Gastroretentive fibrous dosage forms for prolonged delivery of sparingly-soluble tyrosine kinase inhibitors. Part 3: Theoretical models of drug concentration in blood.

In this part, drug concentration in blood after ingesting gastroretentive fibrous and immediate-release particulate dosage forms is modeled. The tyrosine kinase inhibitor nilotinib, which is slightly soluble in low-pH gastric fluid but practically insoluble in pH-neutral intestinal fluid is used as drug. The models suggest that upon ingestion, the fibrous dosage form expands, is retained in the stomach for prolonged time, and releases drug into the gastric fluid at a constant rate. The released drug molecules flow into the duodenum with the gastric fluid, and are absorbed by the blood. The drug is eliminated from the blood by the liver at a rate proportional to its concentration. Thus, as the drug concentration in blood increases due to absorption, the elimination rate increases, too, and will eventually be the same as the absorption rate, so that the drug concentration in blood plateaus out. After the gastric residence time, drug absorption stops, and the drug concentration in blood drops to zero. By contrast, after administering the immediate-release particulate dosage form the drug particles are swept out of the stomach rapidly, and drug absorption stops much earlier. The drug concentration in blood rises and falls without attaining steady state. The gastroretentive fibrous dosage forms enable a constant drug concentration in blood for drugs that are insoluble in intestinal fluids.