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skin pharmacology
Pharmacology
Shatha Kh. Shahwan
18-10-2015
Ahmad Tarifi
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Skin pharmacology
-Topical drugs are the drugs that you apply on the skin (Creams, ointments,
lotions, patches (nicotinic patch))
-Systemic drugs run through the whole body (pills, IV, IM)
The following are the aspects of comparison between the topical and the
systemic drugs
1. Concentrations at the site of infection: topical drugs are more
concentrated at the site of infection bcz you are applying the drug
directly on the site of the infection
2. Side effects : the systemic drugs have more side effects, bcz the drug is
going to run through your whole body, and it’s going to go to the
brain, kidneys, GIT( note : the side effects of the topical drugs( usually
it doesn’t have side effects ) increase when it’s applied for a long time
or the amount that is being applied is more than enough (that it reaches
a point where it can cause prominent side effects)
3. Hypersensitivity reaction in topical drugs is more prominent( Rash,
minor inflammation, blisters) >>>> this is useful in skin test where we
can test the patient if he is allergic to penicillin or not depending on the
results of the skin test.
4. Half-life: topical drugs have longer half-life bcz it doesn’t get
metabolized through the liver (systemic drugs: get metabolised)
5. Bacterial resistance : topical drugs cause more bacterial resistance than
systemic drugs, bcz it has a longer half-life , besides some patients put
an excess amount of the topical drug that eventually leads to bacterial
resistance
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6. Stability over time (packaging): systemic drugs ( pills ) last for a
longer time, where topical drugs may dry and have to be thrown after a
particular short period of time after opening.
7. Site of infection: superficial( we prefer to use topical drugs )/ deep (
systemic drugs )
How to start a topical treatment?
1. always clean the skin or wound before applying the topical
medication, or a new dose of it, or between 2 topical medications, bcz
skin encrustations and dead tissue harbor microorganisms, which might
block the medications from reaching the infected area, also, applying a
new medication over a previously applied medication might not help
with preventing the infection, or it won’t provide the wanted therapeutic
benefit
2. wash your hands before and after applying the medication
3.wear gloves
4 .follow the doctor instruction regarding the doses
The forms of topical drugs
Creams vs. Lotions
1.The base of a cream is oil( creams are thicker than lotions ) >>>> it’s used
for the dry skin bcz it needs to be moisturized and hydrated
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2.The base of a lotion is water ( lotions are more liquid and soft and easier to
spread than creams ) >>>>>it’s used for oily skin
Types of skin
Normal
Sensitive
Oily skin: it’s shiny, usually have breakouts and pimples
Dry skin: ashy skin, wrinkled, usually need botox after the age of 40
Combination skin: oily at the T zone (the forehead and the nose and the chin)
and dry at the cheeks and the jaw line
3.Ointments
Much more thicker and have a higher consistency and they are rarely used in
cosmetics ( unlike creams and lotions ), usually used in drugs
-Vehicles: The active ingredient’s “mode of transport” into the skin, the
substance in which the active ingredient is dissolved (most of the active
ingredients are in the form of powder so we have to dissolve them in
something)
-Lipophilic drugs usually penetrate into the skin faster than hydrophilic drugs.
-Aqueous vehicles/ solutions deliver these lipophilic drugs faster than fatty
vehicles.
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Partition Equilibrium of Vehicle
The relationship between the vehicle and the skin. If the active
ingredient prefers one, it will leave/ “part” with the other.
If the partition equilibrium shifts towards the skin: the active ingredient
prefers the skin and will leave the vehicle.  Good formulation.
If the partition equilibrium shifts towards the vehicle: the active
ingredient prefers the vehicle, and not very much of it will leave onto the
skin.  Bad formulation.
Occlusion
Covering part of the skin after application of a dermatological
preparation ( cover it with a Material that won’t absorb the medication )
Can raise water content of the outermost skin layer from 10-20% to 5075%
Hydration increases permeability, reduces barrier function.
Occlusion therefore enhances the penetration of active drug ingredients
into the skin.
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Site of Administration
We must take into consideration the nature of the area a drug will be used on.
For hairy skin (the head)  easily washable vehicle( patients won’t want
greasy fatty material on their hair>>> not practical >> besides, that would
decrease the compliance which is not good )
In wet skin folds (the armpits)  avoid occlusive vehicles.
Drugs applied in skin folds/ groins/ armpits generally leads to higher uptakebecause of the skin type (thin ) in these areas. (no need for occlusion )
.
The drug is in spray
form which is good
No need for occlusion bcz it
going to be absorbed very
easily
( no greasy material,
easily absorbed )
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Penetration rate
Penetration rate is higher when applied on thin skin (behind the ear/ on
eyelid/ scrotum) than on thick skin (palm of the hand/ sole of the foot
and on top of the nails ).
Damaged skin> intact skin.
Hydrated skin > dry skin
Concentration/ Surface Area
The higher a drug concentration  the more therapeutic it tends to be, as
long as it stays within its therapeutic index.
Drugs in high concentrations are better able to penetrate the skin.
The larger a surface area being treated by a drug, the more a drug is
retained in the body.
Application Method
One of the main aims of dermatological treatment is to restore the skin’s
hydration (i.e. bring it back to a normal level) >>> normal hydration
>>> normal barrier function( one of the most important skin function ) .
Follow the application instructions on the package, wear gloves,
applicator, etc (as previously mentioned)
A rule of thumb is ‘wet on wet and fat on dry’.
Liquid drug forms are applied on wetting skin parts.
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Semi-solid forms with a high fat content are used for dry skin conditions
(psoriasis).
The skin is really dry and inflamed
Skin Condition
Damaged or pathologically changed skin marks an especially higher risk
for inducing systemic side effects.
This is because the natural barrier function of the skin is impaired. It
may be reduced, other times it is completely absent.
-the idea of occlusion is to increase the absorbance of the drug and to make
the skin more hydrated and that happens by preventing the evaporation of the
liquid
- watery preparation will evaporate faster than oily preparation ( occluding
formations ) >> will stay longer >>>increase the hydration of the skin
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- when we increase the hydration of the skin >> the protein content will be
diluted ( inside the skin we have proteins that makes high concentration)>> a
lot of water >> dilution >> the concentration of the drug outside will be
greater than the inside >>>>>>>>the drug goes in .( the occlusion enhances
the absorbance of the drug )
Acute inflammation there is crusting and vesiculation >> we use something
aqueous >> dry preparations or lotions
Chronic >>> scaling or lignification>>>> increased keratinization of the skin
>so we use> oily cream and ointments
Ideal topical antimicrobial
Specificity: specific for the microorganism that produces the disease
Low bacterial resistance
Non allergic
Stable preparation
Where do we use topical anti-microbial preparation?
-Prophylaxis >>> in surgeries >>we use antimicrobial and anti-cyptic >>so
that bacteria don’t get inside the body
-Infective dermatitis and wounds
-Reducing colonization >>Staph aureus( most bacteria )>>nares
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-Management of Acne vulgaris
We combine antimicrobial and Corticosteroids >>>>in treating >>
Infective dermatosis
Diaper dermatitis ( kids )
Otitis externa
Impetiginized eczema (contagious condition (infection of the skin
superimposed on eczema ( inflammatory condition )
‫القوباء‬
Shatha Kh Shahwan
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