Optimal Dose of Irbesartan for Renoprotection in Type 2 Diabetic Patients With Persistent Microalbuminuria

Aim:

The primary aim of our study is to evaluate the antiproteinuric effect of irbesartan 300, 600 and 900 mg once daily in type 2 diabetic patients with microalbuminuria. Secondary to evaluate the effect on 24-h ambulatory blood pressure, glomerular filtration rate (GFR), urinary TGF beta excretion, and markers of endothelial dysfunction, and finally to evaluate the association between treatment response and genotypes with possible implications for the risk of cardiovascular disease.

Patients 60 type 2 diabetic patients with persistent microalbuminuria (at least two out of three 24-h urinary collections with albumin excretion between 30 and 300 mg/24-h).

Duration of study 38 weeks (8 weeks wash-out and 30 weeks of double-blind randomized cross-over (treatment with irbesartan 300, 600 and 900 mg for 10 weeks at each dose level)).

Design The study consists of an eight week wash-out period followed by a double-blind randomized three 10 week treatment period cross-over trial (please see enclosed flow chart).

Wash-out period: Eight weeks prior to randomization all previous antihypertensive medication is discontinued and replaced by hydrochlorothiazide 25 mg once daily throughout the entire study period. Hydrochlorothiazide is added to reduce blood pressure elevation and edema formation during the trial and to eliminate the influence of varying dietary salt intake on the effects of irbesartan during the double blind treatment periods.

Double-blind cross-over periods: All patients receive treatment with irbesartan 300, 600 and 900 mg once daily in random order, without wash-out between treatment periods. All treatment periods are of 10 weeks duration. They consist of an initial two week titration period on irbesartan 300 mg o.d. to minimize the risk of adverse events including hypotension during cross-over in doses followed by an eight week period on the full dose for the given treatment level.

For safety reasons blood pressure, serum potassium and serum creatinine will be measured 4 weeks after the beginning of each treatment period (two weeks after the full dose of the treatment period is reached).

End-points are evaluated after the wash-out period (baseline) and at the end of each treatment period.

Methods Albuminuria is assessed by turbidimetry in three 24-h urinary samples. 24-h ambulatory blood pressure by the Takeda TM-2420/2421 device. GFR by plasma clearance of 51Cr-EDTA. DNA will be extracted from a venous sample to determine genotypes with possible implications for the risk of cardiovascular disease. Initially we will evaluate the influence of the ACE/ID- , Angiotensin II type I receptor (A1166C) - and the angiotensinogen (M235T) polymorphisms.

Endpoints Primary endpoint: change in albuminuria Secondary endpoints: 24-h ambulatory blood pressure, glomerular filtration rate (GFR), and to evaluate the association between treatment response genotypes with possible implications for the risk of cardiovascular disease

Inclusion criteria

• Type 2 diabetes (WHO criteria) and age above 18 years.
• Persistent microalbuminuria (urinary albumin excretion between 30 and 300 mg/24-h in at least two out of three 24-urinary collections
• Systolic blood pressure > 110 mmHg

Exclusion criteria

• Serum creatinine > 150 micromol/l
• Known non-diabetic renal disease
• Pregnancy or fertile women not using adequate contraception (intrauterine device, sterilization or oral anticonception)
• Systolic blood pressure persistently > 180 mm Hg or < 100 mm Hg
• Diastolic blood pressure persistently > 105 mm Hg
• Plasma potassium > 4.8 mmol/l
• Heart failure, acute myocardial infarction, unstable angina or coronary by-pass surgery within the previous three months.
• Known intolerance to angiotensin II receptor blockers