Impurity Profile of Active Pharmaceutical Ingredient : A Review

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Mr.Anand M. Kudal

Mr.Anand M. Kudal

Impurity profile is a description of the identified and unidentified impurities
present in a typical batch of API (Active Pharmaceutical Ingredient) produced
by a specific controlled production process. It includes the identity or some
qualitative analytical designation (e.g. retention time), the range of each
impurity observed, and type of each identified impurity.

For each API there should be an impurity profile describing the identified
and unidentified impurities present in a typical batch. The impurity profile
is normally dependent upon the process or origin of the API­1

A number of recent articles have described a designed approach and guidance
for isolating and identifying process-related impurities and degradation products
using mass spectrometry, Nuclear Magnetic Resonance (NMR), high-performance
liquid chromatography (HPLC), Fourier transform ion cyclotron resonance mass
spectrometry (FTICR-MS), and tandem mass spectrometry for pharmaceutical substances.2,3,4.

In general, according to ICH guidelines on
impurities in new drug products,5identification
of impurities below the 0.1% level is not considered to be necessary unless the
potential impurities are expected to be unusually potent or toxic. In all
cases, impurities should be qualified. If data are not available to qualify the
proposed specification level of an impurity, studies to obtain such data may be
needed (when the usual qualification threshold limits given below are
exceeded). According to ICH, the maximum daily dose qualification threshold is
considered as follows:

≤ 2g/day 0. 1 % or
1 mg per day intake (whichever is lower) ≥ 2g/day 0.05%

of Impurities in Medicines

Medicines are the formulated forms of active
pharmaceutical ingredients. There are 2 types of impurities in medicines:(1) Impurities associated in with active
pharmaceutical ingredients and (2) Impurities that form are created during
formulation and or with aging or that are related to the formulated forms.

According to ICH guidelines,6 impurities associated with APIs are
classified into the following categories:

  • Organic impurities (Process and Drug-related)
  • Inorganic impurities
  • Residual solvents

Organic impurities may arise
during the manufacturing process and/or storage of the drug substance. They may
be identified or unidentified, volatile or non-volatile, and include the

Starting materials or intermediates-

These are the most common impurities found in every API unless a proper
care is taken in every step involved in throughout the multi-step synthesis.
Although the end products are always washed with solvents, there are always
chances of having the residual unreacted starting materials may remain unless
the manufacturers are very careful about the impurities. In paracetamol bulk,
there is a limit test for p-aminophenol, which could be a starting material
for some one manufacturer or be an intermediate for the another.


In synthetic organic chemistry, getting a single end product with 100% yield
is very rare; there is always a chance of having by-products. In the case
of paracetamol bulk, diacetylated paracetamol (Figure
may form as a by-product.

Figure 1. Production of Paracetamol from intermediate, p-Aminophenol



Impurities can also be formed by degradation of the end product during manufacturing
of bulk drugs. However, degradation products resulting from storage or formulation
to different dosage forms or aging are common impurities in the medicines.
The degradation of penicillins and cephalosporins is a well-known example
of degradation products. The presence of a ß-lactam ring as well as that of
an a-amino group in the C6/C7 side chain plays a critical role in their degradation.7

ligands, and catalysts

These chemicals are less commonly found in APIs; however, in some cases
they may pose a problem as impurities.

It has also been found that the
presence of certain chemicals such as triethylamine has a degradative effect on
the product. Ampicillin trihydrate samples having triethylamine content of 2000
ppm to 4000 ppm (determined by visual color method developed by Gist- Brocades,
Delft, Holland)8 were found to be stable under accelerated
stability testing. However, the product showed appreciable degradation when triethylamine
content became 7000 ppm.

