Volume 29, Issue 3

Venlafaxine (VEN) is one of the safest and most effective drugs used in the treatment of selective serotonin reuptake inhibitors-resistant depression, and thereby it is nowadays one of the most commonly prescribed antidepressants. Nevertheless, patients treated with antidepressant drugs including VEN have exhibited large inter-individual variability in drug outcomes, possibly due to the influence of genetic and nongenetic factors on the drug pharmacokinetics and/or pharmacodynamics. Among them, an increased interest has emerged over the last few years on the genetic and/or phenotypic profile for drug-metabolizing cytochrome P450 isoenzymes and drug transporters such as potential predictive pharmacokinetic-based biomarkers of the variability found in drug biodisposition and antidepressant response. The integration of some of these key therapeutic biomarkers with classic therapeutic drug monitoring constitutes a promising way to individualization of VEN’s pharmacotherapy, offering to clinicians the ability to better predict and manage pharmacological treatments to maximize the drug effectiveness. Thus, this review provides an extensive discussion of the pharmacokinetics of VEN focusing in particular on metabolism issues, without forgetting the clinically relevant sources of pharmacokinetics variability (mainly the genetic sources) and aiming on the identification of phenotypic and/or genetic biomarkers for therapy optimization.

Human carboxylesterase 1 (CES1) and carboxylesterase 2 (CES2) are serine esterases responsible for the hydrolysis of ester and amide bonds present in a number of pharmaceutical products. Several common genetic variants of the CES1 and CES2 genes have been shown to influence drug metabolism and clinical outcomes. Polymorphisms of the CES1 gene have been reported to affect the metabolism of dabigatran etexilate, methylphenidate, oseltamivir, imidapril, and clopidogrel, whereas variants of the CES2 gene have been found to affect aspirin and irinotecan. Although the findings of these studies may be preliminary, they demonstrate the potential clinical utility of CES polymorphisms; however, more research is required, especially with respect to CES2 . In this review, we outline the functional, molecular, and genetic properties of CES1 and CES2, and highlight recent studies that have shown relations between CES1 and CES2 variants and contemporary pharmacotherapy.

Phase I and II drug metabolizing enzymes (DMEs) play an important role in biotransformation of endogenous and exogenous compounds including drugs currently used in pharmacoterapy. Moreover, the genetic variability of DMEs causes important interindividual differences in drug and metabolite exposure, drug response, and risk of adverse drug reactions. We reviewed pharmacogenetics/pharmacogenomics (PGx) studies that evaluated the influence of polymorphisms in the CYPs genes – mainly CYP1, CYP2 and CYP3 gene families – and in the phase II genes – TPMT, NAT2, GSTs and UGTs – on therapeutic response in Brazilian cohorts. Ethnic admixture of Brazilians resulted in a population characterized by a unique genetic profile, in which ancestry informative markers change continuously among ethnic groups. Therefore, some of the PGx biomarkers have a different distribution among Brazilians and PGx data from well-defined ethnic groups are not applicable to Brazilian populations. PGx data focused on phase I and phase II DMEs from Brazilian studies are needed in order to establish the influence of the genetic diversity on therapeutic response to clinically relevant drugs in a population with a composition from a complex genetic admixture. These studies and their impact are discussed in this review.

