Extra vascular administration

Although the equations become considerably more complex than for the IV case, Cmax and Cm n can be calculated when the drug is administered by an extra-vascular route. The required equations may be developed as follows The equation describing the plasma concentration versus time curve following one extra-vascular administration was discussed previously. Equation (35) may be written as follows ... 

Pharmacokinetics Well absorbed after subcutaneous administration. Undergoes minimal, if any, metabolism. Highly bound to antithrombin 111. Distributed mainly in blood and to a minor extent in extra vascular fluid. Excreted unchanged in urine. Removed by hemodialysis. Haif-Hfe 17-21 hr (prolonged in patients with impaired renal... 

EV, only the extra vascular (EV) administration is needed IV + EV, EV and IV administration or at least per os solution and EV administration are needed simultaneously. 

T. Teorell, Kinetics of distribution of substances administered to the body. I. The extra-vascular modes of administration. Arch Int Pharmacodyn 57 205-225 (1937). 

After intravenous injection, Tc-DTPA penetrates capillary walls to enter the extra-vascular space within 4 min (McAfee et al. 1979). Because of its hydrophilicity and negative charge, Tc-DTPA is excluded from cells and is confined to the extracellular space. Tc-DTPA is removed from the circulation exclusively by the kidneys renal clearance is unaffected by urine flow and by the administration of probenecid (Klopper et al. 1972). However, only the filtered fraction (20%) of the total renal plasma flow is excreted by glomerular filtration (Barbour et al. 1976). 

The problem set provides plasma concentration versus time data following the administration of a drug by an extra vascular route (oral). Once again, it is assumed that the administered drug follows the first-order process and exhibits the characteristics of a one-compartment model. The following are our answers to these questions and it is possible that your answers may differ from these for the reasons discussed in Problem set 1. 

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