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Pharmacokinetics > Administering drugs topically > Flashcards

Administering drugs topically Flashcards

1
Q

Why are some drugs NOT administered orally?

A

Due to biological and chemical properties = the drugs may be destroyed and thus, not carry out the purpose its was created to do.
Due to risk of systemic side effects = whole spread side effects.

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2
Q

Which two effects are demonstrated when drugs are administered?

A
  • Systemic Effect

- Local Effect

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3
Q

Which three routes are used via the systemic administration?

A 
Enteral = Oral  
Parenteral = Injections ( IV / IM / SC / IA / ID )  
Topical = Sub - lingual / Transdermal Patch / Inhalation / Rectal
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4
Q

Which route is used via the local administration?

A

Topical = Creams / Intranasal Sprays / Occular Drops

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5
Q

Explain topical administration in terms of producing a local effect.

A

The drug is applied to a localised area of body surface in order to minimise systemic side effects and systemic absorption.

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6
Q

Explain topical administration in terms of producing a systemic effect.

A

Thee drug is applied to the body surface in order tot provide an alternative / convenient route into the blood.

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7
Q

What happens when a drug is administered via oral tablet?

A

First pass metabolism in the liver occurs = therefore, the drug enters the liver first.

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8
Q

What happens when a drug is administered via IV?

A

Enters the blood directly. (DIRECT ACCESS)

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9
Q

How can you bypass first pass liver metabolism?

A

Increase the dosage of the drug

Administer the drug via another route.

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10
Q

What happens when a drug is administered via buccal?

A

Reaches the body first and then the liver.

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11
Q

What happens when a drug is administered via topical?

A

Reaches the body site DIRECTLY.
Absorption via the skin and thus, systemic action occurs.
Results in stable blood levels.

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12
Q

What conditions is the topical local administration used for?

A 
Skin = Eczema  
Eye = Conjunctivitis
Nose = Hay - Fever
Lung = Asthma
Vagina = Thrush
Rectum = Constipation
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13
Q

What conditions is the topical systemic administration used for?

A

Skin = Contraception

Mouth (mucosal membranes) = Chest Pain

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14
Q

What formulation is used to deliver drugs administered topically for the skin?

A 
Cream 
Ointments
Powder
Lotions
Gels
Transdermal Patch
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15
Q

What formulation is used to deliver drugs administered topically for the nose and lungs?

A

Solutions and Powders

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16
Q

What formulation is used to deliver drugs administered topically for the eye or ear?

A

Solutions
Ointments
Creams

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17
Q

What formulation is used to deliver drugs administered topically for the rectum / colon?

A

Foams
Enemas
Suppositories

18
Q

What formulation is used to deliver drugs administered topically for the vagina?

A

Creams

Pessaries

19
Q

How are drugs are absorbed into the skin?

A

Drugs diffuse from the stratum corneum in to the epidermis into the dermis.
From the dermis it enters the capillary microcirculation.
Then from there, it enters the systemic circulation.

20
Q

What is the stratum corneum?

A

Outer layer of the epidermis.

The permeability barrier of the skin.

21
Q

What does lipophilic drug mean?

A

Utilises the intracellular route (crosses the cell wall)

= Goes THROUGH the cells.

22
Q

What does hydrophilic drug mean?

A

Utilises the intracellular route (diffusing in fluid filled spaces between the cells)
= Goes AROUND the cells.

23
Q

What layer does the drug have to pass in order to reach the site of action?

A

Epidermis Layer.

24
Q

What is the partition coefficient?

A

Ratio of concentrations of compounds in mixture of 2 substances = This mixture is IMMISCIBLE.

25
Q

What are the 2 types of ointments?

A

Non - Emulsifying = Lipophilic

Water Soluble = Lipophilic and Hydrophilic

26
Q

What are non - emulsifying ointments like?

A

Contains beeswax and paraffin = Contains few preservatives.
Messy and inconvenient.

27
Q

What are water soluble ointments like?

A

Allows passage of drugs into the skin.

Easily washed off = promotes hydration.

28
Q

What is the formula like for creams?

A

Either lipophilic or hydrophilic.

This penetrates the stratum corneum and allows the substance to rub in well.

29
Q

What is the disadvantage of using creams?

A

Contains preservatives = risk of immunological sensitisation.

30
Q

Why is formulation base essential and to not change medication?

A

Potency for medication can change if the medication is changed.
The ones with a fatter component = ABSORBS BETTER.

31
Q

How can you tell which ointment is fattier?

A

The one with MORE beeswax.

32
Q

What are the key points of formulations?

A

Target Site = Is the formulation appropriate to the site?
Drug Properties = Is the active ingredient of the drug stable in a particular formulation?
Acceptability to patient = Is the cream easy to apply?

33
Q

How do drugs administered orally enter the body?

A

Pass into the systemic circulation / ESCAPES the first pass metabolism.

34
Q

Examples of topical application for a systemic effect?

A

Inhaled Anaesthetics
Buccal Midazolam
Sublingual GTN tablet
Transdermal nicotine patch

35
Q

What is transdermal application?

A

Delivery system which releases the drug through a rate controlling membrane into the skin = systemic circulation.

36
Q

What are the key features of transdermal application?

A

Time relapsed delivery

Lipid Soluble drugs

37
Q

How does transdermal application work?

A

Polymer matrix = Adhesive which covers the whole patch.

The active compound is released via diffusion and through the membrane which covers the patch.

38
Q

What is a drug reservoir?

A

Drug layer has ‘liquid compartment’ which contains the drug solution.
Often this reservoir is encapsulated in a shallow mould.

39
Q

What are the benefits of a transdermal application?

A

Avoids fluctuation in plasma concentration.
Easy to administer and acceptable to patients.
Can be stopped easily.
There is prolonged drug action.

40
Q

What are the disadvantages of a transdermal application?

A

Only small enough molecules can penetrate the skin this way.
Local side effects.
Slow to initiate effect.
Not applying the patch properly will affect the dosage.

41
Q

What are the advantages of topical administration?

A

Targets the intended site of action.
Reduced risk of systemic side effects.
High drug concentration can be achieved.
Generally accepted by patients.

42
Q

What are the disadvantages of the topical route?

A

Still some systemic absorption of drugs.
Local side effect (stinging).
May be messy or inconvenient.
Rapid clearance = requires regular administration.

Pharmacokinetics (18 decks)

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