Discover the most talked about and latest scientific content & concepts.

Concept: Grapefruit juice


The aim of this study was to investigate possible interactions between grapefruit juice and montelukast for up to 4 hours.

Concepts: Grapefruit spoon, Bioavailability, Grapefruit, Grapefruit juice


Tacrolimus is a widely used immunosuppressive drug in organ transplantation. The oral bioavailability of tacrolimus varies greatly between individuals and depends largely on the activity of both the cytochrome P450 3A (CYP3A) subfamily and P-glycoprotein (P-gp). The possible influence of single nucleotide polymorphisms (SNPs) of CYP3A subfamily and P-gp (MDR-1) in liver transplant recipients has recently been indicated as one of the most important variables affecting the pharmacokinetics of tacrolimus and the renal injury induced by tacrolimus.

Concepts: DNA, Single-nucleotide polymorphism, Grapefruit juice, Liver transplantation, CYP3A4, Pharmacokinetics, Cytochrome P450, Organ transplant


Extracts, subfractions, isolated anthocyanins and procyanidins, and two phenolic acids from aronia [Aronia melanocarpa] were investigated for their CYP3A4 inhibitory effects, using midazolam as the probe substrate and recombinant insect cell microsomes expressing CYP3A4 as the enzyme source. Procyanidin B5 was a considerably stronger CYP3A4 inhibitor in vitro than the isomeric procyanidin B2 and comparable to bergamottin, a known CYP3A4 inhibitor from grapefruit juice. The inhibitory activity of proanthocyanidin-containing fractions was correlated to the degree of polymerization. Among the anthocyanins, cyanidin 3-arabinoside showed stronger CYP3A4 inhibition than cyanidin 3-galactoside and cyanidin 3-glucoside. Thus, the ability to inhibit CYP3A4 in vitro seems to be influenced by the sugar unit linked to the anthocyanidin.

Concepts: Grapefruit juice, Enzyme inhibitor, B type proanthocyanidin, Grapefruit, Bergamottin, Proanthocyanidins, CYP3A4, Cytochrome P450


Statins and dietary modifications are the cornerstone of hypercholesterolemia management. Although it is well known that possible adverse effect of statins can occur due to drug-drug interactions, food-drug interactions are a commonly overlooked aspect. In particular, flavonoids could interfere with statins' bioavailability through different mechanisms, such as competition with cytochrome P450 (CYP) enzymes, esterases, uridine diphosphate glucuronosyltransferases and transporters (P-glycoprotein, multi-drug resistance-associated proteins, organic anion transporting polypeptides, breast cancer-resistance protein and monocarboxylate transporters). Transporters are characterized by low substrate specificity and flavonoid- rich foods could interfere with the bioavailability of all statins at this level. On the other hand, in addition to being substrates of drug metabolism/ transport systems, flavonoids are also able to modulate gene expression of enzymes and transporters. Therefore, long-term transcriptional induction may increase the clearance of statins, despite flavonoids act as competitive inhibitors after bolus consumption. In humans, major interactions were observed between grapefruit juice and statins that are substrates of P-glycoprotein/CYP3A, but also other fruit juices affected the bioavailability of statins that are not metabolised by CYP. Even if flavonoids could play a role in the prevention of hypercholesterolemia, the question whether a helpful or dangerous association between flavonoid-rich foods and statins, due to the interactions between flavonoid-rich foods and statins and the potential associated adverse effects of statins, remains unanswered. Therefore, the anamnesis of patients must include detailed information about their eating habits and the present review suggests monitoring and reporting any possible case of interaction between a prescribed statin and food.

Concepts: Grapefruit juice, Metabolism, Nutrition, Enzyme substrate, Pharmacology, Protein, Enzyme, Cytochrome P450


Aroma extract dilution analyses of the aromas of peels and juices of white and pink grapefruits revealed that rotundone that was responsible for woody odor was detected at higher flavor dilution factors of 256 to 1024. In both juices, rotundone was detected at the highest FD factor of 1024. Rotundone in the grapefruits was quantitated by a stable isotope dilution assay with a newly synthesized deuterium-labeled internal standard, rotundone-d2,3: its levels were 2180 and 1920 ng/kg in white and pink grapefruit peels, and 29.6 and 49.8 ng/kg in white and pink grapefruit juices. On the basis of these results, sensory analysis was performed to assess the effects of rotundone on a white grapefruit juice aroma reconstitute. This sensory analysis revealed that rotundone does not only impart a woody note or affect one of the existing attributes, but also increases various attributes, and thus confirmed that rotundone is indispensable for the aroma of grapefruit juice.

Concepts: Tangelo, Grapefruit spoon, Citrus, Grapefruit juice, Grapefruit


Cytochrome P450 (CYP) enzymes, including CYP2C19 and CYP3A4, participate in the bioactivation of clopidogrel. Grapefruit juice constituents potently inactivate intestinal CYP3A4, and have been shown to inhibit CYP2C19 as well. In a randomized crossover study, 14 healthy volunteers ingested 200 ml of grapefruit juice or water thrice daily for three days. On day three, they ingested a single 600-mg dose of clopidogrel. Grapefruit juice reduced clopidogrel active metabolite Cmax to 13% (range 11 - 17%, P < 0.001) and AUC0-3 h to 14% (range 12 - 17%, P < 0.001) of control, but had no significant effect on parent clopidogrel. Moreover, grapefruit juice markedly decreased the platelet inhibitory effect of clopidogrel, as assessed with the VerifyNow® P2Y12 test in two of the participants. In conclusion, concomitant use of grapefruit juice may impair the efficacy of clopidogrel. Therefore, the use of grapefruit juice is best avoided during clopidogrel therapy.Clinical Pharmacology & Therapeutics (2013); accepted article preview online 25 September 2013 doi:10.1038/clpt.2013.192.

