5.4 Caffeine, Theophylline, and Over-the-Counter Stimulants
Key Takeaways
- Methylxanthines antagonize adenosine receptors and inhibit phosphodiesterase, producing catecholamine excess with tachydysrhythmias, tremor, vomiting, seizures, and a metabolic triad of hypokalemia, hyperglycemia, and metabolic acidosis.
- Hypokalemia in theophylline or caffeine toxicity reflects an intracellular shift rather than total body loss, so potassium is replaced cautiously to avoid rebound hyperkalemia.
- Theophylline seizures are often refractory and can occur without preceding tachycardia; multiple-dose activated charcoal shortens the half-life substantially, and EXTRIP recommends extracorporeal treatment for acute levels above 100 mg/L or for seizures, life-threatening dysrhythmias, or shock.
- Caffeine powders and concentrated energy products have caused deaths in young adults, with roughly 150 to 200 mg/kg considered potentially lethal, and a single teaspoon of pure powder containing several grams.
- Sympathomimetic decongestants and weight-loss supplements cause hypertension with reflex bradycardia (phenylephrine), stroke and dysrhythmias (ephedra-type alkaloids), and severe hyperthermia with 2,4-dinitrophenol, for which there is no antidote.
Methylxanthine Pharmacology
Caffeine, theophylline, and aminophylline (a theophylline-ethylenediamine salt) act through three linked mechanisms:
- Adenosine receptor antagonism, removing adenosine's inhibitory brake on central neurons, the sinoatrial node, and presynaptic catecholamine release. This is the main reason seizures and tachydysrhythmias occur.
- Phosphodiesterase inhibition, raising intracellular cyclic adenosine monophosphate and amplifying beta-adrenergic signaling.
- Increased catecholamine release, producing beta-1 and beta-2 effects clinically indistinguishable from an epinephrine infusion.
The Clinical and Metabolic Signature
| System | Findings |
|---|---|
| Cardiovascular | Sinus tachycardia, supraventricular tachycardia, atrial fibrillation, ventricular ectopy and ventricular tachycardia; beta-2 mediated vasodilation causes a wide pulse pressure and hypotension despite tachycardia |
| Neurologic | Anxiety, tremor, hyperreflexia, agitation, then seizures that are frequently refractory and may be the first manifestation in chronic toxicity |
| Gastrointestinal | Intractable vomiting (a major barrier to oral charcoal), abdominal pain, hematemesis |
| Metabolic | Hypokalemia (beta-2 driven intracellular shift), hyperglycemia, hypophosphatemia, hypomagnesemia, lactic acidosis, and leukocytosis |
Potassium pearl: the hypokalemia is a shift, not a deficit. Aggressive replacement produces rebound hyperkalemia as the drug is cleared. Replace enough to prevent dysrhythmia (generally keeping potassium above about 3.0 mEq/L) and recheck frequently.
Acute Versus Chronic Theophylline Toxicity
| Feature | Acute Overdose | Chronic Accumulation |
|---|---|---|
| Typical patient | Intentional ingestion | Older adult with an illness, heart failure, or a new interacting drug |
| Level at which seizures occur | Usually above 80 to 100 mg/L | Often 40 to 60 mg/L |
| Vomiting and hypokalemia | Prominent | Less prominent |
| Prognosis for a given level | Better | Worse |
Common precipitants of chronic toxicity are drugs that inhibit CYP1A2 (ciprofloxacin, fluvoxamine, cimetidine, erythromycin), viral illness, and heart failure. Smoking cessation also raises levels because tobacco smoke induces CYP1A2.
Management of Methylxanthine Toxicity
- Decontamination: activated charcoal early; multiple-dose activated charcoal is one of the few evidence-supported indications and can shorten the elimination half-life by more than half. Aggressive antiemetics (ondansetron, often in high doses; metoclopramide) are needed to keep charcoal down.
- Seizures: benzodiazepines first, then phenobarbital or propofol. Phenytoin is ineffective.
- Dysrhythmias and hypotension: a short-acting beta-blocker (esmolol infusion, or small doses of propranolol) treats the beta-mediated tachycardia and vasodilation; this is the rare situation where beta-blockade in a hyperadrenergic patient is correct. Fluid resuscitation supports the vasodilated circulation.
- Electrolytes: cautious potassium, magnesium, and phosphate repletion.
- Extracorporeal treatment (EXTRIP): recommended for an acute theophylline level above 100 mg/L, or for seizures, life-threatening dysrhythmias, shock, a rising level despite optimal care, or clinical deterioration. It is suggested for chronic levels above 60 mg/L, for chronic levels above 50 mg/L in patients younger than 6 months or older than 60 years, and when gastrointestinal decontamination cannot be given. Intermittent hemodialysis is preferred, and multiple-dose charcoal continues during dialysis.
