MIRENA® (levonorgestrel-releasing intrauterine system) consists of a T-shaped polyethylene frame (T-body) with a steroid reservoir (hormone elastomer core) around the vertical stem. The reservoir consists of a cylinder, made of a mixture of levonorgestrel and silicone (polydimethylsiloxane), containing a total of 52 mg levonorgestrel. The reservoir is covered by a silicone (polydimethylsiloxane) membrane. The T-body is 32 mm in both the horizontal and vertical directions. The polyethylene of the T-body is compounded with barium sulfate, which makes it radiopaque. A monofilament brown polyethylene removal thread is attached to a loop at the end of the vertical stem of the T-body.

Schematic drawing of MIRENA

INSERTER

MIRENA is packaged sterile within an inserter. The inserter, which is used for insertion of MIRENA into the uterine cavity, consists of a symmetric two-sided body and slider that are integrated with flange, lock, pre-bent insertion tube and plunger. Once MIRENA is in place, the inserter is discarded.

DIAGRAM OF INSERTER

MIRENA is intended to provide an initial release rate of 20 µg/day of levonorgestrel.

Levonorgestrel USP, (-)-13-Ethyl-17-hydroxy-18,19-dinor-17α- pregn-4-en-20-yn-3-one, the active ingredient in MIRENA, has a molecular weight of 312.4, a molecular formula of C₂₁H₂₈O₂, and the following structural formula:

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