Comparison of permitted daily exposure (PDE) values for active pharmaceutical ingredients (APIs) - Evidence of a robust approach.

Permitted Daily Exposure Limits (PDEs) are set for Active Pharmaceutical Ingredients (APIs) to control cross-contamination when manufacturing medicinal products in shared facilities. With the lack of official PDE lists for pharmaceuticals, PDEs have to be set by each company separately. Although general rules and guidelines for the setting of PDEs exist, inter-company variations in the setting of PDEs occur and are considered acceptable within a certain range. To evaluate the robustness of the PDE approach between different pharmaceutical companies, data on PDE setting of five marketed APIs (amlodipine, hydrochlorothiazide, metformin, morphine, and omeprazole) were collected and compared. Findings show that the variability between PDE values is within acceptable ranges (below 10-fold) for all compounds, with the highest difference for morphine due to different Point of Departures (PODs) and Adjustment Factors (AFs). Factors of PDE variability identified and further discussed are: (1) availability of data, (2) selection of POD, (3) assignment of AFs, (4) route-to-route extrapolation, and (5) expert judgement and differences in company policies. We conclude that the investigated PDE methods and calculations are robust and scientifically defensible. Additionally, we provide further recommendations to harmonize PDE calculation approaches across the pharmaceutical industry.

Deriving harmonised permitted daily exposures (PDEs) for paracetamol (acetaminophen) CAS #: 103-90-2.

In the pharmaceutical industry, cleaning criteria are required for multipurpose manufacturing facilities. These Health Based Exposure Limits (HBELs), also called permitted daily exposures (PDEs) values, are derived from toxicological and pharmacological evaluation of the active pharmaceutical ingredients (APIs). The purpose of this publication is to show an example of how authors from different companies evaluate a generic drug, paracetamol, and discuss different approaches and relevance of the nonclinical studies for deriving PDEs. PDE limits of 25 mg/day for the oral route, and 20 mg/day for the intravenous (i.v.) and inhalation (inhal.) routes, respectively, were established herein. However, it has been already recognised that there are acceptable differences in the PDE calculations, which may be based on data accessibility, company-specific science-policy decisions or expert judgments. These differences can cause up to a 3-fold lower or higher values. If unnecessarily high factors are applied, this would result in a very conservative PDE value and unneeded additional cleaning and higher manufacturing costs. The PDE values presented are considered to be protective against adverse and pharmacological effects observed in clinical trials and in this case, a very long postmarketing period of paracetamol.

What to consider for a good quality PDE document?

For the handling of active pharmaceutical ingredients (APIs) and production of medicinal products in shared facilities, the European Medicines Agency (EMA) has introduced the determination of permitted daily exposure (PDE) values to provide limits for cross-contamination. APIs have a desired pharmacological effect in the patient who intendedly uses a certain medicinal product. However, this effect is undesired in a patient that receives this API unintendedly as a cross-contamination of another medicinal product. In particular, for approved APIs for human use, a multitude of data is available on the pharmacological activity as well as adverse effects, which have to be taken into account in PDE setting. Thus, the setting of PDEs for APIs needs a structured scientific evaluation of all properties and identification of the most critical effect, which is the basis for PDE calculation. In this publication, we provide guidance on points for consideration when setting PDEs for APIs, or when evaluating the quality of documents describing the derivation of PDEs received, e.g. by third parties.

Applicability of surface sampling and calculation of surface limits for pharmaceutical drug substances for occupational health purposes.

Within the context of Occupational Hygiene (OH), surface sampling has been employed as a method to assess surface levels of Active Pharmaceutical Ingredients (APIs). There are potentially a number of reasons surface samples are collected including assessing potential health risks, housekeeping and cleaning effectiveness. There are no internationally accepted standards relating to collecting or interpreting surface samples for OH purposes. In the past, surface sampling results have been applied not only for estimating risks due to dermal contact, but also for other routes of exposure (e.g. inhalation, ingestion, etc). In this publication, we provide a decision tree to support the decision and value of performing surface sampling. For scenarios without conceivable skin exposure due to applied risk mitigation measures or for substances that do not penetrate the skin, surface sampling may not be needed. If the workers' health is determined to be at risk for systemic effects via skin, we propose to use the skin Permitted Daily Exposure (PDEskin), a safe skin dose independent of the exposure scenario that takes into consideration skin absorption properties of substances. For the purpose of OH monitoring, the likelihood of dermal exposure has to be understood before taking any samples, using both the PDEskin to calculate the surface limit and appropriate validated monitoring method for the surface.

