Background: The Cystic Fibrosis Foundation recommends both short-term and long-acting insulin therapy when cystic fibrosis-related diabetes has been diagnosed. Diagnosis is based on: an elevated fasting blood glucose level greater than 6.94 mmol/liter (125 mg/deciliter); or oral glucose tolerance tests greater than 11.11 mmol/liter (200 mg/deciliter) at two hours; or symptomatic diabetes for random glucose levels greater than 11.11 mmol/liter (200 mg/deciliter); or glycated hemoglobin levels of at least 6.5%.
Objectives: To establish the effectiveness of insulin and oral agents for managing diabetes in people with cystic fibrosis in relation to blood sugar levels, lung function and weight management.
Search methods: We searched the Cochrane Cystic Fibrosis and Genetic Disorders Group's Trials Register comprising references identified from comprehensive electronic database searches and handsearches of relevant journals and abstract books of conference proceedings. We also handsearched abstracts from pulmonary symposia and the North American Cystic Fibrosis Conferences.Date of the most recent search of the Group's Cystic Fibrosis Trials Register: 18 February 2016.
Selection criteria: Randomized controlled trials comparing all methods of diabetes therapy in people with diagnosed cystic fibrosis-related diabetes.
Data collection and analysis: Two authors independently extracted data and assessed the risk of bias in the included studies.
Main results: The searches identified 22 trials (34 references). Four trials (200 participants) are included: one short-term single-center trial (n = 7) comparing insulin with oral repaglinide and no medication in people with cystic fibrosis-related diabetes and normal fasting glucose; one long-term multicenter trial (n = 100, 74 of whom had cystic fibrosis-related diabetes) comparing insulin with oral repaglinide and placebo; one long-term multicenter trial (n = 73) comparing insulin with oral repaglinide; and one 12-week single-center trial (n = 20) comparing the long-acting insulin glargine to short-term neutral protamine Hagedorn insulin.Two trials with data for the comparison of insulin to placebo did not report any significant differences between groups for the primary outcomes of blood glucose levels, lung function and nutritional status. This was also true for the single trial with data for the comparison of repaglinide to placebo. Two trials (one lasting one year and one lasting two years) contributed data for the comparison of insulin versus repaglinide. There were no significant differences for the primary outcomes at any time point, except at one year (in the two-year trial) when the insulin group had significant improvement in z score for body mass index compared to the repaglinide group. The single trial comparing glargine to neutral protamine Hagedorn insulin also did not report any significant differences in the review's primary outcomes. A few cases of hypoglycemia were seen in three out of the four trials (none in the longest trial), but these events resolved without further treatment.There was an unclear risk of bias from randomization and allocation concealment in two of the four included trials as the authors did not report any details; in the remaining two studies details for randomization led to a low risk of bias, but only one had sufficient details on allocation concealment to allow a low risk judgement, the second was unclear. There was a high risk from blinding for all trials (except for the comparison of oral repaglinide versus placebo) due to the nature of the interventions. Complete data for all outcomes were not available from any trial leading to a high risk of reporting bias. The amounts of insulin and repaglinide administered were not comparable and this may lead to bias in the results. None of the included trials were powered to show a significant improvement in lung function.
Authors' conclusions: This review has not found any significant conclusive evidence that long-acting insulins, short-acting insulins or oral hypoglycemic agents have a distinct advantage over one another in controlling hyperglycemia or clinical outcomes associated with cystic fibrosis-related diabetes. While some cystic fibrosis centers use oral medications to help control diabetes, the Cystic Fibrosis Foundation (USA) clinical practice guidelines support the use of insulin therapy and this remains the most widely-used treatment method. Randomized controlled trials specifically related to controlling diabetes with this impact on the course of pulmonary disease process in cystic fibrosis continue to be a high priority.There is no demonstrated advantage yet established for using oral hypoglycemic agents over insulin, and further trials need to be evaluated to establish whether there is clear benefit for using hypoglycemic agents. Agents that potentiate insulin action, especially agents with additional anti-inflammatory potential should be further investigated to see if there may be a clinical advantage to adding these medications to insulin as adjuvant therapy.