EP2424548A1

EP2424548A1 - Use of n²o gas for treating chronic pain

Info

Publication number: EP2424548A1
Application number: EP10723653A
Authority: EP
Inventors: Baptiste Bessiere; Guy Simonnet
Original assignee: Air Liquide SA; LAir Liquide SA pour lEtude et lExploitation des Procedes Georges Claude
Current assignee: Air Liquide SA; LAir Liquide SA pour lEtude et lExploitation des Procedes Georges Claude
Priority date: 2009-04-29
Filing date: 2010-04-12
Publication date: 2012-03-07
Also published as: JP2012525360A; FR2944969A1; WO2010125271A1; EP2851077A1; US20120045528A1; EP2851076A1; CA2755780A1; FR2944969B1

Abstract

The invention relates to a gas mixture that contains nitrous oxide (N₂O) for use as a breathable drug for the treatment of chronic pain in a mammal, in particular a pain from neuropathic, iatrogenic, dysfunctional or inflammatory origin, in particular in humans. The proportion of N₂O ranges from 15 to 45 vol. %. The gas mixture is administered for a sufficient duration for obtaining a delayed pain hypersensitivity reduction that can be observed at least 6 hours after the end of the inhalation of the gas mixture by said mammal. The pain hypersensitivity is selected from allodynias and hyperalgesias.

Description

Use of gaseous N? O in the treatment of chronic pain

The invention relates to the use of nitrous oxide (N ₂ O) at low concentrations, typically less than 50% by volume, in the treatment of chronic pain, mainly of neuropathic origin, that is, ie related to a nerve injury, dysfunctional origin, inflammatory origin or iatrogenic origin, that is to say consecutive to the taking of drugs, for example drugs used in chemotherapy.

In the general population, it is estimated that one in six people suffers from chronic pain, as described in Breivik, H. et al, Survey of chronic pain in Europe: prevalence, impact on daily life, and treatment. Eur. J. Pain 10, 287-333 (2006).

Among chronic pain, neuropathic pain is considered to be the most severe and persistent.

Neuropathic pain occurs as a result of an injury or dysfunction of the nervous system that may be:

- of peripheral origin, for example a lesion or irritation of traumatic, toxic, metabolic, ischemic, immunoallergic or infectious origin of the peripheral nerves,

- Or of central origin, for example a lesion or an irritation of the spinal cord or the encephalon.

Neuropathic pain does not respond to usual analgesics, such as nonsteroidal anti-inflammatory drugs, paracetamol or salicylates, and is often not sensitive to opioid analgesics.

At the neurobiological level, hypersensitivity to pain, ie hyperalgesia or allodynia, following nerve injury (neuropathic pain) is not only an excess of nociception but involves of pain awareness, as recalled by the TJ documents. Coderre, et al. Peripheral and central hyperexcitability: differential signs and symptoms in persistent pain, Behav. Brain Sci. 20, 404-419 (1997); and CJ. Woolf et al, Neuropathic Bread: Aetiology, Symptoms, Mechanisms, and Management, Lancet 353, 1959-1964 (1999).

The key role played by the NMDA (N-methyl-D-aspartate) receptor in the pain sensitization process makes this receptor a therapeutic target of choice in the treatment of chronic pain mainly of neuropathic origin, as described by CG document. Parsons. NMDA receptors as targets for drug action in neuropathic pain, Eur. J. Pharmacol. 429, 71-78 (2001). Thus, the clinical efficacy of NMDA receptor antagonists, such as ketamine, amantadine or memantine, has been described, particularly by Chizh, BA et al, NMDA antagonists and neuropathic pain-multiple drug targets and multiple uses, Curr. Pharm. From 11, 2977-2994 (2005). However, the adverse effects of current NMDA receptor antagonists, such as memory impairment, psychodysleptic effects, ataxia, and poor motor coordination, largely outweigh the expected benefits and prohibit widespread or prolonged use as explained by the literature. JA Kemp et al, NMDA receptor pathways and drug targets, Nat. Neurosci. Suppl, 1039-1042 (2002) and BAChizh et al., NMDA receptor antagonists as analgesia: focus on the NR2B subtype, Trends Pharma. Sci. 22, 636-642 (2001)

On the basis of this, a problem that arises is that of a treatment or curative drug acting on the level of the NMDA receptor by showing an efficacy in the treatment of chronic pain, in particular those of neuropathic origin, of dysfunctional origin, of Inflammatory origin or iatrogenic origin but generating otherwise little or no adverse effects, that is to say, limited adverse effects compared to those existing when using the current NMDA receptor antagonists. A solution to this problem is a gaseous mixture containing a proportion of nitrous oxide (N ₂ O) of between 15 and 45% by volume for use as an inhalable drug for the curative treatment of chronic pain in a mammal the gaseous mixture being administered for a period of time sufficient to achieve a reduction in hypersensitivity to delayed pain, also known as delayed anti-sensitizing effect, observable at least 6 hours after the end of inhalation of the gaseous mixture by said mammal.

