This is a question that I’ve gotten a few times over the years.  You’ve got a patient in AFIB that has been rate controlled after a bolus of diltiazem and is now on a diltiazem drip.  The hospital has a policy stating a patient on a diltiazem drip must go to a cluster or ICU bed but the patient could go to a general medical floor, or even go home.  What can be done for the patient?
There is a formula that can be used to estimate the total daily oral dose from an IV diltiazem drip.
Oral dose = {IV drip rate (in mg/hr) x 3 + 3}x10
In general the standard rates for diltiazem convert as follows:
5 mg/hr à180 mg/day
7.5 mg/hr à260 mg/day
10 mg/hr à330 mg/day
15 mg/hr à480 mg/day
The total daily dose should be divided q6h.  The immediate release dosage form must be used initially and rounding will be necessary since it’s only available as 30mg, 60mg, 90mg and 120mg.  When actually making the switch, give the first oral dose about 1 hour before you plan to stop the drip. After the first hour, slowly titrate down the diltiazem drip by 2.5mg/hr increments until 0. By then the diltiazem should have time to be absorbed and distributed (time to Tmax is approximately 1 to 1.5 hours).