Antipsychotics learning module

3.12 Important drug interactions

Concomitant administration of an antipsychotic with a drug which is sedative (eg alcohol) or which reduces blood pressure (eg ACE inhibitor) can increase the potential for these effects.

Many antipsychotic drugs have the potential to affect heart rhythm; the risk of arrhythmia is increased when such an antipsychotic drug is combined with other drugs that affect rhythm or drugs that increase the concentration of the antipsychotic (eg azole antifungal drugs). Drugs which reduce serum potassium can increase the risk of adverse effects arising from QT-interval prolongation. The table below lists common drugs that can interact to prolong the QT interval; a comprehensive list of drugs that prolong the QT interval should be consulted where necessary.

Rarely, antipsychotics can reduce white cell and red cell count; concomitant use with other drugs that interfere with bone-marrow function (myelosuppressants) might increase the risk of reducing blood cells and, possibly, platelets.


Consult summaries of product characteristics and other sources of information on the interactions of individual antipsychotics


Interacting drug or drug class Effect of interaction Risk-reduction measures
ACE inhibitors and angiotensin-II receptor antagonists Increased hypotensive effect Monitor blood pressure and ask about postural hypotension
Alcohol Increased sedation Warn patient of excessive sedation and of psychomotor impairment
Amantadine Increased risk of extrapyramidal effects  
Amphotericin Hypokalaemia increases risk of adverse effects of QT-interval prolongation Ensure any hypokalaemia is corrected
Anaesthetics, general Increased hypotensive effect Monitor blood pressure and ask about postural hypotension
Anti-arrhythmics with QT-interval prolonging properties (eg amiodarone, disopyramide, flacainide, and sotalol) Increased risk of QT-interval prolongation Preferably avoid concomitant use of drugs that prolong QT interval
Antidepressants, tricyclic Increased risk of arrhythmias Antimuscarinic effects, especially of phenothiazine antipsychotics, increased  
Antidepressants, tricyclic and SSRIs Increased risk of seizures  

Citalopram and escitalopram

Increased risk of QT-interval prolongation Preferably avoid concomitant use of drugs that prolong QT interval
Antiepileptics Epilepsy control may be impaired  
Antihistamines, sedative Increased sedation Select non-sedative antihistamine; warn patient of excessive sedation and of psychomotor impairment
Anxiolytic and hypnotic drugs (eg benzodiazepines) Increased sedation Warn patient of excessive sedation and of psychomotor impairment
Atomoxetine Increased risk of QT-interval prolongation Preferably avoid concomitant use of drugs that prolong QT interval
Beta-blockers Increased hypotensive effect Monitor blood pressure and ask about postural hypotension
Calcium-channel blockers Increased hypotensive effect Monitor blood pressure and ask about postural hypotension
Clonidine Increased hypotensive effect Monitor blood pressure and ask about postural hypotension
Corticosteroids

Hypokalaemia increases risk of adverse effects of QT-interval prolongation

Increased risk of metabolic effects such as weight gain and diabetes
Ensure any hypokalaemia is corrected
Diuretics (loop and thiazide)

Hypokalaemia increases risk of adverse effects of QT-interval prolongation

Increased hypotensive effect

Ensure any hypokalaemia is corrected

Monitor blood pressure and ask about postural hypotension
Dopamine agonists (eg drugs used for Parkinson’s disease) Antipsychotics inhibit antiparkinsonian effects of dopamine agonists  
Lithium Increased risk of neuroleptic malignant syndrome, extrapyramidal side effects and CNS toxicity If concomitant administration necessary, adjust dose so plasma-lithium concentration is at minimum effective level; monitor closely for side effects
Methadone Increased risk of QT-interval prolongation Preferably avoid concomitant use of drugs that prolong QT interval
Macrolide antibiotics (eg erythromycin, clarithromycin) Increased risk of QT-interval prolongation Preferably avoid concomitant use of drugs that prolong QT interval
Metoclopramide Increased risk of extrapyramidal effects  
Moxifloxacin Increased risk of QT-interval prolongation Preferably avoid concomitant use of drugs that prolong QT interval
Opioid analgesics Increased hypotensive and sedative effect Monitor blood pressure and ask about postural hypotension; warn patient of excessive sedation and of psychomotor impairment
Tramadol Increased risk of seizures  

 

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Page last modified: 17 February 2015