Pharmacokinetics includes the processes of drug absorption, distribution, and elimination via metabolism and excretion. Drug pharmacokinetics change predictably with aging. These changes are of variable clinical significance for the use of antiepileptic drugs (AEDs):72-74
Absorption of AEDs remains complete, unless calcium-containing antacids are taken.
Drug distribution is affected by the decrease in lean body mass that occurs with aging, as well as by decreased albumin levels for drugs that are highly protein bound. These effects tend to oppose each other: lipophilic AEDs would be distributed to tissues other than brain more than in younger people, but there is also more free drug to distribute.
Drug elimination tends to be slower because of decreased hepatic enzyme activity and hepatic blood flow, as well as decreased renal clearance. The net result of these factors for most people and most drugs is to lower drug clearance.72,74,75 Seniors thus are often more sensitive to adverse effects and interactions, including sedation and ataxia. AEDs generally should be started at lower doses in seniors, titrated more slowly, and stabilized at lower doses and levels than in younger patients.
Reviewed and revised June 2004 by Steven C. Schachter, MD, epilepsy.com Editorial Board.
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