Identification of Mechanism and Pathway of the Interaction between the African Traditional Medicine, Sutherlandia Frutescens, and the Antiretroviral Protease Inhibitor, Atazanavir, in Human Subjects Using Population Pharmacokinetic (PK) Analysis.

Although the use of the indigenous Southern African plant, Sutherlandia frutescens (SF) for the treatment of HIV/AIDS has previously been described, the risk which it may pose to the safety and efficacy of ARVs and the potential mechanisms which underlie such effects may have clinical significance and relevance. The protease inhibitor (PI), atazanavir (ATV) is a substrate of the efflux transporter, P-gp which modulates absorption in the small intestine, as well as CYP3A4 and CYP3A5enzymes which facilitate metabolism in the small intestine and liver. The objective of this study was to investigate the effect of SF on the pharmacokinetics (PK) of atazanavir (ATV) and to use a population PK analysis to fit and explain plasma concentration vs. time profiles of ATV generated in a previously conducted study in healthy male subjects in order to understand and postulate on the potential mechanism(s) of the drug-drug interaction. The population PK Compartmental Analysis of ATV before and after a two-week regimen of Phyto Nova Sutherlandia SU1 tablets which contain SF plant material indicated that a two compartment model with a dual absorption mechanism best explained the data. The dual absorption mechanism is hypothesized to reflect "passive" (first-order, Ka parameter) and "active" (zero-order, K0 parameter) absorption processes. The model suggested that the mechanism by which SF reduced the overall bioavailability of ATV may be modulated via the inhibition of the "active" absorption process. This study has highlighted the utility of population PK analyses in postulating probable mechanism(s) whereby an ATM or a herbal medicine interacts with an allopathic drug.

The In Vitro and In Vivo Effects of Hypoxis hemerocallidea on Indinavir Pharmacokinetics: Modulation of Efflux.

Hypoxis hemerocallidea (African potato) is a popular medicinal plant that has been used traditionally for the treatment of various disorders. Some HIV/AIDS patients use this traditional medicine together with their antiretroviral therapy. This study aimed to determine the impact of selected H. hemerocallidea materials (i.e., a commercial product, an aqueous extract, and biomass reference plant material) on the bidirectional permeability of indinavir across Caco-2 cell monolayers as well as the bioavailability of indinavir during an acute, single administration study in Sprague-Dawley rats. All of the selected H. hemerocallidea test materials demonstrated inhibition effects on indinavir efflux across Caco-2 cell monolayers, albeit to different extents. An increase in the bioavailability of indinavir was obtained in vivo when administered concomitantly with the H. hemerocallidea materials, albeit not statistically significantly. The change in bioavailability directly correlated with the in vitro permeability results. It can therefore be concluded that the change in permeability and bioavailability of indinavir was caused by efflux inhibition and this effect was dependent on the type of H. hemerocallidea material investigated, which was found to be in the following order: commercial product > aqueous extract > reference plant material. The clinical significance of the combined effect of efflux and metabolism inhibition by H. hemerocallidea should be determined in another in vivo model that expresses the cytochrome P450 3A4 enzyme.

Evaluation of Isolated Fractions of Aloe vera Gel Materials on Indinavir Pharmacokinetics: In vitro and in vivo Studies.

Aloe vera is a plant with a long history of traditional medicinal use and is consumed in different products, sometimes in conjunction with prescribed medicines. A. vera gel has shown the ability to modulate drug absorption in vitro. The aim of this study was to fractionate the precipitated polysaccharide component of A. vera gel based on molecular weight and to compare their interactions with indinavir pharmacokinetics. Crude polysaccharides were precipitated from a solution of A. vera gel and was fractionated by means of centrifugal filtration through membranes with different molecular weight cut-off values (i.e. 300 KDa, 100 KDa and 30 KDa). Marker molecules were quantified in the aloe leaf materials by means of nuclear magnetic resonance spectroscopy and the average molecular weight was determined by means of gel filtration chromatography linked to multi-angle-laser-light scattering and refractive index detection. The effect of the aloe leaf materials on the transepithelial electrical resistance (TEER) of Caco-2 cell monolayers as well as indinavir metabolism in LS180 cells was measured. The bioavailability of indinavir in the presence and absence of the aloe leaf materials was determined in Sprague-Dawley rats. All the aloe leaf materials investigated in this study reduced the TEER of Caco-2 cell monolayers, inhibited indinavir metabolism in LS 180 cells to different extents and changed the bioavailability parameters of indinavir in rats compared to that of indinavir alone. These indinavir pharmacokinetic modulation effects were not dependent on the presence of aloverose and also not on the average molecular weight of the isolated fractions.

