WO2006093401A2

WO2006093401A2 - Liquid non-flammable gas mixture and a container and package therefor

Info

Publication number: WO2006093401A2
Application number: PCT/NL2005/050091
Authority: WO
Inventors: Jan Philip Herweijer
Original assignee: Wartner Medical Products Ag
Priority date: 2004-12-22
Filing date: 2005-12-22
Publication date: 2006-09-08
Also published as: NL1027840C2; WO2006093401A3; WO2006093401A9

Abstract

The invention relates to a liquid, non-flammable gas mixture for locally freezing the skin of a human or an animal. The invention further relates to a container comprising such a gas mixture and a package comprising such a container and at least one application member for freezing a wart, acrochordon or parasite in or on the skin. The gas mixture according to the invention is more economic in use than known mixtures for such applications, and also bring about a better treatment result.

Description

Liquid non-flammable gas mixture and a container and package therefor

The invention relates to a liquid, non-flammable gas mixture for locally freezing the skin of a human or an animal. The invention further relates to a container comprising such a gas mixture and a package comprising such a container and at least one application member.

Such mixtures are applied in minor medical or cosmetic surgery wherein the skin must be frozen, such as in the removal of warts, the removal of acrochordons or the removal of parasites from the skin. In the present patent application a mixture is understood to mean not only a fully homogeneous mixture of the component substances but also a mixture which is not fully homogeneous, because the mixture could for instance not be fully homogeneous under the influence of the low temperatures or the properties of the substances. The percentages stated in this document are percentages by weight.

The currently used gas mixtures are easily combustible and flammable. It is anticipated that within the foreseeable future legal measures will be taken in many countries to limit the use of such easily combustible and flammable substances. The object of the invention is to provide such a mixture that is less combustible and flammable and that is effective for the set purpose; cooling the skin to the temperature at which freezing occurs or lower, and maintaining the temperature at which the desired effect occurs for a length of time such that the desired effect, such as a wart dying off, is achieved. The prerequisite of non-flammability does however impose a great limitation on the choice of substances that can be used for such a gas mixture.

Environmental aspects must also be taken into account here; the substances from the mixture may preferably not affect the ozone layer or have any other impact on the environment. Furthermore, it is important that the substances applied are non-toxic in the quantities used. These requirements make a large number of substances, which are indeed non-flammable, nevertheless unsuitable for the intended applications.

In order to achieve the desired cooling effect for local freezing of warts, or for the purpose of removing parasites and the like, obtaining a suitable temperature curve is of the greatest importance. It is after all necessary to take account of the occurrence of undesired freezing phenomena in surrounding tissue, for which purpose not only the lowest reachable temperature is important but also the period of time for which this temperature is maintained, hi addition to the lowest reachable temperature, the temperature curve is also important in obtaining the desired therapeutic effect. The processes which result in the desired effect, such as killing a wart, paralyzing a parasite or freezing a tissue portion, do after all require some time to achieve the desired purpose.

It is known from FR- A-2 782 639 to make use of a non-flammable liquid gas mixture as cooling agent, wherein the mixture consists of 1,1,1,2 tetrafluoroethane and a hydrofluoroether. 1 , 1 , 1 ,2 tetrafluoroethane and hydrofluoroethers a low combustibility and flammability. A significant drawback of the known gas mixtures however is that a relatively large amount of the gas mixture must be used per treatment in order to reach the temperatures required to freeze the skin.

The object of the invention is to provide a non-flammable liquid gas mixture which is economic in use in applications in which the skin has to be frozen.

The invention provides for this purpose such a gas mixture for local freezing of the skin of a human or an animal, which is characterized in that the liquid gas mixture comprises at least 5% by weight of pentafluoroethane.

