• Simultaneous determination of p-aminohippuric acid, acetyl-paminohippuric acid and iothalamate in human plasma and urine by high-performance liquid chromatography

      Dowling, Thomas C.; Frye, Reginald F.; Zemaitis, Michael A. (1998)
      A sensitive and specific high-performance liquid chromatographic assay was developed for the simultaneous determination of p-aminohippuric acid (PAH), acetyl-p-aminohippuric acid (aPAH), and iothalamate in human plasma and urine. Plasma samples were prepared by protein precipitation with acetonitrile followed by evaporation, reconstitution in mobile phase, and injection onto a C reversed-phase column. Urine samples were diluted with 3 volumes of mobile phase prior to injection. 18 Column effluent was monitored by UV detection at 254 nm. The lower limits of quantification in plasma were 0.5 mg/ l for PAH and aPAH, and 1.0 mg/ l for iothalamate. The within-day and between-day coefficients of variation in plasma and urine were #7.8% for all analytes. This method is well suited for renal function studies using iothalamate and PAH, whether administered as a bolus dose or by continuous infusion, to measure glomerular filtration rate and effective renal plasma flow,respectively.
    • Comparison of Iothalamate Clearance Methods for Measuring GFR

      Dowling, Thomas C.; Frye, Reginald F.; Fraley, Donald S.; Matzke, Gary R. (1999)
      Study Objective. To evaluate the bias and precision of three methods of measuring glomerular filtration rate (GFR) relative to a standard method. Design. Prospective, outpatient study. Setting. University-affiliated general clinical research center. Patients. Twenty-six patients with various degrees of renal function (GFR range 25–151 ml/min/1.73 m2). Interventions. Each patient received iothalamate twice during the study visit, first as a bolus injection and then as a priming dose followed by a constantrate infusion for 2.5 hours. Measurements and Main Results. Plasma (ClpIVB) and renal clearances (ClrIVB) after bolus injection and plasma clearance during constant-rate infusion (ClpINF) were compared with standard renal clearance during constant-rate infusion (ClrINF). All three measures were highly correlated with ClrINF (r>0.90, p<0.001). The mean ClrIVB was not significantly different from ClrINF (106.3 ± 30.4 vs 104.2 ± 28.5 ml/min/1.73 m2) and provided a precise (8.8%, 95% CI 6.5–11.1%) and unbiased measure of GFR. Both ClpIVB and ClpINF were positively biased; values exceeded ClrINF by 11.8 ± 11.1 (p=0.0001) and 10.5 ± 12.5 ml/min/1.73 m2 (p=0.0003), respectively. Use of a nonrenal correction factor of 9.8 and 10.5 ml/min/1.73 m2 for infusion and bolus plasma clearance values, respectively, eliminated bias and improved the precision of these methods. Conclusions. Iothalamate renal clearance after bolus injection is a simple, accurate, and precise measurement of GFR and may be a useful alternative to the standard infusion method in clinical investigations. The corrected plasma clearance provides a simple index of GFR for clinical practice.
    • Determination of famotidine in human plasma and urine by high-performance liquid chromatography

      Dowling, Thomas C.; Frye, Reginald F. (1999)
      An improved, rapid and specific high-performance liquid chromatographic assay was developed for the determination of famotidine in human plasma and urine. Plasma samples were alkalinized and the analyte and internal standard (cimetidine) extracted with water-saturated ethyl acetate. The extracts were reconstituted in mobile phase, and injected onto a C18 reversed-phase column; UV detection was set at 267 nm. Urine samples were diluted with nine volumes of a mobile phase-internal standard mixture prior to injection. The lower limits of quantification in plasma and urine were 75 ng/ml and 1.0 mg/ ml, respectively; intra- and inter-day coefficients of variation were #10.5%. This method is currently being used to support renal function studies assessing the use of intravenously administered famotidine to characterize cationic tubular secretion in man.
    • Characterization of Tubular Functional Capacity in Humans Using Para-aminohippurate and Famotidine

