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Bisoprolol technical analysis: from evidence-based evidence to impurities and nitrosamine risk control

2026-09-29 · CATO · CATO Standards

Clinical location and molecular basis

bisoprololIt is a highly selective β1-adrenergic receptor blocker. There are noteworthy regulatory differences between China, the United States and Europe in its indications: the US FDA label (Zebeta) is only approved for hypertension [1]; the EU SmPC approves it for stable chronic heart failure (with reduced left ventricular systolic function), in combination with ACE inhibitors and diuretics [2]. The evidence base for heart failure indications comes from the CIBIS-II study—among 2647 patients with NYHA class III–IV and LVEF ≤35%, the all-cause mortality was 11.8% in the bisoprolol group and 17.3% in the placebo group (HR 0.66, 95% CI 0.54–0.81, P<0.0001). [3].

Bisoprolol Bisoprolol

molecular level,Bisoprolol free base CAS 66722-44-9, molecular formula C₁₈H₃₁NO₄, molecular weight 325.44[4]; The clinically used salt form is fumarate, CAS 104344-23-2. Its aryloxypropanolamine skeleton and isopropylamine side chain determine not only the drug efficacy, but also the structural characteristics of the impurity spectrum - including the secondary amine group that has been focused on by global regulatory agencies after 2018.

Impurity spectrum: structural types and control difficulties

The synthesis of bisoprolol is based on the aryloxypropanolamine skeleton and isopropylamine side chain chemistry. This skeleton is highly homologous to similar β-blockers such as metoprolol., so there are shared impurities - the most typical one is EP impurity L (CAS 29122-74-5), which is also impurity C of metoprolol (tartrate/succinate). When companies conduct impurity grading and collinear production risk assessment, such cross-variety common impurities are easily missed.

In terms of structural type, the main impurities can be classified into three categories:

① Aldehyde impurities——EP impurity S is 4-hydroxybenzaldehyde (CAS 123-08-0, C₇H₆O₂), which is the starting material residue before the side chain is connected; EP impurity L (C₁₃H₁₉NO₃) is the corresponding aldehyde after the side chain is connected. The two form a complete chain of aldehyde impurities, which are dual signals of oxidative degradation and starting material residues.


② Dimer/bridge type——EP impurity C (CAS 1225195-70-9, C₂₅H₃₈N₂O₄) is a methylene-bridged bisaryloxypropanolamine; EP impurity D (CAS 1225195-71-0, C₂₆H₄₀N₂O₅) is an ether-bridged analog. The molecular weight is nearly twice that of the parent, indicating coupling side reactions in the process. Peaks often appear late on HPLC and the response factors vary greatly.


③ Side chain acetal/ether variants——For example, EP impurity G (CAS 1215342-36-1, C₁₉H₃₃NO₅) has one more CH₂O unit than the parent substance and is a side chain acetal type impurity.

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It is worth noting that the EDQM official does not sell impurity reference standards for each letter separately, but provides a mixed system in the form of Bisoprolol for peak identification CRS (Y0000877) and Bisoprolol for system suitability CRS (Y0000813) [5]. This means that companies must still purchase a single high-purity impurity reference substance when conducting impurity grading, standard recovery, methodology verification and stability studies.

Special Topic: Reevaluation of Limits for N-Nitrosobisoprolol

After the nitrosamine incident in sartan APIs in 2018, global regulatory agencies required nitrosamine risk assessments for APIs containing secondary amine structures.The isopropylamino group in the bisoprolol molecule is a secondary amine that meets the conditions for nitrosation reaction. The corresponding impurity is N-nitrosobisoprolol (CAS 2820170-76-9), for which USP has established an official solution reference substance [6].


The process of setting limits for this impurity is a noteworthy case in the evolution of regulatory science:

  • Initial limit:The FDA gives an acceptable intake AI = 1500 ng/day based on structural analogy (potency category 4) [7];


  • Reassessment in 2025:The Merck Group team published a study in Archives of Toxicology, using error-corrected NGS (ecNGS) combined with Benchmark Dose analysis, supplemented by quantum chemical modeling and CYP docking prediction. The results showed that the mutagenic potential of the impurity was weak - the standard Ames test was negative, and it was only positive under the most stringent enhanced Ames conditions.Based on this, PDE = 400 μg/day and AI = 64 μg/day were re-derived, which are approximately 40 times wider than the original limits [8].


The author clearly points out that the limit based solely on structural warning presumptions "may be overly conservative and should not be uniformly capped at the TTC." The practical significance for enterprises is that nitrosamine limits are not static, and control strategies should track the latest toxicological evidence rather than sticking to early conservative values, which directly affects the process release standards and sensitivity requirements of detection methods.

CATO provides bisoprolol reference substance

Whether it is HPLC quantification of EP letter impurities or LC-MS/MS trace detection of nitrosamines (limit in ng/day), the premise is to obtain a reference substance with confirmed structure and controllable purity. Among them, isotope internal standards (such as bisoprolol-d5, N-nitrosobisoprolol-d5) can effectively compensate for matrix effects and recovery rate fluctuations, and are the key to the verification of nitrosamine quantitative methods. This kind of demand for small batches, multiple varieties, and high purity is the main bottleneck for CRO and API companies to build their own standard product systems.


CATO (Guangzhou Jiatu Technology Co., Ltd.) is a reference material manufacturer that has passed both CNAS (RM0030) and ANAB (AR-2832) ISO 17034 certification.A product matrix covering the full impurity spectrum of bisoprolol has been established. Some representative products are as follows:

  • Covers the full range of EP letter impurities and numbered impurities

  • Provides a variety of salt types (fumarate, hemifumarate, hydrochloride, oxalate, maleate, trifluoroacetate, formate) to meet different solubility and stability requirements

  • Supporting deuterated internal standards (bisoprolol-d5, N-nitrosobisoprolol-d5)

  • Specifications from 1mg to 5g, cold chain storage at 2-8℃

  • Supports custom synthesis and structure confirmation data packages (COA, NMR, MS, HPLC)

It can meet the needs of the whole process of reference standards from method development, impurity grading, stability research to CEP/ANDA registration application.


Advantage supply, welcome to inquire

References

  1. FDA. ZEBETA (Bisoprolol Fumarate) Tablets Prescribing Information. accessdata.fda.gov

  2. Cardicor 2.5mg Film Coated Tablets, Summary of Product Characteristics, Section 4.1. medicines.org.uk/emc/product/7768/smpc

  3. CIBIS-II Investigators and Committees. The Cardiac Insufficiency Bisoprolol Study II (CIBIS-II): a randomized trial. Lancet. 1999;353(9146):9-13.

  4. NIST Chemistry WebBook, Bisoprolol (CAS 66722-44-9).

  5. EDQM CRS Catalog: Y0000877 Bisoprolol for peak identification CRS; Y0000813 Bisoprolol for system suitability CRS.

  6. USP. N-Nitroso Bisoprolol Solution, CAS 2820170-76-9 (Cat. No. 1A04250).

  7. FDA. Recommended Acceptable Intake Limits for Nitrosamine Drug Substance-Related Impurities (NDSRIs).

  8. Simon S, Schlingemann J, et al. Deriving safe limits for N-nitroso-bisoprolol by error-corrected next-generation sequencing (ecNGS) and benchmark dose (BMD) analysis. Arch Toxicol. 2025;99(10):3935-3962.

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