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

Establishment of a threshold of toxicological concern for pharmaceutical intermediates based on historical repeat-dose data and its application in setting health based exposure limits

Availability of toxicological data for pharmaceutical intermediates (IMs) used in the manufacture of small molecules is often limited. Scarcity of data - in particular, repeat-dose toxicity (RDT) - renders the calculation of health-based exposure limits (HBELs) problematic. Establishment of HBELs, including occupational exposure limits (OELs) and permitted daily exposures (PDEs) facilitating worker and patient safety respectively, is however essential. Historic 28-day oral rodent toxicity data was analysed for 103 GSK isolated IMs. No-observed (adverse) effect levels (NO(A)ELs) and critical effects were extracted. The 5th percentile (p05) of the NO(A)EL distribution was 15 mg/kg/day. Substance specific HBELs were calculated, selecting the NO(A)EL as the Point of Departure (PoD); 99% of IMs (n = 102) were assigned an oral PDE ≥1000 μg/day and OEL ≥100 μg/m3. A default oral PDE of 1000 μg/day and OEL of 100 μg/m3 is thus proposed for IMs. Evaluation of an additional PoD - benchmark dose lower confidence limit (BMDL) - further supported the default HBELs. The default oral PDE can also serve as a threshold of toxicological concern (TTC) for IMs. Default limits can aid in setting HBELs for novel data-poor IMs, as well as supporting waiving of RDT in the future through read-across.

Safety assessment of protein A and derivation of a parenteral health-based exposure limit

Protein A (PA) is a bacterial cell wall component of Staphylococcus aureus whose function is to bind to Immunoglobulin G (IgG). Given its ability to bind IgG as well as its stability and resistance to harsh acidic and basic cleaning conditions, it is commonly used in the affinity chromotography purification of biotherapeutics. This use can result in levels of PA being present in a drug product and subsequent patient exposure. Interestingly, PA was previously evaluated in clinical trials as well as supporting nonclinical studies, resulting in a database that enables the derivation of a health-based exposure limit (HBEL). Given the widespread use of PA in the pharmaceutical industry, the IQ DruSafe Impurities Safety Working Group (WG) evaluated the available information with the purpose of establishing a harmonized parenteral HBEL for PA. Based on this thorough, collaborative evaluation of nonclinical and clinical data available for PA, a parenteral HBEL of 1.2 μg/kg/dose (60 μg/dose for a 50 kg individual) is expected to be health protective for patients when it is present as an impurity in a biotherapeutic.

Preliminary human health risk assessment of antibiotic exposures in human waste handling occupations

Exposure to biosolids in human waste handling occupations is associated with a risk for illness due to microbial infections. Although several years of exposure to biosolids might be hypothesized to be a prophylaxis against infection, the risks associated with infections from antibiotic-resistant organisms can also be a potential concern. Therefore, this study aimed to conduct a screening level risk assessment by deriving occupational exposure limits (OELs) characterizing the risks of adverse health effects among workers in human waste handling occupations with a focus on exposure to two pharmaceuticals commonly found in biosolids: ciprofloxacin (CIP) and azithromycin (AZ). Epidemiological and exposure studies of workers exposed to biosolids were identified through searches of major scientific databases. Screening OELs (sOELs) for these antibiotics were derived using a standardized methodology. The airborne concentrations of CIP and AZ antibiotics were determined using an exposure factors approach. The health-based exposure limits (i.e., sOELs) and the acceptable daily exposure (ADE) values for both of these antibiotics were derived as 80 μg/m3 and 12 μg/kg-day, respectively. An exposure factor approach suggested that inhalation route exposures to CIP and AZ are well below the sOELs and ADE daily doses, and likely too low to cause direct adverse health effects through antibiotic inhalation. A critical review of epidemiological studies on different occupations handling biosolids showed that the workers in industries with potential biosolids exposure have experienced an increased incidence of microbial-exposure-related illness. The health effects seen in the workers have been attributed to bacterial, viral, and protozoan infections. To the extent that bacteria are the pathogen of concern, it is not clear whether these bacteria are resistant to antibiotics commonly found in biosolids. It is also unclear whether the presence of antibiotics or antibiotic-resistant bacteria increases the susceptibility of these workers. Additional studies will provide more definitive estimates of inhalation and dermal exposures to CIP and AZ and could verify the exposure estimates in this study based on the literature and common exposure factors.

