Toxicology – Calcium as an Antidotal Therapy

Core Concept

Calcium is an important supportive or antidotal treatment in several toxicologic emergencies.

Major indications include:

• Calcium channel blocker (CCB) poisoning
• Hyperkalemia with cardiac toxicity
• Hypermagnesemia
• Hydrofluoric acid and other fluoride poisoning
• Selected toxin-induced symptomatic hypocalcemia

Older sources also recommended calcium for black widow spider envenomation, but this is no longer considered a reliably effective first-line treatment.

Calcium Preparations

The two major intravenous preparations are:

Calcium Chloride

• Provides substantially more elemental calcium per equivalent volume than calcium gluconate.
• Useful when rapid calcium delivery is required.
• More irritating to peripheral tissues.
• Extravasation can cause severe local tissue injury.

Calcium Gluconate

• Contains less elemental calcium.
• Less irritating to peripheral veins and tissues.
• Often preferred when peripheral IV administration is necessary.
• Commonly used for topical/local treatment of hydrofluoric acid skin exposure.

The preparations are not interchangeable gram-for-gram because they contain different amounts of elemental calcium.

General Mechanisms

Calcium works differently depending on the poisoning.

Hyperkalemia

Stabilizes the cardiac membrane against the electrophysiologic effects of excess potassium.

Hypermagnesemia

Functionally antagonizes some of magnesium’s effects on cardiac and neuromuscular tissues.

Calcium Channel Blocker Poisoning

Raises extracellular calcium availability and may partially overcome impaired calcium entry.

Fluoride Poisoning

Binds fluoride and replaces calcium depleted by fluoride-mediated complex formation.

Calcium Channel Blocker Poisoning

CCB overdose can produce:

• Bradycardia
• Hypotension
• AV block
• Cardiogenic shock
• Vasodilatory shock
• Hyperglycemia
• Altered mental status
• Severe dysrhythmias

Calcium is an important early therapy for clinically significant cardiovascular toxicity.

How Calcium Helps in CCB Poisoning

CCBs reduce calcium entry through L-type calcium channels.

Increasing extracellular calcium can partially overcome this functional blockade and improve:

• Contractility
• Blood pressure
• AV nodal conduction

However, the response is often incomplete or temporary.

Therefore:

Calcium is important, but severe CCB poisoning usually requires more than calcium alone.

Other Treatment in Severe CCB Poisoning

Depending on the clinical pattern, management may also require:

• Hyperinsulinemic euglycemia therapy
• Vasopressors
• Careful fluid resuscitation
• Airway and ventilatory support
• Correction of metabolic abnormalities
• Selected adjunctive therapies
• Extracorporeal circulatory support in refractory shock

Treatment is guided by the mechanism of cardiovascular failure.

Monitoring During CCB Treatment

Monitor:

• Continuous ECG
• Heart rate
• Blood pressure
• Perfusion
• Mental status
• Blood glucose
• Electrolytes
• Acid-base status
• Ionized calcium

Large amounts of calcium may sometimes be required, making repeated measurement particularly important.

Hyperkalemia

Calcium is one of the most important emergency therapies when hyperkalemia produces significant cardiac membrane instability.

ECG abnormalities may include:

• Peaked T waves
• PR prolongation
• P-wave attenuation or loss
• QRS widening
• Bradyarrhythmias
• Sine-wave morphology
• Ventricular dysrhythmias

However, ECG changes do not always follow a predictable sequence.

Severe hyperkalemia may exist without classic ECG findings.

What Calcium Does in Hyperkalemia

Calcium:

Stabilizes the myocardium

but it does not meaningfully remove potassium from the body or lower serum potassium concentration.

Therefore calcium must be followed by therapies that:

• Shift potassium intracellularly
• Remove potassium from the body
• Correct the underlying cause

when clinically indicated.

Hyperkalemia Treatment Concept

Think of treatment as three separate goals:

1. Protect the heart

→ Calcium

2. Temporarily shift potassium into cells

→ Insulin/glucose and selected other therapies

3. Remove excess potassium

→ Renal elimination, gastrointestinal potassium binders in selected settings, or dialysis when necessary

Calcium addresses only the first goal.

