Elimination rate constant renal impairment

The ratio (Q) of the estimated elimination rate constant or total body clearance relative to normal renal function is used to determine the dose or dosing interval alterations needed (CLfaii is the clearance with impaired renal function). 

Upon the administration of 0.27 mg of a therapeutic agent to a normal individual, the elimination rate constant was found to be 0.0315 hour 1. The normal dosing regimen included 0.27 mg qid. If the elimination rate constant in renally impaired condition is 80% of the normal elimination rate constant, how can the dose be adjusted maintaining the same dosing interval of six hours ... 

The elimination rate constants of an antitubercular drug in normal and a renally impaired patient were found to be 0.2 and 0.08 hour1, respectively. It is usually administered once daily in a dose of 300 mg. How can the dose be adjusted in the renally impaired patient to provide similar plasma levels as in the normal patient by maintaining the same dosing interval of 24 hours ... 

A clinical pharmacist has recommended that the dose of a diuretic be reduced from 250 mg to 225 mg in a renally impaired patient. In both the normal and renally impaired patients, the dosing interval was six hours. If the elimination rate constant of the drug in normal individual was 0.18 hour-1, what would be the elimination rate constant value in the renally impaired patient ... 

What is not immediately apparent from Eq. 6.15 is that a small value of either the absorption rate constant (as may occur in a poor oral formulation) or of the elimination rate constant (as may be the case in a renally impaired patient) will have the effect of lengthening the peak time and slowing the onset of action. This may be proved by changing the value of one parameter at a time in Eq. 6.15. 

In patients with renal impairment, the elimination half life of procainamide is reported to be 14 h (range, 9-43 h). When a 250 mg procainamide tablet is administered to a renally impaired subject, the absorption rate constant and the elimination rate constant are reported to be 2.8 h and 0.0495 h , respectively. However, the intercept of the plasma concentration-time profile is observed to be 1.556 pgmL . ... 

Should the patient manifest renal impairment for a drug eliminated by the kidneys, the infusion rate required to maintain the desired steady-state plasma concentration will be smaller and, please note, the elimination rate constant will also be smaller by an identical amount therefore, the ratio of infusion rate over elimination rate constant remains unaffected. This simply suggests, therefore, that it is vitally important to adjust (lower) the infusion rate of drug in a renally impaired subject. However, adjustment in the loading dose is neither necessary nor required. This statement can further be supported upon careful examination of Eq. 10.15, which clearly suggests that the... 

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