basics of degradation of drugs and how to characterize degradants.

1. Degradation and Degradant
characterization
GAGANDEEP
M. Pharm
(Pharmaceutical Analysis)

2. Degradation
It is described as phenomena of change in physicochemical properties of any
substance under study due to various environmental factors or interaction between
components of the formulation. It can lead to :
 Reduction of potency
 Change in color, odor or taste
 Change in stability characteristics
 Formation of toxic products

3. Degradation Products
These are the products formed as a result of the degradation of the substance under
study. These can be sometimes just hydrolyzed or oxidized products of actual
substance whereas in some cases degradation products can be highly altered
molecules on chemical basis arising from the parent substance molecules.

4. Factors affection degradation of
formulations:
 Storage temperature
 Humidity and moisture conditions
 Photolytic degradation
 pH of the formulation
 Interaction between components
 Microbial contaminations
 Interaction with containers and closure systems

5. (A) Storage Temperature
High temperatures provide energy in the form of heat
which is responsible for increased number of effective
collisions.
This results into an increase in rate of reaction of
degradation of ingredients.
Example:
An example of drug degraded due to temperature is :
Thiotepa
Ambient storage temperature for storage of this drug is
22-25℃. At 37℃ this drug showed enhanced acid liability
and rapid decay characteristics as compared to 22℃.
Thiotepa

6. (B) Humidity and Moisture conditions
Presence of humidity or moisture in storage conditions promotes hydrolytic cleavage
of ingredients which results into formation of inactive drug fragments as degradation
products or it may yield toxic degradation products.
Common drug groups susceptible to hydrolysis are:
Esters, Lactones, Amides, Imides etc.
Example:
Aspirin dissociates into Salicylic acid and Acetic acid on hydrolysis.

7. (C) Photolytic Degradation
This means degradation of ingredients due to exposure
to light. Since light is also a source of energy, this
energy acts as activation energy for the degradation
reaction of the system.
For prevention of photolytic degradation of products,
storage in amber colored glass containers is advised.
Example:
Sodium nitroprusside is stable for about 1 year if
stored in dark conditions (absence of light) but can
degrade in about 4 hours in light. Sodium nitroprusside

8. (D) pH Change
Change in pH can also account for degradation of drugs.
Many drugs under acidic or basic pH conditions start degrading at a rate higher than
expected and hence affect potency, pharmacology and shelf life period of formulation.
In order to prevent degradation due to pH change, buffer systems are used. The most
commonly used buffer systems include:
Carbonate buffer, Phosphate buffer, Acetate buffer and Citrate buffer.
Example:
pH change for Aspirin containing formulations render that formulation more
susceptible to hydrolytic degradation.

9. (E) Microbial Contaminations
Many commonly found microbes in water and air can become a cause of microbial
contamination for the formulation which results into degradation of the product.
Commonly found contamination micro organisms are:
Pseudomonas, Xanthamonas, Flavobacterium, Salmonella, Streptococci etc.

10. Degradant Characterization
What is degradant characterization?
This involves complete profiling of the degradation product formed in the
formulation.
Degradation products are impurities in our formulation that arise due to
degradation of drug substance as well as any excipient in the formulation. So they
are also characterized as Impurities and their profiles are also maintained as per
impurity profiling guidelines.
How are degradation products characterized?
Degradation products (DP’s) are characterized using modern analytical hyphenated
techniques such as:
 LC-MS
 GC-MS
 LC-NMR
 HPLC-UV
 HPLC-DAD

11. Why hyphenated techniques?
Hyphenated techniques have been proved to be very useful analytical techniques in
profiling and characterization of analytes. Since for characterization, involved steps are
SEPERATION and the RECHARACTERIZATION of analytes.
In Hyphenated techniques, basically a chromatographic method such as LC, GC or
HPLC is coupled with a detection system like UV, DAD, MS etc.
Recent advancements involve coupling of chromatographic systems with NMR for
even better characterization of Analytes.

12. HPLC-UV and HPLC-DAD
A typical HPLC assay with a single-dimensional detector cannot ensure adequate
purity or specificity without further investigation.
UV is by far most commonly hyphenated technique in analytical chemistry. The
quantitative aspects of UV absorption are dependent on the molar absorptivity, path
length, the incident light, and the stability of the detector. HPLC with UV detection
can detect very small amounts of compounds with extremely high molar extinction
coefficients.
As a characterization technique, UV absorption can be used as an important piece
of confirmatory evidence for a proposed structure. Often, HPLC-DAD data are used
to show that an impurity or degradant is similar (electronically) to the drug substance
by virtue of the same chromophore.

13. Continued
Example:
Given below are spectra for Nitroglycerine tablets studied for degradation. The
component eluting at time 13.7 minutes in HPLC-UV spectra was analysed by MS and
it was a mixture of degradation products of a disachharide excipient.
Nitrogylcerine

14. Fourier Transform Infrared Spectroscopy
(FTIR)
Fourier transform infrared spectroscopy (FTIR) provides a useful "fingerprint" of an
organic molecule. FTIR is insufficiently specific for a de novo identification but
provides useful starting data.
FTIR is useful when the presence or absence of a strongly absorbing functional
group (e.g., carbonyl) can be used to confirm or deny a proposed structure.
Example:
Given is HPLC-FTIR spectra for a combination of Acitaminphen, Caffeine and
Dodecanolactam.

15. Newer scenario in Hyphenated Techniques
Recent commercially used industrial developments include:
 LC-NMR
 HPLC-DAD-NMR-MS
 COSY (CORRELATED SPECTROSCOPY)
 TOCSY (TOTALLY CORRELATED SPECTROSCOPY)

16. Thresholds for impurities:
Maximum Daily Reporting threshold Identification
threshold
Qualification
threshold
<2g/day 0.05% 0.10% or 1m/day
whichever is lesser.
0.15% or 1m/day
whichever is lesser.
>2g/day 0.03% 0.05% 0.05%