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Tadalafil, a phosphodiesterase 5 inhibitor, is being investigated as a treatment for pulmonary arterial hypertension (PAH) in children aged 6 months to less than 18 years. Tadalafil pharmacokinetic (PK) data in children less than 2 years old are unavailable, therefore a physiologically based pharmacokinetic (PBPK) model was developed to enable estimation of tadalafil doses in children less than 2 years old. The model was verified in adults and extended for use in children by modifying CYP3A‐mediated intrinsic clearance to include CYP3A7. To account for co‐dosing of the commonly prescribed moderate CYP3A4 inducer bosentan, predicted exposures were increased by a factor of 1.54 based on changes in exposure in adults with PAH. This factor was predictable using a bosentan PBPK model. The tadalafil model was verified in children aged greater than or equal to 2 years by comparing predicted and observed exposures. Tadalafil doses for children less than 2 years old were calculated as target area under the concentration curve from zero to 24 h (AUC0–24)/predicted AUC0–24, with target AUC0–24 of 10,000 ng*h/ml based on adult 40 mg single dose exposures determined in patients without bosentan background treatment. These doses were 2 mg, 3 mg, 4 mg, and 6 mg, respectively, for children aged birth to less than 1 month, 1 month to less than 6 months, 6 months to less than 1 year, and 1 to less than 2 years. Due to uncertainties in CYP maturation, a nonmechanistic steady‐state volume scalar, and lack of PK data in children less than 2 years old, accumulation of tadalafil to steady‐state in children less than 2 years was not verifiable. Safety of proposed doses is supported by postmarketing research and investigator‐led trials. [ABSTRACT FROM AUTHOR]

Rosuvastatin is commonly prescribed for the treatment of hypercholesterolemia and hepatic transporter‐mediated accumulation in the liver enhances its efficacy. Current guidelines indicate no preference for fed or fasted rosuvastatin administration. We investigated the association between food intake and rosuvastatin disposition in healthy subjects and low‐density lipoprotein cholesterol (LDL‐C)‐lowering effects among patients taking rosuvastatin. We demonstrate that administration with food resulted in a near 40% reduction of rosuvastatin exposure in healthy Asian (n = 12) and Caucasian (n = 11) subjects. Higher rosuvastatin concentrations in Asian subjects also correlated with higher allele frequency of ABCG2 c.421C>A. In mice, a greater rosuvastatin liver:plasma ratio was noted when administered with food. Among rosuvastatin patients (n = 156), there was no difference in dose needed to reach target LDL‐C, measured LDL‐C, or lathosterol concentrations, when administered in a fed or fasting state. Therefore, taking rosuvastatin with food could reduce systemic concentrations, and subsequent myopathy risk, without compromising LDL‐C‐lowering benefit. [ABSTRACT FROM AUTHOR]

Personalized medicine is an emerging field with a goal of applying genomic information as a predictor of disease risk as well as individualization of drug therapy. For optimization of drug therapy, significant progress has been made in the past decade in linking genetic variation in genes associated with drug disposition to prediction of drug response and adverse reactions. For most drugs in clinical use, the interplay of many factors, including genetics, demographics, drug-drug interactions, disease states and the environment, result in the interindividual variability observed during drug therapy. Broadly speaking, such determinants of drug response are mediated through modulation of drug concentrations reflective of pharmacokinetic factors, as well as drug targets, often referred to as pharmacodynamics. It is clear that for personalized medicine to become clinically meaningful, genomic as well as clinical and environmental influences must be considered together. We show, for a number of drugs in clinical use, that genomics-guided treatment options not only are becoming feasible but are also on the cusp of showing superiority in terms of clinical outcomes as well as cost-benefit. One of the most widely studied drugs with regard to genomics-guided dosing options is the oral anticoagulant, warfarin. Genetic polymorphisms in the gene encoding cytochrome P450 2C9 ( CYP2C9) and those in the target gene responsible for the warfarin anticoagulant effect, vitamin K epoxide reductase ( VKORC1), account for much of the variability in the warfarin maintenance dose; however, routine genotyping in warfarin therapy remains controversial. We will outline the importance of understanding all of the variables that mediate warfarin response as the prerequisite to successful utilization of genotype-guided warfarin therapy. Similarly, HMG Co-A reductase inhibitors, commonly known as statins, also display wide interindividual variability in plasma concentration, response and toxicity due in part to polymorphisms in transporter genes, including SLCO1B1 and ABCG2. Genetic factors are also important considerations in treatment with other therapeutic agents discussed, including clopidogrel and tamoxifen. Implementation of personalized medicine-based treatment options for these and other drugs, the pharmacokinetics or pharmacodynamics of which are impacted by functional genetic variations, will require overcoming a number of challenges, including cost, turnaround time, and demonstration of clinical benefit, as well as better training of health care professionals about genomics in general, and pharmacogenomics in particular. [ABSTRACT FROM AUTHOR]

