What is the Difference Between Chlorpheniramine and Diphenhydramine

The key difference between chlorpheniramine and diphenhydramine is that chlorpheniramine is typically administered orally as tablets, and the dosage is low, whereas diphenhydramine is administered either orally or as an injection, and the dosage is comparatively high.

Both chlorpheniramine and diphenhydramine are important as antihistamine drugs that can treat symptoms of allergy, hay fever, and the common cold.

CONTENTS

1. Overview and Key Difference
2. What is Chlorpheniramine 
3. What is Diphenhydramine
4. Chlorpheniramine vs Diphenhydramine in Tabular Form
5. Summary – Chlorpheniramine vs Diphenhydramine

What is Chlorpheniramine?

Chlorpheniramine is a type of antihistamine that is useful in relieving allergy symptoms, hay fever, and the common cold. The symptoms that it can relieve include rash, watery eyes, itchy eye/nose/throat/skin, cough, runny nose, and sneezing.

Chlorpheniramine works by blocking a certain natural substance the body makes during an allergic reaction. It can also help in drying up some boy fluids to relieve symptoms, including watery eyes and runny nose, by blocking another natural substance made by the body: acetylcholine.

However, this product is not considered safe for treating colds or coughs in younger children (below 6 years). Also, the tablet or capsule forms of this drug are not suitable for children younger than 12 years. These products cannot shorten or cure the common cold. Therefore, it can cause many serious side effects as well. Some common side effects of this medication include drowsiness, dizziness, constipation, stomach upset, blurred vision, and dry mouth/nose/throat.

The chemical formula of this substance is C₁₆H₁₉ClN₂, while the molar mass of chlorpheniramine is 274.79 g/mol. It has poor solubility in water, which is about 0.55 g/100 mL. The bioavailability of chlorpheniramine is in the range of 25 to 50%, and its protein binding ability is 72%. Further, the metabolism of this compound occurs in the liver, and the elimination half-life is about 13 – 43 hours. The excretion occurs through the kidney.

What is Diphenhydramine?

Diphenhydramine is a type of drowsy antihistamine that is useful in relieving symptoms of allergy, hay fever, and the common cold. This is called drowsy histamine because it can make us feel sleepy compared to other antihistamines. This drug is useful for short-term sleep problems, including insomnia.

There can be some side effects of using this drug, including dry mouth, drowsiness, nausea, loss of appetite, vomiting, constipation, etc. The routes of administration of diphenhydramine are oral administration, injection into a vein, injection into a muscle, and application on the skin. Typically, we can get the maximum effect 2 hours after the dose. These effects may last up to seven hours.

The chemical formula of diphenhydramine is C₁₇H₂₁NO. The molar mass is 255.36 g/mol. The bioavailability of this medication is around 40-60%, and the protein binding ability is around 99%. The metabolism of diphenhydramine occurs in the liver, and the excretion can occur through urine or feces. The elimination half-life of this drug is around 2.4 – 13.5 hours.

Moreover, diphenhydramine is a diphenylmethane derivative. It is analogous to orphenadrine (which is an anticholinergic drug), nefopam (an analgesic), and tofenacin (an antidepressant). We can chemically quantify this medication in blood, plasma, and serum. The methods we can use for this detection include gas chromatography, mass spectrometry, etc. This quantification is important in monitoring therapy, confirming a diagnosis of poisoning in people, for impaired driving arrest, death investigations, etc.

What is the Difference Between Chlorpheniramine and Diphenhydramine?

Both chlorpheniramine and diphenhydramine are important as antihistamine drugs that can treat allergy symptoms, hay fever, and the common cold. The key difference between chlorpheniramine and diphenhydramine is that chlorpheniramine is typically administered orally as tablets, and the dosage is low, whereas diphenhydramine is administered either orally or as an injection, and the dosage is comparatively high.

The below infographic presents the differences between chlorpheniramine and diphenhydramine in tabular form for side-by-side comparison.

Summary – Chlorpheniramine vs Diphenhydramine

Chlorpheniramine and diphenhydramine are important antihistamine drugs. The key difference between chlorpheniramine and diphenhydramine is that chlorpheniramine is typically administered orally as tablets, and the dosage is low, whereas diphenhydramine is administered either orally or as an injection, and the dosage is comparatively high.

Reference:

1. “Diphenhydramine: Medlineplus Drug Information.” MedlinePlus, U.S. National Library of Medicine.

Image Courtesy:

1. “Chlorphenamine” By Harbin – Own work (Public Domain) via Commons Wikimedia
2. “Diphenhydramine 2D skeletal” By Fvasconcellos (talk · contribs) – Own work (Public Domain) via Commons Wikimedia