Abstract:
Sustained release formulations are disclosed which contain a therapeutically active medicament and a high and low viscosity HPMC and which exhibit a zero order release profile.

Description:
BACKGROUND OF THE INVENTION 
     Sustained release formulations containing a pharmacologically active agent and exhibiting a zero order release rate are particularly useful. 
     Ibuprofen is a well-known analgesic which has been used to treat chronic pain such as that associated with arthritic and rheumatic conditions. In such cases the analgesic is best administered so as to sustain its action over a period of time and to have a uniform level of analgesic action over this extended time period. This objective can partly be achieved by the repeated administration of a rapid release dosage. However, this procedure clearly has patient acceptability problems as well as a repeated raising and lowering of the blood levels of analgesic. 
     Generally, the release profiles in controlled release formulations follow a classical square root of time relationship, i.e., the release rate decreases with time. In a zero order composition a plot of the rate of release of drug vs. time shows a straight horizontal line, i.e., the release rate is independent of time. Zero order sustained release compositions provide a more uniform delivery of the therapeutic agent over long periods of time. 
     Sustained release formulations for ibuprofen have been disclosed in EP publication No. 255,404, however the formulations disclosed do not provide for a zero order release rate. In WO No. 87/00044 a sustained release formulation, exhibiting a bimodal controlled release, is disclosed. The carrier base is composed of a bimodal hydroxypropylmethylcellulose (HPMC) and the medicament selected from an antiflammatory group such as flurbiprofen. The publication is silent on the formulation of zero order release compositions. The Boots Company PLC, EP No. 234,670 has disclosed a sustained release composition containing xanthan gum wherein the medicament may be ibuprofen. The Boots formulation does not solve the problem of a zero order release rate. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention is directed to a carrier base material for therapeutically active medicaments in a solid dosage formulation wherein the carrier base comprises: 
     (a) a high viscosity HPMC; and 
     (b) a low viscosity HPMC wherein the high and low viscosity HPMC are in a ratio yielding a zero order release profile for the medicament. 
     In the present invention it has unexpectedly been found that a zero-order release profile can be obtained by controlling the ratio of high to low viscosity HPMC in a carrier base formulation. 
     A high viscosity HPMC is defined as one having a molecular weight of 60,000 or greater. A low viscosity HPMC is defined as one having a molecular weight of 50,000 or less. 
     The preferred low viscosity HPMC are available as Dow Methocel cellulose ethers E5, E15LV, E50LV, AND K100LV. The preferred high viscosity HPMC are available as Dow Methocel cellulose ethers E4M CR, E10M CR, K4M, K15M, AND K100M. 
     The methocel cellulose ethers are characterized by their methoxy and hydroxypropyl content and viscosity as shown in the following table: 
     
         __________________________________________________________________________Methocel Cellulose Ethers    E5  E15LV            E50LV                K100LV                     E4M E10M                             K4M K15M                                     K100M__________________________________________________________________________Methoxyl %    28-30        28-30            28-30                19-24                     19-24                         28-30                             19-24                                 19-24                                     19-24Hydroxypropyl %     7-12         7-12             7-12                 7-12                      7-12                          7-12                              7-12                                  7-12                                      7-12Viscosity cps    4-6 12-18            40-60                100  4000                         10,000                             4000                                 15,000                                     100,000(2% in water)__________________________________________________________________________ 
    
     The medicament in the present invention may be selected from ibuprofen, or salts of ibuprofen. Most preferably the medicament is ibuprofen lysine which should be taken to mean all stereoisomeric configurations including racemic ibuprofen lysine and (S)-ibuprofen-(S)-lysine; i.e. the salt formed from (S)-ibuprofen and (S)-lysine. 
     It should be appreciated that a zero order release profile is obtained only with a certain relative range of high to low viscosity HPMC. This may be illustrated by the combination of 1 part high viscosity E10M CR and a varying amount of any of the preferred low viscosity HPMC wherein a zero order release was found, for example: 
     (i) 1 part E10M CR: 3 parts E5; 
     (ii) 1 part E10M CR: 2 to 4 parts E15LV; 
     (iii) 1 part E10M CR: 3 to 9 parts E50LV; 
     (iv) 1 part E10M CR: 3 to 9 parts K100LV. 
     These ranges are not limited to combinations where the high viscosity HPMC is E10M CR but are to be expected with any of the other preferred high viscosity HPMC. 
     The medicament, preferably ibuprofen lysine is mixed with Povidone USP (PVP) which functions as a binding agent. Typically the ratio of drug to PVP is 20:1. 
     The percent of drug/PVP granules in the pharmaceutical composition is 33.3 to 83%. 
     The range of ibuprofen in this invention is preferably 100 to 600 mg per tablet. 
     Where the medicament is ibuprofen lysine the weight range is 100 to 600 mg measured in mg ibuprofen. 
     The percent range of HPMC carrier base is 17-66%. 
     An example of the composition and processing of the controlled release dosage form is provided below: 
     
