Drug Guide
Hydrochlorothiazide; Metoprolol Tartrate
Classification
Therapeutic: Antihypertensive, Diuretic
Pharmacological: Beta-blocker (Metoprolol Tartrate), Thiazide diuretic (Hydrochlorothiazide)
FDA Approved Indications
- Hypertension
- Heart failure
- Prevention of myocardial infarction
Mechanism of Action
Hydrochlorothiazide inhibits sodium reabsorption in the distal convoluted tubule, promoting diuresis; Metoprolol selectively blocks beta-1 adrenergic receptors, reducing heart rate, cardiac output, and blood pressure.
Dosage and Administration
Adult: Typically 25-100 mg once daily in divided doses for Hydrochlorothiazide, and 25-100 mg once daily for Metoprolol, adjusted based on clinical response.
Pediatric: Use not established; consult pediatric specialist.
Geriatric: Start at lower doses; monitor renal function and blood pressure closely.
Renal Impairment: Adjust dose accordingly; caution as diuretics may cause electrolyte imbalance.
Hepatic Impairment: Use with caution; monitor closely, as metabolism may be affected.
Pharmacokinetics
Absorption: Hydrochlorothiazide is well absorbed; Metoprolol has moderate bioavailability (~50%).
Distribution: Widely distributed; Metoprolol crosses the blood-brain barrier.
Metabolism: Metoprolol is extensively metabolized in the liver; Hydrochlorothiazide undergoes minimal metabolism.
Excretion: Primarily via renal with active renal tubular secretion for Hydrochlorothiazide; Metoprolol excreted mainly via urine.
Half Life: Hydrochlorothiazide: ~6-15 hours; Metoprolol: ~3-7 hours.
Contraindications
- Known hypersensitivity to thiazides or beta-blockers
- Severe bradycardia
- Second or third degree AV block without pacemaker
Precautions
- Asthma or COPD (beta-blocker caution), Diabetes (may mask hypoglycemia), Liver impairment, Electrolyte disturbances, Peripheral vascular disease
Adverse Reactions - Common
- Dizziness (Common)
- Fatigue (Common)
- Hypokalemia (Common)
Adverse Reactions - Serious
- Bradycardia (Uncommon)
- Hypotension (Uncommon)
- Electrolyte imbalance (hypokalemia, hyponatremia) (Uncommon)
- Bronchospasm (Rare)
Drug-Drug Interactions
- Other antihypertensives, Digoxin, NSAIDs, Diabetes medications
Drug-Food Interactions
- Alcohol may enhance hypotensive effects
Drug-Herb Interactions
- Ginseng, Licorice (may increase potassium loss)
Nursing Implications
Assessment: Monitor blood pressure, heart rate, and electrolytes regularly.
Diagnoses:
- Risk for electrolyte imbalance
- Ineffective tissue perfusion
Implementation: Administer with food to decrease GI upset; monitor for adverse reactions.
Evaluation: Assess blood pressure response, electrolyte levels, and cardiac status.
Patient/Family Teaching
- Take medication exactly as prescribed.
- Report signs of electrolyte imbalance (muscle weakness, cramps), bradycardia, or unusual fatigue.
- Use caution when driving or operating machinery.
- Avoid sudden position changes to reduce dizziness.
Special Considerations
Black Box Warnings:
- None specifically for this combination, but be cautious of abrupt withdrawal leading to chest pain or myocardial infarction.
Genetic Factors: Beta-blocker response may vary based on genetic polymorphisms.
Lab Test Interference: May alter glucose and electrolyte measurements.
Overdose Management
Signs/Symptoms: Bradycardia, hypotension, dizziness, chest pain.
Treatment: Discontinue medication immediately; supportive care, atropine for bradycardia, vasopressors for hypotension, activated charcoal if within 1-2 hours of ingestion.
Storage and Handling
Storage: Store at room temperature away from moisture and heat.
Stability: Stable under recommended conditions for shelf life indicated on packaging.