Mechanism of action
Sodium bicarbonate (NaHCO₃) dissociates in aqueous solution to provide bicarbonate (HCO₃⁻) and sodium (Na⁺) ions. Bicarbonate acts as a physiologic buffer by accepting hydrogen ions according to the equilibrium:
HCO₃⁻ + H⁺ ⇌ H₂CO₃ ⇌ H₂O + CO₂
This buffering action increases blood pH and serum bicarbonate concentration, thereby correcting metabolic acidosis. The carbon dioxide produced is eliminated via the lungs. In the renal tubules, bicarbonate increases urinary pH, promoting ionization and renal excretion of weak acids such as salicylates, methotrexate, and barbiturates. Alkalinization also reduces the cardiotoxic effects of tricyclic antidepressants by decreasing drug binding to sodium channels in cardiac myocytes. The sodium load delivered also contributes to the therapeutic effect in certain overdoses.
- Sodium bicarbonate is first-line for tricyclic antidepressant cardiotoxicity (QRS >100 ms); target pH 7.45-7.55
- Urinary alkalinization (pH 7.5-8.0) dramatically enhances renal elimination of salicylates, methotrexate, and phenobarbital
- Not routinely recommended in cardiac arrest or diabetic ketoacidosis unless pH extremely low (<7.0)
- Generates CO₂ that requires pulmonary elimination; can worsen intracellular acidosis if ventilation inadequate
- Each gram contains 12 mEq sodium; risk of volume overload and heart failure exacerbation in susceptible patients
- Alkalosis shifts potassium intracellularly, causing or worsening hypokalemia and predisposing to arrhythmias
- Alkalosis reduces ionized calcium (increased protein binding), potentially causing tetany and paresthesias
- Hypertonic 8.4% solution (2000 mOsm/L) can cause severe hyperosmolality if given too rapidly, especially in neonates
Indications
Metabolic acidosis: Sodium bicarbonate is indicated for severe metabolic acidosis, particularly when pH is below 7.1-7.2 or serum bicarbonate is critically low. It is used in conditions such as lactic acidosis, renal tubular acidosis, and severe diarrhea-induced acidosis.
Diabetic ketoacidosis: Bicarbonate is NOT routinely recommended in DKA, even as adjunctive therapy, unless pH is extremely low (<6.9-7.0). Routine use does not improve outcomes and may worsen hypokalemia and paradoxical CNS acidosis. Insulin therapy corrects the acidosis.
Cardiac arrest: Used during advanced cardiac life support (ACLS) in prolonged cardiac arrest, particularly when associated with hyperkalemia or tricyclic antidepressant overdose. Routine use in cardiac arrest is no longer recommended.
Poisoning and overdose: Essential for urinary alkalinization in salicylate (aspirin) overdose, methotrexate toxicity, and certain chemotherapy agents. It is also the primary antidote for tricyclic antidepressant cardiotoxicity (QRS widening) by overcoming sodium channel blockade.
Urinary alkalinization: Used to prevent precipitation of certain drugs in renal tubules (methotrexate, sulfamethoxazole) and to enhance renal excretion of weak acids. Also used prophylactically to reduce tumor lysis syndrome risk.
Hyperkalemia: Provides temporary reduction in serum potassium by promoting intracellular shift of potassium ions, though this effect is modest and transient.
Chronic kidney disease: Long-term oral therapy may slow progression of chronic kidney disease in patients with metabolic acidosis.
Pharmacokinetics
Absorption: Oral sodium bicarbonate is rapidly and completely absorbed from the gastrointestinal tract. Intravenous administration provides immediate systemic availability.
Distribution: Bicarbonate is distributed throughout the extracellular fluid compartment. It does not significantly cross cell membranes but participates in the bicarbonate-carbonic acid buffer system in blood and extracellular fluid.