         ______________________________________Composition:______________________________________Ibuprofen Lysine  61.8%PVP               3.0%Carrier Base      34.1%Magnesium Stearate             1.0%Total             99.9%______________________________________ 
    
     Fillers such as Avicel, lactose, manitol, dicalcium phosphate, starch or pregelatin starch 1500 may be added to the composition. Binders such as corn starch, pregelatin starch 1500, Klucel LF, methocel E3, E5, gelatin or acacia may be added as necessary by those skilled in the art. Besides magnesium stearate, other lubricants such as stearic acid, sodium stearate fumerate or calcium stearate may be employed. 
     Processing 
     A batch of ibuprofen lysine granules containing PVP was prepared. An appropriate amount of granules, typically 3.21 grams was removed and mixed in a V-blender for 10 minutes with a carrier base, usually 1.71 grams, chosen from the preferred high viscosity and low viscosity HPMC. The resultant mixture was then mixed in a V-blender for three minutes with magnesium stearate, which had previously been sieved through a #60 mesh screen. Tablets of about 980 mg were compressed on an F-press. 
     Tables I-V provide release profiles for controlled release tablets prepared following the processing described above and containing 600 mg Ibuprofen Lysine and 330 mg carrier base. Dissolution determinations were conducted using an automated dissolution testing unit such as a Beckman Spectrophotometer, model DU65, connected with a Vanderkamp 600 six-spindle dissolution tester. Samples were taken every hour for at least 12 to 24 hours and absorbance was read spectrophotometrically at 260 nm. 
     All the HPMC polymers described are available from the Dow Chemical Company. Racemic ibuprofen lysine may be prepared following the description in U.S. Pat. No. 4,279,926. (S)-ibuprofen-(S)-lysine is prepared as described in copending application Ser. No. 422,466 filed Oct. 18, 1989. 
     
                       TABLE I______________________________________Release Profiles of Ibuprofen Lysine Using 25% E4MCRand 75% of a Low Viscosity HPMC 75% E15LV    75% E50      75% K100LVTime  MEAN         MEAN         MEAN[hr]  ABSORBANCE   ABSORBANCE   ABSORBANCE______________________________________0     0.0000       0.0000       0.00001     0.1125       0.1160       0.08202     0.1885       0.1935       0.14003     0.2570       0.2615       0.19404     0.3180       0.3230       0.24405     0.3735       0.4080       0.29206     0.4265       0.5290       0.33757     0.4945       0.6265       0.38608     0.5975       0.6820       0.44459     0.6855       0.7190       0.504510    0.7280       0.7405       0.575011    0.7520       0.7555       0.635012    0.7540       0.7620       0.684513    0.7500       0.7675       0.722514    0.7445       0.7680       0.751515    0.7405       0.7670       0.769516                              0.778517                              0.782518                              0.7835192021222324______________________________________ 
    
     
                                           TABLE II__________________________________________________________________________Release Profiles of Ibuprofen Lysine Using VariousRatios of E10MCR and a Low Viscosity HPMC                          25% E10MCR                                  10% E10MCR                                          25% E10MCR                                                  10% E10MCR    25% E10MCR:        33.3% E10MCR:                 20% E10MCR:                          75% E50 90% E50LV                                          75% K100LV                                                  90% K100LV    75% E5   66.7% E15LV                 80% E15LV                          MEAN    MEAN    MEAN    MEANTime    MEAN     MEAN     MEAN     ABSOR-  ABSOR-  ABSOR-  ABSOR-[hr]    ABSORBANCE        ABSORBANCE                 ABSORBANCE                          BANCE   BANCE   BANCE   BANCE__________________________________________________________________________0   0.0000   0.0010   0.0010   0.0000  0.0005  0.0000  0.00051   0.0985   0.1140   0.1615   0.1095  0.1250  0.0790  0.11202   0.1670   0.1720   0.2420   0.1855  0.1960  0.1360  0.17753   0.2335   0.2210   0.3130   0.2570  0.2540  0.1845  0.23254   0.3055   0.2630   0.3760   0.3220  0.3065  0.2300  0.28455   0.3960   0.3050   0.4345   0.3870  0.3580  0.2715  0.33256   0.4800   0.3450   0.5265   0.4505  0.4110  0.3125  0.38257   0.5630   0.3840   0.5975   0.5140  0.4810  0.3525  0.43608   0.6505   0.4220   0.6525   0.5780  0.5475  0.3905  0.49009   0.6875   0.4600   0.7095   0.6220  0.5990  0.4305  0.559510  0.7165   0.4970   0.7475   0.6645  0.6525  0.4730  0.623511  0.7235   0.5345   0.7565   0.7020  0.6885  0.5210  0.678512  0.7255   0.5835   0.7590   0.7255  0.7080  0.5685  0.717013  0.7260   0.6410   0.7600   0.7395  0.7200  0.6045  0.736514  0.7245   0.6915   0.7575   0.7510  0.7275  0.6415  0.739015  0.7240   0.7230   0.7530   0.7560  0.7310  0.6715  0.737016  0.7240   0.7395   0.7525   0.7600  0.7290  0.6905  0.736017  0.7240   0.7425   0.7520   0.7630  0.7260  0.7080  0.734018  0.7245   0.7435   0.7520   0.7650  0.7260  0.7225  0.736019  0.7255   0.7455            0.7670          0.734520  0.7265   0.7440            0.7680          0.739521  0.7275   0.7420            0.7700          0.744022  0.7290   0.7420            0.7725          0.745023  0.7290   0.7410            0.774024  0.7310   0.7395            0.7755__________________________________________________________________________ 
    
