Toxicokinetic and toxicodynamic considerations when deriving health-based exposure limits for pharmaceuticals.

The purpose of this paper is to describe the use of toxicokinetic (TK) and toxicodynamic (TD) data in setting acceptable daily exposure (ADE) values and occupational exposure limits (OELs). Use of TK data can provide a more robust exposure limit based on a rigorous evaluation of systemic internal dose. Bioavailability data assist in extrapolating across different routes of exposure to be protective for route-based differences of exposure. Bioaccumulation data enable extrapolation to chronic exposures when the point of departure (PoD) is from a short-term critical study. Applied in the context of chemical-specific adjustment factors (CSAFs), TK data partially replace traditional default adjustment factors for interspecies extrapolation (extrapolation from studies conducted in animals to humans) and intraspecies variability (to account for human population variability). Default adjustments of 10-fold each for interspecies and intraspecies extrapolation are recommended in several guidelines, although some organization recommend other values. Such default factors may overestimate variability for many APIs, while not being sufficiently protective for variability with other APIs. For this reason, the use of chemical specific TK and TD data are preferred. Making full use of existing TK and TD data reduces underlying uncertainties, increases transparency, and ensures that resulting ADEs reflect the best available science.

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.

Examining the differences in current regulatory processes for sunscreens and proposed safety assessment paradigm.

Skin cancers including malignant melanoma which are due to UV radiation constitute a serious public health problem. Recent studies have confirmed the importance of UVA radiation in the pathogenesis of skin cancer, as well as the protective effects of broad-spectrum sunscreen use. Barriers for effective protection of the US public include the lack of effective UV filters, especially in the UVA spectrum. The major reason for the paucity of UVA-effective filters in the US is due primarily to the FDA's reluctance to approve agents which have already been on the market in Europe and elsewhere in the world for more than a decade. The underlying reasons for these discrepancies in new sunscreen approval success between the US and abroad are complex, and include factors such as that the FDA considers UV filters as drugs, whereas they are regulated as cosmetics elsewhere. FDA has not as yet developed a consistent approach for the approval of new UV filters. We provide a paradigm for both non-clinical testing and human safety testing which includes parameters for a human maximum use test (MUsT) that is based upon both ethical and scientific concepts. These suggestions could form the basis of future regulatory guidelines for rational testing thus allowing us to reach the consensus goal of more efficient and timely approval of much-needed UV filters to provide protection for the US public.

Guidance on the establishment of acceptable daily exposure limits (ADE) to support Risk-Based Manufacture of Pharmaceutical Products.

Health-based limits for active pharmaceutical ingredients (API) referred to as acceptable daily exposures (ADEs) are necessary to the pharmaceutical industry and used to derive acceptance limits for cleaning validation purposes and evaluating cross-carryover. ADEs represent a dose of an API unlikely to cause adverse effects if an individual is exposed, by any route, at or below this dose every day over a lifetime. Derivations of ADEs need to be consistent with ICH Q9 as well as other scientific approaches for the derivation of health-based limits that help to manage risks to both product quality and operator safety during the manufacture of pharmaceutical products. Previous methods for the establishment of acceptance limits in cleaning validation programs are considered arbitrary and have largely ignored the available clinical and toxicological data available for a drug substance. Since the ADE utilizes all available pharmaceutical data and applies scientifically acceptable risk assessment methodology it is more holistic and consistent with other quantitative risk assessments purposes such derivation of occupational exposure limits. Processes for hazard identification, dose response assessment, uncertainty factor analysis and documentation are reviewed.

Investigations of the use of bioavailability data to adjust occupational exposure limits for active pharmaceutical ingredients.

Occupational exposure limits (OELs) for active pharmaceutical ingredients have traditionally been established using no-observed-adverse-effect levels derived from clinical studies employing po and iv routes of administration and by applying default uncertainty factors or chemical-specific adjustment factors. However, exposure by the inhalation or dermal route is more relevant in terms of occupational safety. In this investigation, to explore new methods for route-to-route extrapolation, the bioavailability of MK-0679, a leukotriene D(4) receptor antagonist, was compared following iv, po, intranasal (in), or intratracheal (it) administration. The relative bioavailability of MK-0679 was iv congruent with it > po congruent with in. Bioavailability correction factors (BCFs) of 2.0 and 0.6 were derived from these data to adjust a hypothetical OEL of 0.1 mg/m(3) for MK-0679 with particle sizes of 10 and 50 mum, respectively. These BCFs were used to adjust the OEL established using po clinical data, to reflect the differences in bioavailability following deposition in different regions of the respiratory tract. To further investigate how bioavailability data could be used in setting OELs, a preliminary pharmacokinetic (PK) model was developed to describe the time course of plasma concentrations using the data from the route comparison study. An inhalation study was then performed to test the validity of using either empirical data or modeling approaches to derive BCFs when setting OELs. These investigations demonstrated how the use of route-specific PK data could reduce some of the uncertainties associated with route-to-route extrapolation and allow for improved precision and quantitative adjustments when establishing OELs. Further investigations are needed to better understand the factors responsible for differences in systemic uptake following deposition in different regions of the respiratory tract and how these can be generalized across different classes of soluble compounds.

Comparison of the industrial source complex and AERMOD dispersion models: case study for human health risk assessment.

