Dosage forms of drugs / Classification dosage forms of drugs / Dosage forms of drugs pharmacology
Dosage forms of drugs
Dosage form is a product suitable for administration
of a drug to a patient. Every active ingredient
(drug) has to be formulated by adding other
substances (excipients, diluents, preservatives,vehicles, etc.) according to a specific recipe and
packaged into a specific ‘dosage form’ such as
tablet, elixir, ointment, injection vial, etc. which
is then administered to the subject. The dosage
form provides body to the drug, demarkates single
doses, protects the active ingredient(s), and makes
it suitable for administration in various ways.
The important dosage forms are briefly described
below
Solid dosage forms
1. Powders
The drug is in a dry and finely
pulverised state. If the drug is for oral
administration, each dose has to be wrapped
separately or packed in sachets; therefore this
dosage form is inconvenient and unpopular
except when the quantity is several grams,
e.g. oral rehydration salts. Powders for topical
application (dusting powders) are supplied as
bulk powders in metallic or plastic containers
with holes for sprinkling. Effervescent powders
contain granulated sod. bicarbonate and citric
or tartaric acid. They react when dissolved in
water to liberate CO2
causing bubbling.
2. Tablets
The drug is powdered or granulated,
mixed with binding agents, and other
excipients, and compressed/moulded into
discoid, oblong or other shapes suitable for
swallowing. The tablet may be plain or sugar
coated or film coated. Other specialized types
of tablets are:
- Chewable tablets—can be chewed and swallowed, ingredients must be pleasent tasting.
- Dispersible tablets—the tablet is dropped in a small quantity of water, wherein it disperses quickly; the solution is then gulped.
- Sublingual tablets—put under the tongue, the drug is rapidly absorbed from the mouth.
- Enteric coated tablet—the tablet is coated with a material that does not dissolve in the acidic medium of the stomach; the tablet disintegrates only on reaching the duodenum.
- Sustained/Extended release tablets—These contain drug particles which are coated to dissolve at different rates. The active ingredient is made available for absorption over a longer period of time. The duration of action of short acting (2-6 hours) drugs can be extended to 12 hours or more.
- Controlled release tablets—A semipermeable membrane controls the release of the drug – prolonging its duration of action.
3. Pills
These are archaic dosage forms in which
the drug powder is mixed with honey/syrup
to make a sticky mass. This is then rolled into
spherical/oval bodies meant to be swallowed.
The term is often loosely applied to tablets as
well.
SECTION 1
4. Capsules
These are water soluble cylindrical
containers made of gelatin which are filled with
powdered or liquid medicament. The container
dissolves on swallowing so that the drug is
released in the stomach. Soft gelatine capsules
dissolve very rapidly and generally contain
liquid medicament. Enteric coated capsules
are designed to dissolve only on reaching the
ileum. Spansules are extended release capsules
which are packed with granules of the drug
having different coatings to dissolve over a
range of time periods.
5. Lozenges
These are tablet-like bodies of
various shapes containing the drug along with
a suitable gum, sweetening and flavouring
agents. They are to be retained in the mouth
and allowed to dissolve slowly, providing the
drug for local action in the mouth and throat.
6. Suppositories
These are conical bullet- shaped
dosage forms for insertion into the anal canal,
in which the drug is mixed with a mouldable
f
irm base that melts at body temperature and
releases the contained drug. Oval or suitably
shaped bodies for vaginal insertion are called
‘pessaries’, while elongated pencil-like cones
meant for insertion into male or female urethra
are called bougies.
Liquid dosage forms
1. Aqueous solutions
They contain the drug
dissolved in water, and may be meant fororal, topical or parenteral administration.
Oral drug solutions often contain sweetening
and flavouring agents. Preservatives have to
be mostly added because shelf-life of watery
solutions is short.
2. Suspensions
are dispersion of insoluble
drugs in water with the help of a suspending
agent. Emulsions are uniform mixtures of two
immiscible liquids (mostly oil and water) in
which droplets of one (dispersed phase) are
suspended in the other (continuous phase)
with the help of an amphiphilic emulsifying
agent. Milk is a naturally occurring emulsion.
Both suspensions and emulsions tend to settle
down on keeping; should be shaken thoroughly
before use.
