What short‑acting anxiolytic and dose should be used to calm an adult patient with severe anxiety or claustrophobia undergoing MRI, especially if oral administration is not feasible, and what are the contraindications?

Anxiolytic Medication for MRI: Oral Diazepam or Lorazepam

For adults under 65 years with severe anxiety or claustrophobia undergoing MRI, administer oral diazepam 5–10 mg given 30–60 minutes before the procedure, as it provides rapid anxiolysis through high lipophilicity and fast brain penetration. 1

Dosing by Age and Population

Adults Under 65 Years

• Oral diazepam 5–10 mg administered 30–60 minutes before MRI is the preferred first-line agent because of its rapid onset and predictable effect 1, 2
• The oral route is strongly preferred over intramuscular injection, which produces erratic absorption and carries risk of tissue necrosis 1
• In a cardiovascular MRI study, intravenous diazepam (mean dose 7.5 mg, range 2.5–20 mg) achieved a 97% success rate (30 of 31 patients) when oral administration was not feasible 3

Elderly Patients (≥65 Years)

• Reduce diazepam dose to 2–2.5 mg orally, or switch to lorazepam 0.5–1 mg orally to account for increased sensitivity to sedative effects 1
• The European Society for Medical Oncology mandates this dose reduction in older patients 1
• Lorazepam is metabolized by direct glucuronide conjugation rather than cytochrome P450 enzymes, making it safer when hepatic function is reduced 1

Special Populations Requiring Dose Adjustment

Hepatic Impairment

• Lorazepam 0.5–2 mg orally is the preferred benzodiazepine because it does not rely on CYP450 metabolism, reducing accumulation risk 1
• Diazepam and midazolam generate active metabolites that accumulate dangerously in compromised hepatic function 1
• Even with lorazepam, dose reduction is required in severe liver disease 1
• Patients with hepatic or renal impairment require a 20% or greater dose reduction of oral diazepam 2

Renal Impairment

• The European Society of Cardiology recommends lorazepam as the safest benzodiazepine for renal dysfunction, owing to its unchanged glucuronide-conjugation pathway 1
• Diazepam's active metabolite desmethyldiazepam can accumulate in renal impairment, especially with concurrent liver disease 1

Respiratory Insufficiency

• All benzodiazepines depress respiration, but lorazepam is the least hazardous option when a benzodiazepine is essential for baseline respiratory compromise 1
• Diazepam requires dose reduction in severe pulmonary insufficiency to mitigate respiratory depression risk 1

When Oral Administration Is Not Feasible

Intranasal Midazolam Alternative

• Intranasal midazolam 1–2 mg (or alprazolam 0.25–0.5 mg orally) can be used when oral diazepam is not feasible 4
• In a randomized controlled trial, intranasal midazolam 4 mg (six sprayings of 0.5% solution) prevented all scan cancellations compared to four cancellations in the placebo group (0/27 vs 4/27), with improved image quality 5
• Patients experienced transient burning of nasal mucosa but no other adverse effects 5

Intravenous Midazolam (Requires Monitoring)

• Midazolam should be avoided for routine outpatient MRI premedication because it requires IV access, continuous respiratory and cardiac monitoring, and immediate availability of resuscitative equipment 1
• If IV midazolam is necessary, elderly patients require ≥20% dose reduction, with initial IV dose not exceeding 1–2 mg administered slowly over 1–2 minutes 1
• For patients under 60 years, no more than 1.5 mg should be given over no less than 2 minutes, waiting an additional 2 or more minutes to fully evaluate sedative effect 6
• For patients 60 years or older, debilitated, or chronically ill, titrate slowly to desired effect (e.g., initiation of slurred speech); some respond to as little as 1 mg, with no more than 1.5 mg over no less than 2 minutes 6

Critical Safety Precautions

Opioid Co-Administration

• When combining a benzodiazepine with an opioid, reduce the benzodiazepine dose by at least 50% to counteract synergistic respiratory depression 1
• Specifically, diazepam dose should be lowered by 30% when given with opioids 1
• For midazolam co-administered with opioids, limit dose to 0.5–1 mg to avoid excessive sedation 1

Monitoring and Adverse Effects

• Patients must not drive after sedation and should be accompanied home 2
• Monitor vigilantly for paradoxical reactions (agitation, excitement, worsening delirium), which are more common in elderly or frail patients receiving diazepam 1
• All benzodiazepines increase fall risk, particularly in older adults; fall-risk assessment and appropriate precautions are advised 1
• Have flumazenil available (0.01–0.02 mg/kg IV, maximum 0.2 mg) for reversal if severe respiratory depression occurs, though avoid in seizure disorder patients 2

Absolute Contraindications

• Screen for contraindications including respiratory depression and active alcohol use before administering any benzodiazepine 4
• Patients with substance abuse history or dependence should avoid benzodiazepines entirely due to high dependence risk 4
• Use extreme caution in patients with chronic benzodiazepine use due to tolerance and withdrawal risks 2

Non-Benzodiazepine Alternative

• Hydroxyzine (available as tablets or syrup) is an approved anxiolytic alternative for patients in whom benzodiazepines are contraindicated, with few contraindications in both Europe and the United States 1
• Hydroxyzine offers a safer profile when respiratory depression from benzodiazepines is a concern 1

Common Pitfalls to Avoid

• Do not underestimate scan duration: a 45–60 minute MRI requires sustained anxiolysis, not just initial sedation 4
• Long-acting sedative premedication should be avoided within 12 hours of procedures because it impairs immediate recovery by affecting mobility and oral intake 7
• Avoid using standard (non-MR-safe) equipment in the MRI environment, as it can cause serious accidents in the magnetic field 4