Influence of Panax ginseng on the steady state pharmacokinetic profile of lopinavir-ritonavir in healthy volunteers.

STUDY OBJECTIVE: Panax ginseng has been shown in preclinical studies to modulate cytochrome P450 enzymes involved in the metabolism of HIV protease inhibitors. Therefore, the purpose of this study was to determine the influence of P. ginseng on the pharmacokinetics of the HIV protease inhibitor combination lopinavir-ritonavir (LPV-r) in healthy volunteers. DESIGN: Single-sequence, open-label, single-center pharmacokinetic investigation. SETTING: Government health care facility. SUBJECTS: Twelve healthy human volunteers. MEASUREMENTS AND MAIN RESULTS: Twelve healthy volunteers received LPV-r (400-100 mg) twice/day for 29.5 days. On day 15 of LPV-r administration, serial blood samples were collected over 12 hours for determination of lopinavir and ritonavir concentrations. On study day 16, subjects began taking P. ginseng 500 mg twice/day, which they continued for 2 weeks in combination with LPV-r. On day 30 of LPV-r administration, serial blood samples were again collected over 12 hours for determination of lopinavir and ritonavir concentrations. Lopinavir and ritonavir pharmacokinetic parameter values were determined using noncompartmental methods, and preadministration and postadministration ginseng values were compared using a Student t test, where p<0.05 was accepted as statistically significant. CONCLUSION: Neither lopinavir nor ritonavir steady-state pharmacokinetics were altered by 2 weeks of P. ginseng administration to healthy human volunteers. Thus, a clinically significant interaction between P. ginseng and LPV-r is unlikely to occur in HIV-infected patients who choose to take these agents concurrently. It is also unlikely that P. ginseng will interact with other ritonavir-boosted protease inhibitor combinations, although confirmatory data are necessary.

Effect of grapefruit juice and ritonavir on pharmacokinetics of lopinavir in Wistar rats.

Lopinavir (LPV), a newer HIV protease inhibitor, has poor bioavailability being a substrate of both cytochrome P450 3A enzyme system (CYP3A) and permeability-glycoprotein (P-gp). Ritonavir (RTV) is a known inhibitor of both P-gp and CYP3A and is co-administered with LPV in anti-HIV therapy. Grapefruit juice (GFJ) is known to inhibit CYP3A and has conflicting effects, ranging from activation to inhibition, on P-gp. In this research work, the effects of GFJ and RTV on the pharmacokinetics of LPV were compared in rats. A mechanistic evaluation was undertaken using various in vitro and ex vivo studies to support the in vivo pharmacokinetic data. The plasma levels of LPV were found to increase significantly upon co-administration with GFJ in single dose as well as multidose pretreatment studies. Similar, but marginally higher, results were observed upon co-administration of LPV with RTV. No significant change in t(max) was observed in the various treatment groups. The apparent permeability of LPV in the ileum increased significantly after the pre-incubation with GFJ and RTV compared with no pre-incubation. The GFJ and RTV showed a significant and similar inhibitory effect on rat intestinal microsomes in the metabolism of LPV. The GFJ was equally effective as RTV in increasing the bioavailability of LPV.

The effect of ß-carotene supplementation on the pharmacokinetics of nelfinavir and its active metabolite M8 in HIV-1-infected patients.

