Transcript Types of tablets

Tablets
A tablet is a pharmaceutical dosage form. It comprises a mixture of
active substances and excipients, usually in powder form, pressed or
compacted into a solid.
The excipients can include binders, glidants (flow aids) and
lubricants to ensure efficient tabletting; disintegrants to promote
tablet break-up in the digestive tract; sweeteners or flavours to
enhance taste; and pigments to make the tablets visually attractive.
A polymer coating is often applied to make the tablet smoother and
easier to swallow, to control the release rate of the active ingredient,
to make it more resistant to the environment (extending its shelf
life), or to enhance the tablet's appearance.
Tablets can be classified according to their drug-release
characteristics into:
I. According to drug release rate from the
tablet (USP classification):
a- Immediate-release tablet:
The tablet is intended to be released rapidly after administration, or the tablet is
dissolved and administered as solution. It is the most common type and includes
1- Disintegrating tablet (conventional or plain tablet)
2- Chewable tablets
3- Effervescent tablets
4- Sublingual and Buccal tablets
5- Lozenges
6- Soluble tablets
b- Modified-release tablet:
They have release features based on; time, course or location.
-They should normally be swallowed intact.
-Different excipients than immediate release tablets.
-The drug is released from an extended-release tablet slowly at a nearly constant
rate.
Delayed-release tablets
The drug is liberated from the tablet some time after administration.
After this period has elapsed, the release is normally rapid.
e.g. Enteric tablet, for which the drug is released in the upper part of
the small intestine after the preparation has passed the stomach.
Multiple compressed tablets
- Tablet within a tablets: core and shell
- Multilayer tablet
Immediate-release tablet:
1- Disintegrating tablet (conventional or plain tablet)
- Disintegrating tablet is the most common type of tablets that is intended to be
swallowed and to release the drug in a relatively short time thereafter, by
disintegration and dissolution (fast and complete drug release in vivo).
- It includes normally the following type of excipients; filler
(with low dose drug), disintegrant, binder, glidant, lubricant and antiadherent.
- Tablet disintegration may be affected by;
1- Choice of the excipients.
Bilayer tablets
2- Production conditions during manufacture.
- Conventional tablet may be single layer or multilayer.
Multilayer tablets are prepared by repeated compression of powders and are made
primarily to separate incompatible drugs from each other.
Steps of drug release from disintegrating tablets
2- Chewable tablets
Chewable tablets are to be chewed and thus mechanically disintegrated in the
mouth, so NO DISINTEGRANT IS INCLUDED IN ITS COMPOSITION.
Flavoring, sweetening and coloring agents are important.
Sorbitol and mannitol are common examples of fillers in chewable tablets,
(mannitol has negative heat of solution which results in cooling effect and also has
sweetening action)
Advantages of chewable tablets:
- Provide quick and complete disintegration of the tablet and thus obtain a rapid
drug effect after swallowing and dissolution.
- Easy administration, especially for infants and elderly people.
- Could be administered when water is not available.
Examples for chewable tablets are;
- Chewable Aspirin tablets (for children in the treatment of rheumatoid and to
prevent clot formations in adults)
-Chewable Antacid tablets
3- Effervescent tablets:
Effervescent tablets are uncoated tablets generally containing acid substances and
carbonates or hydrogen carbonates which react rapidly in the presence of water to
release carbon dioxide. They are intended to be dissolved or dispersed in water
before administration.
Effervescent tablets are dropped into a glass of water before administration during
which CO2 is liberated. This facilitates tablet disintegration and drug dissolution;
the tablet disintegration
should be complete within few minutes.
(Effervescence is a special mechanism for disintegration)
CO2 is created by the reaction between carbonate or bicarbonate and a weak acid
such as citric acid or tartaric acid.
Effervescent tablets are dropped into a glass of water before
administration, during which carbon dioxide is liberated.
facilitates tablet disintegration and drug
dissolution; the dissolution of the tablet
should be complete within a few
minutes.
Uses of effervescent tablets:
1. Rapid drug action, e.g. analgesic drugs .
2. Facilitate the intake of the drug, e.g. vitamins.
After
Dissolution of
tablets
buffered water
solution will
be obtained
fast drug bioavailability (As drugs are
absorbed more effectively in the small
intestine than in the stomach)
e.g. analgesics
Temporarily
increases the pH
of the stomach
Rapid emptying of the stomach and
shortening the residence time
Drug-induced gastric irritation
can be avoided (short residence
time) e.g. aspirin tablets
As absorption of aspirin in the
stomach can cause irritation
Advantages of effervescent tablets:
1. To obtain rapid drug action, for example analgesics and antacids.
2. To facilitate drug intake, for example vitamins.
3. They are convenient, easy to use, premeasured dosage form as compared with
the powdered dosage forms.
4. They cannot spill as the powdered preparations can.
5. They can be individually packaged to exclude moisture, thereby avoiding the
problem of product instability of the unused contents during storage.
Effervescent tablets package
Effervescent tablets often include a flavor and a colorant.
Effervescent tablets are prepared by direct compression or dry granulation.
Effervescent tablets should be protected from moisture, so that a special package
is needed; each tablet is completely covered with aluminum foil and kept in a
water-proof container, often including a desiccant. Effervescent tablets may be
packed in blister packs.
