Canterbury DHB

Context

Polypharmacy Toxicities

Drugs with similar effects cause toxicity when used in combination, i.e. pharmacodynamic interactions. This is more likely to occur in patients with increased susceptibility to drug effects, such as the frail elderly.

The presence of multiple medicines also increases the risk of pharmacokinetic interactions whereby one medicine increases the concentrations of another medicine, leading to toxicity.

General advice

In This Section

Serotonin Toxicity

Anticholinergic Toxicity

QT Interval Prolongation

Nephrotoxicity

Serotonin Toxicity

The following list is not exhaustive, but shows some common examples:

Common serotonergic drugs

Class

Drugs

SSRIs

citalopram, escitalopram, fluoxetine, paroxetine, sertraline

Serotonin and Noradrenaline Reuptake Inhibitor (SNRIs)

venlafaxine

Monoamine Oxidase Inhibitors (MAOIs)

moclobemide, tranylcypromine

Tricyclic antidepressants (TCAs)

amitriptyline, clomipramine, nortriptyline

Noradrenergic and Specific Serotonergic Antidepressant (NaSSa)

mirtazapine

Analgesics

pethidine, tramadol

Triptans

sumatriptan

Other

buspirone, carbamazepine, lithium, valproate sodium

Complementary and Alternative Products

St John’s wort

Anticholinergic Toxicity

The following list is not exhaustive, but shows common examples:

Drugs with strong, moderate, or weak anticholinergic potency

 

Strong

Moderate

Weak

Antidepressants:

amitriptyline, clomipramine, paroxetine

nortriptyline and all other ‘non-strong’ TCAs

mirtazapine, venlafaxine

Antihistamines:

promethazine

 

cetirizine, loratadine

Antipsychotics:

chlorpromazine, clozapine

olanzapine, quetiapine

aripiprazole, haloperidol, lithium, risperidone

Anticholinergics:

benzatropine, oxybutynin, solifenacin

hyoscine, procyclidine

 

Antiparkinsonian:

 

amantadine

carbidopa-levodopa, entacapone, pramipexole, ropinirole, selegiline

Antiemetic:

prochlorperazine

 

metoclopramide

Others:

 

baclofen, carbamazepine, loperamide (usually local effect on the gut only)

codeine, digoxin, tramadol, warfarin

Inhaled (e.g. tiotropium, ipratropium, glycopyrronium, and umeclidinium) or topical anticholinergic drugs have low systemic exposure, but may have systemic effects at high doses or in susceptible patients.

QT Interval Prolongation

The following table is not exhaustive, but shows common examples:

QTc prolonging drugs

Class

Drugs

antiarrhythmics

amiodarone, flecainide, sotalol

CNS drugs

antipsychotics, SSRIs, TCAs, lithium

Other classes

macrolide antibiotics, e.g. clarithromycin; 5HT3-receptor antagonists, e.g. ondansetron

Other

chloroquine, domperidone, methadone

Classes or drugs causing hypokalaemia or hypomagnesaemia

furosemide, thiazide diuretics, proton pump inhibitors

Predisposing factors

Monitoring

ECG measurement of the QTc interval prior to and early on in treatment (when at, or approaching, steady-state) is recommended for all patients:

Nephrotoxicity

Information about this Canterbury DHB document (93252):

Document Owner:

Not assigned (see Who's Who)

Last Updated:

November 2023 (Polypharmacy Toxicities)

Next Review Due:

November 2027

Keywords:

Note: Only the electronic version is controlled. Once printed, this is no longer a controlled document.

Topic Code: 93252