(dexamethasone)

Brand

Azium

Availability

• Tablets: 0.25 mg, 0.75 mg, 1 mg, 1.5 mg, 2 mg, 4 mg, 6 mg
• Injectable: 2mg/mL
• Elixer: Human approved available in 0.5 mg/5ml and 0.5 mg/0.5ml

(dexamethasone sodium phosphate)

Brand

Azium SP, Dexasone, Decadron

Availability

• A highly soluble form, with more rapid onset and shorter duration.
  (*note: 1.3 mg of dexamethasone sodium phosphate is equal to 1 mg of dexamethasone; 4mg/mL of dexamethasone sodium phosphate [Dexamethasone-SP formulation] injection is equivalent to 3mg/mL of dexamethasone).

Pharmacology

Dexamethasone is a long acting fluorinated glucocorticoid with 25-30 times more potency than an equal weight of hydrocortisone. It is faster acting with longer duration than the intermediate oral agent’s prednisone and prednisolone. In dogs, the drug has been shown to have a half-life of 2 to 5 hours with biologic activity of up to 48 hours.

Dexamethasone stimulates synthesis of enzymes required to decrease the inflammatory response. Its primary efficacy is that of a strong anti-inflammatory, as well as an antiallergic agent.

Besides being an anti-inflammatory, the drug will also suppress the immune response, stimulate bone marrow, and influence fat, protein, and carbohydrate metabolism. Although it is able to cause diuresis, there are more effective drugs for reducing edema.

The drug is readily absorbed into tissue, and rapidly distributed to kidneys, liver, muscle, and intestines. It is metabolized in the liver and primarily excreted by the kidneys. The drug is passed in small amounts in breast milk.

Laboratory animal studies with dexamethasone have shown evidence of teratogenicity producing fetal resorptions, cleft palate, and abnormalities of head, ears and limbs following high dosing or repeated multiples of the therapeutic dose. Dexamethasone should be used during pregnancy, or in lactating females, only if the benefit outweighs the risk.

Dexamethasone can be given oral, topical, or by injection, and can be found in combination applications for use in different health conditions.

Indications

Used as a quick agent to reduce inflammation in ear infections causing wry neck/head tilt.

Can be used as support therapy in respiratory infections unresponsive to antimicrobials alone, or in serious to advanced lung infections (e.g., pneumonia) to reduce allergic response (especially where pathogen suspected to be mycoplasma).

Also used for swelling caused by injury, cerebral edema, neoplasia, autoimmune skin disorders, and septic shock.

Drug Interactions or Contraindications

• Do not give in active untreated infections or viral, and fungal diseases of the eye.
• Use with caution in CHF and inflammatory bowel conditions.
• Incompatible mixed in with doxorubicin HCL, daunorubicin HCL, and vancomycin.
• Has only minor mineralcorticoid effect and should not be used alone to treat adrenal insufficiency.
• When used with NSAIDs will increase GI distress or cause bleeding, use together cautiously, and only when directed to do so by veterinarian.

Adverse Reactions

EENT: cataracts, glaucoma

CV: CHF, edema

GI: Known to increase appetite but may have opposite effect in rats with resulting weight loss.

Skin: delayed wound healing, thinning of dermal tissue, skin atrophy

Local: atrophy at injection site

Other: may mask or exacerbate infections already present

Dosage Recommendations

*Note: based on dexamethasone’s long biologic activity of action it is advised to use the lowest dose for condition being treated which achieves the desired effect.