      Dowling, Thomas C.; Frye, Reginald F.; Fraley, Donald S.; Matzke, Gary R. (2001)
      Characterization of tubular functional capacity in humans using para-aminohippurate and famotidine. Background Renal drug excretion by glomerular filtration and active tubular secretion may be altered by factors such as acute and chronic renal disease, nephrotoxins, and drug interactions. Thus, accurate and reproducible methods for quantitation of glomerular filtration rate (GFR) and tubular functional capacity are critical. Methods We utilized a four-step sequential infusion method to characterize anionic [para-aminohippurate (PAH)] and cationic (famotidine) tubular functional capacity in healthy volunteers. Filtration and secretion rates were quantitated from renal clearance and iothalamate-derived GFR determinations. Results Concentration-dependent renal clearance of PAH was observed at plasma concentrations> 100 mg/L; renal clearances were 442 131 (mean SD), 423 94, 233 45, and 152 18 mL/min/1.73 m2 at plasma concentrations of 18 2, 92 5, 291 47 and 789 28 mg/L, respectively. The apparent affinity (Km) and maximum secretory capacity (TmPAH) were 141 70 mg/L and 71 16 mg/min/1.73 m2, respectively. The unbound renal clearance and tubular secretory clearance of famotidine were 384 70 and 329 78 mL/min/1.73 m2, respectively, and were not significantly correlated with the unbound plasma concentrations, which ranged from 126 to 2659 ng/mL. The rate of tubular secretion was linear at unbound plasma concentrations up to 2659 ng/mL. Conclusions These data indicate that a sequential infusion method using PAH may be used to characterize the anionic secretory component of proximal tubular function. The tubular clearance of famotidine may be a suitable index of the cationic secretory capacity of the proximal tubule in humans. Saturation of the cationic secretory pathway was not observed, and further investigation into parallel pathways of cationic secretion, such as p-glycoprotein, may be warranted.
    • Determination of the benztropine analog AHN-1055, a dopamine uptake inhibitor, in rat plasma and brain by high-performance liquid chromatography with ultraviolet absorbance detection

      Raje, Sangeeta; Dowling, Thomas C.; Eddington, Natalie D. (2002)
      N-Substituted 3α-[bis(4′-fluorophenyl)methoxy] tropanes represent a series of novel potential cocaine abuse therapeutics. AHN-1055, a member of this series, has been assessed to be the most suitable analog for pharmacokinetic studies. A sensitive and specific high-performance liquid chromatography method was developed to quantitate AHN-1055 in rat plasma and brain tissue. Reversed-phase chromatography with ultraviolet detection (λ=220 nm) was utilized to quantitate the eluate. Plasma or brain tissue samples were prepared by liquid–liquid extraction using hexane, followed by evaporation, reconstitution in mobile phase, and injection onto an ABZ+plus column. AHN-1055 and oxprenolol (internal standard) eluted at ∼9.9 and 5.01 min, respectively, without any interfering peaks. The calibration curves were found to be linear in the range of 25–10 000 ng/ml for plasma and 50–5000 ng/g for brain (r2≥0.999). The intra- and inter-day variabilities were ≤10% whereas the intra- and inter-day errors were ≤8.5%. Plasma and brain recoveries of AHN-1055 were 95 and 79%, respectively. Stability studies showed plasma quality control samples to be stable through at least three freeze–thaw cycles (error<3.5%), for at least 24 h when subjected to room temperature (error<3%) and for at least 30 h after loading the processed samples onto the autosampler (error<3%). AHN-1055 stock solution was found to be stable for at least 4 months when stored at 4 °C (error<6%). The validated method accurately quantified AHN-1055 in plasma and brain samples collected from a pharmacokinetic study consisting of an intravenous bolus in the tail vein of adult male Sprague–Dawley rats.
    • Drug Metabolism Considerations in Patients With Chronic Kidney Disease

      Dowling, Thomas C. (2002)
      Chronic kidney disease (CKD) is a progressive process leading to end stage renal disease and either dialysis or transplantation. Patients with CKD often have numerous comorbid conditions such as diabetes, hypertension, and acid-base and electrolyte disorders that can lead to alterations in homeostasis. Changes in drug disposition including hepatic metabolism via phase 1 (ie, cytochrome P-450 enzymes) and phase 2 (ie, conjugation) pathways have been reported. Biotransformation of drugs and endogenous substances within the kidney itself may also be compromised in the presence of CKD. Reduced hepatic and renal clearance leads to systemic accumulation of the parent drug as well as active and toxic metabolites. Characterization of specific hepatic cytochrome (CYP) enzyme pathways in patients with CKD is an area of current research and will lead to an understanding of phenotypic and genotypic expression patterns of several key drug-metabolizing enzymes. The evolving knowledge of CYP enzymes and the alterations that can occur in CKD should allow clinicians to predict adverse consequences of drug therapy and thus prevent these events from occurring. The pharmacy practitioner can also provide important pharmacotherapy interventions in this special patient population, including dose individualization, therapeutic drug monitoring, and evaluation of therapeutic outcomes.
    • Evaluation of P-glycoprotein–Mediated Renal Drug Interactions in an MDR1-MDCK Model

