Last reviewed by Editorial Team on September 5th, 2018.
Mixing Diphenhydramine and Fexofenadine
Benadryl is a Brand name for antihistamine drug that contains diphenhydramine as an active ingredient. This drug reduces the effects of natural histamine during allergic reaction in the body.
It is used for relieving the symptoms of allergy, hay fever and the common cold such as: itching, ash, runny nose, sneezing, watery eyes, itchy eyes, nose or throat, and cough.
It can be also used for the prevention and treatment of nausea, vomiting and dizziness that can be caused by motion sickness. Diphenhydramine also has hypnotic effects and it can help to relax and fall asleep.
This drug can also be used alone or in combination with other medications for the treatment of tremor and muscle stiffness caused by Parkinson’s disease. Certain side effects of psychiatric drugs such as involuntary movements and muscle stiffness can also be treated with this medication.
There are many products on the market containing diphenhydramine such as: Benadryl Allergy Dye-Free LiquiGels, Children’s Triaminic Thin Strips Allergy, Children’s Benadryl Allergy, Alka-Seltzer Plus Allergy, PediaCare Children’s Allergy, Nytol, Simply Sleep, Sominex, QlearQuil Nighttime Allergy Relief, Unisom SleepGels, Unisom SleepMelts, Tranquil Nighttime Sleep Aid, ZzzQuil
Allegra is a Brand name for antihistamine drug that contains fexofenadine as an active ingredient. This drug reduces the effects of natural histamine in the body, that can produce allergy symptoms such as: itching, watery eyes, sneezing, and runny nose.
It is used for the treatment of seasonal allergies (hay fever) in children and adults. Allegra can be also used for the treatment of hives and skin itching caused by chronic idiopathic urticaria.
Other products on the market containing fexofenadine are: Allegra Allergy 24 Hour, Allegra Allergy 12 Hour, Children’s Allegra Allergy, Mucinex Allergy
How does Benadryl and Allegra work in the body
Diphenhydramine is first-generation antihistamine with anticholinergic, antiemetic, sedative and antitussive properties. It is histamine – H1 receptor antagonist. Diphenhydramine can reduce the intensity of allergic symptoms, by reducing the effects of histamine on the capillaries.
This drug crosses the blood–brain barrier in the CNS, where also antagonizes H1 receptors, causing sedation, relaxation and drowsiness. Diphenhydramine is also a potent competitive antagonist of muscarinic acetylcholine receptors.
In high doses it can cause anticholinergic syndrome. This anticholinergic property is used for the treatment of Parkinson’s disease. Diphenhydramine can also act as a sodium channel blocker in cells, so it can be also used as a local anesthetic.
It has been shown that diphenhydramine can inhibit the reuptake of serotonin. Studies on rats showed that this drug is a good potentiator of analgesia induced by morphine, however this is not the case for endogenous opioids.
Fexofenadine is a second-generation antihistamine. This category of antihistamines is less able to pass through the blood-brain barrier in CNS and cause sedation, comparing to first-generation antihistamines.
It is a peripheral high selective antagonist of H1 receptors that blocks H1 receptor activation by histamine, preventing the allergy symptoms to occur. Fexofenadine has no anticholinergic, antidopaminergic, alpha1-adrenergic, or beta-adrenergic-receptor blocking effects; this is why this drug is much safer than older antihistamines.
Can patients take Benadryl and Allegra together
Patients can take Benadryl and Allegra together in recommendable doses if there are no contraindications. They are both antihistamines, their effects will become additive and they will reduce allergic symptoms.
Benadryl can cross into the brain, while Allerga can cross only in small amounts, so if these drugs are taken in recommendable doses there is no significant risk of causing sedation and other CNS side effects.
However, there are no special advantages of this combination and there are more effective treatment strategies compared with this one. If patients have uncontrolled allergies, they should see allergist or dermatologist.
Cough and cold products containing these antihistamines have not been shown to be effective or safe in children younger than 6 years.
Therefore these products and their combinations should not be used to treat cough and cold symptoms in children who are younger than 6 years unless it is specifically directed by the doctor. There are also some products such as long-acting tablets or capsules which are not recommended for use in children younger than 12 years.
The table below shows the incidence of side effects after Benadryl and Allegra administration in recommendable doses. The incidence can be increased if these drugs are overdosed or taken together.
|10-15% (very common)||Vomiting|
|1-10% (common)||Headache, Diarrhea, Back pain, Cough, Dysmenorrhea, Dizziness, Pain in extremity, Somnolence, Rhinorrhea, Pyrexia, Stomach discomfort|
|Postmarketing Reports||Nervousness, Sleep disorders (insomnia, paranoia) and Hypersensitivity reactions (urticaria, anaphylaxis, angioedema, dyspnea, chest tightness, flushing, pruritus, rash)|
|Frequency Not Defined||Xerostomia, Confusion, Dry nasal mucosa, Pharyngeal dryness, Agranulocytosis, Thrombocytopenia, Hemolytic anemia, Convulsions, Hypotension, Palpitations, Urinary retention, Neuritis, Diplopia, Tinnitus|
Special precautions and warnings during Benadryl and Allegra administration:
- These products shouldn’t be used to make a child sleepy.
- Before taking diphenhydramine or fexofenadine patients should tell their doctor or pharmacist if they are allergic to it or if they have any other allergies. These products may have some inactive ingredients, which can also cause allergic reactions or other side effects.
- Before taking these medications patients should tell their doctors or pharmacists if they have some health issues in the past such as: breathing problems (asthma or emphysema), high blood pressure, glaucoma, heart problems, liver disease, stomach or intestine problems, seizures, hyperthyroidism, or enlarged prostate.
- These drugs can make patients dizzy or drowsy. They should not drive, use machinery, or do any activity that requires alertness.
- Alcohol may potentiate effects of antihistamines. Patients should limit alcoholic beverages while using these drugs.
- In elderly patients there is a high-risk after administration of these medications because they may increase: the risk of falls and incidence of anticholinergic effects (exacerbation of existing lower urinary tract conditions, benign prostatic hyperplasia, insomnia, tolerance)
- Pregnant patients shouldn’t use these medications without medical advice. These medicines should not be used if mother is breast-feeding a baby.
- Coadministration of Allegra and fruit juice may decrease efficacy of Allegra.
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