Pharmacology of Doxylamine ; Mechanism of action, Pharmacokinetics, Uses, Effects

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Side Effects

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Doxylamine is a first-generation antihistamine with pronounced sedative properties. It is commonly used to treat insomnia and allergy symptoms, and in combination with pyridoxine (vitamin B6), it is used to treat morning sickness in pregnant women.

Mechanism of Action
Doxylamine works by blocking histamine H1 receptors, which are involved in the body's allergic response. By inhibiting these receptors, it helps reduce symptoms like sneezing, itching, and runny nose1. Additionally, its sedative effects are due to its ability to cross the blood-brain barrier and act on the central nervous system.

Indications
Insomnia: Often used as a short-term sleep aid.

Allergies: Helps alleviate symptoms such as sneezing, itching, and runny nose.

Morning Sickness: Combined with pyridoxine to treat nausea and vomiting during pregnancy.

Administration
Oral: Available in tablets, orally disintegrating tablets (ODT), and syrup.

Over-the-Counter (OTC): Commonly found in nighttime cold and allergy medications (e.g., NyQuil).

Dosage
Insomnia: Typically 25 mg taken 30 minutes before bedtime.

Allergies: Dosage varies based on the severity of symptoms and patient response.

Side Effects
Common: Drowsiness, dizziness, dry mouth, and constipation.

Serious: Potential for QT prolongation and extrapyramidal symptoms (e.g., acute dystonia, akathisia)2.

Precautions
QT Prolongation: Use with caution in patients with a history of QT prolongation or those taking other medications that prolong the QT interval.

Elderly: Increased risk of confusion, dry mouth, constipation, and other anticholinergic effects

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