The paradox of scientific excellence and the search for productivity in pharmaceutical research and development.

Scientific advances in specialty areas are proceeding at a rapid rate, but the research and development enterprise seems unable to take full advantage. Harnessing the steady stream of knowledge and inventions from different disciplines is the critical management issue of our time. This article suggests a framework for a management-directed effort to improve productivity by enhancing interdisciplinary collaboration.

Pharmacometrics and the transition to model-based development.

As the transition to model-based drug development continues, pharmacometric analysis will have an increasingly important role across the entire life cycle of drug discovery, development, regulatory approval, and commercialization. For this reason, pharmacometrics can--and should--have an integrating function in the transformation to model-based development. This essay describes an approach for formalizing the pharmacometrics process using the disciplines encompassed by enterprise engineering.

A population pharmacokinetic-pharmacodynamic analysis and model validation of azimilide.

BACKGROUND: Pharmacokinetic (PK) and pharmacodynamic (PD) models for azimilide were developed and validated with sparse blood sampling and QTc interval data obtained during three clinical trials of azimilide for prevention of supraventricular arrhythmia recurrence. METHODS: Patients were orally administered placebo or azimilide dihydrochloride, 35, 50, 75, 100, or 125 mg/d, for 6 to 9 months. NONMEM was used for data fitting and assessment of selected patient covariates and concomitant medication classes for PK/PD relationships. RESULTS: Results indicate that azimilide clearance (CL) was dependent on body weight (WTKG), gender, and current tobacco use, where CL (L/h) = 3.92 x (WTKG - 43)(0.208), with a 17% increase for male subjects and a 15.5% increase for current tobacco use. Volume of distribution (V) was also dependent on WTKG and total bilirubin (BIL), where V (L) = 9.88 x (WTKG - 43) + 717 x (BIL)(0.348). The PK/PD analysis indicated that the baseline QTc interval was dependent on gender, New York Heart Association Class, digoxin, and paced artificial pacemaker spike, whereas the 50% effective concentration (EC(50)) was dependent on the serum potassium (K) level, where EC(50) = 107 x K. The change in EC(50) was not clinically significant within the normal range for potassium. The mean E(max) (maximum increase in the QTc interval for the E(max) models) was a 61.7 ms increase from baseline. At 125 mg/d the predicted percent increase in the QTc interval at the maximum plasma drug concentration at steady state was 9% and 10% for male and female patients, respectively. The values of the median prediction error were -3% and -0.4% for the PK and PK/PD models, respectively, and the values of the absolute prediction error were 21% and 4% for the PK and PK/PD models, respectively, indicating that both models are essentially unbiased and acceptably accurate. CONCLUSIONS: Azimilide PK parameters are dependent on body weight, gender, smoking status, and bilirubin and are independent of the coadministration of digoxin, warfarin, and cytochrome P4503A4 inhibitors and inducers. The relationship between azimilide concentration and change in QTc is primarily dependent on serum potassium.

Pharmacodynamics of fluoroquinolones against Streptococcus pneumoniae in patients with community-acquired respiratory tract infections.

Fluoroquinolone antibiotic agents have demonstrated efficacy in the treatment of respiratory tract infections. This analysis was designed to examine the relationship between drug exposure, as measured by the free-drug area under the concentration-time curve at 24 h (AUC(24))/MIC ratio, and clinical and microbiological responses in patients with community-acquired respiratory tract infections involving Streptococcus pneumoniae. The study population included 58 adult patients (34 males, 24 females) who were enrolled in either of two phase III, randomized, multicenter, double-blind studies of levofloxacin versus gatifloxacin for the treatment of community-acquired pneumonia or acute exacerbation of chronic bronchitis. Clearance equations from previously published population pharmacokinetic models were used in conjunction with dose and adjusted for protein binding to estimate individual patient free-drug AUC(24)s. In vitro susceptibility was determined in a central laboratory by broth microdilution in accordance with NCCLS guidelines. Pharmacodynamic analyses were performed on data from all evaluable patients with documented S. pneumoniae infection using univariate and multivariable logistic regression; pharmacodynamic breakpoints were estimated using Classification and Regression Tree analysis. A statistically significant (P = 0.013) relationship between microbiological response and the free-drug AUC(24)/MIC ratio was detected. At a free-drug AUC(24)/MIC ratio of <33.7, the probability of a microbiological response was 64%, and at a free-drug AUC(24)/MIC ratio of >33.7, it was 100% (P < 0.01). These findings may provide a minimum target free-drug AUC(24)/MIC ratio for the treatment of infections involving S. pneumoniae with fluoroquinolone antibiotics and provide a paradigm for the selection of fluoroquinolones to be brought forward from drug discovery into clinical development and dose selection for clinical trials. Further, when target free-drug AUC(24)/MIC ratios are used in conjunction with stochastic modeling techniques, these findings may be used to support susceptibility breakpoints for fluoroquinolone antibiotics and S. pneumoniae.