Metabolism: Bicarbonate is converted to carbonic acid (H₂CO₃) when it accepts hydrogen ions. Carbonic anhydrase in red blood cells catalyzes the dissociation of carbonic acid to water and carbon dioxide. The CO₂ is then eliminated via pulmonary ventilation.
Excretion: Bicarbonate is freely filtered at the glomerulus and largely reabsorbed in the proximal tubule. Excess bicarbonate that exceeds reabsorptive capacity is excreted in urine, increasing urinary pH. The kidneys regulate bicarbonate homeostasis according to acid-base status.
Onset and duration: Intravenous sodium bicarbonate acts within minutes to raise blood pH. Duration depends on the underlying condition and rate of continued acid production. Oral preparations typically act within 15-30 minutes.
Adverse effects
Metabolic alkalosis: Overzealous administration can cause metabolic alkalosis, leading to compensatory hypoventilation, decreased cerebral blood flow, cardiac arrhythmias, and tetany. Alkalosis shifts the oxygen-hemoglobin dissociation curve leftward, impairing tissue oxygen delivery.
Sodium and fluid overload: Each gram of sodium bicarbonate contains 12 mEq of sodium. Excessive sodium load can precipitate or worsen heart failure, pulmonary edema, hypertension, and peripheral edema, particularly in patients with renal or cardiac impairment.
Hypokalemia: Alkalosis promotes intracellular shift of potassium, potentially causing or worsening hypokalemia. This can precipitate cardiac arrhythmias, particularly in digitalized patients.
Hypocalcemia: Alkalosis increases protein binding of calcium, reducing ionized calcium levels. This can cause paresthesias, muscle cramps, tetany, and seizures.
Paradoxical intracellular acidosis: In patients with poor ventilation, bicarbonate generates CO₂ that may not be adequately eliminated. CO₂ readily crosses cell membranes and can worsen intracellular acidosis, particularly in the central nervous system and myocardium.
Gastrointestinal effects: Oral administration can cause gastric distention, belching, flatulence, and abdominal discomfort due to CO₂ generation. Rapid oral intake may cause gastric rupture in rare cases.
Extravasation injury: Intravenous extravasation can cause tissue necrosis, ulceration, and sloughing due to the alkaline nature of the solution.
Rebound metabolic acidosis: After discontinuation, particularly if underlying acid production continues, rebound acidosis may occur.
Contraindications and warnings
Contraindications:
- Metabolic or respiratory alkalosis
- Hypocalcemia (may precipitate tetany)
- Severe pulmonary edema or heart failure with sodium retention
- Hypernatremia
- Unknown abdominal pain (oral use may mask surgical conditions)
Warnings and precautions:
Renal impairment: Use with caution as sodium and fluid overload risk is increased. Patients may have impaired ability to excrete excess bicarbonate.
Cardiac disease: The sodium load can exacerbate heart failure and hypertension. Monitor fluid status closely.
Hypokalemia: Correct potassium deficits before or during bicarbonate therapy to avoid dangerous drops in serum potassium.
Pregnancy: Sodium bicarbonate is generally considered compatible with pregnancy when clinically indicated for metabolic acidosis. However, routine use as an antacid should be avoided due to sodium load.
Inadequate ventilation: Ensure adequate ventilation before administering bicarbonate, as CO₂ production requires pulmonary elimination. In patients who cannot increase minute ventilation, bicarbonate may worsen acidosis.
Laboratory monitoring: Monitor arterial blood gases, serum electrolytes (sodium, potassium, calcium), and renal function during therapy. Overshoot alkalosis is common without careful monitoring.
Rate of administration: Rapid intravenous push can cause severe alkalosis, hypernatremia, hyperosmolality, and decreased ionized calcium. Administration should generally be controlled except in emergency situations like tricyclic antidepressant-induced QRS widening.
Drug interactions
Lithium: Urinary alkalinization increases renal lithium clearance, potentially reducing lithium levels and therapeutic efficacy. Conversely, discontinuation of chronic bicarbonate may increase lithium levels.