      Karyekar, Chetan S.; Eddington, Natalie D.; Garimella, Tushar S.; Gubbins, Paul O.; Dowling, Thomas C. (2003)
      Study Objective. To evaluate P-glycoprotein (P-gp)–mediated renal drug interactions in an in vitro model of tubular secretion. Design. In vitro experiment. Setting. University-affiliated pharmacokinetics laboratory. Cell Lines. Madin-Darby canine kidney (MDCK), multidrug-resistant-1 (MDR1)-MDCK, and human colon carcinoma (Caco-2) cells. Intervention. Transepithelial transport (basolateral-to-apical and apical-tobasolateral) of cimetidine was assessed in the absence and presence of various concentrations of the P-gp inhibitors itraconazole and PSC-833 in a renal P-gp cell culture model (MDR1-MDCK). Measurements and Main Results. Apparent permeability of cimetidine was characterized, and level of P-gp expression was determined by Western blot analysis, in MDCK (wild type), MDR1-MDCK, and Caco-2 cells (for relative comparison). In the presence of PSC-833, cimetidine’s apparent permeability value for basolateral-to-apical transport decreased from 2.96 to 1.15 x 10-6 cm/second, coupled with a decrease in efflux ratio from 2.36 to 1.80. The effect of itraconazole was concentration dependent, with cimetidine’s apparent permeability value for basolateral-to-apical transport decreasing from 3.96 to 1.92 x 10-6 cm/second (p<0.05), resulting in a 50% decrease in efflux ratio. Expression of P-gp was negligible in MDCK (wildtype) cells, but high-level expression was confirmed in both MDR1-MDCK and Caco-2 cells. Conclusion. P-glycoprotein plays a significant role in the renal tubular secretion of organic cations such as cimetidine, and the high level of P-gp expression in MDR1-MDCK cells makes this a well-suited model for evaluating mechanisms of renal drug interactions.
    • Nesiritide Does Not Improve Renal Function in Patients with Chronic Heart Failure and Worsening Serum Creatinine

      Wang, David J.; Dowling, Thomas C.; Meadows, Dean; Ayala, Tomas; Marshall, Joanne, R.N.; Minshall, Stacey; Greenberg, Nancy; Thattassery, Emil; Fisher, Michael L.; Rao, Krishnamurti; Gottlieb, Stephen S. (2004)
      Background—Nesiritide (synthetic human brain natriuretic peptide) is approved for the treatment of symptomatic heart failure. However, studies of brain natriuretic peptide in patients with heart failure have come to conflicting conclusions about effects on glomerular filtration rate (GFR), effective renal plasma flow, natriuresis, and diuresis. Methods and Results—To identify a population at high risk of renal dysfunction with conventional treatment, we selected patients with a creatinine level increased from baseline (within 6 months). We examined the effects of nesiritide on GFR (measured by iothalamate clearance), renal plasma flow (measured by para-amino hippurate clearance), urinary sodium excretion, and urine output in a double-blind, placebo-controlled, crossover study. Patients received nesiritide (2 g/kg IV bolus followed by an infusion of 0.01 g/kg per minute) or placebo for 24 hours on consecutive days. Nesiritide and placebo data were compared by repeated-measures analysis and Student t test. We studied 15 patients with a recent mean baseline creatinine of 1.5 0.4 mg/dL and serum creatinine of 1.8 0.8 mg/dL on admission to the study. There were no differences in GFR, effective renal plasma flow, urine output, or sodium excretion for any time interval or for the entire 24-hour period between the nesiritide and placebo study days. For 24 hours, urine output was 113 51 mL/h with placebo and 110 56 mL/h with nesiritide. GFR during placebo was 40.9 25.9 mL/min and with nesiritide was 40.9 25.8. Conclusions—Nesiritide did not improve renal function in patients with decompensated heart failure, mild chronic renal insufficiency, and renal function that had worsened compared with baseline. The lack of effect may be related to renal insufficiency, hemodynamic alterations, sodium balance, severity of heart failure, or drug dose. Understanding the importance of these issues will permit effective and appropriate use of nesiritide.
    • Renal Interaction Between Itraconazole and Cimetidine

