title: Unidirectional cross-tolerance from levetiracetam to carbamazepine in amygdala-kindled seizures.
abstract: OBJECTIVE
  Tolerance is a potential problem in long-term anticonvulsant therapy of epilepsy, bipolar disorder, and neuropathic pain. The present study was designed to determine whether cross-tolerance occurs between levetiracetam (LEV) and carbamazepine (CBZ) in amygdala-kindled rats.
  
  
  METHODS
  Male Sprague-Dawley rats were implanted with an electrode into the left amygdala. While kindling stimulation was started, animals received repeated treatment (i.p.) with saline (n = 7) or LEV (150 mg/kg, n = 8). Saline-injected rats were subsequently challenged with a single dose of 150 mg/kg LEV when full kindling developed (stage > or =4). Both groups of rats were then administered long-term CBZ (5 mg/kg) until rats developed complete tolerance. All CBZ-tolerant rats were subsequently re-exposed to LEV (150 mg/kg) for an additional 10 consecutive days.
  
  
  RESULTS
  Repeated LEV treatment significantly suppressed the increase in seizure stage, seizure duration, and afterdischarge duration induced by amygdala stimulation, markedly increasing the number of stimulations to achieve a kindling major motor seizure. The LEV challenge produced a more robust suppression of seizure stage in saline-injected rats compared with LEV-treated animals. CBZ treatment markedly suppressed fully kindled seizures in rats initially injected with saline, and then anticonvulsant tolerance rapidly developed after 3-4 days of repeated treatment. In contrast, rats that had initially received repeated LEV treatment did not show a response to treatment with CBZ (5 mg/kg). When CBZ-tolerant rats were subsequently exposed to LEV (150 mg/kg), noticeable anticonvulsant effects were observed; but these were gradually lost with increasing numbers of LEV exposures.
  
  
  CONCLUSIONS
  Whereas LEV shows potent antiepileptogenic and anticonvulsant effects in amygdala-kindled rats, its repeated treatment induces anticonvulsant tolerance and unidirectional cross-tolerance to CBZ. In contrast, anticonvulsant tolerance to CBZ does not transfer to LEV. The mechanistic implications of the present results for clinical therapeutics remain to be evaluated.
authors.affiliation: Department of Psychiatry, Uniformed Services University of the Health Sciences, 4301 Jones Bridge Road, Bethesda, MD 20814, U.S.A. zzhang1@usuhs.mil
authors.forename: Zhang-Jin
authors.initials: ZJ
authors.lastname: Zhang
authors.forename: Guo-Qiang
authors.initials: GQ
authors.lastname: Xing
authors.forename: Shani
authors.initials: S
authors.lastname: Russell
authors.forename: Kris
authors.initials: K
authors.lastname: Obeng
authors.forename: Robert M
authors.initials: RM
authors.lastname: Post
mesh_terms: D000679:Amygdala / Q000187:drug effects*; D000818:Animals; D000927:Anticonvulsants / Q000494:pharmacology*; D002220:Carbamazepine / Q000494:pharmacology*; D004361:Drug Tolerance; D004569:Electroencephalography / Q000187:drug effects; D007274:Injections, Intraperitoneal; D007696:Kindling, Neurologic / Q000187:drug effects*; D000077287:Levetiracetam; D008134:Long-Term Care; D008297:Male; D010889:Piracetam / Q000031:analogs & derivatives* / Q000494:pharmacology*; D051381:Rats; D017207:Rats, Sprague-Dawley
chemical_list: D000927:Anticonvulsants; D002220:Carbamazepine; D000077287:Levetiracetam; D010889:Piracetam