Single oral doses of amlodipine maleate equivalent to 40 mg amlodipine/kg and 100
mg amlodipine/kg in mice and rats, respectively, caused deaths. Single oral amlodipine
maleate doses equivalent to 4 or more mg amlodipine/kg or higher in dogs (11 or
more times the maximum recommended human dose on a mg/m² basis) caused a marked
peripheral vasodilation and hypotension.
Overdosage might be expected to cause excessive peripheral vasodilation with marked
hypotension and possibly a reflex tachycardia. In humans, experience with intentional
overdosage of NORVASC is limited. Reports of intentional overdosage include a patient
who ingested 250 mg and was asymptomatic and was not hospitalized; another (120
mg) was hospitalized, underwent gastric lavage and remained normotensive; the third
(105 mg) was hospitalized and had hypotension (90/50 mmHg) which normalized following
plasma expansion. A case of accidental drug overdose has been documented in a 19-month-old
male who ingested 30 mg amlodipine (about 2 mg/kg). During the emergency room presentation,
vital signs were stable with no evidence of hypotension, but a heart rate of 180
bpm. Ipecac was administered 3.5 hours after ingestion and on subsequent observation
(overnight) no sequelae were noted.
If massive overdose should occur, active cardiac and respiratory monitoring should
be instituted. Frequent blood pressure measurements are essential. Should hypotension
occur, cardiovascular support including elevation of the extremities and the judicious
administration of fluids should be initiated. If hypotension remains unresponsive
to these conservative measures, administration of vasopressors (such as phenylephrine)
should be considered with attention to circulating volume and urine output. Intravenous
calcium gluconate may help to reverse the effects of calcium entry blockade. As
NORVASC is highly protein bound, hemodialysis is not likely to be of benefit.