Hypervitaminosis K

Etiology and risk factors

Pathological physiology views vitamin K excess not merely as a quantitative nutrient overload, but as a potent trigger of severe metabolic disorders. The most vulnerable category of patients consists of newborn infants. It has been clinically proven that symptom manifestation most often occurs during a strictly defined period — on the 3rd–5th day of life of the infant.

The development of the pathological condition is based on two main etiological factors:

1. Absolute overdose. Occurs with the inadequate administration of vitamin K preparations, when the dose significantly exceeds the physiological needs and metabolic capacity of the infant's body.
2. Relative overdose associated with enzymopathy. Develops upon administration of the drugs to patients with latent or overt glucose-6-phosphate dehydrogenase deficiency. Under conditions of deficiency of this vital enzyme, even standard therapeutic doses of the vitamin become highly toxic and trigger a cascade of pathological reactions in the blood.

Pathogenesis of Hemolytic Syndrome

The central link in the pathogenesis of this hypervitaminosis is the development of hemolytic syndrome. Intensive hemolysis (massive destruction of red blood cells) and the accompanying severe jaundice are formed under the influence of two key mechanisms that grossly disrupt homeostasis:

• Critical depletion of the antioxidant defense of erythrocytes. In the event of vitamin K excess, a rapid and extremely significant decrease in the concentration of reduced glutathione occurs inside the red blood cells. Deprived of this natural defense, erythrocyte membranes lose stability, become damaged, and undergo premature breakdown within the bloodstream.
• Decreased conjugation function of the liver. The problem is repeatedly compounded by the fact that the liver loses its ability to adequately process the products of massive erythrocyte breakdown. There is a marked decrease in the hepatocytes' ability to form glucuronides. As a result, the binding process of free pigment is disrupted, making its safe elimination from the body impossible.

Clinical manifestations

The clinical picture of the pathology directly stems from the pathogenesis mechanisms described above. Symptoms are most pronounced in infants of the first days of life and include the classical triad of severe manifestations:

• Hemolytic anemia. Is a direct and inevitable consequence of massive erythrocyte destruction. Accompanied by a sharp drop in their count per unit volume of blood.
• Hyperbilirubinemia. Represents the accumulation in blood plasma of a huge amount of unconjugated bilirubin, which physically cannot be utilized by the liver due to an acute deficiency of glucuronides.
• Kernicterus. This is the most formidable and disabling manifestation of hypervitaminosis K. Toxic indirect bilirubin crosses the blood-brain barrier and specifically impregnates the nuclei of the brain.

Features of the Course in Premature Infants

In pediatric practice, special attention is paid to the group of premature infants. The physiological immaturity of liver enzyme systems, in particular, the mechanisms of glucuronide formation, makes them extremely susceptible to the toxic effects of vitamin K excess.

If such an infant additionally exhibits Erythroblastosis, the risk of developing kernicterus increases manifold. Massive hemolysis against the background of a critically reduced level of reduced glutathione leads to a catastrophic surge in hyperbilirubinemia, which the immature liver of a premature infant is absolutely incapable of coping with.

Briefly: answers to topical questions

Class and exam questions

What else to study on this topic

• Mechanisms of reduced glutathione depletion in erythrocytes in vitamin K excess.
• The role of glucose-6-phosphate dehydrogenase in maintaining erythrocyte membrane stability.
• The biochemical process of glucuronide formation in the newborn's liver.
• The pathogenesis of bilirubin penetration across the blood-brain barrier in kernicterus.
• The relationship between erythroblastosis and the severity of hypervitaminosis K in premature infants.

Other topics in "Chapter 14. Vitamin Metabolism Disorders"

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