Limitations of using a single postdose midazolam concentration to predict CYP3A-mediated drug interactions.

Midazolam is a common probe used to predict CYP3A activity, but multiple blood samples are necessary to determine midazolam's area under the concentration-time curve (AUC). As such, single sampling strategies have been examined. The purpose of this study was to assess the ability of single midazolam concentrations to predict midazolam AUC in the presence and absence of CYP3A modulation by Ginkgo biloba extract (GBE). Subjects received oral midazolam 8 mg before and after 28 days of GBE administration. Postdose blood samples were collected during both study periods and midazolam AUC determined. Linear regression was used to generate measures of predictive performance for each midazolam concentration. The geometric mean ratio (90% confidence intervals) of midazolam AUC(0-infinity) post-GBE/AUC(0-infinity) pre-GBE was 0.66 (0.49-0.84) (P = .03). Before and after GBE administration, optimal midazolam sampling times were identified at 3.5 to 5 hours and 2 to 3 hours, respectively. Single midazolam concentrations between 2 and 5 hours correctly predicted the reduction in midazolam AUC following GBE exposure, but confidence intervals were generally wide. Intersubject variability in CYP3A activity (either inherent or from drug administration) alters the prediction of optimal midazolam sampling times; therefore, midazolam AUC is preferred for assessing CYP3A activity in drug-drug interaction studies.

The incidence and natural history of osteonecrosis in HIV-infected adults.

BACKGROUND: Osteonecrosis is increasingly recognized as a debilitating complication of human immunodeficiency virus (HIV) infection, but the natural history has not been well described. We previously documented a high prevalence (4.4%) of magnetic resonance imaging (MRI)-documented osteonecrosis of the hip in a cohort of 339 asymptomatic HIV-infected patients. The present study was designed to determine the incidence of newly diagnosed osteonecrosis in this cohort and to describe the natural history of osteonecrosis in HIV-infected patients. METHODS: Asymptomatic HIV-infected patients with a previous hip MRI negative for osteonecrosis underwent follow-up MRI. Patients with asymptomatic or symptomatic osteonecrosis were enrolled in a natural history study, which included serial MRIs and a physiotherapy follow-up. RESULTS: Two hundred thirty-nine patients underwent a second MRI a median of 23 months after the initial MRI. Osteonecrosis of the femoral head was diagnosed in 3 patients (incidence, 0.65 cases per 100 person-years). During the period of January 1999 through April 2006, symptomatic hip osteonecrosis developed in 13 clinic patients (incidence, 0.26 cases per 100 person-years). Among 22 patients enrolled with symptomatic hip osteonecrosis, 18 had bilateral involvement of the femoral heads, and 7 had osteonecrosis involving other bones. Two (11%) of 18 asymptomatic patients and 13 (59%) of 22 symptomatic patients underwent total hip replacement. The percentage of involvement of the weight-bearing surface of the femoral head and the rate of progression to total hip replacement was significantly greater (P<.001) in symptomatic patients than in asymptomatic patients. CONCLUSIONS: HIV-infected patients are at approximately 100-fold greater risk of developing osteonecrosis than the general population. Disease progression is slower in asymptomatic patients than in symptomatic patients. Given the high frequency of total hip replacement in symptomatic patients, studies to assess preventive and treatment strategies are essential.

Lack of in vivo correlation between indinavir and saquinavir exposure and cytochrome P450 3A phenotype as assessed with oral midazolam as a phenotype probe.

STUDY OBJECTIVE: To investigate a potential correlation between exposure to oral midazolam, a commonly used cytochrome P450 (CYP) 3A probe, and saquinavir and indinavir exposure. DESIGN: Open-label, prospective, pharmacokinetic study. SETTING: Outpatient research center. SUBJECTS: Thirty-six healthy volunteers aged 22-50 years. INTERVENTION: Subjects received a single oral dose of midazolam 8 mg; 4 hours later, blood was drawn to determine their serum midazolam concentrations. Midazolam phenotyping was followed by successive administration of the protease inhibitors indinavir and saquinavir, with blood sampling and pharmacokinetic analyses performed at steady state. MEASUREMENTS AND MAIN RESULTS: Pharmacokinetic parameters of each protease inhibitor were evaluated to assess for a potential relationship with 4-hour concentrations of midazolam. No correlations between phenotype results for midazolam and any pharmacokinetic parameter for indinavir or saquinavir were identified (r(2)=0.00002-0.073). When the results were analyzed based on race, significant correlations were identified in five African-American subjects, including correlations between 4-hour midazolam levels and apparent oral clearance of saquinavir (r(2)=0.734, p=0.064), area under the plasma concentration-time curve from 0-8 hours (r(2)=0.914, p=0.011), minimum concentration (r(2)=0.857, p=0.024), and maximum concentration (r(2)=0.969, p=0.002). These findings for African-American subjects were not seen with indinavir. No correlation was found between indinavir and saquinavir pharmacokinetic parameters (r(2)=0.017-0.261). CONCLUSION: Oral midazolam was not a useful probe for predicting saquinavir or indinavir exposure at steady state. Reasons for the lack of correlation likely included differences between midazolam and protease inhibitor P-glycoprotein specificity, differences in the relative contribution of CYP3A5-mediated metabolism, and/or variation in intestinal and hepatic CYP3A specificity. The strong correlation between midazolam phenotype and pharmacokinetic parameters for saquinavir in African-American subjects indicated a racial difference in one or more of these confounding variables.

