Finger-tip unit in Indian scenario: Is it relevant?

INTRODUCTION

Topical corticosteroids (TCs), since their introduction in 1950, have become the most commonly prescribed drugs by dermatologists in the outpatient setting. They form the mainstay of treatment for many skin conditions, such as atopic eczema, localized vitiligo, psoriasis, chronic hand eczema, and localized bullous pemphigoid, forming the pillars of dermatotherapeutics. They are safe and effective with minimal side effects when used “appropriately.” Moreover, therein lies our concern, with such ambiguity existing regarding the appropriate use of topical steroids. They are increasingly being abused by doctors and patients. “Topical steroid addiction” and “red burning skin syndrome” are legitimate clinical entities that are well-recognized in this decade.^[1]

Hence, a rational prescription and proper advice form the cornerstone of appropriate topical steroid therapy. A rational prescription includes a correct indication of the drug, appropriate class of steroid, appropriate vehicle, adequate dosage, and finally, duration of drug usage. Unfortunately, there is significant ambiguity regarding the dose of topical steroids and frequency of application. To give a reasonably constant dose, the fingertip unit (FTU) and rule of thumb were proposed by Long and Finlay in 1991.^[2,3]

An FTU is the amount of ointment expressed from a tube with a 5-mm diameter nozzle, applied from the distal skin crease to the tip of the palmar aspect of the index finger. One FTU weighs 0.49 g and covers 312 cm² in males and 0.43 g and 257 cm² in females.

Rule of hand states that the area of one side of a flat closed hand requires approximately 0.5 FTU or 0.25 g of ointment, or one “hand area” of involved skin requires 0.5 FTU or 0.25 g of ointment, or 4 hand areas or 2 FTU or 1 g is to 2.14 hand areas in males and 2.17 hand areas in females. The rule of hand states that 4 adult “hand areas” of skin require 2 fingertip units (FTUs) of topical medication, which is equivalent to 1 gram (g) of the product. A hand area is the size of the palmar surface of an adult hand. One FTU, or 0.5 g of medication, covers two such hand areas, or a total area of two adult handprints. The number of FTUs required to treat different anatomic regions are given in Table 1.^[3]

Our study aims to assess the accuracy of FTU as a drug dosing measure in the Indian scenario.

MATERIALS AND METHODS

RESULTS

Out of the 24 tubes assessed, the majority (18/24; 79.1%) were metal [Table 2].

After measuring the diameter of the tubes, the majority had an outer diameter of 0.5 cm [Table 3a]. But on piercing the metal tubes, the effective inner diameter reduced by 0.2 to 0.4 cm. In contrast, all lami tubes had an aluminium foil covering its nozzles, which can be completely peeled off, thereby yielding a consistent inner diameter of 0.5 cm [Table 3b].

Statistical analysis showed a mean outer diameter of 0.492 cm and an inner diameter of 0.342, which gives a standard deviation of 0.0408 and 0.1213, respectively. This shows most of the tubes have a different diameter as compared to the standard after puncturing. The weight of the drug expressed in each FTU was highly variable. Different tubes had different amounts of drug expressed, ranging from 0.316 g to 0.92 g. Even the same tubes while pressing proximally and distally showed a difference. Proximal pressing generally gives a higher amount than distal pressing. It was also noted that metal tubes on subsequent pressing shrink and, thus, give a variable amount every time. The median values obtained from 24 tubes were 0.513 g and 0.662 g for distal and proximal pressing, respectively [Table 4a]. However, the minimum and maximum values varied significantly, especially on proximal pressing and this is of importance as this can lead to significant variation in real life, from patient to patient. The mean FTU ranged from 0.5304 g to 0.6054 g during distal and proximal pressing, with the difference being statistically significant [Table 4b].

DISCUSSION

The topical application of drugs represents a very attractive option for treating a variety of dermatological conditions with minimal systemic side effects. Although there have been many innovations in drug delivery systems, the number of effective cutaneous drug delivery methods remains inadequate. The advantages of topically used drugs are increased patient compliance, avoidance of metabolism by the liver, sustained and controlled delivery over long periods, concentration of the active agents at the site of disease, and prevention of systemic side effects.^[4]

The use of chemical permeation enhancers and physical methods such as sonophoresis, iontophoresis, electroporation, and microneedles have been successfully used to deliver the drugs topically. However, the foundation in drug delivery remains the amount of drug that is to be applied.^[5]

Patient compliance plays a pivotal role in treatment. The term compliance is strongly related to adherence to medications, and it is defined as “the process by which patients take their medications as prescribed.” It is involved with three components: “Initiation, implementation, and discontinuation.”^[6] The implementation part is the area where FTU becomes important which makes it a unified and simplified way of topical application.

TCs are probably the most widely used therapeutic medication in dermatology. Rapid relief from most of the inflammatory conditions is possibly the reason for its rampant use. In the Indian market, more than 18 different corticosteroid molecules of various potency and activity, from mild to super-potent, are available for topical use. These molecules are marketed with many brand names by pharmaceutical companies. It is already known that in India, almost 15% of dermatology outpatients with facial dermatoses are using topical steroids, and the unfortunate part is that 93% of these cases either do not need them, or they are of the wrong potency. To add to that, our study results show that FTU cannot be used as a method of standardization of dosing of TCs in Indian scenario. FTU is defined as the amount of ointment expressed from a tube with a 5 mm diameter nozzle, applied from the distal skin crease to the tip of the index finger.^[2] One FTU is approximately equivalent to 0.49 g and 0.43 g of ointment by weight for males and females, respectively.^[2] This method was introduced with the motive of improving the precision in topical steroid delivery. This has become useful to counsel the patient regarding the dosage of topical steroids.^[7]

However, in the present scenario, FTU as a method fails to be of much use in Indian scenario.

The majority of the steroid tubes (79.1%) available in the Indian market are made of metal and are of the piercing type; hence, their effective diameters differ from the standard definition of 0.5 cm. We found a statistically significant difference in the effective inner diameter compared to standard. The weight of the drug expressed in 1 FTU was highly variable, (0.316–0.92 g), on comparing it with a standard of 0.49 g and 0.43 g for males and females, respectively. FTU was also influenced by the type of pressing – proximal and distal, which is a hitherto unexplored area. The variable effective inner diameter seen with metal tubes itself makes it impractical to deliver a desired amount of drug.

Even though FTU is defined as a method for standardization of topical steroid application, it is applicable to very few formulations. Several formulations of TCs are available, including ointments, creams, gels, lotions, solutions, shampoos, and foams. It is not possible to group FTUs from all these formulations because they differ in their physical properties.^[8] For example, ointments are expected to have a higher concentration of drugs for equal weight of creams. Last and yet another important observation was that the metal tube deformed irreversibly every time on pressing, and hence, the amount of drug that came out varied subsequently.

CONCLUSION

FTU, by definition, is determined by two factors, one is the diameter of the nozzle (0.5 cm) and the other, the drug delivered from such a standard tube. In Indian markets, the nozzle size is not standardized, and secondly, even if it is standardized, the amount of drug delivered cannot be constant, as it is found to be influenced by other factors, including the type of tube, site, and amount of pressure applied. Thus, in the Indian market, steroid delivery tubes differ widely in the amount of drug they disperse per FTU, making it unreliable as a standardized drug delivery method measure. A few recommendations based on our observations are, Lami tubes with peel-off cover with effective inner diameter of 0.5 cm and also uniform strip of medication for uniform delivery.