The warfarin-cranberry juice interaction revisited: A systematic in vitro-in vivo evaluation

Assessing the knowledge of medical undergraduates on oral anticoagulation therapy

Objective

Oral anticoagulant drugs, such as warfarin, are widely used for preventing and treating vascular and thromboembolic disease in patients with chronic atrial fibrillation, venous thrombosis, and coronary heart disease. As oral anticoagulant therapy has such a narrow therapeutic range, complications in administering these drugs can prove to have a detrimental effect on patients such as life-threatening bleeding might occur. It is therefore necessary to have an adequate knowledge about its actions and its interactions with other dietary factors or any other medication involved. This study was therefore formulated in order to evaluate the knowledge as well as to impart proper awareness to the medical undergraduate students about oral anticoagulation therapy such as to prevent any untoward situation that may arise from the process.

Methods

A cross-sectional descriptive study was used to assess the knowledge on oral anticoagulant therapy among the medical undergraduates of a tertiary care hospital. A pre-validated structured questionnaire consisting of 28 questions was adopted, and a separate questionnaire was used for each student. Timing of answering the questionnaire was set at 30 minutes. Scores were evaluated such as a correct answer was given a score of one and wrong answer awarded as zero. Adequate knowledge sore was set above 70% and inadequate knowledge at less than 40%.

Results

The response rate was found out to be 67.33% with gender distribution observed to be 71% females and 29% males. From the answers evaluated, overall average score of 67.3 ± 15.9 was obtained indicating that most of the respondents have adequate knowledge about the different mechanism, drug-drug interactions, drug-food interactions, and side effects of anticoagulant therapy, and 100% of the students are well aware about the complications and procedures involved to dissipate information about warfarin therapy.

Conclusions

Adequate exposure of students to clinical cases will further help them to focus on the importance of anticoagulation and strengthening their knowledge regarding anticoagulant drug therapy. This will influence the process of physician-patient communication for improving anticoagulation outcome.

Physiologically based pharmacokinetic modeling framework for quantitative prediction of an herb-drug interaction

Herb-drug interaction predictions remain challenging. Physiologically based pharmacokinetic (PBPK) modeling was used to improve prediction accuracy of potential herb-drug interactions using the semipurified milk thistle preparation, silibinin, as an exemplar herbal product. Interactions between silibinin constituents and the probe substrates warfarin (CYP2C9) and midazolam (CYP3A) were simulated. A low silibinin dose (160 mg/day × 14 days) was predicted to increase midazolam area under the curve (AUC) by 1%, which was corroborated with external data; a higher dose (1,650 mg/day × 7 days) was predicted to increase midazolam and (S)-warfarin AUC by 5% and 4%, respectively. A proof-of-concept clinical study confirmed minimal interaction between high-dose silibinin and both midazolam and (S)-warfarin (9 and 13% increase in AUC, respectively). Unexpectedly, (R)-warfarin AUC decreased (by 15%), but this is unlikely to be clinically important. Application of this PBPK modeling framework to other herb-drug interactions could facilitate development of guidelines for quantitative prediction of clinically relevant interactions.CPT Pharmacometrics Syst. Pharmacol. (2014) 3, e107; doi:10.1038/psp.2013.69; advance online publication 26 March 2014.

Semisynthesis, cytotoxicity, antiviral activity, and drug interaction liability of 7-O-methylated analogues of flavonolignans from milk thistle

Silymarin, an extract of the seeds of milk thistle (Silybum marianum), is used as an herbal remedy, particularly for hepatoprotection. The main chemical constituents in silymarin are seven flavonolignans. Recent studies explored the non-selective methylation of one flavonolignan, silybin B, and then tested those analogues for cytotoxicity and inhibition of both cytochrome P450 (CYP) 2C9 activity in human liver microsomes and hepatitis C virus infection in a human hepatoma (Huh7.5.1) cell line. In general, enhanced bioactivity was observed with the analogues. To further probe the biological consequences of methylation of the seven major flavonolignans, a series of 7-O-methylflavonolignans were generated. Optimization of the reaction conditions permitted selective methylation at the phenol in the 7-position in the presence of each metabolite's 4-5 other phenolic and/or alcoholic positions without the use of protecting groups. These 7-O-methylated analogues, in parallel with the corresponding parent compounds, were evaluated for cytotoxicity against Huh7.5.1 cells; in all cases the monomethylated analogues were more cytotoxic than the parent compounds. Moreover, parent compounds that were relatively non-toxic and inactive or weak inhibitors of hepatitis C virus infection had enhanced cytotoxicity and anti-HCV activity upon 7-O-methylation. Also, the compounds were tested for inhibition of major drug metabolizing enzymes (CYP2C9, CYP3A4/5, UDP-glucuronsyltransferases) in pooled human liver or intestinal microsomes. Methylation of flavonolignans differentially modified inhibitory potency, with compounds demonstrating both increased and decreased potency depending upon the compound tested and the enzyme system investigated. In total, these data indicated that monomethylation modulates the cytotoxic, antiviral, and drug interaction potential of silymarin flavonolignans.