Digoxin Toxicity and Calcium

Older teaching described calcium as absolutely contraindicated in digoxin toxicity because of concern for so-called “stone heart.”

Modern evidence does not support an absolute prohibition.

If a patient with suspected digoxin toxicity has life-threatening hyperkalemia, calcium is not considered absolutely contraindicated.

However, the definitive antidotal treatment for severe digoxin poisoning is:

Digoxin immune Fab

Management should therefore focus on Fab when clinically indicated rather than relying on calcium.

Hypermagnesemia

Severe magnesium toxicity can produce:

• Nausea
• Flushing
• Hypotension
• Loss of deep tendon reflexes
• Muscle weakness
• Bradycardia
• Conduction abnormalities
• Respiratory depression
• Paralysis
• Cardiac arrest

Calcium can temporarily antagonize magnesium’s effects at cardiac and neuromuscular tissues.

Calcium in Magnesium Toxicity

IV calcium may improve:

• Cardiovascular instability
• Neuromuscular weakness
• Significant conduction abnormalities

But:

Calcium does not remove magnesium from the body.

Definitive management may require:

• Discontinuation of magnesium exposure
• Supportive care
• IV fluids and renal elimination when appropriate
• Dialysis in severe toxicity with renal impairment or refractory manifestations

Hydrofluoric Acid

Hydrofluoric acid (HF) is particularly dangerous because fluoride ions penetrate deeply into tissues.

The fluoride ion binds:

• Calcium
• Magnesium

This can cause:

• Local cellular destruction
• Severe pain
• Hypocalcemia
• Hypomagnesemia
• Hyperkalemia
• QT abnormalities
• Ventricular dysrhythmias
• Cardiac arrest

Small-appearing burns can occasionally produce disproportionately severe toxicity.

Why Calcium Works in HF Exposure

Calcium serves two important functions:

Calcium + fluoride → less biologically active calcium-fluoride complex

and

Calcium replacement → corrects fluoride-induced calcium depletion

Therefore, calcium therapy targets both the toxic fluoride ion and its systemic electrolyte consequences.

HF Skin Exposure

Immediate management begins with:

Prompt, prolonged water irrigation and removal of contaminated clothing

After decontamination, calcium gluconate gel is commonly used for symptomatic dermal HF exposure.

Persistent severe pain can indicate ongoing fluoride activity and deeper tissue injury.

Persistent HF Burns

If pain or tissue toxicity persists despite initial topical treatment, more advanced calcium delivery techniques may occasionally be necessary.

These require specialist management because improperly performed injections or vascular procedures can cause serious complications.

Potential escalation strategies are therefore best handled with:

• Medical toxicology
• Poison-center consultation
• Burn specialists
• Hand/plastic surgery when appropriate

Why Calcium Chloride Is Avoided in Tissue Injection

Calcium chloride is highly irritating and can produce:

• Tissue necrosis
• Severe local injury
• Extravasation damage

Therefore, it should not be injected intradermally or subcutaneously for HF burns.

Calcium gluconate is the safer calcium salt for local tissue treatment.

Systemic HF Poisoning

Severe fluoride exposure may rapidly cause:

• Hypocalcemia
• Hypomagnesemia
• Hyperkalemia
• QT prolongation
• Ventricular dysrhythmias
• Shock
• Cardiac arrest

Aggressive electrolyte monitoring and correction are essential.

Because deterioration can be rapid, severe HF poisoning requires high-acuity monitoring.

ECG in Fluoride Poisoning

ECG abnormalities can provide an early clue to severe electrolyte disruption.

Possible findings include:

• QT prolongation from hypocalcemia
• Conduction abnormalities
• Ventricular ectopy
• Ventricular tachycardia
• Ventricular fibrillation

Continuous ECG monitoring is appropriate in significant systemic exposure.

Other Fluoride Compounds

Similar systemic toxicity may occur with:

• Sodium fluoride
• Ammonium bifluoride
• Other soluble fluoride salts

These can cause:

• Hypocalcemia
• Hypomagnesemia
• Hyperkalemia
• GI injury
• Dysrhythmias

Treatment centers on supportive care and aggressive correction of clinically significant electrolyte disturbances.

