What is the recommended alteplase dose for an elderly patient weighing approximately 45–50 kg?

Alteplase Dosing in Low-Weight and Elderly Patients

Standard Dosing Protocol for Acute Ischemic Stroke

For elderly patients weighing 45–50 kg presenting with acute ischemic stroke, administer alteplase at the standard weight-based dose of 0.9 mg/kg (maximum 90 mg total), with 10% given as an IV bolus over 1 minute and the remaining 90% infused over 60 minutes. 1, 2

Specific Calculation for 45–50 kg Patients

• For a 45 kg patient: Total dose = 40.5 mg (4.05 mg bolus, then 36.45 mg over 60 minutes) 1
• For a 50 kg patient: Total dose = 45 mg (4.5 mg bolus, then 40.5 mg over 60 minutes) 1

The 90 mg maximum dose ceiling does NOT apply to patients under 67 kg—these patients receive the full 0.9 mg/kg without any cap. 1, 2

Age-Specific Considerations

Patients ≤80 Years (0–3 Hour Window)

• Age is NOT a contraindication for alteplase in the 0–3 hour window, regardless of how elderly the patient is. 1, 2
• Patients >80 years presenting within 3 hours should receive the same weight-based dose (0.9 mg/kg) as younger patients. 1, 2
• The symptomatic intracranial hemorrhage rate in patients ≥80 years is comparable to younger patients (2.4–6.4%), indicating age alone does not increase bleeding risk. 1, 2

Patients >80 Years (3–4.5 Hour Window)

• Age >80 years becomes an EXCLUSION criterion only in the extended 3–4.5 hour window. 1, 2
• If an elderly patient presents between 3–4.5 hours and is >80 years old, alteplase should NOT be administered. 1, 2

Critical Dosing Distinctions by Indication

Stroke vs. Myocardial Infarction Protocols

Never use the myocardial infarction dosing regimen for stroke patients—the protocols are completely different and non-interchangeable. 3

• Stroke protocol: 0.9 mg/kg (max 90 mg) over 60 minutes with 10% bolus 1, 2
• MI protocol (DO NOT USE FOR STROKE): 15 mg bolus, then 0.75 mg/kg over 30 min (max 50 mg), then 0.5 mg/kg over 60 min (max 35 mg) 1, 3

Weight-Based Ceiling Thresholds

For patients <67 kg (including your 45–50 kg elderly patient), the dosing formula is straightforward:

• Patients <67 kg: Give exactly 0.9 mg/kg with NO maximum cap 1
• Patients ≥67 kg: Apply the 90 mg maximum ceiling 1

This means a 45 kg patient receives 40.5 mg total, which is well below any safety threshold and appropriate for their body weight. 1

Evidence on Low-Weight Dosing Safety

Hemorrhage Risk in Low-Weight Patients

• The 2024 European Society of Cardiology guidelines note that underweight patients may have increased bleeding risk with antithrombotics, but this applies primarily to anticoagulants, not thrombolytics. 1
• For alteplase specifically, the weight-based 0.9 mg/kg dosing (without a lower weight cap) has been validated in major stroke trials and does not require dose reduction in low-weight patients. 1, 2

Contrast with High-Weight Patients

• Patients >100 kg who receive the capped 90 mg dose (resulting in <0.9 mg/kg) have HIGHER rates of symptomatic ICH (2.6% vs 1.7%) and mortality despite receiving a lower per-kilogram dose. 4
• This paradoxical finding suggests that absolute body weight, not per-kilogram dose, drives hemorrhage risk—supporting the safety of full weight-based dosing in low-weight patients. 4

Practical Administration Algorithm

Step 1: Verify Eligibility (All Patients)

• Perform immediate non-contrast CT to exclude hemorrhage 1, 2
• Check bedside glucose (must be >50 mg/dL) 1, 2
• Lower blood pressure to <185/110 mmHg before starting alteplase 1, 2

Step 2: Calculate Dose Based on Actual Body Weight

• Weigh the patient accurately 1
• For 45–50 kg patients: Calculate 0.9 mg/kg without applying any ceiling 1
• Example: 47 kg patient = 42.3 mg total dose (4.23 mg bolus, 38.07 mg infusion) 1

Step 3: Administer According to Stroke Protocol

• Give 10% of total dose as IV push over exactly 1 minute 1, 2
• Infuse remaining 90% over 60 minutes using an infusion pump 1, 2
• Do NOT dilute alteplase further after reconstitution 3

Step 4: Post-Treatment Monitoring

• Monitor neurological status every 15 minutes during infusion and for 2 hours after 1, 2, 5
• Check blood pressure every 15 minutes for 2 hours, then every 30 minutes for 6 hours, then hourly to 24 hours 1, 2
• Maintain BP <180/105 mmHg for 24 hours post-treatment 1, 2
• Obtain follow-up CT at 24 hours before starting any antiplatelet or anticoagulant therapy 1, 2, 5

Common Pitfalls to Avoid

Dosing Errors

• Do NOT reduce the 0.9 mg/kg dose in elderly or low-weight patients—there is no evidence supporting dose reduction and it may compromise efficacy. 1, 2
• Do NOT apply the 90 mg maximum to patients <67 kg—this ceiling only applies to heavier patients. 1
• Do NOT use the MI dosing regimen (15 mg bolus + tiered infusion) for stroke patients—this is a completely different protocol. 1, 3

Age-Related Errors

• Do NOT withhold alteplase from patients >80 years who present within 3 hours—age is only an exclusion in the 3–4.5 hour window. 1, 2
• Do NOT assume elderly patients have higher bleeding risk—symptomatic ICH rates are similar across age groups when proper protocols are followed. 1, 2

Timing Errors

• Do NOT delay treatment to obtain complete laboratory panels beyond bedside glucose—each 15-minute delay reduces the probability of favorable outcome. 1, 2
• Do NOT wait for CT angiography results before giving alteplase if the patient is within the treatment window. 1, 2

Special Considerations for Frail Elderly Patients

Pre-Existing Disability

• Patients with pre-existing disability (modified Rankin Scale ≥2) or dementia may still receive alteplase when premorbid function and goals of care are appropriate (Class IIa recommendation). 2

Cardiovascular Comorbidities

• End-stage renal disease on hemodialysis with normal aPTT is NOT a contraindication to alteplase. 1, 2
• Prior antiplatelet therapy (single or dual) does NOT contraindicate alteplase in any time window. 1, 2

Blood Pressure Management in Elderly

• Use labetalol or low-dose IV β-blockers for blood pressure control rather than aggressive agents that may cause hypotension in frail patients (Class IIa recommendation). 2

Summary Algorithm for 45–50 kg Elderly Patient

1. Confirm stroke diagnosis and time of onset <4.5 hours 1, 2
2. Obtain non-contrast CT and bedside glucose immediately 1, 2
3. Lower BP to <185/110 mmHg 1, 2
4. Calculate dose: 0.9 mg/kg (40.5–45 mg for 45–50 kg patient) 1
5. Administer 10% bolus over 1 minute, then 90% over 60 minutes 1, 2
6. Monitor intensively per protocol 1, 2, 5
7. Obtain 24-hour CT before starting antithrombotics 1, 2, 5

The key principle is that low-weight and elderly patients receive the same weight-based dose as all other patients, with age >80 years only becoming relevant in the 3–4.5 hour window. 1, 2