Drug interactions: Proteins, pumps, and P-450s

Hydrocodone, Oxycodone, and Morphine Metabolism and Drug-Drug Interactions

Awareness of drug interactions involving opioids is critical for patient treatment as they are common therapeutics used in numerous care settings, including both chronic and disease-related pain. Not only do opioids have narrow therapeutic indexes and are extensively used, but they have the potential to cause severe toxicity. Opioids are the classical pain treatment for patients who suffer from moderate to severe pain. More importantly, opioids are often prescribed in combination with multiple other drugs, especially in patient populations who typically are prescribed a large drug regimen. This review focuses on the current knowledge of common opioid drug-drug interactions (DDIs), focusing specifically on hydrocodone, oxycodone, and morphine DDIs. The DDIs covered in this review include pharmacokinetic DDI arising from enzyme inhibition or induction, primarily due to inhibition of cytochrome p450 enzymes (CYPs). However, opioids such as morphine are metabolized by uridine-5'-diphosphoglucuronosyltransferases (UGTs), principally UGT2B7, and glucuronidation is another important pathway for opioid-drug interactions. This review also covers several pharmacodynamic DDI studies as well as the basics of CYP and UGT metabolism, including detailed opioid metabolism and the potential involvement of metabolizing enzyme gene variation in DDI. Based upon the current literature, further studies are needed to fully investigate and describe the DDI potential with opioids in pain and related disease settings to improve clinical outcomes for patients. SIGNIFICANCE STATEMENT: A review of the literature focusing on drug-drug interactions involving opioids is important because they can be toxic and potentially lethal, occurring through pharmacodynamic interactions as well as pharmacokinetic interactions occurring through inhibition or induction of drug metabolism.

Protein-Ligand Identification and In Vitro Inhibitory Effects of Cathine on 11 Major Human Drug Metabolizing Cytochrome P450s

Cathine is the stable form of cathinone, the major active compound found in khat (Catha edulis Forsk) plant. Khat was found to inhibit major phase I drug metabolizing cytochrome P450 (CYP) enzyme activities in vitro and in vivo. With the upsurge of khat consumption and the potential use of cathine to combat obesity, efforts should be channelled into understanding potential cathine-drug interactions, which have been rather limited. The present study aimed to assess CYPs activity and inhibition by cathine in a high-throughput in vitro fluorescence-based enzyme assay and molecular docking analysis to identify how cathine interacts within various CYPs’ active sites. The half maximal inhibitory concentration (IC₅₀) values of cathine determined for CYP2A6 and CYP3A4 were 80 and 90 μM, while CYP1A2, CYP2B6, CYP2C8, CYP2C9, CYP2C19, CYP2D6, CYP2E1, CYP2J2 and CYP3A5 showed no significant inhibition. Furthermore, in K_i analysis, the Lineweaver-Burk plots depicted non-competitive mixed inhibition of cathine on both CYP2A6 and CYP3A4 with K_i value of 63 and 100 μM, respectively. Cathine showed negligible time-dependent inhibition on CYPs. Further, molecular docking studies showed that cathine was bound to CYP2A6 via hydrophobic, hydrogen and π-stacking interactions and formed hydrophobic and hydrogen bonds with active site residues in CYP3A4. Both molecular docking prediction and in vitro outcome are in agreement, granting more detailed insights for predicting CYPs metabolism besides the possible cathine-drug interactions. Cathine-drug interactions may occur with concomitant consumption of khat or cathine-containing products with medications metabolized by CYP2A6 and CYP3A4.

Prevalence, beliefs and impact of drug-drug interactions between antiretroviral therapy and illicit drugs among people living with HIV in Spain

