Drug dosing during pregnancy—opportunities for physiologically based pharmacokinetic models

Drugs can have harmful effects on the embryo or the fetus at any point during pregnancy. Not all the damaging effects of intrauterine exposure to drugs are obvious at birth, some may only manifest later in life. Thus, drugs should be prescribed in pregnancy only if the expected benefit to the mother is thought to be greater than the risk to the fetus. Dosing of drugs during pregnancy is often empirically determined and based upon evidence from studies of non-pregnant subjects, which may lead to suboptimal dosing, particularly during the third trimester. This review collates examples of drugs with known recommendations for dose adjustment during pregnancy, in addition to providing an example of the potential use of PBPK models in dose adjustment recommendation during pregnancy within the context of drug-drug interactions. For many drugs, such as antidepressants and antiretroviral drugs, dose adjustment has been recommended based on pharmacokinetic studies demonstrating a reduction in drug concentrations. However, there is relatively limited (and sometimes inconsistent) information regarding the clinical impact of these pharmacokinetic changes during pregnancy and the effect of subsequent dose adjustments. Examples of using pregnancy PBPK models to predict feto-maternal drug exposures and their applications to facilitate and guide dose assessment throughout gestation are discussed

SNP genotyping using TaqMan® technology: the CYP2D6*17 assay conundrum

CYP2D6 contributes to the metabolism of many clinically used drugs and is increasingly tested to individualize drug therapy. The CYP2D6 gene is challenging to genotype due to the highly complex nature of its gene locus. TaqMan® technology is widely used in the clinical and research settings for genotype analysis due to assay reliability, low cost, and the availability of commercially available assays. The assay identifying 1023C>T (rs28371706) defining a reduced function (CYP2D6*17) and several nonfunctional alleles, produced a small number of unexpected diplotype calls in three independent sets of samples, i.e. calls suggested the presence of a CYP2D6*4 subvariant containing 1023C>T. Gene resequencing did not reveal any unknown SNPs in the primer or probe binding sites in any of the samples, but all affected samples featured a trio of SNPs on their CYP2D6*4 allele between one of the PCR primer and probe binding sites. While the phenomenon was ultimately overcome by an alternate assay utilizing a PCR primer excluding the SNP trio, the mechanism causing this phenomenon remains elusive. This rare and unexpected event underscores the importance of assay validation in samples representing a variety of genotypes, but also vigilance of assay performance in highly polymorphic genes such as CYP2D6

An economic model of the cost-utility of pre-emptive genetic testing to support pharmacotherapy in patients with major depression in primary care

Item does not contain fulltextThe pharmacokinetics of many antidepressants (tricyclic antidepressants (TCA) or selective serotonin re-uptake inhibitors (SSRI)) are influenced by the highly polymorphic CYP2D6 enzyme. Therefore, pharmacogenetics could play an important role in the treatment of depressive patients. The potential cost-utility of screening patients is however still unknown. Therefore, a Markov model was developed to compare the strategy of screening for CYP2D6 and subsequently adjust antidepressant treatment according to a patient's metabolizer profile of poor, extensive, or ultra metabolizer, with the strategy of no screening ('one size fits all' principle). Each week a patient had a probability of side effects, which was followed by dosage titration or treatment switching. After 6 weeks treatment effect was evaluated followed by treatment adjustments if necessary, with a total time horizon of the model of 12 weeks. The analysis was performed from a societal perspective. The strategy of screening compared with no screening resulted in incremental costs of euro91 (95 percentiles: euro39; euro152) more expensive but also more effect with 0.001 quality adjusted life years (QALYs) (95 percentiles: 0.001; 0.002) gain. The incremental cost-effectiveness ratio (ICER) was therefore euro77,406 per QALY gained, but varied between euro22,500 and euro377,500 depending on the price of screening and productivity losses. According to our model, we cannot unequivocally conclude that screening for CYP2D6 in primary care patients using antidepressants is be cost-effective, as the results are surrounded by large uncertainty. Therefore, information from ongoing studies should be used to reduce these uncertainties

Olmesartan/amlodipine/hydrochlorothiazide in participants with hypertension and diabetes, chronic kidney disease, or chronic cardiovascular disease: a subanalysis of the multicenter, randomized, double-blind, parallel-group TRINITY study

<p>Abstract</p> <p>Background</p> <p>Patients with hypertension and cardiovascular disease (CVD), diabetes, or chronic kidney disease (CKD) usually require two or more antihypertensive agents to achieve blood pressure (BP) goals.</p> <p>Methods</p> <p>The efficacy/safety of olmesartan (OM) 40 mg, amlodipine besylate (AML) 10 mg, and hydrochlorothiazide (HCTZ) 25 mg versus the component dual-combinations (OM 40/AML 10 mg, OM 40/HCTZ 25 mg, and AML 10/HCTZ 25 mg) was evaluated in participants with diabetes, CKD, or chronic CVD in the Triple Therapy with Olmesartan Medoxomil, Amlodipine, and Hydrochlorothiazide in Hypertensive Patients Study (TRINITY). The primary efficacy end point was least squares (LS) mean reduction from baseline in seated diastolic BP (SeDBP) at week 12. Secondary end points included LS mean reduction in SeSBP and proportion of participants achieving BP goal (<130/80 mm Hg) at week 12 (double-blind randomized period), and LS mean reduction in SeBP and BP goal achievement at week 52/early termination (open-label period).</p> <p>Results</p> <p>At week 12, OM 40/AML 10/HCTZ 25 mg resulted in significantly greater SeBP reductions in participants with diabetes (−37.9/22.0 mm Hg vs −28.0/17.6 mm Hg for OM 40/AML 10 mg, −26.4/14.7 mm Hg for OM 40/HCTZ 25 mg, and −27.6/14.8 mm Hg for AML 10/HCTZ 25 mg), CKD (−44.3/25.5 mm Hg vs −39.5/23.8 mm Hg for OM 40/AML 10 mg, −25.3/17.0 mm Hg for OM 40/HCTZ 25 mg, and −33.4/20.6 mm Hg for AML 10/HCTZ 25 mg), and chronic CVD (−37.8/20.6 mm Hg vs −31.7/18.2 mm Hg for OM 40/AML 10 mg, −30.9/17.1 mm Hg for OM 40/HCTZ 25 mg, and −27.5/16.1 mm Hg for AML 10/HCTZ 25 mg) (<it>P</it><0.05 for all subgroups vs dual-component treatments). BP goal achievement was greater for participants receiving triple-combination treatment compared with the dual-combination treatments, and was achieved in 41.1%, 55.0%, and 38.9% of participants with diabetes, CKD, and chronic CVD on OM 40/AML 10/HCTZ 25 mg, respectively. At week 52, there was sustained BP lowering with the OM/AML/HCTZ regimen. Overall, the triple combination was well tolerated.</p> <p>Conclusions</p> <p>In patients with diabetes, CKD, or chronic CVD, short-term (12 weeks) and long-term treatment with OM 40/AML 10/HCTZ 25 mg was well tolerated, lowered BP more effectively, and enabled more participants to reach BP goal than the corresponding 2-component regimens.</p> <p>Trial Identification Number</p> <p>NCT00649389</p