Acetylcysteine (SNAP 12 hour regimen - PREFERRED in GUH) Intravenous Infusion for Adults

Who can administer

May be administered by registered competent doctor or nurse/midwife

Important information

  • This information applies to ORAL paracetamol overdoses, for INTRAVENOUS paracetamol overdoses contact the National Poisons Information Centre (NPIC)
  • The SNAP regimen can also be used in cases of non-paracetamol associated hepatotoxicity (Unlicensed) (ref 2)
  • SNAP (Scottish and Newcastle Acetylcysteine Protocol) (Also known as Modified 12-hour regimen)
    • SNAP (modified 12-hour regimen) is an off label use of acetylcysteine albeit at its licensed dose 
    • This regimen is endorsed by National Poisons Information Service (NPIS) and the Royal College of Emergency Medicine
    • This regimen is the preferred regimen for use in GUH for Adult patients (information on the 21 hour regimen may be found on TOXBASE if required)
    • The total dose of intravenous acetylcysteine is the same as the standard 21-hour regimen (i.e. 300 mg/kg) but the rate and duration of treatment is different which results in a lower peak plasma acetylcysteine concentration and a significantly lower risk of anaphylactoid reactions (ref 1)
  • Anaphylactoid reactions may occur, particularly with initial loading dose.  Patient should be carefully observed.  Most anaphylactoid reactions can be managed by temporarily suspending the acetylcysteine infusion, administering appropriate supportive care and restarting at a lower infusion rate (e.g. administer the first bag over twice as long as usual)(ref 1)
  • A previous anaphylactoid reaction to acetylcysteine may not be a contraindication for use.  Contact NPIC (ref 1)

Available preparations

Parvolex 2g per 10ml ampoule

Acetylcysteine 2g per 10ml ampoule

Reconstitution

Already in solution

Draw up using a 5 micron filter needle

Dilute further prior to administration

Infusion fluids

Glucose 5% preferred (or Sodium chloride 0.9%)

Methods of intravenous administration

Intermittent intravenous infusion

  • Prepare the infusion to the correct concentration- as indicated in tables below
  • Administer over the time specified in the tables below

Dose in adults

Paracetamol poisoning

  • See TOXBASE to determine the management of the patient depending on the number of hours since ingestion.
  • If Acetylcysteine is indicated, follow the tables below

Non-paracetamol associated hepatotoxicity

  • The SNAP regimen can also be used for this indication (unlicensed) (ref 2)

SNAP (Also known as Modified 12-hour regimen)

  • Give 100mg/kg (max 11g) over two hours
  • Followed by 200mg/kg (max 22g) over ten hours
  • See tables below
  • Continued treatment with Acetylcysteine may be necessary (after these two bags have been given over twelve hours total) - see Toxbase for advice on the clinical assessment of the patient
  • If further infusions are required, repeat Infusion 2

 

Table 1:  SNAP (Also known as Modified 12-hour regimen)

Acetylcysteine for Adults WEIGHING 40KG OR MORE 

Each ampoule contains 2g/10ml (200mg per ml)
12 hour regimen First infusion Second infusion
Infusion fluid Add required dose to 200ml infusion fluid (discard 50ml from 250ml bag) Add required dose to 1000ml infusion fluid (no need to withdraw any volume)
Duration of infusion 2 hours 10 hours
Drug dose 100mg/kg  200mg/kg
Patient weight Ampoule volume Infusion rate Ampoule volume Infusion rate
kg mL mL/hour mL mL/hour
less than 40kg- see table 2 below        
40 to 49 23 112                45 105
50 to 59 28 114                55 106
60 to 69 33 117                65 107
70 to 79 38 119                75 108
80 to 89 43 122                85 109
90 to 99 48 124                95 110
100 to 109 53 127               105 111
110kg or more 55 128               110 111

Dose calculations are based on the weight in the middle of each band

 Figures have been rounded up to the nearest whole number

 

Table 2: SNAP (Also known as Modified 12-hour regimen)

Acetylcysteine for Adults WEIGHING LESS than 40KG 

The volume of infusion fluid has been modified to take patient weight into account, as fluid overload is a potential danger

Each ampoule contains 2g/10ml (200mg per ml)
12 hour regimen First infusion Second infusion
Duration of infusion 2 hours 10 hours
Drug dose 100mg/kg  200mg/kg
Concentration of infusion

50mg/mL

(prepare by diluting each 10ml ampoule with 30ml infusion fluid)

Prepare as per table below
Patient weight Total infusion volume Infusion rate

Acetylcysteine injection solution (mL) to be added to infusion bag

(volume of infusion bag in next column)

Infusion volume

(remove excess from next bag size up, and then add drug volume as per previous column) - see example below 

 Total volume after addition of drug solution Infusion rate
kg mL mL/hour mL     mL/hour
20 to 24 44 22 22 418 440 44
25 to 29 54 27 27 513 540 54
30 to 34 64 32 32 608 640 64
35 to 39 74 37 37 703 740 74
40kg or greater- use table 1 above            

Example:  patient weighs 37kg

First infusion: administer 74mL of drug infusion (taken from an infusion of 80mL, prepared by adding 2x10ml ampoules to 60mL infusion fluid)

Second infusion: Add 37mL of injection solution 200mg/mL to 703ml infusion fluid (remove 297mL from a 1000mL infusion bag).  This produces a total of 7.4g in 740mL.  Infuse at 74mL per hour

Dose calculations are based on the weight in the middle of each band

 Figures have been rounded up to the nearest whole number

Storage

Store below 250C

Storage locations- see antidote list

Search Synonym: NAC

References

SPC September 2019

1: Toxbase- accessed 29th Sept 2021

2: Email Communication with Prof L Egan, September 7th, 2023