Gabapentin (Neurontin - Pfizer), which has been available in the US since 1994, is approved by the FDA only for treatment of partial epilepsy and postherpetic neuralgia, but is widely used off-label for a number of other indications, especially neuropathic pain syndromes. According to one report, among Medicaid recipients in Florida receiving gabapentin, 71% of prescriptions were for chronic pain and 8% for seizures and neuralgia ("The Pink Sheet" February 2, 2004; 66:30).

The FDA has required new warnings in the labels of gabapentin (Neurontin, and others) and pregabalin (Lyrica, Lyrica CR, and generics) about the risk of life-threatening or fatal respiratory depression in patients with respiratory risk factors. Respiratory risk factors include chronic obstructive pulmonary disease (COPD) and concurrent use of opioids or other CNS depressants. Elderly patients are also at increased risk.

A nephrologist and longtime reader of The Medical Letter wrote us to say that our recent article entitled Drugs for Anxiety Disorders should have said more about the need for dosage adjustment of gabapentin (Neurontin, and others) and pregabalin (Lyrica, and others) in patients with renal impairment. Both drugs, he pointed out, are exclusively renally eliminated and can accumulate in patients with diminished renal function. Symptoms, which can include altered mental status, may develop so slowly that neither the patient nor the practitioner connect them to the drug. The resolution of...

A new once-daily formulation of gabapentin (Gralise – Depomed) has been approved by the FDA for treatment of postherpetic neuralgia (PHN). Immediate-release (IR) gabapentin (Neurontin, and others), which has been available in the US since 1994, is also approved for this indication, but is taken three times a day. Extended-release gabapentin enacarbil (Horizant) was recently approved by the FDA for treatment of restless legs syndrome.

Gabapentin (Neurontin - Parke-Davis), a cyclohexane acetic acid derivative, has been approved by the US Food and Drug Administration for use in addition to other antiepileptic drugs in patients with partial (focal) seizures with or without secondary generalization. Since this diagnostic category includes the largest number of patients with intractable epilepsy, new drugs with antiepileptic activity are generally tried first for this indication.

A lidocaine 1.8% patch (ZTlido – Scilex) has been approved by the FDA for treatment of pain associated with postherpetic neuralgia (PHN). A lidocaine 5% patch (Lidoderm, and generics) was approved earlier for the same indication and has been used off-label for treatment of other types of localized pain. Both of these patches are available only by prescription. Lidocaine 4% patches (Aspercreme, IcyHot, and others) are available over the counter for back, neck, shoulder, and joint pain.

The FDA has approved a topical 8% patch formulation of capsaicin (Qutenza – NeurogesX), available only by prescription, for local treatment of postherpetic neuralgia. Postherpetic neuralgia occurs after herpes zoster in about one third of patients ≥60 years old and can persist for months or even years.

Difelikefalin (Korsuva – Vifor), an IV kappa opioid receptor (KOR) agonist, has been approved by the FDA for treatment of moderate to severe pruritus associated with chronic kidney disease (CKD) in adults on hemodialysis. It is the first drug to be approved for this indication and the first KOR agonist to become available in the US. Difelikefalin has not been studied in patients on peritoneal dialysis.

Topiramate (Topamax - Ortho-McNeil) has been approved by the US Food and Drug Administration (FDA) for oral use as an adjunct to other drugs in adult patients with partial seizures. Since this diagnostic category includes the largest number of patients with refractory epilepsy, new drugs with antiepileptic activity are usually tried first for this indication. Topiramate (toe pyre' a mate) is a structurally unique agent chemically related to the D-enantiomer of fructose.

Gabapentin enacarbil (Horizant – GlaxoSmithKline), a new extended-release (ER) tablet formulation of gabapentin, has been approved by the FDA for treatment of moderate-to-severe restless legs syndrome (RLS). The immediate-release (IR) formulation of gabapentin (Neurontin,and others), which is approved for treatment of epilepsy and postherpetic neuralgia, has been used for many years to treat RLS. Another ER tablet formulation of gabapentin (Gralise) has been approved by the FDA for treatment of postherpetic neuralgia.