Ethylene Glycol

Ethylene glycol metabolism produces oxalic acid.

Oxalate binds calcium and forms calcium oxalate crystals.

This contributes to:

• Hypocalcemia
• Tissue deposition
• Acute kidney injury

However, calcium should not automatically be administered merely because laboratory hypocalcemia is present.

Calcium is generally reserved for clinically important manifestations such as:

• Tetany
• Seizures attributable to hypocalcemia
• Significant dysrhythmia
• Other symptomatic hypocalcemia

Excessive calcium administration could theoretically promote additional calcium oxalate deposition.

Phosphate Poisoning

Large phosphate exposure can lower serum calcium through calcium-phosphate complex formation.

Severe hypocalcemia may produce:

• Paresthesias
• Tetany
• Seizures
• QT prolongation
• Dysrhythmias

Symptomatic or dangerous hypocalcemia may require calcium, while the underlying phosphate disturbance must also be addressed.

Black Widow Spider Envenomation

The older source recommended IV calcium as a major treatment for black widow envenomation.

This recommendation is now considered outdated.

Although calcium was historically proposed to counter venom-mediated alterations in neurotransmitter release, clinical benefit has been inconsistent.

Modern treatment emphasizes:

• Analgesia
• Supportive care
• Treatment of muscle spasm when necessary
• Antivenom for selected severe cases

Calcium is not routinely considered first-line therapy for latrodectism.

Calcium Chloride vs Calcium Gluconate

A practical distinction:

Calcium Chloride

Advantages:

• More elemental calcium
• Rapid calcium delivery

Disadvantages:

• Greater tissue toxicity
• Severe injury if extravasated

Calcium Gluconate

Advantages:

• Less irritating
• Better suited to peripheral administration
• Appropriate for topical HF treatment

Disadvantage:

• Less elemental calcium for an equivalent amount of solution

Extravasation

Calcium extravasation can cause significant tissue injury, particularly with calcium chloride.

Possible complications include:

• Pain
• Swelling
• Inflammation
• Tissue necrosis
• Calcification

If extravasation occurs:

• Stop administration through the affected line.
• Assess the site promptly.
• Follow an appropriate extravasation-management protocol.

Hypercalcemia from Treatment

Aggressive calcium therapy can produce excessive serum calcium.

Possible manifestations include:

• Nausea
• Weakness
• Confusion
• Hypertension
• Bradycardia or dysrhythmias
• Other conduction abnormalities

This is why ionized calcium and ECG findings should be followed during substantial therapy.

Renal Failure

Calcium therapy requires additional caution in patients with renal impairment because they may have:

• Altered calcium/phosphate balance
• Hyperphosphatemia
• Reduced ability to handle electrolyte loads

Treatment should be individualized according to the toxicologic emergency and measured electrolytes.

Pregnancy

Calcium is a normal physiologic electrolyte and can be administered during pregnancy when clinically indicated.

Life-threatening maternal electrolyte or cardiovascular toxicity should be treated promptly.

Monitoring During Significant Calcium Therapy

Monitor:

• Continuous ECG
• Heart rate and rhythm
• Blood pressure
• Ionized calcium
• Potassium
• Magnesium
• Renal function
• Acid-base status when appropriate

For fluoride toxicity, serial electrolyte measurements may need to be particularly frequent because abnormalities can change rapidly.