Effect of milk thistle on the pharmacokinetics of indinavir in healthy volunteers.

STUDY OBJECTIVE: To characterize the pharmacokinetics of indinavir in the presence and absence of milk thistle and to determine the offset of any effect of milk thistle on indinavir disposition. DESIGN: Prospective open-label drug interaction study. SETTING: Outpatient clinic. SUBJECTS: Ten healthy volunteers. Intervention. Blood samples were collected over 8 hours after the volunteers took four doses of indinavir 800 mg every 8 hours on an empty stomach for baseline pharmacokinetics. This dosing and sampling were repeated after the subjects took milk thistle 175 mg (confirmed to contain silymarin 153 mg, the active ingredient) 3 times/day for 3 weeks. After an 11-day washout, indinavir dosing and blood sampling were repeated to evaluate the offset of any potential interaction. MEASUREMENTS AND MAIN RESULTS: Indinavir concentrations were measured by using a validated high-performance liquid chromatography method. The following pharmacokinetic parameters were determined: highest concentration (Cmax), hour-0 concentration, hour-8 concentration (C8), time to reach Cmax, and area under the plasma concentration-time curve over the 8-hour dosing interval (AUC8). Milk thistle did not alter significantly the overall exposure of indinavir, as evidenced by a 9% reduction in the indinavir AUC8 after 3 weeks of dosing with milk thistle, although the least squares mean trough level (C8) was significantly decreased by 25%. CONCLUSION: Milk thistle in commonly administered dosages should not interfere with indinavir therapy in patients infected with the human immunodeficiency virus.

Gemfibrozil concentrations are significantly decreased in the presence of lopinavir-ritonavir.

OBJECTIVE: The objective of this study was to determine the influence of a 2-week course of lopinavir-ritonavir on the pharmacokinetics of the triglyceride-lowering agent, gemfibrozil. METHODS: The study was conducted as an open label, single-sequence pharmacokinetic study in healthy human volunteers. Gemfibrozil pharmacokinetic parameter values were compared using a Student t test after a single 600-mg dose was administered to healthy volunteers before and after 2 weeks of lopinavir-ritonavir (400/100 mg) twice daily. RESULTS: Fifteen healthy volunteers (eight males) completed the study. All study drugs were generally well tolerated and no subjects withdrew participation. The geometric mean ratio (90% confidence interval) for gemfibrozil area under the plasma concentration-time curve after 14 days of lopinavir-ritonavir compared with baseline was 0.59 (0.52, 0.67) (P < 0.001). All 15 study subjects experienced a reduction in gemfibrozil area under the plasma concentration-time curve after lopinavir-ritonavir (range, -6% to -74%). The geometric mean ratios for gemfibrozil apparent oral clearance and maximum concentration were 1.69 (1.41, 1.97) and 0.67 (0.49, 0.86) after 14 days of lopinavir-ritonavir versus baseline, respectively (P < 0.0001 and 0.01, respectively). Gemfibrozil elimination half-life did not change after lopinavir-ritonavir administration (P = 0.60). CONCLUSION: Lopinavir-ritonavir significantly reduced the systemic exposure of gemfibrozil by reducing gemfibrozil absorption. Clinicians treating HIV-infected patients with hypertriglyceridemia should be aware of this drug interaction.

Effect of Ginkgo biloba extract on lopinavir, midazolam and fexofenadine pharmacokinetics in healthy subjects.