ß-Carotene supplements are often taken by individuals living with HIV-1. Contradictory results from in vitro studies suggest that ß-carotene may inhibit or induce cytochrome P450 enzymes and transporters. The study objective was to investigate the effect of ß-carotene on the steady-state pharmacokinetics of nelfinavir and its active metabolite M8 in HIV-1 infected individuals. Twelve hour nelfinavir pharmacokinetic analysis was conducted at baseline and after 28 days of ß-carotene supplementation (25,000 IU twice daily). Nelfinavir and M8 concentrations were measured with validated assays. Non-compartmental methods were used to calculate the pharmacokinetic parameters. Geometric mean ratios comparing day 28 to day 1 area under the plasma concentration-time curve (AUC(0-12 h)), maximum (C(max)) and minimum (C(min)) concentrations of nelfinavir and M8 are presented with 90% confidence intervals. Eleven subjects completed the study and were included in the analysis. There were no significant differences in nelfinavir AUC(0-12 h) and C(min) (-10%, +4%) after ß-carotene supplementation. The M8 C(min) was increased by 31% while the M8 AUC(0-12 h) and C(max) were unchanged. During the 28 day period, mean CD4+ % and CD4+:CD8+ ratio increased significantly (p < 0.01). ß-carotene supplementation increased serum carotene levels but did not cause any clinically significant difference in the nelfinavir and M8 exposure.

Potential pharmacokinetic interactions between antiretrovirals and medicinal plants used as complementary and African traditional medicines.

The use of traditional/complementary/alternate medicines (TCAMs) in HIV/AIDS patients who reside in Southern Africa is quite common. Those who use TCAMs in addition to antiretroviral (ARV) treatment may be at risk of experiencing clinically significant pharmacokinetic (PK) interactions, particularly between the TCAMs and the protease inhibitors (PIs) and non-nucleoside reverse transcriptase inhibitors (NNRTIs). Mechanisms of PK interactions include alterations to the normal functioning of drug efflux transporters, such as P-gp and/or CYP isoenzymes, such a CYP3A4 that mediate the absorption and elimination of drugs in the small intestine and liver. Specific mechanisms include inhibition and activation of these proteins and induction via the pregnane X receptor (PXR). Several clinical studies and case reports involving ARV-herb PK interactions have been reported. St John's Wort, Garlic and Cat's Claw exhibited potentially significant interactions, each with a PI or NNRTI. The potential for these herbs to induce PK interactions with drugs was first identified in reports of in vitro studies. Other in vitro studies have shown that several African traditional medicinal (ATM) plants and extracts may also demonstrate PK interactions with ARVs, through effects on CYP3A4, P-gp and PXR. The most complex effects were exhibited by Hypoxis hemerocallidea, Sutherlandia frutescens, Cyphostemma hildebrandtii, Acacia nilotica, Agauria salicifolia and Elaeodendron buchananii. Despite a high incidence of HIV/AIDs in the African region, only one clinical study, between efavirenz and Hypoxis hemerocallidea has been conducted. However, several issues/concerns still remain to be addressed and thus more studies on ATMs are warranted in order for more meaningful data to be generated and the true potential for such interactions to be determined.

Approaches for understanding and predicting drug interactions in human immunodeficiency virus-infected patients.

INTRODUCTION: Knowledge of drug interactions is vital to maximize antiretroviral efficacy and avoid drug-related toxicities. Treatment of co-morbidities has become a difficult task in HIV-infected individuals because pharmacokinetic and/or pharmacodynamic interactions are common when other medications are prescribed along with antiretroviral agents. AREAS COVERED: This article provides an update of the most relevant drug interactions that occur between antiretroviral agents and other drugs. The article additionally revisits how these drug interactions can be prevented from occurring as well as how they can be managed. EXPERT OPINION: Interactions between antiretrovirals and other drugs are frequent in clinical practice. The most common are those affecting drug metabolism due to induction or inhibition of the CYP450, leading to abnormal drug exposure. It is by this mechanism that most HIV protease inhibitors, non-nucleoside reverse transcriptase inhibitors and maraviroc often interact with other medications. In contrast, nucleoside reverse transcriptase inhibitors and some integrase inhibitors, which do not or only marginally affect CYP450, are relatively free of significant pharmacokinetic interactions, although nucleoside analogs might be involved in some pharmacodynamic interactions.

