Severity of coeliac disease and clinical management study when using a CYP3A4 metabolised medication: a phase I pharmacokinetic study

OBJECTIVE

Severity of coeliac disease depends in part on the extent of small intestinal mucosa injury. Patients with the most abnormal pathology have loss of duodenal villi CYP3A4, a drug-metabolising enzyme that inactivates many drugs. These patients are hypothesised to have greater systemic concentrations of felodipine, a drug which normally has low oral bioavailability secondary to intestinal CYP3A4-mediated metabolism. It serves as a representative for a class containing many medications.

DESIGN

A phase I, open-label, single-dose, pharmacokinetic study.

SETTING

London, Ontario, Canada.

PARTICIPANTS

Patients with coeliac disease (n=47) with positive serology and healthy individuals (n=68).

MAIN OUTCOME MEASURES

Patients with coeliac disease-upper gastrointestinal endoscopy and oral felodipine pharmacokinetics study within a 3-week period. Healthy individuals-oral felodipine pharmacokinetics study with water and grapefruit juice.

RESULTS

Coeliac stratification categories: Group A (n=15, normal), B+C (n=16, intraepithelial lymphocytosis with/without mild villous blunting) and D (n=16, moderate/severe villous blunting). Groups A, B+C and D had linear trends of increasing felodipine AUC_0-8; mean±SEM, 14.4±2.1, 17.6±2.8, 25.7±5.0; p<0.05) and Cmax (3.5±0.5, 4.0±0.6, 6.4±1.1; p<0.02), respectively. Healthy subjects receiving water had lower felodipine AUC_0-8 (11.9±0.9 vs 26.9±0.9, p=0.0001) and Cmax (2.9±0.2 vs 7.7±0.2, p=0.0001) relative to those receiving grapefruit juice.

CONCLUSIONS

Increased felodipine concentrations in patients with coeliac disease were most probably secondary to decreased small intestinal CYP3A4 expression. Patients with severe coeliac disease and healthy individuals with grapefruit juice had equivalently enhanced effect. Thus, patients with severe coeliac disease would probably experience similarly altered drug response, including overdose toxicity, from many important medications known to be metabolised by CYP3A4. Patients with coeliac disease with severe disease should be considered for other clinical drug management, particularly when there is the potential for serious drug toxicity.

Low-Renin Hypertension

Low-renin hypertension affects 30% of hypertensive patients. Primary hyperaldosteronism presents with low renin and aldosterone excess. Low-renin, low-aldosterone hypertension represents a wide spectrum of disorders that includes essential low-renin hypertension, hereditary forms of hypertension, and hypertension secondary to endogenous or exogenous factors. This review addresses the different conditions that present with low-renin hypertension, discussing an appropriate diagnostic approach and highlighting the genetic subtypes within familial forms.

Pharmacokinetic parameters of ifosfamide in mouse pre-administered with grapefruit juice or naringin

Grapefruit juice (GFJ) and naringin when consumed previously or together with medications may alter their bioavailavility and consequently the clinical effect. Ifosfamide (IF) is an antitumoral agent prescribed against various types of cancer. Nevertheless, there is no information regarding its interaction with the ingestion of GFJ or naringin. The aims of the present report were validating a method for the quantitation of IF in the plasma of mouse, and determine if mice pretreated with GFJ or naringin may modify the IF pharmacokinetics. Our HPLC results to quantify IF showed adequate intra and inter-day precision (RSD < 15%) and accuracy (RE < 15%) indicating reliability. Also, the administration of GFJ or naringin increased C_max of IF 22.9% and 17.8%, respectively, and decreased T_max of IF 19.2 and 53.8%, respectively. The concentration of IF was higher when GFJ (71.35 ± 3.5 µg/mL) was administered with respect to that obtained in the combination naringin with IF (64.12 ± µg/mL); however, the time required to reach such concentration was significantly lower when naringin was administered (p < 0.5). We concluded that pre-administering GFJ and naringin to mice increased the T_max and decreased the C_max of IF.

