How do you determine the correct dose of Amoxicillin for a child or adult?

What is Amoxicillin?

It is an antibiotic belonging to the penicillin family.
Practically speaking, Amoxicillin is the most basic and important antibiotic in pediatrics. It is our first line of treatment for the most common infections out there.

Are there different types of Amoxicillin in the market?

Yes, depending on where you live, you may find Amoxicillin being sold under different brand names, in the Unites States these include Amoxil, Moxilin, Sumox and Trimox.
Amoxicillin is the active ingredient in all of these.

What is the concentration available in these suspensions and why is this important?

Now we’re talking. One tablet contains 500mg. That part is easy for everyone and obvious. Suspensions contain a certain concentration. Every milliliter (ml) of suspension contains a certain amount of milligrams. Most of the suspensions available contain 250mg in every 5ml, but this can vary depending on the brand sold in your country. Or, in other words, if you take 10ml of suspension, you will be receiving the same amount of Amoxicillin found in a 500mg tablet. Kapish?

So, what is the difference between the available suspensions?

Although the concentration is similar among most of the suspensions available, their names, flavours and the companies marketing them may vary. That is why you may receive a different product (strawberry or banana flavor) each time you go to the pharmacy, with the same prescription.

How do you determine the dose of Amoxicillin required for children and adults?

Depending on the type of infection the person is experiencing and their weight, as well as their ability and desire to take tablets versus suspensions.

What are some examples of infections and their corresponding Amoxicillin doses?

On our website, we have an excellent chapter about throat infections caused by streptococcal bacteria. Since this bacteria is very sensitive to antibiotics, the dose required to treat it is relatively low, 50mg/kg per dose, up to 1 gram per day. For example, a child weighing 14kg who needs Amoxicillin because of strep throat will receive 14 times 50mg which is equal to 700mg per day, divided into twice daily, or in other words 350mg twice daily. This is the same as 7ml twice daily.
What else is important to know? In throat infections, the maximal daily dose for adults is 500mg twice daily. There is no need for more than that.
So, if you know a little bit of maths you can already tell that starting at a weight of 20kg, the dose does not change – it remains 500mg twice daily or 10ml twice daily. Low doses are used because this bacteria is super sensitive to this antibiotic.

What is the dose required for ear infections and pneumonia?

Pneumonia and ear infections are both often caused by a bacteria called pneumococcus. This bacteria is resistant to antibiotics and therefore we need higher doses of antibiotics to destroy it. The correct dose for these diagnoses is 80mg/kg per dose, up to a maximum of 1.5g per day. If the infection is severe, you can increase the dose to 3g/day, but this is reserved for exceptional cases.
For example – if you have a child that weighs 14kg and you would like to prescribe them with Amoxicillin due to an ear infection, the correct dose for them would be 14kg multiplied by 80mg, which is equal to 1120mg per day, divided into two doses per day or 560mg per dose, which actually converts to 11.2 ml twice daily. I suggest disregarding numbers after the decimal point for most medications, but especially when it comes to Amoxicillin, and therefore the appropriate dose would be 11ml twice daily.
What else is important? For ear infections and pneumonia, the maximal dose for adults is also 1.5g such as the use of 15ml twice daily is sufficient.
Again, if you know a little bit of maths you can tell that the dose does not change for anyone weighing above 19kg. It remains 750mg twice daily.

Who determines the frequency of Amoxicillin required per day?

The answer to that is the infection that the person is experiencing.
In most childhood and adulthood infections, the daily dose of Amoxicillin required can be divided by two. Your doctor will let you know if this does not apply to your case.

But my doctor prescribed me with 1 tablet of Amoxicillin 3 times daily for my pneumonia?

That’s right. When prescribing a suspension, it is easy to prescribe 750mg twice daily. However, tablets come in 500mg forms, and you cannot prescribe 1.5 tablets twice a day because 1 tablet cannot be divided into two. Often, for adults, the maximal dose will be 500mg 3 times daily.
If someone were to invent a 750mg tablet, we would then be able to prescribe 750mg twice daily in tablet form.

Are there exceptions to the rules?

Of course.
The purpose of this text is just so you can understand your physician’s recommendations and to be able to ask them questions. If there is a significant difference between what your physician has been doing and what I have described above. I am certain that they have good reasoning.
Nonetheless, there are always exceptions, and I have also found myself multiplying the dose of Amoxicillin given to patients in certain situations and writing things up differently. However, any such change must have good medical reasoning.

Are there certain situations where you do not recommend Amoxicillin?

Of course.
Amoxicillin it the first line therapy for certain infections, but every infection is different, and in children and adults there is always a right medication of the right patient. Keep in mind that if a patient is allergic to Amoxicillin, you cannot prescribe them any of the products containing Amoxicillin. Find out more about penicillin allergy, how it is often a misdiagnosis and how to get rid of this misdiagnosis here.

In summary, this is generally all there is to Amoxicillin dosing in children and adults.
Keep healthy my friends!