher for the proximal intestine (fr40 = 0.606) than for the distal segment (fr40 = 0.510). Regarding sodium azide administration and undernutrition status, statistically significant differences between groups were not evidenced in model parameters.
Conclusions: The results of the covariate analysis indicated that disappearance-rate of gefitinib from intestinal lumen is not influenced by undernourishment nor by the presence of azide at the used concentration. These results are in accordance with some of the previous studies, which indicate that gefitinib absorption is not dependent on active transporters and thus the absorption process for gefitinib is most probably governed by a passive diffusion process.
References:
[1] Merino-Sanjuán M, Catalán-Latorre A, Nácher A, Miralles-Arnau S, Jiménez-Torres NV. Animal model of undernutrition for the evaluation of drug pharmacokinetics. Nutr Hosp. 2011; 26(6):1296-304.
[2] TBauer, R. J. NONMEM USERS GUIDE. (2015). at https://nonmem.iconplc.com/nonmem730/Latest_User_Documents/guides/nm730.pdf.
[3] P. Macheras, A. Dokoumetzidis. On the heterogeneity of drug dissolution and release. Pharm Res. 17, 108-112 (2000).
[4] K. Kosmidis et al. A re-appraisal of drug release laws using Monte-Carlo simulations: the prevalence of the Weibull function. Pharm Res. 20, 988-995 (2003).
[5] V. Papadopoulou et al. On the use of the Weibull function for the discernment of drug release mechanisms. Int J Pharm. 309, 44-50 (2006)
[6] Munoz MJ, Merino-Sanjuan M, Lledo-Garcia R, Casabo VG, Manez-Castillejo FJ, Nacher A. Use of nonlinear mixed effect modeling for the intestinal absorption data: application to ritonavir in the rat. Eur J Pharm Biopharm. 2005 Sep;61(1-2):20-6.
Reference: PAGE 27 (2018) Abstr 8453 [www.page-meeting.org/?abstract=8453]
Poster: Drug/Disease Modelling - Absorption & PBPK