The patient remained anuric and his serum gabapentin level was 6.3 mcg/ml. The patient was commenced on CRRT for his metabolic abnormalities, acute on chronic renal failure, and for gabapentin toxicity. Gabapentin levels were drawn prior to the start of renal replacement therapy and, subsequently, levels were drawn pre- and post-filter 60, 360, and 720 minutes after being started on continuous venovenous hemodiafiltration (CVVHDF) using the Gambro Prismaflex® system. CRRT was continued approximately for 3 days and gabapentin levels were measured at multiple time points [Figure 1]. The patient started to produce urine and the CRRT was discontinued. During this period, the patient's symptoms improved significantly and his tremor completely resolved. The patient's renal function improved with his BUN decreasing to 27 and creatinine returning to 2.6. The mean hemofilter clearance of urea, creatinine, and gabapentin were 30.9 ml/min, 36.2 ml/min, and 41.1 ml/ min, respectively. The mean gabapentin clearance was 86% of the mean urea clearance and 75% of the mean CrCl. A plot of gabapentin concentration over time during CVVH showed an exponential decline [Figure 1]. By using an elimination rate constant (k) of 6.3 × 10–4/ hr and the mean gabapentin clearance (K) of 30.9 ml/ min in equation 1, the apparent volume of distribution (Vd) of gabapentin in our patient was 48.8 l. Using the elimination rate constant of gabapentin in equation 2 (detailed in Appendix), the calculated plasma half-life of gabapentin during CVVHDF was 18.23 hours.