Changes In Renal Elimination With Age

Changes in Renal elimination
with age

Renal system: Clinically significant changes include:

(1) Decrease in renal mass (10-20% between
ages 40 and 80)
(2) Decrease in renal blood flow (1-2%
decline/year after age 40)
(3) Decrease in glomerular filtration (50% decline
between 50 and 90 years of age.)
(4) Decreased tubular secretion and absorption
(@ 7% decrease each decade) Drugs
eliminated by tubular secretion include
cimetidine and procainamide.
(5) Decreased creatinine clearance.

It is obvious that dose adjustments are necessary for those drugs that are eliminated renally. A creatinine clearance must be calculated for each patient. The Cockcroft-gault equation is commonly used to estimate renal function:
Creatinine clearance=
[(140-age) x IBW] / 72 x Scr]

Scr= serum creatinine.
IBW (male)= 50kg + 2.3kg for each inch over 5 feet. IBW (female)= 45.5kg + 2.3kg for each inch over 5 feet.

It is important to note that many of the equations used to predict renal function are much less accurate in predicting renal function in the elderly. This is due primarily to an age-related decline in creatinine production and loss of lean body mass that produces lower than expected serum creatinine levels. In many cases, over-estimation of renal function occurs.

Commonly used drugs in the elderly requiring dosage adjustments for creatinine clearance include: allopurinol, amantadine, most antibiotics, atenolol, carteolol, digoxin, lithium, gabapentin, H2-blockers, procainamide, quinidine, sotalol.

Geriatric issues
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