Method of reducing elevated intraocular pressure
The present invention relates to a novel agent which is useful for the treatment of ocular hypertension (elevated intraocular pressure), and glaucoma. More specifically, this invention relates to a pharmaceutical composition for reducing elevated intraocular pressure which comprises as an essential component dilazep of the following formula (1) or any one of pharmaceutically acceptable salts thereof. ##STR2## 
     The present invention also relates to a method of reducing elevated intraocular pressure, which comprises administering the compound (1) to patients suffering from abnormally elevated intraocular pressure. 
     Glaucoma is a disease in which the intraocular pressure (IOP) is persistently or recurrently elevated above the normal range of pressure, which gives organic damage to ocular structures and further impairment of visual function which leads to, for instance, reduction of visual field. &#34;Ocular hypertension&#34; herein used is the term coined to denote an elevated intraocular pressure above the normal level, which is not accompanied by any functional impairment of vision, but, after a long period of time, may develop glaucoma. The medical treatment of ocular hypertension or glaucoma is directed to the reduction of the elevated intraocular pressure down to the normal IOP that induces no functional impairment, and also directed to the maintenance of the normal IOP. 
     In the present specification, an agent which is useful for reducing elevated intraocular pressure which is found in the ocular hypertension and glaucoma may sometimes be referred to as &#34;antiglaucoma agent&#34; for simplicity. 
     Conventional antiglaucoma agents known to be effective in the treatment of ocular hypertension or glaucoma are: carbonic anhydrase inhibitors (oral administration), hyperosmotic agents (injection), pilocarpine, epinephrine and its prodrug dipivefrine (eye drops). More recently, β-blockers (eye drops) are being extensively used for this purpose. However, all these agents have many disadvantages. Carbonic anhydrase inhibitors, for example, are known to have side effects such as gastrointestinal disturbances and general malaise. Hyperosmotic agents are used mainly in the treatment of acute attacks due to postoperative sudden rise in IOP and are not appropriate for the long-term therapy for glaucoma or ocular hypertension. 
     Pilocarpine eye drops are known to have several side effects such as feeling of obfuscation due to miosis-induced arctation of the visual field and accommodation disorders due to contraction of the ciliary muscle. Epinephrine and dipivefrine eye drops induce rebound congestion due to vasoconstriction, ophthalmalgia and tachycardia. The eye drops containing β-blockers as an active ingredient have been reported to cause systemic side effects such as headache and depression through their CNS (central nervous system) action, asthmatic symptoms by acting on the respiratory system and bradycardia and hypotension through its cardiovascular action (Iyaku Journal (Medicine and Drug Journal) 28: 705, 1992). When applied topically, β-blockers produce a feeling of dryness due to reduced lacrimal fluid and irritation at the time of instillation. These β-blockers are disadvantageous in that they are contraindicated for patients with bradycardia or bronchial asthma because the above side effects are particularly augmented in these patients (American Journal of Ophthalmology 102: 606, 1986). As described above, none of these antiglaucoma agents now in widespread use are satisfactory. 
     It is one objective of this invention to provide a novel antiglaucoma agent for treating ocular hypertension or glaucoma, which agent possesses an excellent ocular hypotensive effect (i.e., intraocular pressure-reducing effect) and no significant side effects, in particular, a minimal eye irritating effect. 
     As a result of extensive study seeking for excellent antiglaucoma agents, the present inventors have found that the compound (1) known as a therapeutic agent for treating ischemic heart disease or disorder of cerebral blood flow has an ocular hypotensive effect, an effect unpredicted from the known major pharmacological effects, and minimal eye irritating effect, and therefore, the compound (1) is useful for the treatment of ocular hypertension or glaucoma. This pressure-reducing effect of the compound (1) was discovered by the present inventors in the first place. 
     The pharmacological properties of the compound (1) suggest that the compound (1) has no side effects such as miosis and accommodation disorders found in pilocarpine eye drops or rebound congestion due to vasoconstriction found in epinephrine and dipivefrine eye drops. The compound (1) is further reported to have little effect on heart rate or blood pressue (Kisotorinsho, 9 1791, 1975), and considered to have minor or no effect on respiratory system. Accordingly, the compound (1) is considered to be free of hypotensive effect and side-effect on respiratory system, which are found in β-blocker used as eye drops. 
     As stated above, the compound (1) is a highly useful agent for the treatment of ocular hypertension or glaucoma without having significant side effects possessed by conventional agents. 
     Compound (1) is described in Japanese Pharmacopoeia, and it can be synthesized by referring, for example, to the published literatures listed under &#34;3185. Dilazep&#34; on page 504 in the 11th Edition of Merck Index. A commercially available compound (1) can also be used (Nagusa Kasei Co., Ltd.). 
     Examples of pharmaceutically acceptable salts of the compound (1), which can be the antiglaucoma agent of the present invention, are those formed with inorganic and organic acids, such as hydrochloride, sulfate, nitrate, phosphate, hydrobromate, tartrate, acetate, citrate, fumarate, maleate and oxalate. 
     The antiglaucoma agent of the present invention can be formulated in a pharmaceutical composition having an appropriate unit dosage form by mixing the compound of the formula (1) or a pharmaceutically acceptable salt thereof with conventional vehicles for pharmaceutical use. The unit dosage form can be any one of conventional dosage forms. Examples of the dosage forms for topical administration may be eye drops and eye ointments, and those for systemic administration may be tablets, granules and injections. It is particularly desirous to use the antiglaucoma agent of the present invention in the form of eye drops. 
     When used as an eye drop, it is desirous to prepare the formulation which contains the compound (1) at a concentration ranging from 0.001 to 1.0%. Additives that are usually used in formulating eye drops can be used together with the compound (1). Additives to be used include preservatives such as chlorobutanol, sodium dehydroacetate, benzalkonium chloride, cetylpyridinium chloride, phenethyl alcohol, methyl paraoxybenzoate and benzethonium chloride, buffering agents such as borax, boric acid and potassium dihydrogen phosphate, viscosity-increasing agents such as methylcellulose, hydroxyethylcellulose, carboxymethylcellulose, hydroxypropyl methylcellulose, polyvinyl alcohol, sodium carboxymethylcellulose and chondroitin sulfate, solubilizing agents such as polysorbate 80 and polyoxyethylene hydrogenated castor oil 60, and stabilizers such as disodium edetate and sodium bisulfite. It is desirous that eye drops are isotonic with lacrimal fluid, and, for this reason, isotonicating agents such as sodium chloride, potassium chloride, and glycerin may be added as necessary. The pH of the formulation may be at any point within an ophthalmologically acceptable range and is preferably between pH 5.0 and pH 8.0. 
     The dosage and administration mode of the eye drops of the present invention can vary depending on patients&#39; conditions and age. The usual single dosage, however, is 1-5 drops and administered one to three times daily. For ophthalmic ointments, an appropriate amount is placed in the conjunctival sac one to two times daily. 
    
