Absorption of drug substances across the intestinal epithelium is a complex and dynamic process. Counter transport proteins are responsible for the efflux of specific drug molecules after they have been absorbed. One of the key counter transport efflux proteins, which is of importance in this study, is P–glycoprotein. The efflux pump P–glycoprotein plays a major role in altering the pharmacokinetics of a wide variety of drugs limiting their absorption and therefore also bioavailability. Many flavonoids have been shown to interact with P–glycoprotein mediated efflux in vitro studies. Numerous in vitro methods have been used to study drug absorption across the intestinal membranes, but it is often not possible to use only one in vitro model to accurately predict permeability characteristics. The purpose of this study was to determine the effect of four selected hydroxy– and methoxy– flavonoids on the in vitro transport of Rhodamine 123, a known P–gp substrate, across excised rat and pig intestinal tissue using the Sweetana–Grass diffusion apparatus. The results were further used to determine if the two different animal tissue models corresponded with regard to the flavonoids' effects on P–glycoprotein related efflux. Two control groups were included in the experimental design. In the negative control group, the transport of Rhodamine 123 was tested alone and no modulator was added. In the positive control group, the transport of Rhodamine 123 was determined in the presence of Verapamil, which is a known P–glycoprotein inhibitor. The experiments with the flavonoids Morin, Galangin, 6–Methoxyflavone and 7–Methoxyflavone were done in triplicate to determine repeatability of the results. The transport of Rhodamine 123 was evaluated in both the apical to basolateral (absorptive) and basolateral to apical (secretory) directions. The relative transport of Rhodamine 123, the apparent permeability coefficient (P app) values and flux (J) values in both directions as well as the efflux ratio (ER) and net flux (J net) were calculated. The concentration Rhodamine 123 present in the acceptor chamber was determined by means of a validated HPLC method. Statistical analysis was used to compare the results of the test groups with the control groups in order to indicate significant differences. It has been found that Morin, Galangin and 6–Methoxyflavone have a significant inhibitory effect on the Rhodamine 123 efflux (probably P–glycoprotein related) in both the rat and pig intestinal tissue models with p–values smaller than 0.05. On the other hand, 7–Methoxyflavone showed a significant effect on the efflux of Rhodamine 123 in the pig intestinal tissue model (p < 0.05) but not in the rat intestinal tissue model (p > 0.05). These flavonoids may increase the bioavailability of drugs that are substrates for P–glycoprotein and thereby cause clinically significant pharmacokinetic interactions, however, this should be confirmed with in vivo studies. On the other hand, these flavonoids may be used for drug absorption enhancement when applied under controlled circumstances. With regard to the different animal tissue models used it can be concluded that data obtained from the rat intestinal tissue model cannot be compared and extrapolated to data obtained from the pig intestinal tissue model. It is recommended that the in vitro results be correlated to in vivo findings to identify the most suitable model. / Thesis (M.Sc. (Pharmaceutics))--North-West University, Potchefstroom Campus, 2011.

Absorption of drug substances across the intestinal epithelium is a complex and dynamic process. Counter transport proteins are responsible for the efflux of specific drug molecules after they have been absorbed. One of the key counter transport efflux proteins, which is of importance in this study, is P–glycoprotein. The efflux pump P–glycoprotein plays a major role in altering the pharmacokinetics of a wide variety of drugs limiting their absorption and therefore also bioavailability. Many flavonoids have been shown to interact with P–glycoprotein mediated efflux in vitro studies. Numerous in vitro methods have been used to study drug absorption across the intestinal membranes, but it is often not possible to use only one in vitro model to accurately predict permeability characteristics. The purpose of this study was to determine the effect of four selected hydroxy– and methoxy– flavonoids on the in vitro transport of Rhodamine 123, a known P–gp substrate, across excised rat and pig intestinal tissue using the Sweetana–Grass diffusion apparatus. The results were further used to determine if the two different animal tissue models corresponded with regard to the flavonoids' effects on P–glycoprotein related efflux. Two control groups were included in the experimental design. In the negative control group, the transport of Rhodamine 123 was tested alone and no modulator was added. In the positive control group, the transport of Rhodamine 123 was determined in the presence of Verapamil, which is a known P–glycoprotein inhibitor. The experiments with the flavonoids Morin, Galangin, 6–Methoxyflavone and 7–Methoxyflavone were done in triplicate to determine repeatability of the results. The transport of Rhodamine 123 was evaluated in both the apical to basolateral (absorptive) and basolateral to apical (secretory) directions. The relative transport of Rhodamine 123, the apparent permeability coefficient (P app) values and flux (J) values in both directions as well as the efflux