Depending on the case, the gaseous mixture of the invention may comprise one or more of the following characteristics:

hypersensitivity to pain is chosen from allodynies and hyperalgesia. - the mammal in a human being, ie a man or a woman, including children and newborns.

the proportion of N ₂ O in the gaseous mixture is between 15 and 40% by volume.

the proportion of N ₂ O in the gaseous mixture is at least 20% by volume, preferably at least 25% by volume.

- chronic pain is of neuropathic origin, dysfunctional origin, inflammatory origin or iatrogenic origin.

the gaseous mixture is administered for a time sufficient to obtain an analgesic effect during at least part of the duration of administration by inhalation of the gaseous mixture and a delayed anti-sensitizing effect after the end of the inhalation of the gaseous mixture by said mammal. the gaseous mixture is administered for a period of at least 20 min, preferably at least 30 min, preferably at least 40 min, advantageously at least 1 h.

the gaseous mixture is administered for a time sufficient to obtain a delayed anti-sensitizing effect occurring and observable at least 12 hours after the end of the inhalation of the gaseous mixture.

the gaseous mixture is administered for a time sufficient to obtain a reduction in hypersensitivity to the delayed pain occurring and observable at least 24 hours after the end of the inhalation of the gaseous mixture. the gaseous mixture contains, in addition, between 20 and 60% by volume of oxygen, preferably between 20 and 50% by volume of oxygen.

the gaseous mixture is formed from 15 to 45% by volume of N ₂ O and at least 20% by volume of oxygen.

the gaseous mixture optionally contains one or more other gases chosen from xenon, argon, helium, neon, krypton and nitrogen, preferably between a content by volume lower than that of N ₂ O present in the mixed.

the gaseous mixture is formed from 15 to 45% by volume of N ₂ O, at least 20% by volume of oxygen, and contains, in addition, xenon, argon, helium, neon and krypton or nitrogen, in particular nitrogen or xenon. the gaseous mixture is formed from 15 to 45% by volume of N ₂ O, from 21% to 60% by volume of oxygen, and nitrogen for the remainder.

neuropathic pain is selected from post-herpetic pain, pain of diabetic neuropathies, central pain, pain after stroke, multiple sclerosis pain, neuropathic pain of spinal cord injury, pain neuropathies associated with AIDS or its treatment, neuropathic pain related to cancer, neuropathic pain related to chemotherapy, neuropathic pain related to a surgical procedure that damaged a nerve pathway and postoperative neuropathic pain.

- the pain of dysfunctional origin is related to fibromyalgia, irritable bowel syndrome or headache.

- Inflammatory pain is related to osteoarthritis, arthritis or disc herniation.

- N ₂ O can also be administered in combination with an analgesic included in the levels of the WHO (World Health Organization) namely:

. Level I analgesics, also called "peripheral painkillers" or "non-morphine", which have the lowest analgesic potency, for example paracetamol, aspirin, non-steroidal anti-inflammatory drugs ...

. Level II analgesics called "central" or "weak morphine" because they are active on the perception of pain in the brain. They are used alone, by tramadol, or in combination with level I analgesics, eg codeine-paracetamol.

. Tier III analgesics that include strong morphine agonists and antagonist agonists. In other words, the invention also relates to a use of a gaseous mixture containing nitrous oxide (N ₂ O) according to the invention, that is to say between 15 and 45% by volume of N ₂ O as described above, for producing an inhalable medicament for the curative treatment of chronic pain in a mammal, in particular in a human being, the gaseous mixture being administered for a period of time sufficient to obtain a reduction in hypersensitivity delayed pain, i.e. delayed anti-sensitizing effect, observable at least 6 hours after the end of inhalation of the gaseous mixture by said mammal.