Solvents such as benzene (Class
I, 2 ppm limit) and carbon tetrachloride (Class I, 4 ppm limit) are to be
avoided. On the other hand, the most commonly used solvents such as methylene
chloride (600 ppm), methanol (3000 ppm), pyridine (200 ppm), toluene (890 ppm),
N,N-dimethylformamide (880 ppm), and acetonitrile (410
ppm) are of Class II. Class III solvents (acetic acid, acetone, isopropyl
alcohol, butanol, ethanol, and ethyl acetate) have permitted daily exposures of
50 mg or less per day. In this regard, ICH guidelines9 for limits should be strictly followed

Most vitamins are very labile and on aging they pose a problem of instability
in different dosage forms,10
especially in liquid dosage forms. Degradation of vitamins such as folic acid,
pantothenic acid, cyanocobalamin, and thiamine do not give toxic impurities;
however, potency of active ingredients drops below pharmacopoeial specifications.

Quality Control 11

pharmaceutical tablet production, one of the key measurements of product
quality is the standard active content uniformity test. This provides a measure
of uniformity of the blend from the assay of a number of tablets (typically 10)
taken from the tablet press. The test usually involves dissolving the tablet
for HPLC and only the active content is measured.

However, the tablet comprises a number of other ingredients and it is known
that these ingredients can impact important product properties such as
dissolution — a major regulatory concern at the moment — stability,
bio-availability and various process-quality parameters such as hardness. It is
also known that some properties can depend on microscopic size and distribution
of the ingredients, both actives and excipients.

Modern tablet presses are capable of producing up to 10,000 tablets per minute,
yet the uniformity of content measurement described above is the common
technique used to provide information on the quality of the blend. Often very
little is known about the distribution of ingredients within tablets, which can
have quite an influence on quality.

 The imaging measurement involves
collecting NIR diffuse reflectance spectra over a predefined sample area where
the area is divided into a number of square pixels of either 6.25 x 6.25 or 25
x 25 µm. The sample moves below a linear detector array, generating images of
up to 80 pixels per second. At each pixel, a spectrum in the range 7800-3600
cm-1 is generated. By examining the spectral variation between pixels, one
obtains information on the spatial distribution of ingredients. Due to the
highly scattering nature of the samples, the spatial resolution of the
technique is not  order
to improve the image´s contrast, some spectral pre-processing of the image may
be performed, for example, by converting the spectra to the second derivative
prior to plotting the peak heights. A number of image enhancement methods are
possible, including principal components-based and supervised learning approaches .

Regulatory Compliance 13

Under 21 CFR Part 11, FDA-regulated companies that choose to maintain electronic
records to meet predicate rules are required to validate their electronic
record-keeping systems. This is to ensure accuracy, reliability, and consistent
intended performance of the system and to determine invalid or altered records.
Part 11 works in tandem with a predicate rule, which refers to any FDA regulation
that requires organizations to maintain records.
An example would be 21 CFR Part 820, which requires medical device manufacturers
to maintain records pertaining to design history, quality system, complaint
and complaint investigation, training, etc.

System SOPs

To provide the FDA with documented evidence that your system is Part 11-compliant,
follow a set of system-specific standard operating procedures (SOPs) to support
your validation documents. The three key system SOPs you need are:

System Administration and Configuration SOP

•  Define system configuration, such as settings and security administration

• Include procedures for system functionality, such as creation and administration

•  Define audit trail functionality

•  Define change control to design configuration of system (changes to
configuration upgrade, validation and revalidation of system)

•  Define ownership of system and system issues resolution (system maintenance,
upgrades, backups, disaster recovery)

User Administration and Management SOP

•  Describe creation of new user account and user account types

•  Assign and approve user/workgroup security rights

•  Include old/inactive accounts, password changing

•  Define procedure for electronic signature manifestation

Document Control SOP

•  Include revision numbering, approvals, document numbering

•  Define controlled document distribution

•  Describe records retention

•  Define document lifecycle

Record Retention

The FDA´s requirement for record retention depends on a predicate rule. The
agency encourages companies to base any decision to maintain records on a
justified and documented risk assessment and a determination of the value
of the records over time. Records are retained according to company policy.
Organizations may set up their systems to keep records indefinitely or only
for a specific period. They can make the choice by document type, keeping
some indefinitely and others not, depending on their needs. If necessary,
any deleted InfoCard can be restored. All actions made with any document are
captured in the audit trail.

