title: Rifampin markedly decreases plasma concentrations of praziquantel in healthy volunteers.
abstract: OBJECTIVE
  Praziquantel is extensively metabolized by the hepatic cytochrome P450 (CYP) enzymes. The CYP3A isoforms are likely to be major enzymes responsible for praziquantel metabolism. Rifampin (INN, rifampicin), a potent enzyme inducer of CYP-mediated metabolism (especially CYP2C9, CYP2C19, and CYP3A4), is known to markedly decrease plasma concentrations and effects of a number coadministered drugs. The aim of this investigation was to study the possible pharmacokinetic interaction between rifampin and praziquantel.
  
  
  METHODS
  An open, randomized, 2-phase crossover design was used in each study of single or multiple doses. In the single-dose study, 10 healthy Thai male volunteers ingested single doses of 40 mg/kg praziquantel alone (phase 1) or after pretreatment with 600 mg of oral rifampin once daily for 5 days (phase 2). In the multiple-dose study, all participants received multiple doses of 25 mg/kg praziquantel alone (phase 1) or after 5-day pretreatment with 600 mg of oral rifampin once daily (phase 2). Plasma concentrations of praziquantel in each phase were determined by the HPLC method.
  
  
  RESULTS
  In the single-dose study, rifampin decreased plasma praziquantel concentrations to undetectable levels in 7 of 10 subjects, whereas praziquantel concentrations were reduced by rifampin to undetectable levels in 5 of 10 subjects in the multiple-dose study. In 3 subjects with measurable concentrations in the single-dose study, rifampin significantly decreased the mean maximum plasma concentration (C(max)) and area under the plasma concentration-time curve from 0 to 24 hours [AUC(0-24)] of praziquantel by 81% (P <.05) and 85% (P <.01), respectively, whereas rifampin significantly decreased the mean C(max) and AUC(0-24) of praziquantel by 74% (P <.05) and 80% (P <.01), respectively, in 5 subjects with measurable concentrations in the multiple-dose study. The mean C(max) and AUC(0-24) of praziquantel in subjects whose praziquantel concentrations could not be detected in the single-dose study (7 subjects) after rifampin pretreatment were reduced by approximately 99% (P <.001) and 94% (P <.001), respectively, and in the multiple-dose study (5 subjects), they were reduced by 98% (P <.05) and 89% (P <.01), respectively.
  
  
  CONCLUSIONS
  Rifampin greatly decreased plasma concentrations of single and multiple oral doses of praziquantel to levels lower than that of the minimum therapeutic concentration. Because praziquantel and rifampin are widely used in the treatment of liver flukes (Opisthorchis viverrini) and Mycobacterium tuberculosis, respectively, in Thailand and in some other countries in southeast Asia, the possibility of one drug influencing the pharmacokinetics of the other must be considered. Therefore simultaneous use of rifampin and praziquantel must be avoided in medical practice to optimize the therapeutic efficacy of praziquantel.
authors.affiliation: Clinical Pharmacology Laboratory, Department of Pharmacology, Faculty of Science, Prince of Songkla University, Hat Yai, Thailand. rwibool@ratree.psu.ac.th
authors.forename: Wibool
authors.initials: W
authors.lastname: Ridtitid
authors.forename: Malinee
authors.initials: M
authors.lastname: Wongnawa
authors.forename: Werawath
authors.initials: W
authors.lastname: Mahatthanatrakul
authors.forename: Jarurat
authors.initials: J
authors.lastname: Punyo
authors.forename: Methi
authors.initials: M
authors.lastname: Sunbhanich
mesh_terms: D000328:Adult; D019540:Area Under Curve; D018592:Cross-Over Studies; D051544:Cytochrome P-450 CYP3A; D003577:Cytochrome P-450 Enzyme System / Q000502:physiology; D004347:Drug Interactions; D006801:Humans; D008297:Male; D011223:Praziquantel / Q000097:blood*; D012293:Rifampin / Q000494:pharmacology*
chemical_list: D011223:Praziquantel; D003577:Cytochrome P-450 Enzyme System; C104464:CYP3A protein, human; D051544:Cytochrome P-450 CYP3A; C510163:CYP3A4 protein, human; D012293:Rifampin