Vulcanising and antioxidant agents, plastic’s monomers, dyes, phthalates, silicon oils or toxic inorganic elements are just few examples of substances that might be present as contaminants into a finished medicinal product. They might be released by contact between the finished dosage form and the machinery and materials used for the manufacturing process (i.e. filters, containers, tubes…) or with the primary packaging materials. This sort of impurities are designed under the term “extractables & leachables” (E&L, BOX 1 and 2) and their determination represents an important regulatory request as for the toxicological safety of the finished medicinal product. «The determination of the extractables & leachables in the pharmaceutical sector is very similar to the one of the food contact materials typical of the food industry – tells Antonio Conto, European registered toxicologist and managing director at Chemsafe. – In both cases it has to be determined what are the contaminants present in the food or medicinal product, respectively, which might cause some adverse effects to the patient-consumer».

The different profiles of impurities

There are two main categories of extractables & leachables, the main one being the possible additive contamination of the final dosage form with substances coming from the manufacturing process or packaging materials. In the second case, some of the pharmaceutical active ingredient or excipients are adsorbed into the same packaging material, thus altering the quantities present in the dosage form. In both cases, the main result is a possible alteration/reduction of the stability profile of the medicinal product, of the quantity of the active ingredient or of the impurities profile and the formation of particulate within the formulation. «The first instance is the most worrying one, and it represents an increasing issue we are addressing since the last couple of years upon request of pharma companies. They have been solicited by the Food and Drug Administration to test the finished products intended to be sell in the U.S.», tells Conto.Paragraphs <1663> and <1664> of the USP gives the definition of extractables and leachables: the first term refers to substances that might be “extracted” by the packaging materials, while the second one is in many cases a sub-group of the extractables, representing all substances that might perculate into the finished dosage form. Leachables might also refer to substances that form upon contact with the drug product, and not during the laboratory extraction, thus they might be not included within extractables.  A less known category is the “migrants” one, i.e. substances that accumulate into the finished product upon passage of a physical barrier; they might come from the secondary and tertiary packaging materials or from ancillary components, and they are able to pass through the primary packaging material. «Typical examples of leachables are azo-dyes used in labelling, or plastic phthalates: they are also restricted under the Reach regulation, as they are endocrine disruptors with a critical safety profile, which might impact the human reproductive and hormonal systems. Among inorganic toxic elements I mention lead, cadmium, chromium – further tells Antonio Conto .- Also the plastic’s monomers and dimers can be highly toxic, while they are safe once polimerisation occurred due to the high molecular weight and the low bioavailability of the polymer».

How to develop the better strategy

There are many substances that might pass from the packaging materials to the medicinal product, thus it is very important to correctly address the determination of E&L since the beginning of the process to properly manage its complexity. «The difficult issue is to join the analytical activities and the toxicological ones – explains Antonio Conto. – At a first instance, the analytical part might play a major role: it should be carefully planned, as it might cause many issues and result to be misleading».

The initial laboratory extraction, usually run using ethanol as the solvent, might give a pool of an hundred different chemical substances, which should be then analysed from the toxicological point of view to determine the presence of leachables. These last one might be a pool of very few substances. «It is necessary since the beginning to direct the analytical study from a toxicological perspective, trying to obtain data as close as possible to the true situation. It often occurs that the extracted substances are unknown impurities, and their structural delucidation might have very high costs», tells Chemsafe’s managing director.

The toxicological risk evaluation should be always part of the development of the analytical protocol. For example, tells Conto, one of Chemsafe’s early customers is now working to the development of a routine GMP-validated analytical method for batch release. «Once obtained the E&L’s toxicological profile, the substances are always the same. It is thus possibleupon validation of the safety levels, to demonstrate for each batch to be under the threshold level».

Three steps to be evaluated

The isolation of the extractables from the packaging material or the from the labelling is the first analytical step, but «it is possible that these would be not the ones that percolates. The true pharmaceutical dosage form is the one in contact with the container. The study to determine leachables is run with a simulated formulation under laboratory experimental conditions – explains Antonio Conto. – The toxicological evalutation is placed between these two steps». The study design is strictly dependent upon each single product, and the route of administration may also impact the risk evaluation.  Parenteral administered drugs, for example, are characterised by an higher potential risk with respect to topical drugs. For these last ones, a possible issue might be represented by leachables that are also skin sensitiser. The mixed approach stays in the middle between the to extremes, a purely extractive approach or the simulated product approach. Under the mixed approach, the toxicological evaluation helps to identify the more relevant substances among the extracted ones, which are then further searched in the leachable study. «The hazard profile is connected to the chemical structure of the substance. The risk evaluation gives the uptake threshold level, the impurity’s daily dose that the patient can take without adverse effects during its entire life span, according to the worst case approach», explains the toxicologist. The great part of guidelines for the determination of E&L comes from the United States (BOX 3); among these, the ones from the Product Quality Research Institute (PQRI) working group also provide the specific safety levels for different contaminants and for some type of toxicological endpoints, i.e. genotoxic substances, sensitisers and substances characterised by a generic toxicity. The uptake limit for genotoxic compounds, for example, is 1,5 mg/die. (Table 1)

Biological drugs represent a particular case, as the presence of leachables might also alter the 3D structure of proteins. Metals, for examples, might bind to amino-acids and induce a change of the conformation of the protein, thus causing a reduction/loss of the desired pharmacological activity. A direct interaction between the leachable and the biological drug is another possibility, that might cause loss of post-translational modifications. «The determination of E&L for biological medicines is even more complex than for synthetic drugs, thus it is by now less debated. Upon future experiences it could be deeply discussed in the coming years», comments Antonio Conto.

