Routes of Drug Administration Flashcards
Prof. Soremekun
What are the two major classifications of drug administration route?
i. Enteral e.g. oral, rectal.
ii. Parenteral e.g. IM, IV, SC, ID
The choice of route depends on
convenience and expedience
What is parenteral route?
By definition, parenteral drug administration refers to drugs given by routes other than the digestive tract.
In common medical usage, the term excludes topical and inhalation administration and includes only the various hypodermic routes e.g. IV, IM, SC,
Drug absorption from parenteral sites is determined by ________
i. The physiochemical properties of the drug
ii. The dosage form
iii. Certain physiologic and anatomic factors.
Most drug solutions should be injected over a 1-2 minutes period.
True or False?
True.
This is to avoid excessively high drug concentrations in the blood and other highly perfused tissues immediately after the injection.
There is no absorption involved in the pharmacokinetic process of IV drugs.
True or False?
True.
No membrane is crossed hence no diffusion is required for absorption.
Usual dose of 150-250mg of phenytoin sodium should be injected at a rate not exceeding ______
50mg/min
What happens if an IV drug is injected too rapidly?
The drug may be precipitated in the vein if injected too rapidly and may cause damage to the veins (phlebitis)
Mention 3 advantages of IV administration.
- It is produces rapid response
- The whole dose is delivered to the blood stream. Hence more bioavailability.
- Veins are relatively insensitive to irritant drugs
Mention 4 disadvantages of IV administration.
- It may be difficult to find a suitable vein
- There is risk of toxicity
- Requires a trained personnel
- Greater cost of preparation
- Insoluble materials e.g. drug suspensions cannot be given by intravenous route because they may cause embolism
What are the 3 commonly used sites for IM administration?
i. The arm (deltoid) - highest vascularity
ii. The thigh (vastus lateralis)
iii. The buttocks (gluteus maximus)
Mention 5 factors that influence absorption from the IM sites.
i. Vascularity of the injection site (most important)
ii. Ionisation degree of the drug
iii. Lipid solubility of the drug
iv. Volume of injection
v. Osmolality of the solution
Mention 3 advantages of IM administration.
- Absorption by IM route is relatively fast
- It is used when prompt (not immediate) effect is required.
- It is easier to administer than IV.
Mention 5 disadvantages of IM administration.
- More painful than I.V.
- Does not always assure rapid or complete absorption
- Drug may precipitate at injection site, especially for poorly soluble drugs (e.g. phenytoin, digoxin, diazepam).
- The solvent may be absorbed faster than the drug causing precipitation at site of injection
- Irritation around injection site is common
When is the SC route preferred?
The route is usually chosen when a slower rate of absorption is required, in order to avoid:
- Too intense a response
- Too short a response
- Frequent injections
Mention 2 examples of drugs given via SC route.
- Insulin
- Sodium heparin
- Epinephrine
- Hormones used in contraception
Mention 3 advantages of SC.
- Absorption is slow so they produce a prolonged effect
- Risk of toxicity is lower than IV
- Medical supervision is not required
Mention 3 disadvantages of SC administration.
- Use is limited for small dose drugs.
- Can be painful
- Irritant drugs can cause tissue damage.
Intra-dermal route is commonly used for __________
diagnostic and screening procedures e.g. allergy testing, tuberculin test
Briefly describe intrathecal, intraventricular and intra-arterial routes of administration.
Intrathecal administration involves injecting a drug directly into the spinal canal (subarachnoid space) to reach the cerebrospinal fluid (CSF).
Intraventricular administration involves delivering drugs directly into the ventricles of the brain.
Intra-arterial administration delivers drugs directly into an artery. It is often used in cancer chemotherapy to achieve high drug concentration at tumour site.
What are the factors that facilitate rapid absorption by inhalation?
i. Large surface area of the alveoli
ii. High permeability of the alveolar epithelium
iii. Rich blood supply to this area
What is topical administration?
It is the application of medication to the skin or membranes to produce local or systemic effect.
It may be applied to the skin, eye, nose, throat, ear and vagina.
Briefly describe sublingual and buccal routes of administration.
Sublingual: The tablets are placed beneath the tongue e.g. Nitroglycerin for angina (2 min disintegration)
Buccal: The tablets are placed in the cheek pouch and retained in the mouth. Buccal tablets are often harder tablets (4 hour disintegration time) designed to dissolve slowly.
What are the advantages of sublingual and buccal administration?
- First pass metabolism is by-passed, thus bioavailability is higher
- Rapid absorption due to high vascularity
- Drug stability due to relatively neutral pH in mouth
What are the disadvantages of sublingual and buccal administration?
- Holding drug in the mouth is inconvenient.
- Only small doses can be accommodated easily.
The rectum is highly vascularised, but it has a relatively small surface area, hence absorption is slow.
True or false?
True
Mention 3 advantages of the oral route of administration.
- Causes no pain
- No supervision is required
- It is cheap
- A variety of dosage forms e.g. suspensions, tablets, capsules
Mention 3 disadvantages of the oral route of administration.
- Low solubility drugs may suffer poor bioavailability
- First-pass metabolism may lead to low bioavailability
- Some drugs are not suitable for the pH of gastric acid
- Food and GI motility can affect drug absorption.
- Not useful for unconscious patients.
- May have negative effects on normal flora of the guts
Absorption is slower with food for some drugs such as _______.
- Tetracycline
- Penicillin
Absorption is higher for propranolol after food.
True or False?
True
Absorption is higher after a fatty meal for _________.
i. Griseofulvin
ii. Halofantrine
iii. Artemisinin