    
     FIG. 1 shows the test results on the major pharmacology (ocular hypotensive effect) of the eye drops of the present invention. 
    
    
     The present invention is explained in more detail below by Examples and Experiments, but this invention is not limited to these Examples and Experiments. 
     
         ______________________________________                                    
Example 1                                                                 
Eye Drops                                                                 
______________________________________                                    
Dilazep hydrochloride                                                     
                   1.15      g                                            
(as net Dilazep)   (1.00     g)                                           
Glycerin           1.90      g                                            
1N Sodium hydroxide                                                       
                   1.60      ml                                           
Benzalkonium chloride                                                     
                   0.01      g                                            
Sterile distilled water                                                   
                   appropriate amount                                     
Total              100       ml                                           
______________________________________                                    
 
    
     Production: Dilazep hydrochloride is dissolved in sterile distilled water (90 ml), and glycerin, benzalkonium chloride, and 1N sodium hydroxide are added thereto and admixed. Sterile distilled water is added to the mixture to make 100 ml. pH: about 7; osmotic pressure-ratio: about 1. 
     
         ______________________________________                                    
Example 2                                                                 
Eye Drops                                                                 
______________________________________                                    
Dilazep hydrochloride                                                     
                     0.0115    g                                          
(as net Dilazep)     (0.010    g)                                         
Potassium dihydrogen phosphate                                            
                     0.360     g                                          
Disodium hydrogen phosphate                                               
                     0.571     g                                          
Sodium chloride      0.456     g                                          
Benzethonium chloride                                                     
                     0.010     g                                          
Sterile distilled water                                                   
                     appropriate amount                                   
Total                100       ml                                         
______________________________________                                    
 
    
     Production: Dilazep hydrochloride is dissolved in sterile distilled water (90 ml), and potassium dihydrogen phosphate, disodium hydrogen phosphate, sodium chloride, and benzethonium chloride are added thereto and admixed. Sterile distilled water is added to the mixture to make 100 ml. pH: about 7; osmotic pressure-ratio: about 1. 
     