Efficacy and Safety of Grapefruit Juice Intake Accompanying Tacrolimus Treatment in Connective Tissue Disease Patients

Objective It is well known that grapefruit juice (GFJ) elevates the blood tacrolimus (TAC) concentration. We investigated the efficacy and safety of GFJ intake with TAC in cases of connective tissue diseases in which the TAC blood concentration was insufficiently high for clinical improvement, even when 3 mg/day or more of TAC was administered. Methods Seven patients took 200 mL of GFJ every day. The trough levels of the TAC blood concentration were measured before and after GFJ intake and the clinical courses were monitored thereafter. Results First, we surveyed the blood TAC trough levels of 30 recent patients who took 3 mg/day of TAC, and found that 21 patients (70%) did not achieve the minimum target TAC concentration (>5 ng/mL). Seven patients took GFJ due to a lack of efficacy and a relatively low TAC blood concentration. GFJ increased the TAC level from 4.3±2.4 ng/mL to 13.8±6.9 ng/mL (average increase: 3.3-fold). GFJ was also effective in achieving a clinical improvement in most cases without causing any severe adverse events, and it helped to decrease the dosages of glucocorticoid and TAC. In some cases, the blood TAC concentration fluctuated for no apparent reason. Conclusion GFJ intake was effective for the elevation of TAC concentration by approximately three fold and clinical improvement, but special care is required for monitoring its influence on concomitantly used drugs as well as TAC concentration. The addition of GFJ to TAC treatment could be an efficacious treatment option, when the plasma TAC concentration does not reach the minimal target concentration.

Grapefruit-Drug Interactions: Can Interactions With Drugs Be Avoided?

Grapefruit is rich in flavonoids, which have been demonstrated to have a preventive influence on many chronic diseases, such as cancer and cardiovascular disease. However, since the early 1990s, the potential health benefits of grapefruit have been overshadowed by the possible risk of interactions between drugs and grapefruit and grapefruit juice. Several drugs interacting with grapefruit are known in different drug classes, such as HMG-CoA reductase inhibitors, calcium antagonists, and immunosuppressives. Currently known mechanisms of interaction include the inhibition of cytochrome P450 as a major mechanism, but potential interactions with P-glycoprotein and organic anion transporters have also been reported. This review is designed to provide a comprehensive summary of underlying mechanisms of interaction and human clinical trials performed in the area of grapefruit drug interactions and to point out possible replacements for drugs with a high potential for interactions.

Grapefruit juice--drug interactions: importance for pharmacotherapy

In spite of known health benefits of grapefruit juice, its consumption in combination with drugs requires caution. The drugs most susceptible to pharmacokinetic interactions with clinical significance are those with narrow therapeutic index and low bioavailability due to important first-pass metabolism. Most vulnerable populations are elderly, cirrhotics, subjects with genetic polymorphisms and individuals taking other CYP3A4 inhibitors. The major drug classes that have been reported to present interactions with grapefruit juice are antiallergics, antibiotics, antimalaria drugs, anxiolytics, calcium channel blockers, HIV protease inhibitors, HMG-CoA reductase inhibitors; the degree of pharmacokinetic interaction varies among the compounds of the same class.

[Fruit and berries--interactions with drugs]

Diet is one of many factors that could alter the pharmacokinetics of drugs. Several fruits and berries have recently been shown to contain agents that affect drug-metabolizing enzymes. Grapefruit is the most well-known example, but also Sevillian orange, pomelo and star fruit contain agents that inhibit cytochrome P450 3A4 (CYP3A4), which is the most important enzyme in drug metabolism. The present article reviews published information on potential interactions between drugs and fruits/berries, with main focus on inhibition and induction of metabolizing enzymes.

Clinical relevance of the small intestine as an organ of drug elimination: drug-fruit juice interactions

Most drugs are taken orally. For those intended to act systemically, a significant fraction of the dose can be eliminated during its first passage through a sequence of organs before entry into the general circulation. For some drugs, the degree of first-pass elimination can be large enough such that oral bioavailability is significantly reduced, with the consequent potential for a reduced clinical response. Of these first-pass eliminating organs, the small intestine and liver are the most commonly implicated, in part because they express the highest levels of drug-metabolizing enzymes. For several drugs whose major route of elimination occurs via CYP3A-mediated metabolism, the extent of first-pass metabolism in the small intestine can rival that in the liver. As such, alterations in enteric CYP3A activity alone can significantly influence oral bioavailability. The most extensively studied xenobiotic shown to inhibit only enteric CYP3A is grapefruit juice, the consequences of which can be clinically significant. Although much information has been gained regarding the grapefruit juice effect, progress in the relatively understudied area of drug-diet interactions continues to be sluggish and reactive. In stark contrast, the potential for drug-drug interactions involving any new therapeutic agent must be evaluated, prospectively, before market introduction. To prospectively elucidate mechanisms underlying drug-diet interactions, a multidisciplinary, translational research approach is required, which capitalizes on the collective expertise of drug metabolism scientists and natural products chemists. Such an approach would allow proper between-study comparisons, and ultimately provide conclusive information as to whether specific dietary substances can be taken safely with certain medications.

