Retrospective Analysis Using Pharmacokinetic/Pharmacodynamic Modeling and Simulation Offers Improvements in Efficiency of the Design of Volunteer Infection Studies for Antimalarial Drug Development

Volunteer infection studies using the induced blood stage malaria (IBSM) model have been shown to facilitate antimalarial drug development. Such studies have traditionally been undertaken in single‐dose cohorts, as many as necessary to obtain the dose‐response relationship. To enhance ethical and logistic aspects of such studies, and to reduce the number of cohorts needed to establish the dose‐response relationship, we undertook a retrospective in silico analysis of previously accrued data to improve study design. A pharmacokinetic (PK)/pharmacodynamic (PD) model was developed from initial fictive‐cohort data for OZ439 (mixing the data of the three single‐dose cohorts as: n = 2 on 100 mg, 2 on 200 mg, and 4 on 500 mg). A three‐compartment model described OZ439 PKs. Net growth of parasites was modeled using a Gompertz function and drug‐induced parasite death using a Hill function. Parameter estimates for the PK and PD models were comparable for the multidose single‐cohort vs. the pooled analysis of all cohorts. Simulations based on the multidose single‐cohort design described the complete data from the original IBSM study. The novel design allows for the ascertainment of the PK/PD relationship early in the study, providing a basis for rational dose selection for subsequent cohorts and studies.

Study Highlights

• WHAT IS THE CURRENT KNOWLEDGE ON THE TOPIC?

☑ Volunteer infection studies are routinely used in antimalarial drug development to generate early pharmacokinetic/pharmacodynamic data for compounds.

• WHAT QUESTION DID THIS STUDY ADDRESS?

☑ Can in silico analyses be used to suggest improvements to volunteer infection study designs?

• WHAT DOES THIS STUDY ADD TO OUR KNOWLEDGE?

☑ Multiple dose adaptive trial designs can potentially reduce the number of cohorts needed to establish the dose‐response relationship in volunteer infection studies.

• HOW MIGHT THIS CHANGE CLINICAL PHARMACOLOGY OR TRANSLATIONAL SCIENCE?

☑ Real time data analyses can be used to recommend doses for adaptive volunteer infection studies.

Volunteer infection studies using the induced blood stage malaria (IBSM) model have been recognized as a valuable system for defining the key pharmacokinetic (PK) and pharmacodynamic (PD) relationships for dose selection in antimalarial drug development. ¹ , ² , ³ , ⁴ , ⁵ , ⁶ , ⁷ In such studies, healthy volunteers are inoculated intravenously with a given quantity (with small variability) of Plasmodium‐infected red cells. Parasitemia is then followed by quantitative polymerase chain reaction until a prespecified treatment threshold is reached when the test drug is administered. Parasite and drug concentrations are then measured. These studies are conducted prior to phase II dose‐response (D‐R) trials and can be included in an integrated first‐in‐human study protocol, or after completion of the first‐in‐human PK and safety study. IBSM studies have been typically designed as flexible multiple cohort studies where each volunteer of one cohort receives a single dose of the same amount of drug (“single dose per cohort”). ² , ³ , ⁴ , ⁵ After each cohort, a decision is made to stop or to add a cohort to test a lower or higher dose based on the response observed in the previous cohorts.For the multiple single‐dose‐per‐cohort design, the starting dose is typically selected based on safety and PK information from a phase I single ascending dose (SAD) study and, more recently, on preclinical data from a severe combined immunodeficient mouse model, with the dose selected on the basis of being best able to inform the D‐R relationship, rather than aiming for cure. This approach, where a single dose is tested in all subjects of the initial cohort, risks missing the dose likely to be most informative for defining the PK/PD relationship.An alternative approach is to spread a range of doses across a smaller number of subjects within the initial cohort and use PK/PD models developed based on data from this cohort to support dose selections of subsequent cohorts and studies. Using data from a previous study, ² we undertook an in silico investigation of such an adaptive study design, aiming to reduce the number of subjects exposed to inefficacious doses, and to establish a D‐R relationship. This multiple‐dose‐groups‐per‐cohort design, referred to as the “2‐2‐4” design, is contrasted with the already implemented study design depicted in Figure  1 .Open in a separate windowFigure 1Comparison of standard and adaptive designs of IBSM studies. A/B/C, dose levels to be selected during the progress of the study based on pharmacokinetic/pharmacodynamic results of the initial cohort; CHMI, controlled human malaria infection; D‐R, dose‐response; IBSM, induced blood stage malaria infection; n, number of subjects at each dose.The objectives of this retrospective analysis were to: (i) compare PK/PD parameter estimates from the initial cohort of the 2‐2‐4 study design with the prior results from the data of the full study and (ii) propose a preliminary workflow to establish D‐R early in an IBSM study, and use modeling and simulation (M&S) to support dose selections for subsequent cohorts and later phase clinical trials.     

