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.

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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!