Drug use implies important challenges related to HIV management, particularly due to an increased risk of potential interactions between antiretroviral therapy (ART) and illicit drugs (pDDIs). This study analyses the prevalence and severity of pDDIs among people living with HIV (PLHIV). It also explores their awareness of pDDIs and their beliefs about the toxicity that they may cause, as well as the impact of pDDIs on selected health variables. We conducted an on-line cross-sectional survey across 33 Spanish hospitals and NGOs to collect demographics and clinical data. pDDIs were checked against the Interaction Checker developed by Liverpool University. The sample of the present study was composed of 694 PLHIV who used illicit drugs. They represented 49.5% of the 1,401 PLHIV that participated in the survey. After excluding 38 participants due to lack of information on their ART or illicit drug use, 335 (51.1%) participants consuming drugs presented with some potentially significant pDDIs between their ART and illicit drugs, with a mean of 2.1±1.7 (1-10) pDDIs per patient. The drugs most frequently involved in pDDIs were cocaine, cannabis, MDMA and nitrates ("poppers"). The prevalence of pDDIs across ART regimens was: protease inhibitors (41.7%); integrase inhibitor-boosted regimens (32.1%), and non-nucleoside reverse transcriptase inhibitors (26.3%). An awareness of pDDIs and beliefs about their potential toxicity correlated positively with intentional non-adherence (p<0.0001). Participants with pDDIs exhibited a higher prevalence of intentional non-adherence (2.19±1.04 vs. 1.93±0.94; p = 0.001). The presence of pDDIs was not associated with poorer results in the clinical variables analysed. A significant proportion of PLHIV who use drugs experience pDDIs, thereby requiring close monitoring. pDDIs should be considered in the clinical management of HIV patients. Adequate information about pDDIs and indicators about how to manage ART when PLHIV use drugs could improve ART non-adherence.

It's not all about inhaled treatment: challenges with oral therapy in paediatric respiratory medicine

Advances in therapies and management of conditions encountered by paediatric respiratory specialists have led to improved outcomes and improved survival rates dramatically in chronic diseases such as cystic fibrosis. However, this has also meant an increase in treatment burden. A variety of inhaled treatments are crucial in managing paediatric respiratory diseases, but these patients also have to take many oral medications. It is widely recognised that developing oral formulations appropriate for the paediatric population can affect how well a product is received by patients and their families. Consideration should be given to palatability and the number of medicines to be administered as these can all contribute to treatment adherence.

Polypharmacy specifically in the context of management of patients with cystic fibrosis is not a new concept, but the recently introduced cystic fibrosis transmembrane conductance regulator (CFTR) modulator therapies and their potential for interactions and adverse reactions create novel challenges. There are some strategies that families and healthcare professionals can implement to reduce treatment burden. This review will also provide some insight into the life of a teenager with cystic fibrosis and the relative complexities of her treatment and the impacts on daily life.

In children, medications given by the oral route can be challenging to administer, add to the burden of care and contribute to poor adherence. Additionally, polypharmacy increases the chances of interactions between oral medications.https://bit.ly/3fxgXQU

Antitumor, Anti-Inflammatory and Antiallergic Effects of Agaricus blazei Mushroom Extract and the Related Medicinal Basidiomycetes Mushrooms, Hericium erinaceus and Grifola frondosa: A Review of Preclinical and Clinical Studies

Since the 1980s, medicinal effects have been documented in scientific studies with the related Basidiomycota mushrooms Agaricus blazei Murill (AbM), Hericium erinaceus (HE) and Grifola frondosa (GF) from Brazilian and Eastern traditional medicine. Special focus has been on their antitumor effects, but the mushrooms' anti-inflammatory and antiallergic properties have also been investigated. The antitumor mechanisms were either direct tumor attack, e.g., apoptosis and metastatic suppression, or indirect defense, e.g., inhibited tumor neovascularization and T helper cell (Th) 1 immune response. The anti-inflammatory mechanisms were a reduction in proinflammatory cytokines, oxidative stress and changed gut microbiota, and the antiallergic mechanism was amelioration of a skewed Th1/Th2 balance. Since a predominant Th2 milieu is also found in cancer, which quite often is caused by a local chronic inflammation, the three conditions-tumor, inflammation and allergy-seem to be linked. Further mechanisms for HE were increased nerve and beneficial gut microbiota growth, and oxidative stress regulation. The medicinal mushrooms AbM, HE and GF appear to be safe, and can, in fact, increase longevity in animal models, possibly due to reduced tumorigenesis and oxidation. This article reviews preclinical and clinical findings with these mushrooms and the mechanisms behind them.

