Mechanism of action and pharmacologic effects
Dexamethasone is a synthetic glucocorticosteroid, which is a fluorinated derivative of prednisolone. The presence of a fluorine atom in its chemical structure provides the drug with high potency: it exceeds prednisolone in anti-inflammatory action by 10 times and provides a prolonged systemic effect.
The primary mechanism of its immunosuppressive action consists in marked inhibition of lymphoid tissue proliferation.
The drug's effect on metabolism has two important features (compared to prednisolone):
- Mineral metabolism: Virtually unaffected, meaning it has minimal mineralocorticoid activity (does not cause sodium and water retention).
- Protein metabolism: Exhibits pronounced catabolic activity (stimulates protein degradation) exceeding that of prednisolone. In this parameter, the drug is similar to triamcinolone.
Indications for use
The drug has a resorptive (systemic) effect. Due to active catabolic processes, dexamethasone is recommended primarily for short-term use — during periods of disease exacerbation or in cases of prednisolone intolerance.
In oncohematology: Used for leukemias and lymphomas. Therapy dynamics are characterized by rapid onset of remission. However, relapse is eventually inevitable, and after several courses, the efficacy of glucocorticoids decreases.
Adjuvant use in oncology: Used to manage complications of the tumor process and side effects of chemotherapy. Dexamethasone effectively eliminates:
- Nausea and vomiting;
- Increased intracranial pressure;
- Hypercalcemia;
- Hemolysis.
Premedication: Included in the mandatory premedication regimen (in combination with diphenhydramine) prior to the administration of the cytostatic paclitaxel to prevent severe allergic reactions.
Pulmonology: Highly effective in bronchial asthma; however, systemic use is associated with a high risk of side effects (unlike topical inhaled forms).
Contraindications and side effects
There are no absolute contraindications if the drug is prescribed for life-saving indications to manage acute, urgent conditions.
Relative contraindications require the physician to carefully assess the risk-benefit ratio:
- Infectious processes: Tuberculosis, systemic mycoses, viral eye and skin lesions.
- Endocrine and metabolic disorders: Diabetes mellitus, osteoporosis.
- Cardiovascular pathology: Hypertension.
- Psychoneurological status: Psychoses.
- Ophthalmology: Glaucoma (including history thereof).
- Immunoprophylaxis: Period of vaccination with live vaccines.
Drug interactions and pharmacokinetics
Dexamethasone is a potent P-glycoprotein inducer (a transport protein that removes xenobiotics from cells) and microsomal liver enzymes.
- Effect on P-glycoprotein: By increasing the activity of this transporter, dexamethasone accelerates the elimination of drugs that are its substrates. The clinical consequence is a decrease in the therapeutic efficacy of concomitant drugs. Note: P-glycoprotein gene expression is subject to genetic polymorphism, and in men, it is more than 2 times higher than in women, creating individual pharmacokinetic variability.
- Interaction with caspofungin: As a microsomal enzyme inducer, dexamethasone accelerates the metabolism of the antifungal drug caspofungin, reducing its efficacy. Patient management in this case requires increasing the administered dose of caspofungin.
Dosage forms and prescription writing
The drug is available in several forms:
- Tablets 0.0005 g;
- Solution in ampoules 0.4% — 1 ml;
- Solution in vials 0.1% — 5 ml.
Example of a prescription for the tablet form: Rp.: Tab. Dexamethasoni 0.0005 D.t.d. N. 50 S. Take orally 1 tablet (0.0005 g) in the morning after meals.
Briefly: answers to topical questions
What is the molecular mechanism of the anti-inflammatory action of dexamethasone?
The molecular mechanism of dexamethasone's anti-inflammatory action involves affecting arachidonic acid metabolism at both genomic and non-genomic levels. The drug stimulates the production of lipocortins (annexins), which inhibit the enzyme phospholipase A2. This leads to the following effects:
- Blockade of arachidonic acid release from cell membrane phospholipids of damaged tissues.
- Cessation of pro-inflammatory mediator synthesis along both metabolic pathways: cyclooxygenase (reduced prostaglandin synthesis) and lipoxygenase (reduced leukotriene synthesis).
Additionally, there is suppression of pro-inflammatory factor (cytokine) synthesis due to the repression of corresponding genes.
What systemic side effects occur with long-term use of dexamethasone?
With prolonged systemic use of dexamethasone, a number of side effects develop across various organ systems. The main adverse reactions include:
- Endocrine system — Cushing's syndrome, steroid diabetes mellitus, adrenal suppression.
- Digestive system — steroid gastric and duodenal ulcer, gastrointestinal bleeding, erosive esophagitis.
- Musculoskeletal system — osteoporosis, steroid myopathy, decreased muscle mass.
- Skin — striae, acne, petechiae, delayed wound healing.
In addition, infectious complications, drug dependence, and fluid and sodium retention in the body may develop.
In which emergency conditions is parenteral administration of dexamethasone indicated?
Parenteral (intravenous) administration of dexamethasone is used for the pharmacological prevention of differentiation syndrome in acute promyelocytic leukemia: with a leukocyte count exceeding 10 × 10⁹/L during therapy, 4 mg is prescribed intravenously twice daily for 2–3 days. When dexamethasone is prescribed for life-saving indications to manage acute conditions, there are no absolute contraindications.
Fluorine gives potency but destroys protein: dexamethasone is 10 times stronger than prednisolone, but due to pronounced catabolism, it is used in short courses.
Class and exam questions
Why is dexamethasone preferred over prednisolone in increased intracranial pressure?
Dexamethasone has virtually no mineralocorticoid activity, meaning it does not cause sodium and water retention in the body while exerting a potent anti-inflammatory effect.
How does dexamethasone affect the efficacy of other drugs?
It acts as an inducer of P-glycoprotein and microsomal liver enzymes. This accelerates the clearance and metabolism of many drugs (e.g., caspofungin), reducing their therapeutic efficacy.
Are there absolute contraindications to the administration of dexamethasone?
When prescribed for life-saving indications to manage acute conditions, there are no absolute contraindications to the drug.
What else to study on this topic
- Mechanisms of gene transcription regulation by glucocorticoids.
- The role of P-glycoprotein in pharmacokinetics and the development of multidrug resistance.
- Comparative characteristics of systemic and topical (inhalational) glucocorticoids.
- Premedication protocols for taxane chemotherapy.
- Catabolic action of steroids: pathogenesis of steroid myopathy and osteoporosis.
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