         ______________________________________                                    
Example 3                                                                 
Eye Drops                                                                 
______________________________________                                    
Dilazep hydrochloride                                                     
                    0.00115   g                                           
(as net Dilazep)    (0.0010   g)                                          
Boric acid          1.187     g                                           
Borax               0.073     g                                           
Sodium chloride     0.287     g                                           
Benzalkonium chloride                                                     
                    0.010     g                                           
Sterile distilled water                                                   
                    appropriate amount                                    
Total               100       ml                                          
______________________________________                                    
 
    
     Production: Dilazep hydrochloride is dissolved in sterile distilled water (90 ml), and boric acid, borax, sodium chloride, and benzalkonium chloride are added thereto and admixed. Sterile distilled water is added to the mixture to make 100 ml. pH: about 7; osmotic pressure-ratio: about 1. 
     Experiment 1: 
     Main pharmacodynamics and pharmacology (ocular hypotensive effect) 
     The ocular hypotensive effect of the eye drops of this invention was investigated in rabbits. The same experiment was also conducted using a representative β-adrenergic blocking agent, and its ocular hypotensive effect was compared with that of eye drops of this invention. 
     Methods: According to the formulations described in Examples 1, three eye drops respectively containing 0.001, 0.1 and 1.0% of the compound (1) were prepared. As a negative control, an eye drop not containing compound (1), which was prepared according to the method described in Example 1, was used. The positive control was a commercially available eye drop containing timolol maleate (0.5% equivalent of free base) as an active ingredient. 
     Male Japanese White rabbits (body weight: ca. 2 kg) with normal intraocular pressure were used in the experiment. Each of the test solutions (three eye drops containing 0.001, 0.1, and 1.0% of dilazep) (50 μl ) was instilled into one eye of each rabbit, and the control solution free of dilazep (50 μl ) into the fellow eye which served as a control. For each solution, four to eight rabbits were used. After anesthesia of the corneal surface by instillating 5 μl of 0.4% oxybuprocaine hydrochloride, the intraocular pressure was measured using an applanation pneumatonograph (Alcon) before and after the instillation of the test solution and control solution. Measurement of intraocular pressure after the instillation was conducted with one-hour to two-hour intervals until six hours to eight hours post-instillation. 
     Results: The results of the above test involving the eye drops of the present invention are presented in FIG. 1, wherein difference in IOP between the control and the test eyes are shown. Table 1 compares the test results obtained with a commercial eye drop containing 0.5% timolol maleate as an active ingredient with those obtained with the eye drops of the present invention. The eye drops containing 1.0% and 0.1% of compound (1) produced the maximal IOP reduction two hours after instillation. As for 1.0% eye drop, an average difference of the IOP from the control eye drop was 2.6 mmHg, and this ocular hypotensive effect was retained for eight hours after instillation. Such ocular hypotensive effect obtained by the instillation of 0.1% eye drop remained unchanged six hours after instillation. Ocular hypotensive was observed 0.5, 1.0 and 2.0 hours after instillation in the case of 0.001% eye drop. 
     On the other hand, commercially available thimol eye drop (0.5%) produced IOP reduction of 0.8 mmHg one and two hours after instillation. The degree of the IOP reduction by the thimol eye drop was significantly less than that by the 0.1% eye drop of the present invention which produced IOP reduction of 1.8 mmHg and 2.7 mmHg one and two hours after instillation, respectively. Thus, the eye drop of the present invention produces the same or greater effect as the thimol eye drop at one fifth concentration. 
     These results show the excellent ocular hypotensive effect of the eye drops of the invention which is superior to that of the typical commercial eye drop containing β-adrenoceptor blocker. 
     
