Usually dose of fluvoxamine required for OCD and MDD+OCD is more than the dose required for MDD alone. But it is still a good practice to start with low dose and titrate upwards to find the minimal effective dose. Many times patients respond to as low as 50 mgs  of fluvoxamine but the range is wide ( 50 to 300 mgs). Also the time required for optimal response in OCD is more ( 8 to 12 weeks). So it is better to titre slowly to find the minimal effective dose.