Cetirizine Pharmacology

On this episode of the Real Life Pharmacology Podcast, I discuss cetirizine pharmacology.

Cetirizine, commonly known as Zyrtec, is a 2nd generation antihistamine. Compared to 1st generation antihistamines, like diphenhydramine and chlorpheniramine, 2nd generation antihistamines have fewer anticholinergic effects. Pharmacologically, cetirizine works by selectively blocking histamine from binding to the H1 receptor. The uses for cetirizine are allergic rhinitis, itching, and sometimes acute allergic reactions. Commonly, cetirizine is dosed at 10 mg daily, and can even be escalated to 10 mg twice daily in rare situations. In adults 77 years old and older, the manufacturer recommended dose tops out at 5 mg daily. There are also liquid and chewable formulations for children. 

The adverse drug reactions cetirizine are mostly dose-dependent and related to its pharmacology. Out of all of the 2nd generation antihistamines, like fexofenadine and loratadine, cetirizine is the most sedating. Other adverse drug reactions related to its anticholinergic effects are urinary retention, constipation, confusion, fatigue, and dizziness. Lab monitoring is not necessary when taking cetirizine. It is important to monitor the adverse drug reactions when taking cetirizine, as well as improvement in the signs and symptoms of what it’s used for. 

Cetirizine does not undergo metabolism through liver CYP enzymes, so drug-drug interactions involving those enzymes are uncommon. The interactions that are concerning are additive effects of cetirizine’s adverse drug reactions. Drowsiness can be compounded when cetirizine is taken with opioids, sleep medications, alcohol, or other older anticholinergics with sedative effects. There is also a risk of an increased anticholinergic burden when taking medications like Cogentin, oxybutynin, TCAs, and inhaled anticholinergics. 

The manifestation of overdoses will vary depending on age. In adults, the most common observation made was sedation and somnolence. In children, restlessness and irritability were observed initially, then drowsiness. Cetirizine is not removed by dialysis. When treating overdoses, the symptoms that manifest should be treated.  

Show notes provided by Chong Yol G Kim, PharmD Student.

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Fexofenadine Pharmacology

Fexofenadine is a 2nd generation antihistamine that is primarily used for allergic rhinitis. I cover fexofenadine pharmacology on this podcast episode.

Fruit juices can actually impair the absorption of fexofenadine and increase the risk of treatment failure.

Fexofenadine is mildly anticholinergic but overall has low to no CNS penetration.

Because fexofenadine has low CNS penetration, the risk for sedation and dizziness is much lower than older antihistamines like diphenhydramine.

I discuss important drug interactions on the podcast, be sure to check out my latest project which is a 200+ page book on managing drug interactions in primary care.

Be sure to check out our free Top 200 study guide – a 31 page PDF that is yours for FREE!

Diphenhydramine (Benadryl) Pharmacology

Diphenhydramine is a first generation antihistamine that is highly anticholinergic.

When using medications like diphenhydramine, be sure to watch for side effects like dry eyes, dry mouth, constipation, urinary retention, and CNS changes.

Sedation is a primary effect of diphenhydramine. It can be advantageous in certain situations, and detrimental in others.

Drugs like donepezil, memantine, laxatives, tamsulosin, and artificial tears can be indicators of anticholinergic side effects from diphenhydramine.

I discuss important drug interactions on the podcast, be sure to check out my latest project which is a 200+ page book on managing drug interactions in primary care.

Be sure to check out our free Top 200 study guide – a 31 page PDF that is yours for FREE!

Mometasone Pharmacology (Nasal and Oral Inhalation)

Mometasone is an inhaled corticosteroid and a nasal corticosteroid. The inhaled steroid is called Asmanex by brand name and the nasal version is Nasonex.

Nasonex is primarily used in the management of allergic rhinitis and can help with nasal congestion type symptoms.

Remember that nasal mometasone takes a little while to have its full effect. It can take up to a week or two to provide its maximum benefit.

Systemic absorption of both nasal and oral inhalation mometasone is very low at less than 1%.

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Montelukast Pharmacology

Montelukast Pharmacology

On this episode, I discuss montelukast pharmacology

Montelukast is a leukotriene receptor antagonist. Leukotrienes play an important role in causing inflammation and smooth muscle contraction in asthma and allergic rhinitis.

Because montelukast blocks the effects of leukotrienes, it can be advantageous to use this medication for allergies and asthma.

It is important to remind patients that montelukast is NOT a substitute for an acute relief medication like albuterol in the management of asthma symptoms.

Montelukast has been reported to cause mood and behavioral changes and it is important to monitor our patients for these rare concerns.

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Pseudoephedrine Pharmacology

Pseudoephedrine is commonly used to help relieve nasal congestion.

There are some adverse effects you need to be aware of with pseudoephedrine. Insomnia, increase in blood pressure, and urinary retention are all possible.

When I assess a patient using pseudoephedrine, I like to investigate blood pressure, history of urinary problems and insomnia history.

Pseudoephedrine can cause the prescribing cascade.  I lay out examples in the podcast.

Pseudoephedrine should not be utilized with MAOI’s if possible – I discuss the reason for this in the podcast.

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