Drug Interactions of OTC Antihistamines (1st gen)

Category: Education

Presentation Description

First generation antihistamines (Brompheniramine and Chlorpheniramine) interact with drugs like Antidepressants (SSRIs, SNRIs, TCAs, Trazodone, Vortioxetine, Amoxapine) and Drugs inducing serotonergic system (Lorcaserin, Almotriptan, Hydroxytryptophan, Fentanyl, Tramadol). Chlorpheniramine and diphenhydramine interact with belladonna and metoprolol. Diphenhydramine interact with Drugs with Anticholinergic activity (Clomipramine, Amitriptyline, Triflupromazine, amoxapine and Linezolid), Opioids(Hydromorphone, Oxycodone, Hydrocodone, Fentanyl, Tapentadol) , Other CNS depressants (Zolpidem, Loxapine, Meclizine, Carbinoxamine) and alcohol.


Presentation Transcript

Drug Interactions of OTC Antihistamines (First Generation):

Drug Interactions of OTC Antihistamines ( First Generation ) Dr. P.Naina Mohamed Pharmacologist


Introduction Over-the-counter (OTC) medicines are the medicines which can be obtained without a prescription from doctor . Antihistamines are the drugs helping to relieve or prevent allergy symptoms. Two types of OTC antihistamines are available: First-Generation OTC Antihistamines Brompheniramine Chlorpheniramine Dimenhydrinate Diphenhydramine Doxylamine Second-Generation OTC Antihistamines Loratadine Cetirizine Fexofenadine

Brompheniramine or Chlorpheniramine & Antidepressants:

Brompheniramine or Chlorpheniramine & Antidepressants

Brompheniramine or Chlorpheniramine & Antidepressants:

Brompheniramine or Chlorpheniramine & Antidepressants Brompheniramine inhibit reuptake of the serotonin and has antidepressant properties . chlorphenamine has been shown to work as a serotonin-norepinephrine reuptake inhibitor (SNRI). It inhibits serotonin reuptake less than norepinephrine reuptake. Concomitant use of Antidepressants such as SSRIs ( Fluoxetine ), SNRIs ( Desvenlafaxine , Levomilnacipran ), TCAs ( Amitriptyline), Trazodone , Vortioxetine or Amoxapine and Brompheniramine or Chlorpheniramine should be approached with caution due to additive serotonergic effects and the potential for increased risk of serotonin syndrome. Symptoms of serotonin syndrome include neuromuscular abnormalities (including hyperreflexia , tremor, muscle rigidity, clonus, peripheral hypertonicity , and shivering), autonomic hyperactivity (including tachycardia, mydriasis , diaphoresis, the presence of bowel sounds, and diarrhea), and mental status changes (including agitation and delirium). Serotonin syndrome can be life-threatening. If serotonin syndrome develops, discontinue the offending agents and provide supportive care and other therapy as necessary. Monitoring for signs and symptoms of serotonin syndrome during treatment may be warranted.

Brompheniramine or Chlorpheniramine & Drugs inducing serotonergic system :

Brompheniramine or Chlorpheniramine & Drugs inducing serotonergic system

Brompheniramine or Chlorpheniramine & Drugs inducing serotonergic system :

Brompheniramine or Chlorpheniramine & Drugs inducing serotonergic system Lorcaserin is a selective 5-HT 2C receptor agonist . Almotriptan has a high and specific affinity for serotonin 5-HT 1B/1D receptors . Hydroxytryptophan is a metabolic intermediate in the biosynthesis of the neurotransmitter serotonin from tryptophan. Fentanyl is a proserotonergic drug. Tramadol is a serotonin releaser, reuptake inhibitor of norepinephrine. Concomitant use of Brompheniramine or Chlorpheniramine and Drugs inducing serotonergic system such as Lorcaserin , Almotriptan , Hydroxytryptophan , Fentanyl or Tramadol may increase the risk for serotonin syndrome and should be undertaken with caution. Concomitant use of these agents, is clinically warranted. Careful observation of the patient is recommended, particularly during treatment initiation and dosage increases.

Chlorpheniramine & Phenytoin:

Chlorpheniramine & Phenytoin Monitor patients for evidence of phenytoin toxicity, such as ataxia and nystagmus , with combined chlorpheniramine administration. If the patient exhibits signs of toxicity, a serum phenytoin level should be considered. An alternative antihistamine that has not been reported to cause this interaction, such as diphenhydramine, may be appropriate.

Chlorpheniramine or Diphenhydramine & Metoprolol:

Chlorpheniramine or Diphenhydramine & Metoprolol If concomitant administration is required use with caution. Consider metoprolol dose reduction, and monitor the patient closely.

Chlorpheniramine or Diphenhydramine & Belladonna:

Chlorpheniramine or Diphenhydramine & Belladonna

Chlorpheniramine or Diphenhydramine & Belladonna:

Chlorpheniramine or Diphenhydramine & Belladonna The anticholinergic activity of the active alkaloids present in belladonna may predispose the patient to excessive anticholinergic activity if taken with chlorpheniramine . Belladonna contains L- hyoscyamine , atropine, and scopolamine with a total alkaloid content of at least 0.3% in the leaves and 0.5% in the roots. Excessive anticholinergic activity may be manifested by dry mouth, constipation, urinary retention, tachycardia, decreased sweating, mydriasis , blurred vision, elevated temperature, muscular weakness, and sedation. If such effects are noted, belladonna should be discontinued immediately. In severe cases, paralytic ileus, confusion, psychoses, agitation, delusions, delirium, and paranoia may be encountered as well as tachycardia, dysrhythmia, and hypertension. In severe cases, immediate medical attention should be obtained.

