Dexamethasone

Pronunciation

Dexamethasone 0.5mg

Introduction

Dexamethasone is a steroid with anti-inflammatory and immunosuppressant effects. It is used to treat a wide range of inflammatory and autoimmune conditions.

Indications include:

• Inflammatory bowel disease
• Asthma
• Croup in children
• dermatitis
• Rheumatoid arthritis
• Cerebral oedema associated with malignancy
• Counteract nausea and vomiting effects of cancer chemotherapy
• Administered before antibiotics in cases of baceterial meningitis. It reduces the inflammatory response, thus reducing hearing loss and neurological damage.
• High-attitude cerebral edema (HACE) and high-attitude pulmonary edema (HAPE), help climbers to cope with complications of high-attitude sickness

Equivalent anti-inflammatory doses of steroids

Prednisolone 5 mg is equivalent to	Betamethasone 750 micrograms
	dexamethasone 750 micrograms
	hydrocortisone 20 mg
	methylprednisolone 4 mg
	triamcinolone 4 mg

Mechanism of Action

Immunosuppression agent, Steroid replacement agent, Anti-inflammatory agent

Generic Name 藥名	HA Code 藥物代碼	Classification藥物分類
Dexamethasone Tablet 0.5 mg	DEXA01	P1S1S3
Dexamethasone Tablet 4 mg	DEXA19	P1S1S3
Dexamethasone 0.1% + Chloramphenicol 0.5% Eye Drops 5ml	DEXA16	P1S1S3
Dexamethasone 0.1% + Neomycin 0.5% Eye Drops 10ml	DEXA04	P1S1S3

Dosage

Dosages of steroids vary widely in different diseases and in different patients.

When long-term steroid therapy is used in some chronic diseases, the adverse effects of treatment may be great. To minimize side-effects the maintenance dose should be kept as low as possible.

Steroids are used both topically (by rectum or eye) and systemically (by mouth or intravenously).

Whenever possible local treatment with creams, intra-articular injections, inhalations, eye-drops or enemas should be used in preference to systemic treatment.

The suppressive action of a steroid on cortisol secretion is least when it is given as a single dose in the morning.

Oral: usual range 0.5 – 5 mg daily

Child dose: 10-100 micrograms/kg daily

Cerebral oedema, by intravenous injection: 8-16 mg initially, then 5 mg by intramuscular or intravenous injection every 6 hours until the symptoms of edema subside for 2-4 days, then gradually reduced and stopped over 5-7 days.

By intra-articular injection, 0.8 – 4mg of dexamethasone (as sodium phosphate) are used depending upon the size of the joint.

For soft-tissue injection, 2 – 6 mg are used.

For topical application in various skin disorders, concentrations of dexamethasone in the range of 0.02 to 0.1% is used in creams, ointments and lotions. Whereas for eye or ear preparations, concentrations are commonly 0.05 to 0.1%.

Side Effects

Short-term use include nausea and feeling tired. More severe side effects include psychiatric problems including euphoria, nightmares, insomnia, irritability, confusion, suicidal thoughts and behavioral disturbances. This may occur in about 5% of people.

Adrenal suppression
Steroid-induced diabetes
Osteoporosis, muscle wasting and weakness	which is a danger, particularly in the elderly, as it can result in osteoporotic fractures for example of the hip or vertebrae
Susceptibility to infection
Cushing’s syndrome	moon face, striae, and acne
Endocrine side effects	menstrual irregularities and amenorrhea, hirsutism, weight gain, hyperlipidemia
Neuropsychiatric side effects	aggravation of schizophrenia, aggravation of epilepsy, insomnia, irritability, mood changes
Dermatological effects	easy bruising, impaired wound healing, and thinning of skin
Ophthalmic effects	glaucoma, corneal or scleral thinning and exacerbation of ophthalmic viral or fungal disease

Side-effects can be minimized by using lowest effective dose for minimum period possible.

Pharmacokinetics

Dexamethasone is readily absorbed from the gastrointestinal tract.

Plasma half-life is about 190 minutes.

Binding of dexamethasone to plasma proteins is about 77%.

Up to 65% of a dose is excreted in urine within 24 hours.

Drug Management

Monitoring:

• Elderly (close supervision required particularly on long-term treatment)
• Frequent monitoring required if history of tuberculosis (or X-ray changes)
• blood sugar level, blood pressure, mood change,
• monitoring of the fluid intake and output, and daily weight records may give early warning of fluid retention.
• Sodium intake may need to be reduced and calcium and potassium supplements may be necessary.
• Back pain may signify osteoporosis
• Height should be monitored in children receiving prolonged therapy with inhaled or nasal steroid.

Drug interaction: Interactions do not generally apply to steroid used for topical action including inhalation, unless specified.

Drugs given with steroid	Potential adverse drug interactions
NSAIDs	Increased risk of gastro-intestinal bleeding
Rifampicin	Accelerate metabolism of steroid so reduce the effects of steroid
Antidiabetics	Steroid antagonize hypoglycaemic effect. Requirements of antidiabetics may be increased.
Antiepileptics: Carbamazepine Phenobarbitone phenytoin	Accelerate metabolism of steroid so reduce the effects of steroidd
Antifungals: amphotericin	Increased risk of hypokalaemia
Antivirals: ritonavir	Increase plasma concentration of steroid – increased risk of adrenal suppression
Digoxin	Increased risk of hypokalaemia
Diuretics: frusemide hydrochlorothiazide	antagonize diuretic effect, increased risk of hypokalaemia
Oral contraceptive (oestrogens)	Increase plasma concentration of steroid
Theophylline	Increased risk of hypokalaemia