Severity of effect considerations regarding the use of mutation as a toxicological endpoint for risk assessment: A report from the 8th International Workshop on Genotoxicity Testing (IWGT)

Exposure levels without appreciable human health risk may be determined by dividing a point of departure on a dose-response curve (e.g., benchmark dose) by a composite adjustment factor (AF). An "effect severity" AF (ESAF) is employed in some regulatory contexts. An ESAF of 10 may be incorporated in the derivation of a health-based guidance value (HBGV) when a "severe" toxicological endpoint, such as teratogenicity, irreversible reproductive effects, neurotoxicity, or cancer was observed in the reference study. Although mutation data have been used historically for hazard identification, this endpoint is suitable for quantitative dose-response modeling and risk assessment. As part of the 8th International Workshops on Genotoxicity Testing, a sub-group of the Quantitative Analysis Work Group (WG) explored how the concept of effect severity could be applied to mutation. To approach this question, the WG reviewed the prevailing regulatory guidance on how an ESAF is incorporated into risk assessments, evaluated current knowledge of associations between germline or somatic mutation and severe disease risk, and mined available data on the fraction of human germline mutations expected to cause severe disease. Based on this review and given that mutations are irreversible and some cause severe human disease, in regulatory settings where an ESAF is used, a majority of the WG recommends applying an ESAF value between 2 and 10 when deriving a HBGV from mutation data. This recommendation may need to be revisited in the future if direct measurement of disease-causing mutations by error-corrected next generation sequencing clarifies selection of ESAF values.

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.

Estimating inhalation bioavailability for peptides and proteins 1 to 10 kDa in size

Inhalation is a critical route for occupational exposure. To protect workers from adverse effects, health-based exposure limits (HBELs) are derived using chemical-specific information including inhalation bioavailability. Inhalation bioavailability of large proteins is well studied and generally accepted to be 1% or less. However, the inhalation bioavailability of peptides and proteins 1-10 kDa in size is not well defined. The goal of this study was to expand upon previous analyses and evaluate the inhalation bioavailability of small peptides. Inhalation bioavailability data for 72 peptides and protein samples ranging from 1.1 to 10.9 kDa in size were evaluated. The median inhalation bioavailability was 20%, which is in agreement with previously published analyses. Inhalation bioavailabilities for the vast majority were below 50%. Interestingly, species, peptide size, and peptide identity did not correlate with inhalation bioavailability. Other factors including inhalation dosimetry, peptide degradation, and chemical characteristics also decrease the amount of peptide available for absorption. Together, the median bioavailability of 20% is likely an appropriate estimate of systemic exposure and is sufficiently protective in most cases for the purposes of occupational exposure safety. Thus, in the absence of peptide-specific data or concerns, an inhalation bioavailability default of 20% is recommended for 1-10 kDa peptide and proteins.

Setting impurity limits for endogenous substances: Recommendations for a harmonized procedure and an example using fatty acids

Endogenous substances, such as fatty, amino, and nucleic acids, are often purposefully used in parenterally pharmaceuticals, but may be present as impurities. Currently, no consensus guidance exists on setting impurity limits for these substances. Specific procedures are needed, as the amount and types of toxicity data available for endogenous substances are typically far less than those for other chemical impurities. Additionally, the parenteral route of administration of these substances is inherently non-physiological, resulting in potentially different or increased severity of toxicity. Risk Assessment Process Maps (RAPMAPs) are proposed as a model to facilitate the development of health-based exposure limits (HBELs) for endogenous substances. This yielded a framework that was applied to derive HBELs for several fatty acids commonly used in parenteral pharmaceuticals. This approach was used to derive HBELs with further vetting based on anticipated perturbations in physiological serum levels, impacts of dose-rate, and consideration of intermittent dosing. Parenteral HBELs of 100-500 mg/day were generated for several fatty acids, and a proposed class-based limit of 50 mg/day to be used in the absence of chemical-specific data. This default limit is consistent with the low toxicity of this chemical class and ICH Q3C value for Class 3 solvents.

