No they are not the same. They both have Etodolac molecule as painkiller. But Etova MR has is in 400mg strength instead of 300mg in Etova-300.
Also Etova MR got Thiocolchicoside 4mg as muscle relaxant.
In my opinion you will have less beneficial effect using only Etova 300 instead of Etova MR.
Next Steps
Replace the medicine.
or
Add Cap Myoril 4mg thrice a day with existing Etova 300. The effect will be better, but costlier.
Health Tips
Wear a lumbar support belt and take adequate rest. Sedatives are helpful in acute phase.