Point of departure (PoD) selection for the derivation of acceptable daily exposures (ADEs) for active pharmaceutical ingredients (APIs).

The Acceptable Daily Exposure (ADE) derived for pharmaceutical manufacturing is a health-based limit used to ensure that medicines produced in multi-product facilities are safe and are used to validate quality processes. Core to ADE derivation is selecting appropriate point(s) of departure (PoD), i.e., the starting dose of a given dataset that is used in the calculation of the ADE. Selecting the PoD involves (1) data collection and hazard characterization, (2) identification of "critical effects", and (3) a dose-response assessment including the determination of the no-observed-adverse-effect-level (NOAEL) or lowest-observed-adverse-effect-level (LOAEL), or calculating a benchmark dose (BMD) level. Compared to other classes of chemicals, active pharmaceutical ingredients (APIs) are well-characterized and have unique, rich datasets that must be considered when selecting the PoD. Dataset considerations for an API include therapeutic/pharmacological effects, particularities of APIs for different indications and routes of administration, data gaps during drug development, and sensitive subpopulations. Thus, the PoD analysis must be performed by a qualified toxicologist or other expert who also understands the complexities of pharmaceutical datasets. In addition, as the pharmaceutical industry continues to evolve new therapeutic principles, the science behind PoD selection must also evolve to ensure state-of-the-science practices and resulting ADEs.

A harmonization effort for acceptable daily exposure derivation - Considerations for application of adjustment factors.

Acceptable daily exposures (ADEs) are established to determine the quantity of one drug substance that can contaminate another drug product without causing harm to the patient. An important part in setting an ADE for a drug substance, after identification of the unwanted critical effect(s) of the compound (see Bercu et al., 2016, this issue), is the determination of an appropriate overall margin of safety that is need to be maintained below the dose causing a certain critical effect (i.e., the point of departure or PoD). The overall margin of safety used to protect the general patient population from critical effects is derived as the product (i.e., composite adjustment factor) of various individual factors that account for variability and uncertainty in extrapolating from the PoD to an ADE. These factors address the considerations of interindividual variability, interspecies extrapolation, LOAEL-to-NOAEL extrapolation, exposure duration adjustment, effect severity, and database completeness. The factors are considered individually, but are not necessarily independent and their interdependence should be identified, with subsequent adjustment to the composite factor, as appropriate. It is important to identify all sources of variability and uncertainty pertinent to the derivation of the ADE and ensure each is considered in the assessment, at least by one of the adjustment factors. This manuscript highlights the basis for and selection of factors that address variability and uncertainty as used in the guidance documents on setting ADEs or other related health-based limits.

Using default methodologies to derive an acceptable daily exposure (ADE).

This manuscript discusses the different historical and more recent default approaches that have been used to derive an acceptable daily exposure (ADE). While it is preferable to derive a health-based ADE based on a complete nonclinical and clinical data package, this is not always possible. For instance, for drug candidates in early development there may be no or limited nonclinical or clinical trial data. Alternative approaches that can support decision making with less complete data packages represent a variety of methods that rely on default assumptions or data inputs where chemical-specific data on health effects are lacking. A variety of default approaches are used including those based on certain toxicity estimates, a fraction of the therapeutic dose, cleaning-based limits, the threshold of toxicological concern (TTC), and application of hazard banding tools such as occupational exposure banding (OEB). Each of these default approaches is discussed in this manuscript, including their derivation, application, strengths, and limitations. In order to ensure patient safety when faced with toxicological and clinical data-gaps, default ADE methods should be purposefully as or more protective than ADEs derived from full data packages. Reliance on the subset of default approaches (e.g., TTC or OEB) that are based on toxicological data is preferred over other methods for establishing ADEs in early development while toxicology and clinical data are still being collected.

An in vitro embryotoxicity assay based on the disturbance of the differentiation of murine embryonic stem cells into endothelial cells. II. Testing of compounds.

