title: Influence of the interval between the administration of doxorubicin and paclitaxel on the pharmacokinetics of these drugs in patients with locally advanced breast cancer.
abstract: OBJECTIVE
  The combination of bolus doxorubicin followed by a 3-h infusion of paclitaxel has high antitumor activity in patients with metastatic breast cancer, but is limited by unexpected cardiac toxicity. In contrast, the administration of the two drugs 16 h apart has similar antitumor activity but less cardiac toxicity. The purpose of this study was to compare the pharmacokinetics of these drugs when doxorubicin administration preceded paclitaxel by 30 min or by 24 h.
  
  
  METHODS
  Women with locally advanced breast cancer were treated with doxorubicin (60 mg/m2 i.v. bolus) followed 24 h later by paclitaxel (200 mg/m2 i.v. over 3 h) for six cycles (four before and two after surgery). In one of the first two cycles doxorubicin preceded paclitaxel by 30 min instead of 24 h, with plasma sampling for pharmacokinetic analysis up to 48 h. Determination of drug levels in plasma was done by HPLC.
  
  
  RESULTS
  A total of 28 patients were included. No clinical cardiac toxicity was observed but five patients discontinued doxorubicin-paclitaxel treatment after four cycles because of a decrease in LVEF of at least 15% from baseline or to less than 50%. While paclitaxel pharmacokinetics were not changed, there was a 30% and an 80% increase in the AUC0, 24h for doxorubicin and doxorubicinol, respectively, when the drugs were administered 30 min instead of 24 h apart. Even when paclitaxel was given 24 h after doxorubicin, there was a rebound 240% increase in the plasma concentration of doxorubicinol.
  
  
  CONCLUSIONS
  Paclitaxel interferes with the pharmacokinetics of doxorubicin leading to higher systemic exposure to both doxorubicin and doxorubicinol, which is more evident when the plasma concentration of the anthracyclines is higher. This interference may explain the higher incidence of cardiac toxicity observed when the two drugs are administered within a short interval.
authors.affiliation: Department of Medical Oncology, Instituto Português de Oncologia, Lisbon, Portugal.
authors.forename: A
authors.initials: A
authors.lastname: Moreira
authors.forename: R
authors.initials: R
authors.lastname: Lobato
authors.forename: J
authors.initials: J
authors.lastname: Morais
authors.forename: S
authors.initials: S
authors.lastname: Silva
authors.forename: J
authors.initials: J
authors.lastname: Ribeiro
authors.forename: A
authors.initials: A
authors.lastname: Figueira
authors.forename: D
authors.initials: D
authors.lastname: Vale
authors.forename: C
authors.initials: C
authors.lastname: Sousa
authors.forename: F
authors.initials: F
authors.lastname: Araújo
authors.forename: A
authors.initials: A
authors.lastname: Fernandes
authors.forename: J
authors.initials: J
authors.lastname: Oliveira
authors.forename: J L
authors.initials: JL
authors.lastname: Passos-Coelho
mesh_terms: D000328:Adult; D000970:Antineoplastic Agents / Q000008:administration & dosage / Q000009:adverse effects* / Q000493:pharmacokinetics*; D000972:Antineoplastic Agents, Phytogenic / Q000008:administration & dosage* / Q000009:adverse effects / Q000493:pharmacokinetics*; D000971:Antineoplastic Combined Chemotherapy Protocols / Q000008:administration & dosage* / Q000009:adverse effects / Q000493:pharmacokinetics*; D019540:Area Under Curve; D001943:Breast Neoplasms / Q000188:drug therapy*; D004317:Doxorubicin / Q000008:administration & dosage / Q000009:adverse effects* / Q000493:pharmacokinetics*; D004334:Drug Administration Schedule; D004347:Drug Interactions; D005260:Female; D006321:Heart / Q000187:drug effects; D006801:Humans; D007262:Infusions, Intravenous; D007275:Injections, Intravenous; D008875:Middle Aged; D017239:Paclitaxel / Q000008:administration & dosage* / Q000009:adverse effects / Q000493:pharmacokinetics*; D013318:Stroke Volume
chemical_list: D000970:Antineoplastic Agents; D000972:Antineoplastic Agents, Phytogenic; D004317:Doxorubicin; D017239:Paclitaxel