Drug anti-diabetic drugs are introduced into the market at

Drug
analysis means identification, characterization and determination of drugs 
in  mixtures such as
pharmaceutical formulations and biological
fluids. There is  large
number of cardiovascular and anti-diabetic drugs are introduced into the
market at  an  alarming rate. These drugs may be either new
entity in the market or partial structural modifications of the
existing drugs. Newer analytical methods are developed for these drugs in their
combined dosage form because of the following
reasons:

·        
The drug combinations may not be
official in any official compendia

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·        
Literature survey reveal no analytical
methods are reported

·        
Analytical methods is
hard in  drug combinations due to the
interference from excipient.

On
the other hand, the existing procedure may,

 

·          
Needed expensive instruments, the
reagents, solvents   for analysis

·          
Involve 
time consuming or tedious 
extraction or separation steps

·          
Not be
rapid, accurate, reliable and sensitive

 

The
newly developed analytical method finds their importance in various fields like

 

·          
Government and private Research institutions

·          
Quality control department in industries

·          
Approved drug testing laboratories

·          
Bio-pharmaceutics and Bio-equivalence studies

·          
Clinical pharmacokinetic studies

 

Estimation of Drugs in combined
Dosage Forms:

 

Administration of two
or more drugs at a time becomes crucial for several therapeutic considerations.
The combined dosage form have gained lot of importance now days due to greater patient acceptability, increased
potency, multiple action, fewer side

effects
and quicker relief. The quantitative determining of combined dosage forms(CDF)
are complex in nature as one
component does not interfere with the estimation of the other. There is a need of
analysis of such formulations without prior separation. For the
estimation of multi-component formulation, the instrumental techniques commonly
employed, are spectrophotometry, GLC, HPTLC, HPLC etc. these  methods 
are  based upon the measurement of
specific and nonspecific  physical
properties  of the  substances. Of all the above techniques HPLC
is most widely considered quantitative 
analysis of drugs in CDF.

HIGH PERFORMANCE LIQUID CHROMATOGRAPHY

 

Among
all the chromatographic techniques HPLC8 is one of the most widely used
analytical techniques providing superior qualitative and quantitative  results, reproducibility and higher detection
sensitivity and high reliability of analytical
data. In high performance liquid chromatography
(HPLC) the liquid mobile phase is passed through the stationary phase under
pressure. Chromatographic separation in HPLC
is the result of specific
interactions between sample molecules with both stationary and mobile phases.
HPLC offers a great variety of stationary phases, which  allows 
a greater variety of these selective interactions and more possibilities for separation. A
simple HPLC system consisting of a solvent reservoir to hold the mobile phase,
a pumping system to pressurize the mobile phase, and injector to introduce a
small volume of the sample mixture under high pressure, a column containing
stationary phase,  a detector to  detect the presence of components as they exit the column, and a recorder to record the detector signal.

HPLC
used for analysing

ü  Non
volatile substances

ü  Substances
with high polarity or ionic samples

ü  Substances
with high molecular weight

ü  Thermally
unstable and decomposable substances

 

In HPLC there are various
modes of separations.

normal phase mode
stationary phase polar & mobilephase nonpolar, for this nonpolar compounds
eluted first reason lowaffinityof nonpolar compounds & polar stationaryphase. take more time to
separate . The stationary phases used are SiO2, Al2O3,
-NH2, -CN, -Diol, -NO2.The mobile phases used are
heptanes, hexane, cyclohexane, chloroform, dichloromethane.

Reversed phase mode in analytical field of
chemicalbiological pharmaceuticalbiomedical sciences, stationary phase non
polargroups attached silicagel & mobile
phase polarsolvent. Coloumns are ODS viz:
C8 & C4 C18 The mobile phases used are water, acetonitrile, methanol and buffers.

3

 

Ion exchange chromatography, the
stationary phase contains cation exchanger (SO -, COO-)
and anion exchanger (NR +,NHR +), used separating of
inorganic ions, organic acids, organic bases, proteins and nucleic acids.

Ion pair chromatography
For acidic substances tetraalkyl
ammonium salts and for basic substances alkyl sulfonates are used as ion pair
reagents.

Affinity chromatography
10 involves the covalent attachment of immobilized biochemical to solid
support highly specific biochemical interactions for  separation. When sample is passed through the
column only solutes that selectively bind to complementary ligand is retained while other sample components elute
without retaining  in column. The
stationary phase contains specific groups of molecules
called ligands, This technique was used
to seperate biological samples like proteinsenzymes
&antibodies in High mixtures.