ratio (ER) and net flux (J net) were calculated. The concentration Rhodamine 123 present in the acceptor chamber was determined by means of a validated HPLC method. Statistical analysis was used to compare the results of the test groups with the control groups in order to indicate significant differences. It has been found that Morin, Galangin and 6–Methoxyflavone have a significant inhibitory effect on the Rhodamine 123 efflux (probably P–glycoprotein related) in both the rat and pig intestinal tissue models with p–values smaller than 0.05. On the other hand, 7–Methoxyflavone showed a significant effect on the efflux of Rhodamine 123 in the pig intestinal tissue model (p < 0.05) but not in the rat intestinal tissue model (p > 0.05). These flavonoids may increase the bioavailability of drugs that are substrates for P–glycoprotein and thereby cause clinically significant pharmacokinetic interactions, however, this should be confirmed with in vivo studies. On the other hand, these flavonoids may be used for drug absorption enhancement when applied under controlled circumstances. With regard to the different animal tissue models used it can be concluded that data obtained from the rat intestinal tissue model cannot be compared and extrapolated to data obtained from the pig intestinal tissue model. It is recommended that the in vitro results be correlated to in vivo findings to identify the most suitable model. / Thesis (M.Sc. (Pharmaceutics))--North-West University, Potchefstroom Campus, 2011.

There is a global rise in the use of herbal products in combination with allopathic medicines, while most patients do not inform their health care providers of the use of these natural products. Both pharmacodynamic and pharmacokinetic interactions between herbal products and conventional drugs must be avoided for the wellbeing of the patient. Increasing evidence from in vitro and in vivo studies indicate that changed drug pharmacokinetics by co-administered herbs may be attributed to modulation of efflux drug transporters such as P-glycoprotein (P-gp). Garlic (Allium sativum), lemon (Citrus limonum) and beetroot (Beta vulgaris) are widely used by human immunodeficiency virus (HIV) patients, especially following the pronouncement by a former President of South Africa and the Ministers of Health at that time who promoted the use of these botanicals in HIV patients. The aim of this study was to measure the bi-directional in vitro transport of indinavir, a protease inhibitor, in the presence of crude extracts and pure phytoconstituents of A. sativum (L-alliin and diallyl disulphide), C. limonum (hesperidin and eriocitrin) and B. vulgaris (betaine monohydrate and ß-carotene) across excised porcine intestinal tissue in Sweetana-Grass diffusion chambers. In the negative control group, the transport of indinavir alone (200 M) was determined with no modulator added. In the positive control group, the transport of indinavir was determined in the presence of verapamil (100 M), a known P-gp related efflux inhibitor. The control experiments were used to indicate that the effects of the test compounds were caused by their action and not by chance interferences or external factors. Samples collected at pre-determined time intervals were analysed by means of a validated high performance liquid chromatography (HPLC) method and the transport was expressed as the apparent permeability coefficient (Papp) and the transepithelial flux (J) from which the efflux ratio (ER) and the net flux (Jnet) values were calculated. Statistical analysis was used to compare the results of the test compounds with the control groups in order to indicate significant differences. The mean ER value for indinavir in the negative control group was 1.41 ± 0.170 and in the positive control group it was 0.56 ± 0.0426. Statistically significant (p < 0.05) inhibition of indinavir efflux as indicated by reduced ER values was obtained for L-alliin (ER = 0.280 ± 0.030), diallyl disulphide (ER = 0.505 ± 0.034) and ß-carotene (ER = 0.664 ± 0.075). Inhibition of indinavir efflux will lead to increased transport and therefore a potentially higher bioavailability. Statistically significant (p < 0.05) promotion of indinavir efflux as indicated by increased ER values was obtained for C. limonum crude extract (ER = 5.551 ± 0.575) and hesperidin (ER = 3.385 ± 0.477), which potentially may lead to lower bioavalability. B. vulgaris crude extract (p = 0.8452), betaine monohydrate (p = 0.9982), A. sativum crude extract (p = 0.7161) and eriocitrin (p = 0.4431) displayed no statistically significant effect compared to the negative control group on indinavir transport across excised porcine intestinal tissue. The results from this study demonstrate that L-alliin, diallyl disulphide and ß-carotene have an inhibitory effect on indinavir efflux, which may significantly increase indinavir plasma levels after oral administration. C. limonum crude extract and hesperidin promote indinavir efflux, which may significantly reduce indinavir plasma levels. These pharmacokinetic interactions between certain drugs and plant extracts may negatively affect the anti-retroviral treatment of HIV patients, but deliberate and controlled inclusion of L-alliin, diallyl disulphide and ß-carotene in dosage forms may possibly cause more effective delivery of protease inhibitors after oral administration resulting in less frequent dosing intervals. / Thesis (MSc (Pharmaceutics))--North-West University, Potchefstroom Campus, 2013.

