Intramuscular medication for acutely disturbed behaviour

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Prerequisites to intramuscular use

Each patient will have an individualised  treatment plan including:

  • the use of de-escalation techniques
  • as required or discretionary oral medication as appropriate for the patient 
  • the choice of IM medication where necessary

If IM administration is required the appropriate MHA documentation should be completed if applicable.

When IM sedation is administered, a doctor should be informed and available to attend the patient within 30 minutes if required.

Consider the potential for inadvertent high-dose antipsychotic therapy when prescribing IM antipsychotics.

When prescribing medication for use intramuscularly, write the initial prescription as a once-only dose, do not repeat it until the effect of the initial dose has been reviewed.

If the behavioural disturbance is thought to be related to 'excited delirium' then consider immediate referral to acute care (see RCEM guidance).

Choice of intramuscular medication

Recommended Treatment Choices (NICE Guidance NG10 2015)

  • Lorazepam (or Midazolam, if used locally) or
  • Haloperidol +/- Promethazine

Alternatives not recommended by NICE for the purpose of emergency IM treatment in acutely disturbed patients but may be considered where the use of haloperidol is inappropriate e.g. where there is a risk of prolonged QTc interval

  • Aripiprazole
  • Olanzapine



Medication doses

Use of lower doses in some patient groups e.g. elderly or debilitated.

Care must be taken in struggling patients to avoid inadvertent IV administration.

Be aware of the total dose of medication administered over the last 24 hours.

Lorazepam 2mg

  • Maximum cumulative dose (oral+IM) over 24 hours: 8mg
  • Useful when
    • Insufficient information to guide medication choice or patient is antipsychotic naïve
    • Patient is already on regular antipsychotic and haloperidol is contraindicated
    • Evidence of cardiac disease or no electrocardiogram (ECG) has been carried out
  • Ensure flumazenil IV is available

Midazolam 5mg-7.5mg

  • Maximum cumulative dose over 24 hours: 15mg
  • To be used when lorazepam is not available
  • Further guidance

Haloperidol 5mg

  • Maximum cumulative dose (oral+IM) over 24 hours: 20mg
  • Useful when
    • Patient is benzodiazepine tolerant or prescribed regular benzodiazepine
  • Pre-treatment ECG required
  • Ensure IM procyclidine available

Olanzapine 10mg

  • Maximum cumulative dose (oral+IM) over 24 hours: 20mg
  • If to be repeated wait 2 hours
  • Wait one hour before administering an IM benzodiazepine
  • If benzodiazepine already given, the clinical status of the patient should be assessed and consultant advice obtained prior to IM olanzapine being administered
  • Further guidance

Aripiprazole 9.75mg

  • Maximum cumulative dose (oral+IM) over 24 hours: 30mg

Risks with antipsychotics

  • Cardiovascular complications e.g. QTc prolongation especially with haloperidol
  • Reduction in seizure threshold
  • Adverse side effects e.g. restlessness (akathisia), acute rigidity (dystonia) and involuntary movements (dyskinesia)
  • Altered consciousness
  • Neuroleptic malignant syndrome (increased temperature, sweating, restlessness, altered consciousness or marked muscular rigidity). If suspected: stop all antipsychotics drugs, cool the patient  and get an urgent medical assessment

Promethazine 50mg

  • Maximum cumulative dose over 24 hours: 100mg
  • Useful when
    • Patient is benzodiazepine tolerant or if there is concern over using antipsychotics
  • Risks
    • Contraindicated with CNS depression and those who have taken MAOIs within the past 14 days
    • Cautions include respiratory conditions, coronary artery disease, epilepsy and hepatic/renal insufficiency
    • Possibility of QTc prolongation
    • Reduced seizure threshold


Monitoring requirements

After IM sedation the ward team monitor the following at least every hour until the patient is ambulatory:

  • Adverse effects
  • Pulse
  • Blood pressure
  • Respiratory rate
  • Temperature
  • Level of hydration
  • Level of consciousness

Monitor every 15 minutes if the BNF maximum dose has been exceeded or the patient:

  • Appears to be asleep or sedated
  • Has taken illicit drugs or alcohol
  • Has a pre-existing physical health problem
  • Has experienced any harm as a result of any restrictive intervention
  • Has been given haloperidol in combination with other drugs know to prolong QTc

Where full monitoring is impractical, clearly document the reasons why and ensure minimum observation of respiration and level of consciousness.

Management of problems
Problem Remedial measures
Acute dystonias (including oculgyric crisis) Procyclidine 5-10mg IM
Reduced respiratory rate (<10/minute or oxygen saturation <90%

Give Oxygen.

Give flumazenil if benzodiazepine-induced:

  • Initially 200 microgram IV over 15 seconds – if required level of consciousness not achieved after 60 seconds then:
  • Subsequent dose: 100 microgram over 10 seconds, repeated after 60 seconds if necessary
  • Maximum dose: 1mg in 24 hours (one initial dose and eight subsequent doses)

Monitor respiration until rate returns to baseline level.

If induced by other agent patient may require mechanical ventilation–arrange transfer to ITU immediately.

Reduced respiratory rate (<5/minute)

Medical Emergency–institute emergency treatment and arrange immediate transfer.

Tachycardia (>140/min), irregular heart beat or bradycardia (<50/min) Refer to specialist medical care immediately.
Orthostatic hypotension

Lie patient flat, raise legs if possible, monitor closely including blood pressure.

Fall in blood pressure (systolic <90mmHg or diastolic <50mmHg)

Urgent medical assessment. Lie patient flat, raise legs if possible.

Increased temperature (>37.5oC) Urgent medical assessment. Withhold antipsychotics due to risk of NMS & arrhythmias.
Editorial Information

Last reviewed: 31 May 2019

Next review: 01 March 2021

Author(s): PMG-MH

Version: V2.1

Approved By: MHS Quality& Clinical Governance Group

Reviewer Name(s): Andrew Walker, Suzanne Burke