title: Pharmacokinetic and pharmacodynamic differences between two low dosages of aspirin may affect therapeutic outcomes.
abstract: BACKGROUND
  Meta-analyses of the prevention of major vascular events by aspirin suggest therapeutic equivalence of all dosages. However, the optimal dosage still remains problematic, and a recent trial found aspirin 160 mg/day to be more effective than 80 mg/day for secondary prevention of ischaemic stroke.
  
  
  OBJECTIVE
  To evaluate two low dosages of aspirin in terms of pharmacokinetics and pharmacodynamics (inhibition of platelet thromboxane generation and urinary excretion of thromboxane and prostacyclin metabolites).
  
  
  METHODS
  A randomised cross-over study was performed in 16 healthy volunteers (9 women and 7 men, 33.8 +/- 5.1 years old) given enteric-coated aspirin 80 or 160 mg/day for 7 days.
  
  
  METHODS
  Plasma concentrations of salicylate and aspirin were measured by high-performance liquid chromatography (HPLC) after both the first and the last dose (days 1 and 7). The usual pharmacokinetic parameters were then derived. Serum thromboxane B2 (TxB2) was measured by radioimmunoassay. The urinary excretion of 11-dehydro-TxB2 and 2,3-dinor-6-keto-prostaglandin F1alpha were measured on 8-hour urine samples by immunoassay after extraction and HPLC separation, both before and after 7 days of drug administration.
  
  
  RESULTS
  With the 160 mg dosage, but not with the 80 mg dosage, higher concentrations of aspirin were found at day 7 compared with day 1. For aspirin 80 mg/day, 24-hour area under the concentration-time curve (AUC24) was similar on days 1 and 7 (569 +/- 339 vs 605 +/- 377 microg. h/L), but increased from 904 +/- 356 microg. h/L on day 1 to 1355 +/- 883 microg. h/L on day 7 with the higher dosage. Similarly, the AUC24 for salicylate was similar on days 1 and 7 with the lower dosage, but significantly increased from day 1 to day 7 after the higher dosage. This paralleled inhibition of serum TxB2 levels (99% vs 95% average inhibition by 160 and 80 mg/day) and of urinary excretion of thromboxane metabolite (77% vs 61% average inhibition by 160 and 80 mg/day), without altering the excretion of prostacyclin metabolite.
  
  
  CONCLUSIONS
  Inhibition of serum TxB2 generation and of thromboxane metabolite urinary excretion by the lower dosage of aspirin, although substantial, still appeared incomplete. The small but significant further increase of serum TxB2 inhibition by the higher dosage was accompanied by an even greater inhibition of urinary excretion. We suggest that in some instances this difference would translate into a greater clinical benefit with the higher aspirin dosage. Our findings may also contribute to better definition of the recent concept of 'aspirin resistance'.
authors.affiliation: Centre for High Technology Research and Education in Biomedical Sciences, Catholic University, Campobasso, Italy. ccerletti@rm.unicatt.it
authors.forename: Chiara
authors.initials: C
authors.lastname: Cerletti
authors.forename: Giuseppe
authors.initials: G
authors.lastname: Dell'Elba
authors.forename: Stefano
authors.initials: S
authors.lastname: Manarini
authors.forename: Romina
authors.initials: R
authors.lastname: Pecce
authors.forename: Augusto
authors.initials: A
authors.lastname: Di Castelnuovo
authors.forename: Nicola
authors.initials: N
authors.lastname: Scorpiglione
authors.forename: Vincenzo
authors.initials: V
authors.lastname: Feliziani
authors.forename: Giovanni
authors.initials: G
authors.lastname: de Gaetano
mesh_terms: D000328:Adult; D019540:Area Under Curve; D001241:Aspirin / Q000008:administration & dosage / Q000097:blood / Q000493:pharmacokinetics*; D001792:Blood Platelets / Q000378:metabolism; D002851:Chromatography, High Pressure Liquid; D018592:Cross-Over Studies; D004305:Dose-Response Relationship, Drug; D011464:Epoprostenol / Q000652:urine; D005260:Female; D005343:Fibrinolytic Agents / Q000008:administration & dosage / Q000493:pharmacokinetics*; D006801:Humans; D008297:Male; D010975:Platelet Aggregation Inhibitors / Q000008:administration & dosage / Q000493:pharmacokinetics*; D012459:Salicylates / Q000097:blood; D013608:Tablets, Enteric-Coated; D013929:Thromboxane B2 / Q000096:biosynthesis; D016896:Treatment Outcome
chemical_list: D005343:Fibrinolytic Agents; D010975:Platelet Aggregation Inhibitors; D012459:Salicylates; D013608:Tablets, Enteric-Coated; D013929:Thromboxane B2; D011464:Epoprostenol; D001241:Aspirin