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Theme of the Week: When Does 1 Plus 1 Not Equal 2?

Medications often come in many different strengths - most of the time, when one strength is not available, a lower strength can be dispensed and instructions are adjusted accordingly to provide the same dose. However, here, we highlight some unique situations where substituting with another strength is not feasible.


1) Amoxicillin-clavulanate (Clavulin): As you may know, this two-drug combination antibiotic tablet comes in 250/125 mg and 500/125 mg. Although you may be tempted to substitute 500/125mg with 2 tablets of 250/125 mg, this may actually increase adverse effects such as diarrhea because the clavulanate portion (125mg) is fixed in both tablets - so 2 tablets is actually not the same dose!


2) Semaglutide tablet (Rybelsus): This anti-diabetic tablet comes in 7 mg and 14 mg tablets. Patients are usually titrated from 3 mg to 7 mg to 14 mg. However, it is important to note that 2 tablets of 7 mg are NOT equivalent to 14 mg. The reason is the formulation - each tablet strength is co-formulated with 300 mg of salcaprozate sodium, an enhancer which improves semaglutide absorption. By taking 2 tablets of the 7 mg, this increases the overall content of salcaprozate sodium and affects the absorption.


3) Leuprolide (Lupron Depot): this injectable product comes in 7.5 mg and 22.5 mg strengths. It is important to note that these injectable products are long-acting formulations. The 7.5 mg formulation lasts one month, whereas the 22.5 mg formulation lasts 3 months. It would be incorrect to give 3 injections of the 7.5 mg because although the total dose is the same, the release rate is different, resulting in greater exposure over the month.

Now you know!

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