Zyrtec api?

Did you mean Zyrtec (cetirizine) information or something else called “API”?

If you mean Zyrtec (cetirizine), here are the basics:

• What it’s used for: allergies—sneezing, runny nose, itchy/watery eyes, and hives (urticaria)
• Common forms/doses (adults & kids):
  • Tablet: typically 10 mg once daily
  • Children: dosing is age/weight dependent (often 2.5–10 mg once daily depending on age)
• How it feels: generally non-drowsy to mildly sedating for many people, but some do get sleepy.
• Important cautions:
  • Avoid alcohol or other sedating meds if you get drowsy
  • Kidney disease may require dose adjustment
  • Don’t take double doses

If you meant an actual “Zyrtec API” (like a software/API integration term), tell me what context you’re using it in (programming? a website/app? medical “API” documentation?) and I’ll help.