TABLETS
Tablets are solid dosage forms containing drug substance with or without suitable diluents, and prepared by
compression. This is the most frequently used dosage form of administering a
drug. They are swallowed, chewed, or held sublingually. Scoring of some
tablets into halves or quadrants facilitates breaking them if a smaller dose is
needed. A tablet’s color or shape can
help identify it. Advantages: simplicity and economy, stability and convenience
in packaging, accuracy of dosage, compactness, portability, and ease of
administration.
Tablet
types and their abbreviations:
1.
Tablets
for oral administration
i.
compressed (or plain) tablets (CT) – These tablets are formed by compression and
contain no special coating. They are made from powdered, crystalline or
granular materials, in combination with binders, diluents, etc. (e.g., Analgin,
Aspirin, Paracetamol, Saridon, etc.)
ii.
sublingual tablets :
a)
They are relatively small and
dissolve rapidly.
b)
they are placed under the tongue
and allowed to dissolve
c)
after absorption, the drug enters
the systemic circulation without passing through the portal circulation, thus
avoiding first-pass inactivation in the liver.
d)
absorption of lipid-soluble
molecules through the oral mucosa is rapid and the effect of drugs given in
this way may become apparent within 2 min. Nitroglycerin and organic nitrates
are commonly administered by this route.
e)
Drugs that are destroyed by the
gastrointestinal fluids or are subject to substantial presystemic metabolism
may be formulated into such tablets.
Examples:
Nitroglycerin, Methyltestosterone, Validol, etc.
iii. buccal tablets are small, flat, oval
tablets, intended for buccal administration by inserting them into the buccal
pouch (the space between the teeth and the cheek). They are dissolved or eroded
slowly. Example: Desaminooxytocine (Sandopart)
iv.
chewable tablets are large, hard tablets,
difficult to swallow, intended to be crushed before ingesting. Example:
Combantrin, Centrum junior, etc.
v.
effervescent tablets contain sodium bicarbonate and an organic acid
in addition to the drug substance. In the presence of water, these additives
react liberating carbon dioxide which acts as disintegrator and produces
effervescence. These tablets are soluble and they are taken readily and
absorbed rapidly (e.g., Upsarin, Vit C, Supradin, etc.)
vi. sugar-coated tablets are smooth, oval compressed tablets containing sugar
coatings. Sugarcoating provides both protection and sweet taste but the coating
operations take a long time. Example: Nifedipin, Vitaferro, etc.
vii. film-coated tablets are compressed tablets which are covered with
a thin layer or a film of polymeric substances to protect their contents from
moisture or to mask the taste of the ingredients.
viii. enteric-coated tablets are coated with substances
that resist solution in gastric fluid but disintegrate in the alkaline contents
of the intestine. Enteric coating is used for drugs with a gastric irritant action, for drugs which are unstable
in the acid medium of the gastric contents or if the drug should act on the
intestine. (e.g., Voltaren, Salazopyrin).
ix.
controlled-release tablets
are formulated to release the drug slowly over a prolonged period of time.
These dosage forms have been referred to as prolonged-release
(PR) or sustained-release (SR)
dosage forms as well.
2. Tablets for parenteral
administration
i. inserts
are intended for insertion into body orifices. Metronidazole, Isoconazole,
Clotrimazole are vaginal tablets (tabulettes
vaginales).
ii. pellets (tablets for implantation) are
small, sterile tablets, used by implantation when prolonged and continuous
absorption is desired (Estradiol, Disulfiram, etc.)
iii.
tablets for solutions
are used for preparing solutions for external use
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