Ovid: Handbook of Critical Care Drug Therapy

Chapter 11

Allergy

P.220

TABLE 11.1. Anaphylaxis and Contrast Dye Reactions^a—Prophylaxis

Agent	Dosage	Time Prior to Exposure
Prednisone or Hydrocortisone	50 mg PO 100 mg IV	13 h, 7 h, and 1 h prior to exposure
Diphenhydramine	50 mg PO or IV	13 h, 7 h, and 1 h prior to exposure
H₂-blocker^b	See below	13 h and 1 h prior to exposure
Ephedrine (optional)	25 mg PO	1 h prior to exposure
IV, intravenous; PO, by mouth Note: Consider for patients with prior history of dye reaction; may also consider use of nonionic contrast material
^aThis regimen also appropriate for other prophylactic situations. ^bRanitidine: 150 mg PO or 50 mg IV Famotidine: 20 mg PO/IV Cimetidine: 300 mg PO/IV

P.221

TABLE 11.2. Anaphylaxis—Therapy

Situation	Intervention	Comments
Systemic anaphylaxis	Epinephrine 1:1,000, 0.3 cc SC, repeat at 5–10 min intervals Diphenhydramine 25–100 mg IV H²-blocker^a Hydrocortisone 100–250 mg IV q6h	Repeat doses of diphenhydramine may be required for symptom relief
Special Problems
Upper airway obstruction	Nebulized racemic epinephrine, 0.3 ml diluted in 3 ml 0.9% NaCl	Administer oxygen; consider tracheal intubation and mechanical ventilation
Bronchospasm	Epinephrine 1:1,000, 0.3–0.5 ml SC, may repeat at 5–10 min intervals, or Albuterol, 1–2 puffs metered dose inhaler or 2.5–5 mg nebulized in 2–3 ml 0.9% NaCl, or Aminophylline, 6 mg/kg IV initially (see Table 4.4)	With severe bronchospasm or hypotension, consider epinephrine, 1:10,000, 0.5–1.0 ml IV (rather than SC)
Shock	Volume resuscitation with 0.9% NaCl ≥500 ml rapidly, with or without vasopressors Dopamine 5–20 µg/kg/min, titrated to blood pressure, or Norepinephrine, 2 µg/min, titrated to blood pressure Patients on β-blockers who are hypotensive may also be treated with glucagon, 1 mg IV
IV, intravenous; SC, subcutaneous ^aRanitidine: 50 mg IV Famotidine: 20 mg IV Cimetidine: 300 mg IV

P.222

TABLE 11.3. Desensitization Procedure for Beta-lactam and Other Antibiotics

For patients with severe or life-threatening infections and a history of previous significant allergic reactions to an essential antibiotic (e.g., a history of wheezing, hypotension, an-gioedema, or other symptoms and signs of systemic anaphylaxis on exposure to the antibiotic or class). This may be documented with skin testing to penicillin if reagents are available. For other classes of antibiotics, the decision to desensitize is based on the clinical history.

The procedure should be carried out in a monitored setting with a physician available.
A secure IV line should be established.
Epinephrine, diphenhydramine, parenteral glucocorticosteroids should be immediately available for acute anaphylactic reactions (see Table 11.2).
Six serial 10-fold dilutions of the desired antibiotic dose should be prepared each in 20 ml bags or syringes.
Each dose from the most dilute to the least dilute should be administered intravenously over 20 minutes (1 ml/min).
A physician should examine the patient prior to each dose.

Example: Ceftriaxone
   2 mcg/20 ml over 20 minutes
   20 mcg/20 ml over 20 minutes
   200 mcg/20 ml over 20 minutes
   2 mg/20 ml over 20 minutes
   20 mg/20 ml over 20 minutes
   200 mg/20 ml over 20 minutes
   2 gm/20 ml (full dose) over 20 minutes

In the absence of an allergic reaction, the standard dose of the antibiotic may be administered after approximately 2 hours.
If a mild to moderate reaction such as flushing, wheezing, or chest tightness occurs, the infusion should be stopped and the subject treated with antihistamines, epinephrine, or both.
When the patient's symptoms/signs have resolved, the infusion may be repeated or resumed at 0.5 ml/min.
If a severe reaction occurs, the infusion should be stopped and the line aspirated to remove any residual antibiotic. The subject should be treated as described in the anaphylaxis therapy protocol (Table 11.2) and the desensitization effort discontinued.
When there is a need to provide immediate antibiotic coverage because of severe infection, an alternative antibiotic should be administered for at least one dose prior to the desensitization procedure.
The desensitization procedure should limit or prevent acute allergic reactions to the antibiotic during the initiation of the antibiotic but will need to be reimplemented if a time period greater than 48 hours elapses between doses of therapy.