The Therapeutic Goods Administration (TGA) has been notified of shortages of Imdur Durules and Monodur Durules isosorbide mononitrate 120 mg modified release tablets. The shortages are expected to continue until 19 December 2022.

Imdur Durules and Monodur Durules tablets are indicated for the prophylactic treatment of angina pectoris.

The TGA has made a Serious Scarcity Substitution Instrument (SSSI) to assist patients to access their medicine from their pharmacist without delay, ensure treatment is not interrupted and relieve workload pressure on prescribers and pharmacists.

The Therapeutic Goods (Serious Scarcity and Substitutable Medicine) (Isosorbide Mononitrate) Instrument 2021 has been made to:

• Declare registered medicines that contain 120 mg of isosorbide mononitrate that are modified release tablets as scarce medicines; and
• Specify registered medicines that contain 60 mg of isosorbide mononitrate that are modified release tablets as substitutable medicines that pharmacists are permitted to dispense in substitution for the scarce medicines and specify the circumstances in which that substitution is permitted

The SSSI is in force from 18 September 2021 until 19 December 2022. The TGA may, however, revoke the SSSI before its end date if the serious scarcity is resolved, or safety concerns are identified.

For more information about SSSIs see Substituting scarce medicines and Serious Scarcity Substitution Instruments (SSSIs).

Information for pharmacists

The SSSI allows you to substitute isosorbide mononitrate 60 mg modified release tablets for isosorbide mononitrate 120 mg modified release tablets without prior approval from the prescriber so long as the permitted circumstances provided within the SSSI are met. See both the specific permitted circumstances (in Schedule 1) and general permitted circumstances (in Schedule 2) of the SSSI for isosorbide mononitrate.

Use your professional and clinical judgement to determine whether a patient is suitable for substitution and ensure the patient is fully informed and consents to the change.

You must refer patients back to their prescriber if substitution is not appropriate or where alternative treatments may be more appropriate.

For patients who are dispensed the substitutable medicine:

• Ask the patient if they are allergic or intolerant to certain ingredients
• Calculate the number of tablets of substitutable medicine required to provide the prescribed dose of the scarce medicine
• Ensure correct total quantity of substitutable medicine is provided
• Patients should be advised to swallow tablets whole and ensure that the dose is taken in full according to the prescribed dosage
• Provide the Consumer Medicine Information (CMI) leaflet and discuss possible adverse events.

A list of substitutable medicines that are eligible for dispensing as pharmaceutical benefits under an SSSI is available at the PBS website.

If the substitution requires a quantity increase and there has been no authority approval for the scarce medicine, the substitution can still proceed. Information about how 'Authority Required' PBS items can be managed is available in the FAQs (pdf,184kb) about PBS subsidy arrangements for PBS listed medicines subject to an SSSI.

Information for prescribers

When issuing new prescriptions, be aware of the shortage of isosorbide mononitrate 120 mg modified release tablets when prescribing to your patients.

The PBS listing for isosorbide mononitrate 60 mg modified release tablets provides a maximum quantity of 30 tablets, intended as monthly supply. You need to contact Services Australia to request increased maximum quantity, so the PBS script is valid.

Information for patients

Talk to your doctor or pharmacist if you have any questions regarding this substitution.

The substitutable medicine contains a different strength of the same active ingredient that your doctor prescribed. The pharmacist will supply the correct total dose as prescribed.

If you are concerned about the number of tablets you will need to swallow, talk to your doctor about possible alternative options such as patches.

Excipients (inactive ingredients) vary between brands. Let your pharmacist know if you are allergic or intolerant to certain ingredients. You can also find information about excipients in the Consumer Medicine Information (CMI) leaflet, which is available from your pharmacist or on the TGA website.