A new pharmacokinetic model for 90Y-ibritumomab tiuxetan based on 3-dimensional dosimetry.

Monoclonal antibodies (mAbs) are key components in several therapies for cancer and inflammatory diseases but current knowledge of their clinical pharmacokinetics and distribution in human tissues remains incomplete. Consequently, optimal dosing and scheduling in clinics are affected. With sequential radiolabeled mAb-based imaging, radiation dosing in tissues/organs can be calculated to provide a better assessment of mAb concentrations in tissues. This is the first pharmacokinetic model of 90Y-Ibritumomab tiuxetan (90Y-IT) in humans to be described, based on three-dimensional (3D) dosimetry using single-photon emission computed-tomography coupled with computed-tomography. 19 patients with follicular lymphoma were treated initially with 90Y-IT in the FIZZ trial. Based on a compartmental approach individualising the vascular compartment within studied organs, this study proposes a reliable pharmacokinetic (PK) five-compartment model replacing the currently used two-compartment model and constitutes a new direction for further research. This model provides exchange constants between the different tissues, Area Under the Curve of 111In-IT in blood (AUC) and Mean Residence Time (MRT) that have not been reported so far for IT. Finally, the elimination process appears to occur in a compartment other than the liver or the spleen and suggests the metabolism of mAbs may take place mainly on the vascular compartment level.

How to easily provide zero order release of freely soluble drugs from coated pellets.

Coated pellets offer a great potential as controlled drug delivery systems. However, constant drug release rates are difficult to achieve with this type of dosage forms if the drug is freely water-soluble. This is because diffusional mass transport generally plays a major role and with time the drug concentration within the system decreases, resulting in decreased concentration gradients, which are the driving forces for drug release. Thus, generally "curve-shaped" release profiles with monotonically decreasing slopes are observed. This type of release kinetics might be inappropriate for an efficient and safe drug treatment. Despite the great practical importance of this potentially crucial formulation challenge, surprisingly little is yet known on how to effectively address it. In this study, a novel approach is presented based on sequential layers of drug and polymer (initially free of drug) to provide a non-homogeneous initial drug distribution, combined with lag-time effects, and partial initial drug diffusion towards the pellet's core. Sugar and microcrystalline cellulose beads were used as starter cores, metoprolol succinate as freely soluble drug, ethylcellulose, and poly(vinyl acetate) as release rate controlling polymers. The type, number, thickness, and sequence of the drug and polymer layers were varied. Interestingly, a rather simple four layer system (two drug and two polymer layers) allowed providing about constant drug release during 8h. Compared to previously proposed coated pellets aiming at constant release of freely water-soluble drugs based on non-homogeneous initial drug distribution, the total coating level in this study was very much reduced: to only about 20%. Hence, the suggested formulation approach is relatively simple and can help overcoming a potentially major hurdle in practice. Its applicability has also been demonstrated for another type of drug: propranolol hydrochloride.