It has been found surprisingly that less of such a gas mixture is required to cause the desired local freezing of the skin, for instance in the freeze treatment of a wart. Comparative measurements have shown that compared to known gas mixtures, when the same quantity of the gas mixture according to the invention is used a sufficiently low temperature of the skin is realized for a longer time. Pentafluoroethane is herein also non-combustible and non-flammable, and has relatively favourable toxicological properties. The use of pentafluoroethane is moreover advantageous from an environmental viewpoint, since it has a minimal effect on the ozone layer and makes a relatively small contribution to the greenhouse effect Pentafluoroethane has a boiling point of -48.5°C, so that with a mixture of which this substance forms part lower temperatures can moreover be obtained than with for instance a known substance such as 1,1,1,2 fluoroethane, which has a boiling point of -26.5°C. Lower temperatures are found to make more rapid freezing possible. Another advantage of pentafluoroethane is the ready availability of the substance. Pentafluoroethane is known commercially as cooling agent, for instance for refrigerators, under diverse systematic names and brand names, such as 1,1,2,2,2-pentafluoroethane, R125, HFC 125 and SUVA® 125. ^• .

It is advantageous if the boiling range of the gas mixture lies between -60 and -20?C at atmospheric pressure. Such a boiling range results in a favourable cooling profile on the skin for freezing: the temperature curve in time is such that the desired local freezing is achieved relatively quickly but damage to surrounding tissue is prevented. Atmospheric pressure is understood to mean a pressure of 1 bar.

The gas mixture preferably comprises a maximum of 30% by weight of pentafluoroethane. Such a content of pentafluoroethane between 5-30% by weight results in a particular temperature curve on the skin for freezing that is particularly favourable in the freezing of warts on the skin. It is particularly favourable if the gas mixture comprises between 10 and 20% by weight of pentafluoroethane. The ideal temperature curve is approximated still better with such a composition.

It is advantageous if the gas mixture substantially comprises hydrofluorocarbons. Hydrofluorocarbons are generally not flammable, or not very much so, and have advantageous toxic and environmental properties. Hydrofluorocarbons are moreover readily miscible, so that an homogeneous mixture can be obtained in simple matter. The use of an homogeneous mixture from a supply container thus ensures that the composition of the mixture during an earlier use is the same as the composition during a later use. Reduced activity or accidents due to excessive freezing are thus prevented. Usable hydrofluorocarbons are for instance hydrofiuoroethers, tetrafluoromethane, trifluoromethane, hexafluoroethane, 1,1,2,2-tetrafluoroethane, 1,2,2-trifluoroethane and 1 , 1 -difluoroethane.

In a preferred embodiment the gas mixture consists of at least 50% by weight of 1,1,1,2 tetrafluoroethane. 1,1,1,2 tetrafluoroethane is a propellant gas with favourable environmental and toxicological properties, which is furthermore generally accepted and is readily available. The use of 1,1,1,2 tetrafluoroethane is already known per se for cooling applications, though not together with pentafluoroethane. Both substances have a cooling effect, albeit that the cooling effect of pentafluoroethane with its boiling point of -48.5° C has a greater cooling effect than 1,1,1,2 tetrafluoroethane with its boiling point of -26.5° C. The combination of 1,1,1,2 tetrafluoroethane with pentafluoroethane moreover provides an exceptionally favourable cooling profile. The boiling point of the mixture, and thereby the desired temperature, can be determined by using the mixture of the two substances. Application of a third substance in the mixture is not precluded here. Such a substance can for instance be used to modify specific properties of the mixture, such as the boiling range or the specific heat.

The gas mixture preferably consists substantially of pentafluoroethane and 1 , 1 , 1 ,2 tetrafluoroethane. Such a mixture is easy to prepare owing to the simple composition. A temperature-time profile can moreover be obtained herewith that is highly suitable for treating for instance warts. Nor are other applications, such as combating parasites, acrochordons and other skin disorders, and cosmetic applications precluded. In addition, both substances in the mixture have favourable environmental and toxicological properties, and both substances are readily available. Furthermore, both substances can be produced relatively easily, this having a favourable effect on cost price, ϊn addition, the substances are readily miscible, whereby a homogeneous mixture is created. It is of course possible during production and filling of the containers that quantities of contaminated material enter the mixture which are not significant for the invention but which can nevertheless be measured; the scope of protection of this preferred embodiment is deemed to extend to mixtures provided with these contaminants.

