Histamine-1 receptors are also found in the brain and spinal cord.Antihistamines are very good at relieving symptoms of an allergic reaction, such as: First-generation antihistamines were developed more than seventy years ago and are still in widespread use today.If you need to take both of them, you should take the lowest effective doses.Try to get off of hydrocodone once the indication for it has resolved. If not wanting to take Allegra twice a day, and wanting to add a different antihistamine such as Zyrtec or Xyzal (levocetirizine), (levocetirizine) it is probably enough to take Zyrtec or Xyzal (levocetirizine) (one of them instead of both of them).Zyrtec and Xyzal (levocetirizine) are very similar.
The two medications do not have noticeable interactions with one another. Read more These two medications are for the same type of symptoms. There would be no benefit from taking both, there may be harm from taking both. Read more They both can cause drowsiness, dizziness, motor impairment and respiratory depression.
They act on histamine-1 receptors in the periphery and are unlikely to penetrate the brain, so are less likely to cause side effects or interact with drugs.
Most second-generation antihistamines do not cause drowsiness, although some (such as cetirizine and fexofenadine), may be more likely to do so at higher dosages.
They act on histamine receptors in the brain and spinal cord and in the rest of the body (called the periphery).
They also act on muscarinic, alpha-adrenergic, and serotonin receptors.