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.

2 examples:

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**