title: Detection and validated quantification of the phosphodiesterase type 5 inhibitors sildenafil, vardenafil, tadalafil, and 2 of their metabolites in human blood plasma by LC-MS/MS--application to forensic and therapeutic drug monitoring cases.
abstract: BACKGROUND
  Phosphodiesterase type 5 inhibitors such as sildenafil, vardenafil, and tadalafil are a class of drugs used primarily in the treatment of erectile dysfunction. Sildenafil and tadalafil are also approved for the treatment of pulmonary hypertension. The aim of this study was to develop and validate a procedure for the detection and quantification of these 3 drugs and some of their metabolites in human blood plasma.
  
  
  METHODS
  After liquid-liquid extraction of 0.5 mL of blood plasma using diethyl ether-ethyl acetate (1:1), the analytes sildenafil, norsildenafil, vardenafil, norvardenafil, and tadalafil were separated using a Shimadzu Prominence High-Performance Liquid Chromatography System (C18 separation column, gradient elution, and a total flow of 0.5 mL/min). They were detected using an AB Sciex 3200 Q-Trap LC-MS-MS System (electrospray ionization and multiple reaction monitoring mode). The method was fully validated according to international guidelines.
  
  
  RESULTS
  The assay was found to be selective for the tested compounds. It was linear from 5 to 1000 ng/mL for sildenafil, from 2 to 700 ng/mL for norsildenafil, from 0.5 to 350 ng/mL for vardenafil, from 0.5 to 200 ng/mL for norvardenafil, and from 5 to 1000 ng/mL for tadalafil. The recoveries were generally more than 50%. Matrix effects were not observed. Accuracy, repeatability, and intermediate precision were within the required limits (<15% or <20% near the limit of quantification). No instability was observed after repeated freezing and thawing or in processed samples.
  
  
  CONCLUSIONS
  A liquid chromatography-tandem mass spectrometry assay for the determination of sildenafil, norsildenafil, vardenafil, norvardenafil, and tadalafil in human blood plasma was developed and validated. It has proven to be selective, linear, accurate, and precise for all studied drugs. The method has also proven to be applicable for forensic cases and for therapeutic drug monitoring.
authors.affiliation: Department of Forensic Pharmacology and Toxicology, Institute of Forensic Medicine, University of Zurich, Zurich, Switzerland.
authors.forename: Kristina Y
authors.initials: KY
authors.lastname: Rust
authors.forename: Heinrike
authors.initials: H
authors.lastname: Wilkens
authors.forename: Ralf
authors.initials: R
authors.lastname: Kaiser
authors.forename: Dietmar
authors.initials: D
authors.lastname: Bregel
authors.forename: Jochen
authors.initials: J
authors.lastname: Wilske
authors.forename: Thomas
authors.initials: T
authors.lastname: Kraemer
mesh_terms: D000328:Adult; D000368:Aged; D000959:Antihypertensive Agents / Q000097:blood* / Q000493:pharmacokinetics / Q000627:therapeutic use; D001711:Biotransformation; D002243:Carbolines / Q000097:blood* / Q000493:pharmacokinetics; D002851:Chromatography, High Pressure Liquid; D016903:Drug Monitoring; D065627:Familial Primary Pulmonary Hypertension; D053593:Forensic Toxicology / Q000379:methods; D006801:Humans; D006976:Hypertension, Pulmonary / Q000097:blood / Q000188:drug therapy; D007093:Imidazoles / Q000097:blood* / Q000493:pharmacokinetics; D057230:Limit of Detection; D008297:Male; D058986:Phosphodiesterase 5 Inhibitors / Q000097:blood* / Q000493:pharmacokinetics / Q000627:therapeutic use; D010879:Piperazines / Q000097:blood* / Q000493:pharmacokinetics / Q000627:therapeutic use; D011687:Purines / Q000097:blood / Q000493:pharmacokinetics / Q000627:therapeutic use; D015203:Reproducibility of Results; D000068677:Sildenafil Citrate; D021241:Spectrometry, Mass, Electrospray Ionization; D013450:Sulfones / Q000097:blood* / Q000493:pharmacokinetics / Q000627:therapeutic use; D000068581:Tadalafil; D053719:Tandem Mass Spectrometry; D014227:Triazines / Q000097:blood / Q000493:pharmacokinetics; D000069058:Vardenafil Dihydrochloride
chemical_list: D000959:Antihypertensive Agents; D002243:Carbolines; D007093:Imidazoles; D058986:Phosphodiesterase 5 Inhibitors; D010879:Piperazines; D011687:Purines; D013450:Sulfones; D014227:Triazines; D000069058:Vardenafil Dihydrochloride; D000068581:Tadalafil; D000068677:Sildenafil Citrate