Current Good Manufacturing Practices

Current Good Manufacturing Practices (cGMPs) have become a
way of life for those of us in the healthcare industry. With cGMPs, we´ve
learned how to manufacture in a state of control to make products fit for their
intended use that are both safe and efficacious; however, don´t be complacent
with current practices, because nothing is as sure as change.
The trend toward paperless will continue. New product FDA submissions will
routinely be electronic. Paperless production batch records will be the norm.
Instead of a paper batch record, a PC will be at each workstation for data
entry. QC laboratory management systems (LMS) will be routine with a dramatic
reduction in manual transcriptions (and the resultant huma The
industry has not yet grasped the significance of the FDA´s Process Analytical
Technology (PAT) initiative (1). PAT is the clearest view of the future among
published FDA guidelines. What future manufacturing and QC testing will look
like is written on (and between) the lines of that guideline. The vision of a
monitored and controlled manufacturing process that moves significantly away
from a batch production system is at the center of PAT. Based on the results of
in/on/at line testing, processing decisions will be made without subjective
human intervention (i.e. art gives way to science).
With the ever shrinking world in this global economy, the quest to harmonize
rules, regulations, guidance documents, and pharmacopeias will continue along
with the frustration of getting so many different world organizations and
national bureaucracies to agree.14

Continual Improvement

Moving beyond corrective action (reacting to a defect after it occurs) and
preventive action (taking action when negative trends are detected), firms
will recognize the benefit of continual improvement. Currently continual improvement
is a requirement of the international quality management systems standa Process
validation will continue for many more years as an important component of
quality and good manufacturing practices. In the eighteen years since the
FDA´s "Guideline of General Principles of Process Validation" was
issued in May 1987, there has been a quantum leap in technological breakthroughs
and lots of practical experience with process validation.rd ISO 9001:2000.15

Bar coding is becoming obsolete.
By 2007, the FDA is recommending the use of radio frequency identification
(RFID) tagging as the standard "track and trace" technology. 2 Mass serializations,
which is the ability to store a unique serial number for each pharmaceutical
item, will be achieved with RFID.

Water Activity

Water is critical to the chemical, physical, and
microbiological stability of most pharmaceuticals. They are formulated,
manufactured, and packaged carefully to avoid spoilage and preserve correct
dosage, both chemically and physically. Traditionally, this led formulators and
manufacturers into monitoring water content. Water activity measurements are a
powerful tool in formulating, manufacturing, packaging, and storing
non-sterile, over-the-counter drugs and cosmetics.
The measurement of " water activity "determines
how much water is free from physical and chemical bonds and thus available for
migration, chemical reaction, use by microorganisms, or other activity.

Water activity is measured by placing a sample in a closed chamber and allowing
it to come to equilibrium. The water vapor pressure of the air over the sample
is then measured, and water activity is expressed as the ratio of this sample
vapor pressure to the vapor pressure of pure water at the same temperature.
A sample with water activity of 0 is completely dry, while 1.0 is the water
activity of pure water. By measuring and controlling the water activity of
a formulation, scientists can increase its stability and reduce or eliminate
the risk of microbial growth.

Knowing water activity values can
also help predict moisture migration and shelf stability, especially of
moisture-sensitive substances.

A nutraceutical manufacturer
similarly uses creative packaging to keep a dried acidophilus formulation
stable at a low water activity while the product is on the shelf.16


starch  is one of the most commonly used excipients in a variety of
pharmaceutical formulations. A natural polymer composed of amylose and amylopectin
homopolymers of glucose, native starch is routinely used as filler, binder
and disintegrant in various solid dosage forms.

