Formulations for Analgesia - Routes of Administration Flashcards
Benefits of IV
Rapid, no lag time Physician able to titrate the dose Predictable responses (incomplete absorption and variability is eliminated)
Problem with IV administration?
Trained medical staff needed so only in acute care
Benefit of transmucosal?
Avoid first pass metabolism via entering systemic circulation by jugular vein
How is transmucosal delivery possible? What makes mouth a good site of action?
Oral cavity rich in blood vessels therefore rapid onset and high blood levels
Problem with transmucosal delivery?
Surface area limited to only 100cm2 and only small lipophillic drugs absorbed
What is the main barrier to transdermal administration?
How is this overcome?
Physical barrier of stratum corneum
Main route of absorption through lipid channels to overcome this
Small molecular weight lipophillic drugs
How do transdermal drugs enter the blood?
Diffuse across the epidermis and dermis (rich blood supply)
What are the advantages of transdermal administration?
Can maintain drug plasma profile over several days in the therapeutic window so no dose dips in the night or dose dumping
Patient compliance good
Removal of device causes plasma levels to fall soon after
What is a problem with transdermal drug delivery?
Some drugs can be stored in hydrophobic regions of the skin
Stratum corneum also a major barrier (only able to move via lipid channels)
What are the two types of transdermal patch?
Matrix/monolith systems (drug suspension)
Rate limiting membrane
When may the rectal ROA be used?
If oral not available e.g. nausea and vomiting, upper GI disease affects absorption
If the drug is affected by pH, or enzymatic activity in the GI tract or that cause irritation if taken orally
Benefits of rectal ROA
Useful for infants, elderly and unconscious
For drugs with unacceptable taste
For candidates for abuse
To bypass hepatic first-pass metabolism
Disadvantages of rectal ROA
Unpredictable, erratic incomplete absorption
Inter and intra-subject variation
Difficult to administer for people
Popularity of doses vary
What is an epidural?
Injection into the epidural space via catheter - the outermost part of the spinal cord
Injection can cause loss of sensation by blocking the transmission of signals through nerve fibres in or near the spinal cord
What is intrathecal ROA?
Administration of solution by intrathecal catheter to the spinal cord
-invasive route
Injection into cerebral spinal fluid (CSF) therefore the bulk flow of CSF may be dominant in determining the properties of analgesia