Agaricus blazei-Based Mushroom Extract Supplementation to Birch Allergic Blood Donors: A Randomized Clinical Trial

Since Agaricus blazei Murill (AbM) extract reduced specific IgE and ameliorated a skewed Th1/Th2 balance in a mouse allergy model, it was tested in blood donors with self-reported, IgE-positive, birch pollen allergy and/or asthma. Sixty recruited donors were randomized in a placebo-controlled, double-blinded study with pre-seasonal, 7-week, oral supplementation with the AbM-based extract Andosan^TM. Before and after the pollen season, questionnaires were answered for allergic rhino-conjunctivitis, asthma, and medication; serum IgE was measured, and Bet v 1-induced basophil activation was determined by CD63 expression. The reported general allergy and asthma symptoms and medication were significantly reduced in the AbM compared to the placebo group during pollen season. During the season, there was significant reduction in specific IgE anti-Bet v 1 and anti-t3 (birch pollen extract) levels in the AbM compared with the placebo group. While the maximal allergen concentrations needed for eliciting basophil activation before the season, changed significantly in the placebo group to lower concentrations (i.e., enhanced sensitization) after the season, these concentrations remained similar in the Andosan^TM AbM extract group. Hence, the prophylactic effect of oral supplementation before the season with the AbM-based Andosan^TM extract on aeroallergen-induced allergy was associated with reduced specific IgE levels during the season and basophils becoming less sensitive to allergen activation.

A Week of Oral Terbinafine Pulse Regimen Every Three Months to Treat all Dermatophyte Onychomycosis

Terbinafine has proved to treat numerous fungal infections, including onychomycosis, successfully. Due to its liver metabolization and dependency on the cytochrome P450 enzyme complex, undesirable drug interaction are highly probable. Additionally to drug interactions, the treatment is long, rising the chances of the appearance of side effects and abandonment. Pharmacokinetic data suggest that terbinafine maintains a fungicidal effect within the nail up to 30 weeks after its last administration, which has aroused the possibility of a pulse therapy to reduce the side effects while treating onychomycosis. This study's goal was to evaluate the effectiveness of three different oral terbinafine regimens in treating onychomycosis due to dermatophytes. Sixty-three patients with onychomycosis were sorted by convenience in three different groups. Patients from group 1 received the conventional terbinafine dose (250 mg per day for 3 months). Group 2 received a monthly week-long pulse-therapy dose (500 mg per day for 7 days a month, for 4 months) and group 3 received a 500 mg/day dose for 7 days every 3 months, totaling four treatments. There were no statistical differences regarding the effectiveness or side effects between the groups. Conclusion: A quarterly terbinafine pulse regimen can be a possible alternative for treating onychomycosis caused by dermatophytes.

Understanding the relevance of herb-drug interaction studies with special focus on interplays: a prerequisite for integrative medicine

Integrative medicine refers to the blending of conventional and evidence-based complementary medicines and therapies with the aim of using the most appropriate of either or both modalities for ultimate patient benefits. One of the major hurdles for the same is the chances of potential herb–drug interactions (HDIs). These HDIs could be beneficial or harmful, or even fatal; therefore, a thorough understanding of the eventualities of HDIs is essential so that a successful integration of the modern and complementary alternative systems of medicine could be achieved. Here, we summarize all the important points related to HDIs, including types, tools/methods for study, and prediction of the HDIs, along with a special focus on interplays between drug metabolizing enzymes and transporters. In addition, this article covers future perspective, with a focus on background endogenous players of interplays and approaches to predict the drug–disease–herb interactions so as to fetch the desired effects of these interactions.

A Practical Guide to Curing Onychomycosis: How to Maximize Cure at the Patient, Organism, Treatment, and Environmental Level

Onychomycosis is a fungal nail infection caused by dermatophytes, non-dermatophyte molds, and yeasts. Treatment of this infection can be difficult, with relapse likely to occur within 2.5 years of cure. The objective of this article is to review factors that can impact cure and to suggest practical techniques that physicians can use to maximize cure rates. Co-morbidities, as well as disease severity and duration, are among the many patient factors that could influence the efficacy of antifungal therapies. Furthermore, organism, treatment, and environmental factors that may hinder cure include point mutations, biofilms, affinity for non-target enzymes, and exposure to fungal reservoirs. To address patient-related factors, physicians are encouraged to conduct confirmatory testing and treat co-morbidities such as tinea pedis early and completely. To combat organism-focused factors, it is recommended that disruption of biofilms is considered, and drugs with multiple routes of delivery and unique mechanisms of action are prescribed when traditional agents are not effective. Extending follow-up periods, using combination treatments, and considering pulse regimens may also be of benefit. Through these practical techniques, physicians can maximize cure and limit the risk of relapse and re-infection.

