Impact of pharmacodynamic variability on drug delivery(1)

Beyond Population-Level Targets for Drug Concentrations: Precision Dosing Needs Individual-Level Targets that Include Superior Biomarkers of Drug Responses

The purpose of precision dosing is to increase the chances of therapeutic success in individual patients. This is achieved in practice by adjusting doses to reach precision dosing targets determined previously in relevant populations, ideally with robust supportive evidence showing improved clinical outcomes compared with standard dosing. But is this implicit assumption of translatable population-level precision dosing targets correct and the best for all patients? In this review, the types of precision dosing targets and how they are determined are outlined, problems with the translatability of these targets to individual patients are identified, and ways forward to address these challengers are proposed. Achieving improved clinical outcomes to support precision dosing over standard dosing is currently hampered by applying population-level targets to all patients. Just as "one-dose-fits-all" may be an inappropriate philosophy for drug treatment overall, a "one-target-fits-all" philosophy may limit the broad clinical benefits of precision dosing. Defining individual-level precision dosing targets may be needed for greatest therapeutic success. Superior future precision dosing targets will integrate several biomarkers that together account for the multiple sources of drug response variability.

Exploring the Relationship Between Morphine Concentration and Oversedation in Children After Cardiac Surgery

Titrating analgesic and sedative drugs in pediatric intensive care remains a challenge for caregivers due to the lack of pharmacodynamic knowledge in this population. The aim of the current study is to explore the concentration‐effect relationship for morphine‐associated oversedation after cardiac surgery in children aged 3 months to 3 years. Data on morphine dosing, as well as morphine plasma concentrations, were available from a previous study on the pharmacokinetics of morphine after cardiac surgery in children. Oversedation was defined as scores below 11 on the validated COMFORT–behavioral scale. Population pharmacokinetic‐pharmacodynamic modeling was performed in NONMEM 7.3. The probability of oversedation as a function of morphine concentration was best described using a step function in which the EC₅₀ was 46.3 ng/mL. At morphine concentrations below the EC₅₀, the probability of oversedation was 2.9% (0.4& to 18%), whereas above the EC₅₀ percentages were 13% (1.9% to 52%) (median value [95% prediction interval from interindividual variability]). Additionally, the risk of oversedation was found to be increased during the first hours after surgery (P < .001) and was significantly lower during mechanical ventilation (P < .005). We conclude that morphine concentrations above approximately 45 ng/mL may increase the probability of oversedation in children after cardiac surgery. The clinician must evaluate, on a case‐by‐case basis, whether the analgesic benefits arising from dosing regimen associated with such concentrations outweigh the risks.

A new paradigm for personalized prophylaxis for patients with severe haemophilia A

AIM

For patients with severe haemophilia A, guidelines recommend prophylactic treatment with FVIII, with dose calculations targeting a predetermined FVIII trough level. However, this pharmacokinetic (PK) approach is suboptimal, with some patients experiencing breakthrough bleeds. We aimed to improve FVIII dosing by incorporating the thrombin generation assay, a global haemostasis assay whose main pharmacodynamic (PD) parameter, endogenous thrombin potential (ETP), predicts spontaneous bleeding risk.

METHODS

We performed post hoc combined PK-PD modelling using data from 66 adults who received human-cl rhFVIII (Nuwiq^® , Octapharma AG) in a phase IIIb study. Time-to-event analyses simulated the probability of spontaneous bleeding for different FVIII exposures and baseline ETPs.

RESULTS

Ninety-one spontaneous bleeds occurred in 20/66 patients. The relationship between FVIII:C and ETP was non-linear, and the sigmoid Emax model adequately described the data. Individual PK-PD Bayesian estimation significantly improved predictive performance. Simulations showed that the mean spontaneous annual bleeding rate decreased with increasing baseline ETP or dosing: with ETP values of 200, 400 and 600 (nmol/L)·min annual bleeding rates were 2.36, 1.25 and 0.66, respectively, on 40 IU/kg human-cl rhFVIII every 3 days; and annual bleeding rates were 2.09, 1.10, and 0.60, respectively, on 60 IU/kg every 3 days.

CONCLUSION

Prophylactic FVIII dosing is more clinically meaningful when incorporating ETP alongside FVIII level. For the first time, FVIII dosing can be personalized with the aim of eliminating spontaneous breakthrough bleeds.