Relationship between drug exposure and the efficacy and safety of bupropion sustained release for smoking cessation.

A population pharmacokinetic and pharmacodynamic analysis evaluated the relationships of dose, plasma concentrations of bupropion and metabolites, and patient covariates with the safety and efficacy of bupropion sustained release (SR) for smoking cessation. A total of 519 outpatient chronic cigarette smokers were randomized to one of three bupropion SR doses: 100, 150, or 300 mg/day or placebo. The bupropion plasma concentration time data were fit and subject-specific bayesian estimates of clearance were obtained. Logistic regression analyses evaluated the role of dose, concentrations, and covariates in predicting efficacy and safety endpoints. For the evaluation of efficacy, patients were classified as quitters or non-quitters on the basis of a 4-week quit variable (defined as complete abstinence for weeks 4-7 of the study). For the evaluation of safety, patients were classified into two categories for each adverse event evaluated, corresponding to whether the patient ever experienced the adverse event during the course of the study or never experienced the event, regardless of whether the event was treatment-emergent. The efficacy of bupropion SR in facilitating smoking cessation was found to be related to dose and a mean metabolite concentration, and quitting in general was found to be related to the number of cigarettes smoked per day at baseline. Smoking cessation was 1.42, 1.69, and 2.84 times more likely in patients receiving 100, 150, and 300 mg/day of bupropion SR, respectively, as compared to placebo (p = 0.0001). As the baseline number of cigarettes smoked per day increased, the likelihood of quitting decreased regardless of the treatment condition. Insomnia and dry mouth were positively associated with mean metabolite concentrations, and dry mouth was inversely related to patient weight. Anxiety was inversely related to predicted steady-state concentration (Cpss), suggesting a positive effect on this withdrawal symptom. Bupropion SR exhibits a statistically significant dose/plasma level-response relationship for smoking cessation. Dry mouth and insomnia, related to concentrations, may be managed with dose reduction, with the realization that smoking cessation may be impaired.

Implementation of a nursing home urinary incontinence management program with and without tolterodine.

OBJECTIVE: To evaluate the implementation of a nursing home urinary incontinence management program. DESIGN: A prospective field trial of the program incorporating practice guidelines and principles of continuous quality improvement. SETTING: Five nursing homes in New York, Virginia, and Georgia PARTICIPANTS: One hundred fifty-one residents identified as being incontinent of urine and who met inclusion criteria for ongoing participation in the program. INTERVENTION: Key multidisciplinary staff from the five nursing homes were trained in the program and assumed responsibility for implementing it in their facilities. The program consisted of a clinical assessment, toileting protocols, and the addition of the antimuscarinic drug tolterodine in selected residents who did not respond well to toileting alone. Data on dryness rates during the 60-day toileting protocols, collected by nursing home staff, were analyzed on a weekly basis by an overall project coordinator who sent data back to the nursing homes in an easy-to-read graphical format. MEASURES: (1) The dryness rate, defined as the number of times the resident was dry divided by the number of times the resident was checked (every 2 hours from 7 a.m. to 7 p.m.); and (2) adverse events (eg, dry mouth, increased confusion, need for dosage reduction). RESULTS: Of 645 residents in the 5 nursing homes, 377 (58%) were identified as incontinent of urine, of whom 151 (40%) were placed on an ongoing toileting program. Of these 151 residents, 48 (32%) were prescribed tolterodine, and 117 (78%) completed the 60-day trial. The initial dryness rate was 57%, and for the group as a whole remained essentially unchanged (increase in dryness 1%, P = 0.50). Among 50 clinically stable residents on a toileting program alone, the increase in the dryness rate was 16% (P = 0.001), and for 31 clinically stable residents prescribed tolterodine, the increase in the dryness rate was 29% (P = 0.012). Two residents had their dosage of tolterodine reduced because of dry mouth and nausea,one resident was taken off the drug because of increased pain in the back and legs and increased confusion. CONCLUSIONS: Overall, this program resulted in significant increases in dryness rates for clinically stable incontinent nursing home residents. These residents represented 22% of the total number of residents identified as incontinent in the five participating nursing homes. Tolterodine was prescribed for approximately one-third of incontinent residents as a supplement to a toileting program, and was well tolerated. Nursing homes should be encouraged to implement similar urinary incontinence programs, target toileting protocols to the most responsive residents, and maintain the program using principles of continuous quality improvement.

