Calculating the dose
Drug dosing is a task that requires precision. Too high a dose of the drug causes symptoms of poisoning and, at worst, the death of the patient. Too small a dose will not effectively treat the ailment for which it is prescribed and will accustom the patient to the drug, reducing its effectiveness over time.
Picture Pixabay
Picture PixabayCalculating the dose
A doctor will give a prescription explaining how the medicine should be dosed, and how to administer the medicine. According to the instructions, the dose of solid or liquid medication to be given at one time is calculated for the patient. It may also be necessary to calculate the amount of medication to be given to the patient in one day to ensure it does not exceed the recommended dosage.
The strength of a liquid medicine is indicated, e.g. mg/ml or IU/ml. The number of millilitres of medicine needed to give the prescribed amount of medicine, or dose, is calculated.
For a solid medicine, the strength of the tablet or capsule used, how many tablets or capsules the patient is taking at a time and how many times a day the dose is taken are usually specified. However, it is often necessary to calculate the amount of solid medicine to be given to a patient on the basis of the prescribed dose .
There is no single official way to express the dose given to a patient. For example, 30 mg x 3 and 90 mg/day divided into three doses have the same meaning.
Dose of a solid medicine
Solid medicines include tablets, capsules, powders and chewing gum. The strength of the medicine, i.e. the amount of active ingredient in one capsule, is indicated on the packaging:
Kuva Paracetamol Packaging | Brett Jordan | Flickr
The strength of the paracetamol capsule in this pack is 500 mg. This means that one capsule in the pack contains 500 mg of the active substance (paracetamol).
Kuva Paracetamol Packaging | Brett Jordan | Flickr
The strength of the paracetamol capsule in this pack is 500 mg. This means that one capsule in the pack contains 500 mg of the active substance (paracetamol).
Example 3.
A doctor has prescribed 1000 mg of paracetamol to be taken in the morning and evening.
a) How many capsules should the patient take in the morning and evening?
The patient will receive 500 mg of paracetamol from one paracetamol capsule. When he takes 2 capsules, the active ingredient is 2 x 500 mg or 1000 mg.
b) How many capsules should the patient take per day? How much active ingredient does the patient receive per day?
The patient takes 2 capsules in the morning and 2 capsules in the evening, for a total of 4 capsules per day. The patient will then receive 4 x 500 mg or 2 x 1000 mg = 2000 mg active substance/day.
Liquid medication
In liquid medication (solutions, suspensions and syrups) the active substance is dissolved or suspended in a liquid. The concentration of the active substance in the liquid is indicated on the label.
Picture File:Ibuprofen syrup.jpg - Wikimedia Commons
This solution contains 100 mg of the active substance (ibuprofen) dissolved in 5 ml of liquid. This means that when a 5 ml dose of the solution is taken from the bottle, it contains 100 mg of ibuprofen.
Picture File:Ibuprofen syrup.jpg - Wikimedia Commons
This solution contains 100 mg of the active substance (ibuprofen) dissolved in 5 ml of liquid. This means that when a 5 ml dose of the solution is taken from the bottle, it contains 100 mg of ibuprofen.Example 4.
The patient has been prescribed 200 mg of ibuprofen every 8 hours.
a) How much drug solution should the patient be given every 8 hours?
The patient will therefore receive 100 mg of ibuprofen in 5 ml of solution. When the patient is given 2 x 5 ml or 10 ml of solution, he will receive 2 x 100 mg or 200 mg of ibuprofen.
b) What is the total amount of ibuprofen solution given to the patient per day? How much active substance (ibuprofen) will the patient receive per day?
As 10 ml of the medicine is given every 8 hours, it is given three times a day. In other words, a total of 30 ml of medicine is administered every day. Since 200 mg of ibuprofen is always given at one time, a total of 3 x 200 mg or 600 mg of ibuprofen is given per day.