There is a global rise in the use of herbal products in combination with allopathic medicines, while most patients do not inform their health care providers of the use of these natural products. Both pharmacodynamic and pharmacokinetic interactions between herbal products and conventional drugs must be avoided for the wellbeing of the patient. Increasing evidence from in vitro and in vivo studies indicate that changed drug pharmacokinetics by co-administered herbs may be attributed to modulation of efflux drug transporters such as P-glycoprotein (P-gp). Garlic (Allium sativum), lemon (Citrus limonum) and beetroot (Beta vulgaris) are widely used by human immunodeficiency virus (HIV) patients, especially following the pronouncement by a former President of South Africa and the Ministers of Health at that time who promoted the use of these botanicals in HIV patients. The aim of this study was to measure the bi-directional in vitro transport of indinavir, a protease inhibitor, in the presence of crude extracts and pure phytoconstituents of A. sativum (L-alliin and diallyl disulphide), C. limonum (hesperidin and eriocitrin) and B. vulgaris (betaine monohydrate and ß-carotene) across excised porcine intestinal tissue in Sweetana-Grass diffusion chambers. In the negative control group, the transport of indinavir alone (200 M) was determined with no modulator added. In the positive control group, the transport of indinavir was determined in the presence of verapamil (100 M), a known P-gp related efflux inhibitor. The control experiments were used to indicate that the effects of the test compounds were caused by their action and not by chance interferences or external factors. Samples collected at pre-determined time intervals were analysed by means of a validated high performance liquid chromatography (HPLC) method and the transport was expressed as the apparent permeability coefficient (Papp) and the transepithelial flux (J) from which the efflux ratio (ER) and the net flux (Jnet) values were calculated. Statistical analysis was used to compare the results of the test compounds with the control groups in order to indicate significant differences. The mean ER value for indinavir in the negative control group was 1.41 ± 0.170 and in the positive control group it was 0.56 ± 0.0426. Statistically significant (p < 0.05) inhibition of indinavir efflux as indicated by reduced ER values was obtained for L-alliin (ER = 0.280 ± 0.030), diallyl disulphide (ER = 0.505 ± 0.034) and ß-carotene (ER = 0.664 ± 0.075). Inhibition of indinavir efflux will lead to increased transport and therefore a potentially higher bioavailability. Statistically significant (p < 0.05) promotion of indinavir efflux as indicated by increased ER values was obtained for C. limonum crude extract (ER = 5.551 ± 0.575) and hesperidin (ER = 3.385 ± 0.477), which potentially may lead to lower bioavalability. B. vulgaris crude extract (p = 0.8452), betaine monohydrate (p = 0.9982), A. sativum crude extract (p = 0.7161) and eriocitrin (p = 0.4431) displayed no statistically significant effect compared to the negative control group on indinavir transport across excised porcine intestinal tissue. The results from this study demonstrate that L-alliin, diallyl disulphide and ß-carotene have an inhibitory effect on indinavir efflux, which may significantly increase indinavir plasma levels after oral administration. C. limonum crude extract and hesperidin promote indinavir efflux, which may significantly reduce indinavir plasma levels. These pharmacokinetic interactions between certain drugs and plant extracts may negatively affect the anti-retroviral treatment of HIV patients, but deliberate and controlled inclusion of L-alliin, diallyl disulphide and ß-carotene in dosage forms may possibly cause more effective delivery of protease inhibitors after oral administration resulting in less frequent dosing intervals. / Thesis (MSc (Pharmaceutics))--North-West University, Potchefstroom Campus, 2013.