Table: When Generic Substitution May Not Be Appropriate-Merck Manual Consumer Version

When Generic Substitution May Not Be Appropriate

Drug Category	Examples	Comments
Antiasthmatic drugs taken by mouth		Different versions are generally not bioequivalent. If one version is working, it should not be interchanged for another unless absolutely necessary.
Anticoagulants		Toxic dose for the drug is too close to the effective dose for the drug to be used safely.
Antidepressants		Not all versions are interchangeable. A pharmacist can advise whether the FDA considers a particular generic drug bioequivalent to the brand-name drug.
Antiseizure drugs		Loss of seizure control has occurred after people switch brands. Continuity of the same brand, or the same generic preparation, is recommended.
Antihypertensive drugs		Some generic versions are not bioequivalent to brand-name drugs. Modified-release preparations have different release characteristics and are not interchangeable.
Cardiovascular drugs	heart failure and a very rapid heart rate)	Toxic dose is too close to the effective dose for the drug to be used safely.
Corticosteroid creams, lotions, and ointments		These products are standardized by tests of skin response, and many have been rated as bioequivalent by the FDA. But response varies, and different drug vehicles (creams, ointments, gels) can affect product potency. Response may be unpredictable. So, if one version is effective, it should not be interchanged for another.
Corticosteroid tablets		Generic versions may not be bioequivalent to brand-name drugs and should not be freely interchanged for them.
Gout-control drugs		Generic versions of individual drugs are not bioequivalent to one another.
Hormones	Thyroid-replacement products	Hormones are usually taken in small doses, so differences in brands could produce major swings in response. Some brands are not bioequivalent.
Psychiatric drugs	bipolar disorder)	Toxic dose for the drug is too close to the effective dose for the drug to be used safely.
Other drugs		Generic versions may not be bioequivalent. Although any version can be effective, versions should not be interchanged.
* A generic drug is not available. † Modified-release preparations of drugs are versions of the drug in which the preparation has been changed in some way, usually to slow the release of the active ingredient into the bloodstream. Modified-release drugs may be identified by the designations MR, LA (long-acting), XL (extra long), CR (controlled release), or SR (sustained release).
FDA = Food and Drug Administration.

Drug Category

Examples

Comments

Antiasthmatic drugs taken by mouth

Different versions are generally not bioequivalent. If one version is working, it should not be interchanged for another unless absolutely necessary.

Anticoagulants

Toxic dose for the drug is too close to the effective dose for the drug to be used safely.

Antidepressants

Not all versions are interchangeable. A pharmacist can advise whether the FDA considers a particular generic drug bioequivalent to the brand-name drug.

Antiseizure drugs

Loss of seizure control has occurred after people switch brands. Continuity of the same brand, or the same generic preparation, is recommended.

Antihypertensive drugs

Some generic versions are not bioequivalent to brand-name drugs. Modified-release preparations have different release characteristics and are not interchangeable.

Cardiovascular drugs

heart failure and a very rapid heart rate)

Toxic dose is too close to the effective dose for the drug to be used safely.

Corticosteroid creams, lotions, and ointments

These products are standardized by tests of skin response, and many have been rated as bioequivalent by the FDA. But response varies, and different drug vehicles (creams, ointments, gels) can affect product potency. Response may be unpredictable. So, if one version is effective, it should not be interchanged for another.

Corticosteroid tablets

Generic versions may not be bioequivalent to brand-name drugs and should not be freely interchanged for them.

Gout-control drugs

Generic versions of individual drugs are not bioequivalent to one another.

Hormones

Thyroid-replacement products

Hormones are usually taken in small doses, so differences in brands could produce major swings in response.

Some brands are not bioequivalent.

Psychiatric drugs

bipolar disorder)

Toxic dose for the drug is too close to the effective dose for the drug to be used safely.

Other drugs

Generic versions may not be bioequivalent. Although any version can be effective, versions should not be interchanged.

* A generic drug is not available.

† Modified-release preparations of drugs are versions of the drug in which the preparation has been changed in some way, usually to slow the release of the active ingredient into the bloodstream. Modified-release drugs may be identified by the designations MR, LA (long-acting), XL (extra long), CR (controlled release), or SR (sustained release).

FDA = Food and Drug Administration.