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Ingredient Differences Between Generic and Brand Name Drugs

February 2009

Do generic drugs contain the same ingredients as brand name drugs?

Inactive ingredients of medications may differ, posing a risk to food allergic children

What is a generic drug?

Checking medicine ingredients A generic drug is one that is chemically identical to its brand name equivalent. This means that it must contain the very same active ingredients in the same amounts as the brand name drug, and must pass a series of tests to prove that it is the same in strength, purity, potency, content uniformity, and disintegration time (i.e. in the stomach) as the brand name drug. It must also be the same dosage form - sustained release forms cannot be substituted for fast dissolving forms, etc.

The Food and Drug Administration maintains a list of generically equivalent drugs on its website, called Approved Drug Products with Therapeutic Equivalence Ratings or more commonly, the electronic "Orange Book". It lists prescription, over the counter, discontinued, and orphan (special use drugs for unique diseases) drugs. It is intended primarily for health care professionals’ use and is a bit clumsy to use, but you can search by ingredient or proprietary (brand) name to find other generically equivalent drugs.

A generic drug may not contain the same inactive ingredients

Reporting a reaction to medication
FDA created the MedWatch program to monitor adverse effects and problems with medical products the agency regulates (prescription or OTC drugs and medical devices). MedWatch is a voluntary reporting system available to consumers or health professionals.
A generic drug does not necessarily contain the same inactive ingredients as its brand name drug equivalent. Some of these ingredients may be derived from food products. These inactive ingredients may differ based on dosage form, dosage strength, and/or manufacturer. For example, the antibiotic amoxicillin, is listed in the Red Book (Thomson Healthcare Inc., 2007) as being produced by thirty-one different manufacturers/repackers. Each of these manufacturers may make different strengths of chewable tablets, capsules, regular tablets, combination products (i.e. amoxicillin and clavalunate acid) and powders to be made into suspensions, all with potentially varying inactive ingredients, dyes and flavorings. The brand names of amoxicillin may vary as well.

Ingredients may vary by dose

Even within the same brand name product, such as Singulair® the inactive ingredients may vary. Singular® 10mg. tablets have lactose as one of the ingredients, while Singular® 4mg. and 5 mg. tablets have mannitol and aspartame as the sweetening agent, but no lactose.

Research drug ingredients

If you are concerned for instance, about lactose being in certain medications, you and your health care professionals may still have to call the generic drug company to determine if the product does contain or could be cross contaminated with the offending ingredient. Also generic companies are less likely to be included in standard drug references, such as The Physician’s Desk Reference (Thomson) for ease in searching the ingredients.

What does 'narrow therapeutic index' mean?

Sometimes the question comes up concerning drugs which have a narrow therapeutic index or ratio as to whether the brand name can safely be substituted with a generic product. The term narrow therapeutic index (NTI) is not an official one, but rather a descriptive one ( It refers to drugs in which the level in the blood needed for therapeutic effect and the level in the blood causing serious or toxic results is relatively close. These drugs require careful, individual dosing and patient monitoring. The FDA does not maintain an official roster of NTI drugs, but has a reference list that is used as one factor in many for determining generic drugs for evaluation. The list is in the "Scale-Up and Post Approval Changes for Intermediate Release Products (SURPAC-IR), Appendix A". Some states also have additional drugs included in their pharmacy regulations as NTI drugs, such as North Carolina does for levothyroxine, a thyroid hormone replacement medication.

Ultimately, the decision to substitute any drug product for an available generic product rests on a discussion between the individual patient and his/her health care practitioner and desired effect of that drug in the patient.

Approved by KFA's Medical Advisory Team July 2007. Updated February 2009.

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Page last updated 7/29/2012

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