Topical anesthetic

Details Topical anesthetic Topical anesthetic

2001-12-17

2003-09-16

Kim, Vickie (Department: 1614)

Drug, bio-affecting and body treating compositions

Designated organic active ingredient containing

Nitrogen containing other than solely as a nitrogen in an...

C514S535000, C514S536000, C514S960000, C514S649000, C514S537000

Reexamination Certificate

active

06620852

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to improvements in topical anesthetics and in particular topical anesthetics that may be applied by dripping into a wound or other area without the pressure of an applicator on the wound surface.
BACKGROUND OF THE INVENTION
Many, if not most ailments of the body cause pain or discomfort in some degree. Generally pain is experienced when the free nerve endings which constitute the pain receptors in the skin as well as in certain internal tissues are subjected to mechanical, thermal or chemical stimuli. The pain receptors transmit signals along afferent neurons into the central nervous system and thence to the brain. The causes of pain can include inflammation, injury, disease, muscle spasm and the onset of a neuropathic event or syndrome. Ineffectively treated pain can be devastating to the person experiencing it by limiting function, reducing mobility, complicating sleep, and dramatically interfering with the quality of life.
Inflammatory pain can occur when tissue is damaged, as can result from surgery or due to an adverse physical, chemical or thermal event or to infection by a biologic agent. Although inflammatory pain is generally reversible and subsides when the injured tissue has been repaired or the pain inducing stimulus removed, present methods for treating inflammatory pain have many drawbacks and deficiencies. Neuropathic pain is a persistent or chronic pain syndrome that can result from damage to the nervous system, the peripheral nerves, the dorsal root ganglion or dorsal root, or to the central nervous system. Neuropathic pain syndromes include allodynia, various neuralgias such as post herpetic neuralgia and trigeminal neuralgia, phantom pain, and complex regional pain syndromes, such as reflex sympathetic dystrophy and causalgia. Causalgia is characterized by spontaneous burning pain combined with hyperalgesia and allodynia.
There are many types of anesthetics in use today. One type of anesthetic is a local anesthetic. Local anesthetics act via a loss of sensation in the localized area of administration in the body. The mechanism by which local anesthetics induce their effect, while not having been determined definitively, is generally thought to be based upon the ability to locally interfere with the initiation and transmission of a nerve impulse, e.g., interfering with the initiation and/or propagation of a depolarization wave in a localized area of nerve tissue. The actions of local anesthetics are general, and any tissue where nerve conduction, e.g., cell membrane depolarization occurs can be affected by these drugs. Thus, nervous tissue mediating both sensory and motor functions can be similarly affected by local anesthetics.
Frequently, local anesthetics are administered to the patient by means of an injection. Unfortunately, the injection of the anesthetic can itself be very painful to the individual. Besides the initial insertion of the needle in administering the injection of the anesthetic there are other causes of pain to the patient. For example, the acidity of the anesthetic solution can cause pain. One very common anesthetic lidocaine and others is an acid that burns when it is injected. While this pain can be reduced by, for example, mixing bicarbonate with the injection just before it is given this procedure complicates the treatment of the individual. Another cause of pain from an injection is due to the depth of the injection. Injections into the superficial parts of the skin will hurt more than when injected into the deep layers and beneath the skin. Another factor in causing pain in an injection can be the speed of injection. Injecting as slowly as the needle is removed will also make the pain less.
As a result, there are many instances where an injection is not preferred for administering an anesthetic and the administration of a topical anesthetic is desired. One such instance may be where the pain due to the injection is not desired. Another such instance is in the case of young children. Many children fear an injection sometimes more than the pain they are suffering. As a result, even the sight of a hypodermic needle in an emergency situation can create great discomfort in the patient. As a result, there is a need for a topical anesthetic that may be applied without the use of an injection. In addition, there is a particular need for a topical anesthetic that may be applied to produce a superficial anesthesia that will allow for a painless injection of tissues to produce a deep anesthesia.
One approach to the problem administering anesthetics without an injection is described in U.S. Pat. No. 5,563,153 to Mueller. Mueller discloses a sterile topical anesthetic that employs a product called “GELFOAM®” as the vehicle for the anesthetics of the Mueller composition. GELFOAM® is an absorbable gelatin-based material. The consistency of the Mueller anesthetic is a pasty consistency similar to horseradish or peanut butter. This pasty material once prepared is then applied with an applicator by smearing it over the open wound. The force necessary to apply this paste is rather heavy and the use of the Mueller anesthetic can be very painful and risk further traumitizing an already sensitive injury further.
One of the problems that are encountered with the use of the Mueller composition is that the Mueller formula can inhibit wound healing. This problem stems from the presence of the GELFOAM® in the Mueller composition. The manufacturer of the GELFOAM® product states that the GELFOAM® powder should be made into a doughy paste that can be smeared or pressed against the open wound. The excess should be removed by irrigation prior to closing the wound. Closing over the GELFOAM® may interfere with the healing of the skin edges.
Another issue with respect to the use of GELFOAM® is its stability once formed into a paste. The manufacturer of the GELFOAM® product does not publish stability data on the product once it is removed from the container and formed into a paste. According to the manufacturer the paste must be used immediately. Extemporaneous preparation to avoid the stability issues caused by GELFOAM® would be time consuming and impractical given the need for expediency in the nature of its use. GELFOAM® is also quite expensive. Currently, a single gram of GELFOAM® costs approximately $49.00. Since the Mueller composition requires at least one gram or more of the powder, the use of GELFOAM® would be economically unfeasible in clinical practice due to its high cost.
The Mueller composition has a further infirmity. GELFOAM® has no bacteriostatic agent present. Once exposed to room air, GELFOAM® is an excellent medium for the growth of microbes. The manufacturer of GELFOAM®, however, warns against adding or mixing an antibiotic to the paste to prevent bacterial growth once GELFOAM® has been removed from its sterile container.
There are many types of wounds where the use of an applicator no matter how soft and pliable can create pain or increase the risk of further injury. One such example is eye wounds. The sensitive nature of the ocular tissue makes it very difficult for a topical anesthetic to be applied. Another type of wound that the use of an applicator is not desirable includes wounds to oral mucosa such as canker sores and tooth/gum pain where the slightest pressure of an applicator can cause significant pain to the patient. Those skilled in the art will recognize that there are numerous other types of instances where a topical anesthetic should be administered without the use of an applicator that touches the wound surface.
OBJECTS OF THE INVENTION
It is an object of the invention to provide a topical anesthetic that may be administered without contacting the wound surface with an applicator and causing possible pain.
It is an object of the invention to provide a topical anesthetic that is a fluid that may be dripped onto the surface of a wound.
It is another object of the invention to provide a topical anesthetic of relatively low viscosity such that it can flow over an injured surface.
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