Download Routes of drug administration

Routes of drug
administration
Tuesday, May 2, 2017
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Objectives:
To discuss the peculiar features of the
various routes of drug administration
• To apply the advantages and
disadvantages of the various routes of
drug administration to optimize patient
therapeutic benefit
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Buccal/Sublingual
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Buccal or sublingual dosage form enable drugs to be taken
as smaller tablets held in the mouth or under the tongue.
Buccal tablets are often harder tablets [4 hour disintegration
time], designed to dissolve slowly.
Nitroglycerin, as a softer sublingual tablet [2 min
disintegration time] may be used for the rapid relief of
angina.
This ROA is also used for some steroids such as testosterone
and oxytocin while nicotine-containing chewing gum may be
used for cigarette smoking replacement.
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Advantages of buccal
sublingual administration:
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First pass - The liver is by-passed thus there is no loss of
drug by first pass effect for buccal administration.
Bioavailability thus is higher.
Rapid absorption - Because of the good blood supply to the
area absorption is usually quite rapid.
Drug stability - pH in mouth relatively neutral (cf. stomach acidic). Thus a drug may be more stable.
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Disadvantages
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Holding the dose in the mouth may be
inconvenient.
If any is swallowed that portion must be treated as
an oral dose and subject to first pass metabolism.
Only small doses can be accommodated easily.
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Rectal
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Most commonly used for suppository
or enema.
Some drugs given by this route include
aspirin, dipyrone, paracetamol,
theophylline, chlorpromazine and
some barbiturates
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Advantages of Rectal
route
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By-pass liver - Some of the veins draining
the rectum lead directly to general
circulation, thus by-passing the liver. There
is therefore reduced first-pass effect.
Useful - This route may be most useful for
patients unable to take drugs orally or with
younger children.
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Disadvantages of rectal
route
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Erratic absorption - Absorption is often incomplete
and erratic.
However for some drugs it is quite useful.
Researches are being conducted to look at
methods of improving the extent and variability of
rectal administration.
Not well accepted.
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Some Parenteral Routes of
Administration
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Intravenous
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Drugs may be given into a peripheral
vein over 1 to 2 minutes or longer by
infusion.
Rapid injections are used to treat
epileptic seizures, acute asthma, or
cardiac arrhythmias
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Advantages of IV
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Rapid - A quick response is possible
Total dose - The whole dose is delivered to the
blood stream. Large doses can be given by
extending the time of infusion.
Veins relatively insensitive to irritation by irritant
drugs.
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Disadvantages of IV
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Suitable vein may be difficult to locate.
May be toxic - Because of the rapid response, toxicity can be a
problem with rapid drug administrations (could then be given as an
infusion while monitoring for toxicity).
Requires trained personnel
Expensive - Sterility, pyrogen testing and larger volume of solvent
means greater cost for preparation, transport and storage.
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Subcutaneous
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This involves administration of the drug dose just under
the skin.
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Advantages:
Can be given by patient, e.g. in the case of insulin
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Absorption slow but usually complete.
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Absorption rate can be improved by massage or heat.
Vasoconstrictor may be added to reduce the absorption of a
local anesthetic agent, thereby prolonging its effect at the site
of interest.
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Disadvantages subcutaneous
administration
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Can be painful
Irritant drugs can cause local tissue
damage
Maximum of 2 ml injection thus often
small doses limit use.
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Intramuscular
Injection administered into the deltoid
muscle of the upper arm or the gluteal
muscle of the buttock.
 Advantages:
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Larger volume, than sc, can be given by IM
A depot or sustained release effect is possible
with IM injections, e.g. procaine penicillin
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Disadvantages of
intramuscular injection
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Trained personnel required for injections.
The site of injection will influence the absorption,
generally the gluteal muscle of the buttock is the
best site
Absorption is sometimes erratic, especially for
poorly soluble drugs, e.g. diazepam, phenytoin.
The solvent maybe absorbed faster than the drug
causing precipitation of the drug at the site of
injection.
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Inhalation
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Drugs administered as fine particles of
liquids or solids or as aerosols or spray.
The drug may be required for local or
systemic effects.
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Local effect - bronchodilators
Systemic effect - general anesthesia
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Advantages of inhalation
(Nasal) administration
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Rapid absorption, by-passing the liver
Absorption of gases is relatively efficient,
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solids and liquids are excluded if larger than 20
micron
only 10 % of the dose may be absorbed.
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Example of Drugs administered
by inhalation into the lungs
Drugs
Comments
Corticosteroids
Beclomethasone dipropionate, betamethasone valerate & triamcinolone
acetonide used for relief of brochial asthma
Ergotamine
tartrate
Available as a pressurized aerosol preparation & provides relief from
migraine much faster than from oral preparations
Sympathomimeti
cs
Fenoterol, rimiterol, salbutamol, salmeterol, & terbutaline are well
absorbed from the lungs giving early relief from asthmatic attack.
Sodium
cromoglycate
Well absorbed from the lungs when administered as a fine powder or
spray but poorly absorbed from the gastro-intestinal tract. Inhalation of
the powder may cause bronchospasm; isoprenaline may be
administered concurrently to minimize this effect.
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Topical
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Local effect - eye drops, antiseptic,
sunscreen, callous removal, etc.
Systemic effect - e.g., nitroglycerin
ointment.
Absorption through the skin, especially via
cuts and abrasions but also intact skin, can
be Tuesday,
quite
marked.
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Other Routes of
Administration
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Intra-nasal - some systemic absorption has
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Intra-arterial for cancer chemotherapy to
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Intrathecal directly into the cerebrospinal
been demonstrated for propranolol and some
low dose hormones
maximize drug concentrations at the tumor
site
fluid.
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