title: Toxicity and efficacy of sirolimus: relationship to whole-blood concentrations.
abstract: BACKGROUND
  Sirolimus is a novel macrolide immunosuppressive drug with a mechanism of action distinct from that of both cyclosporine and tacrolimus. Recent clinical studies have demonstrated a decrease in acute rejection episodes in renal transplant patients receiving sirolimus compared with controls. The major toxicities associated with sirolimus treatment are thrombocytopenia and hyperlipidemia. In addition, concern has been raised by the higher serum creatinine levels noted in patients receiving sirolimus and cyclosporine compared with controls receiving cyclosporine and azathioprine.
  
  
  OBJECTIVE
  The objective of the present review is to summarize the efficacy and toxicity data for sirolimus. Special consideration is given to evidence that links these effects to dose or whole-blood concentrations of sirolimus.
  
  
  RESULTS
  The literature indicates that trough concentrations of sirolimus >15 ng/mL appear to be associated with a greater risk of both thrombocytopenia and hyperlipidemia, whereas trough sirolimus concentrations <6 ng/mL have been associated with an increased incidence of acute rejection.
  
  
  CONCLUSIONS
  The evidence to date supports target trough sirolimus concentrations of 6 to 15 ng/mL in most patients. In higher-risk groups and patients receiving cyclosporine-sparing regimens, higher concentrations may be necessary to achieve similar efficacy.
authors.affiliation: Department of Internal Medicine, University of Michigan Medical School, Ann Arbor, USA.
authors.forename: H U
authors.initials: HU
authors.lastname: Meier-Kriesche
authors.forename: B
authors.initials: B
authors.lastname: Kaplan
mesh_terms: D006801:Humans; D007166:Immunosuppressive Agents / Q000009:adverse effects* / Q000097:blood* / Q000493:pharmacokinetics; D020123:Sirolimus / Q000009:adverse effects* / Q000097:blood* / Q000493:pharmacokinetics
chemical_list: D007166:Immunosuppressive Agents; D020123:Sirolimus