Brain specific delivery of pegylated indinavir submicron lipid emulsions.

The aim of this study was to develop stable parenteral pegylated indinavir submicron lipid emulsions (SLEs) for improving brain specific delivery. The O/W SLEs were prepared by homogenization and ultra sonication process. The sizes of oil globules varied from 241.5 to 296.4nm and zeta potential from -26.6 to -42.4mV. During in vitro drug release studies the cumulative amount of drug released within 12h from SLE-5, DSP2-3 and DPP5-3 was 71.8±0.76, 66.09±1.45 and 68.33±1.29, respectively. The total drug content and entrapment efficiencies were determined. The optimized formulations were stable for the effect of centrifugal stress, thermal stress, dilution stress and storage. In vivo pharmacokinetic and tissue distribution studies were performed in Swiss albino mice, the therapeutic availability (TA) of DSP2-3 was 3.59 times and 2.36 times in comparison to drug solution and SLE-5 respectively, where as DPP5-3 showed TA 2.8 and 1.84 times the drug solution and SLE-5, respectively. The brain to serum ratio of indinavir from DSP2-3 and DPP5-3 varied between 0.4 and 0.7 at all time points indicated the preferential accumulation of drug in brain. In conclusion, pegylated SLEs improved brain specific delivery of indinavir and will be useful in treating chronic HIV infection.

Transwell-grown HepG2 cell monolayers as in vitro permeability model to study drug-drug or drug-food interactions.

HepG2 cell monolayers, formed during cell growth on collagen-coated Transwell® (Corning® Inc., Corning, NY, USA) inserts, can be used for the evaluation of interactions between food supplements and drugs that are substrates for P-glycoprotein (Pgp) and/or multidrug resistance-associated protein 2 (MRP-2). Samples obtained during such permeability studies were relatively free of intracellular proteins or cell debris compared to usually performed uptake experiments with HepG2 cells; therefore no special preparation protocol prior to the analysis was needed. In the presence of aged garlic extract the activities of hepatic efflux transporters (Pgp, MRP-2) changed, which was observed as significant permeability changes of tested human immunodeficiency virus (HIV) protease inhibitors. Darunavir efflux significantly increased, whereas that of saquinavir significantly decreased. Because of the observed in vitro interactions between aged garlic extract and HIV protease inhibitors (darunavir, saquinavir), any alterations of in vivo liver transport in the presence of garlic phytochemicals could also significantly influence darunavir/saquinavir hepatocyte intracellular concentrations and hence their bioavailabilities. Therefore this aspect needs further in vivo animal evaluation.

Herb-drug interaction between Echinacea purpurea and darunavir-ritonavir in HIV-infected patients.

The aim of this open-label, fixed-sequence study was to investigate the potential of Echinacea purpurea, a commonly used botanical supplement, to interact with the boosted protease inhibitor darunavir-ritonavir. Fifteen HIV-infected patients receiving antiretroviral therapy including darunavir-ritonavir (600/100 mg twice daily) for at least 4 weeks were included. E. purpurea root extract capsules were added to the antiretroviral treatment (500 mg every 6 h) from days 1 to 14. Darunavir concentrations in plasma were determined by high-performance liquid chromatography immediately before and 1, 2, 4, 6, 8, 10, and 12 h after a morning dose of darunavir-ritonavir on days 0 (darunavir-ritonavir) and 14 (darunavir-ritonavir plus echinacea). Individual darunavir pharmacokinetic parameters were calculated by noncompartmental analysis and compared between days 0 and 14 with the geometric mean ratio (GMR) and its 90% confidence interval (CI). The median age was 49 (range, 43 to 67) years, and the body mass index was 24.2 (range, 18.7 to 27.5) kg/m(2). Echinacea was well tolerated, and all participants completed the study. The GMR for darunavir coadministered with echinacea relative to that for darunavir alone was 0.84 (90% CI, 0.63-1.12) for the concentration at the end of the dosing interval, 0.90 (90% CI, 0.74-1.10) for the area under the concentration-time curve from 0 to 12 h, and 0.98 (90% CI, 0.82-1.16) for the maximum concentration. In summary, coadministration of E. purpurea with darunavir-ritonavir was safe and well tolerated. Individual patients did show a decrease in darunavir concentrations, although this did not affect the overall darunavir or ritonavir pharmacokinetics. Although no dose adjustment is required, monitoring darunavir concentrations on an individual basis may give reassurance in this setting.