Onychomycosis in the 21st Century: An Update on Diagnosis, Epidemiology, and Treatment

Onychomycosis accounts for 50% of all nail disease cases and is commonly caused by dermatophytes. Diabetes, human immunodeficiency virus, immunosuppression, obesity, smoking, and advancing age are predisposing factors of this fungal infection. Potassium hydroxide and culture are considered the current standard for diagnosing onychomycosis, revealing both fungal viability and species identification. Other diagnostic tests currently available include periodic acid-Schiff staining, polymerase chain reaction techniques, and fluorescent staining. Across 6 recently published epidemiology studies, the global prevalence of onychomycosis was estimated to be 5.5%, falling within the range of previously reported estimates (2%-8%). Newly approved onychomycosis treatments include efinaconazole, tavaborole, and laser therapy with lasers only approved to temporarily increase the amount of clear nail. Additional onychomycosis treatments being investigated include iontophoresis and photodynamic therapy with small open-label studies reported thus far. Preventative strategies, to help decrease recurrence and reinfection rates, include sanitisation of footwear and prophylactic topical antifungal agents.

Review and Management of Acneiform Eruptions in Patients with Immune Disorders

Immune disorders are associated with acne or acneiform lesions secondary to the occurrence of acne vulgaris or acneiform eruptions arising as a result of immunosuppressive medication or infection. In this review, we aim to provide an overview of acne and acneiform eruptions that can arise in the immunosuppressed host. Tips for differentiating between various acneiform entities are discussed, as well as a brief overview of treatment considerations.

Viekira Pak Induced Fatal Lactic Acidosis: A Case Report of an Unusual Side Effect

Viekira Pak is a new direct-acting antiviral agent that has an excellent efficacy in treating patients with chronic HCV. FDA released a safety warning that Viekira Pak can cause serious liver injury mostly in patients with underlying advanced liver disease. We report the first case of fatal lactic acidosis presenting 3 days after initiating therapy with Viekira Pak. Although it is very hard to precisely determine the cause of lactic acidosis, our case highlights an unusual side effect that ensued after starting the medication. Given the complexity of drug-drug interactions that can happen with the new direct-acting antiviral agents and the paucity of data regarding coadministration and methods of monitoring, a thorough review should be pursued prior to initiating these medications.

Therapeutic challenges posed by critical drug-drug interactions in cystic fibrosis

This review seeks to re-introduce cystic fibrosis (CF) clinicians to the pharmacology of drug-drug interactions among medications commonly used in CF and provide a framework for understanding these interactions among medications outside the scope of this discussion. We here focus on drugs impacted by the cytochrome P-450 (CYP450) enzyme system and on interactions involving antimicrobials, psychotropic medications, and cystic fibrosis transmembrane conductance regulator (CFTR) modulators. Particular attention is needed when prescribing rifampin, azole antifungals and the CFTR modulators, ivacaftor, and lumacaftor/ivacaftor, in combination with other medications. The complexities of these interactions provide a strong rationale for case management by pharmacists and pharmacologists as a routine part of CF care. Pediatr Pulmonol. 2016;51:S61-S70. © 2016 Wiley Periodicals, Inc.

Is hormonal treatment still an option in acne today?

Hormonal treatment is indicated in cases of papulopustular, nodular and conglobate acne in females with identified hyperandrogenism, in adult women who have monthly flare-ups and when standard therapeutic options are unsuccessful or inappropriate. This review summarizes the latest information on hormonal therapies including: combined oral contraceptives; anti-androgens, such as cyproterone acetate, spironolactone and flutamide; low-dose glucocorticoids and gonadotropin-releasing hormone agonists. It also shares the authors' recommendations for treatment based on the studies discussed here, and personal experience.

