What should you know about pharmacokinetics as a pharmacist? [Detailed Guide]
Do you ever think that whenever you consume any medicine, it affects your body? Will your body allow your medicine to absorb, distribute, and eliminate easily just like any other food, or treat it differently? If you are curious about it then pharmacokinetics will answer you what your body does when you consume a medicine/medicinal drug
This article is designed for beginners or pharmacy students to understand the concept and the following points
- What is pharmacokinetics?
- What are the basic principles and processes of pharmacokinetics?
- Why do we study pharmacokinetics?
- How pharmacokinetics helps us to predict the bioavailability of drugs?
- What information do we have about the pharmacokinetics of the drug?
What is Pharmacokinetics?
Pharmacokinetics is the branch of pharmacology that deals with the brief description of the effect of the body on drugs. It is the opposite of pharmacodynamics that actually tells that will be the effect of the drug on the body. In a simpler way, we can say that pharmacology is an extensive study of drugs that is divided into two main sub-branches:
- Pharmacodynamics: what drugs do to the body
- Pharmacokinetics: what body does to the drug
Basic principles of pharmacokinetics:
There are four main processes that are often known as principles of pharmacokinetics and abbreviated as ADME. Pharmacokinetics based on the following four process
- Absorption of the drug occurs in the small intestine via villi and microvilli. Absorption of dug further depends on Routes of administration, Blood flow, and Concentration
- Distribution of drugs after entering into systemic circulation via blood vessels. The distribution of drug further depends on:
- Size of organ
- Blood flow
- Binding with plasma protein
- The apparent volume of distribution
- Metabolism of the drug into the liver to convert into its metabolites
- Elimination of drugs to remove the drug out of the body. It occurs through the liver or kidneys.
- First-order elimination
- Zero-order elimination
Fundamental parameters of pharmacokinetics:
The fundamental parameters of pharmacokinetics are based on the basic principles of pharmacokinetics. These parameters are
The volume of distribution: It is the ratio of the amount of drug in the body to drug concentration in plasma and blood.
Clearance: It represents the amount and rate of elimination of drugs out of the body. It is the sum of hepatic and renal clearance.
Bio-availability: the amount of drug that reaches systemic circulation or drug is called its bioavailability. The bioavailability of drugs depends upon the route of administration and how fast the drug is being absorbed, distributed, and metabolized.
Dosing: It includes both the maintenance dose and loading dose.
Now u can relate that how the basic principles of pharmacokinetics are linked with the fundamental parameters and help the researchers to determine
- The half-life of the drug
- Therapeutic window
- Loading dose
- Maintenance dose
- Elimination half-life
- The area under the concentration curve
Why do we study pharmacokinetics?
Now we already know that pharmacokinetics deals with what the body does with the drug and also covers the basic principles of pharmacokinetics.
Here a question arises: why do we study it in pharmacy education? So the significance of pharmacokinetics in academic life as well in professional life can be highlighted through dew logical points:
- Pharmacokinetics provide students basic concepts of the factors that may reduce or increase the bioavailability of any medicinal drug in the body
- Pharmacokinetics (PK) clearly gives an idea about how u can formulate your drug either to increase or decrease its bioavailability
- Pharmacokinetics along with pharmacodynamics gives a good understanding of overall pharmacology.
- Pharmacokinetics interrelates the effect of pH and solubility on the absorption of the drug and also discuss the effect of metabolism on the bioavailability of the drug
- It enables the student to give a valid reason why this drug is poorly absorbed in the stomach and highly absorbed in the small intestine or vice-versa.
- Pharmacokinetics is further related to other sub-branches like toxicology and biopharmaceutics
Significance of pharmacokinetics:
Pharmacokinetics help the prescribers/pharmacists/physician to know about the pattern in which drug is being absorbed or metabolized and he will be able to
- Predict bioavailability of the drug
- Evaluate the drug-drug interactions
- Adjust the drug dose and dosing intervals
- Decrease the drug toxicity
- Choose optimal drug regimen
Pharmacokinetics assist the researchers during their research work in process of drug discovery and development in the following ways
- Accurate pH where drug liberates from the dosage form
- The site of absorption of the drug
- To estimate the bio-availability of the drug by testing the drug in vivo.
- To produce modified release drug formulations
- To modify the pre-existing drug
What should we know about pharmacokinetics as a pharmacist?
- The intravenous route of administration gives 100% bioavailability of the drug as it avoids the first-pass metabolism as compared to orally administered drugs whereas the intramuscular route is influenced by blood flow.
- Drugs are weakly acidic or weakly basic therefore its bioavailability depends upon their solubility, lipophilicity, pH value, and pKa value ( dissociation constant).
- Patients with nonfunctional kidneys or who have impaired kidney function should be prescribed low doses of drugs that are eliminated by kidneys otherwise there are high chances of drug toxicity.
- Same in cases of patients with impaired function of the liver such as fatty liver disease or liver cirrhosis. If the drug that follows hepatic clearance is administered to liver compromised patients, its dose must be reduced to avoid any serious side effects.
- Mathematical calculation of the rate of reaction, halflife, and elimination half-life with the help of various formulas and equations.
Before you leave:
Here we go through the main concept, process, and principle of pharmacokinetics. Of Course, pharmacodynamics is a vast subject that can’t be completely discussed on a single page. Every class of medicinal drug possesses its own characteristic pharmacokinetic properties or you can say that the body treats every drug differently depending upon the route of administration and other parameters.