Preterm infants are at risk to develop nephrocalcinosis. Incidence numbers vary according to birth weight and gestation age. Very low birth weight infants have the highest risk index, with ~ 7-10 % of preterm infants developing nephrocalcinosis in the patient population. We, the researchers at the University of Cologne, and others found significantly decreased urinary citrate excretion (hypocitraturia) to be one of the main risk factors. Hence, we hypothesized, that prophylactic treatment with oral alkaline citrate solution (Shol's solution) would help to 1) increase urinary citrate excretion and 2) help to decrease the incidence of nephrocalcinosis.

Inclusion Criteria:

• Preterm infants < 32 weeks gestation age and < 1500 g birth weight

Exclusion Criteria:

• Cardial, renal or gastrointestinal malformations
• Chronic renal failure
• Therapy with vitamin B6
• High dose treatment with furosemide or dexamethasone
• Addison's disease
• Severe metabolic alkalosis
• Worse clinical condition of preterm infant, which makes oral feeding impossible
• Participation in other studies