High dose antipsychotic therapy

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The Consensus statement on high-dose antipsychotic medication (Royal College of Psychiatry Council Report CR190, November 2014) defines high-dose antipsychotic therapy (HDAT) use as:

A total daily dose of a single antipsychotic which exceeds the upper limit stated in the summary of product characteristics (SPC) or BNF with respect to the age of the patient and the indication being treated.


A total daily dose of two or more antipsychotics which exceeds the summary of product characteristics (SPC) or BNF maximum using the percentage method.

HDAT use should be the exception rather than the rule.

The evidence from randomised controlled trials (RCTs) to support the use of combined antipsychotics in schizophrenia remains scarce and there is little convincing evidence that antipsychotics higher than the maximum licensed dose are more effective than standard dosage for treatment-resistant schizophrenia. In addition, the evidence for combining non-clozapine antipsychotics is generally weak.

Key points

1. The responsibility to prescribe HDAT lies with the consultant psychiatrist responsible for the patient’s care.

2. The decision to prescribe HDAT should be discussed with the multidisciplinary team (including a clinical pharmacist). Where this is not possible, consider obtaining an informal second opinion from a local psychiatrist to support the use of HDAT.

3. Reason clearly documented within the patient’s clinical notes.

4. Ensure valid consent obtained and documented. Advice to support obtaining consent can be found at Choice and Medication website.

5. Where appropriate ensure that the statutory treatment plan on a T2 or T3 certificate or section 47 are in place.

6. A local register of patients prescribed HDAT to ensure that the recommended monitoring is undertaken.

7. The use of HDAT in an emergency situation should be authorised by senior psychiatrist.

8. HDAT should be reduced to conventional dosing if no significant improvement is observed at review.

9. Ensure good communication at points of transition.

Risk factors

Risk factors and potential drug interactions must be considered prior to prescribing HDAT and at each review.

Risk factor

Rationale for potential risk of QT prolongation

Cardiac history

Particularly myocardial infarction, arrhythmias, bradycardia, abnormal ECG, long QT syndrome, heart failure

Consider family history

Hepatic impairment

Potential impact on hepatic metabolism and clearance of antipsychotics

QT prolongation is increased in alcoholic liver disease

Renal impairment

Potentially decreases clearance of renally excreted antipsychotics

May increase risk of electrolyte disturbance


Increased risk of hepatic impairment


Increased risk of ischaemic heart disease

Impact on hepatic metabolism of some antipsychotics

Substance misuse

Due to risk of QT prolongation with certain substances

Old age

Elderly more susceptible to QT changes

Extremes of weight

Impact of obesity on CV risk and hepatic function

Very low BMI increases risk of electrolyte abnormalities and dehydration

Female gender

Women have longer QT intervals

Extreme physical exertion

e.g. individuals subject to restraint

Drug interactions

Drug interactions

Rationale for potential risk of QT prolongation

Medications known to prolong QT interval including


A list of medications known to prolong the QT interval can be found at https://www.crediblemeds.org (an American website which categorises medications based on their risk)

Pharmacokinetic interactions

Medications that increase antipsychotic plasma levels.(NB smoking can decrease plasma levels of some antipsychotics, especially clozapine, therefore, smoking cessation will increase plasma levels and may require dose reduction)

Medications known to cause electrolyte disturbance

e.g. diuretics

Electrolyte abnormalities e.g. hypokalaemia, hypocalcaemia, hypomagnesaemia can increase the risk of QT prolongation


At initiation of HDAT, a plan for ongoing monitoring must be agreed and completed by medical staff for the individual patient including;

• frequency of monitoring *

• responsibilities for monitoring and checking results

• regular review of progress

High Dose Antipsychotic Monitoring & Frequency*






If a prolonged QT interval is recorded at baseline (QTc > 450msec in men and > 460msec in women), review treatment. Consider cardiology assessment. If it is decided to continue treatment. Record reasons for doing so in patient’s case notes.

• When steady state serum levels have been reached after each dose increment (consult a clinical pharmacist for advice on appropriate timescales)

• Then every 6-12 months *



• Every 6 months *



• Every 6 months *


Blood glucose and/or HbA1c (for high dose therapies with increased risk of metabolic disturbance)


• Every 6 months *

Standard observations (bp, pulse, temperature)


• At least every 6 months*

• Following dose escalation, monitor for any deterioration in physical health.

