Long term reduction in sodium balance: possible additional mechanism whereby nifedipine lowers blood pressure.

OBJECTIVE

To assess the changes in sodium excretion and sodium balance after withdrawal of long term nifedipine.

DESIGN

Single blind, placebo controlled study in patients receiving fixed sodium and potassium intakes.

SETTING

Blood pressure unit of a teaching hospital in south London.

PATIENTS

Eight patients with mild to moderate uncomplicated essential hypertension who had been taking nifedipine 20 mg twice daily for at least six weeks.

INTERVENTIONS

Withdrawal of nifedipine and replacement with matching placebo for one week.

MAIN OUTCOME MEASURES

Urinary sodium excretion and cumulative sodium balance, body weight, plasma atrial natriuretic peptide concentrations, plasma renin activity and aldosterone concentrations, and blood pressure.

RESULTS

During nifedipine withdrawal there was a significant reduction in urinary sodium excretion (day 1: -62.7 mmol/24 h; 95% confidence interval -90.3 to -35.0) and each patient retained a mean of 146 (SEM 26) mmol sodium over the week of replacement with placebo. Body weight and plasma atrial natriuretic peptide concentrations increased during the placebo period and seemed to be associated with the amount of sodium retained. Systolic blood pressure rose from 157 (9) to 165 (9) mmHg (95% confidence interval of difference -7.1 to 22.1) when nifedipine was replaced with matching placebo, and the rise seemed to be related to the amount of sodium that was retained.

CONCLUSIONS

Nifedipine causes a long term reduction in sodium balance in patients with essential hypertension. This long term effect may contribute to the mechanism whereby nifedipine lowers blood pressure.