OBJECTIVE: Animal and in vitro data suggest that Ginkgo biloba extract (GBE) may modulate CYP3A4 activity. As such, GBE may alter the exposure of HIV protease inhibitors metabolized by CYP3A4. It is also possible that GBE could alter protease inhibitor pharmacokinetics (PK) secondary to modulation of P-glycoprotein (P-gp). The primary objective of the study was to evaluate the effect of GBE on the exposure of lopinavir in healthy volunteers administered lopinavir/ritonavir. Secondary objectives were to compare ritonavir exposure pre- and post-GBE, and assess the effect of GBE on single doses of probe drugs midazolam and fexofenadine. METHODS: This open-label study evaluated the effect of 2 weeks of standardized GBE administration on the steady-state exposure of lopinavir and ritonavir in 14 healthy volunteers administered lopinavir/ritonavir to steady-state. In addition, single oral doses of probe drugs midazolam and fexofenadine were administered prior to and after 4 weeks of GBE (following washout of lopinavir/ritonavir) to assess the influence of GBE on CYP3A and P-gp activity, respectively. RESULTS: Lopinavir, ritonavir and fexofenadine exposures were not significantly affected by GBE administration. However, GBE decreased midazolam AUC(0-infinity) and C(max) by 34% (p = 0.03) and 31% (p = 0.03), respectively, relative to baseline. In general, lopinavir/ritonavir and GBE were well tolerated. Abnormal laboratory results included mild elevations in hepatic enzymes, cholesterol and triglycerides, and mild-to-moderate increases in total bilirubin. CONCLUSIONS: Our results suggest that GBE induces CYP3A metabolism, as assessed by a decrease in midazolam concentrations. However, there was no change in the exposure of lopinavir, likely due to ritonavir's potent inhibition of CYP3A4. Thus, GBE appears unlikely to reduce the exposure of ritonavir-boosted protease inhibitors, while concentrations of unboosted protease inhibitors may be affected. Limitations to our study include the single sequence design and the evaluation of a ritonavir-boosted protease inhibitor exclusively.

Efavirenz induces CYP2B6-mediated hydroxylation of bupropion in healthy subjects.

OBJECTIVE: To characterize the effect of efavirenz on bupropion hydroxylation as a marker of cytochrome P450 (CYP) 2B6 activity in healthy subjects. METHODS: Thirteen subjects received a single oral dose of bupropion SR 150 mg before and after 2 weeks of efavirenz administration for comparison of bupropion and hydroxybupropion pharmacokinetics. Efavirenz plasma concentrations were also assessed. Subjects were genotyped for CYP2B6 (G516T, C1459T, and A785G), CYP3A4 (A-392G), CYP3A5 (A6986G), and multidrug resistance protein 1 (C3435T). RESULTS: The area under the concentration vs. time curve ratio of hydroxybupropion:bupropion increased 2.3-fold after efavirenz administration (P=0.0001). Bupropion area under the concentration vs. time curve and Cmax decreased by 55% and 34%, respectively (P<0.002). None of the CYP2B6 or CYP3A genotypes evaluated were associated with a difference in bupropion or efavirenz clearance. The 2 individuals homozygous for multidrug resistance protein 1 3435-T/T had 2.5- and 1.8-fold greater bupropion and efavirenz clearance, respectively, relative to C/C and C/T individuals (P<0.05). CONCLUSIONS: Our results confirm that efavirenz induces CYP2B6 enzyme activity in vivo, as demonstrated by an increase in bupropion hydroxylation after 2 weeks of efavirenz administration.

Influence of antiretroviral drugs on the pharmacokinetics of prednisolone in HIV-infected individuals.

BACKGROUND: Corticosteroids are cytochrome P450 3A4 substrates, which have been associated with toxicities in patients receiving cytochrome P450 3A4 inhibitors such as human immunodeficiency virus protease inhibitors. In a study in healthy volunteers, ritonavir significantly increased prednisolone exposure. METHODS: We investigated the influence of antiretroviral (ARV) medications on prednisolone pharmacokinetics in 3 groups of 10 human immunodeficiency virus-infected subjects. One group received lopinavir/ritonavir, and another efavirenz, as part of their ARV regimen; a third group did not receive ARV medications. Each subject received a single 20-mg prednisone dose followed by serial blood sampling for prednisolone. Prednisolone pharmacokinetics were compared among the groups. RESULTS: Area under the concentration-time curve was significantly lower in efavirenz recipients versus subjects receiving lopinavir/ritonavir (geometric mean ratio = 0.60, P = 0.01). Average prednisolone area under the concentration-time curve was higher in subjects taking lopinavir/ritonavir versus subjects not on ARVs; however, this difference was not significant (P > 0.05). CONCLUSIONS: These data indicate that prednisolone concentrations may fluctuate widely when human immunodeficiency virus-positive individuals established on efavirenz therapy change to lopinavir/ritonavir or vice versa.

The prevalence of fimbrial pathology in patients with early stages of endometriosis.