The entire life cycle of the product is interested

The responsible for the determination of extractables and leachables is the manufacturer of the finished medicinal product but, according to Chemsafe’s managing director, it might ask its suppliers of packaging materials to demonstrate the absence of certain substances. «We never received such a detailed request, as suppliers are for some instances not so well prepared to face this sort of certification procedures and its costs. Pharmaceutical companies have by now qualified their suppliers according to the GMP. It can be not strictly excluded that a packaging might release E&L; as a toxicologist, this evaluation should be run on all packaging materials», is the final proposal coming from Antonio Conto.

Definitions of E&L according to USP <1663> and <1664>

Extractables <USP 1663> – Extractables are organic and inorganic chemical entities that can be released from a pharmaceutical packaging/delivery system, packaging component, or packaging material of construction under laboratory conditions. Depending on the specific purpose of the extraction study, these laboratory conditions (e.g., solvent, temperature, stoichiometry, etc.) may accelerate or exaggerate the normal conditions of storage and use for a packaged dosage form. Extractables themselves, or substances derived from extractables, have the potential to leach into a drug product under normal conditions of storage and use. Leachables <USP 1664> – Leachables are organic and inorganic chemical entities that migrate from a packaging/delivery system, packaging component, or packaging material of construction into an associated drug product under normal conditions of storage and use or during accelerated drug product stability studies. Leachables are typically a subset of extractables or are derived from extractables. Note that chemical entities can also migrate from packaging/delivery systems to patients via direct contact.

Possible primary sources of extractables according to USP <1663>

  • Chemical additives in individual elastomeric/polymeric packaging components and raw materials, including contaminants in these additives;
  • Monomers and higher molecular weight oligomers derived from incomplete polymerization;
  • Migrants from secondary and tertiary packaging components, such as inks, label adhesives, and volatiles from cardboard shipping containers, plastic storage bags, and wooden pallets;
  • Surface residues, such as heavy oils and degreasing agents on metal canisters and containers;
  • Chemical substances on the surfaces of component fabrication machinery or other drug product manufacturing systems, such as mold release agents, antistatic and antislip agents;
  • Chemical additives, monomers/oligomers, contaminants, etc., in various parts of component fabrication machinery or other drug product manufacturing systems.

The main regulatory guidelines

  • USP <660> Glass
  • USP <661.1> Plastic packaging systems and their materials of construction
  • USP <661.2> Plastic packaging systems for pharmaceutical use
  • USP <1660> Evaluation of the inner surface durability of glass containers
  • USP <1664> Assessment of drug product leachables associated with pharmaceutical-packaging delivery systems
  • USP <1664.1> Assessment of drug product leachables associated with pharmaceutical-packaging/delivery systems: Orally inhaled and nasal drug products
  • USP <1664.2> Parenteral and ophthalmic drug products (proposed)
  • PQRI Leachables and Extractables Working Group. Safety thresholds and best practices for extractables and leachables in orally inhaled and nasal drug products. September2006.
  • ISO 10993-17: 2002. Biological evaluation of medical devices – part 17: establishment of allowable limits for leachable substances.
  • Guideline on plastic immediate packaging materials. CPMP/QWP/4359/03 and EMEA/CVMP/205/04.5/19/05.
  • EMA, Limits for genotoxic impurities EMEA/CHMP/QWP/251344/2006
  • EMA, Specification limits for residues of metal catalysts and metal reagents EMEA/CHMP/SWP/4446/2000
  • ICH Q3A, Impurities in new drug substances
  • ICH Q3B, Impurities in new drug products
  • ICH Q8, Pharmaceutical development
  • ICH Q6A, Test procedure and acceptance criteria for new drug substances and drug products
  • ICH M7 Guideline on mutagenic impurities

Draft published into the Pharmacopeial Forum (PF), 43(3), May-June.2017:

  • USP <1665> – Plastic components and systems used in the manufacturing of pharmaceutical products
  • USP <665> – Plastic components and systems used into pharmaceutical production

The PQRI’s classification

PODP – Parenteral and ophtalmic drug products
Genotoxic (SCT) 1,5 mg/die
Sensitisers 5 mg/die
General toxicity (QT) 150 mg/die
OINDP – Oral inhaled and nasal drug products
Genotoxic (SCT) 0,15 mg/die
Sensitisers Non definito
General toxicity (QT) 5 mg/die