Salicylates: Alkalinization of urine is therapeutically exploited in salicylate overdose to enhance elimination. However, in chronic salicylate therapy, increased renal excretion may reduce therapeutic levels.
Amphetamines: Urinary alkalinization decreases renal excretion of amphetamines and related sympathomimetics, potentially increasing toxicity.
Quinidine and quinine: Alkaline urine reduces excretion, increasing serum levels and risk of toxicity.
Tetracyclines: Oral sodium bicarbonate may reduce absorption of tetracycline antibiotics by increasing gastric pH. Separate administration by at least 2 hours.
Fluoroquinolones: Formation of insoluble complexes in alkaline urine may reduce efficacy, though this is uncommon clinically.
Methotrexate: Urinary alkalinization reduces methotrexate precipitation in renal tubules and enhances excretion, reducing nephrotoxicity. This is a beneficial interaction used therapeutically.
Anticholinergics: Concurrent use with sodium bicarbonate may increase urinary pH, affecting excretion of basic drugs.
Enteric-coated medications: Premature dissolution may occur in the stomach if pH is elevated, potentially increasing gastric irritation or inactivating acid-labile drugs.
Calcium-containing products: Combined use increases risk of milk-alkali syndrome (hypercalcemia, metabolic alkalosis, renal insufficiency), particularly with chronic administration.
Clinical pearls
Do not use bicarbonate routinely in cardiac arrest: Current ACLS guidelines do not recommend routine bicarbonate use during cardiac arrest unless specific indications exist (hyperkalemia, tricyclic antidepressant overdose, preexisting severe metabolic acidosis).
Urinary alkalinization: In salicylate overdose, target urine pH of 7.5-8.0. Hypokalemia must be corrected simultaneously, as low potassium prevents effective urinary alkalinization.
Tricyclic antidepressant overdose: Sodium bicarbonate is first-line therapy when QRS duration exceeds 100 milliseconds in tricyclic antidepressant poisoning. The therapeutic goal is serum pH 7.45-7.55.
Calculate bicarbonate deficit carefully: The formula [0.5 × weight(kg) × (desired HCO₃⁻ - actual HCO₃⁻)] estimates deficit, but give only half initially and reassess.
Ensure CO₂ can be eliminated: Bicarbonate therapy generates CO₂. Without adequate ventilation, this worsens intracellular acidosis. Confirm the patient is adequately ventilated.
Osmolality: Hypertonic sodium bicarbonate (8.4%) has osmolality of approximately 2000 mOsm/L. Rapid administration can cause hyperosmolar states, particularly in neonates.
Extravasation is serious: If IV infiltrates, stop immediately and assess for tissue injury. The alkaline solution causes severe tissue necrosis.
Diabetic ketoacidosis: Bicarbonate is generally not recommended unless pH is below 6.9-7.0. Routine use does not improve outcomes and may worsen hypokalemia and paradoxical CNS acidosis.
Compatibility: Sodium bicarbonate is incompatible with many intravenous medications including calcium, catecholamines, and atropine. Use a separate IV access.
BICARB uses: Buffering acidosis, Intoxication (TCA, ASA), Cardiac arrest (specific indications), Alkalinize urine, Renal tubular acidosis, rhabdomyolysis
Practice questions
1. A 28-year-old woman is brought to the emergency department 2 hours after ingesting 30 tablets of amitriptyline in a suicide attempt. Her blood pressure is 95/60 mm Hg and pulse is 120/min. ECG shows QRS duration of 140 milliseconds and rightward terminal QRS axis. Which of the following is the most appropriate initial pharmacologic therapy?
2. A 19-year-old man with a history of depression is brought to the emergency department after ingesting an unknown quantity of aspirin tablets. Laboratory studies show: pH 7.28, PaCO2 22 mm Hg, serum bicarbonate 10 mEq/L, and salicylate level 85 mg/dL. Urine pH is 5.5. In addition to supportive care, which of the following interventions will most effectively enhance drug elimination?