STUDY OBJECTIVE: The presence of fimbrial pathology in advanced endometriosis is clearly understood. However, little is known about the prevalence of fimbrial pathology in early stages of endometriosis. The purpose of this study is to determine the prevalence of fimbrial pathology in patients with infertility with early stages of endometriosis. DESIGN: Historical cohort study (Canadian Task Force classification II/III). SETTING: Tertiary referral center. PATIENTS: The study group (Group 1) consisted of 315 infertile women who were found to have stage I or stage II endometriosis, and the control group (Group 2) consisted of 152 infertile women without endometriosis (Group 2). INTERVENTION: Laparoscopic evaluation for the presence and type of fimbrial pathology. MEASUREMENTS AND MAIN RESULTS: The prevalence of fimbrial pathology was significantly higher in infertile patients with early stages of endometriosis (50.2%) compared with infertile patients with no endometriosis (17.8%, p <.0001). CONCLUSION: These preliminary data suggest the presence of fimbrial pathology in many patients with early stages of endometriosis. Such pathology may act as a mechanical factor interfering with the ovum pick-up mechanism.

Lack of sex-related differences in saquinavir pharmacokinetics in an HIV-seronegative cohort.

AIMS: To examine the influence of sex on steady-state saquinavir pharmacokinetics in HIV-seronegative volunteers administered saquinavir without a concomitant protease inhibitor. METHODS: Thirty-eight healthy volunteers (14 female) received saquinavir soft-gel capsules 1200 mg three times daily for 3 days to achieve steady-state conditions. Following administration of the 10th dose, blood was collected serially over 8 h for measurement of saquinavir plasma concentrations. Saquinavir pharmacokinetic parameter values were determined using noncompartmental methods and compared between males and females. CYP3A phenotype (using oral midazolam) and MDR-1 genotypes at positions 3435 and 2677 were determined for all subjects in order to characterize possible mechanisms for any observed sex-related differences. RESULTS: There was no significant difference in saquinavir AUC(0-8) or any other pharmacokinetic parameter value between the sexes. These findings persisted after mathematically correcting for total body weight. The mean weight-normalized AUC(0-8) was 29.9 (95% confidence interval 15.5, 44.3) and 29.8 (18.6, 40.9) ng h(-1) ml(-1) kg(-1) for males and females, respectively. No significant difference in CYP3A phenotype was observed between the groups; likewise, the distribution of MDR-1 genotypes was similar for males and females. CONCLUSION: In contrast to previous study findings, results from this investigation showed no difference in saquinavir pharmacokinetics between males and females. The discrepancy between our findings and those previously reported may be explained by the fact that we evaluated HIV-seronegative volunteers and administered saquinavir in the absence of concomitant protease inhibitors such as ritonavir. Caution must be exercised when extrapolating pharmacokinetic data from healthy volunteer studies (including sex-based pharmacokinetic differences) to HIV-infected populations or to patients receiving additional concurrent medications.

Prednisolone pharmacokinetics in the presence and absence of ritonavir after oral prednisone administration to healthy volunteers.

Corticosteroid therapy has been associated with bone toxicities (eg, osteonecrosis) and Cushing syndrome in HIV-infected patients; this may be partially attributable to a pharmacokinetic drug interaction between HIV protease inhibitors and corticosteroids. The purpose of this study was to characterize the influence of low-dose ritonavir on prednisolone pharmacokinetics in healthy subjects. Ten HIV-seronegative volunteers were given single oral doses of prednisone, 20 mg, before (baseline) and after receiving ritonavir, 200 mg, twice daily for 4 and 14 days. After each prednisone dose, serial blood samples were collected and prednisolone concentrations were determined; pharmacokinetic parameter values were compared between the groups. Geometric mean ratios (GMRs, 90% confidence interval [CI]) of the prednisolone area under the plasma concentration versus time curve (AUC0-infinity) after 4 and 14 days of ritonavir versus baseline were 1.41 (90% CI: 1.08 to 1.74) and 1.30 (90% CI: 1.09 to 1.49), respectively (P = 0.002 and P = 0.004, respectively). GMRs of prednisolone apparent oral clearance (Cl/F) were 0.71 (09% CI: 0.57 to 0.93) and 0.77 (90% CI: 0.67 to 0.92) after 4 and 14 days of ritonavir versus baseline, respectively (P = 0.0004 and P = 0.0003, respectively). Ritonavir significantly increased the systemic exposure of prednisolone in healthy subjects. Results from this investigation suggest that corticosteroid exposure is likely elevated in HIV-infected patients receiving protease inhibitors.