Acceptable Intake Thresholds for Nitrosamine Impurities Set by CDER
Recommended Acceptable Intake Limits for Nitrosamine Drug Substance-Related Impurities (NDSRIs)
Guidance for Industry
Control of Nitrosamine Impurities in Human Drugs
Guidance for Industry
Recommended Acceptable Intake (AI) Limits, Implementation Timelines, Emerging Scientific and Technical Issues, and Testing Methods
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On August 4, 2023, the FDA released final guidance on Recommended Acceptable Intake Limits for Nitrosamine Drug Substance-Related Impurities (NDSRIs), providing recommendations for NDSRI AI limits based on estimated carcinogenic potency. Subsequently, FDA released guidance on Control of Nitrosamine Impurities in Human Drugs on September 4, 2024. This guidance outlines two nitrosamine categories: small-molecule nitrosamines and NDSRIs, offering industry recommendations for control measures and their implementation.
The FDA is continually updating the guidance material with key information such as: (1) AI limits for distinct nitrosamine impurities, including NDSRIs; (2) interim AI limits; (3) implementation timelines; (4) current scientific developments; (5) analytical methods for nitrosamine testing; and (6) safety testing protocols.
The guidance represents the FDA’s perspective on the issue, is non-binding, and does not confer rights. Industry is urged to adhere to FDA’s AI limits. If alternative approaches comply with applicable laws, manufacturers may use them.
Public comments can be directed to the docket for these guidances (Docket No. FDA-2020-D-1530) at any time for FDA review. Written comments should be sent to the FDA Dockets Management Staff, Rockville, MD, or electronically via www.regulations.gov with reference to the docket number and guidance title.
Recommended AI Limits for Select Nitrosamine Impurities
Correlation with the predicted Carcinogenic Potency Categorization Approach (CPCA) for APIs at Potential NDSRI Formation Risk and Other Identified Nitrosamines
Nitrosamine impurities arise via nitrosation involving amines and nitrous acid. They consist of small-molecule and NDSRIs, the latter being structurally similar to the API in question. The formation of these impurities can occur during drug formulation or manufacturing processes where residual nitrites are present.
Table 1 outlines recommended AI limits for nitrosamine impurities based on the CPCA methodology, specifying limits relative to specific APIs or categorized under “multiple” sources.
There are potential nitrosamine sources entailed by packaging, where leachates might introduce nitrosamines, indicated by a symbol “#” in the table.
Current recommended AI limits apply to listed nitrosamines. FDA may update these based on newly available data, either providing more specific assessments or altering limits as necessary.
This guidance does not encompass all APIs capable of forming nitrosamines, and inclusion in the table does not guarantee the presence of such impurities in drug products. Any AI limit specified by the FDA illustrates the threshold at which no safety concern is deemed acceptable for patients.
* Chemical structure images sourced from the National Institutes of Health.
Table 1: FDA Recommended AI Limits for Certain Hypothetical NDSRIs and Other Identified Nitrosamine Impurities
(Updated: 11/20/2024)
Based on the CPCA
* The source denotes the form of the drug substance whether it is in free base or free acid form.
** See Table 3.
References
- (Q)SAR model reporting format (QMRF) referenced in Kruhlak NL, et al. Regulatory Toxicology and Pharmacology, June 2024; 150:105640.
AI Limits for Specific Nitrosamines
Guidelines Based on Compound-Specific Data or Surrogate Read-Across
Table 2 shows FDA recommended AI Limits derived from compound-specific evaluations or surrogates. Nitrosamines listed here carry respective AI limits that supersede those determined by the CPCA method.
Table 2: FDA Recommended AI Limits for Certain Nitrosamine Impurities
(Updated: 10/7/2024)
Based on Compound-Specific Data or Surrogate Read-Across
| Nitrosamine Name | Source | Recommended AI Limit (ng/day) | Surrogate | Date Added to Table |
|---|---|---|---|---|
| N-nitroso-duloxetine | Duloxetine | 100 | 4-(methylnitrosoamino)-1-(3-pyridinyl)-1-butanone (NNK) | 8/4/2023** |
| N-nitroso-/fluoxetine | Fluoxetine | 100 | 4-(methylnitrosoamino)-1-(3-pyridinyl)-1-butanone (NNK) | 10/11/2023 |
| N-nitroso-atomoxetine | Atomoxetine | 100 | 4-(methylnitrosoamino)-1-(3-pyridinyl)-1-butanone (NNK) | 12/1/2023 |
| N-nitroso-dimethylamine (NDMA) | Multiple | 96 | Compound specific | 9/4/2024 *** |
| N-nitroso-diethylamine (NDEA) | Multiple | 26.5 | Compound specific | 9/4/2024 *** |
| N-nitroso-piperazine (NPZ) | Ciprofloxacin | 1300 | N-nitroso-piperidine (NPIP) | 9/4/2024 |
| N-nitroso-methylphenidate | Methylphenidate | 1300 | N-nitroso-piperidine (NPIP) | 9/4/2024 |
| N-nitroso-vonoprazan | Vonoprazan | 96 | N-nitroso-dimethylamine (NDMA) | 9/4/2024 |
