Question 1

Why No Sedation?

Accepted Answer

The blood‑brain barrier (BBB) is lined with tight junctions and efflux transporters. Fexofenadine is a substrate for P‑glycoprotein (P‑gp), an efflux pump that actively transports it back into the bloodstream. Combined with its polarity, this results in negligible brain H1 receptor occupancy.

Question 2

How does fexofenadine differ from other antihistamines?

Accepted Answer

Fexofenadine is a non‑sedating, peripherally selective H1 antagonist that does not cross the blood‑brain barrier, so it causes minimal to no drowsiness compared to first‑generation antihistamines.

Question 3

How long does fexofenadine take to start working?

Accepted Answer

Fexofenadine begins to relieve symptoms within 1‑2 hours after taking, with peak effect at around 2‑3 hours. Once‑daily dosing provides 24‑hour control.

Question 4

Why doesn't fexofenadine make me sleepy?

Accepted Answer

Its chemical structure makes it a substrate for P‑glycoprotein efflux pumps at the blood‑brain barrier, actively transporting it back into the bloodstream and preventing entry into the brain.

Question 5

Can I take fexofenadine with fruit juice?

Accepted Answer

It's best to take fexofenadine with water. Grapefruit, orange, and apple juices can reduce its absorption by inhibiting OATP transporters, potentially making it less effective.

Question 6

How is fexofenadine eliminated from the body?

Accepted Answer

Fexofenadine is mostly excreted unchanged in faeces (80%) and urine (11%), with minimal liver metabolism. Its half‑life is around 14 hours.