Midazolam CRI

Short-acting benzodiazepine. Binds the GABA_A receptor benzodiazepine site, enhancing GABA-mediated chloride conductance to produce dose-dependent anxiolysis, sedation, anterograde amnesia, anticonvulsant activity, and centrally mediated muscle relaxation. Water-soluble (unlike diazepam), so IV administration doesn't require propylene glycol vehicle. Onset 1–3 min IV; duration 30–60 min after single bolus, longer with CRI accumulation. Hepatic metabolism (CYP3A) with renal elimination of metabolites. Clearance is impaired in hepatic dysfunction.

Open calculator →

Clinical background

Midazolam is a water-soluble benzodiazepine with a short duration of action that makes it well suited to ICU CRI delivery. The water solubility (in contrast to diazepam, which is propylene-glycol-based) means midazolam tolerates IV bolus and continuous infusion without the venous irritation that limited the use of older benzodiazepines for prolonged delivery. In the ICU it has two principal roles: as adjunct sedation for patients on opioid or other CRI sedation regimens, and as a first-line drug in the management of canine and feline status epilepticus.

Pharmacology

Positive allosteric modulator at the GABA-A receptor. Binds the benzodiazepine site, increasing the frequency of chloride channel opening when GABA is bound, hyperpolarizing the post-synaptic neuron and reducing neuronal firing. The clinically meaningful effects are:

• Anxiolysis and sedation at low doses
• Anticonvulsant activity through the same mechanism, primarily through limbic-system GABAergic potentiation
• Mild skeletal muscle relaxation via spinal interneuron GABA potentiation
• Anterograde amnesia in humans; presumed but not directly demonstrable in veterinary patients
• No direct analgesia. Midazolam reduces the anesthetic and sedative requirement of co-administered agents but does not relieve pain on its own

Cardiovascular effects are minimal at sedation doses, which makes midazolam attractive in hemodynamically unstable patients where propofol or alfaxalone might produce concerning hypotension. There is mild respiratory depression that becomes clinically meaningful when midazolam is combined with opioids or inhalant anesthetics, which is the typical ICU context.

Onset is within 1–3 minutes IV; clinical duration after a single bolus is 30–60 minutes. The half-life is 1–2 hours in dogs and longer in cats, but accumulation is unusual at typical CRI rates. Hepatic metabolism via CYP3A; hepatic dysfunction slows clearance.

Indications

Primary use cases:

• Pre-CRI sedation in ICU patients requiring sustained mechanical ventilation, dressing changes, or extended procedural restraint. Usually combined with an opioid (fentanyl, methadone) and sometimes a low-dose α₂ agonist. The midazolam contribution is anxiolysis and muscle relaxation; the opioid handles analgesia.
• Status epilepticus in dogs and cats, refractory to first-line benzodiazepine boluses. Loading dose (0.2–0.5 mg/kg IV) followed by CRI at 0.1–0.5 mg/kg/hr. Standard place in the status protocol after diazepam or initial midazolam bolus has failed to control seizures and before barbiturate coma is considered.
• Premedication or co-induction before propofol or alfaxalone, reducing the induction dose required.
• Anxiolysis for fractious or stressed patients undergoing diagnostic procedures, frequently combined with butorphanol or a low-dose opioid.

Midazolam is not a hypnotic in dogs and cats at the doses used clinically. Many dogs given midazolam alone become disinhibited rather than sedated, particularly young or healthy patients with intact neurologic reserve. Use it in combination, not as a stand-alone sedative.

Dosing

• Dogs and cats, sedation CRI: 0.1–0.5 mg/kg/hr, titrated against sedation depth.
• Initial maintenance rate: 0.1–0.25 mg/kg/hr.
• Caution above: 0.3 mg/kg/hr in cats (paradoxical excitement risk; see below). Dogs tolerate higher rates with less dysphoria.
• Pre-CRI sedation loading dose: 0.1–0.3 mg/kg IV slowly over 1–2 minutes before starting the CRI.
• Status epilepticus loading dose: 0.2–0.5 mg/kg IV, may repeat once. If seizures persist, follow with CRI at 0.25–0.5 mg/kg/hr.
• Status epilepticus CRI: 0.1–0.5 mg/kg/hr in dogs, 0.1–0.3 mg/kg/hr in cats.

Cat dosing is conservative because of higher reported rates of paradoxical excitement at higher CRI rates. Start at 0.1 mg/kg/hr in cats and titrate up cautiously, watching for restlessness, vocalization, or worsening agitation that does not look like sedation taking effect.

Cat-specific cautions

Paradoxical excitement is well described in cats given benzodiazepines, including midazolam. Manifestations include restlessness, vocalization, hyperalgesia, ataxic struggling, and apparent dysphoria. The mechanism is not fully understood but appears related to disinhibition of normally inhibited circuits when GABA tone is selectively enhanced. Risk rises with dose; at conservative CRI rates (0.1–0.2 mg/kg/hr) the incidence is low.