Metabolism-related pharmacokinetic drug-drug interactions with tyrosine kinase inhibitors: current understanding, challenges and recommendations

Drug-drug interactions (DDIs) occur when a patient's response to the drug is modified by administration or co-exposure to another drug. The main cytochrome P450 (CYP) enzyme, CYP3A4, is implicated in the metabolism of almost all of the tyrosine kinase inhibitors (TKIs). Therefore, there is a substantial potential for interaction between TKIs and other drugs that modulate the activity of this metabolic pathway. Cancer patients are susceptible to DDIs as they receive many medications, either for supportive care or for treatment of toxicity. Differences in DDI outcomes are generally negligible because of the wide therapeutic window of common drugs. However for anticancer agents, serious clinical consequences may occur from small changes in drug metabolism and pharmacokinetics. Therefore, the objective of this review is to highlight the current understanding of DDIs among TKIs, with a focus on metabolism, as well as to identify challenges in the prediction of DDIs and provide recommendations.

Understanding and preventing drug-drug and drug-gene interactions

Concomitant administration of multiple drugs can lead to unanticipated drug interactions and resultant adverse drug events with their associated costs. A more thorough understanding of the different cytochrome P450 isoenzymes and drug transporters has led to new methods to try to predict and prevent clinically relevant drug interactions. There is also an increased recognition of the need to identify the impact of pharmacogenetic polymorphisms on drug interactions. More stringent regulatory requirements have evolved for industry to classify cytochrome inhibitors and inducers, test the effect of drug interactions in the presence of polymorphic enzymes, and evaluate multiple potentially interacting drugs simultaneously. In clinical practice, drug alert software programs have been developed. This review discusses drug interaction mechanisms and strategies for screening and minimizing exposure to drug interactions. We also provide future perspectives for reducing the risk of clinically significant drug interactions.

Drug interactions in dermatology: what the dermatologist should know

A drug interaction is a process by which a drug or any other substance interacts with another drug and affects its activity by increasing or decreasing its effect, causing a side effect or producing a new effect unrelated to the effect of either. Interactions may be of various types-drug-drug interactions, drug-food interactions, drug-medical condition interactions, or drug-herb interactions. Interactions may occur by single or multiple mechanisms. They may occur in vivo or in vitro (pharmaceutical reactions). In vivo interactions may be further subdivided into pharmacodynamic or pharmacokinetic reactions. Topical drug interactions which may be agonistic or antagonistic may occur between two drugs applied topically or between a topical and a systemic drug. Topical drug-food interaction (for example, grape fruit juice and cyclosporine) and drug-disease interactions (for example, topical corticosteroid and aloe vera) may also occur. It is important for the dermatologist to be aware of such interactions to avoid complications of therapy in day-to-day practice.

Clotrimazole, but not dexamethasone, is a potent in vitro inhibitor of cytochrome P450 isoforms CYP1A and CYP3A in rainbow trout

The effects of clotrimazole (CLO) and dexamethasone (DEX), both detected in the aquatic environment, were assessed on inhibition of cytochrome P450 (CYP450) in hepatic microsomes of rainbow trout. Activity of three CYP450 isoforms: ethoxyresorufin O-deethylase (EROD; CYP1A), 7-benzyloxy-4-trifluoromethylcoumarin O-debenzylase (BFCOD; CYP3A) and p-nitrophenol hydroxylase (PNPH; CYP2E1-like protein) was investigated in the presence of four concentrations of CLO and DEX. Clotrimazole in a concentration range of 1-100μM decreased the activity of EROD and BFCOD. The inhibition was reversible, as pre-incubation of the microsomes with CLO, before addition of the substrate, had no effect. EROD activity was non-competitively inhibited with a Ki of 0.5μM, and BFCOD activity revealed competitive inhibition with a Ki of 0.04μM. The relatively low Ki for CLO inhibition of EROD and BFCOD activity may indicate that the ability of CYP1A and CYP3A to metabolize xenobiotics is reduced in the presence of CLO. PNPH activity was not affected by CLO. DEX showed no inhibitory potency on any investigated reaction. CLO, but not DEX, inhibited EROD and BFCOD activity by different mechanisms.