Background: The metabolism of tyrosine kinase inhibitors (TKIs) is mainly mediated via hepatic route, but the mechanism responsible for their hepatocellular accumulation is still unknown. This study was designed to understand the contribution of organic anion transporting polypeptides (OATPs) in the hepatic uptake of selected TKIs – pazopanib, canertinib, erlotinib, vandetanib and nilotinib. Methods: Michaelis-Menten (MM) kinetic parameters for TKIs were determined by concentration-dependent cellular accumulation of selected TKIs using Chinese hamster ovary cells – wild type as well as transfected with humanized OATP-1B1 and OATP-1B3 transporter proteins. Results: The MM constant ( K m ) values of OATP-1B1 for nilotinib and vandetanib are 10.14±1.91 and 2.72±0.25 μM, respectively, and V max values of OATP-1B1 for nilotinib and vandetanib were 6.95±0.47 and 75.95±1.99 nmol/mg protein per minute, respectively. Likewise, K m values of OATP-1B3 for canertinib, nilotinib and vandetanib were 12.18±3.32, 7.84±1.43 and 4.37±0.79 μM, respectively, and V max values of OATP-1B3 for canertinib, nilotinib and vandetanib were 15.34±1.59, 6.75±0.42 and 194.64±10.58 nmol/mg protein per minute, respectively. Canertinib did not exhibit any substrate specificity toward OATP-1B1. Also, erlotinib and pazopanib did not exhibit any substrate specificity toward OATP-1B1 and -1B3. Conclusions: Because selected TKIs are the substrates of OATP-1B1 and -1B3 expressed in hepatic tissue, these compounds can be regarded as molecular targets for transporter-mediated drug-drug interactions (DDIs). Any alteration in the function of these hepatic OATPs might account for the pharmacokinetic variability of TKIs.

Background: To evaluate potential drug-drug interactions with the atypical antipsychotic lurasidone. Methods: Seven phase I studies were conducted to investigate the effects of repeated dosing of ketoconazole, diltiazem, rifampin, or lithium on the pharmacokinetics (PK) of single oral doses of lurasidone, or the effects of repeated dosing of lurasidone on the PK of digoxin, midazolam, or the oral contraceptive norgestimate/ethinyl estradiol. Two 6-week, phase III studies included evaluation of the potential for interaction between lurasidone and lithium or valproate. Maximum serum or plasma concentration ( C max ) and area under the concentration-time curve (AUC) were calculated. Results: Concomitant ketoconazole administration resulted in a 6.8-fold increase in lurasidone C max and a 9.3-fold increase in lurasidone AUC; concomitant diltiazem administration resulted in 2.1- and 2.2-fold increases, respectively. Rifampin decreased lurasidone C max and AUC (one-seventh and one-fifth of lurasidone alone, respectively). Steady-state dosing with lurasidone increased C max and AUC 0 – 24 (AUC from time 0 to 24 h postdose) of digoxin by 9% and 13%, respectively, and of midazolam by 21% and 44%, respectively. There were no significant interactions between lurasidone and lithium, valproate, ethinyl estradiol, or norelgestromin (the major active metabolite of norgestimate). Conclusions: Lurasidone PK is altered by strong cytochrome P450 (CYP) 3A4 inhibitors or inducers, and coadministration is contraindicated; whereas moderate CYP3A4 inhibitors have less effect, and lurasidone dosage restrictions are recommended. No dose adjustment for lurasidone is needed when administered with lithium or valproate. Dose adjustment is not required for lithium, valproate, digoxin (a P-glycoprotein substrate), or midazolam or oral contraceptives (CYP3A4 substrates) when coadministered with lurasidone.

Selective cyclooxygenase-2 inhibitor lumiracoxib was shown to have the strong inhibitory potencies on the renal organic anion transporter (OAT)1 and also on OAT3 from drug transport experiments. The purpose of this study was to examine the effect of lumiracoxib on disposition of phenolsulfonphthalein (PSP) – which is mainly excreted into urine via OATs – from in vivo experiments. After the intravenous injection of PSP and lumiracoxib into rats, pharmacokinetic analysis was performed. After the intravenous injection of PSP as a bolus, its plasma concentration decreased time-dependently. Until 60 min after the injection, 51.1% of the dose was recovered into urine. The simultaneous administration of lumiracoxib increased the plasma levels of PSP and reduced its urinary recovery to 23.6% of the dose. The pharmacokinetic analysis using a two-compartment model exhibited that lumiracoxib affected the parameters implying the elimination of PSP. The present study demonstrates that lumiracoxib interfered with urinary excretion of PSP in rats.