The present invention will now be better understood from the following description and the examples which follow, which are given purely by way of illustration. In the context of the present invention, nitrous oxide (N ₂ O) is used at a concentration of preferably between 15 and 45% by volume in order to reduce chronic pain in a human being for a prolonged period of time. is a man, a woman or a child, an infant, mainly those of neuropathic, dysfunctional, inflammatory or iatrogenic origin. The gaseous mixture containing nitrous oxide (N ₂ O) which can be used as an inhalable medicament for the treatment of chronic pain in a patient suffering from such chronic pain, in particular of neuropathic origin, may be administered by inhalation as part of a therapeutic treatment method of a patient suffering from chronic pain. The gaseous mixture of the invention may be used in the context of a therapeutic treatment method, in which said N ₂ O gas mixture is administered by inhalation, for example by means of a respiratory mask or directly connected to a source of N ₂ O at the required concentration, for example a ready-to-use gas cylinder or at the outlet of a gas mixer fed by several gas sources (O ₂ , N ₂ O _2). .) so as to obtain the desired mixture; is connected to a breathing fan supplied with the desired gas or gases.

Typically, the gaseous mixture administered is formed essentially of nitrous oxide, oxygen and nitrogen, the proportion by volume of nitrous oxide being between 15 and 45% and that of oxygen being typically between 20 and 50 %, especially at least 21% oxygen.

The duration of administration varies according to the patients between a few minutes and several hours, for example between 5 minutes and 4 or 5 hours. The inhalation may be repeated several times in succession, for example several days in a row. The most appropriate concentration and / or duration of administration for a given patient may be selected empirically by the caregiver, for example depending on the health or physical condition of the patient, the severity of the pain, of its sex, age, etc. The gaseous mixture used according to the invention is not only effective at low concentrations (<50% vol.) to treat hypersensitivity to pain, mainly hyperalgesia and allodynia, but also does not cause or cause any adverse effects in patients.

Indeed, nitrous oxide is considered in the medical environment, as a safe gas when its concentration is less than about 50%, as recalled by documents D. Annequin et al. Fixed 50% nitrous oxide oxygen mixture for painful procedures: A French survey. Pediatrics 105, E47 (2000); P. Onody, Safety of inhalation of 50% nitrous oxide / oxygen premix: a prospective survey of 35,828 administrations, Drug Saf 29, 633-640 (2006); and J. T. Knape, Nitrous oxide not used but often, Ned. Tijdschr. Geneeskd. 150, 1053-1054 (2006).

On the other hand, nitrous oxide is a gas which possesses strong N-methyl-D-aspartate receptor (NMDA) receptor antagonist properties, as described by S. K Georgiev et al., Nitrous oxide glutamatergic inhibitors transmission in spinal dorsal horn neurons, Pain 134, 24-31 (2008); P. Nagele et al., Nitrous oxide requires the N-methyl-D-aspartate receptor for Hs action in Caenorhabditis elegans, Proc. Natl. Acad. Sci. U.S. A 101, 8791-8796 (2004), and V. Jevtovic-Todorovic, et al., Nitrous oxide (laughing gas) is an NMDA antagonist, neuroprotectant and neurotoxin, Nat. Med. 4, 460-463 (1998).

In addition, preclinical data recorded in B. Bessiere documents. et al., Nitrous oxide prevents latent pain sensitization and long-term anxiety-like behavior in pain and opioid-experienced rats, Neuropharmacology 53, 733-740 (2007); and P. Richebe et al. Nitrous oxide revisited: evidence for potent antihyperalgesic properties; Anesthesiology 103, 845-854 (2005), showed a preventive effect of N ₂ O on postoperative hyperalgesia, in particular that induced by opioids. However, in the context of the present invention, the gaseous mixture containing nitrous oxide is no longer used preventively, as in the case of the prevention of postoperative hyperalgesia, but in a curative manner in order to treat the chronic pain patients and thereby obtain a reduction in their hypersensitivity to delayed pain. The use according to the invention of this nitrous oxide-based mixture will make it possible to reduce or abolish pain hypersensitivity, mainly hyperalgesia and allodynia, which characterize chronic pain patients. Among the chronic pain referred to by the invention, mention may be made of:

- neuropathic pain, that is to say the pain related to a nerve injury, such as post-herpetic pain, pain of diabetic neuropathies, central pain, pain after stroke, pain of the multiple sclerosis, neuropathic pain of spinal cord injuries, neuropathic pain associated with AIDS, neuropathic pain related to cancer, neuropathic pain related to chemotherapy, postoperative neuropathic pain ...

