Pharmacology Flashcards
Which layer of skin is most important for drug absorption?
Keratin layer
Describe the ‘brick and mortar’ structure of the keratin layer
Brick - corneocytes contain aggregated keratin embedding in filaggrin
Mortar - hydrophobic intercellular lipids that hold the corneocytes together (act as a reservoir for lipid soluble drugs)
What is the name of the substance a drug is carried in?
Vehicle (ointment, cream, gel)
What determines the choice of vehicle?
Physiochemical properties & the clinical condition
Which law is rate of absorption described by? What does it take into account?
Fick's Law Takes into account - partition co-efficient - diffusion co-efficient - length of diffusion pathway - concentration of the drug
Place the following in order of best absorbed to least absorbed; lipophilic drug in lipophilic base hydrophilic drug in hydrophilic base lipophilic drug in hydrophilic base hydrophilic drug in lipophilic base
- lipophilic drug in hydrophilic base
- lipophilic drug in lipophilic base
- hydrophilic drug in lipophilic base
- hydrophilic drug in hydrophilic base
What can be added to a drug to enhance absorption?
Excipients e.g. propylene glycol
What is used in transdermal patches to increase duration of effectiveness?
Excess non-dissolved drug helps to provide a constant rate of delivery
In terms of water content list the following most to least;
gel, paste, cream, powder, lotion, ointment
lotion - cream - ointment - gel - paste - powder
How does increased portioning arise?
From a reduction in the barrier function of the stratum corneum
Briefly outline the mechanism of action of glucocorticoids
Lipophilic molecules diffuse across the membrane and combine with GRalpha to produce shock proteins - the activated receipt which moves to the nucleus binds to DNA to switch on/off transcription
What is subcutaneous administration?
Insertion of a needle into adipose to allow a drug to reach the systemic circulation by diffusion into capillaries and lymphatics
What are the advantages of subcutaneous administration?
Slow absorption, suitable for oil based drugs, can introduce a depot of drug (slow release)
What is the disadvantage of subcutaneous administration?
Limited injection volume
What is the main advantage of giving drugs through skin?
Avoids first pass metabolism and absorption can be terminated rapidly
What drugs are suitable for transdermal delivery?
low molecular weight, moderately lipophilic, potent, short half life
State the advantages of transdermal delivery
Steady rate of delivery & user friendly
State the disadvantage of transdermal delivery
Few drugs are suitable - GTN, estradiol, nicotine
Describe the purpose of chemical enhancers
Used to increase permeability particularly for drugs that already cross the skin reasonably well
Name a chemical enhancer
Water - enhances pore pathway
Name four methods of physical enhancement
- iontophoresis (low voltage drives low weight molecules through skin)
- electroporation (high voltage leads to pore formation)
- sonophoresis (ultrasound increases permeability)
- microneedles (punch holes into skin)
What are the advantages of topical skin therapeutics?
Direct application and reduced systemic effects
What are the disadvantages of topic skin therapeutics?
Time consuming, difficult to get the correct dose & can be messy to use
Describe creams
Semisolid emulsions of oil in water that contain an emulsifier and preservative act to cool and moisturise due to high water content