Pregelatinized Starch

Native starch can be chemically and/or mechanically processed to rupture (gelatinize)
all or part of the starch granules. These pregelatinzed starches (PGS) exhibit
good flow, binding, and compressibility. The degree of starch gelatinization
can be varied to obtain fully pregelatinized or partially pregelatinized starches
(PPS). PPS are used as fillers in hard gelatin capsules (5 to 75 percent),
binders in wet granulation (5 to 20 percent), tablet disintegrants (5 to 10
percent), and direct compression. When used in filling hard capsules, some
of the disadvantages of existing PPS include increased dust generation during
processing and slow dissolution of actives from formulations.17

Added functionality excipients

A single AFE provides multiple functionalities such as direct compressibility,
fast disintegration, excellent flowability, reduced lubricant requirements
or advantages in roller compaction and dry granulation.

Quality Assurance

The quality control unit, particularly in the pharmaceutical
industry, has the authority to release or reject raw materials, intermediates
and finished products; decisions that are in most part based upon the outcome
of laboratory analysis.
A laboratory quality assurance program should consist of a number of components
such as: 18

•  Equipment calibration & maintenance - make sure that all equipment
and instrumentation are in calibration, regularly qualified and documented as
such, including stickers affixed to each piece of equipment that indicates its
calibration status. In the case of instruments consisting of multiple
components such as HPLC systems, execution of installation and operating
qualifications is also recommended.

•  All analytical standards, buffers and reagents
are within their stated expiration dates and are properly stored. Each
standard, buffer and reagent should be labeled with its expiration date and
recommended storage conditions.

•  Current revisions of written analytical methods
for each and every test procedure should be available. Methods should be

•  Documentation - Ensures proper use of
notebooks and traceability of data from the final result back to the receipt of

•  Specifications - Have current specifications
on hand so that there is no misunderstanding as to interpretation of whether or
not something meets or does not meet its predetermined quality attributes.

•  Retention samples (reserve sample) - Retain
reserve portions of all sample submitted to the laboratory for a suitable
length of time, thus allowing for reexamination of samples should a question
arise later about analytical results

•  Retention of glassware - If possible, do not discard any solutions
or clean any glassware used in an analysis until the final results have been

Reporting Impurity Content of Batches

The following information should be provided while reporting Impurity Content
of batches

    • Batch
      identity, strength, and size
    • Date
      of manufacture
    • Site
      of manufacture
    • Manufacturing
      process, where applicable
    • Immediate
    • Degradation
      product content, individual and total
    • Use
      of batch
    • Reference
      to analytical procedure(s) used
    • Batch
      number of the drug substance used in the drug product
    • Storage

Qualification of Impurities

Qualification is the
process of acquiring and evaluating data that establishes the biological safety
of an individual degradation product or a given degradation profile at the
levels specified. .

New Impurities

During the course of
drug development studies, the qualitative degradation profile of a new drug
product may change, resulting in new degradation products that exceed the
identification and/or qualification threshold. In this event, these new
degradation products should be identified and/or qualified. Such changes call
for consideration of the need for qualification of the level of the impurity
unless it is below the threshold values as noted 19

Thresholds for Reporting of Degradation Products in New Drug Products

Maximum Daily Dose1
(less than or equal) 1 g
> 1 g

Thresholds for Identification of Degradation Products in New Drug Products

Maximum Daily Dose1
1mg - 10 mg
> 10 mg - 2 g
> 2 g
1.0% or 5 mcg TDI2 whichever is lower
0.5% or 20 mcg TDI whichever is lower
0.2% or 2 mg TDI whichever is lower

Thresholds for Qualification of Degradation Products in New Drug Products

Maximum Daily Dose1
< 10 mg
10 mg - 100 mg
>100 mg - 2 g
> 2 g
1.0% or 50 mcg TDI whichever is lower
0.5% or 200 mcg TDI whichever is lower
0.2% or 2 mg TDI whichever is lower

1The amount of drug substance
administered per day
2 Total Daily Intake
3Threshold is based on percent of the drug substance


A pharmaceutical ingredient should  pass not only the test such as  CGMP,
, QA tests, water activity but also should
qualify for the specified threshold of a new impurity. Considering all these
factors  the field is further open for isolating and identifying process-related
impurities and degradation products using mass spectrometry, Nuclear Magnetic
Resonance (NMR), high-performance liquid chromatography (HPLC), Fourier transform
ion cyclotron resonance mass spectrometry (FTICR-MS), and tandem mass spectrometry
techniques to gain insight  in the related field.


