What is the best PRN (pro re nata) dose of Ativan (lorazepam) for IM administration in a patient with impaired renal function and a history of seizures, weighing 170 pounds?

IM Lorazepam Dosing for 170 lb Patient

For a 170 lb (77 kg) patient requiring PRN IM lorazepam, order 2-4 mg IM every 10-15 minutes as needed, with careful attention to renal function and respiratory monitoring.

Recommended Dosing Strategy

The standard IM lorazepam dose is 0.05-0.10 mg/kg, which translates to approximately 4 mg for this patient (maximum 4 mg per dose). 1 However, given the context of impaired renal function and seizure history, specific considerations apply:

Weight-Based Calculation

• Patient weight: 170 lbs = 77 kg
• Standard dosing range: 0.05-0.10 mg/kg 1
• Calculated dose: 3.85-7.7 mg
• Practical order: 2-4 mg IM per dose (maximum 4 mg per single dose) 1

Dosing Interval

• May repeat every 10-15 minutes if seizures continue 1
• Monitor closely for respiratory depression between doses 1

Critical Considerations for Renal Impairment

Lorazepam clearance is NOT significantly affected by renal dysfunction, so standard dosing can be used. 2 This is a crucial distinction:

• Lorazepam is primarily eliminated via hepatic glucuronidation, not renal excretion 2
• The inactive glucuronide metabolite accumulates in renal failure but is nontoxic 2
• Drug clearance remains approximately 85 ml/min in renal patients vs 71 ml/min in normal patients (not statistically significant) 2
• No dosage adjustment is necessary for renal impairment 2

Important Caveat - Propylene Glycol Toxicity

Avoid prolonged or high-dose continuous infusions in renal patients due to propylene glycol vehicle accumulation. 3 The vehicle can cause:

• Hyperlactatemia 3
• Elevated osmolar gap 3
• Impaired renal tubular function 3
• Blunted renal compensation for respiratory acidosis 3

However, this concern applies primarily to continuous infusions, not intermittent IM dosing 3

Seizure Management Context

For status epilepticus, underdosing lorazepam significantly increases progression to refractory status epilepticus. 4 Key evidence:

• Patients receiving less than 4 mg had 87% progression to refractory SE vs 62% with 4 mg dosing (p=0.03) 4
• The recommended IV dose is 0.1 mg/kg up to maximum 4 mg 4
• Do not underdose - use the full 4 mg when indicated for seizures 4

For IM administration specifically in seizures: 0.2 mg/kg (maximum 6 mg per dose) may be used, repeating every 10-15 minutes 1

Safety Monitoring Requirements

Prepare for respiratory support regardless of administration route: 1

• Increased apnea risk when combined with other sedatives 1
• Monitor oxygen saturation continuously 1
• Have flumazenil available for life-threatening respiratory depression (though it may precipitate seizure recurrence) 1
• Peak effect occurs 3-5 minutes after IV dosing; IM onset within approximately 5 minutes 1

Practical PRN Order

Recommended order format:

• Lorazepam 2-4 mg IM PRN for agitation/seizures
• Maximum single dose: 4 mg
• May repeat every 10-15 minutes if needed
• Maximum total dose per episode: Consider consultation if >12 mg required
• Hold for respiratory rate <10 or oversedation
• Monitor respiratory status and oxygen saturation

Dose Selection Within Range

• Start with 2 mg for agitation/anxiety 1
• Use 4 mg for seizure activity 1, 4
• Renal impairment does not require dose reduction 2