Important Modernization of the Older Source

Several recommendations in the source require updating:

• Calcium remains an important treatment for CCB toxicity, cardiac effects of hyperkalemia, severe hypermagnesemia, and fluoride toxicity.
• Calcium does not lower serum potassium; it stabilizes the myocardium while other therapies shift or remove potassium.
• The historical absolute contraindication to calcium in digoxin toxicity is no longer supported.
• Digoxin immune Fab remains the specific treatment for severe digoxin poisoning.
• Calcium is not routinely first-line treatment for black widow envenomation.
• In ethylene glycol poisoning, isolated laboratory hypocalcemia does not automatically require calcium; clinically significant symptomatic hypocalcemia is more important.
• Calcium chloride is more tissue-toxic than calcium gluconate and requires particular attention to IV access.
• Advanced HF treatments such as local infiltration, regional perfusion, or intra-arterial calcium should be specialist-directed rather than performed from rigid historical protocols.
• Fixed calcium regimens are less useful than treatment guided by ECG response, hemodynamics, symptoms, and serial ionized calcium measurements.
• Severe CCB poisoning generally requires multimodal therapy rather than calcium alone.

Key Points

• Calcium is an important toxicologic therapy for CCB poisoning, hyperkalemic cardiac toxicity, hypermagnesemia, and fluoride poisoning.
• Calcium chloride contains substantially more elemental calcium than calcium gluconate.
• Calcium chloride causes greater tissue injury if extravasation occurs.
• Calcium gluconate is generally safer through peripheral veins and is used locally for HF skin exposure.
• In CCB poisoning, calcium may improve contractility, blood pressure, and conduction but is often only one component of treatment.
• In hyperkalemia, calcium protects the myocardium but does not lower potassium.
• The old “stone heart” concern does not make calcium absolutely contraindicated in digoxin-associated hyperkalemia.
• Digoxin immune Fab is the definitive antidotal therapy for severe digoxin toxicity.
• In hypermagnesemia, calcium antagonizes magnesium’s physiologic effects but does not eliminate magnesium.
• Fluoride binds calcium and magnesium and can cause rapidly fatal electrolyte abnormalities and ventricular dysrhythmias.
• HF skin exposure requires immediate decontamination; topical calcium gluconate is commonly used for symptomatic burns.
• Severe or persistent HF injury requires specialist toxicology/burn management.
• Calcium chloride should not be injected into tissues for HF burns.
• Calcium is no longer considered reliable first-line treatment for black widow envenomation.
• During substantial calcium therapy, follow ECG, hemodynamics, ionized calcium, potassium, magnesium, and renal function.

194. Toxicology – Calcium as an Antidotal Therapy

Core Concept

Calcium is an important supportive or antidotal treatment in several toxicologic emergencies.

Major indications include:

• Calcium channel blocker (CCB) poisoning
• Hyperkalemia with cardiac toxicity
• Hypermagnesemia
• Hydrofluoric acid and other fluoride poisoning
• Selected toxin-induced symptomatic hypocalcemia

Older sources also recommended calcium for black widow spider envenomation, but this is no longer considered a reliably effective first-line treatment.

Calcium Preparations

The two major intravenous preparations are:

Calcium Chloride

• Provides substantially more elemental calcium per equivalent volume than calcium gluconate.
• Useful when rapid calcium delivery is required.
• More irritating to peripheral tissues.
• Extravasation can cause severe local tissue injury.

Calcium Gluconate

• Contains less elemental calcium.
• Less irritating to peripheral veins and tissues.
• Often preferred when peripheral IV administration is necessary.
• Commonly used for topical/local treatment of hydrofluoric acid skin exposure.

The preparations are not interchangeable gram-for-gram because they contain different amounts of elemental calcium.

General Mechanisms

Calcium works differently depending on the poisoning.

Hyperkalemia

Stabilizes the cardiac membrane against the electrophysiologic effects of excess potassium.

Hypermagnesemia

Functionally antagonizes some of magnesium’s effects on cardiac and neuromuscular tissues.

Calcium Channel Blocker Poisoning

Raises extracellular calcium availability and may partially overcome impaired calcium entry.

Fluoride Poisoning

Binds fluoride and replaces calcium depleted by fluoride-mediated complex formation.

Calcium Channel Blocker Poisoning

CCB overdose can produce:

• Bradycardia
• Hypotension
• AV block
• Cardiogenic shock
• Vasodilatory shock
• Hyperglycemia
• Altered mental status
• Severe dysrhythmias

Calcium is an important early therapy for clinically significant cardiovascular toxicity.

How Calcium Helps in CCB Poisoning

CCBs reduce calcium entry through L-type calcium channels.

