A number of pharmaceutical agents are FDA-approved to treat different types of neuropathic pain. For example, the most recently approved agents include pregabalin (Lyrica, Pfizer) and duloxetine (Cymbalta, Eli Lilly & Company). Additionally Neurontin (gabapentin, Pfizer) and its generics have been available since the 1990s, and have also been used to treat neuropathic pain (it is specifically FDA-approved to treat post-herpetic neuralgia [PHN]).
In June 2005, Lyrica received FDA-approval for treatment of neuropathic pain associated with diabetic peripheral neuropathy (DPN) and PHN as well as for treatment of adults with partial onset seizures. The maximum recommended dose of Lyrica for DPN is 100mg three times daily (TID). When treating patients with a creatinine clearance (CrCL) of < 60 mL/min, initiate at a lower dose (50 mg TID) because it is primarily renally eliminated. When discontinuing Lyrica, it should be gradually tapered over a minimum of one week. The recommended dose for treatment of PHN is 75–150 mg twice daily (BID), or 50–100 mg TID for patients with a CrCL of at least 60mL/min. The dose should be reduced for patients with a CrCL < 60mL/min. If no pain relief is obtained within two to four weeks at this dose, it may be gradually increased to 600 mg/day (200 mg TID or 300 mg BID); however, side effects may be more severe because they are dose-dependent (e.g., ataxia, dizziness, dry mouth, peripheral edema, somnolence, and weight gain).
Other guidelines for dosing in renally impaired patients should be reviewed in the product labeling. Because Lyrica has been reported to cause euphoria, it has been designated as a controlled substance (C-V). There are no specific drug interactions except with the glitazones (weight gain, fluid retention, or congestive heart failure exacerbation may occur) and the possibility of additive central nervous system (CNS) effects if given with other agents that affect the CNS. Lyrica is available in the following strength capsules: 25, 50, 75, 100, 150, 200, 225, and 300mg. Head-to-head comparisons to similar agents are not available.
In August 2004, the FDA approved Cymbalta for treatment of DPN and major depressive disorder (MDD). Dosing for treatment of DPN is 60 mg once daily. A lower starting dose may be used in patients with renal impairment. (It should not be used in patients with a CrCL <30 mL/min.) Common adverse effects include nausea, dizziness, somnolence, constipation, dry mouth, and increased sweating. Serum transaminase elevations have also been reported. Because Cymbalta is metabolized by CYP1A2 and CYP2D6, numerous drug interactions may occur. Drug discontinuation should be performed gradually to avoid withdrawal symptoms. Cymbalta capsules are delayed-release and are available in the following strengths: 20, 30, and 60 mg. (They should not be opened or crushed prior to administration).