Gianluca
Well-Known Member
NEW INSIGHTS INTO DRUG ABSORPTION FROM OIL DEPOTS
This dissertation provides new insights into drug absorption from oil depots. Figure 7.1, which was the assumed model before these new findings, is adapted to Figure 7.2. Here, it is shown that the released prodrug (ND) is not hydrolysed locally (Chapter 6), but remains unchanged in interstitial fluid. Here, it is logical to assume that the lipophilic prodrug adheres to small proteins (<40 kDa) and subsequently drained with the interstitial fluid into the lymph vessels. Alternatively, it cannot be excluded that small oil droplets might be detached from the main oil depot (Chapter 4) and cleared through the lymph. In both ways, ND will end up in the final lymph node to enter the vena cava superior to meet blood cells in the central compartment. These blood cells will finally hydrolyse the prodrug compound to nandrolone
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FUTURE PERSPECTIVES
The open ends of the current research have been indicated above. Both the fate of the oil and the role of the immune system towards drug absorption are still not fully understood. In future research, an option to examine drug release and absorption from an oil depot can be performed with a traceability in vivo study. Ideally, 3 tracers would be integrated in the drug product: 1 in the triglyceride structure of the oil components, 1 in the nandrolone molecule and 1 in the decanoic acid moiety. The distinctiveness between these three tracers and between the tissues must obviously be sufficient enough to determine the three compounds separately. The whole process of drug release, hydrolysis and oil digestion could then be followed. Nowadays, traceability studies can be performed for instance with Single-photon emission computed tomography (SPECT) or PET/MRI-scanners. These imaging techniques use respectively isotopes or fluoride-atoms to visualise compounds in situ. Unfortunately, these labeling materials are unsuitable to use in the suggested traceability study, because these materials will alter the physical-chemical properties of either the oil formulation or the prodrug compound. This may change the oil viscosity, drug partition coefficient, spatial distribution in administered tissue or immune response, which may consequently influence the biopharmaceutical aspects of drug absorption from oil depots when these materials are not applied.
CONCLUSIONS
It is interesting to realize that drug absorption from an oil depot cannot entirely be described by a simple two phase mass transfer model where concentration gradients, diffusion and partition coefficients would enable the calculation of the expected absorption. It is demonstrated in this dissertation that there is a role of the excipient BOH in yielding an initially high absorption. The oil depot forms a continuous phase after injection, but will be dispersed and encapsulated at the injection site after some days. This in turn largely influence the way the prodrug becomes available; after release from the oil depot, it is present in the interstitial fluid which is drained through the lymph into the systemic circulation. Subsequently, the prodrug permeates through the wall of blood cells and is hydrolysed. Both the lymph transport and the cell wall permeation take time which is expressed in a lag time. This lag time is different for each injection site: a subcutaneously administered prodrug will enter the systemic circulation via a short path and at a low drainage flow. This results in a short lag time and a slow absorption rate constant of the prodrug. Deeper administered prodrugs (i.e. intramuscular injections) are suggested to be absorbed via a longer path, but at a higher flow, which results in a longer lag time but a higher absorption rate constant of the prodrug.
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this is awesome, but not sure if I'm understanding well.
So the SubQ is absorbed slower but enter the blood faster
the IM is absorbed faster but enter the blood slower?
basically at the end we have same absorption just it is released in the blood in a different way