      Karyekar, Chetan S.; Eddington, Natalie D.; Briglia, Andrew; Gubbins, Paul O.; Dowling, Thomas C. (2004)
      Renal drug interactions can result from competitive inhibition between drugs that undergo extensive renal tubular secretion by transporters such as P-glycoprotein (P-gp). The purpose of this study was to evaluate the effect of itraconazole, a known P-gp inhibitor, on the renal tubular secretion of cimetidine in healthy volunteers who received intravenous cimetidine alone and following 3 days of oral itraconazole (400 mg/day) administration. Glomerular filtration rate (GFR) was measured continuously during each study visit using iothalamate clearance. Iothalamate, cimetidine, and itraconazole concentrations in plasma and urine were determined using high-performance liquid chromatography/ ultraviolet (HPLC/UV) methods. Renal tubular secretion (CLsec) of cimetidine was calculated as the difference between renal clearance (CLr) andGFR (CLioth) ondays 1 and 5. Cimetidine pharmacokinetic estimates were obtained for total clearance (CLT), volume of distribution (Vd), elimination rate constant (Kel), area under the plasma concentrationtime curve (AUC0-240 min), and average plasma concentration (Cpave) before and after itraconazole administration. Plasma itraconazole concentrations following oral dosing ranged from 0.41 to 0.92 μg/mL. The cimetidine AUC0-240 min increased by 25% (p < 0.01) following itraconazole administration. The GFR and Vd remained unchanged, but significant reductions in CLT (655 vs. 486 mL/min, p < 0.001) and CLsec (410 vs. 311 mL/min, p = 0.001) were observed. The increased systemic exposure of cimetidine during coadministration with itraconazole was likely due to inhibition of P-gpmediated renal tubular secretion. Further evaluation of renal P-gp-modulating drugs such as itraconazole thatmay alter the renal excretion of coadministered drugs is warranted
    • Phase 1 Safety and Pharmacokinetic Study of Chimeric Murine-Human Monoclonal Antibody caStx2 Administered Intravenously to Healthy Adult Volunteers

      Dowling, Thomas C.; Chavaillaz, Pierre A.; Young, David G.; Melton-Celsa, Angela; O'Brien, Alison; Thuninz- Roberson, Claire; Edelman, Robert; Tacket, Carol O. (2005-05)
      Hemolytic-uremic syndrome (HUS) is a serious complication of infection by Shiga toxin-producing Escherichia coli. Shiga toxin type 2 (Stx2) is responsible for the renal toxicity that can follow intestinal infection and hemorrhagic colitis due to E. coli. A chimeric mouse-human antibody, designated cαStx2, that has neutralizing activity in a mouse model was produced and tested in healthy adult volunteers. In this phase I dose escalation study, cαStx2 was generally well tolerated. Pharmacokinetic studies indicated that clearance was stable over the dose range of 1.0 to 10 mg/kg of body weight (0.249 ± 0.023 ml/kg/h) but was higher for the 0.1-mg/kg dose (0.540 ± 0.078 ml/kg/h), suggesting saturable elimination. A similar nonlinear trend was observed for the volume of distribution, where average values ranged from 0.064 ± 0.015 liter/kg for the 1.0- to 10-mg/kg doses and 0.043 ± 0.005 for the 0.01-mg/kg dose. The relatively small volume of distribution suggests that the antibody is limited to the vascular (plasma) compartment. The mean half-life was 165 ± 66 h, with lowest values observed for the 0.1-mg/kg dose (56.2 ± 9.7 h) and the highest values reported for the 10.0-mg/kg dose (206.4 ± 12.4 h). Future studies are needed to confirm the safety of this cαStx2, and innovative clinical trials will be required to measure its efficacy in preventing or treating HUS.
    • Renin-Angiotensin System Genes and Exercise Training-Induced Changes in Sodium Excretion in African American Hypertensives

