Dexamethasone

Dexamethasone is a corticosteroid used to treat rheumatic conditions, a number of skin conditions, severe allergies, asthma, chronic obstructive pulmonary disease, croup, brain swelling, eye pain after eye surgery, and along with antibiotics for tuberculosis. It may be given by mouth, as an injection into a muscle, as an injection into a vein, as a topical cream or ointment for the skin, or as a topical solution for the eye.

Pharmacodynamics

Dexamethasone acts because of its structural similarity to endogenous glucocorticoids. Unbound, it can penetrate the membrane of the cell and then bind with high affinity to intracellular glucocorticoid receptors.

The anti-inflammatory (anti-inflammatory) effect is achieved by interfering with the so-called arachidonic acid metabolism. The active substance causes fewer prostaglandins and leukotrienes to be produced at the end of this metabolism. These are significantly involved in the inflammatory process of the human body.

Dexamethasone has an anti-allergic effect by preventing the release of histamine while reducing the number and activity of certain B and T lymphocytes.

It also has minimal mineralocorticoid activity.

All effects of dexamethasone occur with a time delay of 1-3 days, due to its complex mechanism of action.

Pharmacokinetics

Dexamethasone is approximately 77% protein-bound in plasma. The majority is bound to serum albumin. Dexamethasone is metabolized in the liver by the enzyme CYP3A4, so drug interactions may occur. Corticosteroids are generally excreted predominantly in the urine. However, <10% of dexamethasone is excreted in the urine. The mean half-life of a tablet is 4 hours. After intramuscular injection, the half-life is approximately 3-6 hours.

Drug Interactions

Known drug interactions are:

• Inducers of hepatic microsomal enzymes (CYP450) such as barbiturates, phenytoin, and rifampicin may decrease the half-life of dexamethasone.
• Concomitant treatment with oral contraceptives may increase its volume of distribution.

Side effects

Common and occasional side effects:

• Acne
• Insomnia
• Dizziness
• increased appetite
• Weight gain
• Impaired skin healing
• Depression
• Euphoria
• High blood pressure
• Increased risk of infection
• Increased intraocular pressure
• Vomiting
• Dyspepsia
• Confusion
• Amnesia
• Irritability
• Nausea
• malaise
• Headache
• Cataract (occurs in about 10% of patients on long-term treatment)

Toxicological data

LD50 (rat, oral): 54 mg-kg-1