POSSIBLE SYNERGISTIC EFFECT OF METFORMIN AND ENALAPRIL ON THE DEVELOPMENT OF HYPERKALEMIC LACTIC-ACIDOSIS

A 71 year old hypertensive, non insulin-dependent diabetic patient wit h moderate renal insufficiency taking 500 mg/d of metformin and 5 mg/d of enalapril, developed metabolic acidosis characterized by fairly el evated anion gap, hyperchloremia, severe hyperkaliemia, normal plasma level of 3-hydroxybutyric acid, absence of ketonuria and high plasma l evel of lactic acid. This biochemical feature allowed us to ascribe th e pathogenesis of metabolic acidosis, both to the increased plasma lev el of lactic acid and to the type IV renal tubular acidosis syndrome, the precipitating factor being an infection of urinary tract (as we as sumed on the basis of the urine culture). The patient was dehydrated a nd lethargic; the ECG revealed the presence of nonparoxysmal junctiona l tachycardia. The clinical evolution was favorable under the treatmen t with an infusion of isotonic saline solutions, mild alkalinizing sol utions, low-dose regular insulin and antibiotics. It is likely that me tformin and enalapril, regularly taken by this nephropathic patient, c ould have played an iatrogenic role, even if the doses were low. This case highlights the importance of complying with the contraindications of these drugs, to avoid the rare but reported life-threatening compl ications of metformin administration. (C) 1997 Elsevier Science Irelan d Ltd.