Increasing extracellular calcium can partially overcome this functional blockade and improve:

• Contractility
• Blood pressure
• AV nodal conduction

However, the response is often incomplete or temporary.

Therefore:

Calcium is important, but severe CCB poisoning usually requires more than calcium alone.

Other Treatment in Severe CCB Poisoning

Depending on the clinical pattern, management may also require:

• Hyperinsulinemic euglycemia therapy
• Vasopressors
• Careful fluid resuscitation
• Airway and ventilatory support
• Correction of metabolic abnormalities
• Selected adjunctive therapies
• Extracorporeal circulatory support in refractory shock

Treatment is guided by the mechanism of cardiovascular failure.

Monitoring During CCB Treatment

Monitor:

• Continuous ECG
• Heart rate
• Blood pressure
• Perfusion
• Mental status
• Blood glucose
• Electrolytes
• Acid-base status
• Ionized calcium

Large amounts of calcium may sometimes be required, making repeated measurement particularly important.

Hyperkalemia

Calcium is one of the most important emergency therapies when hyperkalemia produces significant cardiac membrane instability.

ECG abnormalities may include:

• Peaked T waves
• PR prolongation
• P-wave attenuation or loss
• QRS widening
• Bradyarrhythmias
• Sine-wave morphology
• Ventricular dysrhythmias

However, ECG changes do not always follow a predictable sequence.

Severe hyperkalemia may exist without classic ECG findings.

What Calcium Does in Hyperkalemia

Calcium:

Stabilizes the myocardium

but it does not meaningfully remove potassium from the body or lower serum potassium concentration.

Therefore calcium must be followed by therapies that:

• Shift potassium intracellularly
• Remove potassium from the body
• Correct the underlying cause

when clinically indicated.

Hyperkalemia Treatment Concept

Think of treatment as three separate goals:

1. Protect the heart

→ Calcium

2. Temporarily shift potassium into cells

→ Insulin/glucose and selected other therapies

3. Remove excess potassium

→ Renal elimination, gastrointestinal potassium binders in selected settings, or dialysis when necessary

Calcium addresses only the first goal.

Digoxin Toxicity and Calcium

Older teaching described calcium as absolutely contraindicated in digoxin toxicity because of concern for so-called “stone heart.”

Modern evidence does not support an absolute prohibition.

If a patient with suspected digoxin toxicity has life-threatening hyperkalemia, calcium is not considered absolutely contraindicated.

However, the definitive antidotal treatment for severe digoxin poisoning is:

Digoxin immune Fab

Management should therefore focus on Fab when clinically indicated rather than relying on calcium.

Hypermagnesemia

Severe magnesium toxicity can produce:

• Nausea
• Flushing
• Hypotension
• Loss of deep tendon reflexes
• Muscle weakness
• Bradycardia
• Conduction abnormalities
• Respiratory depression
• Paralysis
• Cardiac arrest

Calcium can temporarily antagonize magnesium’s effects at cardiac and neuromuscular tissues.

Calcium in Magnesium Toxicity

IV calcium may improve:

• Cardiovascular instability
• Neuromuscular weakness
• Significant conduction abnormalities

But:

Calcium does not remove magnesium from the body.

Definitive management may require:

• Discontinuation of magnesium exposure
• Supportive care
• IV fluids and renal elimination when appropriate
• Dialysis in severe toxicity with renal impairment or refractory manifestations

Hydrofluoric Acid

Hydrofluoric acid (HF) is particularly dangerous because fluoride ions penetrate deeply into tissues.

The fluoride ion binds:

• Calcium
• Magnesium

This can cause:

• Local cellular destruction
• Severe pain
• Hypocalcemia
• Hypomagnesemia
• Hyperkalemia
• QT abnormalities
• Ventricular dysrhythmias
• Cardiac arrest

Small-appearing burns can occasionally produce disproportionately severe toxicity.

Why Calcium Works in HF Exposure

Calcium serves two important functions:

Calcium + fluoride → less biologically active calcium-fluoride complex

and

Calcium replacement → corrects fluoride-induced calcium depletion

Therefore, calcium therapy targets both the toxic fluoride ion and its systemic electrolyte consequences.