Sizeexclusionchromatography
used 
separation in molecular mass. LSM first and the SSM elute later, it
later defined into GPC and GFC.

 

                     Instrumentation in HPLC 11, 12

 

      Mobile
phase reservoir system with pumps

 

      Sample
injection system

 

      Column

 

      Detectors

 

           
Mobile phase reservoir system with pumps

 

The
HPLC pump is very important component
of the system. Pumps are required  to
deliver a constant flow of mobile
phase at pressure ranging from 14.6 to 8000 psi. Pumps capable of pressures up to 8000 psi provide a wide range of mobile phase  flowrate typically from 0.01- 10 ml / min.

Displacement
viscosity backpressure nondepending with
limitedcapacity.

Reciprocating
pump:
35 -400 ?l ,outputpressure 10,000 psi 
&constantflowrate & pulsed flow.

 

Pneumatic
pump:. less than 2000 psi.

There are two
type of elution process, i.e. isocratic and gradient,

 

Isocratic:
In this system, the things are kept
constant throughout the run. In the case of pumping of mobile phase, the mobile
phase composition is kept constant throughout the run. The nominal flow rate
accuracy required is ±1% of the set flow.

Gradient:
There is
some change purposely incorporated during the particular sample  run to achieve a better or/and faster
separation. In case of pumping mobile phase, the composition of
mobile phase is continuously varied during the particular  run. 
The gradient accuracy of ±1% of
the step gradient composition is typical.

 

           
Column

 

The
Columns in HPLC are fabricated withstand high pressure. The internal diameter of analytical column are 4-5 mm and of length
10-30 cm. The shorter column with 3-6 cm in length
is also available. The particle sizes in column packing are generally 3 or 5 µm. For analysis of single component
shorter  columns are sufficient but for
separation two or more components
longer column are preferable.

Column packing:

 

There are three
main types of column packing in HPLC.

 

a.  polymericporusbeds

 

b. 
Porous bedlayered

 

c. 
Totally Porous silica particles

 

             
Detectors

 

.
The ideal detector should respond to a particular property of the
substance being separated, it should be sensitive and give a linear response
range over a wide concentration range.

Detectors are
basically two types

Bulk
Property Detectors &Solute Property Detectors:.

The commonly
used in HPLC analysis of pharmaceutical substances are

 

i.  
Photometric detectors: These
normally operate in ultraviolet region of spectrum and most widely used. These
detectors consist of light source, dispersing element, flow cell,
photomultiplier cell or diode. These are of five types

Single
wavelength detectors Multi wavelength detectors Variable wavelength detector
Programmable detector Diode array detectors

ii.   Fluorescence
detector it is more sensitive when compared photometric detectors.

 

ii.
Refractive index detectors these detectors
respond to change in bulk property of refractive index of solution of the
component in mobile phase. Its sensitivity is less when compared to bulk
property detectors.

iv.
Electrochemical detectors are detector based on
electrochemical principles involving amperometry, voltammetry, and
polarography.

There
are several detectors available in the market. However UV Visible detector,
photo diode array detector, fluorescence detector, conductometric and
coulometric detector are more commonly used. The new ELSD detector is proving
to be important detector, while the MS detector is outstanding.

 

 

 

Fig.1.1. Instrumentation of HPLC

 

 

 

 

 

 

 

 

           
Quantitative
analysis in HPLC 8

 

The
quantitative analysis in HPLC can performed three methods

 

           
External Standard
calibration:
The external Standard is the same
substance as that being analysed in the sample.
This method is most commonly used for analysis. The external Standard must be pure and its composition must be
known  through  prior analysis. By injecting Standard
solution in different concentration peak 
response  is plotted vs.
concentration. Unknown samples are analysed in similar manner and their
concentration determined from the calibration
curve.

           
Internal Standard
method:
The effect of minor variables in separation parameters, peak size and
injection errors. In this method of
analysis, a fixed concentration of known
compound addconcentration separate peaks.

           
InternalStandard should
have following properties

 

ü  Must
have completely resolved peaks without interference from other compound present
in sample.

ü  Should
have similar chemical properties as the compound of interest.

ü  Should
mimic the analyte in any sample preparation
method.

ü  Must
be stable, compatible with column packing, mobile phase and chemically inert
towards components of sample.

ü  Must
be easily available and with reasonably high
purity.

 

A
calibration is produced by analyzing various concentrations of pure drug with a
fixed concentration of internal Standard. From the chromatogram response factor
is calculated.