**See Table 3.
*** This limit was previously assessed on September 3, 2020 as outlined in the Nitrosamine Guidance.
Interim AI Limits for Specific Nitrosamine Impurities
When nitrosamine impurities exceed recommended limits in distributed drug products and alterations or recalls threaten supply, manufacturers should contact CDER’s Drug Shortage Staff at drugshortages@fda.hhs.gov promptly. FDA will evaluate situations individually and may recommend an interim AI limit as needed; FDA won’t object to the disbursement of drug products within the interim limits during the determined timeframe.
Table 3: Recommended Interim AI Limits* for Select Nitrosamine Impurities** for Approved Products
(Updated: 10/31/2024)
| Nitrosamine Name | Source | Recommended Interim AI Limit (ng/day) | Recommended Interim Control Limit (ppm) | Estimated Duration*** |
|---|---|---|---|---|
| N-nitroso-duloxetine | Duloxetine | 600 ng/day | 5 ppm | 12/31/2024 |
| N-nitroso-ciprofloxacin | Ciprofloxacin | 12,000 ng/day | 8 ppm | 3/31/2025 |
| N-nitroso-dorzolamide | Dorzolamide (single ingredient product only) | 500 ng/day | 139 ppm | 8/1/2025 |
| N-nitroso-sertraline | Sertraline | 600 ng/day | 3 ppm | 8/1/2025 |
*An AI limit can convert into a ppm control limit varying by product as expressed by ppm = AI (ng)/(MDD (mg)).
** A lot release decision remains the manufacturer’s discretion, with full accountability for adherence to standards including CGMP.
*** “Estimated Duration” signifies the date for a potential reassessment of the interim control limit. As stated in both the RAIL and Nitrosamine Guidance, complete confirmatory testing for NDSRI should aim to conclude by August 1, 2025 for marketed products.
Implementation Timelines
Implementation timelines vary by product regulatory status and nitrosamine impurity type. The FDA weighs factors like public health risks, scientific knowledge state, and mitigation efficacy feasibility when establishing these timelines. For new nitrosamines, substantial reformulations requiring time may be advisable, while simpler packaging solutions might necessitate shorter periods. Certain urgent public health exigencies may prompt immediate regulatory actions.
Table 4: Recommended Implementation Timelines
(Updated: 9/4/2024)
| Nitrosamine Impurity | Risk Assessment Performance Date | Confirmatory Testing Date | Submission of Required Changes |
|---|---|---|---|
| Small Molecule Nitrosamines | March 31, 2021 | Upon risk identification | October 1, 2023 |
| NDSRIs | November 1, 2023 | Upon risk identification | August 1, 2025 |
Emerging Scientific and Technical Issues
The FDA will share new findings regarding nitrosamines, addressing their root causes as they emerge and suggesting mitigation actions accordingly.
Recommended Analytical Testing Methods
If risks are identified, confirmatory testing of batches should employ sensitive, validated techniques. Examples of recommended FDA analytical testing methods are available for industry to ensure nitrosamine detection in specific drug products.