Perspectives on variability in pharmacokinetics of an oral contraceptive product

The early literature and reviews have described the pharmacokinetics (PK) of oral contraceptive (OC) compounds such as ethinyl estradiol (EE) and levonorgestrel (LNG) in women as subject to large intersubject variability. This was partly due to the use of diverse radioimmunoassays, limited sampling periods and an incomplete understanding of single- vs. multiple-dose kinetics and the role of EE in causing both inhibition of hepatic metabolism along with induction of sex hormone binding globulin. Over the past two decades, LNG and EE have been used as target drugs for the assessment of possible drug interactions upon introduction of many new therapeutic agents. This has resulted in at least 17 publications that describe the PK of LNG and EE in women using various 150 mcg/30 mcg products under fairly standard multiple-dose conditions. A review of these studies indicates only moderate variability in the C_max and area under the curve both within and across these studies. There is impressive similarity in these drug exposure indices found in studies carried out with several products by investigators at numerous sites and countries.

Individualized dosing regimens in children based on population PKPD modelling: are we ready for it?

Despite profound differences in response between children and adults, and between children of different ages, drugs are still empirically dosed in mg/kg in children. Since maturation of expression and function is typically a non-linear dynamic process which differs between biotransformation routes and pharmacological targets, paediatric dosing regimens should be based on the changing pharmacokinetic-pharmacodynamic (PKPD) relationship in children. In this respect, the population approach is essential, allowing for sparse sampling in each individual child. An example is presented on morphine glucuronidation, for which two covariates were identified and subsequently used to derive a model-based dosing algorithm for a prospective clinical trial in children. Using this novel dosing algorithm, similar morphine concentrations are expected while, depending on age, lower and higher morphine dosages are administered compared to mg/kg/h dosing. As the covariate functions may reflect system-specific information on the maturation of a specific drug-disposition pathway, its use for other drugs that share the same pathway is explored. For this purpose, prospective clinical trials and cross-validation studies are urgently needed. In conclusion, PKPD modelling and simulation studies are important to develop evidence-based and individualized dosing schemes for children, with the ultimate goal to improve drug safety and efficacy in this population.

Optimizing preclinical study design in oncology research

The current drug development pathway in oncology research has led to a large attrition rate for new drugs, in part due to a general lack of appropriate preclinical studies that are capable of accurately predicting efficacy and/or toxicity in the target population. Because of an obvious need for novel therapeutics in many types of cancer, new compounds are being investigated in human Phase I and Phase II clinical trials before a complete understanding of their toxicity and efficacy profiles is obtained. In fact, for newer targeted molecular agents that are often cytostatic in nature, the conventional preclinical evaluation used for traditional cytotoxic chemotherapies utilizing primary tumor shrinkage as an endpoint may not be appropriate. By utilizing an integrated pharmacokinetic/pharmacodynamic approach, along with proper selection of a model system, the drug development process in oncology research may be improved leading to a better understanding of the determinants of efficacy and toxicity, and ultimately fewer drugs that fail once they reach human clinical trials.

Tailor-made drug treatment for children: creation of an infrastructure for data-sharing and population PK-PD modeling

Rational dosing guidelines for drugs in pediatrics are urgently needed. To develop these guidelines, we use population pharmacokinetic-pharmacodynamic (PK-PD) modeling and simulation by: (i) optimization of clinical trial designs based on preliminary data; (ii) development and internal validation of population PK-PD models using sparse data; (iii) external validation using independent data; and (iv) prospective clinical evaluation. Optimized dosing regimens for specific drugs may then serve as a basis to develop dosing guidelines for existing or newly developed drugs with similar disposition and/or effect. In addition to modeling of drug disposition (PK) pathways, we emphasize the need for modeling of effect (PD) pathways and the use of a multidisciplinary infrastructure for data-sharing.

Investigation of a cellular pharmacodynamic model exhibiting sharp response sensitivity and tolerance

The potential relevance of a kinetic model for switch-like behavior in biochemical reactions to pharmacodynamics is explored. This model, which postulates that drug acts by modulating the balance of kinase and phosphatase activities, and their effect on the phosphorylation state of an effector molecule critical in determining drug effect, predicts sharp concentration-effect profiles without explicit incorporation of cooperativity. The degree of sharpness depends on concentration of the critical effector. It is argued that such a model can account for inter-individual differences in pharmacodynamic sensitivity profiles, as well as intra-individual changes in sensitivity associated with time-varying physiological processes or disease. By augmenting the model with a kinetic description of critical effector synthesis and degradation in the nonphosphorylated and phosphorylated forms, a putative mechanism for drug tolerance is revealed. The combined model predicts that tolerance, in addition to attenuating the maximum effect, may lead to a decrease in apparent Hill coefficient.