Cardiovascular risk factors in adults with coarctation of the aorta

Background: The aging patient with adult congenital heart disease (ACHD) faces the risk of developing atherosclerotic disease. Patients with coarctation of the aorta (CoA) are especially vulnerable because of an inherent high risk of developing hy‐ pertension. However, data on the prevalence of other cardiovascular risk factors are scarce. Therefore, this study aimed to describe the prevalence of traditional cardio‐ vascular risk factors (diabetes, hypertension, hyperlipidemia, smoking, obesity, and sedentary lifestyle) in adult patients with CoA.
Methods: Patients with CoA who were registered at the ACHD clinic in Gothenburg were asked to participate in a comprehensive cardiovascular risk assessment. This assessment included a glucose tolerance test, cholesterol profile, ambulatory blood pressure measurements, and a lifestyle questionnaire.
Results: A total of 72 patients participated. The median age was 43.5 years and 58.3% were men. Sixty‐six (91.7%) patients had ≥one cardiovascular risk factor and 40.3% had ≥three risk factors. Three (4.2%) patients were newly diagnosed with diabetes or impaired glucose tolerance. More than half of the patients had hyperlipidemia (n = 42, 58.3%) and 35 patients (48.6%) were overweight or obese. Only three (4.2%) patients smoked regularly. Of the 60 patients who underwent 24‐hour ambulatory blood pressure measurement, 33 (55.0%) were hypertensive. Of the 30 patients with known hypertension only 9 (30.0%) had well‐controlled blood pressure on ambula‐ tory blood pressure measurement.
Conclusions: Cardiovascular risk factors among patients with CoA are prevalent. This may indicate a need for more aggressive screening strategies of traditional risk fac‐ tors to minimize the risk of these patients also developing atherosclerotic disease.     

Dental anxiety in relation to torture experiences and symptoms of post‐traumatic stress disorder

Torture victims often show symptoms of dental anxiety when receiving dental care, but little systematic research is available. The purpose of this study was to explore torture experiences, symptoms of post‐traumatic stress disorder (PTSD), and dental anxiety in refugees in Norway and to test the hypothesis that refugees with torture experiences are more prone to dental anxiety than refugees with no such experiences. A total of 173 refugees were interviewed shortly after an oral examination. The Modified Dental Anxiety Scale (MDAS) and the Harvard Trauma Questionnaire‐PTSS16 were administered verbally through attending interpreters. Among torture victims (47%, n = 81), the prevalence of torture experiences involving mouth or teeth was 35% and 23%, respectively. Harvard Trauma Questionnaire mean sum scores were statistically significantly higher in torture victims (34.3 vs. 24.8). Torture survivors report a larger number of symptoms of PTSD, and dental anxiety shows a higher prevalence in refugees reporting PTSD symptoms than in refugees who do not report such symptoms. When analysed using logistic regression models, the data showed the odds of high levels of dental anxiety being 6.1 times higher in refugees with torture experiences compared with other refugees and 9.3 times higher in torture victims with PTSD symptoms. Oral health professionals should be aware of these associations when providing dental care to refugees. The hypothesis that tortured refugees are more prone to dental anxiety is supported.