Allergic reactions and complications

Adverse drug reactions

The development of side effects is driven by the mechanisms of interaction between administered substances and body tissues. In clinical pathophysiology, it is customary to distinguish several main groups of complications that require a physician's attention.

• Hypersensitivity allergic reactions: can manifest as skin rashes, urticaria, angioedema, severe bronchospasm, and anaphylactic shock. A classic example of the pathogenesis is the reaction to antibacterial drugs: their metabolism produces penicilloic acid. It binds to the amino groups of the body's own proteins, forming a pathological "hapten-carrier" complex, which acquires strong immunogenic properties and triggers a hypersensitivity cascade.
• Gastrointestinal complications: include general dyspeptic symptoms such as diarrhea, nausea, vomiting, and abdominal pain. An extremely dangerous, life-threatening condition is the development of pseudomembranous colitis.
• Local tissue reactions: their nature depends on the route of administration. Intramuscular injections are often accompanied by the formation of painful infiltrates, while intravenous infusions can provoke phlebitis.
• Development of superinfections: alteration of the normal microflora sometimes leads to opportunistic infections, such as vaginal candidiasis or oral candidiasis.

Contraindications to vaccination

To prevent post-vaccination complications, it is necessary to thoroughly collect an allergological history and assess the patient's current condition. All contraindications can be divided into absolute and temporary.

1. Absolute restrictions: the presence of hypersensitivity to any components of the administered vaccine (or its analogues), as well as documented episodes of severe allergies in the past. There are strict rules for two-component vaccines: if severe complications develop following the administration of the first component, the use of the second is strictly prohibited. Such life-threatening conditions include anaphylactic shock, generalized allergic rashes, convulsive syndrome, and fever with a temperature rise above 40 °C.
2. Temporary (acute) conditions: vaccination is postponed during the exacerbation of chronic illnesses, as well as at the height of acute infectious and non-infectious pathologies. The standard period for resuming immunization is considered to be two to four weeks after achieving remission or complete recovery. Exceptions are mild forms of acute intestinal infections and mild acute respiratory viral infections (ARVI)—in such cases, administration of the drug is permitted immediately after the patient's body temperature has steadily normalized.

Shock: etiological classification and forms

Shock is a systemic disturbance of tissue perfusion leading to severe hypoxia. Since there is no single universal classification of this syndrome, the baseline criterion for differentiation in pathophysiology is the leading etiological factor and the initial link in the pathogenesis.

• Traumatic shock: occurs as a result of massive mechanical trauma (fractures, wounds, tissue crushing, traumatic amputations), which is often complicated by blood loss and infection. This group also includes conditions caused by thermal exposure (burn, cold) and electrical injury.
• Hemorrhagic (hypovolemic) shock: develops against the background of acute post-hemorrhagic blood loss or due to profound dehydration (dehydration type).
• Septic (toxic-infectious) shock: complicates the course of generalized purulent infections. Its trigger is most frequently gram-negative flora (E. coli, Proteus, Klebsiella), and somewhat less frequently gram-positive pathogens (staphylococci, pneumococci, streptococci).
• Cardiogenic shock: accompanies severe cardiac damage, including myocardial infarction, cardiomyopathies, and acute heart failure.

Additionally, anaphylactic (arising as an acute allergic reaction), post-transfusion, and psychogenic shock are distinguished. In routine clinical practice, it is customary to assess the severity of the syndrome using a three-point scale: from mild (grade I) to severe (grade III).

Pathogenetic features of specific types of shock

Determining the primary pathogenetic mechanism is critically important for selecting the correct intensive care tactics. Vascular and cardiogenic hemodynamic disorders occupy a special place.

Vascular (distributive) shock develops due to total vasodilation, a sharp increase in capillary network permeability, and pathological arteriovenous shunting. This leads to a significant drop in total peripheral vascular resistance and redistribution of blood volume. Distributive shock includes anaphylactic shock and neurogenic shock (triggered by pain syndrome, spinal cord injury, or occurring as a complication of anesthesia).

Cardiogenic shock is regarded as the extreme degree of acute heart failure. It is characteristic of patients with myocardial infarction (specifically with ST-segment elevation) and manifests as pronounced organ hypoperfusion. The following pathogenetic variants are distinguished:

1. True: develops with primary hypokinesia and loss of left ventricular contractile function.
2. Arrhythmic: a hemodynamic catastrophe against the background of critical bradyarrhythmias or tachyarrhythmias.
3. Hypovolemic: associated with absolute or relative intravascular volume deficit. Reflex shock is pathogenetically close to it, representing a systemic reaction to an acute pain attack.

In modern cardiology, the international SCAI classification is used to detail the patient's condition, dividing cardiogenic shock into five stages: from the risk group to the refractory terminal phase.

Class and exam questions

What else to study on this topic

• Biochemical mechanisms of formation of the "hapten-carrier" complex using penicilloic acid as an example.
• Pathogenesis and risk factors for the development of pseudomembranous colitis during pharmacotherapy.
• Detailed characteristics of the 5 stages of cardiogenic shock according to the SCAI classification.
• The role of gram-negative bacteria (E. coli, Proteus, Klebsiella) in triggering the septic shock cascade.

Prepared by WhiteCoat Pro faculty in accordance with the medical school curriculum. For educational purposes only.