Intestinal Drug Transporter Expression and the Impact of Grapefruit Juice in Humans

The goals of this study were to assess the extent of human intestinal drug transporter expression, determine the subcellular localization of the drug uptake transporter OATP1A2, and then to assess the effect of grapefruit juice consumption on OATP1A2 expression relative to cytochrome P450 3A4 and MDR1. Expression of drug uptake and efflux transporters was assessed using human duodenal biopsy samples. Fexofenadine uptake by different transporters was measured in a transporter-transfected cell line. We investigated the influence of grapefruit juice on pharmacokinetics of orally administered fexofenadine. The effect of grapefruit juice on the expression of intestinal transporters was determined using real-time polymerase chain reaction and Western blot analysis. In the duodenum of healthy volunteers, an array of CYP enzymes as well as uptake and efflux transporters was expressed. Importantly, uptake transporters thought to be liver-specific, such as OATP1B1 and 1B3, as well as OATP2B1 and 1A2 were expressed in the intestine. However, among OATP transporters, only OATP1A2 was capable of fexofenadine uptake when assessed in vitro. OATP1A2 colocalized with MDR1 to the brush border domain of enterocytes. Consumption of grapefruit juice concomitantly or 2 h before fexofenadine administration was associated with reduced oral fexofenadine plasma exposure, whereas intestinal expression of either OATP1A2 or MDR1 remained unaffected. In conclusion, an array of drug uptake and efflux transporters are expressed in the human intestine. OATP1A2 is likely the key intestinal uptake transporter for fexofenadine absorption whose inhibition results in the grapefruit juice effect. Although short-term grapefruit juice ingestion was associated with reduced fexofenadine availability, OATP1A2 or MDR1 expression was unaffected.

Grapefruit juice and drug interactions. Exploring mechanisms of this interaction and potential toxicity for certain drugs

Concomitant administration of grapefruit juice can increase the plasma concentration of numerous drugs in humans and decrease the concentration of a few others. Such elevations of drug plasma concentrations have, on occasion, resulted in adverse clinical effects. Increased concentrations are primarily mediated by chemicals in grapefruit juice, which inhibit the CYP 3A4 drug-metabolizing enzyme in the small intestines. This inhibition decreases the first-pass metabolism of drugs using the CYP 3A4 intestinal system and increases the bioavailability and maximal plasma drug concentrations (Cmax) of the CYP 3A4 substrates. The effect of grapefruit juice on drug metabolism is most pronounced in drugs with a high first-pass metabolism (eg, felodipine, amiodarone), in which it inhibits the first-pass metabolism of the CYP 3A4 substrates leading to an increase in Cmax and area under the concentration time curve (AUC). The use of grapefruit juice with a few specific drugs (eg, fexofenadine, digoxin) may lower plasma drug concentrations by inhibiting drug absorption catalyzed by the organic anion transporting polypeptide (OATP).

Interaction of grapefruit juice and calcium channel blockers

Drug-drug interactions are commonly recognized occurrences in the hypertensive population. Drug-nutrient interactions, however, are less well appreciated. The grapefruit juice-calcium channel blocker interaction is one that has been known since 1989. The basis for this interaction has been diligently explored and appears to relate to both flavanoid and nonflavanoid components of grapefruit juice interfering with enterocyte CYP3A4 activity. In the process, presystemic clearance of susceptible drugs decreases and bioavailability increases. A number of calcium channel blockers are prone to this interaction, with the most prominent interaction occurring with felodipine. The calcium channel blocker and grapefruit juice interaction should be incorporated into the knowledge base of rational therapeutics for the prescribing physician.

The statins: drug interactions of significance to the dental practitioner

This report outlines the potential for concomitant use of dentally prescribed medication to increase the risk of statin-induced myopathy. The associated signs and symptoms of statin-induced myopathy are also highlighted, as well as the need for an accurate and updated drug history for all dental patients.

CLINICAL RELEVANCE

This article describes the recognized adverse interactions associated with concomitant drug therapy for patients on statins.

Eosinophilic Gastroenteritis and Citrus-Induced Urticaria

The immunological basis of eosinophilic gastroenteritis (EGE) is an interesting contrast between the enigma of urticaria and the increasing usage of molecular technology in clinical allergy. Little is known about the natural history of EGE. It has been known to spontaneously remit, but the typical course, especially in adults, is one of chronic and intermittent disease. Given the often chronic nature of this disease, it is important to use relatively benign treatments initially and limit the use of systemic corticosteroids. Also, given the fact that eosinophilic infiltration of the gastrointestinal tract may also be a manifestation of other potentially dangerous disease processes, such as malignancy or hypereosinophilic syndrome, which may be initially diagnosed as EGE, routine surveillance of the cardiopulmonary and gastrointestinal systems is important. We present a patient who demonstrates the variability of presentation and treatment response in this multifaceted disease. The fact that he has apparently entered remission also makes his an uncommon presentation of EGE.

