Profile of pegvisomant in the management of acromegaly: an evidence based review of its place in therapy

Pegvisomant (PEG) is a genetically engineered growth hormone (GH) analog able to bind and block the GH receptor. PEG blocks all metabolic effects of GH hypersecretion, normalizes insulin-like growth factor I (IGF-I) level and paradoxically produces an increase in GH secretion. When PEG was commercialized, there were some concerns regarding whether the increased GH secretion could cause growth of the residual tumor or cause the overcoming of receptor blockade with loss of efficacy. PEG commercialization was followed by the onset of two main prospective observational studies aiming to evaluate the safety and outcome of PEG long-term treatment: the German Pegvisomant Observational Study and ACROSTUDY. These observational studies, along with several independent studies have provided comprehensive information regarding the actual use, efficacy and safety of long-term treatment with PEG. The efficacy of PEG in clinical setting is somewhat lower than that reported in the pivotal studies, nevertheless PEG normalizes IGF-I levels ranging between 65% and 97% of cases. Side effects in observational studies were uncommon and rarely caused discontinuation of treatment. Liver dysfunction developed in 2.5% of cases, was usually transient and no permanent liver damage was reported. Increased tumor size was developed by about 2.2%-3.2% of acromegalic patients treated with PEG, without differences to that described for other modalities of treatment. Only one third of cases corresponded with true growth after initiation of PEG treatment. Involved mechanism is currently unknown. New modalities of treatments by the combined use of PEG with somatostatin analog or cabergoline have been developed with promising results. Recently, two clinical guidelines written to optimize the use of these treatment modalities and to monitor possible adverse events have been published.