Just a note at the start. It is possibly better to use the word formulation rather than make as some tablets are available under two different names - e.g. Accord and Almus, or Aristo and Vencamil.
All formulations of levothyroxine tablet contain the same active ingredient - Levothyroxine sodium. This is the case for every levothyroxine product I’ve ever seen – gel cap, oral solution, as well as tablets.
There is no fundamental reason you cannot take multiple formulations of these medicines.
The problems in doing so are due to how each formulation interacts with your individual body. The same possible issues apply whether this is the case of changing entirely to another formulation, or taking two (or more) formulations at the same time.
Some of the issues are very minor. Unless you know there is an issue with a particular formulation you might be absolutely fine.
Why mix formulations?
It seems obvious that by always taking the same formulation, you sidestep the possibility of issues from mixing. However, there are some circumstances in which it is difficult to avoid mixing formulations:
- If a formulation is not made in all the dosages you have been prescribed.
- If a formulation is temporarily unavailable from the pharmacy you are using, or more widely. Or they supplied the wrong formulation.
(In the past we have seen that sometimes different dosages sold under one company name are actually different formulations. This no longer occurs within the UK.)
Managing Mixed Formulations
If possible, always take the same dosage tablet(s) of the same formulation.
- Check the available products and their excipients. If you notice an excipient that you know you do not tolerate, avoid it.
- Record every formulation and every dosage you ever take.
- Record every change in how you feel whether change of batch, change of formulation, change of tablet dosage(s), or a real change in dose.
Many of us have to do this.
If you need to take two (or more) formulations, don’t panic. It is only a problem if there is a problem!
Avoiding Issues
If you are taking mixed formulations and something changes, you very likely have no idea which formulation, which product, is causing the problem.
If possible, stagger changes. For example, if you were taking 100 microgram and 25 microgram tablets, then see if you can change to a new box of the 100 on one day, and of the 25 about 14 days later. This means that you avoid making two changes at the same time.
This might help even if they are the same formulation. But would definitely be a good idea if the formulation you are taking changes. Say, you get a different formulation of the 25 microgram tablets.
If possible, change before you run out. By so doing, if you have an issue, you might be able to (at least temporarily) revert to the formulation you had been taking.
If you need to put in a Yellow Card report, you might have to make two reports and leave the MHRA and the companies to work out which is the actual cause. Don't let that make you hesitate to do so!
Other Options
If you need a dose that cannot be dispensed in tablets of the formulations you tolerate, you can always suggest either alternate day dosing or splitting.
For example, 100 + 50 one day, 100 only the next. Averaging 125. (Though many do not like this approach as they feel they are never on a steady dose.)
Or getting dispensed 50 microgram tablets and splitting them as needed. (Not all tablets split readily.) Some prescribers and pharmacists do not like to let you split tablets.
Excipients
One formulation might contain an excipient you do not tolerate, or just tolerate less well than another excipient. Three common excipients are often suspected of causing problems in some individuals:
• Lactose (even in those who have no known sensitivity to lactose or dairy);
• Mannitol (for reasons unknown);
• Acacia.
You might find that while you can tolerate a small amount of an excipient, if you consume larger quantities, you are more likely notice some effects.
Obviously, once you have proved intolerance to a particular excipient, avoid it!
Absorption
Absorption depends on both chemical and physical properties of the formulation. Relatively minor differences, such as the pressure applied when forming the tablet, can change absorption. This can result in differences between dosages of one formulation, and between batches of exactly the same dosage/formulation.
Each formulation is likely to be absorbed slightly differently. With one being absorbed faster: another being slightly slower. One being more completely absorbed: another being slightly less completely absorbed.
The differences should be small but even a small difference can affect us.
Impurities
No ingredient is absolutely pure. For example, a common ingredient is magnesium stearate. And common impurities found in that are magnesium oleate and magnesium palmitate. But the quantities present might vary depending on the sourcing of the magnesium stearate product. And they will not be separately listed.
For each excipient, there are standards which they must meet. However, one source might only just meet the standard while another exceeds it by a large margin.
Size
The total volume of Levothyroxine sodium in any tablet is tiny. Something like a single crystal of ordinary sugar. A 100 microgram tablet might weigh 50 milligrams. That works out as just 0.2% of the tablet being the active ingredient. Different dosages and different tablets sizes will mean the exact percentage varies. But it is always going to be well under 1%.
Tablets consist almost entirely of their excipients. Obviously a physically larger tablet will contain a greater quantity of excipients than a smaller tablet.
Some companies use the same mixture to make tablets in multiple dosages (e.g. 50 and 100 micrograms). They just use twice as much! Which obviously means that a 100 microgram tablet is bigger than a 50 microgram tablet.
Other companies change the balance of the excipients depending on the size of tablet.
This can sometimes be clearly seen when the 25 microgram tablet of a particular formulation is physically larger than the 50 or even 100 microgram tablets.
In countries (such as the USA) which have a very wide range of dosages, it is usual that every tablet is physically identical in size. The difference will be the amount of Levothyroxine sodium. (And, often, a colouring agent.)
An issue that seems to be cause by size is that some people do fine on two 50 microgram tablets of a particular formulation, but not on a single 100 microgram tablet of the same formulation. Or vice versa.
Informing Pharmacist
There might also be a difficulty in expressing what formulations you want. Imagine you are on 100 + 25 micrograms.
You cannot request “Always Accord” because they don’t make a 25 microgram tablet.
You cannot request “Always Wockhardt” because they don’t make a 100 microgram tablet.
You cannot request “Never Teva” because other formulations might also contain excipients you do not tolerate.
You can be forced into a complex explanation of what you want, what you will accept if you have to, and what you will always reject. Maybe spend a few minutes making it clear on a piece of paper and handing that your pharmacist?
Liothyronine
All but one liothyronine products contain the same active ingredient - liothyronine sodium. (For some reason, Thybon Henning contains the very similar liothyronine hydrochloride.)
The same arguments apply as for levothyroxine. But, due to prescribing and dispensing practice, it is less likely to happen.
If you wish to link to this page on HealthUnlocked, copy the entire dark red text below and paste into a post or reply.
[i][b]helvella - Mixing Levothyroxine Formulations[/b]
A discussion about mixing (and switching) formulations of levothyroxine.[/i]
https://helvella.blogspot.com/p/helvella-mixing-levothyroxine.html
If you find anything incorrect, misleading, typos, links
that don’t work, etc., please let me know. Go to my profile and use the contact details there:
https://www.blogger.com/profile/17095075774834042563
The index page to helvella’s blog is here: helvella - Index of Blog Pages
No comments:
Post a Comment