Substitution instrument to address shortage of COUMADIN warfarin 5mg tablets

The Therapeutic Goods Administration (TGA) has published a statement about the shortage of several warfarin products due to manufacturing issues. Since then, the supply of several strengths has improved.

Warfarin is an anticoagulant used to prevent blood from excessive clotting or forming harmful clots for patients at risk of heart attack and stroke.

As the shortage of Coumadin 5mg tablets is expected to continue until 31 July 2023, the TGA has made a Serious Scarcity Substitution Instrument (SSSI) Therapeutic Goods (Serious Scarcity and Substitutable Medicine) (Warfarin) Instrument 2023 (SSSI) to assist patients to access their medicine from their pharmacist without delay or interruption to treatment.

The SSSI allows a pharmacist to offer the patient or their carer a lower strength of COUMADIN warfarin tablet if the 5mg tablet is unavailable without prior approval from the prescriber. The SSSI:

• declares COUMADIN warfarin sodium 5 mg tablet (AUST R: 42279) a scarce medicine

• specifies that either: can be offered as substitute medicines

  • COUMADIN warfarin sodium 1 mg tablet (AUST R: 42269)
    OR
  • COUMADIN warfarin sodium 2 mg tablet (AUST R: 14937)

  can be offered as substitute medicines

• does NOT allow a combination of 1mg an 2mg tablets to be dispensed as a substitute
• includes specific conditions that must be met to allow substitution.

The SSSI is in force from 17 March 2023 until 7 August 2023. 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 provide the patient with the specified substitutable medicine 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 warfarin.

Warfarin is an important medicine, with a narrow therapeutic index. Explain to the patient the potential for the INR to change and the need for frequent monitoring.

Ensure the patient is aware of their current dose. The dose on the prescription of warfarin often will not match the dose that the patient has been advised to take, due to frequent dose changes (according to INR results).

Advise the patient that whilst there are different brands of warfarin, these have not been shown to be bioequivalent and should not be interchanged without the prescriber’s advice.

Assess the patient’s health literacy and capacity to understand the substitution. If you have determined that the patient is not suitable to receive the substitutable medicine, contact the sponsor, Viatris on 1800 314 527 to enquire about emergency stock of COUMADIN 5mg tablets.

For patients who are dispensed the substitutable medicine:

• calculate the number of tablets and ensure correct total quantity of substitutable medicine is provided
• explain to the patient/carer the differences between the products and ensure they understand the substitution. Explain that:
  • a different strength of the medicine has been supplied due to the prescribed strength being unavailable
  • the substitutable medicine is of the same brand and contains the same active ingredient, however, is of a different strength, and
  • if the patient takes the medicine as directed by you , the patient will receive the same dose they were prescribed.
• provide written instructions to the patient to support quality use of medicines and minimise confusion and error. You can download this patient information sheet that includes images of the scarce and substitutable tablets to ensure patients are supported with clear instructions:

• this information sheet will also be distributed by Viatris. Consider using this information sheet and Consumer Medicine Information (CMI) leaflet as part of your patient counselling.
• advise the patient to take the dose as per the written instructions.

Discuss with the patient if a pill organiser or blister pack may be suitable for their individual circumstances.

Strongly encourage patients to record their dose, when they take their tablets, as well as their INR results, using a calendar, diary or ‘anticoagulant book’.

To ensure patient safety, ensure you notify the prescriber of the substitution as soon as practical after dispensing the substitutable medicine. The patient may require more frequent monitoring.

Information on Pharmaceutical Benefits Scheme (PBS) subsidy arrangements for medicines substituted using an SSSI can be found on the PBS website.

Information for prescribers

Be alert to the current shortage of COUMADIN warfarin 5mg tablets when prescribing to your patients.

The pharmacist is required to notify you of the substitution as soon as practical after dispensing the substitutable medicine. Consider the need for increased monitoring in these patients.

Patients are advised to contact you if the prescribed brand of warfarin is not available for dispensing.

Due to the narrow therapeutic index of warfarin and the lack of data on bioequivalence between the 2 registered warfarin products, COUMADIN and MAREVAN, these products are not considered interchangeable. If substituting or switching is unavoidable, close monitoring with frequent INR testing is recommended.

Information for patients

COUMADIN 5mg warfarin tablets are currently unavailable due to manufacturing issues and your pharmacist may provide you with a different strength of COUMADIN tablet for a short period of time.

There are two different brands of warfarin available in Australia - COUMADIN and MAREVAN. These tablets are formulated differently and are NOT the same. It is preferable for you to take a different strength of COUMADIN, rather than the different brand of warfarin, unless your prescriber has told you to change.

It is important that you are aware of your current warfarin dose. It is recommended that you record the following things in a diary, on this patient information sheet, or in your ‘anticoagulant book’:

If your pharmacist gives you a substitute COUMADIN medicine:

• one (1) COUMADIN 5mg tablet will be substituted by five (5) COUMADIN 1mg tablets OR two-and-a-half (2.5) COUMADIN 2mg tablets as shown in the table below.

Unavailable medicine	Substitute medicine	Substitute dosage regimen
COUMADIN 5mg tablet	COUMADIN 1mg tablet	Five (5) COUMADIN 1mg tablets
	OR	OR
	COUMADIN 2mg tablet	Two-and-a-half (2.5) COUMADIN 2mg tablets

Your pharmacist should tell you that:

• the substitute tablet is the same COUMADIN brand and the same active ingredient but is a different strength
• which COUMADIN tablets you will take to make up your prescribed dose
• you will receive the same dose you were prescribed if you take the COUMADIN tablets as directed by the pharmacist.

Please note: All three strengths of COUMADIN tablets are now packaged in blue bottles with blue lids. You can tell the difference between the three strengths of COUMADIN tablets by the colour of the tablets and the strength embossed into them.

Please take extra care when taking your COUMADIN warfarin dose.

Ask your pharmacist about dose administration aids, such as a pill organiser or blister pack. These packs can help you take the correct medication in the correct amount at the correct time.

Talk to your prescriber or pharmacist if you have any questions or require assistance with this substitution.

If you are unable to fill your prescription for the prescribed brand of warfarin, you should speak to your pharmacist or prescriber for further advice.

If you have a PBS prescription for COUMADIN 5mg tablets and the pharmacist has provided a different strength of COUMADIN tablet, you will be able to receive this medicine at a PBS subsidised price without the need to obtain a new prescription from your prescriber.

More information on how the substitute COUMADIN medicines are subsidised on the Pharmaceutical Benefits Scheme (PBS) can be found on the PBS website