Somavert (Pegvisomant) Drug Information: Side Effects and Drug Interactions

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May 27, 2012

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SIDE EFFECTS

Laboratory Changes

Elevations of serum concentrations of ALT and AST greater than ten times the ULN were reported in two subjects (0.8%) exposed to SOMAVERT (pegvisomant) in pre-approval clinical studies (see PRECAUTIONS, Liver Tests [LTs]).

General

Nine acromegalic patients (9.6%) withdrew from pre-marketing clinical studies because of adverse events, including two patients with marked transaminase elevations (see PRECAUTIONS, Liver Tests [LTs]), one patient with lipohypertrophy at the injection sites, and one patient with substantial weight gain. The majority of reported adverse events were of mild to moderate intensity and limited duration. Most adverse events did not appear to be dose dependent. Table 5 shows the incidence of treatment-emergent adverse events that were reported in at least two patients treated with SOMAVERT (pegvisomant) and at frequencies greater than placebo during the 12-week, placebo-controlled study.

Table 5: Number of Patients (%) with Acromegaly Reporting Adverse Events in a 12-week Placebo-controlled Study with SOMAVERT (pegvisomant) *

Event	SOMAVERT			Placebo n=32
Event	10 mg/day n=26	15 mg/day n=26	20 mg/day n=28	Placebo n=32
Body as a whole
Infection†	6 (23%)	0	0	2 (6%)
Pain	2 (8%)	1 (4%)	4 (14%)	2 (6%)
Injection site reaction	2 (8%)	1 (4%)	3 (11%)	0
Accidental injury	2 (8%)	1 (4%)	0	1 (3%)
Back pain	2 (8%)	0	1 (4%)	1 (3%)
Flu syndrome	1 (4%)	3 (12%)	2 (7%)	0
Chest pain	1 (4%)	2 (8%)	0	0
Digestive
Abnormal liver function tests	3 (12%)	1 (4%)	1 (4%)	1 (3%)
Diarrhea	1 (4%)	0	4 (14%)	1 (3%)
Nausea	0	2 (8%)	4 (14%)	1 (3%)
Nervous
Dizziness	2 (8%)	1 (4%)	1 (4%)	2 (6%)
Paresthesia	0	0	2 (7%)	2 (6%)
Metabolic and nutritional disorders
Peripheral edema	2 (8%)	0	1 (4%)	0
Cardiovascular
Hypertension	0	2 (8%)	0	0
Respiratory
Sinusitis	2 (8%)	0	1 (4%)	1 (3%)
*Table includes only those events that were reported in at least 2 patients and at a higher incidence in patients treated with SOMAVERT (pegvisomant) than in patients treated with placebo. †The 6 events coded as “infection” in the group treated with SOMAVERT (pegvisomant) 10 mg were reported as cold symptoms (3), upper respiratory infection (1), blister (1), and ear infection (1).The 2 events in the placebo group were reported as cold symptoms (1) and chest infection (1).

Immunogenicity

In pre-marketing clinical studies, approximately 17% of the patients developed low titer, non-neutralizing anti-GH antibodies. Although the presence of these antibodies did not appear to impact the efficacy of SOMAVERT (pegvisomant) , the long-term clinical significance of these antibodies is not known. No assay for anti-pegvisomant antibodies is commercially available for patients receiving SOMAVERT (pegvisomant) .

Post-Marketing Experience

Lipohypertrophy has been reported in < 5% of patients following pegvisomant administration.

Asymptomatic, transient elevations in transaminases up to 15 times ULN have been observed in < 2% of patients in the post-marketing experience. These reports were not associated with an increase in bilirubin, and there were no clinical consequences for these patients. Transaminase elevations normalized with time, most often after suspending treatment (SOMAVERT (pegvisomant) should be used in accordance with the information presented in Table 4 with respect to liver test abnormalities).

DRUG INTERACTIONS

Acromegalic patients with diabetes mellitus being treated with insulin and/or oral hypoglycemic agents may require dose reductions of these therapeutic agents after the initiation of therapy with SOMAVERT (pegvisomant) . In clinical studies, patients on opioids often needed higher serum pegvisomant concentrations to achieve appropriate IGF-I suppression compared with patients not receiving opioids. The mechanism of this interaction is not known.

Drug/Laboratory Test Interactions

Pegvisomant has significant structural similarity to GH, which causes it to cross-react in commercially available GH assays. Because serum concentrations of pegvisomant at therapeutically effective doses are generally 100 to 1000 times higher than endogenous serum GH levels seen in patients with acromegaly, commercially available GH assays will overestimate true GH levels. Treatment with SOMAVERT (pegvisomant) should therefore not be monitored or adjusted based on serum GH concentrations reported from these assays. Instead, monitoring and dose adjustments should only be based on serum IGF-I levels.

Last reviewed on RxList: 8/13/2010
This monograph has been modified to include the generic and brand name in many instances.