RF= Ap/AISTD

 

Similarly the analyte is to added to the fixed
concentration of internal Standard and response factor is calculated

RF = Ax/AISTD

 

Where Ax
is the
peak area
of analyte
and 
AISTD   is
the peak
area of
internal Standard. From the interpolation of calibration curve the
concentration of analyte calculated.

Use
of internal Standard addition method is not always advantageous as precision is
less when compared to external Standard method.

           
Standard addition
method: In
these method different concentrations of.
The response from Standard addition
to extrapolated to zero  addition  concentration. The negative intercept on the
X-axis will be the concentration of analyte. The important aspect in this method is detector response should be adequate
to produce S/N ratio >10 otherwise results are not precise.

 

           
Method Development and design of
separation method 13

           
Plate number (N): It
is an important property of the column. It reflects
its quality of separation and its
ability to produce sharp, narrow peaks and good
resolution of peaks. Column with N ranging from
5,000 to 1,00,000 plates/meter are ideal for a good system. The factors
influencing plate number are

Ø  Well
packed column

Ø  Larger columns

Ø  Less
flow rate

Ø  Low
viscosity of mobile phase

Ø  Small
sample molecules

 

           
Resolution factor (RS)
:
It measures
the quality of  separation of   adjacent bands. It is defined as distance centers of band peaks divided by average band width.

           
RS =
Rt2- Rt1/ 0.5(W1 + W2)

 

 

 

 

 

Rtension1
&Rtension2 retention time and W1 & W2
peak width

The fundamental
which influences the resolution factor are

    Capacityfactor Selectivity factorColumn efficiency

 

Column
efficiency: It represents
the number of theoretical plates per meter (N) and HETP. HETP height equivalent
to theoretical plates is a section in a column in which
mobile phase and stationary phase are
in
equilibrium. Lower the HETP value more efficiency is the column

HETP = L/N

 

L=
length of column

 

N
= no. of theoretical plates

 

Its value depends upon particle size, flow rate,
viscosity of mobile phase and quality of packing

           
Peak Assymetry (As): It
is a practical measurement of peak shape. Peak asymmetry is measured at 10% of
full peak height. Good columns produce peaks with As values of 0.95-1.1.

           
VALIDATION OF ANALYTICAL METHOD 14-17

 

Validation
is the assessment of the defined test method. The result of any successful
validation is a comprehensive set of data
that will 
support the suitability of test method  for its intended use.

The validation
parameters are:Specificity Precision LinearityAccuracyLimit of detection

Limit of quantitationRuggednessRobustness Stability solutions

Specificity

a. 
inject sample as well
as other related compounds decomposition/ degradation products, intermediates,
solvent, chemicals used in analysis.
All compounds should separate from main
analyte peak.

b.  placebo
to demonstrate the lack of interference
from excipients.

 

c.  
stressed placebo to
show that degradation products from excipients will not interfere with
degradation products of drug substance.

d.  
sample subjected to
degradation studies to  achieve 10-20 % of degradation of  analyte in conditions of 0.1 N HCl, 0.1 N NaOH, 3% H2O2 ,50 °C , UV radiation. All the degradation products if any should be
separated from analyte.

           
Precision

 

a.    
Repeatability of  method can be determined by multiple
replicate preparations of sample.
These can be done either by multiple
sample preparations (n=6) in same experiment or by preparing three replicates
at three different concentrations. % RSD should be less than 2 %.

b. 
Intermediate %
RSD should be less than 2 %.

c.  Reproducibility
expresses
the precision between laboratories.

 

           
Linearity
of analytical procedure is its ability
to obtain test results that is directly proportional to the concentration of
analyte in the sample. The following results 
should  be reported slope,
correlation coefficient, y intercept and residual sum of squares.

This
is to verify that the method performance is not affected by typical changes in normal
experiments. The method parameters that is investigated for robustness are

¨      HPLC
column (lot, age, brand)

¨      Mobile
phase composition (pH ± 0.05 unit, percent organic ± 2 % )

¨     
HPLC instrument
(detection wavelength ± 2 nm , column temperature ± 5 °C, flow rate ± 0.2 ml/min)

Ø  Different
operators in same laboratory

Ø  Different
equipment in same laboratory

 

Ø  Different
source of reagents and solutions

Ø  Different
source of column

Ø  Different laboratory

 

           
Stability
solutions used for the analysis is required to be
stable for a period more than 24 hr to
produce precise and reliable results.