HIV protease inhibitors: garlic supplements and first-pass intestinal metabolism impact on the therapeutic efficacy.

BACKGROUND/AIMS: The aim of this study was to elucidate the impact of first-pass intestinal metabolism to therapeutic efficacy of antiretrovirals and to ascertain interaction mechanisms between garlic supplements (aged garlic extract) and HIV-protease inhibitors. METHODS: In vitro permeability through rat jejunum, Caco-2 cell monolayers was determined and CYP3A4 metabolism studies were performed. RESULTS: Saquinavir and darunavir efflux from enterocytes into gastrointestinal lumen significantly increased in the presence of aged garlic extract, whereas their CYP3A4 metabolism was inhibited. In the case of saquinavir a significant increase of its efflux was observed also in the presence of lower ritonavir doses. Because both drugs bound to different binding sites on P-glycoprotein and/or multidrug resistance associated protein 2 than garlic phytochemicals or ritonavir, lower amounts of antiretrovirals were absorbed. CONCLUSIONS: The fractions of tested anti-HIV drugs absorbed could decrease significantly during self-medication with garlic supplements or ritonavir dose adjustments. Due to distinct saquinavir and darunavir preferences for binding sites on efflux transporters, the presence of other compounds (garlic phytochemicals, ritonavir), capable of influencing intestinal transporter-enzyme interplay, might lead to pharmacokinetic interactions observed in clinical studies and case reports with anti-HIV drugs.

The influence of aged garlic extract on the uptake of saquinavir and darunavir into HepG2 cells and rat liver slices.

Bioavailability and therapeutic outcome of treatment with HIV-protease inhibitors depends on intestinal and hepatic transporter-enzyme interplay. Liver transport of HIV protease inhibitors (saquinavir, darunavir) was assessed in the presence of aged garlic extract, because the HIV-infected often consume garlic supplements together with prescribed therapy. The in vitro uptake of both drugs into HepG2 cells and precision cut rat liver slices significantly increased in the presence of Pgp and MRP-2 inhibitor ritonavir. The incubation medium containing aged garlic extract caused significant inhibition of saquinavir efflux from HepG2 cells and precision cut liver slices, while the activity of darunavir efflux transporters in both liver models significantly increased. Due to opposite in vitro interactions observed between aged garlic extract and HIV protease inhibitors, darunavir and saquinavir most probably bind to different binding sites on one or both efflux transporters. Based on this study, coadministration of investigated compounds with garlic supplements could result in significant in vivo modification of hepatic transport-enzyme interplay, possibly leading to further bioavailability change.

Pharmacokinetics, protein-binding-adjusted inhibitory quotients for atazanavir/ritonavir 300/100 mg in treatment-naïve HIV-infected patients.

OBJECTIVES: Studies have shown the importance of having a high protein-binding-adjusted inhibitory quotient (IQ) for protease inhibitors (PIs) boosted with ritonavir. The objective of this study was to explore the virological response when combination atazanavir/ritonavir was administered to treatment-nai¨ve patients. METHODS: Protein-binding-adjusted IQs were calculated in 100 treatment-nai¨ve patients initiating therapy with atazanavir 300 mg/ritonavir 100 mg plus two nucleoside reverse transcriptase inhibitors. RESULTS: The median atazanavir trough level was 635 ng/mL [interquartile range (IQR) 342-1000] and the median atazanavir protein-binding-adjusted IQ was 45 (IQR 24-71). Eighty-four per cent of patients had a successful virological response, and those who failed did not develop resistance. The IQ for boosted atazanavir is high, resulting in rare treatment failure without resistance mutations. CONCLUSIONS: This study showed that the protein-binding-adjusted IQ of atazanavir is close to those measured for lopinavir and darunavir used once daily in first-line treatment. Finally the selection of resistance in the case of virological failure (plasma viral load 4400 HIV-1 RNA copies/mL) to atazanavir/ritonavir used in first-line therapy seems uncommon, as it is for all boosted PIs.

