# Zero Order Kinetics: Definition, Pharmacology & Examples

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• 0:03 An Interest-ing Analogy
• 0:27 What Is Zero Order Kinetics?
• 1:48 Importance
• 2:16 Mind Your P's and Wheats
• 3:33 Lesson Summary

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Lesson Transcript
Instructor: Rachel Nall

Rachel Nall is a critical care-certified registered nurse.

This lesson helps you apply the principle of zero order kinetics, which is a way of describing how the body breaks down some types of medicine. You can use this knowledge to predict how long certain medicines will last when they're given to a patient.

## An Interest-ing Analogy

When you put your money in a savings account, you earn interest on that money. But what if, no matter how much money you put in, you always got the same amount in interest, such as \$5 for every deposit, whether you deposited \$1 or \$1,000? This is the same principle that medical professionals apply to zero order kinetics, which is what we will be discussing in this lesson.

## What Is Zero Order Kinetics?

Zero order kinetics is a way of describing how the body uses and breaks down some medicines. While the rate at which the body eliminates most drugs is proportional to the concentration administered, known as first order kinetics, drugs that work by zero order kinetics work at a predictable, constant rate. Knowing that a medicine works by zero order kinetics lets the person administering it know exactly how long to expect that it will work.

To better understand zero order kinetics, let's look at its counterpart, which is first order kinetics. Drugs that the body breaks down by first order kinetics break down at a percentage rate based on how much a person has been given. This percentage rate is known as a half-life; about 50 percent of the drug is used each hour.

For example, if a person took 100 milligrams of a drug that works by first order kinetics, after an hour, there would be 50 milligrams left in his system. The next hour, there would be 25 milligrams left, and the next, 12.5 milligrams. But if a person took the same drug and it worked by zero order kinetics at a rate of 10 milligrams an hour, his body would use the exact same amount every hour. After the first hour, there would be 90 milligrams left in his body, then 80 milligrams after the next hour, and so on. After 10 hours, the zero order drug would be all gone!

## Importance

Knowing about zero order kinetics can help a medical professional predict how long a medicine will last for a patient. One example of a medicine that works by zero order kinetics is warfarin, or its trade name Coumadin. This medicine is a blood thinner, which can be very important for a person who has had a history of blood clots or heart attacks. Doctors who know how fast the body breaks down a warfarin dose can tell a person to take a dosage that's enough medicine to last them the whole day.

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