Evaluation of tablets
EVALUATION
OF TABLETS
The following
tests are carried out to evaluate a tablet
1. General appearance
2. Diameter size and shape
3. Thickness
4. Weight variation test
5. Hardness test
6. Friability test
7. Disintegration test
8. Dissolution test
9. Percentage of medicament/ Assay
1. GENERAL
APPEARANCE :
The general
appearance of a tablet, its visual identity and overall “elegance”, is
essential for consumer acceptance, for control of lot-to-lot uniformity and
general tablet-to-tablet uniformity, and for monitoring trouble-free
manufacturing. The control of the general appearance of a tablet involves the
measurement of a number of attributes such as a tablet’s size, shape, color,
presence or absence of an odor, taste, surface texture, physical flaws and
consistency, and legibility of any identifying markings.
2. DIAMETER SIZE
AND SHAPE
The diameter
size and shape of tablets depends on the die and punches selected for making
the tablets. The tablets of various sizes and shapes are prepared but generally
they are circular with either flat or biconvex faces.
3. THICKNESS
The thickness
of tablets can vary without any change in its weight. This is generally due to
the difference of density of granules, pressure applied for compression and the
speed of compression. The thickness of a tablet can be determined with the help
of slide calipers. The thickness variation limits allowed are ±5% of the size
of the tablet. The variation in thickness leads to counting and packing
problems.
4. WEIGHT
VARIATION TEST
Principle:
The total
weight of a tablet is determined by the depth of the die cavity, bulk density
of granules or powder and uniformly of particulate flow. Even with a proper
granulation having uniform flow, a volume fill is not as accurate as a fill based
on weight. Therefore, tablet weight variation must fall within certain
specification established by the USP. It is desirable that all the tablets of a
particular batch should be uniform in weight. But it is quite impossible to
make all the tablets of same weight accurately. So weight variation is a
general things but variation should follow a certain limit. The test is
considered correct if not more than two tablets fall outside the range if 20
tablets are taken for the test and not more than one tablet falls outside the
range if only ten tablets are taken for the test. The difference of weight in
tablets can lead to variation in doses. Therefore all the tablets of a batch
must conform to this test.
Procedure
At first 10
tablets were taken randomly and the individual weight of the tablets was taken
and also average weight of the tablet was calculated. The weight of the
individual tablets were then compared with the average weight calculated and
saw that not more than one tablet fall outside the range.
Limit
The limit
depends on average weight of the tablets and in terms of USP specification as
follows.
Average weight
of tablets (mg)
130 or less ±10 %
130 – 324 ±7.5 %
More than 324 ±5 %
5. HARDNESS TEST:
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| EVALUATION OF TABLETS, pharmavoicebd24, |
Principle:
Hardness test
is very important for a good quality of a finish tablet. Because if the
finished tablet is too hard, it may not disintegrate in the required period of
time and if the finished tablet is too soft, it may not withstand the handling
during packing and transporting. The hardness of the tablet depends on the –
a. Weight of material
b. Space between the upper and lower
punches at the time of compression
c. In appropriate pressure applied on the upper punches
d. Excessive proportion of fatty lubricants
such as Magnesium stearate
e. Therefore it is very necessary to check
the hardness of the tablet.
Apparatus:
A number of
testers are used for determination the tablet hardness but Monsanto and Pfizer
hardness testers are commonly used. Monsanto hardness testers consists of the
following parts-
a. Spring
b. Screw
knob
c. Fixed jaw
d. Moving jaw
e. Scale
f.
Indicator
Figure:
Monsanto hardness testers
The tablet to
be tested was placed between a fixed and moving jaw and reading of the
indicator was adjusted to zero. Then the force was applied to the edge of the
tablet is gradually increased by moving the screw knob forward until the tablet
break. The reading noted from the Scale.
6. FRIABILITY TEST OF TABLETS
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| EVALUATION OF TABLETS, pharmavoicebd24, |
Apparatus
Use a drum with
an internal diameter between 283 and 291 mm and a depth between 36 mm and 40
mm, made of a transparent synthetic polymer with polished internal surfaces and
not subject to static build-up (see Fig. 17G–1). One side of the drum is
removable. The tablets are tumbled at each turn of the drum by a curved
projection with an inside radius between 75.5 mm and 85.5 mm that extends from
the middle of the drum to the outer wall. The drum is attached to the
horizontal axis of a device that rotates at 25 ± 1 r/m. Thus, at each turn the
tablets roll or slide and fall onto the drum wall or onto each other.
Figure: Tablet
friability apparatus
Method
For tablets
weighing up to 0.65 g each, take a sample of 20 tablets; for tablets weighing
more than 0.65 g each, take 10 tablets. Place the tablets on a sieve no. 1000
and remove any loose dust with the aid of air pressure or a soft brush.
