Foscarnet Intravenous Infusion for Adults

Who can administer

May be administered by registered competent doctor or nurse/midwife

Important information

• Restricted antimicrobial: It will ONLY be supplied on the direct recommendation of Microbiology/Infectious Diseases/Haematology team
• Important: The infusion bottle contains an excess of drug - eg patient 50kg, for 60mg/kg dose = 3g. The infusion bottle contains 6g so excess 3g must be removed
• Hydration is very important for this drug - see under dose for details
• For fluid restricted patients, see SPC

Available preparations

Foscavir 6,000mg in 250ml bottle (24mg/ml)

Note: The 12g/500ml solution for infusion is NOT routinely available in GUH

Reconstitution

Already in solution

Dilute further prior to administration (peripheral use)

Infusion fluids

Sodium chloride 0.9% or Glucose 5%

Methods of intravenous administration

Intermittent Intravenous Infusion (administer using an electronically controlled infusion device)

Peripheral line (ref 1,2)

• Gloves, protective eyewear and a mask should be worn by those handling this drug
• The drug solution needs to be diluted to give a 12mg per ml solution. This can be done in one of two ways:
• 1: (PREFERRED method)
  • Calculate required dose, and withdraw excess drug from infusion bottle and discard it
  • Administer the volume left in the infusion bottle (the required dose) over at least 60 minutes (120 minutes for doses greater than 60mg/kg) while....
  • Piggybacking 1000ml sodium chloride 0.9% through the same catheter/cannula as the foscarnet infusion (at the same rate as foscarnet)- this dilutes the injection solution to the required concentration as it is being administered

• 2: (ALTERNATIVE method) (ref 1)
  • Dilute required dose with an equal volume of infusion fluid
  • Calculate the volume of drug solution required for the dose
  • Remove a volume of infusion fluid from a 500ml bag to leave an equal volume to the drug solution in the bag- and add in the foscarnet solution. example: patient dose is 4200mg = 175ml drug solution. Remove 325ml infusion fluid from a 500ml bag (to leave 175ml in bag)- add the 175ml drug solution
  • Administer the required dose over at least 60 minutes (120 minutes for doses greater than 60mg/kg)

Central line

• Calculate required dose, and withdraw excess drug from infusion bottle
• Administer undiluted over at least 60 minutes (120 minutes for doses greater than 60mg/kg)
• Hydration also required: 500 to 1000ml

Glass bottle precautions as follows: (ref 3)

• As the drug is supplied in glass bottles, precautions need to be taken during administration to prevent possible air embolism - particularly in central line administration.
• Bottles must be vented in one of two ways
  • Directly by means of a filter needle into the bottle which goes through the rubber stopper and opens into the air, or
  • Direct air vent on the air inlet of the administration set, located between the drip chamber and piercing pin, it is covered with a bacterial retentive filter to reduce the chance of contamination

Dose in adults

Hydration

• Renal toxicity can be reduced by adequate hydration of the patient
• Hydration is recommended with each infusion to reduce renal toxicity - this is in addition to the dilution of the drug as outlined above
• Hydrate with 500 to 1000ml of Sodium chloride 0.9% at each infusion. In compliant patients, oral hydration with similar hydration regimens has been used. Clinically dehydrated patients should have their condition corrected before initiating foscarnet therapy

CMV disease induction

• Give 60mg/kg every eight hours or 90mg/kg every twelve hours (BNF) for two to three weeks

CMV disease maintenance

• Give 60mg/kg daily (occasionally 90mg/kg has been given as an initial maintenance dose)
• Increase to 90 to 120mg/kg if tolerated and/or progressive retinitis
• If disease progression on maintenance dose, repeat induction dose

Mucocutaneous herpes simplex infections unresponsive to aciclovir in immunocompromised patients

• Give 40mg/kg every eight hours for two to three weeks or until lesions heal

Renal dose adjustments

CMV Induction therapy
Creatinine clearance (ml/kg/min)(see below for calculations)	CMV Dose in mg/kg every EIGHT hours	HSV Dose in mg/kg every EIGHT hours
greater than 1.6	60	40
1.6 to 1.4	55	37
1.4 to 1.2	49	33
1.2 to 1	42	28
1 to 0.8	35	24
0.8 to 0.6	28	19
0.6 to 0.4	21	14
less than 0.4	Treatment not recommended

CMV Maintenance therapy
Creatinine clearance (ml/kg/min) (see below for calculations)	One infusion dose (mg/kg/day)
greater than 1.6	60*
1.6 to 1.4	55
1.4 to 1.2	49
1.2 to 1	42
1 to 0.8	35
0.8 to 0.6	28
0.6 to 0.4	21
less than 0.4	Treatment not recommended

* a number of patients have received 90mg/kg as a starting dose for maintenance therapy

Creatinine clearance is calculated using the following formula (this gives the answer in ml/kg/min- as per table above)

N * (140-Age in yrs) / Serum creatinine (micromol/l)

Where N is 1.23 for male patients, 1.04 for female patients (This formula may not be accurate for patients at extremes of body weight- ie obese or very underweight)

Monitoring

• Monitor serum creatinine every second day during induction therapy, and once weekly during maintenance therapy
• Adequate hydration must be maintained in all patients
• Monitor serum calcium and magnesium levels

Further information

• Each 250mg bottle contains 1.38g Sodium (equivalent to 69% of the WHO recommended maximum daily intake of 2g)

References

UK SPC 03/11/2020

1: Injectable medicines- downloaded from http://www.medicinescomplete.com/ 27/10/2021

2: Injectable Medicines Administration Guide UCL hospitals, downloaded from Medusa 27/10/2021

3:Glass bottle reference - see below