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Routes of drug administration

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Most drugs can be administered by a variety of routes. The choice of appropriate route in a given situation depends both on drug as well as patient related factors.

Factors governing choice of route:

⦁    Physical and chemical properties of the drug (solid/liquid/gas; solubility, stability, ph, irritancy).
⦁    Site of desired action – localized and approachable or generalized and not approachable.
⦁    Rate and extent of absorption of the drug from different routes.
⦁    Effect of digestive juices and first pass metabolism on the drug.
⦁    Rapidity with which action is desired (emergency or routine treatment).
⦁    Accuracy of dose required (IV or inhalation can provide fine tuning).
⦁    Condition of the patient (unconscious, vomiting).

Routes divided into:

1.    Local routes
2.    Systemic routes

Local routes

Local routes can only be used for localized lesions at accessible sites and for drugs whose systemic absorption from these sites are minimal or absent.

High concentrations are attained at the desired site without exposing the rest of the body. Systemic side effects or toxicity are consequently minimized.

Local routes include:

1.    Topical – refers to external application of the drug to the surface for localized action. Its more convenient and encouraging to the patient. Drugs can be conveniently delivered to localized lesions on skin, nasal mucosa, eyes, ear canal, anal canal or vagina in form of lotion, ointment, cream, powder, paints, suppositories or pessaries.

⦁    Non- absorbable drugs given orally for action on g.i. mucosa (sucralfate, vancomycin),

⦁    Inhalation of drugs for action on bronchi (salbutamol).

⦁    Irrigating solutions/jellys (povidone iodine, lidocaine)

2.    Deeper tissues – certain deep areas can be approached by using a syringe and needle but the drug should be such that systemic absorption is slow e.g. intra-articular injection (hydrocortisone acetate or infiltration around a nerve.

3.    Arterial supply – close intra-arterial injection is used for contrast media in angiography, anticancer drugs can be infused in femoral or bronchial artery to localize the effect for limb malignancy.

Systemic routes

The drug is intended to be absorbed into the blood stream and is distributed all over, including the site of action, through circulation.

1.    Oral – oldest and commonest mode of drug administration.


⦁    Safer
⦁    Convenient
⦁    Does not need assistance
⦁    Non invasive
⦁    Often painless
⦁    Cheaper
⦁    Medication does not need to be sterile.
⦁    Both solid dosage forms (tablets, capsules, powders, spansules) and liquid dosage forms (elixirs, syrups, emulsion, mixtures) can be given orally.


⦁    Slower action of drugs – not suitable for emergencies.
⦁    Unpalatable drugs (chloramphenicol) are difficult to administer. Drug administered in capsule form.
⦁    May cause nausea and vomiting (emetine).
⦁    Cannot be used in uncooperative / unconscious / vomiting patient.
⦁    Variable and erratic absorption of certain drugs, certain drugs not absorbed (streptomycin).destruction of some drugs by digestive juices (penicillin G, insulin) or liver (GTN, testosterone, lidocaine).

2.    Sublingual or buccal

⦁    Tablet or pallet containing the drug is placed under the tongue or crushed in the mouth and spread over the buccal mucosa.
⦁    Only lipid soluble and non-irritating drugs can be administered.
⦁    Absorption is relatively rapid – action can be produced within minutes.
⦁    The liver is by passed and drugs with high first pass metabolism can be absorbed directly into systemic circulation.
⦁    Drugs given sublingually include, GTN, desamino-oxytocin.

3.    Rectal

⦁    Certain irritant and unpleasant drugs can be put into rectum as suppositories or retention enema for systemic effect.
⦁    Can be used in patient with recurrent vomiting or unconscious.
⦁    Rather inconvenient and embarrassing and absorption slower, irregular and unpredictable, though diazepam solution is rapidly and dependably absorbed from the rectum in children.
⦁    Drug absorbed into the external haemorrhodal veins (about 50% by passes the liver), but not that absorbed into the internal haemorrhoidal veins.
⦁    Rectal inflammation can result from irritant drugs.
⦁    Diazepam, indomethacin, paraldehyde, ergotamine and few other drug can be given rectally.

4.    Cutaneous
⦁    Highly lipid soluble drugs can be applied over skin for slow and prolonged absorption. The liver is by passed.
⦁    Absorption of the drug can be enhanced by rubbing the preparation or using an oily base.
⦁    Examples include: transdermal patches of GTN, fentanly, nicotine and estradiol.
⦁    Most have been designed to last 1-7 days.
⦁    Local irritation and erythema may occur but is generally mild and may be reduced rotation of the site of application.
⦁    It avoids plasma concentration fluctuations and also by passes the first pass effect.
⦁    Better patient compliance.

5.    Inhalation
⦁    Volatile liquids and gases are given by inhalation for systemic action e.g. general anesthetics.
⦁    Absorption takes place from alveoli and action is very rapid.
⦁    When administration is discontinued the drug diffuses back and is rapidly eliminated in expired air.

6.    Nasal
The mucosal membrane can readily absorb many drugs; digestive juices and liver are by passed. Examples includes: desmopressin as nasal spray or nebulized solution.

7.    Parenteral (par – beyond; enteral – intestinal)
⦁    Administration by injection which takes the drug directly into the tissues fluid or blood without having to cross the intestinal mucosa.

⦁    Overcomes limitations of oral administration.
⦁    Faster and sure drug action.
⦁    Can be used in unconscious, uncooperative, vomiting patient.
⦁    By passes liver and digestive juices.

⦁    Preparation has to be sterile.
⦁    Cost
⦁    Painful
⦁    Assistance by another person needed, though self injection possible e.g. insulin.
⦁    Chances of tissue injury.

i.    Subcutaneous (s.c)
Drug injected into the loose subcutaneous tissue which is richly supplied by nerves (irritant drugs can not be administered)
⦁    Absorption slower than intramuscular injection.
⦁    Only small volumes can be injected s.c.

ii.    Intramuscular (i.m)
⦁    Drug injected into one large skeletal muscle – deltoid, triceps, gluteus maximus.
⦁    Self injection not possible but is less painful.

iii.    Intravenous (i.v)
⦁    Drug injected as a bolus or infused slowly over hours into one superficial vein.

⦁    The drug reaches directly into the blood stream and action produced immediately (useful in emergency).
⦁    Highly irritant drugs can be given.
⦁    Small dose of drug required, bioavailability is 100%.
⦁    Large volumes can be infused.

⦁    Only aqueous solutions can be given.

Post References

  • MSD Manuals, Katzung textbook of basic and clinical pharmacology, NCBI

  • Revised on: 2021-06-24 01:50:23