Drug administration and distribution Flashcards
Main routes of drug administration
Oral, sublingual, rectal, topical, inhalation and injection
Two main ways in which drugs move
Bulk flow, through blood stream, lymph vessels or cerebrospinal fluid
Diffusion- molecule by molecule over a shorter distance
Oral administration explained
Small molecule drug swallowed- little absorption occurs until drug enters the small intestine. Peptides are prone to digestion so little success with oral administration of biopharmaceuticals
Sublingual definition
Drug is kept in contact with the oral mucosa (dissolves in mouth).
When is sublingual absorption used? explained
Absorption from the oral cavity is sometimes useful when a rapid response is required, especially if the drug is unstable at gastric pH and denatured.
Drugs absorbed in this way pass directly into systemic circulation with outing entering the portal system
Example of sublingual absorption
Glyceryl trinitrate used in this way to relieve symptoms of angina
Rectal administration explained
Used for drugs that are required to produce a local effect- mesalazine suppositories or enemas or drugs that produce systemic effects.
Rapid and more complete than oral, as only a fraction of capillary drainage returns to the portal system via the portal vein.
Beneficial in patients who cannot swallow food.
Different forms of topical administration
Cutaneous, sniffing, eye
Cutaneous administration explained
Used when a local effect on skin is required. Can be absorbed, such as ibuprofen, however relatively poorly through unbroken skin.
Lipid soluble drugs can be absorbed through stick on patches, such as fentanyl, and hormones
Nasal sprays explained
Drugs with local effects, such as saline solution to relieve symptoms of congestion. Also drugs such as antidiuretic hormone and calcitonin.
Absorption believed to take place through mucosa overlying nasal associated lymphoid tissue.
Eye drops explained
Rely on absorption through the epithelium of the conjunctival sac. Little systemic absorption.
Example of eyedrop
Dorzolamide, a carbonic anhydrase inhibitor, given to patients to lower ocular pressure in patients with glaucoma
Administration by inhalation explained
Route used for volatile and gaseous anaesthetics, with the lung surging as the route of administration and elimination.
Drugs in aerosol form, such as salbutamol. Limit systemic effects, however still can occur, such as tremor from salbutamol.
Different forms of injection
intravenous, subcutaneous, intramuscular, intraspinal
Intravenous injection explained
Fastest route of drug administration. Involves needle insertion right into the vein
Subcutaneous injection explained
Delivered between the skin and the muscle. Usually injected into the fat tissue behind the arm, insulin and MMR
Intramuscular injection explained
Delivers substance deep into muscles, which is rapidly absorbed by surrounding blood vessels. Most vaccinations in this form
Intraspinal injection explained
Into the subarachnoid space via a lumbar puncture used for specialised purposes, such as general anaesthetic, epidural or antibiotics in the case of rapid sepsis
Important as do not need to diffuse across the blood brain barrier as automatically in cerebrospinal fluid.
Factors governing choice of route
- rate of absorption from site of administration and transport to site of action
- desire to administer drug close to its site of action
- susceptibility of drug to degradation or metabolism
- desired time course of action
What is the blood brain barrier?
A continuous layer of epithelial cells joined by tight junctions and surrounded by pericytes . The brain is consequently inaccessible to many drugs of low lipid solubility