- dysfunctional pain, that is to say with no known lesion, such as those related to fibromalgia, irritable bowel, headache, ...

inflammatory pain, that is to say inflammatory lesions, such as those related to osteoarthritis, arthritis, herniated disc, etc.

At the neurobiological level, these three major types of chronic pain are underpinned by a process of sensitization to pain that results in intense hyperalgesia and allodynia and little sensitivity to current therapeutic compounds.

The present invention using an inhalable gas mixture containing nitrous oxide is therefore intended to reduce or abolish these hypersensitivities to pain, that is to say, hyperalgesia and allodynia, to improve the rehabilitation of patients "painful ".

In other words, the present invention is therefore based on the use of a therapeutic gas mixture containing less than 45% by volume of N ₂ O to produce an inhalable medicament with curative effects intended to treat chronic pain, in particular hyperalgesia and allodynia.

Nitrous oxide (N ₂ O) in a volume fraction of less than 50% is therefore usable in the context of a therapeutic treatment method, in which N ₂ O is administered by inhalation to a mammal, in particular a human, to achieve a cure for chronic pain in it. Examples

In order to demonstrate the curative efficacy of the N ₂ O gas according to the invention, tests were conducted with several gas mixtures containing different concentrations of N ₂ O, as given in Table 1 below.

Table 1

The tests were carried out as follows.

Materials and methods

In male Sprague-Dawley rats (8 per group), mononeuropathy was induced by constriction of the sciatic nerve. More precisely, at OJ, the rats are anesthetized under halothane and the sciatic nerve (lesioned paw side) is made using 4 chromium catgut filaments. Neuropathic pain of more than 40 days is thus induced.

On day 7, the rats are placed in an airtight chamber where they will inhale for 75 minutes, the gaseous mixture to be tested or medical air in control rats (Sham). Repeated exposures to mixtures occur on D7, D8, D9.

Other rats are subjected to comparative treatments with conventional painkillers, namely ketamine (3 x 10 mg / kg, sc) and morphine (1 mg / kg, sc).

Then, a measurement of the nociceptive threshold is performed via a vocalization test in response to a mechanical stimulus (Randall-Selitto).

The data obtained by measurement are expressed on average (± standard deviation). The level of signi fi ciency is set from P <0.05.

Results

Figure 1 shows the persistent reduction in pain hypersensitivity (-40%) on the injured paw side following a 50% by volume nitrous oxide treatment (Trial 3).

Beyond its well-known analgesic effect, 50% nitrous oxide reduced the hypersensitivity to pain in the neuropathic rat by approximately 40% in the injured paw. This decrease in hypersensitivity to pain is observed for more than 30 days.

For comparison, morphine, which is an opioid analgesic conventionally used in hospital, causes an analgesic effect only for 30 minutes (day 14) without delayed effect (following days), as is the case with nitrous oxide.

Trial 3 shows that treatment with the gas mixture containing 50% nitrous oxide is significantly more beneficial than morphine in reducing neuropathic pain.

In Figures 1 and 2, the following abbreviations are used:

- Sham: witness or control. These control neuropathic rats underwent the same manipulations as the neuropathic rats (anesthetized, surgery, ...) but not sciatic nerve ligation that induces neuropathy. The goal is to vary only one parameter at a time (neuropathy or not, breathe air or N2O). - CCI (for Chronic Constriction Injury): constriction of the sciatic nerve. It is a well-established denomination in the literature for the neuropathic animal model used (CCI model). In this case, CCI / N2O refers to the group of neuropathic rats treated with N ₂ O, whereas CCI / Air refers to the group of neuropathic rats breathing air. These two groups make it possible to deduce the effect of N ₂ O in the neuropathic rat.

Figure 2 shows the abolition of pain hypersensitivity in the uninjured paw following a 50% nitrous oxide treatment. In parallel with its effect on the injured paw, nitrous oxide 50% abolishes hypersensitivity at the level of the uninjured paw (contro lateral), demonstrating a central action of the gaseous mixture with nitrous oxide at 50%. % in volume.

Furthermore, these data suggest that N ₂ O, due to its action at the central system level, could reduce hypersensitivity to pain regardless of the etiology of chronic pain, ie neuropathic pain, dysfunctional pain, pain inflammatory, as long as a central sensitization component is present.

