Ondansetron Carbamazepine

ONDANSETRON CARBAMAZEPINE, PHENYTOIN Reports of 1 ondansetron levels Induction of metabolism of ondansetron Watch for poor response to ondansetron care with other 5-HT3 antagonists... 

Fig. 4.3 CSF concentration/free (unbound) plasma concentration ratios for neutral and basic drugs 1, ritropirronium 2, atenolol 3, sulpiride 4, morphine 5, cimetidine 6, meto-prolol 7, atropine 8, tacrine 9, digoxin 10, propranolol 11, carbamazepine 12, ondansetron 13, diazepam 14, imipramine 15, digitonin 16, chlorpromazine and acidic drugs, a, salicylic acid b, ketoprofen c, oxyphenbutazone and d, indomethacin compared to log D.

Other than slow taper, no consistently effective treatment to alleviate withdrawal symptoms has been reported. Although several compounds have been studied (e.g., b-blockers, clonidine, carbamazepine, abercamil, ondansetron), results have been contradictory ( 250). Carbamazepine, however, may be useful in seizure-prone patients (251). Valproate (VPA) has also been reported to benefit patients undergoing BZD discontinuation after long-term dependence ( 252), which may be related to VPA s potential anxiolytic properties, its ability to alleviate withdrawal phenomena, or both. The azaspirone anxiolytic buspirone has been reported ineffective in suppressing withdrawal symptoms, particularly in long-term BZD users (253, 254). Hydroxyzine has also been found beneficial in treating patients for lorazepam withdrawal (255). 

Among the recently evaluated treatments for BZD withdrawal are anticonvulsants (carbamazepine and VPA) ( 256), melatonin (257), and ondansetron (258). Of these, odansetron had no significant effects on severity of withdrawal symptoms melatonin was found to effectively facilitate discontinuation of BZD therapy while maintaining good sleep and carbamazepine and VPA may be beneficial in the management of BZD discontinuation but not in decreasing the severity of BZD withdrawal (259, 260). 

The manufacturer notes that concurrent use of carbamazepine, dexamethasone, H2-receptor antagonists, ondansetron, phenobarbital, phenytoin or prochlorperazine did not affect the clearance of temozolomide, based on an analysis of population pharmacokinetics from phase II studies. However, valproic acid modestly reduced the clearance of temozolomide. 

Potent P450 inducers, including phenytoin, rifampicin, and carbamazepine, can significantly increase the clearance and decrease the blood concentration of ondansetron. However, there are not sufficient data to support dosage adjustment for patients taking these drugs. 

---