What Are Residual Solvents?

Helen Akers

Residual solvents are chemicals that pharmaceutical companies use to manufacture different prescription drugs. They have various degrees of toxicity that are classified according to three levels. Sometimes, residual solvents are by-product of the manufacturing process. They are considered to be organic volatile chemicals that most drug manufacturers are required to remove as much as possible from their finished products.

Residual solvents are sometimes by-products of the drug manufacturing process.
Residual solvents are sometimes by-products of the drug manufacturing process.

The pharmaceutical industry uses residual solvents in a variety of manufacturing methods. Sometimes the chemicals are used to combine a drug's ingredients. Solvents may also be used to transform drug ingredients into a different form, such as crystals. They might be used to prepare the ingredients prior to the manufacturing process. At other times, residual solvents are produced as a result of combining the drug's ingredients.

Residual solvents may be products or byproducts of chemical manufacturing.
Residual solvents may be products or byproducts of chemical manufacturing.

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Since drugs are essentially a combination of isolated chemical compounds, mixing them together can sometimes result in by-products that the manufacturing process is unable to remove completely. If manufacturers are aware that the production process of certain drugs is likely to result in residual solvents, they are usually required to test for them. Toxicity levels and types of solvents are measured. In order to adhere to national safety guidelines and ethics regarding human exposure to chemicals, manufacturers can only allow certain levels of solvents to remain in their finished products.

Residual solvents are sometimes used to combine a drug's ingredients.
Residual solvents are sometimes used to combine a drug's ingredients.

According to product specifications, drug manufacturers must remove certain amounts of residual solvents from their final products. There are a set of solvents that should not be used during the drug manufacturing process due to high levels of toxicity and safety concerns. Some of those organic chemicals include benzene and carbon tetrachloride. Other solvents that most manufacturers attempt to avoid include dichlorethene and trichlorethene.

Low toxicity solvents are permitted to be used to manufacture drugs, but must not be used excessively.
Low toxicity solvents are permitted to be used to manufacture drugs, but must not be used excessively.

A second group of residual solvents that might be used in the drug manufacturing process is considered to be somewhat lower in toxicity. Manufacturers are still required to limit the use of these chemicals, but are permitted to include them in the process under certain circumstances. Some of those chemicals include sulfolane, tetralin and chloroform. The level of these chemicals permitted to remain in finished drug products must not exceed national safety levels.

Low toxicity solvents are permitted to be used to manufacture drugs, but must not be used excessively. Similar to their somewhat more toxic counterparts in group two, only the maximum amounts per national safety levels are permitted. The risk that these solvents pose to humans is usually considered to be insignificant enough that their formal identification is not required by national governments and manufacturers.

Residual solvents are used by pharmaceutical companies to manufacture various prescription drugs.
Residual solvents are used by pharmaceutical companies to manufacture various prescription drugs.

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