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http://thyroid.about.com/b/2008/10/02/usp-announces-a-revision-to-levothyroxine-sodium-tablets.htmUSP Announces a Revision to Levothyroxine Sodium Tablets

Thursday October 2, 2008

The requirements for the thyroid medication that most thyroid patients take are changing.

The USP (United States Pharmacopeia, the official public

standards–setting authority for all prescription and over–the–counter

medicines) has announced a change to the specification information --

known as the monograph -- for levothyroxine sodium tablets.

Levothyroxine is the generic name for the thyroid hormone replacement

drugs Synthroid, Levoxyl, Levothroid, and Unithroid, for example. The

majority of patients taking thyroid hormone replacement are on a

levothyroxine drug.

This change is being made to help ensure that levothyroxine retains its

potency over its shelf life -- a problem that levothyroxine has had in

the past, and continues to have. The current requirement is that each

pill must contain "not less than 90.0 percent and not more than 110.0

percent of the labeled amount of levothyroxine sodium." The change is

mandating that each pill will need to contain "not less than 95.0

percent and not more than 105.0 percent of the labeled amount of

levothyroxine sodium" throughout their labeled shelf-lives. This change

goes into effect October 3, 2009.

What does this mean for you?

This narrowing of the range of acceptable potency will reduce the

amount of dosage fluctuation patients experience, and help stabilize

thyroid function by providing a more stable dose. Right now, when you

get a refill of your medication, if you get medication from a different

manufacturer, you could go from a pill that is at 90% of potency, to

one that is 110% of potency, or vice versa. Effectively, you've changed

your dosage.

This latest development comes after the FDA's notification a year ago

to all companies making levothyroxine sodium drug products, indicating

that they would require that manufacturers meet the 95.0 percent to

105.0 percent range within 24 months. (You can read the letter the FDA

sent to the drug manufacturers online.)