The fillers used in Eythyrox and Eltroxin tablets

Over the last 2 years, both pharmaceutical companies changed the ingredients of Euthyrox and Eltroxin. The active ingredient, levothyroxine sodium, is the same. But what makes up the rest of the tablets?

I have been using Euthyrox for about 10 years.  Then, about 2 years ago, they changed the formula.  While the active ingredient was exactly the same, the fillers have been changed.  

I started feeling more “swollen”, tired all the time, and just not the same.  Then, on the one Facebook group, others also complained of experiencing symptoms.  

So, I decided to switch to Eltroxin.  Only to find out, a few months later, that they too changed the formula!  

So, in today’s post, let’s look at the excipient ingredients (the non-active ingredients) that are in Euthyrox and Eltroxin and what it means.  

The ingredients

The active ingredient in both Euthyrox and Eltroxin is the synthetic T4 hormone called levothyroxine sodium, or levothyroxine for short.  

The inactive ingredients, called excipients, are added to the active ingredient to make the tablet.  

Excipients for Eythyrox:  mannitol, maize starch, gelatin, crosscarmellose sodium, magnesium stearate.

Excipients for Eltroxin: colloidal silica, magnesium stearate, microcrystalline cellulose, pregelatinised maize starch, talc.  

Let’s have a look at the role of each of these ingredients in the manufacturing process.  It may be that you could be sensitive to a specific ingredient that is now in the “new formulation”.  If you believe it could be contributing to your symptoms, speak to your doctor about switching to another brand which may not have that ingredient, or have a compounding pharmacy provide you with the medication without the excipient.

Mannitol

Mannitol is a sugar alcohol that is typically derived from corn or wheat. Mannitol is also found in small amounts in some fruits and vegetables such as mushrooms, onions, and asparagus.

In the pharmaceutical industry, mannitol is used as a sweetener (it is a low-calorie sweetener and poorly absorbed by the intestines), a lubricant, and a diuretic.  It helps to prevent the ingredients from sticking to the machinery during the manufacturing process.

It is generally well tolerated by most people, though some people may experience gastrointestinal side effects such as gas, bloating, and diarrhea.

Crosscarmellose sodium

Crosscarmellose sodium is a type of thickener or binder that is often used in pharmaceuticals and food products. It is a derivative of cellulose, which is a natural substance found in plants. Crosscarmellose sodium is used to help hold ingredients together and give a product a desired consistency. It is considered safe for consumption and is generally recognized as safe (GRAS) by the US Food and Drug Administration.

It can swell when it comes into contact with water, which may cause problems for people who have certain medical conditions (such as swallowing difficulties).  

Some people may have a senstitivity or allergy to cellulose or crosscarmelose sodium, and should therefore avoid it. 

Gelatin

Gelatin is used in pharmaceuticals as a gelling agent and a binder. It is a protein derived from collagen, which is found in animal bones, skin, and connective tissue (typically bovine and porcine).

Gelatin is used in both the manufacturing of capsules and tablets.  It is considered safe for consumption by the US Food and Drug Administration (FDA).

Maize starch and pregelitinised maize starch

Maize (corn) starch is used in pharmaceuticals as a filler, a binder, and a disintegrant. 

As a filler, it is added to medication to bulk it up and make it easier to handle and swallow.

As a disintegrant, it is added as it helps tablets and capsules to break apart when they come into contact with water.  This allows the active ingredients to be released more quickly and effectively.

Pregelatinized maize (corn) starch is a type of starch that has been pre-treated by heating and then cooling it under high pressure, this process is called “pregelatinization”. This process causes the starch molecules to become partly gelatinized.  It is more easily dispersed in water.  

It is generally well tolerated by most people, though some people may have an allergy to corn.

Colloidal silica dioxide

Colloidal silica dioxide, also known as colloidal silicon dioxide or silica gel.  is used as a flow agent, which helps to prevent ingredients from sticking together and clumping during the manufacturing process.

It aids in the tablet and capsule formulations as a glidant, which is a substance that helps to reduce friction and increase the flowability of powders and granules, making them easier to handle and fill into capsules or tablet molds.

It is also an anti-caking agent, so it helps to keep the consistency of the products over time and ensures that the active ingredients are evenly distributed throughout the medication.  

It is considered safe for use in pharmaceuticals by the US Food and Drug Administration (FDA) and it is generally well tolerated by most people, although some people may have an allergy or sensitivity to silicon.

Magnesium stearate

Magnesium stearate is used as a lubricant and a flow agent.  It helps to prevent ingredients from sticking to the machinery during the manufacturing process, making it easier to produce tablets and capsules.  It helps to ensure that the active ingredients in a medication are evenly distributed throughout the tablet or capsule. 

It is considered safe for use in pharmaceuticals by the US Food and Drug Administration (FDA) and it is generally well tolerated by most people. Although, some people may have an allergy or sensitivity to magnesium.

Microcrystalline cellulose

Microcrystalline cellulose (MCC) is used as a filler, binder, and disintegrant (helping tablets and capsules to break apart when they come into contact with water).  MCC is made from cellulose, a natural substance found in plants.  

MCC is added to medications to bulk them up and make them easier to handle and swallow.

It is plant-based and gluten-free, and generally well tolerated by most people. 

Talc

Talc is used as a lubricant, a glidant, and an anti-adherent.

As a lubricant, talc helps to prevent ingredients from sticking to the machinery during the manufacturing process.  

Talc is also used as an anti-adherent, which prevents ingredients from sticking together and clumping. 

This helps to maintain the consistency of the product over time and ensures that the active ingredients are evenly distributed throughout the medication.

Talc is a naturally occurring mineral made mostly of magnesium silicate, it is considered safe for use in pharmaceuticals by the US Food and Drug Administration (FDA) and it is generally well tolerated by most people.

But, you don’t want to inhale it, as it can cause lung irritation.   Talc must also be verified to be asbestos-free. 

Closing thoughts

If you suspect that an excipient (non-active ingredient) could be contributing to your symptoms, I recommend that you speak to your treating doctor about it.  Remember that most thyroid patients must drink these hormone replacement pills every day, so while it may seem like a very small exposure, over time an ingredient can cause irritation and inflammation if you are sensitive to it it or have an allergy for an ingredient.  

Adele du Rand
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The fillers used in Eythyrox and Eltroxin tablets

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