Request for feedback on Patches strength representation

Stuart Abbott I have just looked at hyoscine patch: Scopoderm 1.5mg Patch

https://www.medicines.org.uk/emc/product/13379/smpc

It is a flat, round reservoir patch approximately 1.8 cm in diameter. One side of the patch is tan; the other side is silver and is placed on an oversized clear hexagonal film. Each patch is a flat system of laminates, sealed around the edge, containing a clear oily filling. Each system has a contact surface area measuring 2.5cm2 and hyoscine content of 1.5mg. The average amount of hyoscine absorbed from each system in 72 hours is 1mg.

In the international edition we have 769509004 |Product containing precisely scopolamine 13.889 microgram/1 hour prolonged-release transdermal patch (clinical drug)|

I think to my mind this raises the issue of presentation strength (1.5 mg patch)  v concentration strength described as 1 mg per 72 hours and SCT have done the maths to equal 13.889 micrograms/1 hour (note: our Ed guidance for rounding is to 3 decimal places).

Linda Bird Matt Cordell Ian Spiers Julie M. James  and others - if you are able to document your thoughts here I am hoping to move forward with this speedily once we have consensus.

Hi Nicola Ingram ,

As discussed this week, I think a better approach is to consider the denominator as a single (value = 1) block of a prescribed amount of time. For example 1 by 24 hours, or 1 by 16 hours, where 24 hours or 16 hours are a single indivisible block of time.

This means keeping the denominator value of 1, and having unit of measure concepts for the required blocks of time - e.g. 8 hours, 16 hours, 24 hours, 72 hours etc.

The advantage of this approach is that the ratio strength doesn't appear divisible and comparable to other equivalent ratios, which for these products they are not.

For example a 24 mg 24 hour patch does not produce a linear 1 mg/h - the exact rate is complex and unknown. All that we know is that over 24 hours a 24 mg dose is delivered, probably with a higher rate at first that drops off over time.

Going back over 10 years in AMT we had this debate and extensive conversations with industry and our clinical safety team. The conclusions were that given the 24 mg 24 hour patch example we

• definitely couldn't represent this as 1 mg/h, because that is not correct.
• couldn't represent this as follows because this can be divided down and is equivalent to 8 mg / 8 hours or 1 mg / 1 hour which is incorrect
• numerator = 24
• numerator unit = mg
• denominator = 24
• denominator unit = hour

Instead we represented it as 24 mg / 24 hours where "24 hours" is a single unit of measure concept. This is effectively

• numerator = 24
• numerator unit = mg
• denominator = 1
• denominator unit = 24 hours

It is then not possible to equate this to 1 mg/h, 8 mg / 8 hours or any other ratio.

I'd provide some examples from AMT but I can't add files here so I can't include screen shots

So here's a link https://browser.ihtsdotools.org/?perspective=full&conceptId1=45044011000036104&edition=MAIN/SNOMEDCT-AU/2025-03-31&release=&languages=en and an example product registration data is at http://www.ebs.tga.gov.au/servlet/xmlmillr6?dbid=ebs/PublicHTML/pdfStore.nsf&docid=125489&agid=%28PrintDetailsPublic%29&actionid=1

The unit of measure "mg/24 hours" in this example is defined using the "24 hour" concept - you can find these at https://browser.ihtsdotools.org/?perspective=full&conceptId1=258836006&edition=MAIN/SNOMEDCT-AU/2025-03-31&release=&languages=en and https://browser.ihtsdotools.org/?perspective=full&conceptId1=258703001&edition=MAIN/SNOMEDCT-AU/2025-03-31&release=&languages=en

Note that for other patches that do quote mg/h in the registration data we model them that way. Here's an example https://browser.ihtsdotools.org/?perspective=full&conceptId1=933196301000036101&edition=MAIN/SNOMEDCT-AU/2025-03-31&release=&languages=en. You can find its registration data at http://www.ebs.tga.gov.au/servlet/xmlmillr6?dbid=ebs/PublicHTML/pdfStore.nsf&docid=163067&agid=%28PrintDetailsPublic%29&actionid=1

I hope that helps,

Dion

This is one of the problems or complexities with patches. 

Scopolamine (hyoscine in the UK) patches contain 1.5mg in the patch, and the amount absorbed on average is 1mg in 72hours. 

So what does SNOMED, or any drug dictionary, do about that. We could represent the total amount actually in the patch. but be aware that not all companies and patches will tell you that. 

Instead we generally represent the strength as the amount of drug that gets into the patient as stated by the regulatory information. As this is expressed differently between patches, we represent that even where the amount is not expressed as a per one hour. 

The scopolamine patch is interesting as at no point does the regulatory information imply an amount per hour. Only an average of 1mg over 72 hours. 

To divide that down may mean you create false equivalence between two patches that have the same per hour if you calculate it, but are not equivalent in usage.