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How Medications "Go Through" the Older Body
By Ron Finley7/1/2009
"Wrinkles and age spots aren't the only changes that happen to our bodies as we age. Changes also happen within our bodies - affecting the way we handle medications. AARP"
Drug therapy is the mainstay in the treatment of many medical and psychiatric conditions experienced by older adults. Unfortunately, elders experience more adverse drug reactions than younger adults. There are a number of reasons, one of which is that as we grow older our bodies change in ways that impact how a drug "travels through our body". An awareness of how medications travel or pass through our body assist us in "partnering" with our health care providers and to prevent adverse drug reactions.
Although numerous drug references and articles refer to the "elderly", meaning anyone over the age of 64 years, the same drug may "travel" very differently through a 66 year old body when compared to an 86 year old body. As we grow older we tend to be come more diverse throughfore it is imperative health care providers appreciate these individual differences and the affect they may have on drug disposition. Sometimes we need to remind them.
The vast majority of medications are administered orally. Drugs taken orally must be absorbed from the gastrointestinal tract, which includes the stomach and primarily, as it relates to drug absorption, the small intestine.
As we grow older there are changes that occur as part of the aging process. Many of these changes, at least theoretically, could impair the rate and extent of drug absorption. This is important because if the drug is not absorbed it cannot be effective. In other words the pain medication you took several hours ago cannot relieve your headache.
Changes such as slower passage through the stomach, reduced gastric acidity (some drugs need an acid environment to be absorbed) are frequently mentioned as possible causes of impaired drug absorption in older adults. In fact, unless the individual is suffering from a medical condition that might impair drug absorption, drug absorption is not impaired in old age-even in the very old. In fact some of the earlier observations of impairment were not due to age but to disease or other drugs the study participants were taking.
However it is important to mention that food and some drugs may alter drug absorption. So, it is important to ask the pharmacist, when picking up a prescription, if food or other drugs will impair the absorption of the new medication or other medications you take.
Once a drug is absorbed it must be "distributed" in the body via the blood circulatory system to various organs and tissues. We all notice changes in our body as we grow older. However, many bodily changes are not evident to the eye. The composition of body changes in subtle ways, such as a reduction in lean muscle mass, an increased ratio of muscle to body fat, less total body water (much of our bodies weight is water). These changes may affect drug distribution and in some cases drug activity. For example the same amount of alcohol we could consume at 25 years of age will produce higher blood levels when we are 80 years of age. This occurs even though our liver may metabolize the "drug" just efficiently at 80 years of age as it did at 25 years of age.
Our bodies "detoxify" drugs primarily by "breaking them down" in the liver. Some drugs are converted in the liver in to their active form. Drugs metabolized in the liver may be converted to active (new drugs) or inactive products, either to be excreted by the body or "recycled" to be further "broken down" by passing once more through the liver.
In general, probably because the human liver has such a great degree of "margin for error" the impact of the aging process appears to have minimal effect on the livers drug metabolizing function. However, there is increasing evidence that some important liver enzymes decline much earlier in men than in women, and some of the differences in metabolism are related more to gender than age.
It is important to note that certain medical conditions, the excessive use of alcohol and some drugs (herbal and western drugs-prescription and non prescription) may damage the liver and negatively alter the normal course of drug metabolism.
The primary route of drug removal is the kidney. Various changes in kidney physiology and function may occur with aging, resulting in the kidney’s impaired function. These negative changes in kidney function are the most pronounced for individuals with kidney disease, hypertension and/or diabetes-especially if any of these conditions are poorly controlled. It appears, healthy elders, those not suffering from kidney disease, hypertension or diabetes, maintain good kidney/renal function well in to very old age. Not as good as they might have had at age 21, but not clinically impaired.
Because kidney function is so important to drug removal from the body it is very important for practitioners to not only know how drugs "go through the body", but also accurately assess their patient’s kidney function. In the elderly usual laboratory values may not correctly determine an elder’s kidney function. There are simple mathematical equations to estimate kidney function.
References
Reading
Health Notes: Medications and Older adults. California State Board of Pharmacy. 2003
AARP Health: Medication Safety for the Elderly
Health notes: Medications and Older adults
California State Board of Pharmacy. 2003
Articles on medications issues for older adults. Includes topics on polypharmacy, depression, Alzheimer’s disease and pain management.
Selected References/Reading
Gurwitz JH, Field TS, Harrold LR, et al. Incidence and preventability of adverse drug events among older persons in the ambulatory setting. JAMA 2003; 289(9):1107-16.
Juurlink, et al. Drug-drug interactions among elderly patients hospitalized for drug toxicity.JAMA 2003; 289:1652-1658.
Hurwitz A, Ruhl CE, Kimler BF, et al. Gastric function in the elderly: effects on absorption of ketoconazole.J Clin Pharmacol 2003; 43(9):996-1002.
Shih GL, Brensinger C, Katzka DA, et al. Influence of age and gender on gastric acid secretion as estimated by integrated acidity in patients referred for 24 hour pH monitoring. Am J Gastroenterol 2003; 98(8):1713-8.
Lucey MR, Hill EM, Young JP, et al. Influences of age and gender on blood ethanol concentrations in healthy humans. J Stud Alcohol 1999; 60(1):103-10.
Grandison MK, Boudinot FD. Age-related changes in protein binding of drugs: implications for therapy.Clin Pharmacokinet 2000; 38(3):271-90.
Bressler R, Bahl JJ. Principles of drug therapy for the elderly patient. Mayo Clin Proc 2003; 78(12):1564-77.
Onder G, Pedone C, Landi F, et al. Adverse drug reactions as cause of hospital admissions: results from the Italian Group of
Pharmacoepidemiology in the Elderly. J Am Geriatr Soc 2002; 50(12):1962-8.
Friedman H, Greenblatt DJ, Scavone JM, et al. Clearance of the antihistamine doxylamine. Reduced in elderly men but not in elderly women.Clin Pharmacokinet 1989; 16(5):312-6
Ron Finley
R. Ronald (Ron) Finley, BS Pharm, RPh recently retired, after 28 years as a lecturer for the University of California, San Francisco (UCSF) School of Pharmacy. Ron continues as an Assistant Clinical Professor in the School of Pharmacy and as Clinical Pharmacist in Neurology at the UCSF Memory and Aging Center-Alzheimer’s Research Center where he works closely with neurologist and psychiatrist. Mr. Finley also is a Consultant Pharmacist for the Institute on Aging at the Alzheimer’s Day Care Center in San Francisco and a consultant to the Parkinson’s Disease Institute. He received his pharmacy degree from St. Louis College of Pharmacy in 1959.
Ron has focused his recent research efforts on assessing pharmacotherapy in the areas of frontal temporal dementia and Creutzfeldt-Jakob disease, in addition to evaluating use of alternative medicine in neurology and their potential interactions with medications. He has spoken as an invited lecturer for numerous international, national, and local seminars and has authored or contributed to numerous articles, monographs, book reviews, and various other publications in his field. He as also associate editor of the Rx Consultant, a nationally distributed drug therapy newsletter.
Mr. Finley also has developed many continuing education programs at UCSF in the area of geriatric pharmacy practice. He is an active member in many professional societies, including the American Society of Health Systems Pharmacists, American Geriatrics Society, American Pharmaceutical Association, American Society of Consultant Pharmacists. American Academy of Neurology, and the American Association for the Advancement of Science.
