Dose Dependent Urine Concentrations of Gabapentin (Neurontin)

Abstract

Sheng Feng, Lauren F Ward, Britt Parish, Erin C Strickland, Jeffrey R Enders and Gregory L McIntire

Gabapentin (Neurontin®) is frequently prescribed for a number of conditions including adjunctive therapy for partial seizures and neuropathic pain. Gabapentin is unique to most drugs in that it is titrated quickly to high doses (1,800-3,600mg/day or greater) due to its low toxicity. It is not metabolized but excreted primarily unchanged in the urine at extremely high levels ranging from 5µg/ml to >30,000µg/ml. The work reported here looks at gabapentin urine drug testing (UDT) results from 6 months of clinical urine specimens in which gabapentin was detected (n=35,526), prescribed (n=23,432, 66%) or not prescribed (n=12,094, 34%). In the prescribed population, gabapentin was primarily prescribed to females (61%). The overall age for positive results ranged from 14 to 97 years with an average age of 56.5 years. Interestingly, the average age of those patients positive for gabapentin without a prescription and positive for any illicit was 42.7 years. These data indicate that at a maximum, 34% of the total gabapentin positive samples are from abuse (no prescription). Attempts at normalization and transformation of drug concentration data using creatinine normalization did lead to a near Gaussian distribution where +/- 3 standard deviations may be estimated. It remains difficult to determine if a patient is abusing the drug when the UDT values are extremely high for patients prescribed gabapentin.

PDF