Identifying non-hazardous substances in pharmaceutical manufacturing and setting default Health-Based Exposure Limits (HBELs)

Contract Development and Manufacturing Organizations (CDMOs) that manufacture large, diverse portfolio of chemical and pharmaceutical substances require pragmatic risk-based decisions with respect to the safe carry-over between different chemical entities, as well as for worker protection. Additionally, CDMOs may not have access to primary study data or data is generally lacking for a specific substance. While pharmaceuticals require the establishment of health-based exposure limits (HBELs) (e.g., occupational exposure limits, permitted daily exposure limits), the limits for non-hazardous substances could be set in a protective and pragmatic way by using default values, when internally required. Since there is no aligned definition provided by authorities, nor agreed default values for non-hazardous substances, we provide a decision tree in order to help qualified experts (such as qualified toxicologists) to identify the group of non-hazardous substances and to assign default HBEL values for specific routes of exposure. The non-hazardous substances discussed within this publication are part of the following subgroups: (I) inactive pharmaceutical ingredients, (II) pharmaceutical excipients or cosmetic ingredients, (III) substances Generally Recognized as Safe (GRAS), and (IV) food ingredients, additives and contact materials. The proposed default limit values are 1 mg/m³ for the OEL, and 50 mg/day for the PDE oral and IV (intravenous) route.

PDE concept for controlling cleaning agent residues in pharmaceuticals- A critical analysis

Cleaning agents (CAs) are used in multipurpose facilities to control carryover contamination of active pharmaceutical ingredients (APIs) to scientifically justified limits. While this is often done with the PDE methodology used for API impurities, it is unclear if it is justifiable and necessary for cleaning agents, which generally represent a comparatively lower health risk. Comparing calculated oral PDE values for CA ingredients (CAIs) from four companies with PDEs of a selected number of small-molecule APIs showed that the toxicity of CAIs is several orders of magnitude lower. Furthermore, a critical review of the toxicity and everyday exposure to the general population of the main CAIs functional groups showed that the expected health risks are generally negligible. This is particularly true if the associated mode of actions cause local toxicity that is usually irrelevant at the concentration of potential residue carryover. This work points towards alternative approaches to the PDE concept to control CAIs' contamination and provides some guidance on grouping and identifying compounds with lower health risks based on exposure and mode of action reasoning. In addition, this work supports the concept that limit values should only be set for CAIs of toxicological concern.

Challenges in setting Permitted Daily Exposure (PDE) Limits for pharmaceuticals: A review

BACKGROUND

When more than one drug is manufactured at a shared facility or equipment in pharmaceutical manufacturing, the potential carry-over of the retained residue of existing drug product on product contact parts of the equipment to the next product can be a source of cross contamination. Permitted daily exposure (PDE) is derived based on the complete nonclinical and clinical data available and is a dose that is unlikely to cause adverse effects if an individual is exposed, by any route, at or below this dose every day over a lifetime.

OBJECTIVE

The objective was to present a comprehensive review of available scientific knowledge for derivation of PDE.

METHODS

PubMed and ScienceDirect databases were searched using keywords "PDE" and "pharmaceuticals" and all the relevant literature up to March 2021 was reviewed. We have also calculated PDEs for Tobramycin (CAS No. 32986-56-4) and Acetyl Salicylic Acid (ASA, CAS No. 50-78-2).

RESULTS

This research will be useful for scientists working in the PDE domain. The given examples emphasize the importance of use of human data in calculating PDE.

CONCLUSION

The duty of the risk assessor entrusted with setting PDEs is to derive a data driven, scientifically justified value that is safe for patients, while avoiding unjustified conservativeness that puts unnecessary burden on manufacturing.

