The problem here is obvious. What if the patient has an adverse reaction to the drug? If they took a single dose, you can discontinue the drug. But you can't discontinue a multiple dose drug delivered in a single shot.
I don't see a problem here. As with most other drugs for which a time-release form already exists, you would start on the instant-release form until your reaction is known and your dosage is dialled in. Then your doctor is able to calculate the correct dosage for the time-release form -- often there is a guideline for conversion between the two forms which is distributed by the pharma company.