Chemical structure and mechanism of action
The strophanthin K molecule has a chemical structure typical of cardiac glycosides, consisting of two components:
- Aglycone (genin): has a steroid nature — the base is represented by a cyclopentanoperhydrophenanthrene ring with an attached unsaturated lactone ring. In strophanthin K, the aglycone is distinguished by the presence of an aldehyde group (-CHO) and additional hydroxyl groups (-OH). It is the aglycone that provides the pharmacodynamic role — specific cardiac effects and the mechanism of action depend on it.
- Glycone (sugar moiety): consists of two monosaccharides (glucose and cymarose). The glycone performs the pharmacokinetic role: it determines the degree of solubility, absorption, excretion, and cumulation capacity.
Since the strophanthin K molecule is a pronounced polar compound, it has specific distribution and elimination characteristics.
Pharmacokinetics and biological standardization
The pharmacokinetic profile of strophanthin K is characterized by the following key parameters:
- Absorption: The drug is practically not absorbed from the gastrointestinal tract, making oral administration impossible. The route of administration is strictly intravenous.
- Time parameters: It has a very short latent period. The effect begins in 2–10 minutes (in some cases up to 20 minutes), reaching a maximum in 30–120 minutes. The total duration of the pharmacological effect is 1 to 3 days.
- Binding and metabolism: It binds to plasma proteins by approximately 40%. It does not undergo biotransformation (is not metabolized) in the body.
- Elimination: Completely excreted by the kidneys in an unchanged form.
- Cumulation: Due to its short circulation time, material cumulation is significantly less pronounced than with digitalis glycosides, though the risk of intoxication is not entirely ruled out.
Biological standardization: Since plant raw materials contain enzymes that alter the structure of primary glycosides, preparations are subject to strict standardization by comparison with a standard reference. Activity is evaluated in frog units (FU). Pure strophanthin possesses the highest biological activity among glycosides: 1 gram of the substance contains 44,000–56,000 FU.
Indications for use
Due to the rapid onset of its effect, strophanthin K is used in the following pathological conditions:
- Acute heart failure (AHF) — the drug of choice as an emergency medical treatment.
- Chronic heart failure (CHF) functional classes III–IV.
- Tachy-form of atrial fibrillation.
Side effects and intoxication risks
Despite the low degree of cumulation compared to non-polar glycosides (such as digitoxin), the use of strophanthin K carries a risk of glycoside intoxication.
The risk of intoxication increases with rapid infusion or impaired renal excretion, as drug elimination depends entirely on renal clearance. Rapid administration can provoke severe rhythm and conduction disorders.
Administration features and prescription example
Strophanthin K is administered strictly intravenously and slowly. To avoid developing complications, a single dose of 0.5–1 ml of a 0.05% solution is pre-diluted in 10–20 ml of a 20% or 40% glucose solution and injected as a bolus over 5–6 minutes.
Dosage:
- Maximum single dose (MSD): IV 0.0005 g (1 ml of 0.05% solution).
- Maximum daily dose (MDD): IV 0.001 g (2 ml of 0.05% solution).
Prescription example:
`Rp.: Sol. Strophanthini K 0,05% - 1 ml` `D.t.d. N. 5 in ampullis` `S. Intravenously slowly 0.5–1 ml in 10–20 ml of 40% glucose solution (administer over 5–6 minutes).`
Briefly: answers to topical questions
How does the cumulation mechanism of polar cardiac glycosides differ from non-polar ones?
Polar cardiac glycosides have less pronounced cumulation due to their short circulation time. Digitoxin is characterized by the most pronounced material cumulation due to slow metabolism, tight plasma protein binding, and enterohepatic recirculation.
Which enzymes break down primary glycosides in strophanthus plant material?
The sources do not specify the exact names of the enzymes that break down primary glycosides in strophanthus plant material; they only provide general information on the presence of enzymes capable of modifying the structure of glycosides and converting primary genuine glycosides into secondary ones.
STROPHANTHUS — Swift Toxin: Administered intravenously only, acts in 2–10 minutes, excreted by the kidneys.
Class and exam questions
Why is Strophanthin K administered exclusively intravenously?
Strophanthin K is a highly polar compound and is practically not absorbed from the gastrointestinal tract, so oral administration is ineffective.
What are the onset and duration of action of Strophanthin K?
The effect begins rapidly — 2–10 minutes after IV administration, reaches a maximum in 30–120 minutes, and lasts for 1–3 days.
By what route is Strophanthin K eliminated from the body?
The drug does not undergo hepatic metabolism and is excreted by the kidneys unchanged.
What else to study on this topic
- Pharmacological differences between polar (Strophanthin) and non-polar (Digitoxin) cardiac glycosides
- Methods of biological standardization of plant raw materials and determination of frog units
- The role of the aglycone and glycone in the pharmacodynamics and pharmacokinetics of cardiac glycosides
- Dosing principles and prevention of intoxication in acute heart failure
- Comparative characteristics of Strophanthin K and Corglycon
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