Derivation of an occupational exposure limit for β-glucans

β-Glucans are abundant bacterial, yeast, and fungal cell wall polysaccharides that have been shown to activate the immune system. Establishment of an occupational exposure limit (OEL) for β-glucan exposure is critical to the protection of worker health, as these exposures have been linked to immunosuppressive and inflammatory reactions and possibly the development of respiratory diseases. Detectable concentrations of β-glucans have been identified in common occupational inhalation exposure scenarios, such as in the agricultural and waste management sectors. However, no published exposure benchmarks for inhalation of β-glucans are available for workers or the general population. Thus, a health-based OEL for inhalation exposure of workers to β-glucans was derived based on consideration of human and non-human effect data for this class of compounds and contemporary risk assessment methods. The weight of the evidence indicated that the available data in humans showed significant methodological limitations, such as lack of a representative study size, appropriate control population, and clear dose-response relationship. Thus, an OEL of 150 ng/m³ was derived for β-glucans based on the most relevant nonclinical study. This OEL provides an input to the occupational risk assessment process, allows for comparisons to worker exposure, and can guide risk management and exposure control decisions.

Active pharmaceutical contaminants in dietary supplements: A tier-based risk assessment approach

The presence of active pharmaceutical ingredients (APIs) in adulterated or contaminated dietary supplements is a current product safety concern. Since there are limited guidelines, and no published consensus methods, we developed a tier-based framework incorporating typical lines of evidence for determining the human health risk associated with APIs in dietary supplements. Specifically, the tiered approach outlines hazard identification and decision to test for APIs in products based on criteria for likelihood of contamination or adulteration, and evaluation of manufacturer production standards. For products with detectable levels of APIs, a variety of default approaches, including the use of fraction of the therapeutic dose and the threshold of toxicological concern (TTC), as well as health-based exposure limits (HBELs) are applied. In order to demonstrate its practical use, as well as any limitations and/or special considerations, this framework was applied to five dietary supplements (currently available to the public). We found that the detected levels of APIs in some dietary supplements were above the recommended dose of the drugs, and thus, pose a significant health risk to consumers and potentially workers involved in manufacturing of these supplements. The results support the value of increased product quality surveillance and perhaps regulatory activity.

Deriving Compound-Specific Exposure Limits for Chemicals Used in Pharmaceutical Synthesis: Challenges in Expert Decision-Making Exemplified Through a Case Study-Based Workshop

A workshop entitled "Deriving Compound-Specific Exposure Limits for Chemicals Used in Pharmaceutical Synthesis" was held at the 2018 Genetic Toxicology Association annual meeting. The objectives of the workshop were to provide an educational forum and use case studies and live multiple-choice polling to establish the degree of similarity/diversity in approach/opinion of the industry experts and other delegates present for some of the more challenging decision points that need to be considered when developing a compound-specific exposure limit (ie, acceptable intake or permissible or permitted daily exposure). Herein we summarize the relevant background and case study information for each decision point topic presented as well as highlight significant polling responses and discussion points. A common observation throughout was the requirement for expert judgment to be applied at each of the decision points presented which often results in different reasoning being applied by the risk assessor when deriving a compound-specific exposure limit. This supports the value of precompetitive cross-industry collaborations to develop compound-specific limits and harmonize the methodology applied, thus reducing the associated uncertainty inherent in the application of isolated expert judgment in this context. An overview of relevant precompetitive cross-industry collaborations working to achieve this goal is described.

Filling data gap for nicotinic acid, nicotinate esters and nicotinamide for the determination of permitted daily exposure by a category approach

This study aimed to obtain necessary toxicological data using experimental and computational methods for the calculation of a common permitted daily exposure (PDE) which can be relevant for nicotinic acid and its esters and nicotinamide according to European Medicines Agency Guideline on setting health-based exposure limits. PDE calculation is mainly based on critical toxicological endpoints. During this procedure, critical toxicological endpoints data of an active pharmaceutical ingredient (API) may not be able to find satisfactorily. Hence, using toxicological data for another API that has a similar chemical structure can be a useful way. In this study, toxicological endpoints of nicotinic acid and its esters and nicotinamide were evaluated. Then, the data gaps in the toxicological endpoints were filledusing the read-across approach. Based on the current existing data, nicotinic acid and its esters and also nicotinamide are not genotoxic and do not have skin sensitization potential. These compounds do not present a concern for carcinogenicity and developmental/reproductive toxicity. Based on these critical endpoints and available experimental data, the final PDE of 10 mg/day was calculated for all category members. Our study showed the utility of the read-across for PDE calculation of APIs with experimental toxicological data gap.