HF Skin Exposure

Immediate management begins with:

Prompt, prolonged water irrigation and removal of contaminated clothing

After decontamination, calcium gluconate gel is commonly used for symptomatic dermal HF exposure.

Persistent severe pain can indicate ongoing fluoride activity and deeper tissue injury.

Persistent HF Burns

If pain or tissue toxicity persists despite initial topical treatment, more advanced calcium delivery techniques may occasionally be necessary.

These require specialist management because improperly performed injections or vascular procedures can cause serious complications.

Potential escalation strategies are therefore best handled with:

• Medical toxicology
• Poison-center consultation
• Burn specialists
• Hand/plastic surgery when appropriate

Why Calcium Chloride Is Avoided in Tissue Injection

Calcium chloride is highly irritating and can produce:

• Tissue necrosis
• Severe local injury
• Extravasation damage

Therefore, it should not be injected intradermally or subcutaneously for HF burns.

Calcium gluconate is the safer calcium salt for local tissue treatment.

Systemic HF Poisoning

Severe fluoride exposure may rapidly cause:

• Hypocalcemia
• Hypomagnesemia
• Hyperkalemia
• QT prolongation
• Ventricular dysrhythmias
• Shock
• Cardiac arrest

Aggressive electrolyte monitoring and correction are essential.

Because deterioration can be rapid, severe HF poisoning requires high-acuity monitoring.

ECG in Fluoride Poisoning

ECG abnormalities can provide an early clue to severe electrolyte disruption.

Possible findings include:

• QT prolongation from hypocalcemia
• Conduction abnormalities
• Ventricular ectopy
• Ventricular tachycardia
• Ventricular fibrillation

Continuous ECG monitoring is appropriate in significant systemic exposure.

Other Fluoride Compounds

Similar systemic toxicity may occur with:

• Sodium fluoride
• Ammonium bifluoride
• Other soluble fluoride salts

These can cause:

• Hypocalcemia
• Hypomagnesemia
• Hyperkalemia
• GI injury
• Dysrhythmias

Treatment centers on supportive care and aggressive correction of clinically significant electrolyte disturbances.

Ethylene Glycol

Ethylene glycol metabolism produces oxalic acid.

Oxalate binds calcium and forms calcium oxalate crystals.

This contributes to:

• Hypocalcemia
• Tissue deposition
• Acute kidney injury

However, calcium should not automatically be administered merely because laboratory hypocalcemia is present.

Calcium is generally reserved for clinically important manifestations such as:

• Tetany
• Seizures attributable to hypocalcemia
• Significant dysrhythmia
• Other symptomatic hypocalcemia

Excessive calcium administration could theoretically promote additional calcium oxalate deposition.

Phosphate Poisoning

Large phosphate exposure can lower serum calcium through calcium-phosphate complex formation.

Severe hypocalcemia may produce:

• Paresthesias
• Tetany
• Seizures
• QT prolongation
• Dysrhythmias

Symptomatic or dangerous hypocalcemia may require calcium, while the underlying phosphate disturbance must also be addressed.

Black Widow Spider Envenomation

The older source recommended IV calcium as a major treatment for black widow envenomation.

This recommendation is now considered outdated.

Although calcium was historically proposed to counter venom-mediated alterations in neurotransmitter release, clinical benefit has been inconsistent.

Modern treatment emphasizes:

• Analgesia
• Supportive care
• Treatment of muscle spasm when necessary
• Antivenom for selected severe cases

Calcium is not routinely considered first-line therapy for latrodectism.

Calcium Chloride vs Calcium Gluconate

A practical distinction:

Calcium Chloride

Advantages:

• More elemental calcium
• Rapid calcium delivery

Disadvantages:

• Greater tissue toxicity
• Severe injury if extravasated

Calcium Gluconate

Advantages:

• Less irritating
• Better suited to peripheral administration
• Appropriate for topical HF treatment

Disadvantage:

• Less elemental calcium for an equivalent amount of solution

Extravasation

Calcium extravasation can cause significant tissue injury, particularly with calcium chloride.

