Foscarnet Sodium (Phosphonoformic Acid)

A to Z Drug Facts

Foscarnet Sodium (Phosphonoformic Acid)

	Action
	Indications
	Contraindications
	Route/Dosage
	Interactions
	Lab Test Interferences
	Adverse Reactions
	Precautions
Patient Care Considerations
	Administration/Storage
	Assessment/Interventions
	Patient/Family Education

(foss-CAR-net SO-dee-uhm)

Foscavir

Class: Anti-infective/Antiviral

Action Inhibits replication of all known herpes viruses, including cytomegalovirus (CMV), herpes simplex virus types 1 and 2 (HSV-1, HSV-2), human herpes virus 6 (HHV-6), Epstein-Barr virus (EBV) and varicella-zoster virus (VZV).

Indications Treatment of CMV retinitis in patients with AIDS; treatment of acyclovir-resistant mucocutaneous HSV infections in immunocompromised patients; combination therapy with ganciclovir for patients who have relapsed after monotherapy with either drug.

Contraindications Standard considerations.

Route/Dosage

CMV Retinitis

ADULTS: IV Initially 60 mg/kg/dose at constant rate over at least 1 hr q 8 hr for 2 to 3 wk. Adjust for clinical response and renal function. Maintenance dose: 90 mg/kg/day infused over 2 hr, individualized; maximum maintenance dose is 120 mg/kg/day.

HSV Infections

ADULTS: IV Initially 40 mg/kg/dose (minimum 1 hr infusion) every 8 or 12 hr for 2 to 3 wk or until healed. Maintenance: 90 mg/kg/day given as an IV infusion over 2 hr, individualized; maximum maintenance dose is 120 mg/kg/day.

Interactions

Nephrotoxic drugs: Elimination of foscarnet may be impaired by drugs that inhibit renal tubular secretion. Increased potential for nephrotoxicity with aminoglycosides, amphotericin B, and IV pentamidine. Pentamidine: Concomitant IV pentamidine may cause hypocalcemia. Zidovudine: Increased risk of anemia. INCOMPATIBILITIES: Do not give other drugs or supplements via same IV catheter.

Lab Test Interferences None well documented.

Adverse Reactions

CV: Hypertension; palpitations; ECG abnormalities including sinus tachycardia, first-degree heart block, nonspecific ST-T segment changes; hypotension; flushing; cerebrovascular disorder. CNS: Headache; paresthesia; dizziness; involuntary muscle contractions; hypoesthesia; neuropathy; seizures; depression; confusion; anxiety; tremor; ataxia; dementia; stupor; generalized spasms; sensory disturbances; meningitis; aphasia; abnormal coordination; leg cramps; EEG abnormalities; insomnia; somnolence; nervousness; amnesia; agitation; aggressive reaction; hallucination. DERM: Rash; increased sweating; pruritus; skin ulceration; seborrhea; erythematous or maculopapular rash; skin discoloration; facial edema. EENT: Vision abnormalities; eye pain; conjunctivitis; sinusitis; rhinitis; taste perversions; pharyngitis. GI: Anorexia; nausea; diarrhea; vomiting; abdominal pain; constipation; dysphagia; dyspepsia; rectal hemorrhage; dry mouth; melena; flatulence; ulcerative stomatitis; pancreatitis. GU: Alterations in renal function, including decreased creatinine clearance, abnormal renal function; albuminuria; dysuria; polyuria; urethral disorder; urinary retention; UTI; acute renal failure; nocturia; abnormal albumin-globulin ratio; increased AST and ALT. HEMA: Anemia; bone marrow suppression; granulocytopenia; leukopenia; thrombocytopenia; platelet abnormalities; thrombosis; WBC abnormalities; lymphadenopathy. META: Mineral and electrolyte imbalances, including hypo- or hypercalcemia, hypokalemia, hypomagnesemia, hypo- or hyperphosphatemia, hyponatremia; decreased weight; increased alkaline phosphatase, LDH, BUN; acidosis. RESP: Coughing; dyspnea; pneumonia; respiratory disorders or insufficiency; pulmonary infiltrates; stridor; pneumothorax; hemoptysis; bronchospasm. OTHER: Fever; fatigue; rigors; asthenia; malaise; arthralgia or myalgia; cachexia; thirst; infection; sepsis; death; back or chest pain; edema; influenza-like symptoms; abscess; lymphoma-like disorders; sarcoma; injection site pain or inflammation.

Precautions

Pregnancy: Category C. Lactation: Undetermined. Children: Safety and efficacy not studied. Drug is deposited in teeth and bone. Mineral and electrolyte imbalances: Patients, especially those on concomitant drugs known to influence serum minerals or electrolytes or those with cardiac or neurological abnormalities, may experience changes in electrolytes (eg, calcium, potassium, magnesium, phosphate) that could cause cardiac disturbances or seizures. Replacement therapy may be needed. Renal impairment: Major toxicity; occurs to some degree in most patients. If creatinine clearance drops below 0.4 ml/min/kg, drug should be discontinued. Toxicity/local irritation: Infuse into veins with adequate blood flow to permit rapid dilution and distribution and avoid local irritation. Drug is excreted in urine and may cause irritation or ulceration of penile or vulvovaginal epithelium.

PATIENT CARE CONSIDERATIONS

Administration/Storage

Administer by IV infusion only, at rate not to exceed 1 mg/kg/min. Use infusion pump to prevent rapid or bolus injection.
When administering through central vein, 24 mg/ml solution may be used. In peripheral veins, dilute with D5W or normal saline to 12 mg/ml.
Administer only with normal saline or D5W; incompatible with many drugs and supplements.
Do not use same tubing or catheter for any other drug or IV solution.
Prehydrate patient with 0.9% Sodium Chloride to decrease chance of renal damage.
Use prepared solutions within 24 hr of first entry into sealed bottle.

Assessment/Interventions

Obtain patient history, including drug history and any known allergies. Note cardiac, neurologic, or renal disorders.
Ensure that baseline serum electrolyte levels (eg, calcium, magnesium, potassium, phosphate) have been obtained before beginning therapy, and repeat 2 to 3 times/wk during induction therapy and 1 to 2 times/wk during maintenance therapy.
Ensure that baseline renal function tests have been obtained before beginning therapy, and repeat 2 to 3 times/wk during induction therapy and 1 to 2 times/wk during maintenance therapy. Dosage will be adjusted or drug discontinued if creatinine clearance decreases.
Assess renal function before and after administration in elderly patients.
Monitor I&O and ensure that patient is well hydrated. Note urine pH.
Monitor for anemia; obtain CBC frequently.
Monitor for seizures, especially in patients with CNS disorder such as toxoplasmosis or HIV encephalopathy.
Observe for fever, nausea, diarrhea, vomiting, and headache. Report these and other common side effects to physician.
If symptoms of electrolyte imbalance, such as complaints of perioral tingling, numbness in extremities, or paresthesia occur, notify physician immediately. Infusion may need to be discontinued and electrolyte supplementation initiated.

OVERDOSAGE: SIGNS & SYMPTOMS
	Electrolyte disturbances, paresthesia, renal dysfunction, seizures, coma

Patient/Family Education

Emphasize that drug does not cure CMV retinitis but may help prevent worsening of symptoms.
Explain that good hygiene and drinking plenty of fluids may help reduce risk of genital irritation or ulceration.
Instruct patient to report the following symptoms to physician: Perioral tingling, numbness in extremities, paresthesia, fever, nausea, diarrhea, vomiting, headache, increased or decreased frequency or amount of urination, or other bothersome side effects.
Caution patient not to take any otc medications without consulting physician. Explain that serious drug interactions may result.