Dr Ibanda Hood explains the benefits of the different routes of drug administration.

1. Routes of drug administration
Dr Ibanda Hood

2. What determines the route by which a drug
should be administered to a patient?
1. Properties of a drug
 Water/lipid solubility of a drug
 Ionisation of a drug
2. Therapeutic objectives
 Desire to limit side effect
 need to achieve quick onset of action
 need to prolong action of a drug

3. Mention at least four routes of drug
administration.
• Oral
• Sublingual
• Intravenous
• Intravenous
• Intramuscular
• Subcutaneous
• Oral inhalation
• Nasal inhalation
• Intrathecal/intraventricular
• Topical
• Transdermal
• Rectal

4. What are the Advantages and
Disadvantages of each Routes of Drug
Administration?

5. Oral route
advantages
• Safe
• Convenient
• Economic (no needles .etc.)
• May easily reverse drug
overdose.
disadvantages
• Limited absorption of some
drugs e.g. polar drugs.
• Food may affect absorption.
• One needs patient’s
compliance.
• First pass effect: drug may
get metabolised before
reaching circulation

6. Intravenous
advantages
• Absorption is not needed for a
drug to reach sit of action.
• Quick onset of action.
• Its Ideal if a drug is given in
large volumes
• Good for irritating drugs.
• Better a patient is unconscious.
• You can titrate the dose
• It’s Ideal for peptides and other
High molecular weight drugs
Disadvantages
• Its unsuitable for drugs that
are oily or poorly absorbed.
• Bolus injection may cause
serious adverse effects
• It’s not economic like oral is.
• Most drugs must be given
slowly
• Needs strict aseptic technique
• It may not be easy to reverse
ovedose

7. Subcutaneous
absorption depends on diluents used; aqueous diluents lead to prompt absorption, whereas depot preparation
are slow and sustained
advantages
• Suitable for slow release
drugs e.g. Insulin
• Ideal for poorly soluble
suspension
Disadvantages
• pain and necrosis if the drug
is irritating
• Not good if drug is given in
large volumes

8. Intramuscular
absorption depends on diluents used, aqueous diluents lead to prompt absorption,
whereas depot diluents are slow and sustained
Advantages
• Suitable if drug volume is
moderate
• May be used when vehicle is
oily
• May be used when substance
is mildly irritating e.g.
Benzathine penicillin
• Better than IV if the patient
has to inject himself.
• Can be used if patient is
unconscious
• No first pass effect
Disadvantages
• Can be painful
• Intramuscular hemorrhage if
patient has bleeding disorder
• Requires aseptic technique
• Not as economic as oral
• LAB tests like Creatine kinase
may be affected
• Not good for irritating drugs
like anti-cancer agents
• May not easy to reverse
overdose e.g. by lavage and
chelation

9. Transdermal (patch)
It leads to slow and sustained absorption
Advantages
• Not affected by First pass
effect
• Good for lipophilic drugs
• Ideal for drugs the are
quickly metabolised and
eliminated from the body
• Self administration is easy
• It’s convenient
• It’s painless
• Economical compared to IV
Disadvantages
• Some patients are allergic
to patches.
• The drug must be lipophilic.
• May cause delayed delivery
of a drug to the site of
action.
• It’s useful in drugs that can
be taken in small daily doses
e.g. Contraceptives e.t.c

10. Rectal
absorption is erratic and variable
Advantages
• Partially bypasses first-pass
effect.
• Drugs are not destroyed by
stomach acid.
• Ideal for drugs that cause
vomiting
• It’s Ideal in patient who are
vomiting, convulsing or
comatose.
Disadvantages
• Drug may irritate rectal the
mucosa
• Many patients don’t like this
route

11. Inhalation
Advantages
• Absorption is rapid
• Drug can have an immediate
effect
• Effective for patients with
respiratory problems
• Dose can be titrated
• We use lower doses compared
to oral route (for a given drug).
This is because the drug is
delivered directly to site of
action-the lungs.
• There are fewer systemic side
effects
Disadvantages
• A drug can enter the brain
quickly leading to addiction (
Clark et al 2012, pp. 5)
• Patient may have difficulty
regulating dose
• Some patients may have
difficulty using inhalers
• Spacers may introduce costs.

12. sublingual
Advantages
• Bypasses first pass effect
• Bypasses destruction of the
drug by stomach acid
• Drug’s stability is not
affected. This is because
saliva has a relatively
neutral PH.
• It may cause immediate
pharmacological effect.
Disadvantages
• It limited to certain types of
drugs.
• Limited to drugs that can be
taken in small quantities.
• Part of the drug is
swallowed and this reduces
the drug that reaches the
site of action.