Accurately weigh the tablet sample and place the tablets in the drum. Rotate
the drum 100 times and remove the tablets. Remove any loose dust from the
tablets as before. If no tablets are cracked, split or broken, weigh the
tablets to the nearest milligram.
Generally, the
test is run once. If the results are doubtful or if the mass loss is greater
than 1%, repeat the test twice and determine the mean of the three tests. A
maximum loss of 1% of the mass of the tablets tested is considered to be
acceptable for most products.
For tablets
having a diameter of 13 mm or greater, problems of reproducibility may be
encountered due to frequent irregular tumbling. In such cases, adjust the drum
so that the tablets may fall freely and do not bind together when lying next to
each other; adjusting the drum so that the axis forms a 10° angle with the base
is usually satisfactory.
Expression of
the results. The friability is expressed as the loss of mass and it is
calculated as a percentage of the initial mass. Indicate the number of tablets
used.
7. TABLET THICKNESS:
The thickness
of a tablet can vary without any change in its weight . this is generally due
to
i. Difference in the density of the
granules
ii. The pressure applied to the tablets
iii. The speed of tablet compression
The thickness
of a tablet can be determined with the help of micrometer calipers. The
thickness variation limits allowed are ± 5% of the size the tablet. The
variation in thickness lead to counting and packaging problems.
8. CONTENT UNIFORMITY
:
Weight
variation test should be a satisfactory method of determining the drug content
uniformity of tablet. If the tablet were or essentially all (90% – 95% )
aspirin is save drug. (1-2µg) digoxine, lidocain, zentamycine therapeutic index id narrow. This factor are
not applicable for API in content uniformity.
For 10 tablet
assay ,
9
must be 85-115%
1
must be 75-125%
9. DISINTEGRATION TEST :
(disintegrating tablet)
(disintegrating tablet)
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| EVALUATION OF TABLETS, pharmavoicebd24, |
The
disintegration test is performed to find out that within how much time the
tablet disintegrates. This test is very important and necessary for all the
tablets coated or uncoated to be swallowed because the dissolution rate depends
upon the time of disintegration which ultimately affects the rate of absorption
of drugs.
The apparatus
used for this test is known as disintegration test apparatus. This apparatus
consists of a glass or plastic tube which is open at one end and the other end
is fitted with a rust proof No. 10 mesh sieve.
The tube is
suspended in a bath of water or suitable liquid which is thermostatically
maintained at a temperature of 370C. The tube is allowed to move up and down at
a constant rate i.e. 30 times per minute through a distance of 75 mm. The
volume of the liquid and distance of movement is adjusted in such a way that at
the highest point the mesh screen just breaks the surface of the liquid to give
a turbulent movement to the tablets and at the lowest point the mesh screen
remains about 2.5 cm. above the bottom of the container.
Figure:
Disintegration test machine
About three
tablets are placed in the tube along with a plastic disk over the tablets. The
plastic disk does not allow the tablets to float and imparts a slight pressure
on the tablets. The tube is allowed to move up and down and disintegration time
noted when all the tablets have passed through the sieve.
Generally the
disintegration time for uncoated tablets is not more than 15 minute except
diazepam ( 30 minute ) and for coated tablets disintegration time is 30 min.
10. DISSOLUTION TEST
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| EVALUATION OF TABLETS, pharmavoicebd24, |
The rate of
dissolution of a solid drug plays an important role in the absorption and
physiological availability of the drug in the blood stream. Therefore
determination of dissolution rate of any solid drug is very necessary. For this
purpose there are a number of tests available in the literature but none is
official. The test is performed for tablets and capsules when stated in the
individual drug monograph.
The apparatus
for dissolution test consists of –
i. A cylindrical stainless steel basket
which is attached to the end of the stirred shaft.
ii. A 1000 ml vessel made of glass or
other inert, transparent material fitted with a cover.
iii. A variable speed motor driven stirrer which
can rotate at a speed of 25 – 150 revolutions per minute.
iv. A suitable thermostatically controlled
water bath to maintain the temperature of the dissolution medium at a
temperature of 370C ± 0.50C.
Figure: Tablet
disssolution test apparatus
8.4 ml of HCl
was measured by using graduates cylinder. Then it was transferred to a 1000 ml
volumetric flask containing about 500 ml of water. Sufficient amount of water
was added to adjust the volume and mixed well.
For performing
the test 900ml of dissolution medium (0.1N HCl) is filled in the glass vessel
which is submerged in the water bath maintain at 370C. The tablet to be tested
is introduced in the basket and fitted in position. For standard claimed amount
of Ranitidine hydrochloride powder is introduce in the basket and fitted in
position. The motor is started with 50 revolutions per minute.
The samples are
withdrawn at 5 minute intervals and replaced immediately through a 0.1N HCl
solution. 5 ml sample solution is withdrawn each time which is replaced with 5
ml of medium at 370C in order to maintain a constant volume in the vessel. The
samples are collected and 10 times dilution of each and measured the absorbance
at 313 nm wavelength.
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