Effervescent tablets usually contain
Carbonate or
bicarbonate and a
weak acid such as
citric or tartaric
The amount of
sodium bicarbonate
in an effervescent
tablet is often quit
high (about 1 gram)
Flavor and a
colourant
N.B. Binder
and
disintegrant are
normally not
included in the
composition
A water-soluble
lubricant is
preferable in order
to avoid a film of
hydrophobic
lubricant on the
surface of the water
after tablet
dissolution
4- Sublingual and Buccal tablets:
 They are used for drug release in mouth followed by systemic
uptake of the drug.
 A rapid systemic drug effect can thus be obtained without firstpath liver metabolism, because the drug diffuses into the blood,
directly through tissues under the tongue in case of sublingual
tablets and through oral mucosa in case of buccal tablets.
 They are often small and porous, the latter facilitating fast
disintegration and drug release.
Sublingual tablets are placed under the tongue.
Ex. Nitroglycerin sublingual tablet; it exerts its action within two minutes for
rapid relief of "Angina pectoris" attack, because the sublingual area is rich in blood
supply. Nitroglycerine suffers from first-pass metabolism if taken orally. Also other
cardiovascular drug, barbiturates, and vitamins are prepared as sublingual tablet
dosage form.
Buccal tablets are placed in the side of the cheek for
absorption through oral mucosa.
N.B. Buccal tablets may be also prepared for their local
application.
5-Lozenges
They are tablets that dissolve slowly in the mouth and so release
the drug dissolved in the saliva.
Lozenges may be used for;
- Local medication for mouth or throat, e.g. local anesthetics,
antiseptics and antibiotics.
- Systemic drug uptake.
Compressed lozenges:
are made by using tablet machine with large and flat punches,
with high pressure is applied to produce hard tablets, so that they
dissolve slowly in mouth.
Bradoral® compressed loyenges
for treatment of sore throat
NO DISINTEGRANT IS INCLUDED IN
COMPRESSED LOZENGES COMPOSITION
Other additives (binder and filler) must have pleasant taste
or feeling during dissolution. High concentration of fillers which
are mainly sugars as glucose, sorbitol or mannitol.
High concentration of binder is used. Common binder used in
compressed lozenges is gelatin.
6- Soluble tablets
Soluble tablets are uncoated or film-coated tablets.
They are intended to be dissolved in water before
administration.
The solution produced may be slightly opalescent due to
the added excipients used in the manufacture of tablets.
Allowing the reduction
in dosing frequency.
Modified-release tablet
1-Extended-release tablet
2- Delayed-release tablet
Slowly release the drug in the GIT at a constant rate
Prolonged release and sustained release (12-24 hours)
- The aim is to increase the time period
during which a therapeutic concentration
level in the blood is maintained
- To increase the release time for drugs
that can cause local irritation in the
stomach or intestine if they are released
quickly (iron salts)
Immediate release
tablet
Drug release is delayed due to physiological
conditions e.g. pH (a lag period followed by
normal release).
The best example is enteric coated tablets, the drug
is released in the upper part of the small intestine
after which the preparation has passed the
stomach.
If the drug is sensitive to acid, or is irritant to the
stomach lining, an enteric coating can be used.
Extended release
tablet
Cumulative
amount of drug
released
Time
II. According to method of manufacturing:
a- Compressed tablet:
It is obtained by compressing uniform volume of particles using "Tablet
compression machine". It's used for large scale production.
b. Molded tablets:
Molding means shaping and hardening of semi- solid mixture of drug
and excipients.
It is obtained using ʺtablet mold“. It is restricted for small-dose tablet
and for small scale production.
Tablet mold
Tablets administered by other routes
These tablets are administered by other routes except for the
oral cavity and so the drugs avoided from passing
through the gastrointestinal tract.
These tablets may be inserted into other body cavities or
directly placed below the skin to be absorbed into
systemic circulation from the site of application.
Vaginal tablets
These tablets undergo slow dissolution and drug release •
in the vaginal cavity of women. The shape kept ovoid
or pear shaped to facilitate retention in vagina.
These tablets release generally antibacterial, antiseptics •
or astringents to treat vaginal infections or release
steroids for systemic absorption.
The tablet should be made compatible with plastic tube •
inserters which are designed to place the tablet in the
upper region of vaginal tract.
Implants
These tablets are inserted into subcutaneous tissue by •
surgical procedures where they are very slowly absorbed
over a period of one month or one year.
A special injector with a hollow needle and plunger is •
used to administer the rod shaped tablet for other shapes
surgery is required. The tablets may be pellets cylindrical
or rosette shaped with diameter not more than 8 mm.
They are sterile formulation without excipients and made
hard with large particle size to achieve gradual drug
release. Mainly, these tablets are prepared to deliver
growth hormones.
Definition:
Coated tablets
Coated tablets are defined as tablets covered with one or
more layers of mixtures of various substances with the
intention of (adding) conferring benefits and properties to
the dosage form over the uncoated one.
Press-coating (Enteric-coated tablets)
Sugar-coated tablets
Film-coated tablets
 Sugar coated tablets:
1- Protect tablets from moisture
2- Mask odor and flavor
3- Elegance
 Film coated tablets:
1- Thin film coat
2- Soluble or insoluble polymer film
 Enteric coated tablets:
compressed tablets coated with substances that resist solution in
gastric fluid but disintegrate in the intestine. It can be used for
tablets containing drug substances which are inactivated or
destroyed in the stomach, for those which irritate the mucosa or as
a means of delayed release of the medication.