Medical treatment for growth-hormone secreting tumours do not cause significant shrinkage of the pituitary adenoma. Medical treatments are used to reduce growth hormone (GH) concentrations whilst radiotherapy is beginning to take effect, and for patients who fail treatment with surgery and radiotherapy.
- dopamine agonists - except in mammosomatotroph tumours (ie tumours that secrete GH and prolactin), these are generally not very effective (1)
- dopamine agonists (DAs) stimulate GH release in normal individuals, but paradoxically in patients with acromegaly suppress GH secretion
- unfortunately, bromocriptine suppresses serum GH below the suboptimal level of 10mU per litre in less than 20 per cent of patients and normalises serum IGF-I in 10 per cent (2)
- newer DAs like cabergoline and quinagolide normalise serum IGF-I in approximately 40 per cent of patients and are better tolerated (2)
- DAs are more effective where there is co-secretion of prolactin
- somatostatin anologues e.g. octreotide
- currently the most effective medical treatment of acromegaly and reduces growth hormone concentrations in most cases
- reduction of growth hormone concentrations is to below 5 mU/l in 30% of cases and below 10 mU/l in 50%
- the ability of octreotide to normalise serum IGF-I is dependent on pre-octreotide serum GH levels and SMS receptor expression by the pituitary tumour (2)
- combinations of octreotide and DAs may prove more effective than either treatment alone (2)
- long-acting depot preparations of SMS analogues have been developed for fortnightly or monthly administration
Reference:
- Prescribers' Journal (2000); 40 (2): 86-92.
- Prescriber (2003); 15 (14): 55-62.
- Editorial (1993).Acromegaly:treatment after 100 years. BMJ; 307:1505-6.