     
                                           TABLE III__________________________________________________________________________Release Profiles of Ibuprofen Lysine Using VariousRatios of K4M and a Low Viscosity HPMC   50% K4M  25% K4M  25% K4M  25% K4M   50% E5   75% E15LV                75% E5   75% K100LVTime   MEAN     MEAN     MEAN     MEAN[hr]   ABSORBANCE       ABSORBANCE                ABSORBANCE                         ABSORBANCE__________________________________________________________________________0  0.0000   0.0000   0.0000   0.00001  0.1155   0.1010   0.0995   0.08152  0.1795   0.1700   0.1565   0.13903  0.2315   0.2335   0.2110   0.18954  0.2815   0.2905   0.2630   0.23655  0.3655   0.3490   0.3130   0.28156  0.4095   0.4360   0.4395   0.32607  0.4465   0.5510   0.5270   0.37058  0.4925   0.6430   0.5815   0.42259  0.5695   0.6990   0.6305   0.485010 0.6550   0.7405   0.6580   0.543511 0.7045   0.7560   0.6775   0.600012 0.7235   0.7565   0.6950   0.650013 0.7360   0.7515   0.7060   0.674014 0.7400   0.7445   0.7175   0.692015 0.7460   0.7415   0.7245   0.704016 0.7535   0.7450   0.7260   0.722017 0.7525   0.7435   0.7275   0.731518 0.7555   0.7415   0.7270   0.738019 0.7605   0.7405   0.730520 0.7605   0.7400   0.730521 0.7650   0.7425   0.732022 0.7635            0.731023 0.7660   24__________________________________________________________________________ 
    
     
                                           TABLE IV__________________________________________________________________________Release Profiles of Ibuprofen Lysine Using VariousRatios of K15M and a Low Viscosity HPMC   25% K15M 25% K15M 25% K15M 25% K15M   75% E5   75% E15LV                75% E50  75% K100LVTime   MEAN     MEAN     MEAN     MEAN[hr]   ABSORBANCE       ABSORBANCE                ABSORBANCE                         ABSORBANCE__________________________________________________________________________0  0.0000   0.0000   0.0000   0.00001  0.1280   0.0935   0.0855   0.09502  0.2110   0.1540   0.1425   0.16403  0.2830   0.2085   0.1915   0.22254  0.3640   0.2590   0.2390   0.27405  0.4350   0.3070   0.2810   0.32156  0.5060   0.3530   0.3265   0.36657  0.6475   0.3980   0.3970   0.41208  0.7215   0.4470   0.4890   0.45759  0.7360   0.5505   0.5535   0.504010 0.7415   0.6200   0.5945   0.548511 0.7410   0.6655   0.6125   0.591012 0.7395   0.6815   0.6400   0.624513 0.7435   0.6850   0.6590   0.649014 0.7475   0.7040   0.6910   0.665015 0.7490   0.7250   0.7085   0.684516 0.7520   0.7365   0.7295   0.703517 0.7505   0.7395   0.7395   0.716018 0.7515   0.7390   0.7400   0.723519 0.7485   0.7405   0.7330   0.730520 0.7525   0.7405   0.7355   0.734521 0.7500   0.7360   0.7255   0.738522                            0.7415__________________________________________________________________________ 
    
     
                       TABLE V______________________________________Release Profiles of Ibuprofen Lysine Using 25% K100Mand 75% of a Low Viscosity HPMC.     75% E15LV    75% E50Time      MEAN         MEAN[hr]      ABSORBANCE   ABSORBANCE______________________________________0         0.0000       0.00001         0.0820       0.10052         0.1330       0.16153         0.1800       0.21804         0.2225       0.26805         0.2630       0.31506         0.3025       0.36307         0.3405       0.42308         0.3805       0.49509         0.4240       0.546510        0.4880       0.594011        0.5510       0.635012        0.5945       0.671513        0.6335       0.700014        0.6650       0.721515        0.6950       0.737016        0.7195       0.748517        0.7395       0.757518        0.7530       0.765519        0.7680       0.771020        0.7740       0.775521        0.7795       0.777022        0.7825       0.778523                     0.780024                     0.7820______________________________________