The P-glycoprotein transport system and cardiovascular drugs

Permeability glycoprotein (P-gp) mediates the export of drugs from cells located in the small intestine, blood-brain barrier, hepatocytes, and kidney proximal tubule, serving a protective function for the body against foreign substances. Intestinal absorption, biliary excretion, and urinary excretion of P-gp substrates can therefore be altered by either the inhibition or induction of P-gp. A wide spectrum of drugs, such as anticancer agents and steroids, are known P-gp substrates and/or inhibitors, and many cardiovascular drugs have recently been observed to have clinically relevant interactions as well. We review the interactions among commonly prescribed cardiovascular drugs that are P-gp substrates and observe interactions involving P-gp that may be relevant to clinical practice. Cardiovascular drugs with narrow therapeutic indexes (e.g., antiarrhythmic agents, anticoagulant agents) have demonstrated large increases in concentrations when coadministered with potent P-gp inhibitors, thus increasing the risk for drug toxicity. Therefore, dose adjustment or use of alternative agents should be considered when strong P-gp-mediated drug-drug interactions are present. Finally, interactions between novel drugs and known P-gp inhibitors are now being systematically evaluated during drug development, and recommended guidelines for the administration of P-gp substrate drugs will be expanded.

Prevalence and risk of potential cytochrome P450-mediated drug-drug interactions in older hospitalized patients with polypharmacy

BACKGROUND

As rates of polypharmacy rise and medication regimens become more complex, the risk of potential cytochrome P450 (CYP)-mediated drug-drug interactions (DDIs) is a growing clinical concern for older adults.

OBJECTIVE

To determine the prevalence of potential CYP-mediated DDIs in older hospitalized adults with polypharmacy and analyze the relationship between the number of drugs dispensed and the probability of these interactions in this high-risk population.

METHODS

A prospective 16-week cohort study was conducted among consecutive new patients aged 65 years and older with polypharmacy (>5 drugs) admitted to a community hospital. The medication profiles of these patients were analyzed with a new multidrug cytochrome-specific software program. The prevalence of potential CYP-mediated DDIs was determined, with the probability calculated as a function of the number of medications dispensed using multivariate Poisson regression adjusted for age and sex. Comparative performance of the software program and a standard 2-drug alert program for detecting these DDIs was evaluated using the Wilcoxon-Mann-Whitney rank-sum test. Pharmacists' decisions to recommend medication adjustment based on the probability of CYP-mediated DDIs were recorded.

RESULTS

The prevalence of potential CYP-mediated DDIs detected among 275 older adults with polypharmacy was 80%. The probability of at least 1 CYP-mediated DDI was 50% for persons taking 5-9 drugs, 81% with 10-14 drugs, 92% with 15-19 drugs, and 100% with 20 or more drugs. Addition of each medication to a 5-drug regimen conferred a 12% increased risk of a potential CYP-mediated DDI after adjustment for age and sex (OR 1.12; 95% CI 1.09-1.14). The multidrug software identified a median increase of 3 (95% CI 2.5-3.5) potential CYP-mediated DDIs per patient, compared to use of the standard 2-drug alert software. Pharmacists targeted patients for medication adjustment or close clinical monitoring in 23% of cases.

CONCLUSIONS

The prevalence of potential CYP-mediated DDIs is high in geriatric patients with polypharmacy. The risk of DDIs increases as a function of the number of medications dispensed. Pharmacists' decision to intervene for potential CYP-mediated DDIs depends on clinical judgment in addition to the output from drug alert software programs, but may be facilitated by a single multicomponent, multidrug potential CYP-mediated DDI assessment.

Herb-drug interaction of Fucus vesiculosus extract and amiodarone in rats: a potential risk for reduced bioavailability of amiodarone in clinical practice

