Sarah M Robertson

Silver Spring Networks, 레드우드시티, California, United States

Are you Sarah M Robertson?

Claim your profile

Publications (15)46.15 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: Objectives: Literature reports regarding the efficacy of efavirenz (EFV) 600 mg with rifampin (RIF) are not consistent. Evaluation of a drug-drug interaction (DDI) study and supportive semi-mechanistic population pharmacokinetic (PK) analyses were undertaken to help delineate this issue. Design/methods: DDI study and supportive semi-mechanistic population PK analyses were provided by BMS. Population PK analysis was based on six studies with intensive EFV PK sampling. An ACTG study with sparse PK sampling was used for model evaluation. Simulations compared EFV exposure at various doses in combination with RIF to EFV exposures at 600 mg once daily (QD). Effects of CYP2B6 genotypes on the magnitude of EFV-RIF interaction were also explored. Results: In DDI study, co-administering EFV 600 mg QD and RIF reduced mean EFV exposure by ~ 30%. Population PK model provided acceptable predictive performance of central tendency and variability for EFV C0, Cmax, and AUC. Simulations predicted that increasing EFV to 800 mg QD with RIF would result in EFV AUC and Cmax similar to EFV 600 mg QD alone. EFV AUC and Cmax were ~ 2 times higher in subjects with reduced function CYP2B6 genotypes. However, the RIF effect was consistent across all genotypes. EFV dose adjustment to 800 mg QD did not increase the risk of overexposure compared to 600 mg EFV QD within each genotype. Conclusion: Dose adjustment based on matching systemic exposure was recommended to mitigate the potential for sub-therapeutic EFV exposures. Our review did not reveal any safety concerns in subjects receiving EFV 800 mg QD with RIF.
    No preview · Article · Apr 2014 · International journal of clinical pharmacology and therapeutics
  • Sarah M. Robertson · Stephen C. Piscitelli · Kimberly A. Struble
    [Show abstract] [Hide abstract]
    ABSTRACT: Despite great strides in human immunodeficiency virus (HIV) drug development the management of drug interactions remains a key component of patient care. A number of new drugs have been approved in the past 5 years ­including two new classes of antiretrovirals: CCR5 antagonists and integrase ­inhibitors. HIV treatment is complex generally requiring at least three antiretrovirals in addition to medications for supportive care and concomitant infections. Many antiretrovirals have clinically significant drug interactions that require dosage adjustment. This chapter reviews important drug interactions for the newest antiretrovirals and provides detailed tables to guide clinicians on patient management.
    No preview · Chapter · Sep 2011
  • Vikram Arya · Sarah M Robertson · Kimberly A Struble · Jeffrey S Murray

