MEDIHALER-EPI
Clinical safety rating: caution
Comprehensive clinical and safety monograph for MEDIHALER-EPI (MEDIHALER-EPI).
Epinephrine is a direct-acting sympathomimetic amine that acts on alpha- and beta-adrenergic receptors. Alpha-adrenergic stimulation increases peripheral vascular resistance and blood pressure, while beta-adrenergic stimulation increases heart rate, myocardial contractility, and bronchodilation.
| Metabolism | Metabolized by monoamine oxidase (MAO) and catechol-O-methyltransferase (COMT) in the liver, kidneys, and other tissues. |
| Excretion | Epinephrine is primarily metabolized in the liver and other tissues by catechol-O-methyltransferase (COMT) and monoamine oxidase (MAO). The metabolites, including metanephrine and vanillylmandelic acid (VMA), are excreted in urine. Less than 5% of the drug is excreted unchanged in urine. Fecal elimination is negligible. |
| Half-life | The terminal elimination half-life of epinephrine is approximately 2-3 minutes. Clinically, this short half-life necessitates repeated dosing or continuous infusion for sustained effect during anaphylaxis or cardiac arrest. |
| Protein binding | Epinephrine is approximately 50% bound to plasma proteins, primarily albumin and alpha-1-acid glycoprotein. |
| Volume of Distribution | The volume of distribution (Vd) of epinephrine is approximately 0.3-0.5 L/kg. This relatively low Vd indicates limited extravascular distribution, consistent with its rapid onset and short duration. |
| Bioavailability | Epinephrine is poorly bioavailable orally due to extensive first-pass metabolism (<2%). Intramuscular administration yields near-complete absorption (bioavailability ~80-100%). Subcutaneous administration has variable bioavailability (50-80%) due to local vasoconstriction. Inhalation (Medihaler-Epi) delivers about 10-20% of the dose to the lungs, with systemic absorption occurring from the respiratory tract. |
| Onset of Action | Intravenous: immediate (seconds); Intramuscular: within 5-10 minutes; Subcutaneous: 5-15 minutes; Inhalation (as in Medihaler-Epi): within 1-2 minutes for bronchodilation. |
| Duration of Action | Intravenous: 5-10 minutes; Intramuscular: 10-20 minutes; Subcutaneous: 20-30 minutes; Inhalation (Medihaler-Epi): 1-3 hours for bronchodilation, though systemic effects are shorter. Note: Duration is dose-dependent and may be prolonged in overdose or with impaired metabolism. |
Each inhalation delivers 0.22 mg epinephrine (base equivalent). Acute asthma exacerbation: 1-2 inhalations every 4 hours as needed. Maximum 12 inhalations in 24 hours.
| Dosage form | AEROSOL, METERED |
| Renal impairment | No specific dose adjustment recommended for renal impairment. Use with caution in severe renal impairment (eGFR <30 mL/min/1.73 m²) due to potential for systemic accumulation. |
| Liver impairment | No specific dose adjustment recommended for hepatic impairment. Use with caution in severe hepatic impairment (Child-Pugh class C) due to potential for reduced drug clearance. |
| Pediatric use | Weight-based dosing: 0.1 mg/kg per inhalation (nebulized equivalent). MEDIHALER-EPI is not approved for use in children <2 years. For children 2-12 years: 1-2 inhalations every 4 hours as needed. Maximum 12 inhalations in 24 hours. |
| Geriatric use | Initial dose: 1 inhalation. Titrate cautiously due to increased sensitivity to beta-agonists and higher prevalence of cardiovascular comorbidities. Monitor heart rate, blood pressure, and ECG in elderly patients. |
| 1st trimester | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
Comprehensive clinical and safety monograph for MEDIHALER-EPI (MEDIHALER-EPI).
| Breastfeeding | Epinephrine is excreted into breast milk in minimal amounts; the M/P ratio is not established. The oral bioavailability is low, and it is rapidly metabolized in the infant's gastrointestinal tract. Short-term use is considered compatible with breastfeeding. However, monitor infant for signs of sympathetic stimulation (e.g., tachycardia, irritability). |
| Teratogenic Risk | Epinephrine is a sympathomimetic amine. In animal studies, high doses have been associated with teratogenicity (e.g., gastroschisis). Human data: Inadequate evidence in pregnant women. First trimester: Potential risk of malformations based on case reports and animal data. Second and third trimesters: May cause uterine vasoconstriction and reduced placental perfusion, leading to fetal hypoxia and bradycardia. Use only if maternal benefit outweighs fetal risk. |
■ FDA Black Box Warning
None
| Serious Effects |
["Hypersensitivity to epinephrine","Narrow-angle glaucoma (for ophthalmic use)","In conjunction with general anesthetics that sensitize the heart to catecholamines (e.g., halothane) — relative contraindication"]
| Precautions | ["May cause hypertension, myocardial ischemia, or arrhythmias","Use with caution in patients with cardiovascular disease, hypertension, hyperthyroidism, or diabetes","Risk of pulmonary edema with excessive doses","May worsen hypokalemia"] |
| Food/Dietary | No direct food interactions. However, patients with food allergies should avoid known allergens. Caffeine and stimulants may potentiate side effects like tachycardia. Alcohol may increase drowsiness or hypotension. Maintain adequate hydration to support circulation during anaphylaxis. |
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| Fetal Monitoring | Maternal: Monitor heart rate, blood pressure, cardiac rhythm, and signs of uterine hypertonus. Fetal: Monitor fetal heart rate pattern, especially after administration. In high-risk pregnancies, continuous fetal monitoring is recommended. Assess for signs of placental insufficiency. |
| Fertility Effects | No specific human studies on fertility. Animal studies: No adverse effects on fertility at therapeutic doses. Theoretical concern: Vasoconstrictive effects could potentially affect uterine or ovarian blood flow, but no evidence of clinically significant fertility impairment. |
| Clinical Pearls | Epinephrine auto-injector (Medihaler-EPI) is indicated for emergency treatment of anaphylaxis. Administer intramuscularly into the anterolateral thigh, not into the gluteal muscle or vein. Can be injected through clothing. Repeat dose every 5-15 minutes if symptoms persist. Monitor for paradoxical bronchospasm with inhaled epinephrine. Patients with severe asthma may require higher doses. Store at room temperature, protect from light, and check for particulate matter or discoloration before use. |
| Patient Advice | Carry the auto-injector at all times and know how to use it. Practice with a trainer device. · Administer immediately into the outer thigh at the first sign of a severe allergic reaction, even if symptoms are mild. · Call emergency services (911) after using the device. Do not drive yourself to the hospital. · After injection, go to the nearest emergency room for observation, as a second wave of symptoms may occur. · Keep the device away from extreme temperatures (do not freeze or expose to direct heat). · Check expiration date regularly and replace before expiry. Dispose of used devices properly. · Avoid injecting into buttocks, veins, or fingers. If accidental injection to fingers occurs, seek immediate medical attention. |