Dosage when using Dexamethasone Sodium Phosphate

0.23 mg/lb to 0.9 mg/lb, PO or SQ, BID, then decreasing dose x 3-14 days  ^3, 12

Dexamethasone dosages

0.5 mg/lb to 1 mg/lb, SQ or IM (if using this dose range in lbs. and changing to kg. It will be 1.0 mg/kg to 2.0 mg/kg) ⁴

or

0.5 mg/kg to 2.0 mg/kg, PO or SQ, (then decreasing dose q12h x 3-14 days). ^{1, 26, 34, 35, 41, 44}(anti-inflammatory)

or

0.6 mg/kg, IM (as antiinflammatory)  ^{1, 26, 27, 34}

or

FOR SHOCK ONLY give 4 mg/kg to 5 mg/kg, SQ, IM, IP, IV  ^{1, 26, 34, 41, 44}

*Note: The use of glucocorticoids in rodents for the treatment of shock remains controversial. While it can be a useful drug in instances of shock, treatment should be directed at correcting the cause of shock. Supportive oxygen therapy, fluid volume replacement therapy, correction of metabolic acidosis, rewarming of the animal, vasopressors and antibiotic therapy where required are important measures in helping to correct the condition.

Dexamethasone In Treatment Regimen

The following are dosage guidelines recommended by “Dr. Mike” Hutchinson, DVM; Animal General, Cranberry Township, PA. This incorporates the use of dexamethasone in a treatment regimen for rats with respiratory infection where mild to moderate, or serious to advanced lung involvement is present. This schedule is based on Dr. Hutchinson’s experience treating rats, and also from what he gleaned from current literature:

• Early to moderate respiratory illness (where lung involvement is present, especially where pathogen suspected to be mycoplasma)
  
  Dexamethasone at 0.5 mg/lb can be added to the treatment regimen, weaning down as follows:
  0.5 mg/lb BID injectable or PO (oral) for 3 days
  0.5 mg/lb SID for 3 days
  0.25 mg/lb SID for 3 days
  0.25 mg/lb orally every other day, three doses

• Serious and Advanced Respiratory Illness (or more difficult to treat lower respiratory illness)
  
  Dexamethasone 1 mg/lb BID, added to treatment regimen, then weaned down as follows:
  1 mg/lb BID injectable or PO (oral) for 3 days
  1 mg/lb SID for 3 days
  0.5 mg/lb SID for 3 days
  0.5 mg/lb orally every other day, three doses
  

  *Note: other veterinary recommended dosing and reduction schedules for dexamethasone may also be used.

For a complete treatment regimen incorporating dexamethasone along with antimicrobials: enrofloxacin and
doxycycline, as well as nebulized treatments of gentocin and Albuterol see articles: Mycoplasma or Pneumoniain the Health section of the Rat Guide. Also see individual monographs for more information on specific antimicrobials and respiratory agents in the Medication section of the Rat Guide.

Dexamethasone has been shown, in the controlled studies cited below, to reduce plasma leakage, resolve Mycoplasma induced inflammation, and also reduce the number of Mycoplasma organisms even when used as the only therapy.

• Am. J. Respir. Crit. Care Med., Vol 150, No. 5, Nov 1994, 1391-1401; Dexamethasone and oxytetracycline reverse the potentiation of neurogenic inflammation in airways of rats with Mycoplasma pulmonis infection; J.J. Bowden, TR Schoeb, J. R. Lindsey and D.M. McDonald; Cardiovascular Research Institute and Department of Anatomy, UCSF.
• Am. J. Respir. Crit. Care Med., Vol 164, No. 10 Nov 2001, S39-S45; Angiogenesis and Remodeling of Airway Vasculature in Chronic Inflammation; Donald M. McDonald; Cardiovascular Research Institute and Department of Anatomy, UCSF.

Considerations

• Recommended for single injection or for short duration.
• Sudden withdrawal of drug may be fatal if given over an extended period of time. Check with veterinarian prior to stopping or to gradually reduce dosage.
• Dexamethasone is preferred over prednisone for use in rats.
• Store at room temperature and protect from light.

References

1. Bonamin, L. V., de Moraes, C. L., Sanches, F., Cardoso, T. N., Sato, C., Duran Filho, C., & Martini, L. C. (2012). Rats Born to Mothers Treated with Dexamethasone 15 cH Present Changes in Modulation of Inflammatory Process. Evidence-based complementary and alternative medicine : eCAM, 2012, 710923. https://doi.org/10.1155/2012/710923