Therapeutic Equivalence (Orange Book)
Therapeutic equivalence is the FDA designation indicating that a generic drug product is both pharmaceutically equivalent and bioequivalent to a reference brand-name drug, as published in the FDA's Orange Book with AB-rated approval codes.
Exam Tip
AB-rated = therapeutically equivalent, can substitute. B-rated = NOT equivalent, cannot substitute. Orange Book is the FDA reference. Know NTI drugs (warfarin, levothyroxine) may have extra restrictions on the ExCPT.
What Is Therapeutic Equivalence?
Therapeutic equivalence means that a generic drug can be expected to produce the same clinical effect and safety profile as its brand-name counterpart. The FDA publishes therapeutic equivalence evaluations in "Approved Drug Products with Therapeutic Equivalence Evaluations," commonly known as the Orange Book.
Requirements for Therapeutic Equivalence
A drug must meet ALL of the following:
| Requirement | Description |
|---|---|
| Pharmaceutical equivalence | Same active ingredient, dosage form, strength, and route of administration |
| Bioequivalence | Same rate and extent of absorption (AUC and Cmax within 80-125% of reference) |
| Adequate labeling | Compliant with FDA labeling requirements |
| cGMP compliance | Manufactured under current Good Manufacturing Practice |
| Same batch-to-batch consistency | Meets approved specifications |
Orange Book Rating Codes
| Code Prefix | Meaning |
|---|---|
| A | Therapeutically equivalent (can substitute) |
| B | NOT therapeutically equivalent (cannot substitute) |
Common A-Rated Codes
| Code | Meaning |
|---|---|
| AB | Bioequivalence demonstrated; most common for substitution |
| AA | No known or suspected bioequivalence problems (solutions, gases) |
| AP | Injectable aqueous solutions |
| AT | Topical products |
| AN | Solutions, aerosol (nasal) |
Common B-Rated Codes
| Code | Meaning |
|---|---|
| BC | Extended-release products NOT shown to be bioequivalent |
| BD | Documented bioequivalence problems |
| BP | Potential bioequivalence problems |
| BX | Insufficient data for determination |
Generic Substitution Rules
| Factor | Details |
|---|---|
| AB-rated | Can be substituted in all states (unless prescriber writes DAW) |
| B-rated | Cannot be automatically substituted |
| State laws | Most states require or permit generic substitution for AB-rated products |
| Narrow therapeutic index (NTI) | Some states restrict substitution for NTI drugs (warfarin, levothyroxine, phenytoin) |
Pharmacy Technician's Role
- Check Orange Book ratings when selecting generic alternatives
- Verify AB rating before generic substitution
- Apply correct DAW code on insurance claims
- Understand that B-rated products require specific prescriber approval to substitute
Exam Alert
Therapeutic equivalence is tested in both the Dispensing Process and Drugs/Drug Therapy domains. Key points: AB = can substitute, B = cannot substitute. Know that Orange Book ratings determine generic substitution and that NTI drugs may have additional state restrictions.
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DAW Codes (Dispense As Written)
DAW codes are standardized numeric codes (0-9) used on pharmacy claims to indicate whether a brand-name or generic drug should be dispensed and who is requesting the specific product.
NDC Number (National Drug Code)
The NDC (National Drug Code) is a unique 10-digit, 3-segment numeric identifier assigned to each medication product in the United States, identifying the labeler, product, and package size.
Formulary
A formulary is a list of prescription drugs approved for coverage by a health insurance plan, pharmacy benefit manager (PBM), or healthcare institution, organized into tiers that determine patient cost-sharing.
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