Pomegranate juice and pomegranate extract do not impair oral clearance of flurbiprofen in human volunteers: divergence from in vitro results

Nutrient interactions with prescription drugs are a topic of ongoing basic and clinical research. Pomegranate juice and a 1-g capsule containing pomegranate extract were evaluated in vitro and in vivo as inhibitors of cytochrome P450 2C9 (CYP2C9), with flurbiprofen serving as the index substrate. Fluconazole was the positive control inhibitor. The in vitro 50% inhibitory concentration (IC(50)) values for pomegranate juice and extract were below 1% (vol/vol), with no evidence of mechanism-based (irreversible) inhibition. In clinical studies, flurbiprofen pharmacokinetics were unchanged by pomegranate juice or extract as compared to a low-polyphenol placebo control beverage. However, fluconazole significantly reduced the oral clearance of flurbiprofen. Despite inhibition of CYP2C9 in vitro, pomegranate juice and extract had no effect on CYP2C9 activity in human subjects, and can be consumed by patients taking CYP2C9 substrate drugs with negligible risk of a pharmacokinetic interaction.

Impact of organic solvents on cytochrome P450 probe reactions: filling the gap with (S)-Warfarin and midazolam hydroxylation

(S)-Warfarin 7-hydroxylation and midazolam 1'-hydroxylation are among the preferred probe substrate reactions for CYP2C9 and CYP3A4/5, respectively. The impact of solvents on enzyme activity, kinetic parameters, and predicted in vivo hepatic clearance (Cl(H)) associated with each reaction has not been evaluated. The effects of increasing concentrations [0.1-2% (v/v)] of six organic solvents (acetonitrile, methanol, ethanol, dimethyl sulfoxide, acetone, isopropanol) were first tested on each reaction using human liver microsomes (HLMs), human intestinal microsomes (midazolam 1'-hydroxylation only), and recombinant enzymes. Across enzyme sources, relative to water, acetonitrile and methanol had the least inhibitory effect on (S)-warfarin 7-hydroxylation (0-58 and 9-96%, respectively); acetonitrile, methanol, and ethanol had the least inhibitory effect on midazolam 1'-hydroxylation (0-29, 0-22, and 0-20%, respectively). Using HLMs, both acetonitrile and methanol (0.1-2%) decreased the V(max) (32-60 and 24-65%, respectively) whereas methanol (2%) increased the K(m) (100%) of (S)-warfarin-hydroxylation. (S)-Warfarin Cl(H) was underpredicted by 21-65% (acetonitrile) and 13-84% (methanol). Acetonitrile, methanol, and ethanol had minimal to modest impact on both the kinetics of midazolam 1'-hydroxylation (10-24%) and predicted midazolam Cl(H) (2-20%). In conclusion, either acetonitrile or methanol at ≤0.1% is recommended as the primary organic solvent for the (S)-warfarin 7-hydroxylation reaction; acetonitrile is preferred if higher solvent concentrations are required. Acetonitrile, methanol, and ethanol at ≤2% are recommended as primary organic solvents for the midazolam 1'-hydroxylation reaction. This information should facilitate optimization of experimental conditions and improve the interpretation and accuracy of in vitro-in vivo predictions involving these two preferred cytochrome P450 probe substrate reactions.

Cranberries and lower urinary tract infection prevention

Lower urinary tract infections are very common diseases. Recurrent urinary tract infections remain challenging to treat because the main treatment option is long-term antibiotic prophylaxis; however, this poses a risk for the emergence of bacterial resistance. Some options to avoid this risk are available, including the use of cranberry products. This article reviews the key methods in using cranberries as a preventive measure for lower urinary tract infections, including in vitro studies and clinical trials.