Clinically Important Drug Interactions of OTC Medicines:

Ø The FDA warns consumers that all Over the Counter (OTC) medicines should be taken carefully to avoid serious problems. 

Ø Many are not aware that OTC medicines can cause potentially serious adverse effects when used in combination with other common medications such as anticoagulants, corticosteroids, or antihypertensive agents.

Ø The common OTC medicines include…

¨   OTC Analgesics (Acetaminophen (Paracetamol), Aspirin, Ibuprofen, Naproxen, etc)

¨   OTC Antihistamines (Chlorpheniramine, Diphenhydramine, Fexofenadine, etc)

¨   OTC Decongestants (Pseudoephedrine, Oxymetazoline,  Xylometazoline)

Ø The risk of hepatotoxicity is elevated by the coadministration of Acetaminophen and CYP inducers (Carbamazepine, Oxcarbazepine, Phenytoin, Fosphenytoin, Deferasirox, Piperaquine, Barbiturates, Isoniazid, Rifampin, and Rifabutin), Smoking or Alcohol.

Ø Concomitant use of Acetaminophen and warfarin may increase the risk of bleeding.

Ø It is contraindicated to use live influenza virus vaccine and Aspirin in children 2 to 17 years of age due to the potential for Reye's syndrome.

Ø The risk of bleeding is increased by Aspirin, Ibuprofen, Ketoprofen or Naproxen in patients taking Warfarin, Heparin, Low Molecular Weight Heparins (LMWHs) (Enoxaparin, Dalteparin, Tinzaparin, etc.), Coumarins and other anticoagulants (Acenocoumarol, Dicumarol, Phenprocoumon, Anisindione, Phenindione), Antiplatelets (Clopidogrel, Prasugrel, Ticagrelor, Ticlopidine, Dipyridamole, Abciximab, Eptifibatide, Tirofiban), Tissue Plasminogen Activators (Alteplase, Reteplase), Direct thrombin inhibitors (Dabigatran, Desirudin, Lepirudin, Bivalirudin, Argatroban), Direct factor Xa inhibitors (Apixaban, Rivaroxaban),Anagrelide, Cilostazol, Selective serotonin reuptake inhibitors (SSRIs) (Escitalopram, Fluvoxamine, Paroxetine, Vortioxetine, Sertraline, Nefazodone, vilazodone) and Selective serotonin and norepinephrine reuptake inhibitors (SNRIs) (Venlafaxine, Desvenlafaxine, Duloxetine, Milnacipran, Levomilnacipran, Sibutramine).

Ø Concomitant use of Ibuprofen, Ketoprofen or Naproxen and ACE Inhibitors (Captopril, Enalapril, Imidapril, Temocapril, Delapril, Ramipril, Perindopril, Cilazapril), Angiotensin II receptor blockers (ARBs) (Losartan, Valsartan, Telmisartan), Beta adrenergic blockers, Calcium Channel Blockers, Thiazide Diuretics, Loop Diuretics or Potassium sparing Diuretics could reduce the antihypertensive efficacy.

Ø The risk of serotonin syndrome (hypertension, hyperthermia, myoclonus, mental status changes) is elevated by the concomitant administration of Brompheniramine or Chlorpheniramine with Antidepressants (SSRIs, SNRIs, TCAs, Trazodone, Vortioxetine, Amoxapine) or serotonergic drugs (Lorcaserin, Almotriptan, Hydroxytryptophan, Fentanyl and Tramadol).

Ø Excessive anticholinergic activity (severe dry mouth, constipation, decreased urination, excessive sedation, blurred vision) may resulted due to combination of Chlorpheniramine or Diphenhydramine and drugs having anticholinergic activity (Belldonna, Clomipramine, Amitriptyline, Triflupromazine, amoxapine and Linezolid).

Ø Coadministration of Diphenhydramine and Opioids (Hydromorphone, Oxycodone, Hydrocodone, Fentanyl, Tapentadol), Other CNS depressants (Zolpidem, Loxapine, Meclizine, Carbinoxamine) or Ethanol increase the risk of CNS depression.

Ø Amiodarone may elevate the risk of “Torsades de pointes” by blocking CYP3A4 induced metabolism of Loratadine or Fexofenadine.

Ø Fruit Juices like Grapefruit juice, Orange juiceand Apple juice decrease the effectiveness of Fexofenadine by inhibiting organic anion transporting polypeptide (OATP).

Ø Concomitant use of Pseudoephedrine and MAO Inhibitors such as Selegiline, Rasagiline, Clorgyline, Pargyline, Toloxatone, Iproniazid, Moclobemide, Nialamide, Procarbazine, Phenelzine , Isocarboxazid, Tranylcypromine, Furazolidone is contraindicated, due to elevated risk of hypertensive crisis characterized by hypertension, hyperpyrexia and headache.

Ø Co-administration of Pseudoephedrine and Dihydroergotamine is contraindicated, due to extreme elevation of blood pressure.

Ø It is contraindicated to use Pseudoephedrine and Linezolid concomitantly, due to increased blood pressure.

Ø Bitter orange contains synephrine which can interact with Pseudoephedrine and increase the risk of hypertensive crisis.

Ø People with heart disease, high blood pressure, diabetes, hyperthyroidism and enlarged prostate should consult a doctor or pharmacist before they take decongestants because side effects can be dangerous.

Ø Patients should thoroughly read the labels of all over-the-counter and prescription medicines.

Ø Patients should talk to their doctor or pharmacist before taking any new prescription or over the counter medication.

Ø Physicians should be aware of potential drug interactions with OTC medicines when prescribing new medications.

Ø Pharmacists can be instrumental in assisting patients with using OTC medications safely and effectively.

Ø Pharmacists should warn consumers of the risks of misusing OTC pain relievers.