USP 232 Elemental Impurities - Limits

The standard "USP 232 Elemental Impurities - Limits," published by the United States Pharmacopeia (USP), specifies limits for the amount of elemental impurities in drug products. Elemental impurities include catalysts and environmental contaminants that may be present in drug substances, excipients, or drug products. These impurities can occur naturally, be intentionally added, or be introduced unintentionally (for example, through interactions with processing equipment and container closure systems).

Where elemental impurities are known to be present, added, or have the potential to be introduced, compliance with the specified levels must be assured. A risk-based control strategy may be appropriate when determining how to ensure compliance with this standard. Due to the ubiquity of arsenic, cadmium, lead, and mercury, these should be considered in the risk assessment. Regardless of the approach used, compliance with the specified limits is required for all drug products unless otherwise specified.

Drug products containing purified proteins and polypeptides, their derivatives and products of which they are components, and drug products containing synthetically produced polypeptides, polynucleotides and oligosaccharides are within the scope of this standard.

This standard does not apply to products based on genes (gene therapy), cells (cell therapy), or tissue (tissue engineering). The limits presented here do not apply to excipients and drug substances other than those specified in this standard. However, the levels of elemental impurities present in drug substances and excipients must be known, documented, and made available upon request. This standard does not apply to substances used solely for veterinary purposes.

In short, USP 232 is a critical pharmaceutical standard designed to control levels of potentially toxic elemental impurities in drug products. Its purpose is to ensure patient safety by setting strict limits for the amount of heavy metals and other harmful elements that can be present in pharmaceuticals.

Elemental impurities (impurities) such as arsenic, lead, cadmium, and mercury can inadvertently enter pharmaceutical products through raw materials, manufacturing processes, packaging, or environmental contamination. These impurities can pose serious health risks, especially with long-term exposure.

Prior to the development of this standard, control of elemental impurities often relied on outdated, nonspecific tests for heavy metals that lacked sensitivity and specificity. USP 232 replaced these tests with a modern, toxicology-based approach consistent with international standards.

The USP 232 standard applies to:

• Recent drug products (especially oral, parenteral and inhalation products)
• Ingredients and excipients, if they contribute to elemental impurity levels
• Products manufactured or marketed in accordance with USP or NF monographs

The main features of the USP 232 standard can be listed as follows:

• Risk-based limits: Limits are based on:
  • Route of administration (oral, parenteral, inhalation)
  • Daily dose of the drug
  • Permissible daily exposure values ​​derived from toxicological data
• List of elements: The USP 232 standard defines 24 elemental impurities divided into four classes:
  • Class 1: Extremely toxic (e.g. arsenic, cadmium, mercury, lead)
  • Class 2A: Generally toxic (e.g. cobalt, vanadium, nickel)
  • Class 2B: Toxic only in certain ways (e.g. thallium, gold)
  • Class 3: Low toxicity for oral administration but applicable for other routes (e.g. barium, chromium)
• Unit of measure: Limits are expressed in µg/day relative to a patient's maximum daily dose of the drug.
• Harmonization: This standard aligns with the ICH Q3D guideline on elemental impurities, ensuring consistency with international regulatory expectations (e.g. Food and Drug Administration (FDA), European Medicines Agency (EMA), Medicines and Medical Devices Agency (PMDA)).

In terms of testing requirements, USP 232 does not prescribe analytical methods; instead, it defines the limits. Actual testing procedures are described in USP 233 Elemental Impurities - Procedures, which provides guidelines for sample preparation, confirmation criteria, and the use of inductively coupled plasma mass spectrometry (ICP-MS) or optical emission spectroscopy (ICP-OES).

USP 232 does not directly describe the test methods to be performed, but instead refers to the complementary USP 233 standard. USP 233 contains analytical procedures and validation requirements for testing elemental impurities. The primary test methods used to identify elemental impurities are:

• ICP-MS (inductively coupled plasma-mass spectrometry): This technique is best used for the detection of trace levels (parts per billion) of elemental impurities. This technique has high sensitivity, multi-element capability, and a wide dynamic range. It is often used to detect toxic elements such as arsenic, cadmium, mercury, and lead.
• ICP-OES (inductively coupled plasma-optical emission spectroscopy): This technique is best used for measuring elements at moderate to high concentrations. It has good sensitivity and robustness, and greater speed for some matrices. It is typically used to detect elements such as copper, zinc, or nickel when present at higher levels.

Before analysis, the sample must be properly digested or thawed. The USP 233 standard allows:

• Closed-pot microwave digestion
• Open-cup acid digestion
• Direct solution methods (if the sample is already dissolved)

The USP 233 standard requires the following validation criteria (system conformity):

• Accuracy: Recovery of sharpened sample between 70 percent and 150 percent

• Precision: The relative standard deviation (RSD) should not exceed 20 percent.
• Specificity: No interference from the sample matrix

• Limit of quantitation: At or below the specification limit

For implementation and compliance purposes, pharmaceutical manufacturers should:

• A risk assessment should be carried out to identify possible sources of elemental impurities.
• Must ensure compliance through testing, supplier qualification, or process controls
• The control strategy used must be documented and justified.

The USP 232 standard represents a modern, science-based approach to controlling elemental impurities in pharmaceuticals. By focusing on toxicological data and route-specific exposure-based safety thresholds, it provides robust patient protection while promoting global harmonization. Compliance with this standard is not only a regulatory requirement but also a vital component of pharmaceutical quality and safety.

Our organization, which has been supporting businesses across all sectors for years through a wide range of testing, measurement, analysis, and evaluation activities, has a strong team of employees who closely follow global developments in science and technology and are constantly improving themselves. In this context, we also provide testing services in accordance with the USP 232 Elemental Impurities - Limits standard.