Air quality models are typically used to predict the fate and transport of air emissions from industrial sources to comply with federal and state regulatory requirements and environmental standards, as well as to determine pollution control requirements. For many years, the U.S. Environmental Protection Agency (EPA) widely used the Industrial Source Complex (ISC) model because of its broad applicability to multiple source types. Recently, EPA adopted a new rule that replaces ISC with AERMOD, a state-of-the-practice air dispersion model, in many air quality impact assessments. This study compared the two models as well as their enhanced versions that incorporate the Plume Rise Model Enhancements (PRIME) algorithm. PRIME takes into account the effects of building downwash on plume dispersion. The comparison used actual point, area, and volume sources located on two separate facilities in conjunction with site-specific terrain and meteorological data. The modeled maximum total period average ground-level air concentrations were used to calculate potential health effects for human receptors. The results show that the switch from ISC to AERMOD and the incorporation of the PRIME algorithm tend to generate lower concentration estimates at the point of maximum ground-level concentration. However, the magnitude of difference varies from insignificant to significant depending on the types of the sources and the site-specific conditions. The differences in human health effects, predicted using results from the two models, mirror the concentrations predicted by the models.

Application of the threshold of toxicological concern concept to pharmaceutical manufacturing operations.

A scientific rationale is provided for estimating acceptable daily intake values (ADIs) for compounds with limited or no toxicity information to support pharmaceutical manufacturing operations. These ADIs are based on application of the "thresholds of toxicological concern" (TTC) principle, in which levels of human exposure are estimated that pose no appreciable risk to human health. The same concept has been used by the US Food and Drug Administration (FDA) to establish "thresholds of regulation" for indirect food additives and adopted by the Joint FAO/WHO Expert Committee on Food Additives for flavoring substances. In practice, these values are used as a statement of safety and indicate when no actions need to be taken in a given exposure situation. Pharmaceutical manufacturing relies on ADIs for cleaning validation of process equipment and atypical extraneous matter investigations. To provide practical guidance for handling situations where relatively unstudied compounds with limited or no toxicity data are encountered, recommendations are provided on ADI values that correspond to three categories of compounds: (1) compounds that are likely to be carcinogenic, (2) compounds that are likely to be potent or highly toxic, and (3) compounds that are not likely to be potent, highly toxic or carcinogenic. Corresponding ADIs for these categories of materials are 1, 10, and 100 microg/day, respectively.

Use of personal protective equipment for respiratory protection.

Management of hazards in biomedical research facilities requires the application of the traditional industrial hygiene responsibilities of anticipation, recognition, evaluation, and control to characterize the work environment, evaluate tasks and equipment, identify hazards, define exposure groups, and recommend controls. Generally, the diversity and unique characteristics of hazards faced by laboratory and animal facility employees and the short-term and low-level nature of the exposures factor into the selection of proper exposure control measures in the laboratory. The proper selection of control measures is based on a hierarchy of elimination and minimization by engineering controls, followed last by personal protective equipment when exposures cannot be eliminated. Once it is decided that personal protective equipment is needed, specific regulations and guidelines define safety standards for research facilities, including the elements of a sound respiratory protection program. These elements include respirator selection (including appropriate protection factors), medical evaluation, fit testing, training, inspection, maintenance and care, quality, quantity and flow of breathing air, and routine and emergency use procedures.

Is hexavalent chromium carcinogenic via ingestion? A weight-of-evidence review.

Hexavalent chromium [Cr(VI)] is recognized as a human carcinogen via inhalation, based on elevated rates of lung cancer among occupationally exposed workers in certain industries. Cr(VI) is also genotoxic in bacterial and mammalian cell lines. In contrast, scientific panels in the United States and abroad have reviewed the weight of evidence (WOE) and decided that the available data are insufficient to conclude that Cr(VI) is an oral carcinogen. A criterion of 0.2 ppb was established by a California agency for Cr(VI) in drinking water to prevent cancer, however, this criterion was withdrawn in November, 2001. This criterion was remarkably lower than the promulgated California and federal drinking-water standards for total chromium of 50 ppb and 100 ppb, respectively. Both of the promulgated standards are designed to be protective of humans who ingest Cr(VI). This article describes a WOE analysis to examine the likelihood that Cr(VI) in drinking water poses a cancer hazard at the current U.S. drinking-water standard. The results indicate that: (1) From the historical epidemiological studies, there are a few reports of increased rates of digestive system cancer among Cr(VI)-exposed workers, although most are not statistically significant; (2) the preponderance of evidence from recent epidemiological studies of Cr(VI)-exposed workers does not support an increased risk of cancer outside of the respiratory system; (3) studies of four environmentally exposed populations are negative; (4) there is only one lifetime animal feeding study, and the findings from that study are considered to be flawed and inconclusive; and (5) recent kinetics and in vivo genotoxicity data demonstrate that Cr(VI) is reduced to nontoxic Cr(III) in saliva, in the acidic conditions of the stomach, and in blood. In short, at concentrations at least as high as the current U.S. maximum contaminant level (100 ppb), and probably at least an order of magnitude higher, Cr(VI) is reduced to Cr(III) prior to or upon systemic absorption. The weight of scientific evidence supports that Cr(VI) is not carcinogenic in humans via the oral route of exposure at permissible drinking-water concentrations.