Over- and underprescribing is very common when prescribing a cream when treating a skin condition. Two simple rules can avoid this:
the fingertip unit (FTU)
-it is a specific amount of cream on the index. It was initially designed for topical steroid treatment but is valid for any treatment with a semi-solid topical substance (cream, lotion, ointment…):
- between the distal crease and the tip of the index.
- for a tube exit diameter of 0.5cm it is equivalent to: 0.5grams (may vary if the palm size is extremely big or small); 2% of the total body area (TBSA). As a rule, the surface of one palm is 1% of the TBSA.
the rule of 9’s
-each aspect of the body is equivalent to 9 or a multiple of 9 of the TBSA:
-the head is equivalent to 9% (1 times 9) of the TBSA.
-each arm is equivalent to 9% (1 times 9) of the TBSA.
-the body (trunk) is equivalent to 36% (4 times 9) of the TBSA.
-each leg is equivalent to 18% (2 times 9)( of the TBSA.
-The genital area is the only remaining area left and is equivalent to 1% (100-99 (11 x 9)) of the TBSA.
When calculating the amount of cream it is therefore important to know:
-the above following two rules.
-the duration of treatment.
Example no 1: treatment of a fungal infection on both feet plantar surfaces. We would like to give the treatment for 2 weeks (one fortnight) before following-up the patient
-consider a plantar surface as being 1.5 times that of a palm. This means 1.5 times 0.5g=0.75g for each foot plantar surface.
-this amounts to 1.5g for both feet plantar surfaces per day.
-for two weeks: 1.5g x 14 = 21g of cream is needed.
-In practice, round the quantity higher to the lowest cream quantity available. It is always better to give slighly more than not enough!
Example no 2: treatment of nummular eczema (discoid eczema) occupying roughly 10% of the surfaces of the legs. We want to prescribe a steroid ointment for one month (28 days) before following up the patient.
-considering 10% of the surface of the legs (10% of 36% = 3.6%), it represents approximately 4 palms
-4 palms are equivalent to 1g (2 x 0.5g)
-3 weeks of treatment represent: 1g x 28days = 28g of cream is needed. Again in practice, round the quantity higher to the lowest cream quantity available. It is always better to give slightly more than not enough!
Source of information: here