OBJECTIVES: To characterize the multiple continuous renal replacement therapy (CRRT) techniques available for the management of critically ill adults, and to review the indications for and complications of use, principles of drug removal during CRRT, drug dosage individualization guidelines, and the influence of CRRT on patient outcomes. DATA SOURCES: MEDLINE (January 1981-December 1996) was searched for appropriate publications by using terms such as hemofiltration, ultrafiltration, hemodialysis, hemodiafiltration, medications, and pharmacokinetics; selected articles were cross-referenced. STUDY SELECTION: References selected were those considered to enhance the reader's knowledge of the principles of CRRT, and to provide adequate therapies on drug disposition. DATA SYNTHESIS: CRRTs use filtration/convection and in some cases diffusion to treat hemodynamically unstable patients with fluid overload and/or acute renal failure. Recent data suggest that positive outcomes may also be attained in patients with other medical conditions such as septic shock, multiple organ dysfunction syndrome, and hepatic failure. Age, ventilator support, inotropic support, reduced urine volume, and elevated serum bilirubin concentrations have been associated with poor outcomes. Complications associated with CRRT include bleeding due to excessive anticoagulation and line disconnections, fluid and electrolyte imbalance, and filter and venous clotting. CRRT can complicate the medication regimens of patients for whom it is important to maintain drug plasma concentrations within a narrow therapeutic range. Since the physicochemical characteristics of a drug and procedure-specific factors can alter drug removal, a thorough assessment of all factors needs to be considered before dosage regimens are revised. In addition, an algorithm for drug dosing considerations based on drug and CRRT characteristics, as well as standard pharmacokinetic equations, is proposed. CONCLUSIONS: The use of CRRT has expanded to encompass the treatment of disease states other than just acute renal failure. Since there is great variability among treatment centers, it is premature to conclude that there is enhanced survival in CRRT-treated patients compared with those who received conventional hemodialysis. This primer may help clinicians understand the need to individualize these therapies and to prospectively optimize the pharmacotherapy of their patients receiving CRRT.