Effects of plant extracts and phytoconstituents on the intestinal transport of indinavir
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.
- Health Sciences