Pegvisomant

Trade Names:Somavert- Injection 10 mg- Injection 15 mg- Injection 20 mg

Pharmacology

Selectively binds to growth hormone receptors on cell surfaces, where it blocks the binding of endogenous growth hormone, interfering with growth hormone transduction.

Pharmacokinetics

Absorption

Following subcutaneous administration, C _max is generally not attained until 33 to 77 h.

Distribution

Mean apparent Vd is 7 L.

Elimination

After multiple dosing, the mean total body clearance is estimated to range between 36 to 28 mL/h for subcutaneous doses ranging from 10 to 20 mg/day, respectively. Following either single or multiple doses, the mean elimination t _½ is approximately 6 days.

Indications and Usage

Treatment of acromegaly in patients who have had an inadequate response to surgery or radiation therapy or other medical therapies.

Contraindications

Standard considerations.

Dosage and Administration

Subcutaneous 40 mg loading dose under health care provider supervision; then instruct patient to begin daily injections of 10 mg. Measure serum insulin-like growth factor-I (IGF-I) levels every 4 to 6 wk, at which time, increase the dose in 5 mg increments if IGF-I levels are still elevated or decrease the dose in 5-mg decrements if IGF-I levels have decreased below the normal range.

General Advice

• For subcutaneous administration only. Not for intradermal, IM, or IV administration.
• Follow manufacturer's instructions for reconstitution of powder for injection.
• Do not shake vial during reconstitution process.
• Do not administer if particulate matter, cloudiness, or discoloration noted.
• Rotate injection sites (eg, thigh, abdomen, upper arm). Give new injections at least 1 inch from old site and never into areas where the skin is tender, bruised, red, or hard.
• Discard any unused solution. Do not save unused solution for later administration.

Storage/Stability

Store unopened vials in refrigerator (36° to 46°F). Do not freeze. Use reconstituted solution within 6 h.

Drug Interactions

Dose may need to be reduced after starting pegvisomant.

May need higher pegvisomant serum levels to achieve appropriate IGF-I suppression.

Laboratory Test Interactions

Because of structural similarities, pegvisomant may cross-react in commercially available growth hormone assays.

Adverse Reactions

Cardiovascular

Hypertension.

CNS

Dizziness.

Dermatologic

Injection site reaction.

EENT

Sinusitis.

GI

Diarrhea; nausea.

Hematologic

Elevated ALT and AST.

Miscellaneous

Infection; accidental injury; back pain; pain; peripheral edema; chest pain; flu-like syndrome; paresthesia.

Precautions

Pregnancy

Category B .

Lactation

Undetermined.

Children

Safety and efficacy not established.

Elderly

Select dose with caution, reflecting greater frequency of decreased hepatic, renal, or cardiac function, and comorbidity.

Glucose metabolism

Because growth hormone opposes the effects of insulin on carbohydrate metabolism by decreasing insulin sensitivity, glucose tolerance may increase in some patients. Monitor blood sugar in diabetic patient when drug is started or dose is changed. Report significant changes to health care provider. Be prepared to reduce the dose of insulin or oral hypoglycemic agents.

Growth hormone deficiency

A state of functional growth hormone deficiency may occur.

LFTs

Elevations of serum concentrations of ALT and AST greater than 10 times the upper limit of normal have been reported.

Tumor growth

Tumors that secrete growth hormone may expand and cause serious complications.

Overdosage

Symptoms

Fatigue.

Patient Information

• Advise patient or caregiver that dose will be carefully adjusted based on results of lab tests that are done periodically.
• If patient or caregiver will be administering at home, review “Patient Information” insert with the patient or caregiver. Ensure that the patient or caregiver understands how to store, prepare, and administer the dose, and dispose of used equipment and supplies. The first injection should be performed under the supervision of a qualified health professional.
• Advise patient that if a dose is missed, to inject the missed dose as soon as remembered and then inject the next dose at the regularly scheduled time.
• Advise patient to report any of the following to health care provider: intolerable injection site reactions, fatigue, persistent nausea or vomiting, unexplained bruising, bloating, stomach pain, or swelling.
• Instruct patient to stop taking and immediately inform health care provider if yellowing of skin or eyes is noted.
• Instruct diabetic patient to monitor blood glucose more frequently when drug is started or dose is changed and to inform health care provider of significant changes in readings.

Copyright © 2009 Wolters Kluwer Health.