Use of the permitted daily exposure (PDE) concept for contaminants of intravitreal (IVT) drugs in multipurpose manufacturing facilities

A toxicological evaluation to determine the product specific permitted daily exposure (PDE) value is an accepted method to determine a safe limit for the carry-over of product residues in multipurpose manufacturing facilities. The PDE calculation for intravitreal (IVT) injection of small and large molecular weight (MW) drugs follows the guiding principles set for systemic administration. However, there are specific differences with respect to the volume administered with IVT administration, pharmacokinetic and pharmacodynamics (PK-PD) parameters and potential for toxicity. In this publication, we have proposed a method to derive PDE_IVT in the presence of IVT dose. In the absence of an IVT dose we have a proposed default extrapolationof the systemic PDE for intravenous (IV) administration to the PDE_IVT dose by applying a factor of 500 based on comparison of the volume of vitreous humour with the plasma volume, as well as provided examples for PK-PD and toxicity considerations.

Bioavailability of protein therapeutics in rats following inhalation exposure: Relevance to occupational exposure limit calculations

Protein therapeutics represent a rapidly growing proportion of new medicines being developed by the pharmaceutical industry. As with any new drug, an Occupational Exposure Limit (OEL) should be developed to ensure worker safety. Part of the OEL determination addresses bioavailability (BA) after inhalation, which is poorly understood for protein therapeutics. To explore this, male Sprague-Dawley rats were exposed intravenously or by nose-only inhalation to one of five test proteins of varying molecular size (10-150 kDa), including a polyethylene glycol-conjugated protein. Blood, lung tissue and bronchoalveolar lavage (BAL) fluid were collected over various time-points depending on the expected test protein clearance (8 minutes-56 days), and analyzed to determine the pharmacokinetic profiles. Since the BAL half-life of the test proteins was observed to be > 4.5 h after an inhalation exposure, accumulation and direct lung effects should be considered in the hazard assessment for protein therapeutics with lung-specific targets. The key finding was the low systemic bioavailability after inhalation exposure for all test proteins (∼≤1%) which did not appear molecular weight-dependent. Given that this study examined the inhalation of typical protein therapeutics in a manner mimicking worker exposure, a default 1% BA assumption is reasonable to utilize when calculating OELs for protein therapeutics.

Derivation of a no-significant-risk-level for tetrabromobisphenol A based on a threshold non-mutagenic cancer mode of action

A no-significant-risk-level of 20 mg day-1 was derived for tetrabromobisphenol A (TBBPA). Uterine tumors (adenomas, adenocarcinomas, and malignant mixed Müllerian) observed in female Wistar Han rats from a National Toxicology Program 2-year cancer bioassay were identified as the critical effect. Studies suggest that TBBPA is acting through a non-mutagenic mode of action. Thus, the most appropriate approach to derivation of a cancer risk value based on US Environmental Protection Agency guidelines is a threshold approach, akin to a cancer safe dose (RfDcancer ). Using the National Toxicology Program data, we utilized Benchmark dose software to derive a benchmark dose lower limit (BMDL10 ) as the point of departure (POD) of 103 mg kg-1  day-1 . The POD was adjusted to a human equivalent dose of 25.6 mg kg-1  day-1 using allometric scaling. We applied a composite adjustment factor of 100 to the POD to derive an RfDcancer of 0.26 mg kg-1  day-1 . Based on a human body weight of 70 kg, the RfDcancer was adjusted to a no-significant-risk-level of 20 mg day-1 . This was compared to other available non-cancer and cancer risk values, and aligns well with our understanding of the underlying biology based on the toxicology data. Overall, the weight of evidence from animal studies indicates that TBBPA has low toxicity and suggests that high doses over long exposure durations are needed to induce uterine tumor formation. Future research needs include a thorough and detailed vetting of the proposed adverse outcome pathway, including further support for key events leading to uterine tumor formation and a quantitative weight of evidence analysis.