Diphenhydramine & Drugs with Anticholinergic activity:

Diphenhydramine & Drugs with Anticholinergic activity

Diphenhydramine & Drugs with Anticholinergic activity:

Diphenhydramine & Drugs with Anticholinergic activity Patients should be warned that taking antihistamines, including over-the-counter sleeping pills and cold and allergy preparations, may increase the side effects of clomipramine. Patients should be monitored for dry mouth, drowsiness, and problems with urination. Lower dose of diphenhydramine might be considered, particularly in elderly individuals. Concomitant Antidepressants with strong anticholinergic effects ( eg , amitriptyline, trimipramine , amoxapine , doxepin, imipramine, nortriptyline , maprotiline ) or Phenothiazines with strong anticholinergic effects ( eg , chlorpromazine, triflupromazine , thioridazine ) and antihistamines may increase the possibility of adynamic ileus, urinary retention, or chronic glaucoma. This interaction may be more prominent in elderly patients

Diphenhydramine & Opioids:

Diphenhydramine & Opioids When concomitant use is required, dose reduction of one or both medications should be considered.

Diphenhydramine & Other CNS depressants:

Diphenhydramine & Other CNS depressants Concomitant use of Diphenhydramine with other CNS depressants, including alcohol, tranquilizers, or sedatives, may have additive effects and is therefore not recommended. If diphenhydramine and CNS depressants are used concurrently, consider a dose reduction of the CNS depressant and use with caution . Counsel patients on the risk of additive CNS cognitive and motor effects if coadministration is required.

Diphenhydramine and Alcohol:

Diphenhydramine and Alcohol The combination may significantly impair psychomotor performance. Use caution when driving or operating dangerous equipment.

Antihistamines & Procarbazine:

Antihistamines & Procarbazine Coadministration of procarbazine and antihistamines should be used with caution to minimize CNS depression and possible potentiation.

1st Generation OTC Antihistamines & Pregnancy:

1 st Generation OTC Antihistamines & Pregnancy Brompheniramine has been associated with an increased frequency of congenital malformations in humans. Based on available safety data in humans, there is no risk of teratogenicity with the use of chlorpheniramine during pregnancy. The American Congress of Obstetricians and Gynecologists (ACOG) and the American College of Allergy, Asthma and Immunology (ACAAI) recommend C hlorpheniramine as the antihistamine of choice during pregnancy . During pregnancy, D iphenhydramine or D imenhydrinate should be administered only if clearly needed.

1st Generation OTC Antihistamines & Breast Feeding:

1 st Generation OTC Antihistamines & Breast Feeding The potential for adverse effects in the nursing infant from exposure to the drugs such as brompheniramine or chlorpheniramine are unknown. It is possible that H1 antagonists may theoretically reduce milk production and may be excreted in small quantities into the breast milk. According to the World Health Organization, use of chlorpheniramine in nursing mothers should be avoided if possible. Use of Diphenhydramine is contraindicated in nursing mothers . Dimenhydrinate is contraindicated for use in neonates and premature infants .

Tips for patients to avoid OTC Drug interactions:

Tips for patients to avoid OTC Drug interactions Patients should thoroughly read the labels of all over-the-counter and prescription medicines. Patients should make sure that they know the benefits as well as the potential risks of both prescription and over-the-counter medications they are taking. They should look specifically for the section called "Warnings" on the labels of over-the-counter medicines. Patients should talk to their doctor or pharmacist before taking any new prescription or over the counter medication. Patients should maintain a record containing the list of prescription or over the counter medications and share it with their doctors and their pharmacist. Patients should use one pharmacy for all of their family's prescription and over-the-counter medication needs . By filling all prescriptions at one pharmacy, all the important information about (what and when the patients take) could be found in a central location. The pharmacist can help the patients by retrieving all the informations about possible drug interactions from any OTC, prescription or herbal medications. Learning about interactions with commonly used OTC remedies can also assure smart choices. Talk to doctor or pharmacist if you have any medical conditions or take other medications. They can help explain what risks you may have and what precautions to take.


Conclusion Physicians should be aware of potential drug interactions with OTC medicines when prescribing new medications. Pharmacists can be instrumental in assisting patients with using OTC medications safely and effectively. To achieve maximum efficacy of a medication, drug-drug interactions, drug-disease interactions, and the timing of administration with respect to food should be examined thoroughly before co-administration of multiple medications. Physicians and Pharmacists should make patients aware of the potential for toxicity and adverse drug interactions associated with the long-term and inappropriate use of OTC analgesics. They should advise Patients to use OTC analgesics not in higher-than-recommended doses or not in combinations that magnify the risk of adverse interactions. Patients should be notified that OTC analgesics are also found in many common cough, cold, or flu medications. Pharmacists may provide educational materials to patients so that they may learn to recognize the generic names of OTC medications. Pharmacists should warn consumers of the risks of misusing OTC pain relievers.


References Stockley’s Drug Interactions, 9e Karen Baxter http :// www.micromedexsolutions.com http ://otcsafety.org/en/experts/safely-using-otc-medicines-while-taking-rx-drugs/ http:// familydoctor.org/familydoctor/en/drugs-procedures-devices/over-the-counter/antihistamines-understanding-your-otc-options.html http :// www.merckmanuals.com/home/drugs/over-the-counter_drugs/precautions_with_over-the-counter_drugs.html http ://www.pharmacytimes.com/publications/issue/2005/2005-03/2005-03-9391

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