Table 5: Recommended Analytical Testing Methods
(Updated 10/1/2024)
| Drug name (nitrosamine) | Method | Date Added to Table |
|---|---|---|
| Rifampin (MNP) and Rifapentine (CPNP) | LC-ESI-HRMS method | 10/1/2024* |
| Metformin (NDMA) | LC-HRMS method | 10/1/2024* |
| Metformin (NDMA, NDEA, NEIPA, NDIPA, NDPA, NMPA, NDBA, NMBA) | LC-ESI-HRMS method | 10/1/2024* |
| Angiotensin II Receptor Blocker (ARB): Valsartan, Losartan, Irbesartan (NDMA, NDEA) | Combined headspace method | 10/1/2024* |
| Angiotensin II Receptor Blocker (ARB): Valsartan, Losartan, Irbesartan (NDMA, NDEA) | Combined direct injection method | 10/1/2024* |
| Angiotensin II Receptor Blocker (ARB): Valsartan, Losartan, Irbesartan (NDMA, NDEA, NDIPA, NEIPA, NDBA) | Direct injection GC-MS method | 10/1/2024* |
| Angiotensin II Receptor Blocker (ARB): Valsartan, Losartan, Irbesartan (NDMA, NDEA, NDIPA, NEIPA) | Headspace GC-MS method | 10/1/2024* |
| Angiotensin II Receptor Blocker (ARB): Valsartan, Losartan, Irbesartan (NDMA, NDEA, NDIPA, NEIPA, NDBA, NMBA) | LC-HRMS method | 10/1/2024* |
| Angiotensin II Receptor Blocker (ARB): Valsartan, Losartan, Irbesartan (NDIPA, NEIPA, NDBA, NMBA) | RapidFire-MS/MS method | 10/1/2024* |
| Ranitidine (NDMA) | LC-HRMS method | 10/1/2024* |
| Ranitidine (NDMA) | LC-MS/MS method | 10/1/2024* |
| Varenicline | LC-ESI-HRMS Method | 2/23/2024 |
| Bumetanide | LC-ESI-HRMS Method | 2/23/2024 |
| Propranolol | LC-ESI-HRMS Method | 2/23/2024 |
* Previous methods were also made available on the FDA’s official site.
Recommended Safety Testing Methods for Nitrosamine Impurities
A manufacturer might pursue an AI limit above FDA’s recommendations by providing scientific justification. Alternative methods using robust safety data may be accepted to support a higher limit, which could involve enhanced Ames assays in vitro for mutagenic risk. A negative outcome in this test could warrant a higher limit; however, manufacturers should note that FDA might call for further data in support.
In addition to the enhanced Ames test, the Agency is now requesting a secondary in vitro mammalian cell mutation assay to confirm limits of 1500 ng/day. Negative results in these tests will support the standards, although additional in vivo data may be requested to validate higher limits.
The following represents FDA’s current perspective; certain information gaps require ongoing research for comprehensive risk assessments associated with nitrosamines.
For nitrosamines, FDA endorses enhanced testing conditions for the Ames assay due to previously recognized sensitivity issues. The testing specifications and suggestions will be updated as necessary.
References
- OECD Test Guideline No. 471 “Bacterial Reverse Mutation Test” 2020.
- Li X, et al. Revisiting the mutagenicity and genotoxicity of N-nitroso propranolol. Regul Toxicol Pharmacol. 2023 June; 141:105410.
Revision Table
Revision Table for Updated Information
| Revision | Nitrosamine Name | Change | Date Posted* |
|---|---|---|---|
| 0 | Original Webpage Posting | Initial posting for Updated Information/Recommended Acceptable Intake Limits for Nitrosamine Drug Substance-Related Impurities (NDSRIs) | 8/4/2023** |
| 1 | N-nitroso-arformoterol | Added to Table 1 | 10/11/2023 |
| 1 | N-nitroso-hydrochlorothiazide | Added to Table 1 | 10/11/2023 |
| 1 | N-nitroso-quinapril | Added to Table 1 | 10/11/2023 |
| 1 | N-nitroso-nortriptyline | Added to Table 1 | 10/11/2023 |
| 1 | N-nitroso-desmethyl-imipramine | Added to Table 1 | 10/11/2023 |
| 1 | N-nitroso-avacopan | Added to Table 1 | 10/11/2023 |
| 1 | N-nitroso-belumosudil | Added to Table 1 | 10/11/2023 |
| 1 | N-nitroso-benzonatate | Added to Table 1 | 10/11/2023 |
| 1 | N-nitroso-deucravacitinib | Added to Table 1 | 10/11/2023 |
| 1 | N-nitroso-exametazime | Added to Table 1 | 10/11/2023 |
