Elantan to Imdur conversion (SR isosorbide mononitrate)

Availability:

• Elantan Long 50mg [ sustained release]
• Imdur 60mg

Rationale for ISMN

•  Most patients are maintained on a modified release (MR) preparation which is usually taken once daily in the morning to maintain a nitrate-low period and thus minimise tolerance.
•  ISMN is preferred over isosorbide dinitrate as isosorbide dinitrate requires more frequent dosing
• Compliance has been shown to improve when transferring from multiple dose regimens to once-daily regimens.
• The low plasma nitrate level at 24 hours following ingestion appears to minimise tolerance

Bioequivalence

• no published comparative studies of asymmetric dosing of plain isosorbide mononitrate with the slow-release form that inform dose equivalence.
• Limited data exists regarding switching from normal release to MR tablets but initially a mg per mg substitution would be appropriate (i.e. same daily dose overall) in most patients, and where available formulations allow.
• Because information on the dose equivalence of these products is uncertain, clinical oversight to consider further dose adjustment may be required
• There is significant cost variation between the ISMN MR products available and the product of lowest cost should be provided

Conversion

• Most patients can be changed initially on a mg per mg substitution of their total daily dose (i.e. same daily dose overall) where available formulations allow
• If changing between preparations results in an overall increase in daily ISMN dose, patients should be advised that they might experience a nitrate headache for a few days after conversion or potential drop in postural BP

Immediate Release 10mg tablet	Elantan Long 25/50mg Capsule	Imdur 30/60mg Tab
10mg BD	25mg OD	30mg OD
20mg BD	50mg OD	60mg OD
30mg BD		60mg OD 90mg OD
40mg BD	100mg OD	120mg OD

*Underlined- available strength at hospital

References:

1. Isosorbide Mononitrate (ISMN) Prescribing. NHS PrescQIPP, Buletin 85, November 2014.
2. PRESCRIBING SUPPORT TEAM AUDIT: ISOSORBIDE MONONITRATE. NHS Dumfires and Galloway, 2009.
3. Isosorbide Mononitrate – Briefing paper for GPs/Nurses