Routes Of Drug Administration

Dr. Onuwe A.

Outline

• Pre-test
• Introduction
• Factors governing choice of route
• Classification of drug routes
• Advantages and Disadvantages
• Clinical Scenarios
• Post-test
• Assignments

PRE-TEST

Label the routes of drug administration

Introduction

A drug

A substance which has a physiologic effect when INGESTED or otherwise INTRODUCED into the body.

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How do these substances get introduced into the body?

Choice of Route

• 1. Characteristics of the drug.
• 2. Emergency/routine use.
• 3. Site of action of the drug—local or systemic.
• 4. Condition of the patient (unconscious, vomiting, diarrhoea).
• 5. Age of the patient.
• 6. Effect of gastric pH, digestive enzymes and first-pass metabolism.
• 7. Patient’s/doctor’s choice (sometimes).

Classification of Routes of Drug Administration

ROUTES

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LOCAL SYSTEMIC

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ENTERAL PARENTERAL

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• Local route… drug is administered directly at point of lesion. Absorption of particular drug is minimal/absent from this point.
• Systemic route… drug is administered through one or a number of routes where absorption of said drug into blood stream is high and furthermore distributed all over the body.

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• Enteral route… administration of a drug through the gastrointestinal tract.

(recall anatomy of the G.I)

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• Parenteral route… any route of drug administration other than the enteral route

(attempt examples)

Local routes

1. Topical

Application of a drug to skin or mucous membrane.

1. Oral cavity
• Suspension e.g. Nystatin
• Troche e.g. clotrimazole
• Cream e.g. acyclovir
• Spray e.g. 10% lignocaine hydrochloride

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b. Gastrointestinal tract

a. Suspension e.g. antacids

b. tablets e.g. Neomycin

c. liquids e.g. Paraffin oil

c. Rectum/Anal canal

• Enema (administration of liquid form of drug into rectum) e.g. soap (evacuant), Methyprednisolone (retention)
• Suppository (administration of solid form of drug into rectum) e.g. bisacodyl

d. Ear, Eye, Nose drops e.g Gentamycin

e. Bronchi

As Inhalational drug e.g. Salbutamol

f. Skin

As creams, ointments or lotions e.g. Calamine lotion

g. Vagina

• Creams e.g. 1% clotrimazole
• Suppositories e.g. Clotrimazole

2. Deep tissues

Local administration of a drug can be achieved by use of needle and syringe to reach a deep tissues

Examples

• Intra-articular injection
• Nerve infiltration
• Retrobulbar injection

3. Intra-arterial route

administration of drug into and artery

• Diagnostic e.g. Angiography
• Therapeutic e.g. Limb malignancies

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Systemic routes

• Drugs administered by this route enter blood and produce systemic effects

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• Enteral vs Parenteral

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Oral Route 

• It is the most common and acceptable route for drug administration. Dosage forms are tablet, capsule, syrup, mixture, etc., e.g., paracetamol tablet for fever, omeprazole capsule for peptic ulcer are given orally.

Advantages

• Safer.
• Cheaper.
• Painless.
• Convenient for repeated and prolonged use.
• Can be self-administered.

Disadvantages

• Not suitable for emergency as onset of action of orally administered drugs is slow.

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• It is not suitable for/in:
• Unpalatable and highly irritant drugs.
• Unabsorbable drugs (e.g. aminoglycosides).
• Drugs that are destroyed by digestive juices (e.g. insulin).
• Drugs with extensive first-pass metabolism (e.g. lignocaine).
• Unconscious patients.
• Uncooperative and unreliable patients.
• Patients with severe vomiting and diarrhoea.

Sublingual Route

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• The preparation is kept under the tongue. The drug is absorbed through the buccal mucous membrane and enters the systemic circulation directly, e.g. nitroglycerin for acute anginal attack and buprenorphine for myocardial infarction.

Advantages

• Quick onset of action.
• Action can be terminated by spitting out the tablet.
• Bypasses first-pass metabolism.
• Self-administration is possible.

Disadvantages

• It is not suitable for:
• Irritant and lipid-insoluble drugs.
• Drugs with bad smell and taste.

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Rectal Route

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• Drugs can be given in the form of solid or liquid.

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1. Suppository: It can be used for local (topical) effect as well as systemic effect, e.g. indomethacin for rheumatoid arthritis.

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2. Enema: Retention enema can be used for local effect as well as systemic effect. The drug is absorbed through rectal mucous membrane and produces systemic effect, e.g. diazepam for status epilepticus in children.

Parenteral route

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• Routes of administration other than enteral route are called parenteral routes.

Advantages

• Onset of action of drugs is faster; hence it is suitable for emergency.
• Useful in:
• Unconscious patient.
• Uncooperative and unreliable patients.
• Patients with vomiting and diarrhoea.
• It is suitable for:
• Irritant drugs.
• Drugs with high first-pass metabolism.

