The dosage calculator finds what dose of a medication is appropriate for your weight. It can also recalculate the dosage expressed in mg/kg into doses of liquid medication. Read on to learn what is the drug dosage calculation formula and how to use it. With our text, you will learn more about various kinds of dosing which you may meet while using different medications. You will also find out what are advantages of adjusting the dose to the patient.

Are you looking for a healthy antypyretic medication dose for kids? Make sure to take a look at the ibuprofen dosage calculator and paracetamol dosage calculator!

Dosage forms

Depending on the route of administration, dosage forms come in several types. You may take drugs through different methods. The most popular one is oral. However, in some medical situations this route is unavailable, ineffective or associated with a high number of adverse reactions. That is why patients may receive drugs also through parenteral way (this includes: subcutaneous, intramuscular, intraosseous, intravenous and other). Moreover, some drugs are only given topically, directly on the skin, to the eye, rectum, vagina or as an inhalation.

You should know that the route of administration of the drug dramatically influences the dosage and efficacy, thus always check if you administer appropriate drug to the appropriate person, through the appropriate route in the appropriate dose!

What is an appropriate dose?

When treating a patient or just taking yourself any medication we always need to wonder what exact dose of the drug should we choose. And the truth is that we dose (or should dose) nearly everything in our life, from cooking dinner, to taking medications! However, regarding the drugs, there are certain different kinds of dosing, that depend on the specific drug and/or the patient.

1. One dosage
Drugs with one fix dosage are the easiest in use, you just take it and forget about all the stuff. You don't need to use any dosage calculation formulas! (e.g. vaccines)

2. Different, fixed dosages
The dosage of such drugs is usually set by the doctor regarding the patient's need or age. In this case you also don't have to worry about medical dosage calculations! (e.g. hypotensive drugs)

3. Different, variable dosages
In this case the doctor usually suggests patient a sample dosage; the patient modifies it regarding his/ her needs and the situation. (e.g. insulin)

4. Blood concentration-dependent dosage of the drug
This is a relatively small group of drugs. The doses are different regarding the serum concentration of the active substance of the drug. (e.g. Vitamin K antagonists, lithium)

5. The dosage of the drug depending on the patient's body weight
The doses of the drug depend on the weight of the patient. It means, that two patients with the same disease may receive a different amount of the same drug!
Our dosage calculator will help you calculate appropriate doses of this kind of drugs!

Why do we need to calculate doses?

Living in the sixteenth-century Swiss scientist Paracelsus said:

"All substances are poisons; there is none which is not a poison. The right dose differentiates a poison and a remedy."

Nowadays, this sentence is equally true. We know that every substance, especially every drug may be toxic if given in an inappropriate dose. This is why we should perform our dosage calculations with carefulness and accuracy. It is critical in the management of children, as a slight mistake in the dose of the drug may cause a significant change in the effect of its action. The usage of pediatric dose calculator seems to be a responsible choice that reduces the risk of a mistake!

Contemporary scientists are also looking at the issue of drug dosage. There are plenty of on-going clinical trials, in which different doses of the drugs are being compared. Moreover, there are more and more scientific data suggesting that individually performed dosage calculations (not only in pediatric patients) improve patient survival when compared with standard treatment with fix doses. For instance, in 2016 a group of scientists from France published an article in Journal of Clinical Oncology in which they summarized the results of their trial performed on the patients treated due to metastatic colorectal cancer (cancer of large bowel in the IV stage of the disease - with metastases). The group of them, which was treated with individually adjusted dose of fluorouracil (antimetabolite drug used in the treatment of many cancers, including colon cancer) had better response to the therapy, higher survival rate and lower grade of toxicity, than those treated with standard doses.

As you can see, it's worth to use drug dosage calculators!

Calculating medication dosage by weight

Medical dosage calculations considering patient's weight are very common in obese patients and on pediatric wards. It's easy to imagine that the weight of the body of an adolescent may be 40 times bigger than the newborn child, so the need to dose drugs accurately seems to be obvious.

Moreover, some specific drugs need to be dosed according to an adult patient's weight. These are e.g. heparin, antibiotics and muscle relaxants.

Dosage calculation formulas

If you want to calculate the dose of a medication, you need to use the following equation:

dose = weight * dosage

  • Weight is your weight, expressed in kg or lb. Don't cheat - type in your real body mass!
  • Dosage is the prescribed amount of drug in mg per kg of body weight. You can usually find this number on the medicament box or the prescription.
  • Dose is the total amount of medication you need to take.

The situation gets more complicated if your medicament is liquid. After all, how are you supposed to know how many ml of your drug contain, for example, 50 mg of active substance? Our dosage calculator can help you with this as well. All you have to do is use the following formula:

liquid dose = dose / medicine concentration

  • Medicine concentration is the amount of active substance per a given volume of your drug. It can be expressed in mg per ml.

This function of our dosage calculator is especially useful when giving fluid drugs (e.g. syrup) to the children and in hospitals, where many drugs are given to the patient not orally but intravenously.
Conversion from mg to ml is essential in situations like these!

How to calculate drug dosage

If you want to find what is the appropriate dosage of a drug for your body weight, you need to follow these steps:

  1. Determine the dosage of the medication. Let's say the appropriate dosage of the active substance is 2 mg/kg of body weight.
  2. Weigh yourself. Let's assume you weigh 80 kg.
  3. Multiply these two values to get the dose of medication in mg: 2*80 = 160 mg. You need to take 160 mg of active substance.
  4. What if your medication is liquid? Type the concentration into the proper box. Let's say the concentration of your medicine is 2 mg/ml.
  5. Divide the dose by medicine concentration to obtain the liquid dose: 160/2 = 80 ml.

Make sure to take a look at our drug conversion calculators, such as steroid and opioid conversion calculators!

Łukasz Białek, MD and Bogna Haponiuk

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Dosage Calculator - How to Calculate Dosage?