Mechanism of Action and Pharmacological Effects
Dexamethasone is a synthetic glucocorticosteroid and a fluorinated derivative of prednisolone. The presence of a fluorine atom in its chemical structure provides high potency: it exceeds prednisolone in anti-inflammatory activity by 10-fold and produces a prolonged systemic effect.
The primary mechanism of immunosuppressive action involves pronounced suppression of lymphoid tissue proliferation.
The drug's effects on metabolism have two key features (compared to prednisolone):
- Mineral metabolism: Practically negligible effect, meaning it has minimal mineralocorticoid activity (does not cause significant sodium and water retention).
- Protein metabolism: Exhibits pronounced catabolic activity (stimulates protein degradation), surpassing that of prednisolone. In this parameter, the drug is similar to triamcinolone.
Indications for Use
The drug acts systemically (resorptive action). Due to active catabolic processes, dexamethasone is recommended primarily for short-term use during acute disease exacerbations or in cases of prednisolone intolerance.
In Oncohematology: Used in leukemias and lymphomas. Therapy dynamics are characterized by rapid remission induction. However, relapse is ultimately inevitable, and after several courses, the efficacy of glucocorticoids decreases.
Adjuvant Oncology Support: Used to manage tumor-related complications and chemotherapy side effects. Dexamethasone effectively alleviates:
- Nausea and vomiting;
- Elevated intracranial pressure;
- Hypercalcemia;
- Hemolysis.
Premedication: Included in mandatory premedication regimens (combined with diphenhydramine) prior to the administration of the cytotoxic agent paclitaxel to prevent severe allergic reactions.
Pulmonology: Highly effective in bronchial asthma, though systemic use carries a high risk of adverse effects (unlike topical inhaled formulations).
Contraindications and Adverse Effects
Absolute contraindications do not exist 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 ocular and skin infections.
- Endocrine and metabolic disorders: Diabetes mellitus, osteoporosis.
- Cardiovascular pathology: Hypertension.
- Psychoneurological status: Psychoses.
- Ophthalmology: Glaucoma (including a history of it).
- Immunoprophylaxis: Period of vaccination with live vaccines.
Drug Interactions and Pharmacokinetics
Dexamethasone is a potent inducer of P-glycoprotein (an efflux transporter protein that pumps xenobiotics out of cells) and hepatic microsomal enzymes.
- Effect on P-glycoprotein: By increasing the activity of this transporter, dexamethasone accelerates the elimination of substrate drugs. The clinical consequence is a reduction in the therapeutic efficacy of co-administered medications. Note: P-glycoprotein gene expression is subject to genetic polymorphism, and in males, it is more than twice as high as in females, creating individual pharmacokinetic variability.
- Interaction with Caspofungin: As a microsomal enzyme inducer, dexamethasone accelerates the metabolism of the antifungal drug caspofungin, reducing its efficacy. Management in this case requires increasing the administered dose of caspofungin.
Dosage Forms and Prescription Writing
The drug is available in several forms:
- 0.0005 g tablets;
- 0.4% solution in 1 ml ampoules;
- 0.1% solution in 5 ml vials.
Example 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.