Applying epidemiology-based outcomes research to clinical decision-making. A hypothetical model of biotechnology therapy in gram-negative sepsis.

OBJECTIVE: Sepsis occurs in a heterogeneous population. A prospective nationwide surveillance study found that populations stratified by infection type had significant differences in the incidence of sepsis syndrome, rate of complications and mortality. The objective of this study was to explore whether successful identification of population-specific risk factors for disease-associated morbidity and mortality may allow for more accurate assessment of the cost effectiveness of treatment strategies. DESIGN: A decision analytic model was developed using outcomes data on incidence and resolution of major complications in sepsis syndrome. Healthcare resource utilisation data were based on length of hospital stay, intensive care unit stay versus hospital ward stay, and cost of treating sepsis-related complications. SETTING: This modelling study, conducted from the perspective of the healthcare institution, used actual outcomes data on 2 infection-specific patient populations. PATIENTS AND PARTICIPANTS: The 2 populations studied were patients with nosocomial respiratory tract infection or community-acquired urinary tract infection who subsequently developed sepsis syndrome. INTERVENTIONS: Treatment options modelled were standard therapy plus biotechnology therapy versus standard therapy alone in the treatment of gram-negative sepsis complications. MAIN OUTCOME MEASURES AND RESULTS: The incremental cost-effectiveness ratios differed between the 2 study populations, due to differences in the incidence and rate of resolution of major sepsis-associated complications. The use of biotechnology therapy is always more cost effective in the respiratory tract infection population. CONCLUSIONS: Cost-effectiveness results for a therapy may change when the epidemiology of the disease state is known and incorporated into the decision analytic model. An infection-specific approach is important in the treatment of sepsis.

Population pharmacokinetics of tirilazad: effects of weight, gender, concomitant phenytoin, and subarachnoid hemorrhage.

PURPOSE: Data collected during Phase I and II in the development of tirilazad were pooled and analyzed using nonlinear mixed effects models to assess covariates which might affect tirilazad pharmacokinetics. METHODS: Four single dose and five multiple dose studies in normal volunteers were combined with two multiple dose studies performed in patients with subarachnoid hemorrhage (SAH) to identify factors related to intersubject variability in clearance (CL) and central compartment volume (Vc). Data from 253 subjects, which consisted of 7,219 tirilazad concentrations, were analyzed. The effects of weight, gender, patient versus volunteer status, and phenytoin use were evaluated. RESULTS: Relative to male volunteers not receiving concomitant phenytoin, significant effects on clearance included: a 46% increase in volunteers receiving phenytoin, and an 82% increase in clearance associated with SAH patients (all of whom received phenytoin). Significant effects on Vc were: a 26% increase for female volunteers not receiving phenytoin, a 12% decrease for volunteers receiving concomitant phenytoin, a 152% increase for male SAH patients, and a 270% increase for female SAH patients. Incorporating patient covariate effects substantially reduced the interindividual variability (from 27.9% to 24.7% for clearance and from 48.2% to 37.5% for Vc). Residual variability was estimated at 66% coefficient of variation (CV) in SAH patients and at 22-48% CV over the range of predicted concentrations in normal volunteers. CONCLUSIONS: The most important factors affecting tirilazad pharmacokinetics are the administration of phenytoin (increased CL) and SAH (increased Vc and residual variability). The effect of gender on tirilazad pharmacokinetics was modest.