Fucus vesiculosus is a seaweed claimed to be useful for obesity management. Therefore, considering the relationship between obesity and cardiovascular diseases, this work aimed to assess the potential for an herb-drug interaction among a standardized F. vesiculosus extract (GMP certificate) and amiodarone (a narrow therapeutic index drug) in rats. In a first pharmacokinetic study, rats were simultaneously co-administered with a single-dose of F. vesiculosus (575 mg/kg, p.o.) and amiodarone (50 mg/kg, p.o.); in a second study, rats were pre-treated during 14 days with F. vesiculosus (575 mg/kg/day, p.o.) and received amiodarone (50 mg/kg, p.o.) on the 15th day. Rats of the control groups received the corresponding volume of vehicle. After analysis of the pharmacokinetic data it deserves to be highlighted the significant decrease in the peak plasma concentration of amiodarone (55.4%) as well as the reduction of systemic exposure to the parent drug (~30%) following the simultaneous co-administration of F. vesiculosus extract and amiodarone. This paper reports, for the first time, the herb-drug interaction between F. vesiculosus and amiodarone, which determined a considerable decrease on amiodarone bioavailability in rats. Therefore, the therapeutic efficacy of amiodarone may be compromised by the concurrent administration of herbal slimming medicines/dietary supplements containing F. vesiculosus.

Clinically based evidence of drug-herb interactions: a systematic review

IMPORTANCE OF THE FIELD

Healthcare practitioners are deeply concerned about drug-herb interactions and how concurrent administration may affect both the safety and effectiveness of prescribed drugs. Interactions between botanical medicines and synthetic drugs can be clinically relevant and it is important to understand what kinds of interactions are possible. Better knowledge in this area will help avoid negative interactions and may also help enable synergistic interactions.

AREAS COVERED IN THIS REVIEW

Includes articles related to the investigation of Western botanicals or whole herbal extracts in human subjects, investigating either the impact on Cytochrome P450 isoenzymes or an assessment of specific drug-herb interactions within a clinical trial. Searches were conducted in both Pubmed and EMBASE from inception to March 2009.

WHAT THE READER WILL GAIN

Knowledge regarding specific interactions to consider in clinical practice. The reader will also gain an appreciation of the complexities associated with the area of drug-herb interactions. Summary tables of relevant drug-herb interactions are presented both for the individual herbs included and at the level of the CYP450 enzymes.

TAKE HOME MESSAGE

Knowledge of drug-herb interactions is limited and much more research needs to be done to further document clinically relevant interactions. Even though preclinical data are often poorly generalizable to the human situation, caution must be taken in the absence of clinical evidence especially where drugs with narrow therapeutic windows are concerned.

Herb-drug interaction of silymarin or silibinin on the pharmacokinetics of trazodone in rats

Silymarin, one of the most popular herbal medicines, has been widely used for its hepatoprotective effects. This study investigates the effects of repeated dose of silymarin and its major ingredient, silibinin, on the pharmacokinetics of the antidepressant trazodone. Treatment groups included vehicle control group, concomitant silymarin at 1.0g/kg dose, and four 7-day repeated dose induction groups of 0.5 and 1.0g/kg silymarin and 0.175 and 0.35g/kg silibinin. Microdialysis coupled with high performance liquid chromatography (HPLC) was used to simultaneously monitor blood and bile concentrations of trazodone in the rats. Results indicate that pretreatment with an extremely high dose of 1.0g/kg silymarin significantly decreases trazodone's area under concentration curve (AUC), distribution half-life (t(1/2,alpha)), elimination half-life (t(1/2,beta)), and mean residence time (MRT). In conclusion, the present study finds no marked effects of silymarin and silibinin on the pharmacokinetics of trazodone under normal daily doses and the relative safety of taking the herb with trazodone.

Inhibition of P-glycoprotein in Caco-2 cells: effects of herbal remedies frequently used by cancer patients

1. The herbal products Natto K2, Agaricus, mistletoe, noni juice, green tea and garlic were investigated for in vitro inhibitory potential on P-glycoprotein (P-gp)-mediated transport of digoxin (30 nM) in differentiated and polarized Caco-2 cells. 2. Satisfactory cell functionality was demonstrated through measurements of assay linearity, transepithelial electric resistance (TEER), cytotoxicity, mannitol permeability, and inclusion of the positive inhibition control verapamil. 3. The most potent inhibitors of the net digoxin flux (IC(50)) were mistletoe > Natto K2 > Agaricus > green tea (0.022, 0.62, 3.81, >4.5 mg ml(-1), respectively). Mistletoe also showed the lowest IC(25) value, close to that obtained by verapamil (1.0 and 0.5 microg ml(-1), respectively). The IC(50)/IC(25) ratio was found to be a good parameter for the determination of inhibition profiles. Garlic and noni juice were classified as non-inhibitors. 4. This study shows that mistletoe, Natto K2, Agaricus and green tea inhibit P-gp in vitro. Special attention should be paid to mistletoe due to very low IC(50) and IC(25) values and to Natto K2 due to a low IC(50) value and a low IC(50)/IC(25) ratio.

