Origin and chemical nature
Epinephrine is naturally a biogenic catecholamine. Under physiological conditions, it is the main hormone of the adrenal medulla, where it is continuously synthesized and stored by specialized chromaffin cells.
For practical medicine and pharmacology, the drug is obtained in two main ways: either via targeted chemical synthesis or by extraction from the adrenal tissues of slaughtered cattle.
Pharmacodynamics and receptor profile
The main pharmacological feature of epinephrine is its non-selectivity. Unlike norepinephrine (noradrenaline), which practically does not interact with $\beta_2$-adrenoceptors, epinephrine is a potent agonist of both $\alpha$- and $\beta$-adrenoceptors.
It is precisely the effect on vascular $\beta_2$-adrenoceptors, stimulation of which leads to vasodilation (blood vessel widening), that determines the specific hemodynamic pattern. When epinephrine is administered, a phase of a sharp increase in blood pressure (BP) is inevitably followed by a phase of its subsequent decrease. Norepinephrine lacks such a blood pressure decrease phase entirely.
Effect on metabolism and clinical use
In addition to its pronounced pressor effect on the cardiovascular system, epinephrine actively interferes with the body's metabolic processes, primarily carbohydrate metabolism. The drug has a proven ability to rapidly increase glucose levels in the systemic circulation.
In clinical practice, this metabolic effect is used to provide emergency care. Epinephrine is used to relieve hypoglycemic coma—a life-threatening condition caused by a critical drop in blood sugar (e.g., in case of an overdose of insulin or other hypoglycemic agents).
Pharmaceutical features: epinephrine salts
In pharmacies and hospitals, the drug is available in the form of two different salts: hydrochloride (Adrenalini hydrochloridum) and hydrotartrate.
From the standpoint of pharmacodynamics and therapeutic action, these forms are completely identical. However, the physician must remember an important nuance when dosing: the molecular mass of hydrotartrate is significantly greater than that of hydrochloride. Because of this difference, achieving a comparable clinical effect requires administering a higher dose of epinephrine hydrotartrate compared to hydrochloride.
Dosage forms and administration guidelines
According to the prescription reference book, the drug has the following dosage forms and routes of administration:
- Ampoule solution: 0.1% solution, 1 ml. Administered subcutaneously (s.c.), intramuscularly (i.m.), and intravenously (i.v.).
- Ophthalmological forms: 0.5% eye drops, as well as a 2% solution in 10 ml vials. Prescribed topically, 1–2 drops into the conjunctival sac.
- Dosing for injections: A single dose ranges from 0.0003 to 0.00075 g. Before intravenous administration, the drug must be diluted in 15–20 ml of physiological saline (0.9% NaCl solution).
- Dosage limits: The maximum single dose (MSD) for subcutaneous administration is strictly limited to 0.001 g. The maximum daily dose (MDD) for subcutaneous administration must not exceed 0.005 g.
Briefly: answers to topical questions
What are the main side effects and contraindications for the use of epinephrine?
The sources describe the following risks and limitations:
- Halothane anesthesia: Halothane increases the heart's sensitivity to catecholamines; administering adrenaline against this background can cause severe arrhythmias.
- For the combination of articaine + epinephrine, contraindications include paroxysmal tachycardia, tachyarrhythmia, and glaucoma.
- In the drug "Ultracaine D-S", a low concentration of adrenaline (1:200,000 dilution) ensures safety for pregnant women and individuals with concomitant cardiovascular diseases.
Adrenaline hits all targets ($\alpha$ and $\beta$), whereas norepinephrine forgets about $\beta_2$ (does not dilate vessels, blood pressure does not drop).
Class and exam questions
Why might blood pressure decrease after epinephrine administration?
This is due to the stimulation of vascular $\beta_2$-adrenoceptors, which cause vasodilation. Norepinephrine lacks this effect, hence there is no blood pressure drop phase.
What is the clinical difference between epinephrine hydrochloride and hydrotartrate?
Pharmacologically they are completely identical. The difference lies in the molecular mass: hydrotartrate is heavier, therefore its dose must be higher to achieve a similar effect.
How does epinephrine affect blood sugar levels and where is this applied?
The drug increases blood glucose levels. Due to this property, it is used in emergency medicine to pull a patient out of hypoglycemic coma in case of insulin overdose.
What are the maximum doses of epinephrine for subcutaneous administration?
The maximum single dose (MSD) is 0.001 g, and the maximum daily dose (MDD) is 0.005 g.
What else to study on this topic
- Biosynthesis of catecholamines in chromaffin cells of the adrenal medulla.
- Differences in the affinity of epinephrine and norepinephrine for adrenoceptor subtypes.
- Mechanisms regulating carbohydrate metabolism upon activation of the sympathoadrenal system.
- Principles of managing anaphylactic shock (additional reading on the drug).
- Comparison of the direct and reflex effects of catecholamines on heart rate.
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