| 1 | N-nitroso-finerenone | Added to Table 1 | 10/11/2023 |
| 1 | N-nitroso-leniolisib | Added to Table 1 | 10/11/2023 |
| 1 | N-nitroso-desmethyl-maralixibat | Added to Table 1 | 10/11/2023 |
| 1 | N-nitroso-maribavir | Added to Table 1 | 10/11/2023 |
| 1 | N-nitroso-omidenepag isopropyl | Added to Table 1 | 10/11/2023 |
| 1 | N-nitroso-pafolacianine | Added to Table 1 | 10/11/2023 |
| 1 | N-nitroso-viloxazine | Added to Table 1 | 10/11/2023 |
| 1 | N-nitroso-lorcaserin | Deleted from Table 1 | 10/11/2023 |
| 1 | N-nitroso-isoxsuprine | Deleted from Table 1 | 10/11/2023 |
| 1 | N-nitroso-desmethyl-azithromycin | Added to Table 1 | 10/11/2023 |
| 1 | N-nitroso-fluoxetine | Added to Table 2 | 10/11/2023 |
| 2 | N-nitroso-ciprofloxacin | Added to Table 1 | 12/1/2023 |
| 2 | N-nitroso-ciprofloxacin | Deleted from Table 2 | 12/1/2023 |
| 2 | N-nitroso-atomoxetine | Deleted from Table 1 | 12/1/2023 |
| 3 | N-nitroso-duloxetine | Added to Table 3 | 2/23/2024 |
| 3 | N-nitroso-bumetanide | Added Testing Method | 2/23/2024 |
| 3 | N-nitroso-propranolol | Added Testing Method | 2/23/2024 |
| 3 | N-nitroso-varenicline | Added Testing Method | 2/23/2024 |
| 4 | N-nitroso-varenicline | Deleted from Table 2 | 3/5/2024 |
| 4 | N-nitroso-varenicline | Added to Table 1 | 3/5/2024 |
| 5 | N-nitroso-ciprofloxacin | Added to Table 3 | 4/18/2024 |
| 6 | N-nitroso-dimethylamine | Added to Table 2 | 9/4/2024 |
| 6 | N-nitroso-diethylamine | Added to Table 2 | 9/4/2024 |
| 6 | N-nitroso-N-methyl-4-aminobutyric acid | Added to Table 1 | 9/4/2024 |
| 6 | N-nitroso-isopropylethylamine | Added to Table 1 | 9/4/2024 |
| 6 | N-nitroso-diisopropylamine | Added to Table 1 | 9/4/2024 |
| 6 | 1-methyl-4-nitrosopiperazine | Added to Table 1 | 9/4/2024 |
| 6 | 1-cyclopentyl-4-nitrosopiperazine (or 1-Nitroso-4-cyclopentylpiperazine) | Added to Table 1 | 9/4/2024 |
| 6 | N-nitroso-methylphenylamine | Added to Table 1 | 9/4/2024 |
| 6 | N-nitroso-methylphenidate | Added to Table 2 | 9/4/2024 |
| 6 | N-nitroso-vonoprazan | Added to Table 2 | 9/4/2024 |
| 6 | Updated Section on Emerging Scientific and Technical Issues | 9/4/2024 | |
| 6 | Updated Recommended Implementation Timelines Section | 9/4/2024 | |
| 6 | N-nitroso-piperazine (NPZ) | Added to Table 2 | 9/4/2024 |
| 7 | N-nitroso-duloxetine | Updated interim limit in Table 3 to 12/31/2024 | 9/27/2024 |
| 8 | Multiple | Added acronyms to Tables 1 and 2 for certain nitrosamines | 10/1/2024 |
| 8 | Multiple | Updated Testing Methods for ARBs and other compounds in Table 5 | 10/1/2024 |
| 8 | Created Table 5 for Recommended Analytical Testing Methods | 10/1/2024 | |
| 9 | 7-nitroso-3-(trifluoromethyl)-5,6,7,8-tetrahydro[1,2,4]triazolo-[4,3-a]pyrazine (NTTP) | Added to Table 1 | 10/7/2024 |
| 9 | 7-nitroso-3-(trifluoromethyl)-5,6,7,8-tetrahydro[1,2,4]triazolo-[4,3-a]pyrazine (NTTP) | Updated Table 2, deleting previous AI limit | 10/7/2024 |
| 10 | N-nitroso-dorzolamide | Added to Table 3 | 10/15/2024 |
| 11 | N-((2-isopropylthiazol-4-yl)methyl)-N-methylnitrous amide (NITMA) aka N-nitroso-2,4-thiazoleamine (NNTA) | Added to Table 1 | 10/28/2024 |
| 11 | N-((2-isopropylthiazol-4-yl)methyl)-N-methylnitrous amide (NITMA) aka N-nitroso-2,4-thiazoleamine (NNTA) | Ritonavir details added to Emerging Issues section | 10/28/2024 |
| 12 | N-nitroso-sertraline | Added to Table 3 | 10/31/2024 |
| 13 | N-nitroso-sertraline | Corrected duration in Table 3 | 11/1/2024 |
| 14 | N-nitroso-ribociclib-1 | Added to Table 1 | 11/20/2024 |
| 14 | N-nitroso-ribociclib-2 | Added to Table 1 | 11/20/2024 |
| 14 | Added (Q)SAR Model Reporting Format (QMRF) for CPCA | 11/20/2024 |
* Changes for the FDA guidelines are immediately actionable as of their posting dates.
** Effective date of the guidance is August 7, 2023, and September 5, 2024 for Control of Nitrosamine Impurities in Human Drugs.