Quantitative structure-pharmacokinetic/pharmacodynamic relationships

Quantitative structure-activity relationships have long been considered a vital component of drug discovery and development, providing insight into the role of molecular properties in the biological activity of similar and unrelated compounds. Recognition that in vitro bioassay and/or pre-clinical activity are insufficient for anticipating which compounds are suitable leads for further development has shifted the focus toward integrated pharmacokinetic (PK) and pharmacodynamic (PD) processes. Over the last decade, considerable progress has been made in constructing empirical and mechanistic quantitative structure-PK relationships (QSPKR), as well as diverse mechanism-based pharmacodynamic models of drug effects. In this review, traditional and contemporary approaches to developing QSPKR models are discussed, along with selected examples of attempts to couple QSPKR and pharmacodynamic models to anticipate the intensity and time-course of the pharmacological effects of new or related compounds, or quantitative structure-pharmacodynamic relationships modeling. Such models are in accordance with the goals of systems biology and the ideal of designing drugs and delivery systems from first principles.

Aqueous-Soluble, Non-Reversible Lipid Conjugate of Salmon Calcitonin: Synthesis, Characterization and In Vivo Activity

PURPOSE

A novel, non-reversible, aqueous-based lipidization strategy with palmitic acid as a model lipid was evaluated for conjugation with salmon calcitonin (sCT).

MATERIALS AND METHODS

A water-soluble epsilon-maleimido lysine derivative of palmitic acid was synthesized from reaction of palmitic acid N-succinimidyl ester and epsilon-maleimido lysine. The latter was generated from reaction of alpha-Boc-lysine and methylpyrrolecarboxylate, with subsequent deprotection of the Boc group. The palmitic derivative was further conjugated with sCT via a thio-ether bond to produce Mal-sCT in aqueous solution. The identity and purity of Mal-sCT was confirmed by Electrospray Ionisation Mass spectrometry (ESI-MS) and HPLC.

RESULTS

Yield of Mal-sCT was 83%. Dynamic light scattering and circular dichroism data suggested that Mal-sCT presented as a stable helical structure in aqueous solutions of varying polarity, with a propensity to aggregate at concentrations above 11 microM. Cellular uptake of Mal-sCT was twice that of sCT in the Caco-2 cell model, and the conjugate was more resistant to liver enzyme degradation. Mal-sCT exhibited comparable hypocalcemic activity to sCT when administered subcutaneously in the rat model at sCT equivalent dose of 0.114 mg/kg. Peroral Mal-sCT, however, produced variability in therapeutic outcome. While four out of six rats did not respond following intragastric gavage with Mal-sCT, two rats showed significantly suppressed plasma calcium levels (approximately 60% of baseline) for up to 10 h.

CONCLUSION

A novel non-reversible, water-soluble lipid conjugate of sCT was successfully synthesized that showed (1) different aggregation behavior and secondary structure, (2) improved enzymatic stability and cellular uptake, and (3) comparable hypocalcemic activity in vivo compared to sCT.

Tissue engineering solutions for traumatic bone loss

Tissue engineering strategies for the repair, replacement, or augmentation of bone defects involves the use of cells, matrices, and bioregulatory factors. The source (endogenous, exogenous) and character of these factors, however, may vary greatly among the many approaches taken by current investigators. Although the results of current tissue engineering methods for regenerating bone have shown great promise, the extent of damage to extremities associated with war injuries may require the development of techniques that differ substantially from current practice.

Review article: moderate sedation for endoscopy: sedation regimens for non-anaesthesiologists

BACKGROUND

Moderate sedation is a drug-induced depression of consciousness during which patients respond purposefully to verbal commands with or without light tactile stimulation. Moderate sedation is typically accepted in the anaesthesia community as an appropriate target for sedation by non-anaesthesiologists.

AIM

To describe drug regimens that can be successfully and safely targeted to moderate sedation for endoscopy by non-anaesthesiologists.

RESULTS

Moderate sedation can be achieved using narcotics and benzodiazepines. There is interest in some countries in propofol for endoscopy, which is often viewed as an agent for deep sedation. Indeed, propofol cannot be targeted to moderate sedation for endoscopy as a single agent because of coughing during upper endoscopy and pain withdrawal responses during colonoscopy. Pre-treatment with low doses of narcotic and/or benzodiazepine blocks these effects, allowing propofol to be targeted to moderate sedation. Fospropofol, a prodrug of propofol in clinical development, can also be targeted to moderate sedation if co-administered with narcotic.

CONCLUSION

Moderate sedation provides a safety margin when compared with deep sedation and general anaesthesia. Development of protocols that target agents such as propofol to moderate sedation will expand the sedation agents available to non-anaesthesiologists and help ensure that this expansion occurs safely.

