carrier base comprises 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.