Renal Drug Transporters and Drug Interactions.

Transporters in proximal renal tubules contribute to the disposition of numerous drugs. Furthermore, the molecular mechanisms of tubular secretion have been progressively elucidated during the past decades. Organic anions tend to be secreted by the transport proteins OAT1, OAT3 and OATP4C1 on the basolateral side of tubular cells, and multidrug resistance protein (MRP) 2, MRP4, OATP1A2 and breast cancer resistance protein (BCRP) on the apical side. Organic cations are secreted by organic cation transporter (OCT) 2 on the basolateral side, and multidrug and toxic compound extrusion (MATE) proteins MATE1, MATE2/2-K, P-glycoprotein, organic cation and carnitine transporter (OCTN) 1 and OCTN2 on the apical side. Significant drug-drug interactions (DDIs) may affect any of these transporters, altering the clearance and, consequently, the efficacy and/or toxicity of substrate drugs. Interactions at the level of basolateral transporters typically decrease the clearance of the victim drug, causing higher systemic exposure. Interactions at the apical level can also lower drug clearance, but may be associated with higher renal toxicity, due to intracellular accumulation. Whereas the importance of glomerular filtration in drug disposition is largely appreciated among clinicians, DDIs involving renal transporters are less well recognized. This review summarizes current knowledge on the roles, quantitative importance and clinical relevance of these transporters in drug therapy. It proposes an approach based on substrate-inhibitor associations for predicting potential tubular-based DDIs and preventing their adverse consequences. We provide a comprehensive list of known drug interactions with renally-expressed transporters. While many of these interactions have limited clinical consequences, some involving high-risk drugs (e.g. methotrexate) definitely deserve the attention of prescribers.

Biases affecting injected doses of an experimental drug during clinical trials.

BACKGROUND: During clinical trials, researchers rarely question nominal doses specified on labels of investigational products, overlooking the potential for inaccuracies that may result when calculating pharmacokinetic and pharmacodynamic parameters. This study evaluated the disparity between nominal doses and the doses actually administered in two Phase I trials of a biosimilar drug. METHODS: In Trial A, 12 healthy volunteers received various doses of an interferon ß-1a biosimilar via either subcutaneous or intravenous injection, prepared by partially emptying 0.53 ml syringes supplied by the manufacturer. In Trial B, 12 volunteers received three different formulations of the drug via intravenous injection (biosimilar with and without albumin and a comparator), followed by multiple subcutaneous injections. In both trials, the dose administered was calculated as D = C × V - losses, where C is the drug concentration assessed using ELISA, V is the volume administered calculated using syringe weighing and losses are deduced from in-vitro experiments. Interferon binding to added albumin and infusion lines was evaluated using a (125)I-interferon tracer with gel-filtration chromatography. RESULTS: In Trial A, measured concentrations were close to the nominal strength indicated by the manufacturer (median bias: -6 %), whereas in Trial B they differed significantly for all three formulations (median biases: +67 %, +73 % and +31 % for the biosimilar with albumin, the biosimilar without albumin and the comparator, respectively). In Trial A, the doses actually administered showed large variability and biases, especially at the lowest doses. Indeed, actually injected volumes differed by as much as 74 % from theoretical volumes - a phenomenon mainly attributed to unnoticed fluid re-aspiration through the syringe needle. This was corrected in Trial B. Interferon was not significantly adsorbed on the infusion lines used for intravenous administration. Its binding to albumin was slow, reaching 50 % after a 16 h incubation. CONCLUSIONS: These examples illustrate the importance of assessing the actual doses administered in clinical trials, to ensure accuracy in the determination of clearance, distribution volume, bioavailability and dose-response relationships. TRIAL REGISTRATION: Clinicaltrials.gov NCT02515695 (Trial A) and NCT02517788 (Trial B). Registered on 24 July and 5 August 2015, respectively.

[Pharmacovigilance and teratovigilance 2008]. / Pharmacovigilance et teratovigilance 2008.

Various signals and alerts of pharmacovigilance were issued in 2008. Frequent neuropsychiatric adverse events are reported with varenicline and rimonabant and the marketing authorization of the latter has been suspended. Ezetimibe/simvastatin combination is suspected of causing cancer while it's clinical utility remains to be proved. Neuroleptics, typical and atypical, are associated with an increased risk of death in elderly with dementia. Safety is a concern with various biological drugs. Rituximab, natalizumab and efalizumab are involved in rare cases of progressive multifocal leukoencephalopathy with fatal issue. Screening of HLA-B*5701, a good predictor of hypersensitivity reaction to abacavir, is recommended prior to starting therapy. Mycophenolate turns out to be a human teratogen.

[Principles of therapeutic drug monitoring]. / Suivi thérapeutique des médicaments (I). Les principes.