Review of progress and ongoing need for HDAT


• Every 3 months

Symptom rating scales e.g. CGI


• At 6 weeks

• At 3 months

• Then at least annually *

Side rating scales e.g. GASS or LUNSERS


• At 6 weeks

• At 3 months

• Then at least annually *

If a patient refuses to consent to HDAT monitoring, then this should be clearly documented within their clinical notes. Ongoing refusal to engage with monitoring must prompt review and consideration of cessation of high dose antipsychotic therapy.

* It is recommended that increased monitoring is undertaken when using higher risk therapy e.g. haloperidol, diuretics, concurrent medications known to cause QT prolongation or those with other risk factors.

Management of problems- QTc

Management of QTc prolongation in high dose antipsychotic therapy 1

QTc Interval*







No action unless abnormal

T-wave morphology 2

Borderline prolonged

>450 ms but <500ms

>460ms but <500ms

Consider dose reduction and/or switching to a drug of lower effect on QTc

Repeat ECG




Immediate review and cessation of high dose therapy

Switch to drug of lower effect on QTc

Repeat ECG

A change in baseline QTc of >20ms should raise concern and should beassessed in conjunction with the overall QTc interval.

* The QT interval varies with heart rate. A number of formulas are used to correct the QT interval for heart rate. Once corrected, it is expressed as the QTc interval, which is reported on the ECG printout. The QTc is commonly normalised to a heart rate of 60bpm and may be inaccurate in patients with faster or slower heart rates.

1 NHS GG&C Medicines Update Extra. Drug induced QT prolongation. Issue 8 July 2018

2 Taylor D, Paton C, Kapur S. The Maudsley Prescribing Guidelines in Psychiatry. Wiley Blackwell. 12th edition

Management of other adverse effects

Management of electrolyte disturbance in high dose antipsychotic therapy

Electrolyte disturbance

Reference range





K < 3.5mmol/l

Mg < 0.7mmol/l

Adjusted Ca < 2.1mmol/l

Low K and Mg in particular can increase the risk of QTc prolongation.

Consider the risk of electrolyte disturbance in the event of diarrhoea/vomiting or if diuretic therapy commenced.

Address electrolyte disturbance, repeat U&Es and ECG


Management of adverse effects in high dose antipsychotic therapy

(Weigh up any perceived benefits of high dose treatment vs adverse effects)

Adverse effects


Extrapyramidal side effects (EPSE)

Consider decreasing antipsychotics to conventional dosing

Metabolic side effects

Where high dose treatment or combination is associated with an increased risk of metabolic adverse effects, consider a change to treatment or manage metabolic changes appropriately


Off-licence use of medication

The use of HDAT is an off-license use of medication, further information can be found here.

Roles and responsibilites

For information on the roles and responsibilities of staff in HDAT see full guideline


Maximum doses of antipsychotics

In defining what constitutes HDAT for patients receiving more than one antipsychotic, use the percentage method for calculating high dose status. When expressed as a percentage of their respective recommended maximum dose and added together, a cumulative dose of greater than 100% is considered ‘high dose’.

For example:

  • clozapine 700mg and amisulpride 400mg daily.
  • Sum %= 78% + 33% = 111% (>100%, therefore high dose)

Use of ‘as required’ (or ‘prn’) antipsychotic medication should also be taken into account.


Maximum licensed adult dose (mg/day)

100% BNF maximum





Aripiprazole oral/IM








Haloperidol oral/ IM *




Olanzapine oral/IM















750 (Mania 800)






50 (suggested by POMH)




Depots/ Long-acting injections

Maximum licensed adult dose (mg/ time interval)

100% BNF maximum

Aripiprazole LAI

400 /month

Flupentixol decanoate

400 /week

Haloperidol decanoate

75 /week

Olanzapine embonate***

300 /fortnight

Paliperidone LAI (Xepilon)

150 /month

Paliperidone 3/12 LAI (Trevicta)***

525 /3 months

Risperidone LAI (Consta)

50 /fortnight

Zuclopenthixol decanoate

600 /week


* The use of haloperidol is contraindicated in combination with drugs that prolong the QTc interval and therefore, where possible the use of haloperidol in combination with other antipsychotics should be avoided. Haloperidol and QTc interval prolongation 

** Subject to annual ECG irrespective of dosage.

*** Non formulary preparations within NHS GG&C MHS


Editorial Information

Last reviewed: 29 August 2019

Next review: 31 August 2021

Author(s): PMG-MH

Version: 3.1

Approved By: Mental Health Quality & Clinical Governance Group

Reviewer Name(s): Andrew walker, Suzanne Burke