Fixed dosing of alpelisib for children with vascular anomalies: Can we do better?

Severe forms of vascular malformations (VM) can highly impact patients' quality of life and lead to life-threatening organ dysfunction. Numerous VM are caused by somatic activating mutations in the PI3K/AKT/mTOR signalling pathway. Alpelisib, a PIK3CA inhibitor was recently FDA-approved for paediatric PIK3CA-related overgrowth syndrome (PROS). However, an empiric and fixed dose of 50 mg was selected, irrespective of weight, in the absence of any pharmacokinetic (PK) data. We aim to report novel alpelisib PK data in children to support dosing decisions. Nine patients with severe VM (PROS: n = 4, other VM: n = 5) were included. Mean age was 10.5 years (SD = 5.2 years), and mean weight was 43 kg (SD = 24 kg). AUC on the fixed dose of 50 mg/day was highly variable (mean = 7035 ng*h/mL, SD = 4057, CV = 58%). AUC was correlated with weight. As short- and long-term adverse effects to alpelisib in children are unknown, a dosing based on PK data is urgently needed.