Tolterodine Pharmacology

On this episode, I discuss tolterodine pharmacology, adverse effects, and drug interactions.

Tolterodine (Detrol) is an anticholinergic medication used to manage the symptoms of overactive bladder.

Tolterodine’s anticholinergic activity can lead to a significant number of adverse effects like dry mouth, dry eyes, constipation, and urinary retention.

Elderly patients may be at greater risk for anticholinergic adverse effects from tolterodine compared to younger patients.

Tolterodine can have additive effects from other anticholinergics like diphenhydramine or TCAs which enhance its potential for side effects.

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Oxybutynin Pharmacology

On this episode, I discuss oxybutynin pharmacology, drug interactions, and adverse effects.

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Doxylamine Pharmacology

In the podcast this week, I talk about doxylamine pharmacology. Doxylamine is a first-generation antihistamine; it is commonly an active ingredient in night-time medications like Unisom, Nyquil, and Mucinex. The pharmacology of doxylamine is similar to other first-generation antihistamines, it competitively inhibits the binding of histamine at H1 receptors. Its main uses are as sleep aides, in cough-and-cold medications, but doxylamine has also been given with pyridoxine to treat nausea and vomiting during pregnancy.

Doxylamine’s adverse reactions are related to its anticholinergic properties, they include dry eyes, dry mouth, increased fall risk, sedation, urinary retention, constipation, and confusion. Contraindications include concurrent use with a monoamine oxidase inhibitor, known hypersensitivities, concomitant alcohol use, and if the patient has the following conditions: elevated intraocular pressure, narrow-angle glaucoma, asthma, peptic ulcer disease, urinary bladder neck obstruction, or gastric outlet obstruction. It is also a Beer’s list drug due to its anticholinergic effects. The normal dose in adults is 25 mg. In cases of overdosage, the most common manifestation is exacerbations of its anticholinergic effects. The major complications of an overdose include arrhythmia, respiratory failure, seizures, hyperthermia, rhabdomyolysis, and coma. 

When you know a patient is taking doxylamine, it’s important to be cognizant of their occupation, as well as what other conditions they may have. For example, doxylamine should be used with caution in patients that drive heavy machinery due to its sedating properties. You might be able to tell if a patient’s experiencing an adverse reaction exacerbation if they begin having worsening dementia symptoms or increased urinary retention. Other indications include the use of artificial tears, or saliva, or increased complaints of constipation. To monitor for doxylamine, it’s important to monitor the patient’s tolerability. The onset of doxylamine is relatively quick as well, with a peak concentration within 2-4 hours.

For drug-drug interactions, CYP interactions aren’t as concerning as usual. The main interaction to consider when a patient is taking doxylamine is additive anticholinergic effects. Sedative effects can increase when benzodiazepines, skeletal muscle relaxants, opioids, or antihistamines are concurrently taken. Doxylamine can also counteract the usefulness of dementia or BPH medications due to its anticholinergic properties. There is also a risk of increased anticholinergic burden when taken with skeletal muscle relaxants or tricyclic antidepressants. 

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

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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!

Hyoscyamine Pharmacology

Hyoscyamine is an anticholinergic medication that is primarily used for GI problems like spasms and pain associated with IBS.

Because of the highly anticholinergic nature of hyoscyamine, it can cause dry eyes, dry mouth, urinary retention, and constipation.

Be aware of the risk for the prescribing cascade with hyoscyamine. Saliva substitutes for dry mouth, artificial tears for dry eyes, etc.

Sedation is a concern with hyoscyamine and this can be exacerbated by drugs like benzodiazepines, opioids, and older antihistamines.

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!

Dicyclomine Pharmacology

Dicyclomine is an anticholinergic agent that is used to help manage GI pain associated with IBS.

Dicyclomine has a very short half-life which means that it can be dosed multiple times per day.

Be careful with patients who have predominant constipation with their IBS as dicyclomine can exacerbate this.

Bentyl is the brand name of dicyclomine. This drug blocks the action of acetylcholine.

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!

Doxepin Pharmacology

Doxepin is under the class of tricyclic antidepressants. It can inhibit the reuptake of serotonin and norepinephrine.

In addition to the serotonin and norepinephrine reuptake inhibition mechanism, doxepin also has antihistamine type effects.

Because of the anticholinergic activity of doxepin, it is recommended to avoid this medication in the elderly, particularly at high doses.

Be aware that anticholinergics like doxepin can reduce the benefit of dementia medications.

CYP2D6 is an important enzyme in the metabolism of doxepin and drugs like bupropion that inhibit CYP2D6 can increase the concentrations of doxepin.

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!