rtPA dose limit should not be raised in heavy patients
MedWire News: Obese stroke patients often receive a lower than standard dose of recombinant tissue plasminogen activator (rtPA), but this does not appear to affect the efficacy of the treatment, shows an analysis of the SITS-ISTR.
"Our results support the current practice of the upper dose limit for rtPA," Niaz Ahmed (Karolinska University Hospital, Stockholm, Sweden) and colleagues write in the journal Stroke.
In Europe, rtPA is licensed at a dose of 0.9 mg/kg, but the upper total dose limit is set at 90 mg. This means that patients weighing more than 100 kg receive a lower than recommended rtPA dose.
In all, 4.3% of the 27,910 patients registered in the SITS-ISTR (Safe Implementation of Treatment in Stroke-International Stroke Thrombolysis Register) at the time of the study weighed more than 100 kg (median 110 kg). This group received an average rtPA dose of 0.82 mg/kg, compared with 0.90 mg/kg among patients who weighed 100 kg or less (median 75 kg).
The heavier group of patients was younger than the lighter group, at a median of 62 versus 70 years, and had less severe strokes, with median National Institutes of Health Stroke Scale (NIHSS) scores of 10 versus 12. However, more of the heavier patients had cardiovascular risk factors, including hypertension, diabetes, hyperlipidemia, and current smoking.
Despite the difference in rtPA doses, 27.7% of both groups had achieved at least an 8-point improvement in NIHSS score, or a score of 0, by 24 hours after therapy, which Ahmed et al took to indicate successful recanalization.
Functional outcomes were also similar for the two groups, with 59.7% of the heavier group and 53.6% of the lighter group achieving independence (modified Rankin Scale 0-2) at 3 months - a difference that was not significant after accounting for confounders.
However, symptomatic intracerebral hemorrhage (≥4-point NIHSS deterioration plus Type 2 parenchymal hemorrhage) occurred in 2.6% versus 1.7% of the heavier and lighter groups, respectively. On multivariate analysis, this amounted to a 1.60-fold risk increase in risk for heavier patients.
Mortality rates at 3 months appeared similar in both groups, at 14.4% and 15.1% among heavier and lighter patients, respectively. But accounting for confounders revealed a 1.37-fold increased risk for dying if patients weighed more than 100 kg.
Editorialists Marta Rubiera and Carlos Molina (Hospital Universitari Vall d'Hebron, Barcelona, Spain) noted that just 15% of patients in the study were actually weighed. They referred to a previous study showing that health professionals misjudge the weight of about 40% of thrombolysis patients.
They said that efforts should be made "to avoid standard eye-balling body weight - and tPA dose - estimation."
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By Eleanor McDermid