Confusion Between Diltiazem Generics For Tiazem And Cardizem CD

In our latest Q+A, the pharmacist discusses the difference between two diltiazem extended-release products and why they can't be interchanged.

Confusion Between Diltiazem Generics For Tiazem And Cardizem CD
Nov 25, 2019

Jim asked

I have a question regarding diltiazem 360 mg extended-release capsules. I have been taking this for many years. When my pharmacy fills this, I receive one of two different items, both from Sun Pharma, but the pricing is vastly different ($140 for 90 capsules vs. $400 for 90 capsules). I’ve researched both and see no difference. Is there a difference between these two items and why is there such a price difference? The NDC (national drug code) for the green capsule is 47335-0673-81 (which costs around $140) and the NDC for the blue/white capsule is 47335-0679-81 (which costs about $400). Thanks!

At a glance

  • There are multiple diltiazem extended-release capsule formulations available, including Cardizem CD and Tiazac. They are not all considered equivalent to one another.
  • A generic drug is approved based on bioequivalence studies for a particular brand name drug (i.e. reference drug) and is assigned a corresponding Orange Book code (e.g. AB1, AB2).
  • A generic diltiazem extended-release capsule product is only legally substitutable with its reference drug (e.g. Cardizem CD or Tiazac etc...), which will have the same Orange Book Code (e.g. AB1 for AB1).
  • Generic diltiazem extended-release capsules, even if they are the same strength, cannot be substituted for one another if they have different Orange Book codes. Therefore, generics for Cardizem CD cannot legally be substituted with generics for Tiazac since they have different Orange Book codes.


pills capsules isolated on white background, 3D rendering

Hello and thank you for submitting your question! I am more than happy to help you decipher this somewhat confusing situation.

You are correct that both of the products you mention in your question are diltiazem 360 mg extended-release capsules.

However, they are each generic versions for different brand name drugs.

'Diltiazem 360 mg extended-release capsules (NDC 47335-0679-81)' is the generic for the brand name drug Cardizem CD while the other diltiazem 360 mg extended-release capsule product (NDC 47335-0673-81) is the generic for Tiazac.

This is somewhat of an unusual situation since both of these brand name drugs (Cardizem CD and Tiazac) contain the same active ingredient (diltiazem), but they are nonetheless different drug products, each with unique properties.

I'll discuss what all this means in more detail below but as a general point, your pharmacy shouldn't be switching between them since they technically are not considered therapeutically equivalent by the FDA. In other words, they are not interchangeable.

Therapeutic Equivalence

Most states have 'generic substitution laws' that require pharmacies to dispense a 'therapeutically equivalent' generic product for a brand name one. There are exceptions to this, but in general, if your doctor writes you a prescription for a brand name product, it will be filled generically (if one is available).

This concept of 'therapeutic equivalence' can be a little confusing, but basically, it is a system that exists that links drugs (namely brand and generic products) based on their 'bioequivalence' to each other (bioequivalence in this sense is defined as two drugs having the same rate and extent of absorption). Drugs that have the same rate and extent of absorption should, in theory, exhibit the same clinical effect.

When your pharmacy substitutes a generic drug for a brand name that your doctor has written for, the generic drug must be classified as 'therapeutically equivalent'.

The FDA defines 'therapeutic equivalence' as the following:

  1. Drugs@FDA: Tiazac. FDA
  2. Drugs@FDA: Cardizem CD. FDA
  3. Cardizem CD Prescribing Information. AccessFDA
  4. Tiazac Prescribing Information. AccessFDA
  5. Comparisons of the effects of different long-acting delivery systems on the pharmacokinetics and pharmacodynamics of diltiazem. Oxford Academic
  6. Orange Book Preface. FDA

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