Caffeine in Modern Products
| Source | Typical Caffeine Content |
|---|---|
| Brewed coffee, 8 oz | 95 to 165 mg |
| Energy drink, 16 oz | 150 to 300 mg |
| Energy "shot," 2 oz | 200 to 250 mg |
| Caffeine tablet | 100 to 200 mg |
| Pure caffeine powder, 1 teaspoon | About 3,000 to 5,000 mg |
- Toxicity begins around 10 to 15 mg/kg, serious toxicity above roughly 50 mg/kg, and death has occurred near 150 to 200 mg/kg.
- Deaths in healthy young adults have followed the use of bulk caffeine powder measured with a kitchen spoon, which is why the specialist asks specifically whether a powder or concentrated liquid was used rather than tablets.
- Neonates are an exception: caffeine citrate is therapeutic for apnea of prematurity, and neonates tolerate levels that would be toxic in adults.
Sympathomimetic Decongestants and Diet Products
| Agent | Mechanism | Overdose Features | Notes |
|---|---|---|---|
| Pseudoephedrine | Mixed direct and indirect sympathomimetic | Hypertension, tachycardia, agitation, mydriasis; seizures in large ingestions | Common in pediatric exploratory ingestions |
| Phenylephrine | Selective alpha-1 agonist | Hypertension with reflex bradycardia, headache, pallor | The bradycardia is baroreflex-mediated, not a second toxin |
| Ephedrine and pseudoephedrine-containing botanicals (ephedra, ma huang) | Indirect release of norepinephrine | Hypertensive crisis, stroke, myocardial infarction, dysrhythmias | Removed from US dietary supplements in 2004 but still found in imported products |
| Bitter orange (synephrine) and caffeine blends | Adrenergic stimulation | Palpitations, hypertension, chest pain | Frequently sold as "ephedra-free" |
| Yohimbine | Central alpha-2 antagonist | Anxiety, hypertension, tachycardia, diaphoresis, priapism | Opposite of clonidine |
| Thyroid hormone in "metabolism" products | Adds adrenergic effects | Delayed tachycardia and tremor | Covered with endocrine medications |
| 2,4-Dinitrophenol (DNP) | Uncouples oxidative phosphorylation | Profuse sweating, tachypnea, extreme hyperthermia above 42 °C, rigor, death; yellow skin staining | Illegal but sold online for fat loss; no antidote, aggressive cooling and sedation only |
Management of Stimulant Ingestions
- Benzodiazepines are the cornerstone for agitation, hypertension, tachycardia, and hyperthermia.
- Active cooling for temperatures above 40 °C; antipyretics do not work.
- For sustained severe hypertension, use a titratable vasodilator (nicardipine, nitroglycerin) or phentolamine rather than a pure beta-blocker in cocaine-type exposures. Methylxanthines are the exception where beta-blockade is indicated.
- Check glucose, potassium, creatine kinase, and an ECG; look for QT prolongation and ischemia.
Poison Center Case: Bulk Caffeine Powder
A 22-year-old bodybuilder is brought in after mixing "a couple of scoops" of bulk caffeine powder into a pre-workout drink. He is vomiting repeatedly, tremulous, and anxious. Heart rate is 165 with a narrow-complex rhythm, blood pressure is 88/40, potassium is 2.6 mEq/L, glucose is 265 mg/dL, and lactate is 6 mmol/L.
Specialist actions. The CSPI recognizes the classic methylxanthine picture: hyperadrenergic tachycardia with beta-2 mediated hypotension plus hypokalemia, hyperglycemia, and lactic acidosis. Recommendations are ondansetron to control vomiting so that multiple-dose activated charcoal can be given, intravenous fluids, cautious potassium and magnesium replacement with frequent rechecks because the hypokalemia is a shift, an esmolol infusion for the tachydysrhythmia and vasodilatory hypotension, benzodiazepines at the bedside for seizure precautions, and a caffeine level with nephrology notified because severe caffeine toxicity, like theophylline, responds to hemodialysis.
A 19-year-old with a theophylline overdose has a potassium of 2.4 mEq/L, glucose of 280 mg/dL, and a heart rate of 170. The resident wants to give 60 mEq of potassium chloride over 2 hours. What is the best advice?
A 68-year-old on chronic theophylline for COPD was started on ciprofloxacin five days ago and now has a seizure. Her theophylline level is 52 mg/L. Which statement is most accurate?
A 24-year-old who bought "fat-burner" capsules online presents with profuse diaphoresis, tachypnea, agitation, yellow-tinged skin, and a rectal temperature of 42.3 °C. There is no muscle rigidity. Which agent and management pair is correct?