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

Campion EW,deLabry LO, Glynn RJ. The effect of age on serum albumin in healthy males: Report from the Normative Aging Study. J Gerontol. 1988;43:M18-M20.

Feely J, Coakley D.  Altered pharmacodynamics in the elderly.  Clin Geriatric Med. 1990; 6:269-283.

Greenblatt DJ, Sellers EM, Koch-Weser J. Importance of protein binding for the interpretation of serum or plama drug concentrations. J Clin Pharmacol. 1982;22:259-263.

Hammarlund ER, Ostrom JR, Kethley AJ. The effects of drug counseling and other educational strategies on drug utilization in the elderly. Med Care. 1985;23:165-170.

Hanlon JT, Schmader KE, Koronkowski Mj, et al.  Adverse drug events in high risk older patients. J Am Geriatr Soc. 1997; 45(8):945-8.

Frontera WR, Hughes VA, Lutz KJ, Evans WJ. A cross-sectional study of muscle strength and mass in 45- to 78-year-old men and women. J Appl Physiol. 1991;71:644-650.

Lamy PP. Physiological changes due to age: pharmacodynamic changes of drug action and implications of therapy.  Drugs Aging. 1991;1:385-404.

Levy RA.  Therapeutic inequivalence of pharmaceutical alternates.  Amer Pharm.  1985; April: 28-39.

MacLennan WJ, Martin P, Mason BJ. Protein intake and serum albumin levels in the elderly. Gerontology. 1977;23:360-367.

Schmucker DL. Aging and drug disposition: An update. Pharmacol Rev. 1985;37:133-148.

Thoreson J. Drug Metabolism and Drug/Drug Interactions from a Geriatrics Perspective. Clin Ger. 1997; 5: 57-74.

Tregaskis BF, Stevenson IH.  Pharmacokinetics in old age.  Br Med Bulletin. 1990; 46: 9-21.

Wilcox SM, Himmelstein, Inappropriate drug prescribing for the community-dwelling elderly. JAMA. 1994; 272:292-296

Changes in Renal elimination with age