                       TABLE 1                                                     
______________________________________                                    
Difference in IOP between the control and test eyes (mmHg)                
       Con-                                                               
       centration                                                         
       of free                                                            
drug   base (%)  1 hr    2 hr  4 hr  6 hr  8 hr                           
______________________________________                                    
Com-   1.0       -0.63   -2.59 --    --    -1.41                          
pound(1)                                                                  
Com-   0.1       -1.81   -2.67 -1.81 -0.44 --                             
pound(1)                                                                  
Com-    0.001    -0.83   -0.33 -0.04  0.17 --                             
pound(1)                                                                  
Timolol                                                                   
       0.5       -0.80   -0.80 -0.25 -0.10 --                             
maleate                                                                   
______________________________________                                    
 
    
     Experiment 2: 
     Eye irritation test 
     The eye irritating effect of the eye drop of the present invention was investigated in rabbits. 
     Methods: According to the descriptions in Experiment 1, eye drops containing different concentrations of compound (1) as an active ingredient were prepared, and their eye irritating effects were evaluated by modified Draize test (Gendaino Rinsho (Modern Clinics) 4: 277, 1970). 
     Male Japanese White rabbits (body weight: ca. 2 kg) were used in the experiment. The test solutions containing compound (1) at various concentration (50 μl ) was instilled into one eye of an animal and the control solution free from compound (1) into the fellow eye in the same manner. The degree of ocular irritation was scored according to the modified Draize method. 
     Results: The test results for the 1.0% eye drop of the invention which has the highest concentration with respect to compound (1) are shown in Tables 2 and 3. There was no difference between the test solution and the control solution with respect to the degree of irritation on the cornea and conjunctiva irrespective of the time when the degree of irritation was measured. As for the iris, a slight congestion was found 0.5 and 2 hours after instillation of the test solution. However, the congestion disappeared after 2.5 hours. 
     Similar test results were obtained when 0.1% eye drop of the invention was used. However, the degree of the congestion of the iris was very slight as compared with that in the case of the 1.0% eye drop. There was no substantial difference between the test solution and the control solution in all tests when 0.001% eye drop of the invention was used. Thus, the experiment results demonstrate that the eye drops of the present invention give negligible irritation to rabbit eyes. 
     
                       TABLE 2                                                     
______________________________________                                    
Degree of irritation on eyes (Test solution)                              
          Time after instillation (min)                                   
          before                                                          
          instillation                                                    
                  30     60     90   120  150                             
______________________________________                                    
Cornea:                                                                   
Opaqueness   0*       0      0    0    0    0                             
Opaque region                                                             
            0         0      0    0    0    0                             
Iris:                                                                     
Irritation value                                                          
            0         1      1      0.5                                   
                                         0.3                              
                                            0                             
Conjunctiva:                                                              
Degree of flare                                                           
              0.6       0.8    0.5                                        
                                    0.6                                   
                                         0.5                              
                                              0.6                         
on tunica                                                                 
conjunctiva                                                               
Degree of Edema                                                           
            0         0      0    0    0    0                             
on tunica                                                                 
conjunctiva                                                               
Degree of flare                                                           
              0.3     0      0    0    0    0                             
on eye ball                                                               
conjunctiva                                                               
Condition of haw                                                          
            0         0      0    0    0    0                             
Secrete     0         0      0    0    0    0                             
______________________________________                                    
 *: Average score of four rabbits tested                                  
 
    
     
                       TABLE 3                                                     
______________________________________                                    
Degree of irritation on eyes (Control solution)                           
          Time after instillation (min)                                   
          before                                                          
          instillation                                                    
                  30     60     90   120  150                             
______________________________________                                    
Cornea:                                                                   
Opaqueness   0*       0      0    0    0    0                             
Opaque region                                                             
            0         0      0    0    0    0                             
Iris:                                                                     
Irritation value                                                          
            0         0      0    0    0    0                             
Conjunctiva:                                                              
Degree of flare                                                           
              0.6       0.6    0.5                                        
                                    0.6                                   
                                         0.6                              
                                              0.6                         
on tunica                                                                 
conjunctiva                                                               
Degree of Edema                                                           
            0         0      0    0    0    0                             
on tunica                                                                 
conjunctiva                                                               
Degree of flare                                                           
              0.1       0.3  0    0    0    0                             
on eye ball                                                               
conjunctiva                                                               
Condition of haw                                                          
            0         0      0    0    0    0                             
Secrete     0         0      0    0    0    0                             
______________________________________                                    
 *: Average score of four rabbits tested                                  
 
    
     The pharmaceutical composition of the present invention shows an excellent ocular hypotensive effect and a minimal eye-irritating effect, and these advantages promise that the composition of the present invention is highly useful in the treatment of ocular hypertension and glaucoma.