    No preview · Article · Jun 2011 · The Journal of Clinical Pharmacology
  • [Show abstract] [Hide abstract]
    ABSTRACT: A number of herbal preparations have been shown to interact with prescription medications secondary to modulation of cytochrome P450 (CYP) and/or P-glycoprotein (P-gp). The purpose of this study was to determine the influence of Panax ginseng on CYP3A and P-gp function using the probe substrates midazolam and fexofenadine, respectively. Twelve healthy participants (8 men) completed this open-label, single-sequence pharmacokinetic study. Healthy volunteers received single oral doses of midazolam 8 mg and fexofenadine 120 mg, before and after 28 days of P ginseng 500 mg twice daily. Midazolam and fexofenadine pharmacokinetic parameter values were calculated and compared before and after P ginseng administration. Geometric mean ratios (postginseng/preginseng) for midazolam area under the concentration-time curve from zero to infinity (AUC(0-∞)), half-life (t(1/2)), and maximum concentration (C(max)) were significantly reduced at 0.66 (0.55-0.78), 0.71 (0.53-0.90), and 0.74 (0.56-0.93), respectively. Conversely, fexofenadine pharmacokinetics were unaltered by P ginseng administration. Based on these results, P ginseng appeared to induce CYP3A activity in the liver and possibly the gastrointestinal tract. Patients taking P ginseng in combination with CYP3A substrates with narrow therapeutic ranges should be monitored closely for adequate therapeutic response to the substrate medication.
    No preview · Article · Jun 2011 · The Journal of Clinical Pharmacology
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: . To determine the influence of Echinacea purpurea on the pharmacokinetics of lopinavir-ritonavir and on cytochrome P450 (CYP) 3A and P-glycoprotein activity by using the probe substrates midazolam and fexofenadine, respectively. Open-label, single-sequence pharmacokinetic study. Outpatient clinic in a federal government research center. Thirteen healthy volunteers (eight men, five women). Subjects received lopinavir 400 mg-ritonavir 100 mg twice/day with meals for 29.5 days. On day 16, subjects received E. purpurea 500 mg 3 times/day for 28 days: 14 days in combination with lopinavir-ritonavir and 14 days of E. purpurea alone. In order to assess CYP3A and P-glycoprotein activity, subjects received single oral doses of midazolam 8 mg and fexofenadine 120 mg, respectively, before and after the 28 days of E. purpurea. On days 15 and 30 of lopinavir-ritonavir administration (before and after E. purpurea administration, respectively), serial blood samples were collected over 12 hours to determine lopinavir and ritonavir concentrations and subsequent pharmacokinetic parameters by using noncompartmental methods. Neither lopinavir nor ritonavir pharmacokinetics were significantly altered by 14 days of E. purpurea coadministration. The post-echinacea: pre-echinacea geometric mean ratios (GMRs) for lopinavir area under the concentration-time curve (AUC) from 0-12 hours and for maximum concentration were 0.96 (90% confidence interval [CI] 0.83-1.10, p=0.82) and 1.00 (90% CI 0.88-1.12, p=0.72), respectively. Conversely, GMRs for midazolam AUC from time zero extrapolated to infinity and oral clearance were 0.73 (90% CI 0.61-0.85, p=0.008) and 1.37 (90% CI 1.10-1.63, p=0.02), respectively. Fexofenadine pharmacokinetics did not significantly differ before and after E. purpurea administration (p>0.05). Echinacea purpurea induced CYP3A activity but did not alter lopinavir concentrations, most likely due to the presence of the potent CYP3A inhibitor, ritonavir. Echinacea purpurea is unlikely to alter the pharmacokinetics of ritonavir-boosted protease inhibitors but may cause modest decreases in plasma concentrations of other CYP3A substrates.
    Full-text · Article · Aug 2010 · Pharmacotherapy
  • [Show abstract] [Hide abstract]
    ABSTRACT: To characterize the effect of efavirenz on bupropion hydroxylation as a marker of cytochrome P450 (CYP) 2B6 activity in healthy subjects. 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). 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). 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.
    No preview · Article · Dec 2008 · JAIDS Journal of Acquired Immune Deficiency Syndromes
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: 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.
    Full-text · Article · Jul 2008 · The Journal of Clinical Pharmacology
  • [Show abstract] [Hide abstract]
    ABSTRACT: One of the numerous regulatory functions of the Food and Drug Administration (FDA) is the evaluation of drug-drug interactions and the determination of appropriate dose adjustments, if necessary, to ensure the safe and effective use of medications. The FDA considers several data sources when determining the significance of drug-drug interactions. The majority of dose adjustment recommendations are based on specific drug-drug interactions studies. The FDA reviews individual patient pharmacokinetic and safety data from drug interaction studies, determines appropriate dose adjustments, and provides recommendations to update the respective product labeling. Sometimes literature references are submitted to the FDA to support dosing recommendations. Determining an appropriate dose adjustment recommendation based on literature reports is a challenge for the FDA due to the lack of individual patient pharmacokinetic or safety data from these studies. Recently, the FDA encountered a challenging regulatory situation when evaluating literature reports to determine the appropriate dose of efavirenz and rifampin. Although numerous studies were found in the literature about this combination, a dosing recommendation cannot be concluded from the reported data. This article reviews the process the FDA used to evaluate literature to support potential dose adjustments for efavirenz when coadministered with rifampin and the challenges encountered during the process.
    No preview · Article · May 2008 · The Journal of Clinical Pharmacology
  • [Show abstract] [Hide abstract]
    ABSTRACT: 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. 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. 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. 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.
    No preview · Article · Mar 2008 · Current Medical Research and Opinion
  • Sarah M Robertson · Scott R Penzak · Alice Pau
    [Show abstract] [Hide abstract]
