Abstract:
An extended release analgesic for controlling pain comprised of an opioid or non-opioid analgesic drug ionically bound to hyaluronic acid, poly-γ-glutamic acid or other ionic polymers, and injected into a body either subcutaneously, intramuscularly or intraperitoneally, utilizing counter-ions of different valences to control the rate of release into the body.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims priority of Provisional application Ser. No. 60/371,790, filed on Apr. 11, 2002. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to extended release analgesic for pain control. 
     BACKGROUND OF THE INVENTION 
     Analgesics are used to control pain in various situations such as post surgical, post injury, cancer treatment, AIDS treatment and more. Analgesics used include steroidal, non-steroidal, opioid, and non-opioid analgesics. Many of these drugs have very short residence times in the body, ranging from 6 to 12 hours for steroids and non-steroids, to as low as 1 to 3 hours for opioids. Pain from the procedures described can last several days. These analgesics thus must be administered many times in order to be effective in controlling pain. 
     There are several methods for extending the time over which analgesics are effective. One is advanced chemical entities. Whereas analgesics such as morphine have a mean residence time of only a few hours, advanced synthetic analgesics such as OxyContin® have an effective residence time in the body of 8 hours. Some drawbacks to this material are the fact that it is orally delivered, and as a result the unit dose may be improperly modified by a patient, resulting in a dangerous overdose, or the patient may not be capable of swallowing the medication. 
     Another method for extending the effective time of analgesics is to meter them into the body via a trans-dermal patch. This method has the advantage of extending the release of analgesics to several days. The drawbacks to this method are that it is external to the body, and thus it may still be manipulated by the patient. For example, some of the patients are pets who scratch at and eat the patches. Another drawback is that the patches are both species and body weight specific. A patch used on a person cannot be used on a dog, and a dog patch may not be used on a cat. Different types of patches must be used for people of different body weights, etc. 
     SUMMARY OF THE INVENTION 
     Given the state of the art, there is a definite need for a novel method of analgesic release where, (1) the release of analgesic is measured in days, (2) the release of the analgesic can not be manipulated by the patient or other external sources, (3) fine motor control, such as swallowing, is not required to administer the analgesic, and (4) the amount of analgesic administered is determined by the doctor or nurse depending on the patients&#39; needs (weight, species, etc). 
     The invention features an analgesic drug ionically bound to an ionic polymer. The polymer may be hyaluronic acid, poly-γ-glutamic acid, or another ionic polymer. The polymer may be anionic, in which case the drug would be cationic, or the polymer may be cationic and the drug anionic. The polymer-drug matrix is injected either subcutaneously, intramuscularly, or intraperitoneally. The matrix is degraded over time via the enzymatic machinery of the body, thus releasing the drug. The rate at which the polymer matrix is degraded by the body may be modified be using various counter-ions in the polymer matrix. Counter cations used can include sodium (Na 1+ ), calcium (Ca 2+ ), and the ferric form of iron (Fe 3+ ), and counter anions used can include chloride (Cl 1− ) and sulfate (SO 4   2− ). The greater the valence on the counter-ion, the slower the polymer matrix will degrade. This is because higher valence ions provide better electrostatic shielding of the polymer&#39;s ionic sites, and hence the hydrodynamic radius decreases, inhibiting access of enzymes to the polymer degradation sites. This invention may be administered by a doctor or nurse who has the ability to modify the actual dose to allow for differences in species and body weight. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Other objects, features and advantages will occur to those skilled in the art from the following description of the preferred embodiments, and the accompanying drawings, in which: 
         FIG. 1  is a graph of blood morphine concentrations over time resulting from the injection of aqueous morphine sulfate, and several extended release compounds of the invention; 
         FIG. 2  is a graph of blood morphine concentrations resulting from the injection of aqueous morphine sulfate, and two different extended release compounds of the invention using different amounts of calcium as the counter-ion; and 
         FIG. 3  is a graph showing the pain control effect of the two different inventive compounds also reflected in FIG.  2 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The following is a description of the preferred embodiment of the invention. The preferred polymer is hyaluronic acid having an average molecular weight of over 1 million Daltons. Purified sterile polymer that is pyrogen free is placed in a clean environment (class 100 or cleaner). The amount of analgesic required for the duration of treatment is weighed out and dissolved in sterile saline for injection. The solution is then sterile filtered since the analgesic powder was not sterile. The polymer is then added and the material is mixed for 24 hours, or until all polymer is dissolved. All beakers, stirbars and instruments were sterilized via autoclaving prior to product contact. 
     In the following examples, four prototypes were tested to determine the release rates for the various conditions explained. These prototypes were formulated as follows: 
     EXAMPLE 1 
     Sodium hyaluronate with morphine: All work was performed in a class 100 clean hood. 54 mg of morphine hexahydrate was placed in a depyrogenated beaker. 3 ml of sterile saline (0.9% NaCl) was added to the morphine and swirled until it was dissolved. The solution was then drawn up into a syringe. The syringe was fitted with a sterilizing filter, and the solution was passed through the filter into a clean sterile beaker. 45 mg of sterile and pyrogen free hyaluronic acid was weighed, and placed in the beaker with the solution. The hyaluronic acid had a molecular weight in excess of 1 million Daltons. A sterilized stir-bar was placed in the beaker, and the solution was stirred for 24 hours. The solution was then placed in syringes (1 ml per syringe) and stored for subsequent animal tests. 
     EXAMPLE 2 
     Calcium hyaluronate with morphine: All work was performed in a class 100 clean hood. 54 mg of morphine hexahydrate was placed in a depyrogenated beaker. 2.25 ml of sterile water was added to the morphine and swirled until it was dissolved. The solution was then drawn up into a syringe. The syringe was fitted with a sterilizing filter, and the solution was passed through the filter into a clean sterile beaker. 45 mg of sterile and pyrogen free hyaluronic acid was weighed, and placed in the beaker with the solution. The hyaluronic acid had a molecular weight in excess of 1 million Daltons. A sterilized stir-bar was placed in the beaker, and the solution was stirred for 24 hours. 0.0135 grams of calcium chloride was added to 0.75 ml of water, and swirled until dissolved. The solution was then drawn into a syringe, the syringe fitted with a sterile filter, and the solution was added via this sterile filter to the polymer solution. The final solution was then placed in syringes (1 ml per syringe) and stored for subsequent animal tests. 
     EXAMPLE 3 
     Ferric hyaluronate with morphine: All work was performed in a class 100 clean hood. 54 mg of morphine hexahydrate was placed in a depyrogenated beaker. 2.25 ml of sterile water was added to the morphine and swirled until it was dissolved. The solution was then drawn up into a syringe. The syringe was fitted with a sterilizing filter, and the solution was passed through the filter into a clean sterile beaker. 45 mg of sterile and pyrogen free hyaluronic acid was weighed, and placed in the beaker with the solution. The hyaluronic acid had a molecular weight in excess of 1 million Daltons. A sterilized stir-bar was placed in the beaker, and the solution was stirred for 24 hours. 0.010 grams of ferric chloride was added to 0.75 ml of water, and swirled until dissolved. The solution was then drawn into a syringe, the syringe fitted with a sterile filter, and the solution was added via this sterile filter to the polymer solution. A sterile solution of 1M NaOH was used to neutralize the solution, which becomes acid when the ferric chloride is added. The solution was then placed in syringes (1 ml per syringe) and stored for subsequent animal tests. 
     EXAMPLE 4 
     Sodium poly-γ-glutamate with morphine: Same materials and procedures as #1, except using poly-γ-glutamic acid instead of hyaluronic acid. 
     Table 1 shows the effect of the use of the sustained release preparations detailed above when injected into rats. Time duration was measured using observation of rat mobility. 
     
