P. . Wongsiridej, S. . Ngerncham, S. . Usaha, W. . Chandranipapongse, Tim R. Cressey, and W. . Bowornkitiwong, “Serum Theophylline Concentrations in very Preterm Neonates Receiving Intravenous Aminophylline for Apnea”, Siriraj Med J, vol. 73, no. 8, pp. 526–531, Aug. 2021.