All of these drugs are second-generation antihistamines, used to treat:
- Seasonal allergies (hay fever)
- Urticaria (hives)
- Itchy or runny nose
- Itchy eyes
Second-generation antihistamines are less sedating than first-generation ones like diphenhydramine (Benadryl).
| Drug | Sedation | Onset (hrs) | Duration (hrs) | Metabolism | OTC? | Notes |
|---|---|---|---|---|---|---|
| Loratadine | Low | ~1–3 | ~24 | Liver → Desloratadine | Yes | May be less effective in some users |
| Desloratadine | Very Low | ~1–3 | ~24–27 | Active metabolite of above | Yes | More potent than loratadine |
| Cetirizine | Moderate | ~0.5–1 | ~24 | Minimal liver metabolism | Yes | Slightly sedating in 10–15% of users |
| Levocetirizine | Low | ~0.5–1 | ~24 | Isomer of cetirizine | Yes | Less sedating than cetirizine |
| Fexofenadine | Minimal | ~1–2 | ~12–24 | Not significantly metabolized | Yes | Least sedating; very clean side effect profile |
Loratadine (Claritin):
Oldest second-gen antihistamine. Needs liver activation → slower onset. Weakest among these for many. Desloratadine is its active metabolite.
Desloratadine (Clarinex):
More potent, longer-acting. Minimal sedation. Often works when loratadine doesn't.
Cetirizine (Zyrtec):
Fast onset, very effective. Can cause mild drowsiness. Good for hives/skin symptoms.
Levocetirizine (Xyzal):
The purified isomer of cetirizine. Same effectiveness, less sedation.
Fexofenadine (Allegra):
Least sedating. Doesn't cross the blood-brain barrier. Fewer drug interactions.
Sedation ranking (most to least):
Cetirizine > Loratadine > Desloratadine ≈ Levocetirizine > Fexofenadine
- Fast, strong relief: Cetirizine or Levocetirizine
- Minimal drowsiness: Fexofenadine or Desloratadine
- Long-acting: All (~24 hrs)
- Sensitive to liver metabolism: Fexofenadine or Cetirizine
- Best for hives / skin symptoms: Cetirizine / Levocetirizine
- Cheap & OTC: Loratadine or Cetirizine (store brands ~$0.03/pill)
- Rupatadine: Newer, not widely available in US
- Bilastine: Very low sedation, available in EU/Asia
- Ebastine: Used in some countries; similar to loratadine
- Hydroxyzine: First-generation; sedating; used for anxiety, itching