title: The effect of atovaquone on etoposide pharmacokinetics in children with acute lymphoblastic leukemia.
abstract: OBJECTIVE
  The use of trimethoprim/sulfamethoxazole in the prevention of Pneumocystis carinii pneumonia in patients with acute lymphoblastic leukemia (ALL) may cause undesirable adverse effects: fungal overgrowth, neutropenia, and drug resistance. A possible alternative is atovaquone, a hydroxynaphthoquinone with anti-Pneumocystis carinii activity. However, it is not known if atovaquone alters the disposition or adverse effects of antileukemic drugs.
  
  
  METHODS
  Using a crossover study design, we compared the pharmacokinetics of etoposide and its CYP3A4-formed catechol metabolite when given as a 300 mg/m2 i.v. infusion following daily atovaquone versus trimethoprim/sulfamethoxazole in nine patients.
  
  
  RESULTS
  The area under the concentration time curve (AUC) of etoposide, etoposide catechol and the catechol to etoposide AUC ratio were slightly higher (a median of 8.6%, 28.4%, and 25.9%) following atovaquone as compared to trimethoprim/sulfamethoxazole (P=0.055, P= 0.031 and P=0.023), respectively. In vitro analysis in human liver microsomes showed modest inhibition of etoposide catechol formation in the presence of atovaquone. Using uptake of 3H-vinblastine in L-MDR1 cells, atovaquone was shown to inhibit P-glycoprotein with an apparent Ki of 95.6 microM.
  
  
  CONCLUSIONS
  Although the effect of atovaquone on etoposide disposition was modest, in light of the fact that the risk of etoposide-related secondary acute myeloid leukemia has been linked to minor changes in schedule and concurrent therapy, we suggest caution with the simultaneous administration of atovaquone and etoposide, particularly if used with other CYP3A4/P-glycoprotein substrates.
authors.affiliation: Department of Pharmaceutical Sciences, St Jude Children's Research Hospital, Memphis, TN 38105, USA.
authors.forename: M E
authors.initials: ME
authors.lastname: van de Poll
authors.forename: M V
authors.initials: MV
authors.lastname: Relling
authors.forename: E G
authors.initials: EG
authors.lastname: Schuetz
authors.forename: P L
authors.initials: PL
authors.lastname: Harrison
authors.forename: W
authors.initials: W
authors.lastname: Hughes
authors.forename: P M
authors.initials: PM
authors.lastname: Flynn
mesh_terms: D000293:Adolescent; D000935:Antifungal Agents / Q000494:pharmacology*; D000972:Antineoplastic Agents, Phytogenic / Q000493:pharmacokinetics*; D019540:Area Under Curve; D053626:Atovaquone; D002648:Child; D002675:Child, Preschool; D018592:Cross-Over Studies; D004347:Drug Interactions; D005047:Etoposide / Q000493:pharmacokinetics*; D005260:Female; D006801:Humans; D008228:Lymphoma, Non-Hodgkin / Q000188:drug therapy / Q000378:metabolism*; D008297:Male; D009285:Naphthoquinones / Q000494:pharmacology*; D010865:Pilot Projects; D054198:Precursor Cell Lymphoblastic Leukemia-Lymphoma / Q000188:drug therapy / Q000378:metabolism*; D015662:Trimethoprim, Sulfamethoxazole Drug Combination / Q000494:pharmacology*
chemical_list: D000935:Antifungal Agents; D000972:Antineoplastic Agents, Phytogenic; D009285:Naphthoquinones; D005047:Etoposide; D015662:Trimethoprim, Sulfamethoxazole Drug Combination; D053626:Atovaquone