If paradoxical excitement appears: discontinue the infusion, give flumazenil to reverse the benzodiazepine effect, and consider an alternative sedation regimen (an opioid-based regimen, an α₂ agonist at a hemodynamically tolerable dose, or alfaxalone CRI).

Administration

Stock concentration in the US is 5 mg/mL (1 mg/mL pediatric vials are also available but less common in veterinary practice). For CRI delivery the stock is diluted into 0.9% sodium chloride or 5% dextrose. The InfusionFox calculator preselects three weight-banded preparations (1, 0.5, or 0.2 mg/mL) to keep the pump rate in the precision range across patient size.

Compatibility is broad. Midazolam can be co-administered through a Y-site with most other ICU drugs including fentanyl, dexmedetomidine, and most fluids. Avoid concurrent administration with sodium bicarbonate or any alkaline solution; the drug is in salt form and precipitates above pH 5.

Light protection is not required. Stability is good at refrigerator and room temperature for the typical 24-hour hang time.

Drug interactions

• Opioids, α₂ agonists, inhalant anesthetics, propofol, alfaxalone all have additive sedation and respiratory depression with midazolam. This is usually the intended combination effect; the implication is that the dose of each can usually be reduced when combined.
• CYP3A inhibitors (ketoconazole, erythromycin, fluconazole, ciprofloxacin) slow midazolam metabolism and prolong duration. Relevant for patients on those drugs concurrently for unrelated reasons.
• CYP3A inducers (phenobarbital, rifampin) accelerate metabolism and shorten duration. The clinical implication for status patients on chronic phenobarbital is that higher midazolam doses may be required.
• Cimetidine modestly inhibits midazolam clearance; effect is small.

Adverse effects

• Paradoxical excitement, particularly in cats; see above
• Respiratory depression, primarily when combined with opioids or inhalant anesthetics. Dose-limiting at higher infusion rates
• Hypotension at very high doses or in volume-depleted patients; minimal at sedation rates
• Prolonged sedation in patients with hepatic dysfunction or after extended CRI (12+ hours), from accumulating parent drug or active metabolites
• Dependence with very prolonged infusion (multi-day) has been reported in human ICU; rebound agitation on abrupt discontinuation, withdrawal-like signs. Wean the dose down rather than stopping abruptly after multi-day infusions

Monitoring

• Sedation depth, scored against a clinical scale (Ramsay or similar) or simply described in the chart at consistent intervals
• Respiratory rate and effort, particularly when combined with opioids. Continuous capnography is ideal in mechanically ventilated patients
• Heart rate and blood pressure at intervals; midazolam itself produces minimal hemodynamic change but the combination drugs (opioids, propofol) can drop both
• Hepatic function in patients on extended CRIs (3+ days), as accumulation in hepatic dysfunction is the principal late-infusion concern
• Mental status on weaning, watching for prolonged sedation if hepatic clearance is reduced

Weaning and reversal

For sedation CRIs running less than 24 hours, abrupt discontinuation is usually well tolerated. For longer CRIs, reduce the rate by 25–50% every 4–6 hours, watching for emergence agitation that may suggest underlying pain or anxiety needing alternative management.

Flumazenil (0.01–0.05 mg/kg IV slowly) is a specific benzodiazepine receptor antagonist and reverses midazolam effect within 1–2 minutes. Useful for reversing oversedation, paradoxical excitement, or for rapid neurologic assessment of a patient on a midazolam CRI. The half-life of flumazenil (~1 hour) is shorter than the clinical duration of midazolam after CRI, so re-sedation can occur and repeat doses may be needed. Flumazenil can precipitate seizures in patients with underlying seizure disorders or those on long-term benzodiazepine therapy; weigh the benefits against this risk before reversing in a status patient.

Sources

• Plumb’s Veterinary Drugs, midazolam monograph (current edition).
• Patterson EE, Eickhoff TC, Schwartz S. Status epilepticus. In: Silverstein DC, Hopper K, eds. Small Animal Critical Care Medicine. 3rd ed. Elsevier; 2023. Chapter 86. (Status epilepticus protocols including midazolam loading and CRI.)
• Hopper K. Care of the critically ill cat. In: Côté E, ed. Clinical Veterinary Advisor: Dogs and Cats. 4th ed. Elsevier; 2020. (Paradoxical excitement in cats and dose adjustments.)
• Robertson SA, Lascelles BDX. Long-term pain in cats: how much do we know about this important problem? J Feline Med Surg. 2010;12(3):188–199. (Benzodiazepine use in feline analgesia and sedation contexts.)