Effects of St. John's wort extract on indinavir pharmacokinetics in rats: differentiation of intestinal and hepatic impacts.

AIMS: To evaluate the possible herb-drug interaction of St. John's wort (SJW) extracts with indinavir in rats and to set up a model for characterizing pre-systemic sites for the interactions between orally administered herbs and pharmaceuticals. MAIN METHODS: The in vivo pharmacokinetic study and in situ single-pass intestinal perfusion model were employed in the research. Plasma indinavir concentration and cytochrome P450 3A activities were measured by high-pressure liquid chromatography and spectrophotometric assays, respectively. KEY FINDINGS: Oral administration of either 150 or 300 mg/day SJW for 15 days significantly reduced indinavir plasma levels with certain pharmacokinetic parameter changes. The cytochrome P450 3A analysis suggested that this interaction was attributable to the induction of indinavir metabolism. Further perfusion study demonstrated that both small intestine and the liver contributed significantly to the reduction of indinavir bioavailability and was flow rate-dependent. Moreover, the small intestine was the major site for the pre-systemic metabolism of indinavir, whether with or without SJW pretreatment. SIGNIFICANCE: Herb-drug pharmacokinetic interactions between SJW and indinavir can be clearly observed in the Wistar rat model. Particularly, the respective first-pass effect contributed by the small intestine and the liver could be differentiated and quantified. The application of the animal model to investigating herb-drug interactions or other relevant research purposes is envisioned.

Effects of minocycline and valproic acid coadministration on atazanavir plasma concentrations in human immunodeficiency virus-infected adults receiving atazanavir-ritonavir.

Minocycline and valproic acid are potential adjuvant therapies for the treatment of human immunodeficiency virus (HIV)-associated cognitive impairment. The purpose of this study was to determine whether minocycline alone or in combination with valproic acid affected atazanavir plasma concentrations. Twelve adult HIV-infected subjects whose regimen included atazanavir (300 mg)-ritonavir (100 mg) daily for at least 4 weeks were enrolled. Each subject received atazanavir-ritonavir on day 1, atazanavir-ritonavir plus 100 mg minocycline twice daily on days 2 to 15, and atazanavir-ritonavir plus 100 mg minocycline twice daily and 250 mg valproic acid twice daily on days 16 to 30 with meals. The subjects had 11 plasma samples drawn over a dosing interval on days 1, 15, and 30. The coadministration of minocycline and valproic acid with atazanavir-ritonavir was well tolerated in all 12 subjects (six male; mean [+/- standard deviation] age was 43.1 [8.2] years). The geometric mean ratios (GMRs; 95% confidence interval [CI]) for the atazanavir area under the concentration-time curve from 0 to 24 h at steady state (AUC(0-24)), the plasma concentration 24 h after the dose (C(min)), and the maximum concentration during the dosing interval (C(max)) with and without minocycline were 0.67 (0.50 to 0.90), 0.50 (0.28 to 0.89), and 0.75 (0.58 to 0.95), respectively. Similar decreases in atazanavir exposure were seen after the addition of valproic acid. The GMRs (95% CI) for atazanavir AUC(0-24), C(min), and C(max) with and without minocycline plus valproic acid were 0.68 (0.43 to 1.06), 0.50 (0.24 to 1.06), and 0.66 (0.41 to 1.06), respectively. Coadministration of neither minocycline nor minocycline plus valproic acid appeared to influence the plasma concentrations of ritonavir (P > 0.2). Minocycline coadministration resulted in decreased atazanavir exposure, and there was no evidence that the addition of valproic acid mediated this effect.