Concepts: Clopidogrel, Enzyme inhibitor, Grapefruit juice, Pharmacology, CYP2C19, CYP3A4, Metabolism, Cytochrome P450


Tuberculosis (TB) remains a deadly disease and infects one-third of the world’s population. Given the low success rates encountered in clinical development, there is an urgent need to identify structurally novel antimicrobials for tuberculosis. The present report details the anti-mycobacterial activities, structure-activity relationships (SARs) and mechanism of action of amphiphilic xanthone derivatives. The xanthones exhibited potent MIC, rapid time-kill and no cross-resistance with the current anti-TB drugs. Evidence is presented that these compounds disrupted the inner membrane and led to ATP depletion. Amphiphilic xanthone derivatives exhibited superior metabolic stability, low cytotoxicity and low activity against the common cytochrome P450. Compound 5 was selected for an in vivo pharmacokinetic study. Its bioavailability at an oral dose of 2 mg/kg was 15%. The xanthones thuse provide valuable insight for the development of a new class of membrane targeting antimycobacterial agents that may assist in overcoming the limitations of the current TB medications.

Concepts: Grapefruit juice, Steroid, Metabolism, Chemical compound, Pharmacokinetics, Cytochrome P450, Pharmacology


Midazolam is the preferred probe to phenotype cytochrome P450 (CYP) 3A activity. This study evaluated a single-concentration, midazolam limited sampling strategy utilizing a population pharmacokinetic (PK) approach to estimate area under the curve, and thus CYP3A activity. Midazolam concentrations from adults during CYP3A constitutive conditions were obtained from previous studies after single, oral or intravenous administration. Population PK modeling was conducted by nonlinear mixed-effects modeling. Potential covariates of clearance, volume of distribution, and bioavailability were evaluated. A limited sampling model at 1, 2, 4, or 6 hours was selected and fitted with post hoc estimation with the final population PK model. Preset criterion for the limited sampling model selection was a coefficient of determination ≥0.9. Bias and precision were also evaluated. The studies provided 2122 observations from 152 healthy adults. Midazolam concentrations were adequately described by a two-compartment model with first order absorption. Age and sex were significant covariates of central volume (V2 ) and were retained in the final model. An estimate (interindividual variability) of midazolam clearance was 32.5 L/hr (52.9%), covariate of central volume was 67 L (39.1%), and oral bioavailability was 0.33 (45.5%). The final population parameter estimates were within the 95% confidence intervals and were similar to the median bootstrap estimates. Upon comparison to the population PK model, the 4-hour limited sampling model estimated area under the curve had an acceptable coefficient of determination and acceptable bias and precision limits. A 4-hour, but not the 1-, 2-, and 6-hour, single concentration accurately estimated midazolam area under the curve during constitutive CYP3A conditions in healthy adults.

Concepts: Mathematics, Bioavailability, Estimator, Estimation, Grapefruit juice, Statistics, Cytochrome P450, Pharmacokinetics


Midazolam has been successfully used for sedation, which the tablets, injections and oral solutions were available in market. However, the oral bioavailability of midazolam is less due to the first effect, while injection formulation has a low patient compliance. The purpose of this study was to obtain midazolam rectal gel to meet the production and market requirements. We evaluated the in vitro release behavior of midazolam powder, a physical mixture of midazolam and HPMC, and midazolam gel. The results showed that the midazolam gel has superior release degree compared to the other. Correspondingly, midazolam gel produced relevant plasma concentrations result in the rats. At the same dose (1 mg/kg), the Cmaxand AUC (0-t) of midazolam after administration of the midazolam rectal gel were 8-10 times higher than that of the oral solution. The midazolam rectal gel was evaluated for physico-chemical tests including pH, viscosity, drug content at 40°C /75%RH (relative humidity) for 180 days (6 months). It provides information about the shelf lives of medicine, as well as the conditions for their storage. Rectum irritation test demonstrated that frequent application of midazolam rectal gel did not induce rectal mucosal damage. In conclusion, midazolam rectal gel was a potential new dosage form, which could alleviate the feeling of alien, discomfort and refusal during application of the patients. It was likely to be a more convenient and effective sedative medicine form specifically for infants and children.

Concepts: Dosage forms, Route of administration, Pharmacology, Grapefruit juice, Sedative, In vivo, Relative humidity, In vitro


Dependence on antipsycotic drugs like aripriprazole (ARI) is increasing at alarming rate, hence, this study was undertaken to support the hypothesis that supplementation of Citrus paradisi (Grapefruit) juice having high concentration of polyphenols might potentiate and synergize the therapeutic effect of ARI, by increasing its bioavailability and inherent antioxidant potential. These benefits together might decrease the daily dosage of the ARI and thus alleviate the possible side effects of drug.

Concepts: Citrus, Synergy, Vitamin C, Oxidative stress, Hydrogen peroxide, Grapefruit juice, Pharmacology, Grapefruit