When DMSO is used as a processing solvent in pharmaceutical manufacturing, some may remain after isolation and drying. A common question is whether that residue must stay below 5,000 ppm.
In this article
The short answer: concentration and dose belong together
ICH Q3C(R9), section 4.3 and Table 3, places DMSO in Class 3. Its general Class 3 reference is 50 mg/day or less without further justification. The corresponding 5,000 ppm, or 0.5%, uses the Option 1 assumption of a 10 g daily product intake. It is not a universal release specification or a separately derived DMSO-specific PDE.
Read the concentration together with the maximum daily mass of the relevant drug product. The same ppm result can represent different daily exposures.
Understand the units first
For a residual result expressed on a mass basis, 5,000 ppm equals 5,000 mg/kg, 5 mg/g or 0.5% by weight. Confirm the reporting basis before using a result in a calculation.
These figures describe DMSO remaining in the tested pharmaceutical material. They are not the water-content limit or purity requirement for purchased DMSO. A solvent supply COA and a residual-solvent report therefore answer different questions.
For incoming material, establish the relevant water and impurity limits separately; the DMSO quality guide explains why a purity label alone is insufficient.
Calculate daily DMSO exposure
For a concentration measured in the drug product on a mass basis:
Daily DMSO exposure (mg/day) = residual DMSO (ppm) × daily product dose (g/day) ÷ 1,000.
| Maximum daily product dose | Residual DMSO | Calculated DMSO exposure |
|---|---|---|
| 2 g/day | 5,000 ppm | 10 mg/day |
| 10 g/day | 5,000 ppm | 50 mg/day |
| 20 g/day | 5,000 ppm | 100 mg/day |
These are calculation examples, not approved release limits. At 20 g/day, 5,000 ppm corresponds to twice the 50 mg/day reference amount. A concentration of 2,500 ppm would correspond to 50 mg/day in that example. Conversely, a lower daily dose does not automatically authorize a higher concentration specification.
If the result comes from an API or another ingredient rather than the finished drug product, use the mass of that ingredient administered per day to calculate its contribution. Add contributions from other ingredients where relevant. Do not multiply an ingredient concentration by the total product mass unless that concentration represents the finished product.
Establish what the analytical result covers
The laboratory needs the material identity, the target limit and the reporting basis. The method must be appropriate for the matrix and capable of supporting the intended acceptance decision. A general solvent-purity chromatogram does not establish residual DMSO in an API or formulation.
Q3C(R9), section 3.4, permits a properly validated non-specific method such as loss on drying when only Class 3 solvents are present, and calls for considering solvent volatility during validation. This does not mean that an unvalidated loss-on-drying result specifically measures DMSO; water and other volatile components may contribute.
Connect the analytical endpoint to the actual isolation and drying process. The DMSO removal guide discusses screening of washing, precipitation and solvent-removal options without assigning one drying condition to every product.
Set the release limit for the product
Class 3 does not mean unrestricted use. The guideline allows higher amounts in relation to manufacturing capability and good manufacturing practice, but this is not blanket permission to increase a specification. Product-specific requirements, daily exposure and the applicable quality assessment still govern the decision.
DMSO deliberately used as an excipient needs a separate assessment; a process-residue reference does not approve its intended formulation level. A defined DMSO solvate also requires evaluation against the product’s solid-form and drug-substance requirements. For that distinction, see the trametinib DMSO-solvate article.
Questions to resolve before accepting a result
Confirm which material was tested, whether ppm is on the intended mass basis, what daily administered mass applies, whether other ingredients contribute DMSO, and whether the method and release limit are appropriate for that product. Keep the incoming solvent specification separate from this downstream residual assessment.
For incoming DMSO sourcing, share your solvent specification and process requirements with YUJI. The pharmaceutical-grade product page provides the listed supply parameters; downstream residual limits remain part of the pharmaceutical manufacturer’s quality assessment.