Both have high aqueous solubility, and the volume of distribution of each is similar (0.8 L/kg and 0.5 L/kg for gabapentin and pregabalin, respectively). Neither agent is bound by great extent to any plasma proteins, decreasing the likelihood of drug interactions due to protein binding. 3ĭistribution of gabapentin and pregabalin is very similar. In contrast, the AUC of pregabalin is unaffected by food, though absorption is slower. 3įinally, food increases the AUC of gabapentin by about 10%, with no change in time to maximum concentration (tmax). Variability among patients is believed to be 10% to 15% with pregabalin and 20% to 30% with gabapentin. Gabapentin’s bioavailability for its intended patient population is also more variable than pregabalin’s bioavailability. 3,4 This differs greatly from pregabalin, which boasts a greater than 90% bioavailability across a dosage range from 75 mg to 900 mg daily in divided doses. The bioavailability of generic gabapentin in tablet and capsule formulations equivalent to brand-name Neurontin is about 80% at lower doses such as 100 mg every 8 hours, but only 27% bioavailable at doses of 1600 mg every 8 hours. Unlike gabapentin, absorption of pregabalin is not saturable, and the drug has a linear pharmacokinetic profile. As gabapentin doses increase, the area under the curve (AUC) does not follow proportionally. It reaches peak blood concentrations within an hour after ingestion.Ībsorption of gabapentin is saturable, leading to a non-linear pharmacokinetic profile. Pregabalin is quickly absorbed, with the maximum rate of absorption being 3 times that of gabapentin. Gabapentin is more slowly and variably absorbed, with peak plasma concentrations around 3 hours post-dose. In addition, absorption of gabapentin is limited to the small intestine, while pregabalin is absorbed throughout the small intestine and extending to the ascending colon. However, pregabalin may either have an additional system of absorption or be better transported than gabapentin, as it is almost completely absorbed, while gabapentin is not. 3 This is the major form of absorption for gabapentin and pregabalin, with the exception of an extended-release gabapentin prodrug to be discussed later. Because of this, they can both undergo facilitated transport across cellular membranes through system L-amino acid transporters. Overall, the pharmacokinetic profiles of these 2 medications are somewhat similar, but they also have some significant differences.įor example, both drugs are structurally similar to the amino acid leucine. 4 Pregabalin is indicated for the same uses as gabapentin, plus the management of fibromyalgia and neuropathic pain associated with diabetes, specifically diabetic neuropathy. Gabapentin is indicated as adjunct therapy for partial seizures and postherpetic neuralgia. This binding decreases neurotransmitter release in the CNS as a result of reduced calcium influx through the gated channels. Pharmacokinetics of pregabalin and gabapentinīoth pregabalin and gabapentin are antiepileptic medications that bare structural resemblance to gamma-aminobutyric acid (GABA), though neither agent has activity in GABA’s neuronal systems.Īlthough the exact mechanism of action is somewhat unclear, the drugs’ efficacy in neuropathic pain is linked to their ability to bind to voltage-gated calcium channels in the central nervous system (CNS), specifically to the alpha-2-delta protein. 1 Because the products are so variable, this article compares the pharmacokinetics (PK) and pharmacodynamics (PD) of pregabalin with various gabapentin formulations, and also covers conversion regimens. Pregabalin and gabapentin are often considered first-line treatments for various neuropathic pain syndromes, generally irrespective of cause. Unfortunately, there are few head-to-head trials comparing agents for neuropathic pain, so selecting the best option can be difficult. 2 More than 85% of patients with neuropathic pain caused by peripheral neuropathy will require pharmacotherapy. 1 Of the 14 million US individuals with diabetes, roughly 25% experience painful diabetic neuropathy.ĭespite advances in vaccination for varicella zoster virus, around 25% of patients with a herpes zoster infection will develop persistent neuropathic pain. The incidence of peripheral neuropathy is estimated at about 2.4% of the population. Neuropathic pain causes significant morbidity in the United States. For an update to this article, read Appropriate Gabapentin Dosing for Neuropathic Pain here.
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