FDA Warning Letter: Missing Method Validation - From a QC Topic to a Market-Access Problem

In mid-May, the U.S. Food and Drug Administration (FDA) published a new Warning Letter dated 4 May 2026 to a drug manufacturing facility in South Korea.

The letter illustrates how missing method validation can rapidly escalate from a QC topic to a broader compliance, supply, and market-access issue. In this case, the firm was already placed on Import Alert in March 2026.

Method Validation

A central theme of the Warning Letter is FDA’s conclusion that the company failed to establish and validate scientifically sound laboratory controls as required by 21 CFR 211.160(b). Specifically, FDA states that the company:

• did not appropriately establish and validate its gas chromatographic (GC) assay method for testing its finished drug products;
• did not validate its GC method for determining volatile impurities in the raw material; and
• did not test the raw material for the presence of specific impurities.

FDA also finds the firm’s response insufficient. Although the firm indicated it would discontinue unvalidated methods and establish/validate new GC methods, FDA notes that the company did not provide a risk assessment addressing the impact of the unvalidated methods and did not address testing of retain samples for finished products potentially manufactured using untested or inadequately tested raw materials.

Further Deficiencies

Beyond laboratory method validation, FDA lists additional significant CGMP deficiencies:

• Written procedures for production and process control: FDA describes a lack of procedures for operation, cleaning, and maintenance.
• Process and equipment cleaning validation: The firm did not conduct process validation or equipment cleaning validation.
• Quality Unit oversight: FDA states the quality unit did not adequately exercise its responsibilities, citing examples such as an inadequate stability program, inadequate batch production and control records, and missing routine equipment calibration.

FDA also recommends engaging a qualified CGMP consultant to support remediation and to perform a comprehensive audit.

For further information, see the complete Warning Letter to IDO Pharm Co., Ltd. on FDA’s website.