       
         
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                 Material injected 
                 Time duration of analgesic effects 
               
               
                   
               
             
             
               
                 Aqueous Morphine, control 
                 2 hours 
               
               
                 Sodium hyaluronate and morphine 
                 8 hours 
               
               
                 Calcium hyaluronate and morphine 
                 &gt;12 hours    
               
               
                 Ferric hyaluronate and morphine 
                 &gt;12 hours,   
               
               
                   
                 with onset delayed by 2 hours 
               
               
                 Sodium poly-γ-glutamic acid and 
                 &gt;6 hours,  
               
               
                 morphine 
                 with onset delayed by 2 hours 
               
               
                   
               
             
          
         
       
     
       FIG. 1  shows the blood morphine concentrations resulting from the injection of aqueous morphine sulfate, and several extended release compounds made by the processes described above. All formulas had an identical morphine concentration of 18 milligrams of morphine pentahydrate per milliliter. There are several conclusions to be drawn from FIG.  1 . First, all the non-aqueous polymer formulas have a longer release of morphine than the standard aqueous dose. Second, the sodium hyaluronate formula has a very high initial peak, followed by a very fast decline of morphine in the blood stream. Third, calcium hyaluronate has a lower peak than both the sodium hyaluronate and the ferric hyaluronate. In addition, it has an elevated “shoulder” between the times of 5 and 12 hours that the other formulas do not have. This is unique because one would have predicted the ferric formula to be more closely packed than the calcium formula, resulting in a slower initial release, followed by elevated levels after the peak, due to its higher valence than calcium. The data, however, contradict this theory because the calcium formula exhibited a slower release than the ferric formula. 
       FIG. 2  shows the blood morphine concentrations resulting from the injection of aqueous morphine sulfate, and two extended release compounds of the invention. The purpose of this experiment was to expand the knowledge of the effects of the divalent cation calcium (Ca 2+) on hyaluronic acid and morphine release. The data clearly shows that increasing the concentration of calcium, results in a lower maximum peak, and a higher “shoulder”. This is a very beneficial kinetic for extended release drug delivery. 
     The rats injected with the compounds of  FIG. 2  were also tested using an Electrovon frey Analgesiometer to asses their pain response. Each rat had an incision made on one of its hind paws. The amount of force required to illicit a response (rat raises its paw) was measured. The more force required, the greater the analgesia. The results are in FIG.  3 . This graph clearly shows that the formula with the most calcium also provides the longest lasting pain control. 
     Non-opioids for Controlled Release 
     A person skilled in the art, will understand that the extended release demonstrated for morphine, will also have implications for other opioid drugs such as codeine and oxycodone, as well as non-opioid drugs. Morphine sulfate is comprised of two morphine groups ionically associated with a sulfate group. In solution, the morphine groups are free floating and each have a molecular weight of 285 Daltons. 
     Three typical non-opioid analgesics comprise acetaminophen (4′-hydroxyacetanilide), acetylsalicylic acid (aspirin), and ibuprofen. Each of these molecules is similar to morphine both structurally (each contains at least one unsaturated aromatic ring), and each is a small molecular weight species, having a range of molecular weights from 130 for acetaminophen to over 200 for ibuprofen. Since these non-opioid molecules are similar to morphine, the release properties for these molecules out of the ionic polymer/counter ion matrix of the invention is expected to be similar to that of morphine.