3. A 65-year-old man with chronic kidney disease is admitted with severe metabolic acidosis (pH 7.05, bicarbonate 8 mEq/L). He is alert but tachypneic. After initial sodium bicarbonate infusion, repeat blood gas shows pH 7.58 and bicarbonate 32 mEq/L. He now complains of perioral tingling and muscle cramping. Which of the following best explains his new symptoms?
Frequently asked questions
How does sodium bicarbonate work?
Sodium bicarbonate dissociates to provide bicarbonate ions (HCO₃⁻) that act as a buffer by accepting hydrogen ions (H⁺), forming carbonic acid that breaks down to water and carbon dioxide. This buffering action increases blood pH and corrects metabolic acidosis. In the kidneys, bicarbonate raises urinary pH, promoting excretion of weak acids like salicylates. The CO₂ produced must be eliminated through the lungs, so adequate ventilation is essential for bicarbonate therapy to work effectively.
What are the side effects of sodium bicarbonate?
The main side effects include metabolic alkalosis from excessive dosing, which can cause confusion, arrhythmias, and decreased tissue oxygen delivery. Sodium and fluid overload can precipitate heart failure and pulmonary edema, especially in susceptible patients. Hypokalemia occurs because alkalosis shifts potassium into cells, potentially causing dangerous arrhythmias. Hypocalcemia manifests as tetany and paresthesias. Paradoxical intracellular acidosis can develop if CO₂ generation exceeds pulmonary elimination capacity, particularly affecting the brain and heart. Gastrointestinal distress and extravasation tissue injury are also possible.
When is sodium bicarbonate used in cardiac emergencies?
Sodium bicarbonate is used in cardiac arrest primarily for specific indications rather than routinely. These include hyperkalemia-induced arrest, tricyclic antidepressant overdose with QRS widening, and preexisting severe metabolic acidosis. In tricyclic poisoning, bicarbonate overcomes sodium channel blockade and is first-line when QRS exceeds 100 milliseconds. Current ACLS guidelines do not recommend routine bicarbonate use during standard cardiac arrest because the acidosis is primarily respiratory and requires ventilation, not chemical buffering. Inappropriate use can worsen outcomes by causing alkalosis and paradoxical intracellular acidosis.
Why is sodium bicarbonate given in salicylate overdose?
Sodium bicarbonate is given to alkalinize the urine (target pH 7.5-8.0) in salicylate overdose. Salicylate is a weak acid that becomes ionized in alkaline urine, trapping it in the renal tubules and dramatically enhancing renal excretion. This urinary alkalinization can increase salicylate clearance several-fold and is a cornerstone of treatment for moderate to severe toxicity. Additionally, systemic alkalinization may reduce salicylate distribution into the central nervous system. The therapy requires frequent monitoring of urine pH and serum electrolytes, as hypokalemia can prevent successful alkalinization.
Sodium bicarbonate vs sodium chloride — what is the difference?
Sodium bicarbonate contains sodium and bicarbonate ions and acts as an alkalinizing agent that buffers acids and raises pH. It is used therapeutically to treat metabolic acidosis and alkalinize urine. Sodium chloride (normal saline) contains sodium and chloride ions and serves as isotonic fluid replacement without directly affecting acid-base balance. While both provide sodium load, sodium bicarbonate specifically addresses acidosis and can cause metabolic alkalosis if overused, whereas sodium chloride maintains neutral pH. In hyperchloremic metabolic acidosis, excessive saline administration can worsen acidosis, while bicarbonate would be corrective.
Conditions it is used for
Related drugs
Sources and further reading
DailyMed (FDA labels)StatPearls (NCBI Bookshelf)MedlinePlusWHO ATC/DDD index: B05XA02WHO ATC/DDD index: B05CB04
Educational content for medical students, prepared by the WhiteCoat Pro editorial team with AI assistance; every page is reviewed by a second AI model for factual errors. It is not medical advice and does not replace the product label, local guidelines or a clinician.