Renal Failure II Flashcards
Gentamicin and Vancomycin drug dosing in renal failure
Toxicity tends to correlate with elevated trough levels which reflects prolonged exposure to high drug concentrations. Thus, KEEPING THE DOSE THE SAME AND INCREASING THE INTERVAL will result in similar peak and trough values in patients with renal failure compared to those with normal kidney function
If the CLcr is reduced by 50%, how should the dosing rate be adjusted?
Decreased by 50% in order to achieve a Css in the
patient with renal failure that is the same as that in a patient with normal kidney function.
This can be achieved by doubling the dosing interval while keeping the dose the same, or cutting the dose in half, while keeping the dosing interval the same
In this method of DR adjustment, the desired average steady-state
concentration will be similar, however, the peak will be lower and
the trough higher
adjusting the dose
In this method of DR adjustment, the peak and trough concentrations
in the patient with reduced renal function will be similar to
those in the patient with normal renal function
adjusting the dosing interval
Penicillin drug dosing in renal failure
Decreasing the dose while
maintaining the same dosing interval or adjusting both the dose and dosing
interval
Quantitation of a patient’s renal function can be accomplished by measurement of?
creatinine clearance or estimation based on the serum creatinine
The equation which describes dosing rate is:
DR = dose X F/ T
where F is bioavailability and T is dosing interval
The equation which describes the concentration of a drug at steady state is:
Css=DR/CL
The principal choices to change the DR are:
to increase the dosing interval (doubled in this example) while
keeping the dose the same
to reduce the dose (halved in this case) while keeping the dosing
interval unchanged
to adjust both the dose and dosing interval
The volume of distribution is decreased in patients with renal insufficiency
which makes the estimation of dosing regimen more complex.
Digoxin
This dosage adjustment method is often preferred because it is likely
to yield significant cost savings as a result of a reduction in nursing
and pharmacy time, as well as a reduction in the supplies associated
with frequent drug administration
adjusting the dosing interval
This is an example of a drug which does not require a dosage adjustment in
renal insufficiency because the drug is metabolized in the liver and excreted
primarily in the feces
Erythromycin
usually produces few serious adverse effects, however, it can
cause seizures especially in patients with renal dysfunction. Thus, the dose
needs to be adjusted and patients monitored for signs of neurotoxicity
Penicillin
