[Switching to e-cigarettes affects drug concentration]. / Overstap op e-sigaret beïnvloedt medicijnconcentratie.

BACKGROUND: Cytochrome P450 subtype 1A2 (CYP1A2) is responsible for the metabolism of several drugs, including the antipsychotic agent clozapine. Smoking cigarettes induces CYP1A2. Due to this induction, a higher dosage of the drug is required by patients who smoke tobacco. CASE DESCRIPTION: The dosage of clozapine was changed for a 34-year-old male because of suspected active psychosis. However, serum levels of clozapine did not change according to expectations. It appeared that the patient had switched from smoking normal cigarettes to using e-cigarettes and then started smoking cigarettes again during the time of the dosage change. This gave a plausible explanation for the observed clozapine concentrations. CONCLUSION: When patients switch from smoking normal cigarettes to using e-cigarettes induction of the CYP1A2 enzyme stops. A switch of this type may result in a major, undesirable increase in drug concentrations. Doctors should be alert to this when prescribing medication metabolised by CYP1A2 with a narrow therapeutic window.

A simple dried blood spot method for therapeutic drug monitoring of the tricyclic antidepressants amitriptyline, nortriptyline, imipramine, clomipramine, and their active metabolites using LC-MS/MS.

Therapeutic drug monitoring (TDM) of tricyclic antidepressants (TCAs) is considered useful in patients with major depressive disorder, since these drugs display large individual differences in clearance, and the therapeutic windows of these drugs are relatively small. We developed an assay for determination of amitriptyline (ATP), nortriptyline (NTP), imipramine (IMP), desipramine (DSP) clomipramine (CMP) and desmethyl-clomipramine (DCMP) in dried blood spots (DBS). A fast and robust LC-MS/MS method was developed and analytically validated for simultaneous determination of ATP, NTP, IMP, DSP, CMP, and DCMP in DBS. Six mm circles were punched out from DBS collected on Whatman DMPK-C paper and mixed with acetonitrile: methanol 1:3 containing the internal standard. The extract was analyzed by LC-MS/MS. Total LC-MS/MS runtime was 4.8 min. The assay was linear in the range 20-500 µg/L for all compounds. Overall-assay accuracy and precision were<20% for the lower limit of quantification (LLOQ), except for CMP (CV=22.3%), and <15% at other concentrations. The initial LLOQ was 20 µg/L however for CMP and DMCP it was increased to 40 µg/L. The blood volume per spot did not influence the results, but a low hematocrit (≤ 30%) was associated with a >15% negative bias for all compounds. Punching at the perimeter of the blood spot instead of the center was associated with a positive bias. A good correlation was found between patients plasma and DBS samples of ATP, NTP and DMCP, but not for CMP. In addition, proportional differences were found. This LC-MS/MS method was analytically validated for determination of TCAs in DBS. Future validation will focus on the clinical application of the method.

Determination of venlafaxine and O-desmethylvenlafaxine in dried blood spots for TDM purposes, using LC-MS/MS.

Dried blood spot (DBS) sampling and quantitative analyses of many current therapeutic drug monitoring (TDM)-guided drugs are advantageous because of the minimal invasive sampling strategy. Here, a fast and robust LC-MS/MS method was developed and analytically validated for simultaneous determination of venlafaxine (VEN) and O-desmethylvenlafaxine (ODV) in DBS. Six-millimeter circles were punched out from DBS collected on Whatman DMPK-C paper, and the DBS was extracted with acetonitrile/methanol at 1:3. The total run time was 4.8 min. The assay was linear in the range of 20-1,000 µg/L for both VEN and ODV. Assay accuracy and precision was well within limits of acceptance (LLOQ = 20 µg/L). Normal hematocrit concentrations (0.30-0.50) did not influence the results neither did a normal spot volume (40-80 µL). Punch position at the perimeter instead of the center of the blood spot gave a bias ranging from 2.4 to 10.4%. Correlation between plasma and spiked DBS samples was high. The concentrations found in spiked DBS samples were higher than those in plasma, indicating that a conversion factor for translation of DBS to plasma values is needed. This analytically validated method is suitable for determination of VEN and ODV in DBS and applicable for TDM. The method will be used for TDM of VEN in the Dutch CYSCE multicenter trial (NCT01778907).