Population pharmacokinetics of lamotrigine adjunctive therapy in adults with epilepsy.

Plasma concentrations of lamotrigine, an antiepileptic drug obtained in three adult controlled clinical trials conducted in the United States were pooled and analyzed using NONMEM, a population pharmacokinetic computer program, to facilitate development of dosing guidelines. A total of 2,407 lamotrigine plasma concentrations from 527 patients with epilepsy were analyzed. Regression equations for oral clearance were developed as a function of body size, age (18-64 years), gender, race, and use of concomitant antiepileptic drugs. The population mean apparent oral clearance of lamotrigine in adult patients receiving one concomitant enzyme-inducing antiepileptic drug and not valproic acid was estimated to be 1 mL/min/kg. Gender and age did not affect clearance significantly. On average, clearance was reduced by 25% in non-whites and increased by 13% in patients receiving more than one concomitant enzyme-inducing antiepileptic agent. Lamotrigine did not influence the disposition of phenytoin or carbamazepine. Dosing adjustments for lamotrigine in patients receiving concomitant enzyme-inducing antiepileptic drugs and not valproic acid should not be necessary for age, gender, or the number of concomitant enzyme-inducing antiepileptic drugs. Lamotrigine does not influence the dosing requirements for phenytoin or carbamazepine.

Relationship between didanosine exposure and surrogate marker response in human immunodeficiency virus-infected outpatients.

We used information available from routine clinic visits to characterize the pharmacokinetics of didanosine in 82 human immunodeficiency virus-infected patients. A total of 271 blood samples were collected for the measurement of didanosine concentrations in plasma (mean +/- standard deviation [SD], 3.30 +/- 2.21 samples/patient). Bayesian estimates of didanosine oral clearance (CL[oral]) were obtained for these patients by the POSTHOC option within the NONMEM software package. Population priors from a previous NONMEM analysis of didanosine pharmacokinetics were used. The mean +/- SD CL(oral) was 132 +/- 27.7 liters/h, which agrees reasonably well with estimates obtained from previous pharmacokinetic studies of didanosine. Estimates of individual didanosine exposure were then used to consider potential relationships between drug exposure and surrogate marker response over a 6-month period. No correlations were found between the didanosine area under the concentration-time curve from 0 to 6 months and the absolute CD4 cell count (r = 0.305; 0.1 < P < 0.2), weight response (r = 0.0857; P > 0.4), or percentage of CD4 lymphocytes (r = 0.0559; P > 0.4). Future efforts to characterize didanosine exposure in outpatients by random sampling methods should involve more directed efforts to limit residual variability in the data.

Zalcitabine population pharmacokinetics: application of radioimmunoassay.

Zalcitabine population pharmacokinetics were evaluated in 44 human immunodeficiency virus-infected patients (39 males and 5 females) in our immunodeficiency clinic. Eighty-one blood samples were collected during routine clinic visits for the measurement of plasma zalcitabine concentrations by radioimmunoassay (1.84+/-1.24 samples/patient; range, 1 to 6 samples/patient). These data, along with dosing information, age (38.6+/-7.13 years), sex, weight (79.1+/-15.0 kg), and estimated creatinine clearance (89.1+/-21.5 ml/min), were entered into NONMEM to obtain population estimates for zalcitabine pharmacokinetic parameters. The standard curve of the radioimmunoassay ranged from 0.5 to 50.0 ng/ml. The observed concentrations of zalcitabine in plasma ranged from 2.01 to 8.57 ng/ml following the administration of doses of either 0.375 or 0.75 mg. A one-compartment model best fit the data. The addition of patient covariates did not improve the basic fit of the model to the data. Oral clearance was determined to be 14.8 liters/h (0.19 liter/h/kg; coefficient of variation [CV] = 23.8%), while the volume of distribution was estimated to be 87.6 liters (1.18 liters/kg; CV = 54.0%). We were also able to obtain individual estimates of oral clearance (range, 8.05 to 19.8 liters/h; 0.11 to 0.30 liter/h/kg) and volume of distribution (range, 49.2 to 161 liters; 0.43 to 1.92 liters/kg) of zalcitabine in these patients with the POSTHOC option in NONMEM. Our value for oral clearance agrees well with other estimates of oral clearance from traditional pharmacokinetic studies of zalcitabine and suggests that population methods may be a reasonable alternative to these traditional approaches for obtaining information on the disposition of zalcitabine.

