If they are perscribed 450, unless it is specifically written out and signed by the doctor that one 450mg pill is needed, most of the time the pharmacy will give the 300+450.
IT is up to the insurance company actually since they have the final say in what gets approved/rejected nowadays. Ask you doctor or pharmacist how many prior auths they send to the insurance companies in order for a claim on some drugs to be paid. IGXT just needs to market/price this right imo.