           
Advantages of analytical method validation

 

ü  Reliability
of analytical results and assurance of quality
product

ü  Performance
capability of the method can be confirmed by analysts using the
method

ü  Awareness
about importance of protocols for
validation work

ü  Motivation
for improvement in quality of work

ü  Provides
opportunity for training to QC staff

ü  Helps
in scientific communication on
technical matters

 

           
FORCED DEGRADATION
STUDIES AND STABILITY INDICATING ANALYTICAL METHOD 18

The
pharmaceutical molecules chemical stability is a matter of great worth as it make impact on safety and efficacy of the drug product. To study the FDA and
ICH laid guidelines for  the  requirement of analytical 
stability testing data. Knowledge about stability of molecule beneficial
in choosing proper formulation and packaging requirements as well as storage
conditions maintenance and shelf
life, which is essential in filling documentation for  regulatory. 
In 
Forced degradation studies the drug products and drug
substances undergo degradation at conditions more intense than accelerated conditions
and thus produce degradation  products
which can be used to assess the
stability of the molecule. According to the
ICH guideline the intention in stress
testing is further helps investigation of the
intrinsic stability of the molecule and elucidating
possible degradation pathways, and for validation of the stability indicating
method used. For filling the new drug moiety in registration dossier it is
mandatory to perform stability studies. The duration for stability studies in long term studies is 12

 

months
and for accelerated stability studies it is 6
months. The intermediate studies are performed for 6 months can be at mild
conditions when compare  to  accelerated studies. So it will take long
time for separation, identification and quantification of degradation products.
When compared to stability studies in
forced degradation  studies  the degradation
products are generating in shorter time. The samples generated from forced
degradation studies was further useful for the development of the stability
indicating methods which can be applied 
for the  analysis of  samples generated  from accelerated and long term stability studies.

      Objective
of FDS

 

Forced
degradationstudies are carried out achieve following purposes:

 

v  To
investigate degradation pathways of drug substances and drug products.

v  To
differentiate degradation products of drug products from those of non-drug product in a formulation.

v  For
structural elucidation of degradation products.

v  To
assess the intrinsic stability of a
drug substance in formulation.

v  To
reveal the drug degradation mechanisms in pure and formulations

v  To
examine the stability indicating nature of a
developed method.

v  To
understand the chemical properties of drug molecules.

v  To
produce more stable formulations.

v  To
predict stability-related problems

 

A
stability indicating method (SIM) is
an analytical procedure which is used to estimate  the decrease in the concentration of the active pharmaceutical ingredient
(API) in drug product when it exposed to various degradation conditions. As per FDA guidance document a
stability-indicating method is a validated quantitative analytical  procedure 
that can be used for the study in variation in the stability of the drug substances and drug products with time. A
stability-indicating method accurately measures the changes in active
ingredients concentration without interference from other generated degradation
products, related impurities and formulation excipients. The suitable platform
in pre-formulation studies, stability studies and proper storage conditions for
drug substance and drug product.

 

      Degradation conditions

 

           
Hydrolytic conditions

 

Hydrolysis
is one of the two most common mechanisms of drug
degradation over a wide range of pH. Hydrolysis is a chemical
process that involves degradation of a chemical compound by reaction with
water. Hydrolytic reactions are mainly acid or base catalyzed. For hydrolytic
study acidic, neutral and basic conditions should be employed which susceptibly
attacks at ionizable functional groups present in the molecule. The type and concentrations
of acid or base used for hydrolysis is
based on the stability of the drug
substance. Generally HCl or H2SO4 in the concentration range of 0.1–1 M are
used  for
acid hydrolysis and NaOH or
KOH in the concentration range of 0.1–1M
for base hydrolysis. If the
compounds have low solubility in water, then inert water miscible co- solvents
can be used. Hydrolytic stress studies is normally performed  at 
room  temperature and if there is
no sign of degradation then elevated temperature (50–70 °C)  are recommended. The duration of stress testing should not exceed more than one week.

           
Oxidation conditions

 

Oxidative
reactions are one of the two most common mechanisms of drug degradation.
Hydrogen peroxide is most widely used reagent for oxidation of drug 
substances  in forced degradation
studies but other oxidizing agents such as metal ions, oxygen, and radical
initiators (e.g., azobisisobutyronitrile, AIBN) can also be used. Selection of
an oxidizing agent, its concentration, and conditions depends on the drug
substance. It is recommended to
expose sample with 0.3–3 % hydrogen peroxide at neutral pH and room temperature
in dark for seven days or 5- 20 % degradation could potentially produce
relevant degradation products.

           
Photolytic conditions

 

Photolytic
degradation is a degradation that results from
exposure of drug substance or
drug product to UV or visible light in the wavelength range of 300-800 nm.
Exposure to radiation at wavelengths