Dose proportionality of cisatracurium.

The dose proportionality of cisatracurium pharmacokinetics was assessed using a population approach by incorporating the collection of sparse blood samples from patients in clinical trials. Plasma concentration-time data from 131 patients with limited concentration-time data and 38 patients with full sampling were pooled and analyzed using nonlinear mixed-effects modeling (NONMEM). Dose proportionality was assessed using dichotomous parameterization and a linear model. The population pharmacokinetic approach revealed that the pharmacokinetics of cisatracurium are independent of dose between 0.1 mg/kg and 0.4 mg/kg, as was expected based on the importance of Hofmann elimination, a chemical process dependent on pH and temperature.

Symptomatic cardiotoxicity associated with 5-fluorouracil.

A prospective cohort study was conducted in 35 hospitals with oncology units to determine the incidence of symptomatic cardiotoxicity in patients receiving continuous infusions of 5-fluorouracil (5-FU), and to identify risk factors that could contribute to the development of 5-FU-associated cardiotoxicity. A sample of 483 patients [197 (41%) women, overall average age +/- SD 60.9 +/- 11.9 yrs] were followed for one cycle of 5-FU infusion. Thirty-eight (7.9%) patients had abrupt termination of the infusion. There were 9 (1.9%) cases of suspected or documented cardiotoxic events. Cardiotoxicity occurred in 7 (3.35%) of 209 patients receiving their first course of 5-FU and in 2 (0.73%) other patients (p=0.044). Based on univariate analysis, the following patient groups were at elevated risk of cardiotoxicity: those with preexisting cardiac disease (RR=6.83, p=0.0023); patients receiving calcium channel blockers (RR=4.75, p=0.014); those receiving nitrates (RR=9.18, p=0.007); and patients receiving concomitant etoposide (RR=10.32, p=0.022). Patients with underlying cardiac disease require close monitoring while receiving continuous infusions of 5-FU. They should be observed for signs and symptoms of cardiotoxicity, and vital signs should be measured frequently. Continued reporting of 5-FU-associated cardiotoxicity is necessary to identify other patients at risk.

Prospective use of population pharmacokinetics/pharmacodynamics in the development of cisatracurium.

PURPOSE: The population PK/PD approach was prospectively used to determine the PK/PD of cisatracurium in various subgroups of healthy surgical patients. METHODS: Plasma concentration (Cp) and neuromuscular block data from 241 patients in 8 prospectively-designed Phase I-III trials were pooled and analyzed using NONMEM. The analyses included limited Cp-time data randomly collected from 186 patients in efficacy/safety studies and full Cp-time data from 55 patients in pharmacokinetic studies. The effects of covariates on the PK/PD parameters of cisatracurium were evaluated. The time course of neuromuscular block was predicted for various patient subgroups. RESULTS: The population PK/PD model for cisatracurium revealed that anesthesia type, gender, age, creatinine clearance, and presence of obesity were associated with statistically significant (p < 0.01) effects on the PK/PD parameters of cisatracurium. These covariates were not associated with any clinically significant changes in the predicted recovery profile of cisatracurium. Slight differences in onset were predicted in patients with renal impairment and patients receiving inhalation anesthesia. Based on the validation procedure, the model appears to be accurate and precise. CONCLUSIONS: The prospective incorporation of a population PK/PD strategy into the clinical development of cisatracurium generated information which influenced product labeling and reduced the number of studies needed during development.

Pretreatment regimens for adverse events related to infusion of amphotericin B.