Figure 3 compares the analgesic effect with the anti-hyperalgesic effect of nitrous oxide at 50%. As can be seen, the anti-hyperalgesic (anti-sensitizing) effect of N ₂ O is independent of its analgesic effect. Indeed, the blocking of the analgesic effect of nitrous oxide 50% (J7) by naltrexone, which is an opioid receptor antagonist, does not modify its anti-sensitizing beneficial effect for the following days (black triangle on Figure 3). .

In other words, the delayed beneficial effect, i.e., during the days following the N ₂ O treatment, and long-term 50% N ₂ O is independent of its analgesic effect.

In Figure 3, the abbreviation "NaI" is used for naltrexone and the abbreviation "SaI" means saline.

FIG. 4 compares the effect of N ₂ O with 50% on ketamine which is an NMDA receptor antagonist used in a hospital environment but whose use remains very limited in humans because of its important adverse effects, in particular psychodysleptics. .

As can be seen, the effect of ketamine is limited to 2 days compared to the prolonged effect, greater than 30 days, obtained with 50% N ₂ O treatment, which does not have the adverse effects of ketamine.

In the end, these preclinical data showed an unexpected effect of treatment with nitrous oxide at 50% since this gas is capable of significantly reducing and prolonging (> 1 month) the chronic pain of the neuropathic type. In comparison, the effect of morphine is limited to a few minutes following its administration without any long-term anti-hyperalgesic effect. The anti-hyperalgesic effect of an NMDA receptor antagonist such as ketamine is limited to 2 days. Thus, beyond its analgesic effect, N ₂ O, via its anti-hyperalgesic properties, could represent a particularly beneficial therapeutic strategy in the management of chronic pain patients, in particular in patients whose central mechanisms of sensitization to pain predominates.

These data obtained with a gas mixture with 50% N ₂ O also suggest that lower concentrations of N ₂ O, that is to say concentrations of less than 50% by volume, should have the same beneficial effects. -sensitizers, ie reduction of hypersensitivity to delayed pain, while reducing the "acute" sedative / analgesic effect of nitrous oxide.

In fact, at concentrations of N ₂ O less than 50% by volume, ie said "sub-anesthetic" concentrations, only a slight amnesia and few sedative and / or analgesic effects are present in humans, as illustrated. in Table 2 below, which allows easy use and without major risk of said gas mixture outside the hospital, especially at home.

Table 2

In order to demonstrate the effectiveness of N ₂ O concentrations of less than 50% by volume, additional tests were carried out in neuropathic rats, according to the same protocol as above, with gaseous mixtures containing N ₂ O, from oxygen and possibly nitrogen, ie (% by volume):

mixture A: 12.5% N ₂ O + 50% O ₂ + 37.5% N ₂

- mixture B: 25% N ₂ O + 50% O ₂ + 25% N ₂

C: 35% N ₂ O + 50% O ₂ + 15% N ₂ The results obtained show that the delayed anti-sensitizing effect is more pronounced with the C mixture than with the A and B mixtures. other words, it is preferable to use N ₂ O concentrations greater than 15%, advantageously greater than 25% but less than or equal to 45%. Indeed, these N ₂ O concentrations being less than 50%, the harmful secondary sedative effects are significantly less than with the 50% N ₂ O mixture previously tested, as recalled in Table 2 above.

In addition, these tests have also shown that it is advantageous to carry out several successive inhalations of N ₂ O several days in succession, for example 1 inhalation of 1 hour 15 min for 3 successive days. In fact, performing several inhalation several days in a row increases the desired effect of reducing hypersensitivity to delayed pain.

This is illustrated in FIGS. 5A, 5B, 6A and 6B which show the delayed anti-sensitizing effect of mixtures A, B and C as well as a mixture of 50% N ₂ O and air (control) on a loosely constricted rat paw (CCI) of the sciatic nerve (FIG.

6A) and on an uninjured rat paw (FIGS. 5B, 6B), on which mechanical pressures are applied in order to measure the pain threshold.

As seen, administering N ₂ O 3 times in a row (1 administration per day) for 15 minutes at each inhalation provides a reduction in hypersensitivity to delayed, long-lasting, occurring and observable pain. approximately 24 hours after the first inhalation and continuing to occur for approximately 1 week after the last inhalation for mixture B, C and the 50% mixture. On the other hand, the mixture A (12.5%

N ₂ O) did not show in this case a significant difference with the control (air), which confirms that it is preferable to use N ₂ O concentrations of at least 15% by volume in the rat .

