Chemical Structure and Mechanism of Action
The Strophanthin K molecule features a classical cardiac glycoside structure consisting of two components:
- Aglycone (Genin): Has a steroid nature—the core is represented by a cyclopentanoperhydrophenanthrene ring with an attached unsaturated lactone ring. Strophanthin K's aglycone differs by having an aldehyde group (-CHO) and additional hydroxyl groups (-OH). The aglycone 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 solubility, absorption, excretion, and cumulative capacity.
Because Strophanthin K is a pronounced polar compound, it has specific distribution and elimination properties.
Pharmacokinetics and Biological Standardization
The pharmacokinetic profile of Strophanthin K is characterized by the following key parameters:
- Absorption: The drug is virtually unabsorbed from the gastrointestinal tract, making oral administration impossible. The route of administration is strictly intravenous.
- Time Parameters: Features a very short latent period. Action begins within 2–10 minutes (in some cases up to 20 minutes), peaking in 30–120 minutes. The total duration of the pharmacological effect is 1 to 3 days.
- Binding and Metabolism: Binds to plasma proteins by approximately 40%. It undergoes no biotransformation (is not metabolized) in the body.
- Excretion: Completely excreted by the kidneys in unchanged form.
- Accumulation: Due to its short circulation time, material accumulation is significantly lower than that of digitalis glycosides; however, the risk of toxicity is not completely excluded.
Biological Standardization: Because plant materials contain enzymes that alter the structure of primary glycosides, preparations are subject to strict standardization by comparison with a standard reference. Activity is measured in frog units (FUD or LD). Pure strophanthin has the highest biological activity among glycosides: 1 gram of the substance contains 44,000–56,000 FUD.
Indications
Due to its rapid onset of action, Strophanthin K is used for the following pathological conditions:
- Acute heart failure (AHF) — the drug of choice for emergency medical care.
- Chronic heart failure (CHF) functional classes III–IV.
- Tachyarrhythmic form of atrial fibrillation.
Adverse Effects and Toxicity Risks
Despite a lower degree of accumulation compared to non-polar glycosides (such as digitoxin), the risk of glycoside intoxication persists with Strophanthin K.
The risk of toxicity increases during rapid infusion or impaired renal excretory function, as drug elimination depends entirely on renal clearance. Rapid administration can trigger severe rhythm and conduction disturbances.
Administration Guidelines and Prescription Example
Strophanthin K is administered strictly via slow intravenous injection. To prevent complications, a single dose of 0.5–1 ml of the 0.05% solution is pre-dissolved in 10–20 ml of a 20% or 40% glucose solution and administered 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).`