**6. Drug interactions involving anticholinergic agents**

Besides the anticholinergic drug–drug interactions that lead to an increased anticholinergic burden, anticholinergic agents are involved in other potential drug– drug interactions.

The use of an anticholinergic agent with an acetylcholinesterase inhibitor (i.e., donepezil, galantamine and rivastigmine) results in opposing pharmacodynamic effects and can negate any small, positive benefits seen with the Alzheimer's disease agents [30]. Conversely, acetylcholinesterase inhibitors have the potential to interfere with the therapeutic effects of anticholinergic agents. Concomitant use is not recommended [31–33].

The concomitant administration of an anticholinergic agent and an oral solid dosage form of potassium supplement can increase the risk of GI bleeding. A liquid formulation of potassium supplement should be utilized instead if concurrent therapy is required [34–36].

Anticholinergic agents also interact with carbonic anhydrase inhibitors such as topiramate and zonisamide potentiating the risk of oligohidrosis and hyperthermia. Patients should be monitored for decreased sweating and increases in body temperature. These combinations should be avoided [37, 38].

Concurrent use of opioids and anticholinergics can lead to severe constipation (resulting in paralytic ileus), sedation, dizziness, confusion, cognitive and psychomotor impairment, dry mouth and urinary retention. Caution is advised [39].

'Moderate' (i.e., drug–drug interactions for which combination therapy should be avoided or used only under special circumstances) anticholinergic drug–drug interactions include abobotulinumtoxin A, acebutolol, acetylcholine

#### *Assessing Anticholinergic Effects in Older Adults DOI: http://dx.doi.org/10.5772/intechopen.94555*

ophthalmic, aclidinium, acrivastine, alfentanil, aluminum hydroxide, amantadine, ambenonium, amitriptyline, amoxapine, arbutamine, aripiprazole, asenapine, atenolol, azatadine, belladonna, benztropine, betaxolol, bethanechol, biperiden, bisoprolol, brexanolone, brexpiprazole, brompheniramine, buprenorphine, butorphanol, calcium carbonate, carbachol ophthalmic, carbinoxamine, cariprazine, carteolol, carvedilol, cevimeline, chlorcyclizine, chlorpheniramine, chlorpromazine, cisapride, clemastine, clidinium, clomipramine, clozapine, cyclizine, cyclobenzaprine, cyproheptadine, darifenacin, demecarium bromide ophthalmic, desipramine, dexbrompheniramine, dexchlorpheniramine, dezocine, dicyclomine, dimenhydrinate, diphenhydramine, disopyramide, doxepin, doxylamine, echothiophate iodide ophthalmic, edrophonium, eluxadoline, ethanol, fesoterodine, flavoxate, flibanserin, fluphenazine, glycopyrrolate, glycopyrronium topical, guanidine, haloperidol, hydroxyzine, hyoscyamine, iloperidone, imipramine, incobotulinumtoxin A, ipratropium, isoflurophate ophathalmic, kaolin, ketoconazole, labetalol, lasmiditan, levodopa, loperamide, loxapine, lumateperone, lurasidone, macimorelin, magaldrate, magnesium carbonate, magnesium hydroxide, maprotiline, meclizine, memantine, mepenzolate, mesoridazine, methdilazine, methotrimeprazine, methscopolamine, metoclopramide, metoprolol, molindone, nadolol, nalbuphine, nebivolol, neostigmine, nortriptyline, olanzapine, olopatadine nasal, onabotulinumtoxin A, orphenadrine, oxybutynin, paliperidone, penbutolol, perphenazine, phenindamine, phenylephrine, physostigmine, pilocarpine, pimozide, pindolol, prabotulinumtoxin A, pramlintide, prochlorperazine, procyclidine, promazine, promethazine, propantheline, propiomazine, propranolol, protriptyline, prucalopride, pyridostigmine, pyrilamine, quetiapine, quinapril, remifentanil, revefenacin, rimabotulinumtoxin B, risperidone, scopolamine, sodium bicarbonate, solifenacin, sotalol, sufentanil, thiethylperazine, thioridazine, thiothixene, timolol, tiotropium, tizanidine, tolterodine, trifluoperazine, triflupromazine, trihexyphenidyl, trimeprazine, trimipramine, tripelennamine, triprolidine, trospium, umeclidinium and ziprasidone [40].
