General Principles in Older Adults
Persons 65 years or older comprise approximately 13% of the U.S. population, yet they are prescribed the greatest proportion of medication; 90% are prescribed at least 1 prescription drug and 65% 3 or more prescription drugs in the last month. They also represent the fastest growing segment of prescription drug users in the United States. Thus, with an increasing number of patients surviving to older age and consuming larger amounts of drugs, it is necessary for clinicians to understand the risk, benefits, and consequences of drug therapy in older patients. This is especially true for anticoagulants, a class of drugs essential for the optimal management of many thromboembolic and vascular disorders that are highly prevalent among older patients. Anticoagulants are unique compared to most pharmacologic agents because even small deviations from “therapeutic levels” place patients at risk for life-threatening complications. While older patients with multimorbidity are particularly susceptible to thrombosis, they also have higher risks of bleeding than the general population. This chapter briefly reviews current anticoagulant therapy and focuses on the newer agents and recommendations for their use in older patients.
Health, United States, 2012, with Special Feature on Emergency Care. United States Department of Health and Human Services, Centers for Disease Control and Prevention, National Center for Health Statistics, May 2013, DHHS Publication No. 2013-1232 Table 1, Page 45, and Table 9, page 282 at http://www.cdc.gov/nchs/data/hus/hus12.pdf#listtables
(last accessed December 6, 2013).
Available Classes of Anticoagulant Therapy
Current anticoagulants that are available for use within the United States include unfractionated heparin (UFH), vitamin K antagonists (VKAs), low-molecular weight heparins (LMWHs), indirect selective factor Xa inhibitor, and the direct thrombin (parental and oral) and factor Xa inhibitors. Tables 55–1 and 55–2 summarize the specific pharmacologic characteristics of these agents.
Table 55–1.Pharmacologic properties of parental anticoagulants. |Favorite Table|Download (.pdf) Table 55–1. Pharmacologic properties of parental anticoagulants.
| ||Heparin and Derivatives ||Parental Direct Thrombin Inhibitors |
|Properties ||UFH ||LMWH ||Specific Anti-Xa Inhibitor ||Argatroban ||Desirudin ||Bivalirudin |
|Subtype || ||Enoxaparin, Dalteparin, Tinzaparin ||Fondaparinux || || || |
|Elimination ||Reticuloendothelial system ||Renal ||Renal ||Hepatic ||Renal ||Enzymatic, 20% renal |
|Time to peak concentration || |
SQ: 20–60 minutes
|∼1.5 hours ||∼2 hours || || || |
|Half-life ||∼1.5 hours ||∼2–5 hours ||∼17–21 hours ||∼45 minutes ||∼120 minutes ||∼25 minutes |
|Lab monitoring ||aPTT, anti-Xa heparin levels ||Not required; can measure anti-Xa LMWH levels ||Not required; can measure anti-Xa fondaparinux levels ||aPTT, ACT ||Not required; can monitor aPTT ||aPTT, ACT |
|Prolongation of INR at therapeutic concentrations ||No ||No ||No ||Significant ||Minor ||Minor |
|Reversible (antidote) ||Complete with protamine ||Partial with protamine ||No ||No ||No ||No |
|Dose adjustments ||None ||Renal impairment, extremes of weight: titrate to desired anti-Xa level ||Renal impairment: titrate to desired anti-Xa level || ||CrCl <31–60 mL/min: DR unnecessary || |
|FDA Indications |