Several cases of overdosage with metoprolol have been reported, some leading to death. No deaths have been reported with hydrochlorothiazide.
Oral LD50's (mg/kg): mice, 1,158 (metoprolol); rats, 3,090 (metoprolol), 2,750 (hydrochlorothiazide).
Signs and Symptoms
Potential signs and symptoms associated with overdosage with metoprolol are bradycardia, hypotension, bronchospasm, and cardiac failure.
The most prominent feature of poisoning is acute loss of fluid and electrolytes.
Cardiovascular: Tachycardia, hypotension, shock.
Neuromuscular: Weakness, confusion, dizziness, cramps of the calf muscles, paresthesia, fatigue, impairment of consciousness.
Digestive: Nausea, vomiting, thirst.
Renal: Polyuria, oliguria, or anuria (due to hemoconcentration).
Laboratory Findings: Hypokalemia, hyponatremia, hypochloremia, alkalosis; increased BUN (especially in patients with renal insufficiency).
Combined Poisoning: Signs and symptoms may be aggravated or modified by concomitant intake of antihypertensive medication, barbiturates, curare, digitalis (hypokalemia), corticosteroids, narcotics, or alcohol.
There is no specific antidote.
On the basis of the pharmacologic actions of metoprolol tartrate tablets and hydrochlorothiazide, the following general measures should be employed:
Elimination of the Drug
Inducement of vomiting, gastric lavage, and activated charcoal.
Atropine should be administered. If there is no response to vagal blockade, isoproterenol should be administered cautiously.
The patient's legs should be elevated and lost fluid and electrolytes (potassium, sodium) should be replaced. A vasopressor should be administered, e.g., levarterenol or dopamine.
A beta2-stimulating agent and/or a theophylline derivative should be administered.
A digitalis glycoside and diuretic should be administered. In shock resulting from inadequate cardiac contractility, administration of dobutamine, isoproterenol, or glucagon may be considered.
Fluid and electrolyte balance (especially serum potassium) and renal function should be monitored until conditions become normal.