3. Elixirs
are hydro-alcoholic solutions of drugs,
usually sweetened with syrup and flavoured by
fruit extracts. Syrups have higher concentration
of sugar and are thicker in consistency. Drugs
that deteriorate in aqueous medium can be
dispensed as ‘dry syrups’ which is reconstituted
by adding water and shaking. The reconstituted
syrup must be used within a few days. Linctus
is a viscous syrupy liquid meant to be licked
slowly for soothing the throat. It generally has
menthol to impart cooling sensation, and an
antitussive.
4. Drops
These are relatively more concentrated
solutions of medicaments meant for oral
ingestion or external application to eye, nose or
ear canal. Oral drops are the preferred dosage
form for infants and young children. Eye/
nasal drops should be isotonic. Eye drops need
sterilization. Drops are supplied in vials with
a nozzle or alongwith a dropper for accurate
dosing.
5. Lotions
These are solutions, suspensions or
emulsions meant for external application to
the skin without rubbing. They generally have
soothing, cooling, protective or emollient
property and are better suited than creams
or ointments for hairy skin. Liniments are
similar preparations which generally contain
counterirritants, and are to be rubbed on the
skin to relieve pain and cause rubefaction.
6. Injections
These are sterile solutions or
suspensions in aqueous or oily medium for
subcutaneous or intramuscular administration.
Only aqueous solutions (not suspensions)
are suitable for intravenous (i.v.) injection,
because particles in suspension and oils
injected i.v. can cause embolism. Injections
are supplied in sealed glass ampoules or
air tight rubber capped vials. Ampoules are
broken just before injection, and usually
contain a single dose. Drug from the vial is
sucked in a syringe by piercing the rubber
cap. Vials may be single or multi-dose. Drugs
which are unstable in solution are supplied as
dry powder vials. Sterile solvent is injected
in the vial just before it is to be administered,
and the dissolved/suspended drug is then
sucked out into the syringe. Some drugs like
insulin are also supplied in prefilled syringes
and pen injectors. Large volume i.v. infusions
are marketed in glass/polypropylene bottles.
Semisolid dosage forms
1. Ointments
These are greasy semisolid
preparations meant for external application to
the skin, eye, nasal mucosa, ear or anal canal.
The drug is incorporated in an oily base, such
as soft or hard paraffin, wool fat, bee’s wax,
etc. Ointments are not suitable for oozing
surfaces, because they are more occlusive and
donot allow evaporation of water. Rather they
are good for dry, chronic lesions. Creams are
similar to ointment but the base is a water in oil
emulsion. The medicament is better absorbed
into the skin from creams than from ointments,
and creams are cosmetically more acceptable
than ointments.
2. Pastes
These are nongreasy preparations
of thick consistency containing hydrophilic
adhesive powders such as starch, prepared
chalk, aluminium/magnesium hydroxide,
zinc oxide, carboxy methylcellulose, etc.
which swell by absorbing water. Pastes may
contain viscous nonoily liquids like glycerol
or propylene glycol. Pastes can be applied to
inflamed or excoriated skin, oozing surfaces
and mucous membranes. Toothpastes are items
of personal hygiene, and medicated toothpastes
are extensively used in dentistry.
3. Gels
The medicament is incorporated in
a viscous colloidal solution of gelatin or
similar material and is usually dispensed in
collapsible tubes. They are meant for external
application to the skin or mucosa and provide
longer duration contact, but are nongreasy
and washable with water. Gels are suitable for
application to hairy skin, and are commonly
applied to oral ulcers because they are better
retained than aqueous solutions.
Inhalations
Drugs which are gases or volatile liquids can
be administered by inhalation carried into air or
oxygen with the help of a mouth piece, face mask,
hood or endotracheal tube. Nonvolatile liquids
and fine particle solids can be aerosolized using
a metered dose inhaler, jet nebulizer, rotahaler
or spinhaler for inhalation through the mouth.
Pressurized metered dose inhalers (PMDIs)
are hand-held devices which use a propellant,
mostly hydrofluoroalkane (HFA), and deliver a
specified dose of the drug in aerosol form per
actuation. Jet nebulizers produce a mist of the
drug solution generated by pressurized air or
oxygen. Rotahaler is also a portable device in
which a capsule (rotacap) containing very fine
powder of the drug is punctured during actuation
and the released particles are aerosolized by the
inspiratory airflow of the patient. A propellant can
also be used in some spin halers. Efficacy of the
aerosolized drug depends on the particle size: 1–5
mm diameter particles deposit on the bronchioles
and effectively deliver the drug. Larger particles
settle on the oropharynx, while <1 mm particles
donot settle anywhere and are exhaled out.
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