Acid Base Pharmacotherapy

Acid base pharmacotherapy corrects metabolic acidosis and alkalosis when the cause cannot be removed quickly or the disturbance threatens organ function. Treating the cause (restoring perfusion, insulin in diabetic ketoacidosis, removing toxins, relieving obstruction) comes first. Alkali therapy buys time in selected cases only.

Classification. Alkalinising agents (sodium bicarbonate, sodium lactate, sodium acetate, citrate, tromethamine); carbonic anhydrase inhibitors (acetazolamide); chloride and potassium replacement for alkalosis; antidotes for toxic acidosis.

Mechanism. Bicarbonate buffers hydrogen ions directly and raises pH. Acetazolamide increases renal bicarbonate excretion and corrects metabolic alkalosis. Chloride-rich fluids correct chloride-responsive alkalosis. Oral alkali in kidney disease reduces bone and muscle loss.

Drug	Dose	Use
Sodium bicarbonate 8.4%	50 mL (50 mmol) over 15 to 30 minutes, central line preferred	Severe acidosis, hyperkalaemia, tricyclic or sodium channel blocker poisoning
Sodium bicarbonate 1.26% or 1.4%	250 to 500 mL over 1 to 4 hours	Mild to moderate acidosis with volume depletion
Oral sodium bicarbonate	500 mg to 1 g (6 to 12 mmol) two to three times daily	Chronic metabolic acidosis in kidney disease; target serum bicarbonate 22 mmol/L or more
Sodium citrate	10 to 30 mL of 1 mol/L solution in divided doses	Renal tubular acidosis, stone prevention
Acetazolamide	250 to 500 mg once or twice daily, or 500 mg intravenously	Metabolic alkalosis with fluid overload, altitude sickness
Sodium chloride 0.9% with potassium chloride	As required	Chloride-responsive alkalosis (vomiting, diuretics)
Hydrochloric acid or ammonium chloride	Specialist use	Severe alkalosis unresponsive to other measures
Fomepizole	15 mg/kg, then 10 mg/kg every 12 hours	Methanol and ethylene glycol poisoning (toxicology advice)

Calculating bicarbonate. Dose in mmol approximates 0.3 multiplied by weight (kg) multiplied by the base deficit. Give half, then recheck.

Acute use. Reserve for pH under 7.1 or 7.2 with acute kidney injury, or specific toxic causes. Routine use in lactic acidosis or diabetic ketoacidosis does not improve outcomes.

First-line. Treat the cause; oral alkali for chronic acidosis in kidney disease; saline with potassium for vomiting-related alkalosis.
Alternative. Citrate in renal tubular acidosis and stone disease; acetazolamide in volume-overloaded alkalosis.
Specialist. Dialysis, continuous renal replacement therapy, tromethamine, ventilator strategies, toxic alcohol poisoning.
Emergency. Severe acidosis with arrhythmia, hyperkalaemia, tricyclic or sodium channel blocker toxicity, or salicylate poisoning.

Selection. Use bicarbonate for specific indications and avoid it as a routine. Use central lines for concentrated solutions. Correct the cause and check the anion gap.

Contraindications. Bicarbonate: metabolic alkalosis, hypocalcaemia that is not corrected, hypokalaemia, severe volume overload. Acetazolamide: sulfonamide allergy, severe kidney or liver disease, hyperchloraemic acidosis.

Serious adverse effects.

Sodium and fluid overload, hypernatraemia, pulmonary oedema.
Hypokalaemia and hypocalcaemia, overshoot alkalosis, paradoxical intracellular acidosis.
Tissue necrosis with extravasation of concentrated bicarbonate.
Acetazolamide: paraesthesia, metabolic acidosis, kidney stones, rash.

Major interactions. Bicarbonate precipitates with calcium; raises urine pH and changes excretion of salicylate, lithium and aspirin; acetazolamide with aspirin (toxicity), phenytoin and topiramate.

Common prescribing errors.

Giving bicarbonate in a peripheral line at high concentration.
Using it routinely in lactic acidosis or diabetic ketoacidosis.
Forgetting the sodium load.
Overcorrecting and causing alkalosis and hypokalaemia.
Treating the number without finding the cause.

Special groups.

Pregnancy: treat the cause; bicarbonate acceptable if needed.
Breastfeeding: compatible.
Children: weight-based; seek paediatric advice.
Older adults: sodium and fluid load can precipitate heart failure.
Kidney: oral bicarbonate is the usual treatment for chronic acidosis, but watch for fluid retention and blood pressure.
Liver: lactate-based solutions are poorly metabolised; use bicarbonate or acetate.
East Africa: severe dehydration with metabolic acidosis from diarrhoea is common in children, and oral rehydration solution is the first treatment; 8.4% bicarbonate may be stocked but isotonic bicarbonate may not be, so dilute 8.4% under a written local procedure.

Monitoring. Arterial or venous blood gas, serum bicarbonate, anion gap, potassium, calcium, sodium and lactate; repeat 30 to 60 minutes after bolus.

Referral and escalation. pH under 7.1, rising lactate, toxic ingestion, kidney failure needing dialysis, or unexplained gap.

Comparison with alternative classes. Alkali therapy supports the patient while the cause is treated. Dialysis corrects acidosis and toxins together. Fluids and ventilation correct many disturbances without alkali.

Acid Base Pharmacotherapy

Class Overview And Mechanism

Members And Pharmacological Differences

Clinical Uses And Class Selection

Class Safety, Contraindications, Monitoring And Comparison With Alternative Classes