Pharmacokinetic/pharmacodynamic modeling of total lymphocytes and selected subtypes after oral budesonide

In the present pharmacokinetic/pharmacodynamic (PK/PD) evaluation, cortisol, total lymphocytes, and lymphocyte subpopulations were monitored following single oral doses of two oral formulations of 3 mg budesonide (BUD) (Dosage Forms A and B) in order to assess the differential effects that BUD may have on cortisol suppression and the modulation of blood lymphocyte subtypes. On a single occasion, five subjects received one 3 mg capsule of Dosage Form A, four received three capsules of Dosage Form A (single dose of 9 mg), and five received three capsules of Dosage Form B (single dose of 9 mg). Placebo capsules were administered to six subjects in the study. Cortisol concentrations, total lymphocyte counts, and lymphocyte subpopulation counts for the CD3, CD4, CD8, CD19, and CD56/16 were fitted to an in direct PK/PD response model that described the effects of BUD on serum cortisol concentrations as well as the combined effects of BUD and cortisol on total lymphocytes and the CD3, CD4, CD8, CD19, and CD56/16 subtypes. Data were also analyzed using noncompartmental methods. The PK/PD model fitted the data with the exception of data for CD56/16. The IC(50) value for unbound BUD acting on total lymphocytes was 0.276 ng/ml while the IC(50) values for unbound BUD acting on lymphocyte subtypes ranged from 0.150 ng/ml for CD4 to 0.364 ng/ml for CD8. The IC(50) values for the effects of BUD on serum cortisol were lower (0.079 ng/ml). The results of PK/PD modeling and noncompartmental analysis indicate that BUD has a smaller effect on the CD8 subtype and larger effects on the CD4 and CD19 subtypes, relative to the effect on total lymphocytes, and that cortisol suppression, although not a direct immunological biomarker, may be a more sensitive marker for the systemic effect of corticosteroids.

Gastrointestinal transit and disintegration of enteric coated magnetic tablets assessed by ac biosusceptometry

The oral administration is a common route in the drug therapy and the solid pharmaceutical forms are widely used. Although much about the performance of these formulations can be learned from in vitro studies using conventional methods, evaluation in vivo is essential in product development. The knowledge of the gastrointestinal transit and how the physiological variables can interfere with the disintegration and drug absorption is a prerequisite for development of dosage forms. The aim of this work was to employing the ac biosusceptometry (ACB) to monitoring magnetic tablets in the human gastrointestinal tract and to obtain the magnetic images of the disintegration process in the colonic region. The ac biosusceptometry showed accuracy in the quantification of the gastric residence time, the intestinal transit time and the disintegration time (DT) of the magnetic formulations in the human gastrointestinal tract. Moreover, ac biosusceptometry is a non-invasive technique, radiation-free and harmless to the volunteers, as well as an important research tool in the pharmaceutical, pharmacological and physiological investigations.

Efficacy and cytotoxicity of cationic-agent-mediated nonviral gene transfer into osteoblasts

Ex vivo gene transfer into osteoblastic cells is an advantageous strategy for bone tissue engineering. This study investigated the efficacy and cytotoxicity of in vitro cationic-agent-mediated nonviral gene transfer into osteoblasts. Various cationic agents, lipid, gelatin, and polyethylenimine (PEI) were tested. Each was formulated in various concentrations to form a complex with plasmid DNA encoding red fluorescent protein. The cationic agent/DNA complexes were transfected into human fetal osteoblastic cell line and rat bone-marrow-derived primary osteoblasts, as well as NIH 3T3 fibroblast controls. Rat primary osteoblasts were transfected more with cationic lipid and PEI agents than with gelatin carrier, yielding transfection efficacy up to 18.1% and 12.7 %, respectively. In contrast, human fetal osteoblastic cell line was transfected more with cationic lipid and gelatin than with PEI. There was a positive correlation between the lipid and PEI doses and cytotoxicity. When the lipid and PEI were used to transfect the rat primary osteoblasts in a dose that yielded the highest transfection efficacy, cell survival rates decreased as low as 40%. When their transfection efficacies into primary osteoblasts were compromised at two thirds of the highest value, that is, 12.6% and 8.3% for the lipid and PEI, respectively, the cell survival rate was nearly 80%. Cationic gelatin was associated with cell survival rates over 60 % in any cell type, regardless of the doses tested. These results suggest that different types of osteoblastic cells may possess different ability to the uptake and expression of cationic-agent-bound DNA. There seemed to be agent-specific threshold doses that dropped the cell survival rate. Cationic-agent-mediated nonviral gene transfer into osteoblastic cells may be successful when the agent- and dose-dependent transfection efficacy and cytotoxicity are optimized.