MIDAZOLAM HYDROCHLORIDE (AUTOINJECTOR)
Clinical safety rating: avoid
CNS depressants including alcohol and opioids increase sedation risk Can cause profound respiratory depression and hypotension.
Midazolam is a short-acting benzodiazepine that potentiates GABA-A receptor activity by binding to the benzodiazepine site, enhancing chloride ion conductance and neuronal hyperpolarization, leading to anxiolytic, sedative, amnestic, anticonvulsant, and muscle relaxant effects.
| Metabolism | Primarily metabolized by cytochrome P450 3A4 (CYP3A4) and, to a lesser extent, by CYP3A5. The major metabolite is 1-hydroxymidazolam (active). |
| Excretion | Renal excretion of metabolites (glucuronide conjugates) accounts for approximately 90% of elimination; less than 1% excreted unchanged; minimal fecal excretion (< 5%). |
| Half-life | Terminal elimination half-life is 1.8–6.4 hours (mean ~3 hours) in healthy adults; prolonged in elderly, obese, hepatic impairment (up to 15–20 hours), and critical illness. |
| Protein binding | ~97% bound to albumin. |
| Volume of Distribution | 1–3 L/kg (mean ~1.5 L/kg) indicating extensive tissue distribution; increased in obesity and critical illness. |
| Bioavailability | IM: >90%; oral: ~40% (due to extensive first-pass metabolism); nasal: ~50–80% (variable). |
| Onset of Action | IM (autoinjector): 15–30 minutes; IV: 1–2 minutes; nasal: 10–15 minutes; oral: 30–60 minutes. |
| Duration of Action | Sedation/anxiolysis: 1–2 hours after IV/IM; can be prolonged with hepatic/renal impairment or repetitive dosing due to active metabolites (α-hydroxymidazolam). |
| Molecular Weight | 325.77 |
10 mg intramuscularly once via autoinjector for acute seizure control.
| Dosage form | SOLUTION |
| Renal impairment | No specific dose adjustment recommended; use with caution in severe renal impairment (CrCl <30 mL/min) due to prolonged sedative effects. |
| Liver impairment | Child-Pugh A: no adjustment; Child-Pugh B: reduce dose by 50%; Child-Pugh C: contraindicated. |
| Pediatric use | Not FDA-approved for pediatric use via autoinjector; alternative formulations (e.g., buccal or intravenous) are preferred. Weight-based dosing for status epilepticus: 0.2 mg/kg IM (max 10 mg) per current guidelines. |
| Geriatric use | Reduce dose by 50% due to increased sensitivity and prolonged half-life; monitor for excessive sedation and respiratory depression. |
| 1st trimester | Midazolam crosses the placenta and is associated with congenital abnormalities in early pregnancy. Use only if clearly needed; avoid prolonged use. |
| 2nd trimester | Risk of fetal CNS depression and respiratory depression; use only if benefit outweighs risk. Avoid high doses or prolonged use. |
| 3rd trimester | Potential for neonatal sedation, hypotonia, respiratory depression, and withdrawal. Use only if necessary; monitor newborn closely. |
Clinical note
CNS depressants including alcohol and opioids increase sedation risk Can cause profound respiratory depression and hypotension.
| FDA category | Positive |
| Placental transfer | Midazolam crosses the placenta readily with a cord-to-maternal plasma ratio of approximately 0.6-0.7. Fetal levels can reach therapeutic concentrations. |
■ FDA Black Box Warning
Risk of respiratory depression and apnea, especially when used with opioids or other CNS depressants. Resuscitative equipment and personnel trained in airway management must be immediately available. Do not administer by rapid IV bolus. Use in neonates may cause severe hypotension and seizures. Concomitant use with alcohol or opioids may result in profound sedation, respiratory depression, coma, or death.
| Common Effects | anesthesia |
| Serious Effects |
Hypersensitivity to midazolam or any benzodiazepineAcute narrow-angle glaucomaSevere respiratory insufficiency (e.g., COPD, sleep apnea)
| Precautions | Respiratory depression and arrest, Hypotension, especially in neonates and elderly, Paradoxical reactions (agitation, aggression), Dependence and withdrawal, Use with caution in hepatic impairment, renal impairment, obesity, and myasthenia gravis, Not recommended for prolonged use in neonates due to benzyl alcohol content |
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| Breastfeeding |
| Midazolam is excreted into breast milk in low concentrations (milk:plasma ratio ~0.2). Short-term use is likely compatible, but due to risk of infant sedation and hepatic clearance immaturity, especially in neonates, caution is advised. Monitor infant for drowsiness, poor feeding, and respiratory depression. |
| Lactation Rating | L2 (Safer) |
| Teratogenic Risk | Midazolam is a benzodiazepine. First trimester: increased risk of congenital malformations (e.g., oral cleft) based on case-control studies; avoid use. Second/third trimesters: risk of fetal CNS depression, respiratory depression, and hypotonia (floppy infant syndrome) with prenatal exposure. Use only if clearly needed. |
| Fetal Monitoring | Monitor maternal respiratory rate, oxygen saturation, and level of sedation. Fetal heart rate monitoring is recommended, especially near term. Neonatal monitoring for respiratory depression, hypotonia, and sedation after delivery. |
| Fertility Effects | Animal studies do not indicate impaired fertility. Human data limited; no established effect on fertility. |
| Food/Dietary |
| No specific food interactions known. Grapefruit juice may slightly increase midazolam levels via CYP3A4 inhibition, but clinical significance is minimal with single IM injection. Avoid alcohol due to additive CNS depression. |
| Clinical Pearls | Midazolam hydrochloride autoinjector is used for acute seizure management, typically by non-medical personnel. Onset of action is 1-3 minutes intramuscularly. Monitor respiratory depression, especially with concurrent CNS depressants or in elderly. Autoinjector delivers 10 mg IM; may repeat once after 10 minutes if needed. Do not use for status epilepticus if IV access is available due to slower IM onset. Store at controlled room temperature; protect from freezing. |
| Patient Advice | Administer into the outer thigh muscle through clothing if necessary. · Do not inject into a vein or buttocks. · After use, place the autoinjector into the provided case and seek emergency medical care. · Avoid alcohol and other sedatives within 24 hours of use. · Common side effects include dizziness, drowsiness, and injection site pain. |