The nitrosamine risks that microcrystalline cellulose may bring to the preparation should not be ignored!

Cause

On a Tuesday at the end of June 2022, Manager Yang of the Technology Department, who was analyzing the test data, received a phone call from a customer in Jiangsu Province. On the phone, the customer repeatedly exclaimed, "Amazing! Microcrystalline cellulose of Topchain Pharmaceutical is amazing!”

Why was this customer so excited? It turned out that the customer had made an application for a product to the CDE earlier, but the approval result came out recently, which was “failed” because the nitrite was out of specification. The customer found in the preparation prescription that the dosage of microcrystalline cellulose was up to 60%, so the customer gave priority to the nitrite content determination (trace analysis).

They respectively compared and tested the microcrystalline cellulose of the same performance commercially available in the United States and Germany, and from Topchain Pharmaceutical, and other several patterns of domestic microcrystalline cellulose, and the results were unexpected, and startled them.

The content of nitrite in microcrystalline cellulose commercially available in the United States was 5 times higher than that in microcrystalline cellulose from Topchain Pharmaceutical, and that in microcrystalline cellulose commercially available in Germany was 15 times higher than that in microcrystalline cellulose from Topchain Pharmaceutical, while that in any other domestic product was far beyond the detection range.

These test results were something that they had never thought of before. Because of the long-standing inertial thinking that imported excipients would be better than domestic excipients in all directions, the test results surprised them and made them see the possibility and hope of the rise of domestic excipient brands. Especially under the influence of such factors as the repeated epidemic, the rising prices of raw materials, the surge of transportation costs, and the international tension, it was too important for them to have an excellent brand of domestic excipients that can achieve import substitution in the real sense.

Therefore, the customer did not hesitate to call Topchain Pharmaceutical to  put forward praise and expectations without sparing and express the willingness to long-term deep cooperation.

Analysis of causes

In the subsequent communication with the customer, both parties made it clear that the functional indexes and characteristics of the microcrystalline cellulose produced by Topchain Pharmaceutical were highly consistent with those of the import brands. On this basis, both parties discussed the possible reasons for the low nitrite content of the microcrystalline cellulose produced by Topchain Pharmaceutical:

Firstly, the microcrystalline cellulose produced by Topchain Pharmaceutical all was produced by the ammonia-free low-temperature hydrolysis and spray drying process. In the whole process, ammonia water would never be used to neutralize the excess acid in the hydrolysis reaction, and ammonium ions would not be introduced in any other link. Therefore, the microcrystalline cellulose produced by Topchain Pharmaceutical did not have the problem of residual ammonium ions, while other products on the market had residual ammonium ions to varying degrees, as shown in Figure 1.

Figure 1. Comparison of ammonium content of different brands on the market

Secondly, in terms of raw materials, the imported wood pulp used by Topchain Pharmaceutical was specially used for the production of 

pharmaceutical grade cellulose acetate and microcrystalline cellulose, which had quite strict restrictions on nitrite, genetic impurities, pesticide 

residues, etc. If viscose wood pulp (mainly used for clothing) and paper pulp were used as raw materials for the production of some 

microcrystalline cellulose, it would be difficult to guarantee the content of each of such impurities as sulfonating agent, nitrate, nitrite, 

whitening agent, and fluorescent powder, let alone the content of each of these impurities in finished products of microcrystalline cellulose.

Finally, the acid used in the hydrolysis step of Topchain Pharmaceutical was food grade, and purified water and drinking water used for 

production were both in accordance with the requirements for the pharmaceutical production grade, with nitrite content strictly limited. For 

example, according to the requirements of Chinese Pharmacopoeia (2020), the content of nitrite in purified water shall be less than 0.02 ppm.

Conjecture on the Mechanism of Ammonia Conversion into Nitrite

Since the performance indexes and applications of the microcrystalline cellulose produced by Topchain Pharmaceutical were highly consistent with those of import brands and the only difference found at present was that the content of residual ammonium ions in the products was different, we speculated that ammonium ions were likely to be converted into nitrite under certain conditions.

For these reasons, Topchain Pharmaceutical inquired about relevant literature and consulted some university experts, and they proposed a direction for in-depth research: Nitrification involving ammonia-oxidizing bacteria.

What are ammonia-oxidizing bacteria?

Ammonia-oxidizing bacteria (AOB), namely nitrosobacteria, belong to Gram-negative bacteria, and prefer slightly alkaline environment. The optimum pH for the growth is 7.0-8.5, and the optimum temperature is 24-28 °C. They are widely distributed in soil, ocean and fresh water in nature, are a kind of inorganic autotrophic bacteria that can convert ammonia into nitrite, and play an important role in nitrification.

What is the mechanism of action of ammonia-oxidizing bacteria?

The nitrification of ammonia-oxidizing bacteria can be divided into two stages: the first stage is nitrification, in which NH4+ - N is oxidized to NO2- - N by ammonia-oxidizing bacteria; in the second stage, nitrobacteria oxidize NO2- - N to NO3- - N[2-4].

What is possible nitration during the manufacture of microcrystalline cellulose?

Ammonia-oxidizing bacteria are widely distributed in soil and water, and the raw material sources of microcrystalline cellulose and the production processes of finished products are inseparable from water, so it is difficult to guarantee that there are no ammonia-oxidizing bacteria in them. Once ammonia-oxidizing bacteria and NH4+ are present, nitration takes place under appropriate conditions, and the nitrite finally generated always exists in the whole production process and remains in the finished product, thus affecting the nitrite content of the preparation.

Conclusion

The "Huahai Valsartan Event" in 2018 was triggered by the detection of a carcinogenic impurity, N-nitrosomethylamine, in valsartan APIs, which promptly caused the close attention from the FDA and the EMA. Later, the event continued to ferment, expanding the variety to all sartan drugs to be put under review. The places of origin also involved India, etc., resulting in the recall of sartan drugs by Pfizer, Novartis and other enterprises.

Figure 2. ACCURETIC from Pfizer

How much damage did the Valsartan Event cause to Huahai? As could be seen from the 2018 financial report, Huahai reckoned a loss of about 

CNY 413 million due to the Valsartan Event, the company's share price and market value suffered a severe blow, and Pu Lin Johnson, its 

grandson company, abandoned its plan to list in the United States. What a heavy price!

This event also accelerated the National Medical Products Administration to issue the “Technical Guidelines for the Study of Nitrosamine 

Impurities in Chemical Drugs (Interim)” in 2020, which provided guidance for the registration application for marketing authorization and the 

study and control of nitrosamine impurities in marketed chemical drugs, and indicated that marketing authorization holders/drug 

manufacturers should earnestly fulfill the subject responsibilities of drug quality management, carry out life-cycle management on drug safety 

and quality, and evaluate and control the introduction and residue of nitrosamine impurities.

Figure 3. Microcrystalline Cellulose of Topchain Pharmaceutical

Excipients are indispensable components in drugs and even account for a relatively large proportion. For example, microcrystalline cellulose, as a

 diluent, can account for up to 90% in the prescription. Therefore, the introduction and residue of nitrosamine impurities should be strictly 

evaluated and controlled.

Moreover, as a responsible and conscientious excipient enterprise, we should take the initiative to undertake this work and its responsibilities to 

reduce the burden and risk for the preparation customers, and provide safe and reliable, quality guaranteed excipient products.

As excipient users, customers should pay enough attention to this issue and improve risk awareness. When selecting excipients, they should pay 

attention to the huge risks that various impurities may bring in addition to the indexes, performance and price, choose the brand that can

make them feel assured and at ease, undertake their own responsibilities for the development of enterprises and national health and make due 

contributions.