      Jones, Jennifer M., Ph.D.; Park, Jung-Jun, Ph.D.; Johnson, Jennifer, M.A.; Vizcaino, Dave; Hand, Brian, M.S.; Ferrell, Robert; Weir, Matthew R., 1952-; Dowling, Thomas C.; Obisesan, Thomas; Brown, Michael, Ph.D. (2006)
      Objective: To determine whether angiotensinconverting enzyme (ACE) and angiotensinogen (AGT) genotypes could predict changes in urinary sodium excretion in response to short-term aerobic exercise training (AEX). Design: Longitudinal intervention. Setting: The study was conducted at the University of Maryland at College Park and at Baltimore, and the University of Pittsburgh General Clinical Research Center. Participants: 31 (age 53 6 2 years) sedentary, hypertensive (146 6 2/88 6 2 mm Hg) African Americans. Intervention: Aerobic exercise training (AEX) consisted of seven or eight consecutive days, 50 minutes per day, at 65% of heart rate reserve. Participants underwent a 24-hour period of ambulatory blood pressure (BP) monitoring and urine collection at baseline and 14–18 hours after the last exercise session. Main Outcome Measures: Angiotensiongen (AGT) M235T and ACE I/D genotype and sodium excretion and ambulatory BP. Results: Average sodium excretion for the entire group independent of genotype increased after AEX (108 6 9 vs 143 6 12 mEq/day, P5.003). Sodium excretion significantly increased after exercise training in the ACE II (114 6 22 vs 169 6 39 mEq/day, P5.04), but not in the ID (100 6 8 vs 133 6 17 mEq/day, P5.12) or DD (113 6 18 vs 138 6 11 mEq/day, P5.13) genotype groups. In the II genotype group, the increase in sodium excretion was significantly and inversely correlated with decreases in 24-hour diastolic (r52.88, P5.02) and mean (r52.95, P5.004) BP. The AGT TT and MT+MM genotype groups similarly increased their sodium excretion by 34 6 16 (P5.05) and 37 6 17 (P5.05) mEq/day respectively. Conclusions: These results suggest that African American hypertensives with the ACE II genotype may be more susceptible to sodium balance and BP changes with exercise training compared with those with the ID and DD genotypes.
    • Role of Potassium Excretion and Percent Body Fat on Ethnic Differences in Plasma Aldosterone Levels

      Jones, Jennifer M., Ph.D.; Park, Jung-Jun, Ph.D.; Dowling, Thomas C.; Phares, Dana; Park, Joon-Young, M.S.; Brown, Michael, Ph.D. (2006)
      Objective: To determine whether plasma aldosterone (PA) levels differed between African American and White prehypertensives and if so, could the difference be explained by ethnicity-related variability in urinary K⁺ and Na⁺ excretion, body mass index (BMI), and percent body fat. Design: Ethnic comparison Setting: The University of Maryland College Park and the University of Maryland School of Pharmacy. Participants: 61 (African American, n528; White, n533) prehypertensives (systolic blood pressure [SBP] 131 6 10 mm Hg, diastolic blood [DBP] 85 6 6 mm Hg). Intervention: 6-week dietary stabilization and medication tapering period. Main Outcome Measures: PA levels, Na⁺ and K⁺ excretion, blood pressure, and percent body fat and BMI. Results: We saw no differences in SBP (P5.36) and DBP (P5.54) between the two ethnic groups. PA levels were lower in African Americans compared to Whites (62 6 7 vs 107 6 12 pg/mL, P5.002). 24-hour K⁺ excretion was lower among African Americans compared to Whites (51 6 7 vs 70 6 4 mmol/day, P5.002). We saw no difference in percent body fat, BMI, SBP, or DBP between African Americans and Whites. After separately accounting for K+ excretion and Na⁺excretion and BMI, plasma aldosterone levels remained significantly different between the two ethnic groups. After adjusting for percent body fat, PA levels were not significantly different between the two ethnic groups (P5.06). Conclusions: The findings of the current study indicate that PA levels differ between African American and White prehypertensives and this difference may partly be due to ethnic variability in K⁺ excretion and percent body fat.
    • Development and Assessment of Internet Case Based Multi-disciplinary Infectious Disease Workshops as a Learning Tool in Antimicrobial Therapeutics

      Wilks, Angela; Pandit, Neha Sheth; Tucker, Shannon R. (American College of Clinical Pharmacy Annual Meeting 2008, 2008)
    • Integrating Virtual Case-Based Activities into Online Courses

      Ruane, Richard, M.A.; Pandit, Neha Sheth; Klimas, Christopher (American College of Clinical Pharmacy Annual Meeting 2009, 2009)
    • Estimated GFR vs Creatinine Clearance for Drug Dosing