The embryonic stem cell test (EST) developed by Spielmann et al. [Spielmann, H., Pohl, I., Doering, B., Liebsch, M., Moldenhauer, F., 1997. The embryonic stem cell test, an in vitro embryotoxicity test using two permanent mouse cell lines: 3T3 fibroblasts and embryonic stem cells. In Vitro. Toxicol. 10, 119-127] is currently the most promising in vitro assay to predict the embryotoxic potential of compounds. In this assay the disturbance of the differentiation of embryonic stem (ES) cells into contracting cardiomyocytes by test compounds as well as the direct cytotoxicity of the test compounds on ES cells and 3T3 fibroblasts is analyzed. On the basis of these results and by applying a biostatistical prediction model (PM) [Genschow, E., Scholz, G., Brown, N., Piersma, A., Brady, M., Clemann, N., Huuskonen, H., Paillard, F., Bremer, S., Becker, K., Spielmann, H., 2000. Development of prediction models for three in vitro embryotoxicity tests in an ECVAM validation study. In Vitr. Mol. Toxicol. 13, 51-66; Genschow, E., Spielmann, H., Scholz, G., Pohl, I., Seiler, A., Clemann, N., Bremer, S., Becker, K., 2004. Validation of the embryonic stem cell test in the international ECVAM validation study on three in vitro embryotoxicity tests. Altern. Lab. Anim. 32, 209-244; Genschow, E., Spielmann, H., Scholz, G., Seiler, A., Brown, N., Piersma, A., Brady, M., Clemann, N., Huuskonen, H., Paillard, F., Bremer, S., Becker, K., 2002. The ECVAM international validation study on in vitro embryotoxicity tests: results of the definitive phase and evaluation of prediction models. European Centre for the Validation of Alternative Methods. Altern. Lab. Anim. 30, 151-176] test compounds can be classified as non-embryotoxic, weakly or strongly embryotoxic. In order to introduce a further endpoint into the EST, the disturbance of vasculogenesis and/or angiogenesis, a protocol to differentiate ES cells into endothelial cells, was established in the accompanying paper. PECAM-1 and VE-Cadherin gene expressions, quantified by real-time TaqMan PCR, were shown to be appropriate molecular markers for the differentiation of ES cells into endothelial cells. In the present study, the disturbance of the differentiation of ES cells into endothelial cells (i.e. the reduction in the expression of PECAM-1 and VE-Cadherin) by six test compounds with known embryotoxic potential was investigated: all-trans-retinoic acid (RA) and 5-fluorouracil (5-FU) are strongly embryotoxic, diphenylhydantoin (DPH) and valproic acid (Val) are weakly embryotoxic and saccharin (Sacch) and penicillin G (Pen G) are non-embryotoxic. In a first step the concentration of the test compound resulting in a 50% inhibition of PECAM-1 and VE-Cadherin gene expression and the concentration leading to a 50% decrease in the viability of ES cells and 3T3 fibroblasts were determined. In a second step and in a first attempt to assess the predictive potential of the newly developed test system the concentration values obtained were applied in the PM of the established EST to classify the selected test compounds. All six test compounds were correctly classified (i.e. the data obtained in vitro correlated with their known embryotoxic potential in vivo). Taken together it can be concluded that the disturbance of the differentiation of murine ES cells into endothelial cells represents a very promising new endpoint in a broadened EST with PECAM-1 and VE-Cadherin as specific differentiation marker genes.

An in vitro embryotoxicity assay based on the disturbance of the differentiation of murine embryonic stem cells into endothelial cells. I: Establishment of the differentiation protocol.

The aim of the present study was to establish an experimental protocol to differentiate murine embryonic stem (ES) cells into endothelial cells in vitro. The spinner flask technique as well as the hanging drop method were used to generate so-called embryoid bodies (EBs). In order to find out the optimal differentiation environment, EBs were cultured under various experimental conditions for up to 14 days. The influence of basic fibroblast growth factor (bFGF) alone, vascular endothelial growth factor (VEGF) alone, bFGF and VEGF together and a cocktail consisting of bFGF, VEGF, interleukin-6 (IL-6) and erythropoietin (Epo) on the induction of differentiation of ES cells into endothelial cells was studied. Different concentrations of growth factors and times of treatment were applied. Endothelial cells were characterized by analyzing the expression of platelet-endothelial cell adhesion molecule (PECAM-1), the endothelial-specific vascular endothelial cadherin (VE-Cadherin), the angiopoietin receptor Tie-2, VEGF receptors 1 and 2 (Flt-1 and Flk-1, respectively) and the soluble form of Flt-1 (sFlt) at the mRNA level. PECAM-1 and VE-Cadherin were also studied at the protein level. The data clearly showed that EBs generated by the hanging drop method, followed by their transfer into suspension culture on day 3 of differentiation and their subsequent plating on day 5 is the best of the studied methods to differentiate ES cells into endothelial cells. Addition of VEGF alone or a cocktail consisting of VEGF, bFGF, IL-6 and Epo resulted in the strongest gene expression levels of the above mentioned endothelial cell markers in the differentiated ES cells.