The invention also provides a container comprising a gas mixture according to any of the foregoing claims. The gas mixture can be transported and stored easily and safely in liquid form in such a container.

It is advantageous if the container comprises a dispensing device for controlled discharge of the gas mixture out of the container. A desired quantity of gas mixture can thus be allowed out of the container so that the quantity of cooling mixture required for a determined treatment can be applied in simple manner, for instance to a wart. The dispensing device is preferably adapted to generate an aerosol of the gas mixture. This aerosol can be used to form droplets which are created by collecting the aerosol in an absorption member. Nor is allowing the droplets to leave the valve directly precluded. Because the present invention is used for medical, cosmetic and veterinary applications, it is important that, as a result of the use of an aerosol, there is no contact between the container of the mixture and the skin to which the mixture is administered. An aerosol provides a fine distribution of the cooling agent with a relatively large evaporation area, whereby cooling and freezing can take place within a short time. An example of a dispensing device for generating an aerosol is a spray can provided with a spray head which can optionally be combined with an absorbent medium such as a foam structure with which the aerosol can be applied in controlled and specific manner to the intended location on the skin.

In a preferred embodiment the dispensing device is adapted for local freezing of the skin during a treatment chosen from the following group: the removal of warts, the removal of acrochordons and the removal of parasites from the skin. It will be apparent that in respect of design and dimensioning the embodiment can be modified to the desired application or multiple applications.

A specific field of application is the treatment of warts. A preferred embodiment provides for this purpose the measure that the mixture is arranged in a package for treating warts. Known from WO-A-9949797 is a container for generating an aerosol wherein the container and administering means are adapted to administer the aerosol to the skin for the purpose of combatting warts on the skin. The mixture according to the present invention is therefore particularly suitable for use in the administering device according to this document. Applications other than for warts are however by no means precluded.

The invention further provide a package comprising at least one container according to the invention, and at least one application member adapted for co-action with the dispensing device for local freezing of the skin of a human or an animal. The application member can for instance be an application member as known from cooling devices for the treatment of warts similar to application members as known from EP 1065980 or US 6 387 090. The application member can be for once-only use (disposable article). The package forms an assembly for once-only or multiple treatment of warts, the removal of acrochordons or the removal of parasites from the skin, wherein use is made of local freezing of the skin and/or the wart, acrochordon or parasite present therein or thereon.

The invention will now be elucidated on the basis of the following non-limitative examples and preferred embodiments.

Example 1

A representative, known cooling agent (mixture A) was compared in a test to a gas mixture according to the invention, comprising 15% by weight of pentafluoroethane (R125) and 85% by weight of 1,1,1,2 tetrafluoroethane (R134a) (mixture B). The gas mixture B according to the invention has a boiling range of about -49° C to -26° C at a pressure of 1 bar (1013 kPa), and is not flammable. Both mixtures A and B were each applied separately as aerosol to an absorption element in reproducible manner from a spray can under pressure. Application of the mixtures took place for 4 seconds with a constant outflow of aerosol. The temperature curve of the absorption element was then measured both in the core and on the surface. Each experiment was repeated at least 10 times. The following characteristic figures from the measured curves were then analyzed:

T_sur: the average temperature of the surface of the absorption element during the measurement time below -40⁰C.

Tcoret the average temperature of the core of the absorption element during the measurement time below -4O⁰C.

Δt₄o: the time in seconds between the point in time at which the temperature of the surface falls below -4O⁰C and the point in time at which the temperature rises again above -40° C. At_3nMo is a measure of the time in which the temperature is low enough to be efficiently used for freezing for instance a wart on the skin.

