P-Glycoprotein Limits Oral Availability, Brain Penetration, and Toxicity of an Anionic Drug, the Antibiotic Salinomycin▿

Salinomycin is a polyether organic anion that is extensively used as a coccidiostatic antibiotic in poultry and commonly fed to ruminant animals to improve feed efficiency. However, salinomycin also causes severe toxicity when accidentally fed to animals in high doses. In addition, humans are highly sensitive to salinomycin and severe toxicity has been reported. Multidrug efflux transporters like P-glycoprotein (P-gp), BCRP, and MRP2 are highly expressed in the intestine and can restrict the oral uptake and tissue penetration of xenobiotics. The purpose of this study was to investigate whether the anionic drug salinomycin is a substrate for one or more of these efflux pumps. Salinomycin was actively transported by human MDR1 P-gp expressed in polarized MDCK-II monolayers but not by the known organic anion transporters human MRP2 and murine Bcrp1. Using P-gp-deficient mice, we found a marked increase in plasma salinomycin concentrations after oral administration and decreased plasma clearance after intravenous administration. Furthermore, absence of P-gp resulted in significantly increased brain penetration. P-gp-deficient mice also displayed clearly increased susceptibility to salinomycin toxicity. Thus far, P-gp was thought to affect mainly hydrophobic, positively charged or neutral drugs in vivo. Our data show that P-gp can also be a major determinant of the pharmacokinetic behavior and toxicity of an organic anionic drug. Variation in P-gp activity might thus directly affect the effective exposure to salinomycin and possibly to other anionic drugs and toxin substrates. Individuals with reduced or absent P-gp activity could therefore be more susceptible to salinomycin toxicity

Transport of diclofenac by breast cancer resistance protein (ABCG2) and stimulation of multidrug resistance protein 2 (ABCC2)-mediated drug transport by diclofenac and benzbromarone,” Drug Metabolism and Disposition

ABSTRACT: Diclofenac is an important analgesic and anti-inflammatory drug, widely used for treatment of postoperative pain, rheumatoid arthritis, and chronic pain associated with cancer. Consequently, diclofenac is often used in combination regimens and undesirable drug-drug interactions may occur. Because many drug-drug interactions may occur at the level of drug transporting proteins, we studied interactions of diclofenac with apical ATP-binding cassette (ABC) multidrug efflux transporters. Using Madin-Darby canine kidney (MDCK)-II cells transfected with human P-glycoprotein (P-gp; MDR1/ABCB1), multidrug resistance protein 2 (MRP2/ABCC2), and breast cancer resistance protein (BCRP/ABCG2) and murine Bcrp1, we found that diclofenac was efficiently transported by murine Bcrp1 and moderately by human BCRP but not by P-gp or MRP2. Furthermore, in Sf9-BCRP membrane vesicles diclofenac inhibited transport of methotrexate in a concentration-dependent manner. We next used MDCK-II-MRP2 cells to study interactions of diclofenac with MRP2-mediated drug transport. Diclofenac stimulated paclitaxel, docetaxel, and saquinavir transport at only 50 M. We further found that the uricosuric drug benzbromarone stimulated MRP2 at an even lower concentration, having maximal stimulatory activity at only 2 M. Diclofenac and benzbromarone stimulated MRP2-mediated transport of amphipathic lipophilic drugs at 10-and 250-fold lower concentrations, respectively, than reported for other MRP2 stimulators. Because these concentrations are readily achieved in patients, adverse drug-drug interactions may occur, for example, during cancer therapy, in which drug concentrations are often critical and stimulation of elimination via MRP2 may result in suboptimal chemotherapeutic drug concentrations. Moreover, stimulation of MRP2 activity in tumors may lead to increased efflux of chemotherapeutic drugs and thereby drug resistance. Diclofenac is a nonsteroidal anti-inflammatory drug (NSAID) that exhibits potent analgesic and anti-inflammatory properties and is extensively used to treat postoperative pain, rheumatoid arthritis, osteoarthritis, and acute gouty arthritis Because it is recognized more and more that many interactions of drugs occur at the level of drug-transporting proteins, we investigated whether diclofenac is a substrate of one of the apical ABC transporters, using MDCK-II cells transfected with human P-gp, MRP2, BCRP, or murine Bcrp1 cDNA. We further used the MDCK-II cells transduced with human and mouse MRP2/Mrp2 to examine whether diclofenac could modulate MRP2-mediated transport of taxane anticancer drugs. To date, several compounds, e.g., probenecid, sulfinpyrazone, and sulfanitran, have been shown to stimulate the MRP2-mediated transport of lipophilic amphipathic drugs (Huisman et al., Article, publication date, and citation information can be found at http://dmd.aspetjournals.org. doi:10.1124/dmd.108.023200. ABBREVIATIONS: NSAID, nonsteroidal anti-inflammatory drug; MTX, methotrexate; ABC, ATP-binding cassette; MRP, multidrug resistance protein; MDCK, Madin-Darby canine kidney; P-gp, P-glycoprotein; BCRP, breast cancer resistance protein; GF120918, N-(4-[2-(1,2,3,4-tetrahydro-6,7-dimethoxy-2-isoquinolinyl)ethyl]-phenyl)-9,10-dihydro-5-methoxy-9-oxo-4-acridine carboxamide; Ko143, 3-(6-isobutyl-9-methoxy-1,4-dioxo-1,2,3,4,6,7,12,12␣-octahydropyrazino[1Ј,2Ј:1,6]pryrido[3,4-b]indol-3-yl)-propionic acid tert-butyl ester; E 2 17␤G, estradiol-17␤-glucuronide

