Calculating these clearances are very important in practice because depending on the drug, you may need to make dose adjustments so that the patient avoids drug toxicity and is benefitting from the drug itself. For example, if a patient is given a drug that is cleared at 6 L/hr but has 50% renal impairment, I would have to calculate what both the original hepatic and renal clearances were and then account for the 50% reduction in renal clearance to find the new total clearance. Let’s assume that the drug has a renal and hepatic clearance of 3 L/hr each for a total clearance of 6 L/hr. I would then take 50% of the renal clearance and add that to the 3 L/hr of hepatic clearance for an adjusted total clearance of 4.5 L/hr (ClT). I would then use this value to determine the adjusted dose I need to administer. Other factors are accounted for such as bioavailability (F), how often the dose is given (Q), and the desired concentration at steady state (Css). The equation that sums all this up is FD/Q = ClT *
Calculating these clearances are very important in practice because depending on the drug, you may need to make dose adjustments so that the patient avoids drug toxicity and is benefitting from the drug itself. For example, if a patient is given a drug that is cleared at 6 L/hr but has 50% renal impairment, I would have to calculate what both the original hepatic and renal clearances were and then account for the 50% reduction in renal clearance to find the new total clearance. Let’s assume that the drug has a renal and hepatic clearance of 3 L/hr each for a total clearance of 6 L/hr. I would then take 50% of the renal clearance and add that to the 3 L/hr of hepatic clearance for an adjusted total clearance of 4.5 L/hr (ClT). I would then use this value to determine the adjusted dose I need to administer. Other factors are accounted for such as bioavailability (F), how often the dose is given (Q), and the desired concentration at steady state (Css). The equation that sums all this up is FD/Q = ClT *