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 (PDE_skin), 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 PDE_skin to calculate the surface limit and appropriate validated monitoring method for the surface.

Integration of a plasma protein binding factor to the Chemical-Specific Adjustment Factor (CSAF) for facilitating the estimation of uncertainties in interspecies extrapolations when deriving health-based exposure limits for active pharmaceutical ingredients: Investigation of recent drug datasets

The objective was to challenge cross-species extrapolation factors with which to scale animal doses to human by any route for non-carcinogenic endpoints. The conventional hypothesis of the toxicokinetics (TK)-toxicodynamics (TD) relationship was equal toxicity at equal plasma level of the total drug moiety in each species, but this should also follow the free drug assumption, which states that only the unbound drug moiety in plasma may elicit a TD effect in tissue. Therefore, a protein binding factor (PBF) was combined with the Chemical-Specific Adjustment Factor (CSAF) (i.e., CSAF x PBF). The value of PBF of each drug was set equal to the ratio between human and animals of the unbound fraction in plasma (fu_p). Recent drug datasets were investigated. Our results indicate that any CSAF value would be increased or decreased while PBF deviates to the unity, and this required more attention. Accordingly, further testing indicated that the CSAF values set equal to basic allometric uncertainty factors according to the conventional hypothesis (dog∼2, monkey∼3.1, rat∼7, mouse∼12) would increase by including PBF for 30% of the drugs tested that showed a superior fu_p value in human compared to animals. However, default uncertainty factors in the range of 10-100 were less frequently exceeded. Overall, PBF could be combined with any other uncertainty factor to get reliable estimate of CSAF for each bound drug in deriving health-based exposure limits.

Topical otic drugs in a multi-purpose manufacturing facility: a guide on determination and application of permitted daily exposure (PDE)

Due to newly introduced EU GMP (Good Manufacturing Practice) guideline for Medicinal Products for Human and Veterinary use, product specific permitted daily exposure (PDE) for toxicological evaluation in multi-purpose facilities are required within a documented process for risk assessment. European Medicines Agency (EMA) guidance on setting PDE limits so far focused on systemic administration routes such as intravenous (IV), oral or inhalation. This article provides guidance on setting PDE values for risk management purposes in multi-purpose facilities for active pharmaceutical ingredients (APIs) applied as topical otic drugs to the outer ear canal. The therewith determined PDE otic, is used for the calculation of maximum safe carry-over (MSC) in manufacturing scenarios where a topical otic product is manufactured followed by another topical otic product.

Determination and application of the permitted daily exposure (PDE) for topical ocular drugs in multipurpose manufacturing facilities

Limits for the carry-over of product residues should be based on toxicological evaluation such as described in the "Guideline on setting health based exposure limits for use in risk identification in the manufacture of different medicinal products in shared facilities". The toxicological evaluation should be performed also for locally administered drugs to ensure patient safety. Currently, there is no guidance on setting PDE for ocular drug substances in particular. The purpose of this investigation was to identify and describe a method for calculating a PDE value for topical ocular drugs (PDE_ocular). As an alternative method, extrapolation of a PDE for systemically administered drugs to a PDE_ocular is presented. These methods may be applied in cross-contamination risk assessments for manufacturing of topical ocular drugs. Similarly, the methods apply to systemically administered drugs, if their production precedes manufacturing of a topical ocular drug. We have examined pharmacokinetic (PK) properties of topical ocular drugs and compared them to the PK parameters of systemically administered drugs. Furthermore, we examined possible adverse effects of the carry-over in topical ocular drugs at therapeutic doses.

