Drug Half Life Calculator

Use the drug half life calculator to determine the amount of a drug still present in a patient's body when half time and dosage are known.

What Does Half Life Mean In Drugs?

The half life of a drug is the estimation of the time that the amount of a drug takes to be reduced by one-half. The symbol t1/2 is used for the half-life.

Patient-Specific Variables That May Affect Half-Life:

Age
Blood circulation
Diet
Excessive fluid
Gender
Kidney function
Liver function
Obesity
Smoking

What is the formula for calculating half-life?:

The formula that is used to find the half life of drug is as follows:

\(\ Dosage(t) =\ Dosage(0)\times\ 0.5^{(\frac{t}{T})}\)

Where

T is the representative of the Half-life of a drug;
t is the Time that has passed from the administration of the drug;
Dosage(t) – The drug amount present in a patient's body
Dosage(0) shows the drug quantity administered

How do you Calculate the Half-life of a Drug?

Go through the steps outlined below:

Measure the quantity of the drug dosage
Determine the half-life time
Put these values in the half-life formula as we have done in the following example.

Example:

Suppose you have the following values:

Half Life Drug = 1 minute
Dosage = 10 g

Find the half life?

Solution:

Convert Grams to milligrams:

\(\ Dosage =\ 10\ \times\ 1000 =\ 10000\ mg\)

Put the given values in the half life drugs formula:

\(\ Dosage(t) =\ Dosage(0)\times\ 0.5^{(\frac{t}{T})}\)

\(\ Dosage(t) =\ 10000\ mg\times\ 0.5^{(\frac{1}{1})}\)

\(\ Dosage(t) = 5000\ mg\)

Half-Life of Drugs Chart:

In the following table, we have mentioned some most commonly used substances and their half life.

Generic Name	Brand Name Examples	*Half-life (T1/2)**
Alprazolam	Xanax	6-12 hours
Amiodarone	Pacerone	15-142 days
Amphetamine	Adderall, Dexedrine	10-12 hours
Atenolol	Tenormin	6-7 hours
Clonazepam	Klonopin	18-50 hours
Cocaine	-	50 minutes
Diazepam	Valium	20-100 hours
Donepezil	Aricept	70 hours
Dutasteride	Avodart	5 weeks
Erenumab	Aimovig	28 days
Fluoxetine	Prozac	2-4 days
Lead	-	28-36 days
Mercury	-	65 days
Methamphetamine	Desoxyn	6.4-15 hours
Methylphenidate	Concerta, Ritalin	2-3 hours
Plutonium	-	40 years (liver), 100 years (bone)
Phenytoin	Dilantin, Phenytek	7-42 hours
Tetrahydrocannabinol (cannabis/marijuana)	-	Infrequent users: 1.3 days Regular users: 13 days

FAQ’s:

Is Half Life The Same As Drug Duration?

No, The time that the drug takes to be eliminated from the body is the half life while the drug duration is the total time the drug remains inside the body.

How many half-lives does it take to get rid of medication?

A drug approximates takes 4 to 5 half lives to be eliminated from the body. When 4 to half-lives are passed the amount of the drug goes below the clinically relevant concentration and is normally considered eliminated. If you double the amount the elimination time also increases.

References:

goodrx.com: What does drug half-life mean?