Pegvisomant

INTRODUCTION

Indications

Treatment of acromegaly in patients who do not respond to or are not candidates for surgery, radiation, or other medical therapies.

Action

Binds to growth hormone (GH) receptor sites on cell surfaces, blocking the effects of endogenous growth hormone. Bound to polyethylene glycol (PEG) to reduce clearance and increase duration of action. Therapeutic Effects: Decreased manifestations of acromegaly and normalized insulin-like growth factor-1 (IGF-1) levels.

Adverse Reactions/Side Effects

CV: hypertension, peripheral edema. GI: ↑ LFTs. MS: back pain. Endo: growth hormone deficiency, ↑ glucose tolerance. Derm: lipohypertrophy.

PHYSICAL THERAPY IMPLICATIONS

Examination and Evaluation

• Assess blood pressure periodically (See Appendix F). Report a sustained increase in blood pressure (hypertension) to the physician.

• Assess peripheral edema using girth measurements, volume displacement, and measurement of pitting edema (See Appendix N). Report increased swelling in feet and ankles or a sudden increase in body weight due to fluid retention.

• Monitor signs of increased glucose tolerance, as indicated by weakness, malaise, irritability, and fatigue. Patients with diabetes mellitus should check blood glucose levels frequently.

• Assess any back pain to rule out musculoskeletal pathology; that is, try to determine if pain is drug induced rather than caused by anatomic or biomechanical problems.

• Periodically assess body weight and other anthropometric measures (body mass index, body composition). Report a rapid or unexplained weight gain or increased body fat.

Interventions

• Do not apply physical agents (heat, cold, electrotherapeutic modalities) or massage at or near the injection site; these interventions will alter drug absorption from subcutaneous tissues.

Patient/Client-Related Instruction

• Instruct patient to report signs of liver dysfunction, including loss of appetite, abdominal pain, severe nausea and vomiting, yellow skin or eyes, skin rashes, flu-like symptoms, and muscle/joint pain. Periodic liver function tests (LFTs) may be needed to monitor hepatic function.

Pharmacokinetics

Absorption: 57% absorbed following SC administration.

Distribution: Does not distribute extensively into tissues.

Metabolism and Excretion: Unknown.

Half-life: 6 days.

Contraindications/Precautions

Contraindicated in: Hypersensitivity; Latex allergy (vial stopper contains latex).

Use Cautiously in: Diabetes mellitus; Patients with growth hormone–secreting tumors; Lactation/Pedi: Safety not established; OB: Use only if clearly needed.

Interactions

Drug-Drug: Patients receiving opioid analgesics often require ↑ doses of pegvisomant to normalize IGF-1.