2.Alsante KM, Hatajik TD, Lohr LL, and Sharp TR. Isolation and identification
of process related impurities and degradation products from pharmaceutical
drug Candidates. Part 1. American Pharmaceutical Review. 2001; 4(1):70-78.  

3. LL , Sharp TR, Alsante KM, and Hatajik TD.
Isolation and identification of process related impurities and degradation
Products from pharmaceutical drug Candidates Part II: The roles of NMR and
Mass Spectrometry. American Pharmaceutical Review. Fall issue 2001

4. Winger  BE, Kemp CAJ. Characterization of pharmaceutical compounds
and related substances by using HPLC FTICR-MS and Tandem Mass Spectrometry.
American Pharmaceutical Review. Summer issue 2001;.

5. International Conferences on Harmonization, Draft Revised Guidance
on Impurities in New Drug Products. Q3B(R). Federal Register. 2000;65(139):44791-44797.

6. International Conferences on Harmonization, Draft
Revised Guidance on Impurities in New Drug Substances. Q3A(R). Federal Register.

7. Van Krimpen, PC, Van Bennekom WP, and Bult A. Penicillins and cephalosporins:
Pphysicochemical properties and analysis in pharmaceutical and biological
matrices. Pharm Weekbl [Sci].1987;9:1-23.

8. Roy J, Mohammad G, and Banu A. Pharmaceutical analysis and stability of
locally manufactured ampicillin trihydrate. Indian Drugs. 1993;5(30)5:211-218,

International Conferences on Harmonization, Impurities-- Guidelines for residual
Residual Solvents. Q3C. Federal Register. 1997;62(247):67377                

9. Buhler V. Vademecum for Vitamin Formulation. Stuttgart, Germany: Wiss. Verl-Ges;

10. "Comparing Near-IR and mid-IR microscopic reflectance FT-IR Imaging;"
Spragg, Hoult, Sellors"; presented at FACCS conference2002

11. "NIR Microscopy of Pharmaceutical Dosage Forms, Clarke, Hammond;

12. Eur. Pharma. Rev.; Issue 1, 2003, p 41.

13. Jason Clegg, of MasterControl Inc.,

14. Guidance for Industry, PAT - A Framework for Innovative Pharmaceutical Development, Manufacturing, and Quality Assurance, CDER/CVM/ORA,Pharmaceutical CGMPs, September 2004

15. Combating Counterfeit Drugs, A Report of the Food and Drug Administration,
    February 2004, Rockville, MD.

16. Anthony Fontana and Julia Mumford

17. Ashish A. Joshi, Ph.D. and Sergio Neves Ph.D

18 . Cliff Nilsen


About Authors

Mr.Anand M. Kudal

M. Kudal*

Working as
Lecturer at MAEER’s,Maharastra Institute of Pharmacy, MIT
Campus, Pune. He has completed M.Pharm in Medicinal and Pharmaceutical
Chemistry from Department of Pharmacy, SGSITS,Indore, RGPV, Bhopal.,

Mr. Satish A. Polshettiwar

Satish A. Polshettiwar

Working as
Lecturer at MAEER’s, Maharashtra Institute of Pharmacy, MIT Campus, Pune. He has done his M.Pharm in Quality Assurance from Nagpur university. He is a Life member
of APTI. He has published and presented several research articles in national
Cell No. 09422842838

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