Usage Examples
- Mixing time and impeller speed were designated CPPs after the DoE showed both moved blend uniformity.
- The granulation design space covers three interacting CPPs: water amount, spray rate, and inlet air temperature.
- The batch ran outside the CPP range for two minutes, so it is quarantined pending the deviation investigation.
What is Critical Process Parameter (CPP)?
Critical Process Parameter is a manufacturing process input whose variability measurably impacts a critical quality attribute, and which therefore must be monitored or controlled within a justified range so the process delivers the intended quality.
Critical Process Parameter designations exist because quality cannot be tested into a batch. A release assay samples a fraction of the material and cannot see the mixing step that drifted three hours earlier. ICH Q8(R2) pushes control upstream instead: find the process inputs whose variation actually moves a quality attribute, then hold them there.
A Critical Process Parameter covers inputs you set and can hold: granulation water amount, spray rate, drying temperature, compression force, bioreactor pH, hold time. It does not cover outputs. Dissolution, content uniformity and impurity level are critical quality attributes, the things CPPs are chosen to protect. A parameter with no demonstrated CQA impact is not critical, however carefully it is logged.
In practice, each Critical Process Parameter carries a justified range in the batch record and a control in the control strategy, which ICH Q8(R2) says must include, at a minimum, control of the critical process parameters and material attributes. The same parameters and their in-process controls are described in CTD sections P.3.3 and P.3.4, and every excursion becomes a deviation to investigate.
Not to be confused with
- Critical Quality Attribute (CQA)
- a CQA is a property of the material (dissolution, assay, sterility); a CPP is an input you set on the equipment. Criticality of a parameter is derived from its effect on a CQA, never the reverse.
- Key Process Parameter (KPP)
- a common industry tier for parameters that affect yield or process consistency without moving a CQA. ICH Q8(R2) defines no such category, so a KPP label carries whatever meaning your own quality system gives it, and reviewers will ask.
- Proven Acceptable Range (PAR)
- a PAR is a characterised range for one process parameter with the others held constant. ICH Q8(R2) states that a combination of proven acceptable ranges does not constitute a design space, because univariate ranges miss interactions.
- Design space
- the multidimensional combination and interaction of input variables and process parameters demonstrated to provide assurance of quality. A CPP is one axis of it. The design space is proposed by the applicant, subject to regulatory assessment and approval, and moving outside it is a change.
The obligations sit across ICH Q8(R2) for identification and the CGMP regulations for execution.
What you must do
- 1Identify, in the manufacturing process development or process improvement programme, the process parameters that should be monitored or controlled to ensure the product is of the desired qualityICH Q8(R2) Part I, Section 2.3
- 2Justify each CPP designation by demonstrating that the parameter's variability has an impact on a named critical quality attributeICH Q8(R2) Part II, Section 4
- 3Build control of the critical process parameters and material attributes into the control strategy as a minimum, based on product, formulation and process understandingICH Q8(R2) Part II, Section 2.5
- 4Establish and follow written production and process control procedures covering each CPP, designed to assure the drug product has the identity, strength, quality and purity it purports to possess21 CFR 211.100
- 5Set valid in-process specifications for the characteristics those parameters control, consistent with final product specifications and derived from process average and variability estimates using suitable statistical procedures21 CFR 211.110
Common mistakes
Calling every logged parameter critical
Criticality follows demonstrated CQA impact, not caution. When everything is a CPP, every minor excursion becomes a recorded deviation that must be justified under 21 CFR 211.100, which buries the quality unit and dilutes attention from the parameters that actually break the product.
Filing a stack of PARs as a design space
ICH Q8(R2) is explicit that a combination of proven acceptable ranges does not constitute a design space. Univariate ranges cannot show interactions, so the flexibility you thought you registered is not there, and each range change is handled as an ordinary post-approval change.
Freezing the CPP list at filing
Process knowledge keeps arriving through scale-up, deviation investigations and trending. ICH Q8(R2) treats expansion, reduction or redefinition of the design space as a lifecycle activity subject to regional requirements, so a parameter reclassified as critical needs change control and a CMC action proportional to the impact.
When This Matters
- Mixing time and impeller speed were designated CPPs after the DoE showed both moved blend uniformity.
- The granulation design space covers three interacting CPPs: water amount, spray rate, and inlet air temperature.
- The batch ran outside the CPP range for two minutes, so it is quarantined pending the deviation investigation.
Frequently Asked Questions
A CQA is a property of the material; a CPP is an input you set on the process. ICH Q8(R2) defines a critical quality attribute as a physical, chemical, biological or microbiological property that must stay within an appropriate limit, and a critical process parameter as a parameter whose variability impacts that attribute.
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