Severe lactic acidosis in a diabetic patient after ethanol abuse and floor cleaner intake

An intoxication with drugs, ethanol or cleaning solvents may cause a complex clinical scenario if multiple agents have been ingested simultaneously. The situation can become even more complex in patients with (multiple) co-morbidities. A 59-year-old man with type 2 diabetes mellitus (without treatment two weeks before the intoxication) intentionally ingested a substantial amount of ethanol along with ~750 mL of laminate floor cleaner containing citric acid. The patient was admitted with severe metabolic acidosis (both ketoacidosis and lactic acidosis, with serum lactate levels of 22 mM). He was treated with sodium bicarbonate, insulin and thiamine after which he recovered within two days. Diabetic ketoacidosis and lactic acidosis aggravated due to ethanol intoxication, thiamine deficiency and citrate. The high lactate levels were explained by excessive lactate formation caused by the combination of untreated diabetes mellitus, thiamine deficiency and ethanol abuse. Metabolic acidosis in diabetes is multi-factorial, and the clinical situation may be further complicated, when ingestion of ethanol and toxic agents are involved. Here, we reported a patient in whom diabetic ketoacidosis was accompanied by severe lactic acidosis as a result of citric acid and mainly ethanol ingestion and a possible thiamine deficiency. In the presence of lactic acidosis in diabetic ketoacidosis, physicians need to consider thiamine deficiency and ingestion of ethanol or other toxins

Toxicokinetics of a dipyridamole (Persantin) intoxication: Case report

We report a case of a 51-year-old woman who was admitted to the hospital after ingestion of large doses of dipyridamole (12 g), temazepam (1 g) and oxazepam (0.2 g) with suicidal intent. The highest dipyridamole concentration that was measured in serum was 9.2 mg/L, which was paralleled by impaired platelet activation. For temazepam and oxazepam, peak serum concentrations were 8.5 and 1.3 mg/L, respectively. The patient was treated with activated charcoal, magnesium sulfate and aminophylline and could be discharged in good physical condition within 17 hours. This is the first report that provides toxicokinetic data and a corresponding pharmacodynamic effect after an intoxication with dipyridamol