Of two random measurements in the series figure 1 shows the temperature curve of the core temperature with mixture A (T_COΓC,A), and the surface temperature of the known mixture A (T_SUr,A) and the mixture B according to the invention (T_Su_r,_B)₅ wherein it is also indicated how the time between the point at which the temperature of the surface falls below -40° C and the point at which the temperature rises again above -40° C can be determined from this curve (ΔtrøA and At_4O1B). Table 1 shows the results, wherein the values are averages of at least 10 experiments, and the figure after the ± symbol indicates this variation in the measurement values.

Table 1

Table 1 shows clearly that the mixture B according to the invention reaches an average lower core temperature than the same quantity of mixture A, which is representative of known mixtures. Even more important is that the period in which the low surface temperature below -40° C relevant for the application is achieved is about twice as long for mixture B according to the invention as for the known mixture A. It is therefore apparent that using gas mixture B the desired effect can be achieved for a longer time with the same quantity of gas. In order to achieve the same effect with mixture A as with mixture B, a larger quantity of the mixture A will therefore be required. Mixture B is thus hereby economic in use.

Example 2

In a subsequent test local freezing of the skin was simulated in reproducible manner. In the test an application member, in this case the sponge-like absorption element of example 1 , was treated with the gas mixtures A and B as described in example 1. A test surface was then cooled with the cold application member, wherein the temperature of the cooled surface was measured for a determined time. As a measure for the time in which the cooled surface retained an effective temperature, the average period of time Δtsu_r-₂0 was determined during which the surface was colder than -20° C. The average temperature T_sur of the surface cooled with the application member was also determined during this time Δt_sur-₂o- At least 10 independent experiments were carried out for each measuring point. The temperature curve is shown in figure 2, which shows two random experiments from the series for mixture A (T_SUΓJA) and for mixture B (T_sur>B)₅ as well as the period of time Δt_sur.₂o,A and Δt_sur-2o,_B to be determined from this graph within which the surface was colder than -20° C. Table 2

This measurement shows once again that, with the same quantity of gas mixture, mixture B brings about an effective cooling temperature for a longer time. Mixture B according to the invention is hereby thus more economic in use than the known mixture A. A significantly lower cooling temperature is also reached on the surface using mixture B. When used in a desired application, for instance the freezing of a wart, acrochordon or parasite in or on the skin, this results in a better treatment result.

It will be apparent that many further variants and preferred embodiments are possible for a skilled person in the field.

Claims

1. Liquid, non-flammable gas mixture for locally freezing the skin of a human or an animal, characterized in that the gas mixture comprises at least 5% by weight of pentafluoroethane.

2. Gas mixture as claimed in claim 1 , characterized in that the boiling range of the gas mixture lies between -60 and -2O⁰C at atmospheric pressure.

3. Gas mixture as claimed in claim 1 or 2, characterized in that the gas mixture comprises a maximum of 30% by weight of pentafluoroethane.

4. Gas mixture as claimed in claim 3, characterized in that the gas mixture comprises between 10 and 20% by weight of pentafluoroethane.

5. Gas mixture as claimed in any of the foregoing claims, characterized in that the . gas mixture substantially comprises hydrofluorocarbbns.

6. Gas mixture as claimed in any of the foregoing claims, characterized in that the gas mixture consists of at least 50% by weight of 1 , 1 , 1 ,2 tetrafluoroethane.

7. Gas mixture as claimed in any of the foregoing claims, characterized in that the gas mixture consists substantially of pentafluoroethane and 1,1,1,2 tetrafluoroethane.

8. Container comprising a gas mixture as claimed in any of the foregoing claims.

9. Container as claimed in claim 8, characterized in that the container comprises a dispensing device for controlled discharge of the gas mixture out of the container.

10. Container as claimed in claim 9, characterized in that the dispensing device is adapted for local freezing of the skin during a treatment chosen from the following group: the removal of warts, the removal of acrochordons and the removal of parasites from the skin. _1Q

11. Package, comprising

- at least one container as claimed in either of the claims 9 or 10, and

- at least one application member adapted for co-action with the dispensing device for local freezing of the skin of a human or an animal.