Cetirizine, sold under the brand name Zyrtec among others, is a second generation Cetirizine is available over-the-counter in the US in the form of 5 and 10 mg dose has been found to be 257 ng/mL for 10 mg and 580 ng/mL for 20 mg. This is then hydrolyzed with aqueous HCl and extracted to give an...