Infusion-related adverse events (IRAEs) such as nausea, vomiting, fever, chills, and thrombophlebitis that are associated with amphotericin B therapy often lead clinicians to prescribe a number of adjunctive pretreatment medications in an attempt to reduce the incidence and severity of these events. The purpose of this study was to determine the incidence of IRAEs during the first week of systemic amphotericin B therapy and to identify pretreatment regimens that are effective in preventing these IRAEs. Three hundred ninety-seven adult inpatients receiving amphotericin B therapy were prospectively monitored, and data regarding IRAEs and pretreatment regimens were collected. Of these patients, 282 (71%) developed at least one IRAE during the first 7 days of therapy. The IRAEs most commonly reported were fever (51% of patients) and chills (28%), followed by nausea (18%), headache (9%), and thrombophlebitis (5%). The most common regimens included diphenhydramine, a corticosteroid, acetaminophen, and heparin, administered alone or in combination with these or other drugs. Overall, common pretreatment regimens were similar in efficacy to no pretreatment in the prevention of IRAEs. Thus empirical premedication for IRAEs associated with amphotericin B cannot be routinely advocated; instead, patients should be treated when symptoms first arise and then premedicated for subsequent amphotericin B infusions.

Adverse drug reaction reporting in a multicenter surveillance study.

OBJECTIVE: To evaluate the performance of a multicenter, prospective surveillance program in identifying adverse events, and to seek explanations for misclassification bias. DESIGN: The design was a prospective observational study of patients with documented or suspected bacterial pneumonia. SETTING: Data were collected in 74 acute care hospitals across the US. PATIENTS: This evaluation was based on a consecutive sample of 1822 adult patients (> 18 years of age) with documented or suspected bacterial pneumonia who were being treated with a cephalosporin, a penicillin, or an aminoglycoside over a 3-month period. Patients were followed for the duration of antibiotic therapy and were excluded if antibiotic therapy was < 3 days or if the pneumonia was judged to be nonbacterial. INTERVENTIONS: Clinical pharmacists documented patient demographics, concurrent illnesses and medications, antibiotic administration, relevant laboratory data, and the occurrence of nephrotoxicity and neutropenia. MAIN OUTCOME MEASURES: Validity of investigators' identification of neutropenia and nephrotoxicity as compared with objective laboratory data was assessed by using sensitivity, specificity, and positive and negative predictive value measures. RESULTS: Among the 1502 patients with sufficient data to evaluate neutropenia, there was agreement in 1270 patients (84.6%); likewise, among 1291 patients with sufficient data to evaluate nephrotoxicity there was agreement in 1186 patients (91.9%). Sensitivity of the researchers' assessments was 50.9% and 71.0% for neutropenia and nephrotoxicity, respectively. The negative predictive value was > 95% for both events. CONCLUSIONS: Overall, this evaluation demonstrated that the Drug Surveillance Network can successfully identify targeted adverse events. Moreover, this study highlights the importance of validation for all types of outcomes-oriented research studies.

Sepsis syndrome and associated sequelae in patients at high risk for gram-negative sepsis.

We conducted a prospective surveillance study of 80 hospitals across the United States to determine the incidence of sepsis syndrome and its associated sequelae in hospitalized patients over age 18 years who were administered antibiotics for suspected or documented gram-negative infection. A sample of 1754 hospitalized patients were followed from onset of antimicrobial therapy to discharge or death. Mortality rates (MR) varied depending on the suspected source of sepsis syndrome. For patients in whom the syndrome was associated with community-acquired urinary tract infections, mortality was 20% (relative risk [RR] = 0.51, p < 0.05), for those with trauma 20.6% (RR = 0.51, p < 0.05), and patients with nosocomial respiratory tract infections 57.1% (RR = 1.66, p < 0.05). More than two complications occurred in 65.2% of patients under age 60 years (MR 31%), 40.8% of those age 60-80 (MR 42%), and 35.6% of patients older than 80 years (MR 33.3%, p > 0.05). Various patient populations had significant differences in both the incidence of the syndrome and its complications, and consequent mortality. Perhaps morbidity as well as mortality should be used as outcomes when testing the efficacy of innovative therapies for sepsis.