Toxicological risk evaluation of extractable and leachable from single use systems used to manufactu

Introduction

Preserving patient safety is a priority for the healthcare industry and regulatory authorities.Regulatory guidance states and industry best practices encourage drug safety specification include data to address potential issues that are not addressed during clinical studies.Patient safety has emerged as a distinct healthcare discipline to deal with these concerns.

The pharmaceutical industry is witnessing a swift change towards the use of single use systems to manufacture drugs. Along with this change is an increasing awareness of the potential for harmful substances to migrate from these single use systems into the drug product and compromise patient safety.  Patient Toxicological Risk Evaluations are being performed to mitigate this risk and realize the benefits of single use systems.

Low and middle-income countries (LMIC) are increasingly manufacturing and supplying their own drugs to domestic markets utilizing single use process technology, and they too will want to conduct these evaluations.

Patient Toxicological Risk Evaluations consider all the components in the process train from the bioreactor to the final filling assembly.  These evaluations identify and quantify all the potential compounds that may leach into the drug product and then correlate the toxicity of these compounds to patient safety with respect to a specific drug.

Risk Evaluation

Toxicological risk evaluations determine whether or not a product poses a potential risk for the toxicological endpoints measured.  Regulatory guidance requires identification and quantification of the impurities and characterization of their toxicological profile to determine impact on patient safety.  The Parenteral Drug Association (PDA) technical report No 26, states that "It is the user’s responsibility to demonstrate that the product does not contain objectionable levels of extractables from the filter. . . . The filter user is responsible for obtaining extractable data for the drug product formulation". This assessment utilizes extractable and/or leachable data from the drug manufacturing process to evaluate the toxicological risk for patients exposed to potential leachables. The risk evaluation considers the quantity of extracted or leached compounds, patient population, patient dose, frequency of dosage and route of administration.

The toxicological evaluation of impurities and the determination of acceptable levels in the final product is a challenge not described in detail in any guideline or reference. In the absence of such data usually needed for the application of one of the established risk evaluation methods, i.e. data from long term carcinogenicity studies or data providing evidence of threshold mechanisms of genotoxicity, implementation of a generally acceptable approach as defined by application of the Threshold of Toxicological concern(TTC) is proposed.

While guidance documents establish high level strategies, practical implementation is problematic because it suggests that all extractables/leachables, regardless of their accumulated levels, must undergo full toxicological safety evaluation. Such an evaluation would be necessary even when the concentration is so low that there is no adverse effects to humans. However, some extractables may not be detected in the final drug product(i.e., they do not leach)and some leachables may be at so low a level that they have no effect on patient safety. This evaluation is not productive since the regulatory and industry resources are most effectively used when they are focussed on substances that are present at high levels that affect patient safety.

With the aim of balancing absolute safety risk and the level of effort required to establish that risk, it is reasonable to propose dose thresholds for extractables or potentialleachables, combined with a risk evaluation of the manufacturing process.

Approach and Process

Impurities are identified and quantitated through extraction of all the materials in the process equipment or devices that contact the drug product using either model solvents or a leaching process using the actual drug formulation and multiple analytical methods.

Following identification of these compounds, an overall risk evaluation needs to be performed.  The factors that determine the toxicity of the extracted or leached compounds are:

1. Toxicological data on compounds
2. Concentration in final dosage
3. Dose size, regimen, dose delivery
4. Patient population

To control the effect of the above mentioned factors, a threshold representing the amount of any individual substance that will not produce an undesirable safety outcome needs to be established.   The toxicity risk is based on the dose-response relationship.

A toxicological profile is established by reviewing in-house studies, scientific publications, databases and regulatory guidelines for the compounds identified. The no observable effect level (NOEL) is the highest dose or exposure level of a compound that produces no noticeable toxic effect.  In situations where data are not available, an in silico analysis is performed using quantitative structure-activity relationship (QSAR) analysis.Knowledge-based systems, such as Derek, CPDB, and DSSTOX that have international bioassay literature data for several acute and chronic conditions with qualitative and quantitative data for positive and negative experiments,can serve as ready references for decision-making.

Guidelines and Regulatory Expectations

Toxicological information is not often readily available for a number of substances. In such situations, the Threshold of Toxicological Concern (TTC), which was developed by the Food and Drug Administration (FDA) Office of Food Additive Safety and is based on linear regression of more than 600 carcinogens, can be referred to as a standard value. TTC is a principle that refers to the establishment of a generic human exposure threshold value for (groups of) chemicals below which there would be no appreciable risk to human health. The TTC established a universal safety threshold at 1.5 mg/day, whether or not there is compound-specific toxicity data.

Additionally, the Product Quality Research Institute (PQRI) classifies compounds into three classes of Cramer compounds based on the degree of toxicity and the complexity of the SAR.