Requesting a blood level measurement of a drug is part of the global approach known as "Therapeutic Drug Monitoring". Diverse situations require this monitoring approach, such as inadequate response to treatment or organ failure. Every drug however does not possess all the characteristics for a TDM program. The therapeutic range of a TDM drug has indeed to be narrow and its interindividual pharmacokinetic variability to be wide. As the development of new drugs is currently slowing down, the precise management of existing treatments certainly deserves progress, but needs however to be applied rationally, starting from a valid indication to blood sampling, and ending with a sound dosage adaptation decision.

[Pharmacogenetic testing: soon before every prescription?]. / Tests pharmacogénétiques: bientôt avant chaque prescription?

Genetic polymorphisms have currently been described in more than 200 systems affecting pharmacological responses (cytochromes P450, conjugation enzymes, transporters, receptors, effectors of response, protection mechanisms, determinants of immunity). Pharmacogenetic testing, i.e. the profiling of individual patients for such variations, is about to become largely available. Recent progress in the pharmacogenetics of tamoxifen, oral anticoagulants and anti-HIV agents is reviewed to discuss critically their potential impact on prescription and contribution/limits for improving rational and safe use of pharmaceuticals. Prospective controlled trials are required to evaluate large-scale pharmacogenetic testing in therapeutics. Ethical, social and psychological issues deserve particular attention.

Imatinib metabolite profiling in parallel to imatinib quantification in plasma of treated patients using liquid chromatography-mass spectrometry.

Besides affecting the systemic bioavailability of the parent drug, drug metabolizing enzymes (DMEs) may produce bioactive and/or toxic metabolites of clinical interest. We have investigated the capability to analyze simultaneously the parent drug and newly identified metabolites in patients' plasma by liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS). The anticancer drug, imatinib, was chosen as a model drug because it has opened a new area in cancer therapy and is given orally and chronically. In addition, resistance and rare but sometimes severe side effects have been reported with this therapy. The quantification of imatinib and the profiling of its metabolites in plasma were established following three steps: (1) set-up of a generic sample extraction and LC-MS/MS conditions, (2) metabolite identification by LC-MS/MS using either in vitro incubations performed with human liver microsomes (HLMs) or patient plasma samples, (3) the simultaneous determination of plasma levels of imatinib and 14 metabolites in the plasma samples of 38 patients. Partial or cross method validation has been done and revealed that precise determinations of metabolite levels can be performed whereas pure standards are not available. Preliminary results indicate that the disposition of imatinib and its metabolites is related to interindividual variables and that outlier metabolite profiles can be revealed. This article underscores that, in addition to usual therapeutic drug monitoring (TDM), LC-MS/MS methods can simultaneously record a complete drug metabolic profile enabling various correlation studies of clinical interest.

Misleading tacrolimus concentration value in blood taken from a catheter used for tacrolimus administration.

PURPOSE: A misleading blood tacrolimus concentration (BTC) value caused by the contamination of a central venous catheter previously used for tacrolimus administration is described. SUMMARY: A 59-year-old woman with severe chronic obstructive pulmonary disease successfully underwent double lung transplantation. In the intensive care unit, she received a continuous i.v. infusion of tacrolimus from days 1 to 5 after transplantation through the distal lumen of a polyurethane triple-lumen central venous catheter. The catheter lumen was flushed twice a day with 0.9% sodium chloride injection. The proximal lumen was used for blood sampling after being flushed; the first 10 mL of blood was discarded. BTCs determined in whole blood one, four, and five days after transplantation were within the therapeutic range of 5-15 ng/mL. On day five the patient was transferred to the thoracic surgery ward and was switched to oral tacrolimus 1.5 mg twice daily. The BTC on day 6 was unexpectedly high at 134.5 ng/mL. The patient's clinical status was normal, and no signs of tacrolimus toxicity were observed. On day 7, blood samples were drawn from a peripheral vein and simultaneously through the central venous catheter. Although the central venous catheter had not been exposed to tacrolimus during the preceding two days, it yielded blood with a BTC eight times higher than the BTC in blood from the peripheral vein (41.4 ng/mL versus 5.1 ng/mL). CONCLUSION: The collection of blood from a central venous catheter lumen that had been used for tacrolimus administration resulted in a BTC about eight times higher than what was measured in peripheral blood.

[Pharmacovigilance and teratovigilance]. / Pharmacovigilance et tératovigilance.

While 2006 did not record as many upsetting revelations of adverse drug reactions as the previous few years, still some data have been produced, which modulate the safety profile of drugs and deserve the attention of the prescribers: cardiovascular events under erythropoietins, macular oedema under rosiglitazone, vascular and renal complications of aprotinine, drawbacks of long-term linezolide administration, intracranial haemorrhage under tipranavir, anyphylaxis with pegaptanib, cardiototoxicity of imatinib, lymphomas with infliximab, bone pain and aches under bisphosphonates, cardiovascular events related to methylphenidate, congenital anomalies ascribed to paroxetine and lamotrigine, neonatal pulmonary hypertension related to serotonine reuptake inhibitors, infantile respiratory depression under promethazine.