[Grapefruit juice: potential drug interaction]

More than a decade has passed since it was unintentionally discovered that grapefruit juice interacts with certain drugs. The coadministration of these drugs with grapefruit juice can markedly elevate drug bioavailability, and can alter pharmacokinetic and pharmacodynamic parameters of the drug. The predominant mechanism for this interaction is the inhibition of cytochrome P-450 3A4 in the small intestine, resulting in a significant reduction of drug presystemic metabolism. An additional mechanism is the inhibition of P-glycoprotein, a transporter that carries drug from the enterocyte back to the gut lumen, resulting in a further increase in the fraction of drug absorbed. Some calcium channel antagonists, benzodiazepines, HMG-CoA reductase inhibitors and cyclosporine are the most affected drugs. A single exposure to one glass of the grapefruit juice can usually produce the maximal magnitude of the interaction. The data available so far, concerning this interaction and its clinical implications, are reviewed in this article. It is likely that more information regarding this interaction will accumulate in the future, and awareness of such is necessary for achieving optimal drug therapy.

Drug interactions of clinical significance for the dermatologist: recognition and avoidance

While it would be impossible for any dermatologist to remember all potential drug interactions, knowledge of the mechanisms of drug interactions can help reduce the risk of serious adverse outcomes. Most drugs are associated with interactions but the majority do not produce significant outcomes. Dealing with drug interactions is a challenge in all clinical practice, including dermatology. New information continues to appear, and dermatologists need to know about the drugs they use.This article focuses on the mechanisms of drug interactions. In particular, the life of a drug in terms of absorption, distribution, metabolism and excretion are reviewed with the focus on points of importance and relevance to drug interactions. The most clinically important drug interactions in dermatological practice are caused by alterations in drug metabolism. The contributions of P-glycoprotein, pharmacogenetic variation and genetic polymorphisms to drug interactions are highlighted, and the best evidence for drug interactions involving drug classes relevant to the dermatologist is presented. Since the initial evidence for clinically relevant drug interactions comes from case reports, prescribing physicians can have a major role in collating information on interactions. By understanding the mechanisms behind drug interactions and staying alert for toxicities, we can help make drug therapy safer and reduce the fear of drug interactions.

Cytochrome P450 drug interactions within the HMG-CoA reductase inhibitor class: are they clinically relevant?

The present review outlines the clinical relevance of pharmacokinetic drug interactions within the HMG-CoA reductase inhibitor class. These interactions can result in markedly increased or decreased plasma concentrations of some drugs within this class. However, the relationship between altered plasma concentrations and adverse effects or toxicity may not be linear. It is likely that other variables affect this concentration-effect relationship including: rapid changes in the concentration, concomitant lipid-lowering therapy or host genetic factors that code for different forms or amounts of metabolising enzymes and drug receptors. It is not currently possible to predict which patients will manifest clinically important drug-drug interactions, nor what concentration of an HMG-CoA reductase inhibitor will cause rhabdomyolysis. Thus, until prescribers have better scientific information from which to develop a 'therapeutic range' for each agent, caution should be exercised. In particular, patients taking a CYP3A4-metabolised agent, e.g. atorvastatin, simvastatin and lovastatin, should not be started on a CYP3A4 inhibitor or inducer without close monitoring.

Effect of grapefruit juice intake on etoposide bioavailability

PURPOSE

Oral administration of etoposide is limited by the high degree of unpredictable variation in systemic availability. This pilot study was conducted to evaluate the potential of pretreatment with grapefruit juice for improving the use of oral etoposide.

METHODS

In a randomized crossover study, six patients were sequentially treated with 50 mg IV etoposide over 1 h, 50 mg orally, or 50 mg orally post grapefruit juice on day 1, day 4, and day 8. Blood samples were drawn up to 24 h after the end of infusion and oral drug administration. Plasma etoposide concentrations were determined by reversed-phase HPLC with UV detection. A two-compartment model was used for pharmacokinetic parameter estimation. Pharmacokinetic parameters were evaluated using descriptive statistics.

RESULTS

Pretreatment with grapefruit juice resulted in an unexpected decrease of 26.2% in the AUC after oral treatment. Median absolute bioavailability with and without pretreatment with grapefruit juice was 52.4% and 73.2%, respectively. Interindividual variability was large in all treatment arms.

CONCLUSION

Grapefruit juice seems to reduce rather than increase oral bioavailability of etoposide. Moreover, we did not observe a reduction in interpatient variability of bioavailability.