Case File #4
"Bella," 2-year-old Beagle
Bella's owner calls in a panic. They came home to find an empty 8-oz box of dark chocolate baking squares on the floor. Bella (10 kg) is now hyperactive, panting, and has vomited twice. The owner says: "I didn't think chocolate could really hurt a dog — I've heard that before." How serious is this? What do you do first? Keep this question in mind as you work through the unit.
Open the Toxicology Files
Unit 4 — Methylxanthines (Chocolate)
What Are Methylxanthines?
Chocolate contains two primary methylxanthines: theobromine and caffeine. Dogs metabolize these far more slowly than humans, making even moderate amounts dangerous.
- Found in chocolate, coffee, medications
- Cases spike at Christmas and Valentine's Day
- Also: caffeine tablets (racehorses), cocoa bean mulch (horses)
⚠ Key Thresholds (Theobromine)
- Minimum toxic level: 100–200 mg/kg
- LD₅₀: 250–500 mg/kg
- Unsweetened baking chocolate: as little as 0.2 oz/kg may kill a dog
🍫 Danger by Chocolate Type
🔴 Unsweetened/baking — Most dangerous
🟠 Dark chocolate — Very dangerous
🟡 Milk chocolate — Less dangerous
⚪ White chocolate — Minimal theobromine
Unit 4 — Methylxanthines (Chocolate)
Mechanism of Action
Three distinct ways methylxanthines disrupt normal physiology:
💥Calcium Dysregulation
🔄Phosphodiesterase Inhibition
☕Adenosine Receptor Antagonism
Blocks adenosine receptors → CNS stimulation, vasoconstriction, tachycardia
Prevents Ca²⁺ reuptake → ↑ cardiac & skeletal contractility → arrhythmias
↑ cyclic AMP and GMP → amplifies all stimulatory effects
Unit 4 — Methylxanthines (Chocolate)
Clinical Signs
⏱ Signs appear within 6–12 hours and can persist for 72 hours due to the long half-life of theobromine.
Early Vomiting, diarrhea, diuresis, restlessness, panting Progressing Tachycardia, hypertension, hyperactivity ("the bounce"), ataxia
Severe (Cardiac)
Tremors, seizures, coma Fatal Death from cardiac arrhythmias or respiratory failure
Unit 4 — Methylxanthines (Chocolate)
Diagnosis & Treatment
Diagnose It
Treat It
Diagnosis
- Chemical analysis of stomach contents, plasma, serum, urine, or liver
- Theobromine detectable in serum for 3–4 days after ingestion
- History of chocolate ingestion + clinical signs
Treatment
- GI Decontamination: Induce emesis + repeated activated charcoal every 3 hours (enterohepatic recirculation!)
- Monitor EKG continuously
- Arrhythmias: Lidocaine (⚠ NOT in cats); if fails → Metoprolol
- Seizures: Diazepam or barbiturates
- Maintain respiration
- Fluid diuresis to increase excretion
⚠ Why repeat activated charcoal? Theobromine undergoes enterohepatic recirculation — it re-enters the GI tract and gets reabsorbed. Multiple charcoal doses interrupt this cycle.
Unit 4 — Methylxanthines (Chocolate)
Apply It - Dose Calculation Challenge
Scenario: Bella weighs 10 kg. She ate a 4 oz (113g) package of unsweetened baking chocolate. Unsweetened baking chocolate contains approximately 450 mg theobromine per oz.
Calculate the Dose
Step 1: Total theobromine ingested = 4 oz × 450 mg/oz = 1,800 mg
Step 2: Dose = 1,800 mg ÷ 10 kg = 180 mg/kg
Unit 4 — Methylxanthines (Chocolate)
❌ The minimum toxic level is 100–200 mg/kg. At 180 mg/kg, Bella is clearly within this range. Do not wait for signs to escalate — treat proactively.
Correct! At 180 mg/kg, Bella is within the minimum toxic range (100–200 mg/kg). This warrants aggressive treatment: induce emesis, administer activated charcoal every 3 hours, and monitor EKG.
Methylxanthines
UF College of Veterinary Medicine
Created on April 6, 2026
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Transcript
Case File #4
"Bella," 2-year-old Beagle
Bella's owner calls in a panic. They came home to find an empty 8-oz box of dark chocolate baking squares on the floor. Bella (10 kg) is now hyperactive, panting, and has vomited twice. The owner says: "I didn't think chocolate could really hurt a dog — I've heard that before." How serious is this? What do you do first? Keep this question in mind as you work through the unit.
Open the Toxicology Files
Unit 4 — Methylxanthines (Chocolate)
What Are Methylxanthines?
Chocolate contains two primary methylxanthines: theobromine and caffeine. Dogs metabolize these far more slowly than humans, making even moderate amounts dangerous.
- Found in chocolate, coffee, medications
- Cases spike at Christmas and Valentine's Day
- Also: caffeine tablets (racehorses), cocoa bean mulch (horses)
⚠ Key Thresholds (Theobromine)🍫 Danger by Chocolate Type
🔴 Unsweetened/baking — Most dangerous 🟠 Dark chocolate — Very dangerous 🟡 Milk chocolate — Less dangerous ⚪ White chocolate — Minimal theobromine
Unit 4 — Methylxanthines (Chocolate)
Mechanism of Action
Three distinct ways methylxanthines disrupt normal physiology:
💥Calcium Dysregulation
🔄Phosphodiesterase Inhibition
☕Adenosine Receptor Antagonism
Blocks adenosine receptors → CNS stimulation, vasoconstriction, tachycardia
Prevents Ca²⁺ reuptake → ↑ cardiac & skeletal contractility → arrhythmias
↑ cyclic AMP and GMP → amplifies all stimulatory effects
Unit 4 — Methylxanthines (Chocolate)
Clinical Signs
⏱ Signs appear within 6–12 hours and can persist for 72 hours due to the long half-life of theobromine.
Early Vomiting, diarrhea, diuresis, restlessness, panting Progressing Tachycardia, hypertension, hyperactivity ("the bounce"), ataxia Severe (Cardiac) Tremors, seizures, coma Fatal Death from cardiac arrhythmias or respiratory failure
Unit 4 — Methylxanthines (Chocolate)
Diagnosis & Treatment
Diagnose It
Treat It
Diagnosis
Treatment
⚠ Why repeat activated charcoal? Theobromine undergoes enterohepatic recirculation — it re-enters the GI tract and gets reabsorbed. Multiple charcoal doses interrupt this cycle.
Unit 4 — Methylxanthines (Chocolate)
Apply It - Dose Calculation Challenge
Scenario: Bella weighs 10 kg. She ate a 4 oz (113g) package of unsweetened baking chocolate. Unsweetened baking chocolate contains approximately 450 mg theobromine per oz.
Calculate the Dose Step 1: Total theobromine ingested = 4 oz × 450 mg/oz = 1,800 mg Step 2: Dose = 1,800 mg ÷ 10 kg = 180 mg/kg
Unit 4 — Methylxanthines (Chocolate)
❌ The minimum toxic level is 100–200 mg/kg. At 180 mg/kg, Bella is clearly within this range. Do not wait for signs to escalate — treat proactively.
Correct! At 180 mg/kg, Bella is within the minimum toxic range (100–200 mg/kg). This warrants aggressive treatment: induce emesis, administer activated charcoal every 3 hours, and monitor EKG.