      Dowling, Thomas C.; Matzke, Gary R.; Murphy, John E., 1945- (2009-11)
    • Evaluation of Renal Drug Dosing: Prescribing Information and Clinical Pharmacist Approaches

      Dowling, Thomas C.; Matzke, Gary R.; Murphy, John E., 1945-; Burckart, Gilbert J. (2010)
      Study Objective. To characterize renal function parameters reported in United States Food and Drug Administration-approved prescribing information (package inserts) to compare dosage recommendations for patients with impaired renal function between prescribing information and tertiary drug dosing references, and to evaluate renal function quantification methods most commonly used by clinical pharmacists to develop dosage regimens. Design. Retrospective analysis and Web-based survey. Data Sources. Prescribing information for all new molecular entities (NMEs) approved from 1998-2007 in which dosing recommendations were proposed for patients with impaired renal function, drug monographs from four tertiary drug dosing references (Micromedex, Lexi-Comp, Epocrates Rx, and American Hospital Formulary Service [AHFS] Drug lnformation) for all identified NMEs, and a Web-based survey of 204 nephrology and critical care pharmacy practitioner. Measurements and Main Results. A total of 44 NMEs included renal dosing recommendations in their prescribing information, For all 44 NMEs, prescribing information was reviewed to determine methods to quantify renal function, units of measure reported, and use of chronic kidney disease terminology. The most common index of renal function was creatinine clearance; the Cockcroft-Gault equation was specified in the prescribing information of 11 NMEs. Standardization for body weight was inconsistent, with prescribing information for four NMEs reporting renal function in ml/minute/l.73m² The prescribing inlormation or tertiary sources did not mention use of estimated glOlnerular filtration rate (eGFR) or the Modification of Diet in Renal Disease Study (MDRD) equation. Epocrates Rx provided the most abbreviated renal dosing information, whereas AHFS Dmg Information was the most comprehensive, and Lexi-Cornp includes a renal function calculator. Nearly all (86%) clinical pharmacists indicated that automated eGFR is reponed at their institutions, although they do not use these predictions for dosing in patients with impaired renal function, and their approaches to renal function estimation varied widely. Conclusion. Reporting of renal function methods and dosing recommendattons for patients with impaired renal function requires standardtzarion in order to ensure optimal dosing. Pharmacy clinicians do not substitute eGFR in place of creatinine clearance for renal dosing, which is consistent with current prescribing information, Studies are needed that will evaluate the validity of using eGFR to predict drug clearance and thereby generate dosage recommendations.
    • Clinical evaluation of natalizumab for formulary consideration

      Bivins, Ashley; Hou, Karolyn; Ayesu, Nana; Ellsworth, Brian, Jr.; Montenegro, Susan; Tu, Xiao; Boyle, Cynthia; Dowling, Thomas C.; Shaya, Fadia T. (UK: Ashley Publications Ltd, 2010)
      Importance of the field: Natalizumab is a monotherapy for relapsing forms of multiple sclerosis (MS) and maintaining remission in Crohn’s disease (CD). Evaluation of natalizumab’s clinical relevance must be performed before considering its place in treatment of these diseases. Areas covered in this review: MEDLINE and PubMed searches were performed using the keywords multiple sclerosis, Crohn’s disease, natalizumab and clinical trials. The manufacturer’s product information was consulted to extract additional data. Pivotal clinical trials included: Natalizumab Safety and Efficacy in Relapsing Remitting Multiple Sclerosis (AFFIRM), Safety and Efficacy of Natalizumab in Combination With Interferon Beta-1a in Patients With Relapsing Remitting Multiple Sclerosis (SENTINEL), Efficacy of Natalizumab as Active Crohn’s Therapy (ENACT)-1 and 2 and Efficacy of Natalizumab in Crohn’s Disease Response and Remission (ENCORE). What the reader will gain: AFFIRM and SENTINEL showed improvements in progression of MS. ENACT-1 failed to show a significant effect, but the follow-up trials ENACT-2 and ENCORE were able to demonstrate a response to natalizumab. Take home message: Two trials on efficacy of Tysabri for treatment of MS demonstrated positive results. Efficacy for CD was mixed. More research demonstrating head-to-head evidence against other agents is necessary to determine if Tysabri’s benefits are significant.