The role of organic cation transporter 1 (OCT1) in humans is gaining attention as data emerges regarding its role in physiology, drug exposure, and drug response. OCT1 variants with decreased in vitro function correlate well with altered exposure of multiple OCT1 substrates in variant carriers. In the current research, we investigate mechanisms behind activity of OCT1 variants in vitro by generating cell lines expressing known OCT1 variants and quantifying membrane OCT1 protein expression with corresponding OCT1 activity and kinetics. Oct knockout mice have provided additional insight into the role of Oct1 in the liver and have reproduced effects of altered OCT1 activity observed in the clinic. To assess the complex effect of Oct1 depletion on pharmacokinetics of prodrug proguanil and its active moiety cycloguanil, both of which are OCT1 substrates, Oct1/2−/− mice were used. Decreased membrane expression of OCT1 was demonstrated for all variant cell lines, although activity was substrate-dependent, as reported previously. Lack of change in activity for OCT1*2 resulted in increased intrinsic activity per pmol of OCT1 protein, particularly for sumatriptan but also for proguanil and cycloguanil. Similar to that reported in humans with decreased OCT1 function, systemic exposure of proguanil was minimally affected in Oct1/2−/− mice. However, proguanil liver partitioning and exposure decreased. Cycloguanil exposure decreased following proguanil administration in Oct1/2−/− mice, as did the systemic metabolite:parent ratio. When administered directly, systemic exposure of cycloguanil decreased slightly; however liver partitioning and exposure were decreased in Oct1/2−/− mice. Unexpectedly, following proguanil administration, the metabolite ratio in the liver changed only minimally, and liver partitioning of cycloguanil was affected in Oct1/2−/− mice to a lesser extent following proguanil administration than direct administration of cycloguanil. In conclusion, these in vitro and in vivo data offer additional complexity in understanding mechanisms of OCT1 variant activity as well as the effects of these variants in vivo. From cell lines, it is apparent that intrinsic activity is not directly related to OCT1 membrane expression. Additionally, in situations with a more complicated role of OCT1 in drug pharmacokinetics there is difficulty translating in vivo impact simply from intrinsic activity from cellular data. [ABSTRACT FROM AUTHOR]

γ-Hydroxybutyrate (GHB), a common drug of abuse, is often coingested with ethanol. Increasing renal clearance via monocarboxylate transporter (MCT) inhibition represents a potential therapeutic strategy in GHB overdose, as does inhibition of GABAB receptors. In this study, we investigate toxicokinetic/toxicodynamic interactions between GHB-ethanol and efficacy of treatment options for GHB-ethanol intoxication in rats. Sedation was assessed using the endpoint of return-to-righting reflex. Respiration was assessed using plethysmography. Coadministration of 2.0 g/kg ethanol i.v. with 600 mg/kg GHB i.v. increased sleep time compared with GHB alone. Administration of ethanol to steady-state concentrations of 0.1-0.2% and 0.3-0.4% (w/v) did not affect toxicokinetics of 600 mg/kg GHB i.v., or respiratory rate, but did result in significantly lower peak tidal volumes compared with GHB alone. Oral administration of 2.5 g/kg ethanol had no significant effect on toxicokinetics of 1500 mg/kg orally administered GHB. Pretreatment with specific receptor inhibitors indicated no effect of GABAA receptor inhibition on sleep time or respiratory depression in GHB-ethanol intoxication. GABAB receptor inhibition partially prevented sedation and completely prevented respiratory depression. Ethanol increased fatality when administered at 0.1-0.2% (4 of 10) and 0.3-0.4% (9 of 10) versus 1500 mg/kg GHB i.v. alone (0 of 10). Treatment with the MCT inhibitor, l-lactate, significantly decreased sleep time after GHB-ethanol and decreased fatality at 0.1-0.2% (0 of 10) and 0.3-0.4% ethanol (5 of 10). Treatment with a GABAB receptor antagonist completely prevented fatality at 0.3-0.4% (0 of 10). These data indicate that ethanol potentiates the sedative and respiratory depressant effects of GHB, increasing the risk of fatality. MCT and GABAB receptor inhibition represent potentially effective treatments in GHB-ethanol intoxication.

Background and Objective: The purpose of the current study was to demonstrate proof-of-concept that monocarboxylate transporter (MCT) inhibition with L-lactate combined with osmotic diuresis increases renal clearance of γ-hydroxybutyrate (GHB) in human subjects. GHB is a substrate for human and rodent MCTs, which are responsible for GHB renal reabsorption, and this therapy increases GHB renal clearance in rats., Methods: Ten healthy volunteers were administered GHB orally as sodium oxybate 50 mg/kg (4.5 gm maximum dose) on two different study days. On study day 1, GHB was administered alone. On study day 2, treatment of L-lactate 0.125 mmol/kg and mannitol 200 mg/kg followed by L-lactate 0.75 mmol/kg/hr was administered intravenously 30 minutes after GHB ingestion. Blood and urine were collected for 6 hours, analyzed for GHB, and pharmacokinetic and statistical analyses performed., Results: L-lactate/mannitol administration significantly increased GHB renal clearance compared to GHB alone, 439 vs. 615 mL/hr (P=0.001), and increased the percentage of GHB dose excreted in the urine, 2.2 vs. 3.3% (P=0.021). Total clearance was unchanged., Conclusions: MCT inhibition with L-lactate combined with osmotic diuresis increases GHB renal elimination in humans. No effect on total clearance was observed in this study due to the negligible contribution of renal clearance to total clearance at this low GHB dose. Considering the nonlinear renal elimination of GHB, further research in overdose cases is warranted to assess the efficacy of this treatment strategy for increasing renal and total clearance at high GHB doses.