    ABSTRACT: Improvement in the availability of antiretroviral (ARV) therapy continues to reduce HIV morbidity and mortality. With more treatment choices and better accessibility, the extent of medication use among patients with HIV/AIDS continues to grow. ARV drugs are particularly prone to drug interactions as a consequence of their metabolic and pharmacokinetic properties. The recognition and management of drug interactions in patients on ARVs is a constant challenge to medical providers. Staying abreast of drug interaction knowledge is complicated by the rate at which new information becomes available through in vivo investigation, case reports and pharmacokinetic studies. In addition, distinguishing the clinical significance of an interaction is difficult due to the large interpatient variability in pharmacokinetics exhibited by most ARV agents. This review provides an update to a previous review article published in 2005, and is intended to improve the reader's knowledge of drug interactions in the management of HIV infection.
    No preview · Article · Jan 2008 · Expert Opinion on Pharmacotherapy
  • [Show abstract] [Hide abstract]
    ABSTRACT: To investigate a potential correlation between exposure to oral midazolam, a commonly used cytochrome P450 (CYP) 3A probe, and saquinavir and indinavir exposure. Open-label, prospective, pharmacokinetic study. Outpatient research center. Thirty-six healthy volunteers aged 22-50 years. 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. 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). 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.
    No preview · Article · Sep 2006 · Pharmacotherapy
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: To examine the influence of sex on steady-state saquinavir pharmacokinetics in HIV-seronegative volunteers administered saquinavir without a concomitant protease inhibitor. 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. 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. 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.
    Full-text · Article · May 2006 · British Journal of Clinical Pharmacology
  • [Show abstract] [Hide abstract]
    ABSTRACT: To evaluate antiretroviral pharmacokinetics in patients who are coinfected with human immunodeficiency virus (HIV) and hepatitis B and/or C virus. Specifically, we sought to determine whether coinfection results in higher than expected concentrations of protease inhibitors and nonnucleoside reverse transcriptase inhibitors (NNRTIs). Case series. Human immunodeficiency virus clinic. Twenty-six patients infected with HIV and hepatitis B and/or C virus. Patients' plasma trough concentrations (Cmeasured) of protease inhibitors and NNRTIs were compared with population average trough concentrations reported in the literature (Cpredicted). Trough concentrations were obtained irrespective of the patients' liver function. A concentration ratio of Cmeasured: Cpredicted was determined for each patient. The mean concentration ratio of the 26 patients was 1.43 (95% confidence interval 1.08-1.78). For the six patients taking nelfinavir, the ratio of nelfinavir's active metabolite (M8): parent drug was calculated. The median M8:nelfinavir ratio for these six patients was 69% lower than what has been reported in a general HIV population. These preliminary findings suggest that trough concentrations of protease inhibitors and NNRTIs may be elevated in patients with HIV infection who are coinfected with hepatitis B and/or C, compared with a general population of patients with HIV infection. Until further investigation defines the relationship between coinfection, metabolic dysfunction, and increased antiretroviral exposure, therapeutic drug monitoring may be helpful to identify coinfected patients at risk for antiretroviral toxicity secondary to elevated plasma drug concentrations.
    No preview · Article · Sep 2005 · Pharmacotherapy
  • Source
    Sarah M Robertson · Scott R Penzak · Jason Lane · Alice K Pau · JoAnn M Mican
    [Show abstract] [Hide abstract]
    ABSTRACT: Although it has not been demonstrated yet, phenytoin is expected to reduce efavirenz exposure through coinduction of cytochrome P450 (CYP) 3A4 and CYP2B6. Conversely, efavirenz has been shown in vitro to inhibit the enzymes responsible for phenytoin metabolism, CYP2C9 and CYP2C19. We report a case in which a potential bidirectional drug interaction between phenytoin and efavirenz resulted in lower-than-expected efavirenz concentrations and elevated phenytoin levels. Therapeutic drug monitoring was used in this case to ensure adequate efavirenz exposure.
    Preview · Article · Aug 2005 · Clinical Infectious Diseases
  • Sarah M Robertson · Scott R Penzak · Alice K Pau
    [Show abstract] [Hide abstract]
    ABSTRACT: The availability of antiretroviral therapy has significantly reduced the morbidity and mortality of HIV infection. In addition, improved treatment of opportunistic infections and comorbidities common to patients with HIV is further prolonging the lives of patients. Improvement in the treatment of HIV has led to a significant increase in the number of medications which caregivers are able to utilise to manage HIV/AIDS. Antiretroviral medications, as well as many of the drugs used in the management of opportunistic infections and primary care (e.g., macrolide antibiotics, azole antifungals, cholesterol-lowering medications), are particularly prone to drug interactions. The interpretation of clinically significant interactions is complicated by the rate at which new information on drug metabolism and transport is becoming available. Management of drug interactions in HIV is further confounded by conflicting study results and differences between documented and theoretical inter-actions. The mechanisms and significance of interactions involving antiretrovirals, drugs used for opportunistic infections, and other medications commonly used in HIV patients will be reviewed.
    No preview · Article · Mar 2005 · Expert Opinion on Pharmacotherapy

Publication Stats

267 Citations
46.15 Total Impact Points


  • 2008-2014
    • Silver Spring Networks
      레드우드시티, California, United States
    • U.S. Food and Drug Administration
      • Office of Clinical Pharmacology
      Washington, Washington, D.C., United States
  • 2011
    • U.S. Department of Health and Human Services
      Washington, Washington, D.C., United States
  • 2005-2010
    • National Institutes of Health
      • • Center for Clinical Research
      • • Pharmacy Department
      Maryland, United States
    • National Institute of Allergy and Infectious Diseases
      • Laboratory of Immunoregulation
      베서스다, Maryland, United States