Summary:

When converting patients on a continuous IV infusion of diltiazem to an oral dose of diltiazem, you can use the following equation:

• Oral dose (in mg per day) = [rate (mg/hr) x 3 + 3] x 10
  

When initially converting someone from an IV infusion of diltiazem to oral diltiazem it recommended that you start off using immediate release (IR) dosage formulations where the equivalent daily dose conversion is divided into doses every 6 hours.  This will allow adjustment to the desired clinical effect. Once that is achieved, you can convert the dosage form to a long acting dosage form for purposes of improved compliance.  Note: Patients on IV infusions of diltiazem for > 24 hrs can sometimes experience decreased diltiazem clearance or a prolonged elimination half-life.

While not based on any known dose equivalency studies, another common accepted conversion includes the following:

• 3 mg/hr IV  =  120 mg daily (in 4 divided doses using IR dosage forms; e.g., 30 mg every 6 hrs)
• 5 mg/hr IV  =  180 mg daily (in 4 divided doses using IR dosage forms)
• 7 mg/hr IV  =  240 mg daily (in 4 divided doses using IR dosage forms)
• 11 mg/hr IV = 360 mg daily (in 4 divided doses using IR dosage forms)
• 15 mg/hr IV = 480 mg daily (in 4 divided doses using IR dosage forms)
  

Steps to Convert from IV to Oral Diltiazem:

• Step 1 = Calculate the equivalent oral daily dose of diltiazem based on the IV infusion rate (see above)
• Step 2 = Divide the equivalent total daily dose by 4 to determine the dose to be given every 6 hours of the IR oral dosage form
• Step 3 = Give the first oral dose ~ 1 hr before titrating down the IV infusion (since the time to maximal absorption is ~ 1-1.5 hrs)
• Step 4 = After ~ 1 hr from the first oral dose, decrease the IV infusion down by 2.5 mg/hr increments until done
• Step 5 = Continue giving the oral diltiazem every 6 hours and adjust dose to desired clinical effect
• Step 6 = Depending on the long acting formulation of diltiazem to be used determine the total daily dose of IR and then convert

Editor-in-Chief:  Anthony Busti, MD, PharmD, FNLA, FAHA
Last Reviewed:  June 2015