Analysis of the variability of the pharmacokinetics of multiple drugs in young adult and elderly subjects and its implications for acceptable daily exposures and cleaning validation limits

The elderly constitute a significant, potentially sensitive, subpopulation within the general population, which must be taken into account when performing risk assessments including determining an acceptable daily exposure (ADE) for the purpose of a cleaning validation. Known differences in the pharmacokinetics of drugs between young adults (who are typically the subjects recruited into clinical trials) and the elderly are potential contributors affecting the interindividual uncertainty factor (UF_H) component of the ADE calculation. The UF_H values were calculated for 206 drugs for young adult and elderly groups separately and combined (with the elderly assumed to be a sensitive subpopulation) from published studies where the pharmacokinetics of the young adult and elderly groups were directly compared. Based on the analysis presented here, it is recommended to use a default UF_H value of 10 for worker populations (which are assumed to be approximately equivalent to the young adult groups) where no supporting pharmacokinetic data exist, while it is recommended to use a default UF_H value of 15 for the general population, to take the elderly into consideration when calculating ADE values. The underlying reasons for the large differences between the exposures in the young adult and elderly subjects for the 10 compounds which show the greatest separation are different in almost every case, involving the OCT2 transporter, glucuronidation, hydrolysis, CYP1A2, CYP2A6, CYP2C19, CYP2D6, CYP3A4 or CYP3A5. Therefore, there is no consistent underlying mechanism which appears responsible for the largest differences in pharmacokinetic parameters between young adult and elderly subjects.

The regulatory framework for preventing cross-contamination of pharmaceutical products: History and considerations for the future

Cross-contamination in multi-product pharmaceutical manufacturing facilities can impact both product safety and quality. This issue has been recognized by regulators and industry for some time, leading to publication of a number of continually evolving guidelines. This manuscript provides a historical overview of the regulatory framework for managing cross-contamination in multi-product facilities to provide context for current approaches. Early guidelines focused on the types of pharmaceuticals for which dedicated facilities and control systems were needed, and stated the requirements for cleaning validation. More recent guidelines have promoted the idea of using Acceptable Daily Exposures (ADEs) to establish cleaning limits for actives and other potentially hazardous substances. The ADE approach is considered superior to previous methods for setting cleaning limits such as using a predetermined general limit (e.g., 10 ppm or a fraction of the median lethal dose (LD50) or therapeutic dose). The ADEs can be used to drive the cleaning process and as part of the overall assessment of whether dedicated production facilities are required. While great strides have been made in using the ADE approach, work remains to update good manufacturing practices (GMPs) to ensure that the approaches are clear, consistent with the state-of-the-science, and broadly applicable yet flexible enough for adaptation to unique products and situations.

Special endpoint and product specific considerations in pharmaceutical acceptable daily exposure derivation

Recently, a guideline has been published by the European Medicines Agency (EMA) on setting safe limits, permitted daily exposures (PDE) [also called acceptable daily exposures (ADE)], for medicines manufactured in multi-product facilities. The ADE provides a safe exposure limit for inadvertent exposure of a drug due to cross-contamination in manufacturing. The ADE determination encompasses a standard risk assessment, requiring an understanding of the toxicological and pharmacological effects, the mechanism of action, drug compound class, and the dose-response as well as the pharmacokinetic properties of the compound. While the ADE concept has broad application in pharmaceutical safety there are also nuances and specific challenges associated with some toxicological endpoints or drug product categories. In this manuscript we discuss considerations for setting ADEs when the following specific adverse health endpoints may constitute the critical effect: genotoxicity, developmental and reproductive toxicity (DART), and immune system modulation (immunostimulation or immunosuppression), and for specific drug classes, including antibody drug conjugates (ADCs), emerging medicinal therapeutic compounds, and compounds with limited datasets. These are challenging toxicological scenarios that require a careful evaluation of all of the available information in order to establish a health-based safe level.

Setting Occupational Exposure Limits for Genotoxic Substances in the Pharmaceutical Industry

In the pharmaceutical industry, genotoxic drug substances are developed for life-threatening indications such as cancer. Healthy employees handle these substances during research, development, and manufacturing; therefore, safe handling of genotoxic substances is essential. When an adequate preclinical dataset is available, a risk-based decision related to exposure controls for manufacturing is made following a determination of safe health-based limits, such as an occupational exposure limit (OEL). OELs are calculated for substances based on a threshold dose-response once a threshold is identified. In this review, we present examples of genotoxic mechanisms where thresholds can be demonstrated and OELs can be calculated, including a holistic toxicity assessment. We also propose a novel approach for inhalation Threshold of Toxicological Concern (TTC) limit for genotoxic substances in cases where the database is not adequate to determine a threshold.