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• Drugs not absorbed orally.
• Drugs destroyed by digestive juices.

Disadvantages

• Require aseptic conditions.
• Preparations should be sterile and is expensive.
• Requires invasive techniques that are painful.
• Cannot be usually self-administered.
• Can cause local tissue injury to nerves, vessels, etc.

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Inhalation

• Volatile liquids and gases are given by inhalation for systemic effects, e.g. general anaesthetics.

Advantages

• Quick onset of action.
• Dose required is very less, so systemic toxicity is minimized.
• Amount of drug administered can be regulated.

Disadvantages

• Local irritation may cause increased respiratory secretions and bronchospasm.

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Intravenous (i.v.) route

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Drugs are injected directly into the blood stream through a vein. Drugs are administered as:

1. Bolus: Single, relatively large dose of a drug injected rapidly or slowly as a single unit into a vein.

• For example, i.v. ranitidine in bleeding peptic ulcer.

2. Slow intravenous injection: For example, i.v. morphine in myocardial infarction.

3. Intravenous infusion: For example, dopamine infusion in cardiogenic shock; mannitol infusion in cerebral oedema; fluids infused intravenously in dehydration.

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Advantages

• Bioavailability is 100%.
• Quick onset of action; therefore, it is the route of choice in emergency, e.g. intravenous diazepam to control convulsions in status epilepticus.
• Large volume of fluid can be administered, e.g. intravenous fluids in patients with severe dehydra- tion.
• Highly irritant drugs, e.g. anticancer drugs can be given because they get diluted in blood.
• Hypertonic solution can be infused by intravenous route, e.g. 20% mannitol in cerebral oedema.
• By i.v. infusion, a constant plasma level of the drug can be maintained, e.g. dopamine infusion in cardiogenic shock.

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Disadvantages

• Once the drug is injected, its action cannot be halted.
• Local irritation may cause phlebitis.
• Self-medication is not possible.
• Strict aseptic conditions are needed.
• Extravasation of some drugs can cause injury, necrosis and sloughing of tissues.
• Depot preparations cannot be given by i.v. route.

Precautions

• Drug should usually be injected slowly.
• Before injecting, make sure that the tip of the needle is in the vein.

Intramuscular (i.m.) route

Drugs are injected into large muscles such as deltoid, gluteus maximus and vastus lateralis, e.g. paracetamol, diclofenac, etc. A volume of 5–10 mL can be given at a time.

Advantages

• Absorption is more rapid as compared to oral route.
• Mild irritants, depot injections, soluble substances and suspensions can be given by this route.

Disadvantages

• Aseptic conditions are needed.
• Intramuscular injections are painful and may cause abscess.
• Self-administration is not possible.
• There may be injury to the nerves.

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Intradermal route

The drug is injected into the layers of the skin, e.g. Bacillus Calmette–Guérin (BCG) vaccination and drug sensitivity tests. It is painful and only a small amount of the drug can be administered.

Subcutaneous (s.c.) route:

The drug is injected into the subcutaneous tissues of the thigh, abdomen and arm, e.g. adrenaline, insulin, etc.

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Advantages

• Self-administration is possible (e.g. insulin).
• Depot preparations can be inserted into the subcutaneous tissue, e.g. norplant for contraception.

Disadvantages

• It is suitable only for nonirritant drugs.
• Drug absorption is slow; hence it is not suitable for emergency.

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• Intrathecal route: Drug is injected into the subarachnoid space (spinal anaesthetics, e.g. lignocaine;antibiotics, e.g. amphotericin B, etc.)

• Transdermal route: The drug is administered in the form of a patch or ointment that delivers the drug into the circulation for systemic effect (Fig. 1.2).
• For example, scopolamine patch for sialorrhoea and motion sickness, nitroglycerin patch/ointment for angina, oestrogen patch for hormone replacement therapy (HRT).

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Advantages

• Self administration is possible
• Adherence is better
• Duration of action is prolonged
• Systemic side effects are reduced
• Provides a constant plasma concentration of drugs

Disadvantages

• Expensive
• Local irritation
• Patch may fall of un-noticed

Intravaginal

Drugs administered into the vagina to achieve systemic effects.

• Suppositories e.g. progestins
• Vaginal rings e.g. oestrogen

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Clinical scenario

• 3yr old female presented at the EPU with a history of Fever, refusal to feed, vomiting, passage of loose watery stool and 2 episodes of convulsions.
• O/E– moderately dehydrated with temp. of 40.2, Tonic-clonic seizures noticed.
• DISCUSS appropriate routes of administration

• 54yr old woman with established menopausal symptoms which are severe, planned for hormone replacement therapy.
• DISCUSS possible routes of hormone replacement.

POST-TEST

Post test

Label

Assignments

• Define a Pessaries and give examples.
• Discuss first-pass metabolism.

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THANK YOU FOR YOUR ATTENTION!!