Foscarnet Intravenous Infusion for Adults

Who can administer

May be administered by registered competent doctor or nurse/midwife

Important information

• This drug 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 = 3,000mg. The infusion bottle contains 6,000mg so excess 3,000mg must be removed
• Hydration is very important for this drug - see under dose for details
• For fluid restricted patients, see SPC
• See under 'Dose' for adjustments required in renal impairment

Available preparations

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

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)}

• Gloves, protective eyewear and a mask should be worn by those handling this drug
• The drug solution needs to be diluted with an equal volume of infusion fluid to give a 12mg per ml solution
• Hydration required: see under 'Dose' below for details

• Doses of 6,000mg or less
  • 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 (because this method means that the drug will be diluted 50:50 (i.e. to produce 12mg/mL))
  • Add in the foscarnet solution
  • Example for 70kg patient
    • Drug solution = 6,000mg in 250mL
    • patient dose is 4,200mg = 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)

• Doses of greater than 6,000 up to 12,000mg
  • 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 1000ml bag to leave an equal volume to the drug solution in the bag (because this method means that the drug will be diluted 50:50 (i.e. to produce 12mg/mL))
  • Add in the foscarnet solution
  • Example
    • Drug solution = 6,000mg in 250mL
    • patient dose is 8,400mg = 350ml drug solution
    • remove 650ml infusion fluid from a 1000ml bag (to leave 350ml in bag)
    • add the 350ml drug solution
  • Administer the required dose over 120 minutes (60 minutes if dose is 60mg/kg or less)

• Doses of greater 12,000mg- see Further information

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

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 for two to three weeks ^{(ref BNF)}

CMV disease maintenance

• Give 90mg/kg once daily
• Increase to 120mg/kg daily if tolerated and/or progressive retinitis
• If disease progression on maintenance dose, repeat induction dose
• Note: the BNF suggests that maintenance doses start at 60mg/kg, increased as tolerated. Specialist input should be sought re doses for maintenance treatment

Herpes infections unresponsive to aciclovir

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

Renal dose adjustments

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

CMV INDUCTION therapy
Creatinine clearance (ml/kg/min)	For 60mg/kg dose	Interval		For 90mg/kg dose	Interval
Greater than 1.4	60 mg/kg	8 hours		90 mg/kg	12 hours
1.4 to 1.1	45 mg/kg	8 hours		70 mg/kg	12 hours
1 to 0.81	35 mg/kg	8 hours		50 mg/kg	12 hours
0.8 to 0.61	40 mg/kg	12 hours		80 mg/kg	24 hours
0.6 to 0.51	30 mg/kg	12 hours		60 mg/kg	24 hours
0.5 to 0.41	25 mg/kg	12 hours		50 mg/kg	24 hours
less than 0.4	No therapy recommendation

CMV MAINTENANCE therapy
Creatinine clearance (ml/kg/min)	For 90mg/kg dose	Interval		For 120mg/kg dose	Interval
Greater than 1.4	90 mg/kg	24 hours		120 mg/kg	24 hours
1.4 to 1.1	70 mg/kg	24 hours		90 mg/kg	24 hours
1 to 0.81	50 mg/kg	24 hours		65 mg/kg	24 hours
0.8 to 0.61	80 mg/kg	48 hours		105 mg/kg	48 hours
0.6 to 0.51	60 mg/kg	48 hours		80 mg/kg	48 hours
0.5 to 0.41	50 mg/kg	48 hours		65 mg/kg	48 hours
less than 0.4	No therapy recommendation

Herpes infection
Creatinine clearance (ml/kg/min)	For 40mg/kg dose	Interval
Greater than 1.4	40 mg/kg	8 hours
1.4 to 1.1	30 mg/kg	8 hours
1 to 0.81	20 mg/kg	8 hours
0.8 to 0.61	25 mg/kg	12 hours
0.6 to 0.51	20 mg/kg	12 hours
0.5 to 0.41	15 mg/kg	12 hours
less than 0.4	Treatment not recommended

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
• Monitor/consider QT prolongation risk

Further information

• Each 250mg bottle contains 1.38g (60mmol) sodium (equivalent to 69% of the WHO recommended maximum daily intake of 2g)
• Doses of greater than 12,000mg
  • Because the drug solution must be diluted with equal quantities of fluid, a 1000ml infusion bag is not large enough to allow this to be prepared (as 12,000mg =500mL), an alternative method must be used - as follows
  • 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 120 minutes (60 minutes for doses of 60mg/kg or less) while at the same time  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
  • 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. Glass bottle precautions  ^{(ref 2)}

References

Tillomed 12/08/2022

1: Injectable medicines guide, downloaded form Medusa 21/11/2024

2: Glass bottle reference - see below