In addition, these tests have also shown that it is advantageous to carry out an inhalation greater than 30 min of N ₂ O, for example 1h. In fact, carrying out an inhalation of more than 30 min makes it possible to increase the desired anti-sensitizing effect.

This is illustrated in FIGS. 7A and 7B of a 50% N ₂ O and air (control) mixture on a loosely constricted rat paw (CCI) of the sciatic nerve (FIG. uninjured rat paw (FIG 7B), on which mechanical pressures are applied to measure the pain threshold.

As seen, administering N ₂ O during Ih provides a reduction in hypersensitivity to delayed pain, i.e., a long-lasting, observable anti-sensitizing effect approximately 24h after the first inhalation and continuing to occur for approximately 1 week after the last inhalation for a 50% mixture. Hence, according to the invention, a gaseous mixture containing nitrous oxide (N ₂ O) is preferably used in a proportion by volume of less than 50%, typically less than 48%, advantageously between 15 and 45% by volume. as an inhalable drug for the curative treatment of chronic pain in a mammal, the gaseous mixture being administered for a time sufficient to achieve a reduction in delayed pain hypersensitivity, i.e. delayed anti-sensitiser, observable for at least 6 hours, usually at least 12 to 24 hours, after the end of the inhalation of the gaseous mixture by said mammal, in particular in humans.

Claims

claims

A gaseous mixture containing a proportion of nitrous oxide (N ₂ O) of between 15 and 45% by volume for use as an inhalable medicament for the curative treatment of chronic pain in a mammal, the gaseous mixture being administered for a time sufficient to achieve a reduction in delayed pain hypersensitivity observable at least 6 hours after the end of inhalation of the gaseous mixture by said mammal.

2. Gas mixture according to claim 1, characterized in that the mammal is a human being.

3. Gas mixture according to one of claims 1 or 2, characterized in that the proportion of N ₂ O in the gaseous mixture is at least 20% by volume, preferably at least 25% by volume.

4. Gas mixture according to one of the preceding claims, characterized in that the gaseous mixture is administered for a time sufficient to obtain an analgesic effect for at least part of the duration of administration by inhalation of the gaseous mixture and an anti-inflammatory effect. -sensitizer delayed after the end of the inhalation of the gaseous mixture by said mammal.

5. Gas mixture according to claim 4, characterized in that the gaseous mixture is administered for a period of at least 20 min, preferably at least 30 min.

6. Gas mixture according to claim 4, characterized in that the gaseous mixture is administered for a time sufficient to obtain a delayed anti-sensitizing effect occurring and observable at least 12 hours after the end of the inhalation of the gaseous mixture.

7. Gas mixture according to one of the preceding claims, characterized in that the gaseous mixture is administered for a time sufficient to obtain a delayed anti-sensitizing effect occurring and observable at least 24 hours after the end of the inhalation of the mixture. gaseous.

8. gas mixture according to one of the preceding claims, characterized in that the gaseous mixture contains, in addition, between 20 and 60% by volume of oxygen.

9. Gaseous mixture according to one of the preceding claims, characterized in that the gaseous mixture is formed from 15 to 45% by volume of N ₂ O and at least 20% by volume of oxygen, and contains xenon argon, helium, neon, krypton and nitrogen.

10. Gaseous mixture according to one of the preceding claims, characterized in that the gaseous mixture is formed from 15 to 45% by volume of N ₂ O, from 21% to 60% by volume of oxygen, and from nitrogen to the rest.

11. Gaseous mixture according to one of the preceding claims, characterized in that the pain of neuropathic origin is selected from post-zosterian pain, diabetic neuropathy pain, central pain, pain after stroke, pain of multiple sclerosis, neuropathic pain of spinal cord injury, neuropathic pain associated with AIDS or its treatment, neuropathic pain related to cancer, neuropathic pain related to chemotherapy, neuropathic pain related to a surgical procedure that damaged a patient. nerve pathway and postoperative neuropathic pain.

12. Gas mixture according to one of the preceding claims, characterized in that the pain of inflammatory origin is related to osteoarthritis, arthritis, cancer or disc herniation.

13. Gaseous mixture according to one of the preceding claims, characterized in that it is administered in combination with an analgesic.

14. Gaseous mixture according to one of the preceding claims, characterized in that the pain of dysfunctional origin is related to fibromyalgia, irritable bowel syndrome or headache.

15. Gaseous mixture according to one of the preceding claims, characterized in that the hypersensitivity to pain is selected from allodynies and hyperalgesia.