Possible complications include:

• Pain
• Swelling
• Inflammation
• Tissue necrosis
• Calcification

If extravasation occurs:

• Stop administration through the affected line.
• Assess the site promptly.
• Follow an appropriate extravasation-management protocol.

Hypercalcemia from Treatment

Aggressive calcium therapy can produce excessive serum calcium.

Possible manifestations include:

• Nausea
• Weakness
• Confusion
• Hypertension
• Bradycardia or dysrhythmias
• Other conduction abnormalities

This is why ionized calcium and ECG findings should be followed during substantial therapy.

Renal Failure

Calcium therapy requires additional caution in patients with renal impairment because they may have:

• Altered calcium/phosphate balance
• Hyperphosphatemia
• Reduced ability to handle electrolyte loads

Treatment should be individualized according to the toxicologic emergency and measured electrolytes.

Pregnancy

Calcium is a normal physiologic electrolyte and can be administered during pregnancy when clinically indicated.

Life-threatening maternal electrolyte or cardiovascular toxicity should be treated promptly.

Monitoring During Significant Calcium Therapy

Monitor:

• Continuous ECG
• Heart rate and rhythm
• Blood pressure
• Ionized calcium
• Potassium
• Magnesium
• Renal function
• Acid-base status when appropriate

For fluoride toxicity, serial electrolyte measurements may need to be particularly frequent because abnormalities can change rapidly.

Important Modernization of the Older Source

Several recommendations in the source require updating:

• Calcium remains an important treatment for CCB toxicity, cardiac effects of hyperkalemia, severe hypermagnesemia, and fluoride toxicity.
• Calcium does not lower serum potassium; it stabilizes the myocardium while other therapies shift or remove potassium.
• The historical absolute contraindication to calcium in digoxin toxicity is no longer supported.
• Digoxin immune Fab remains the specific treatment for severe digoxin poisoning.
• Calcium is not routinely first-line treatment for black widow envenomation.
• In ethylene glycol poisoning, isolated laboratory hypocalcemia does not automatically require calcium; clinically significant symptomatic hypocalcemia is more important.
• Calcium chloride is more tissue-toxic than calcium gluconate and requires particular attention to IV access.
• Advanced HF treatments such as local infiltration, regional perfusion, or intra-arterial calcium should be specialist-directed rather than performed from rigid historical protocols.
• Fixed calcium regimens are less useful than treatment guided by ECG response, hemodynamics, symptoms, and serial ionized calcium measurements.
• Severe CCB poisoning generally requires multimodal therapy rather than calcium alone.

Key Points

• Calcium is an important toxicologic therapy for CCB poisoning, hyperkalemic cardiac toxicity, hypermagnesemia, and fluoride poisoning.
• Calcium chloride contains substantially more elemental calcium than calcium gluconate.
• Calcium chloride causes greater tissue injury if extravasation occurs.
• Calcium gluconate is generally safer through peripheral veins and is used locally for HF skin exposure.
• In CCB poisoning, calcium may improve contractility, blood pressure, and conduction but is often only one component of treatment.
• In hyperkalemia, calcium protects the myocardium but does not lower potassium.
• The old “stone heart” concern does not make calcium absolutely contraindicated in digoxin-associated hyperkalemia.
• Digoxin immune Fab is the definitive antidotal therapy for severe digoxin toxicity.
• In hypermagnesemia, calcium antagonizes magnesium’s physiologic effects but does not eliminate magnesium.
• Fluoride binds calcium and magnesium and can cause rapidly fatal electrolyte abnormalities and ventricular dysrhythmias.
• HF skin exposure requires immediate decontamination; topical calcium gluconate is commonly used for symptomatic burns.
• Severe or persistent HF injury requires specialist toxicology/burn management.
• Calcium chloride should not be injected into tissues for HF burns.
• Calcium is no longer considered reliable first-line treatment for black widow envenomation.
• During substantial calcium therapy, follow ECG, hemodynamics, ionized calcium, potassium, magnesium, and renal function.