The TTC values for the reference would be as follows:

Unknown Compound Type                                                         TTC (µg/day)

Possible carcinogen                                                                                          0.15

Non carcinogenic, possibly genotoxic                                                      1.50

Non genotoxic or carcinogenic grouped by SAR

Organophosphate                                                                                            18

Cramer Class III (high complexity by SARs)                                       90

Cramer Class II (moderate complexity by SARs)                            540

Cramer Class I (low complexity by SARs)                                          1800

The list of leachable and extractable substanceswas initially sorted via ToxTreeinto Cramer classes as follows:

Class 1: substances of simple chemical structure with known metabolic pathways and innocuous end products which suggest a low order of oral toxicity.

Class 2: substances that are intermediate, possess structures that are less innocuous than those in Class 1 but they do not contain structural features that are suggestive of toxicity like those in Class 3.

Class 3: substances with chemical structures that permit no initial presumption of safety and may even suggest significant toxicity.

In addition to the original three Cramer classes that sort chemicals into categories from least toxic to most toxic, a fourth class was added to capture chemicals of known or suspect genotoxic potential using Deductive Estimation of Risk using Existing Knowledge (DEREK) software. Additional safety factors to account for body weight and route of administration differences (oral vs parenteral) were considered to add orders of magnitude to the already conservative estimates established by Cramer and refined by Munro.

The ideal option is to opt for a risk evaluation to assess the toxicological concern for the patient.  The toxicologist establishes the permitted daily exposure (PDE) levels for identified compounds and evaluates the concentrations based on the extractable or leachable testing.

An improper assessment of the risk, or not performing an analysis to correlate the extractable and leachable substances to patient safety, poses multiple concerns for the regulators and could delay the drug approval process:

• Risk to patient safety
• Effect on product quality including efficacy
• Confounding clinical trial results

Case Study – Correlating Patient Safety through Risk Evaluation Approach

A monoclonal antibody at a concentration of 10g/l produced using a fully single use process from bioreactor to bulk drug substance was evaluated for the leachables’ impact on patient safety.  The cumulative leachables from the downstream purification process was measured in the bulk drug substance on day 0 and after 7 days of storage in a single use biocontainer at 2 – 8 °C (Figure 1).  On day seven, 0.87 µg/ml was quantitated in the bulk drug substance.  The single greatest leached compound was hexanal, a volatile organic alcohol, which was quantitated at 110 ppb (0.11 µg/ml) using gas chromatography mass spectrometry (GCMS).

The API is administered in a high dosing regimen of 105 ml (1050 mg at 10 mg/ml) by intravenous infusion once every 14 days with a long term treatment duration.  The total leachables concentration measured by GCMS of 0.87 mg/ml was applied to the 105 ml resulting in 92 mg of leachables being administered to the patient.  This exceeds the 1.5 mg/person/day threshold of toxicological concern (TTC) – a worst case threshold set by the FDA. Similar guidelines are published for ICH, EMA and PQRI.  This conservative threshold assumes the compounds are genotoxic and carcinogenic.  Without further information, thisleachablesconcentration would be considered an unacceptable risk to the patient.

Knowing that no genotoxic or carcinogenic compounds are likely to emanate from the process technology based upon the materials of construction, the toxicologist may consider only the specific compounds that were identified in the leachables study.  In this case, the toxicologist focused on hexanal, the compound present in the highest concentration.  Reviewing the literature, the toxicologist calculated a permissible daily exposure (PDE) for two similar compounds – butanal and pentanal – at 3.75 mg/person/day.  The leachables concentration of hexanal was 0.11 µg/ml resulting in 12 µg/person/day – far below the 3.75 mg/person/day PDE.

Results

The toxicologist determines that it can be reasonably concluded that there is no risk for patients exposed to these potential leachables.  A report suitable for presentation to the regulatory authorities will be issued.

This analysis is a constructive effort to ensure that all possible leachables in proximity of the drug product is quantified and identified. Moreover, a thorough safety risk assessment ensures that the detected compounds do not pose any safety risks to the patient, and allows faster entry into the market without additional regulatory hurdles for the drug manufacturer.

Low and Middle Income Country Producers

Low and middle-income countries (LMIC) have increased their level of pharmacovigilance (PV) over the last 20 years.  A map of LMICs can be found in Figure 2.  These countries have typically depended upon PV from high-income countries from which the drugs they use originated.  As more LMIC drug manufacturers produce drugs for domestic consumption, they will be obliged to perform more comprehensive safety testing prior to commercial distribution and improve their own level of PV as drugs enter the market.

ICH E2E guidance on pharmacovigilance planning states that the safety specification of a drug should summarize important identified and potential risks.  Within this specification, the guidance states that data should be presented to address non-clinical safety findings that have not been adequately addressed by clinical data, such as toxicity.

In Conclusion

Patient safety is best preserved by a comprehensive analysis of impurities that migrate from single use process technology and a risk evaluation to determine their toxicological impact.  While methods continue to evolve, sound approaches do exist to preserve patient safety and meet regulatory expectations.