Functional evolution of the pregnane X receptor

The pregnane X receptor (PXR; NR1I2) is a nuclear hormone receptor (NR) that transcriptionally regulates genes encoding transporters and drug-metabolising enzymes in the liver and intestine. PXR activation leads to enhanced metabolism and elimination of xenobiotics and endogenous compounds such as hormones and bile salts. Relative to other vertebrate NRs, PXR has the broadest specificity for ligand activators by virtue of a large, flexible ligand-binding cavity. In addition, PXR has the most extensive sequence diversity across vertebrate species in the ligand-binding domain of any NR, with significant pharmacological differences between human and rodent PXRs, and especially marked divergence between mammalian and nonmammalian PXRs. The unusual properties of PXR complicate the use of in silico and animal models to predict in vivo human PXR pharmacology. Research into the evolutionary history of the PXR gene has also provided insight into the function of PXR in humans and other animals.

Pharmacokinetic drug interaction profiles of proton pump inhibitors

Proton pump inhibitors are used extensively for the treatment of gastric acid-related disorders because they produce a greater degree and longer duration of gastric acid suppression and, thus, better healing rates, than histamine H(2) receptor antagonists. The need for long-term treatment of these disorders raises the potential for clinically significant drug interactions in patients receiving proton pump inhibitors and other medications. Therefore, it is important to understand the mechanisms for drug interactions in this setting. Proton pump inhibitors can modify the intragastric release of other drugs from their dosage forms by elevating pH (e.g. reducing the antifungal activity of ketoconazole). Proton pump inhibitors also influence drug absorption and metabolism by interacting with adenosine triphosphate-dependent P-glycoprotein (e.g. inhibiting digoxin efflux) or with the cytochrome P450 (CYP) enzyme system (e.g. decreasing simvastatin metabolism), thereby affecting both intestinal first-pass metabolism and hepatic clearance. Although interactions based on the change of gastric pH are a group-specific effect and thus may occur with all proton pump inhibitors, individual proton pump inhibitors differ in their propensities to interact with other drugs and the extent to which their interaction profiles have been defined. The interaction profiles of omeprazole and pantoprazole have been studied most extensively. A number of studies have shown that omeprazole carries a considerable potential for drug interactions, since it has a high affinity for CYP2C19 and a somewhat lower affinity for CYP3A4. In contrast, pantoprazole appears to have lower potential for interactions with other medications. Although the interaction profiles of esomeprazole, lansoprazole and rabeprazole have been less extensively investigated, evidence suggests that lansoprazole and rabeprazole seem to have a weaker potential for interactions than omeprazole. Although only a few drug interactions involving proton pump inhibitors have been shown to be of clinical significance, the potential for drug interactions should be taken into account when choosing a therapy for gastric acid-related disorders, especially for elderly patients in whom polypharmacy is common, or in those receiving a concomitant medication with a narrow therapeutic index.

Co-prescriptions with itraconazole and fluconazole as a signal for possible risk of drug–drug interactions: a four-year analysis from Italian general practice

PURPOSE

To determine the prevalence of concomitant use of drugs potentially responsible for interactions among itraconazole and fluconazole users in general practice.

METHODS

During the years 1999-2002, we obtained information from the 'Health Search Database', (HSD) an Italian general practice research database. Among a total sample of 457 672 eligible patients, we included those aged >16 years, and whose diagnoses could be classified as mycosis. Itraconazole and fluconazole users were then selected. A potentially drug-drug interaction (DDI) occurred when the use of concomitant drugs were recorded within +/-30 days from the date of the first azoles prescription. Interacting drugs were classified according to the summary of product characteristics (SPC) as provided by the Italian Pharmaceutical Repertory (REFI).

RESULTS

From 18 323 cases of mycosis, we selected 4843 itraconazole and 1446 fluconazole users. Potentially interacting drugs were prescribed in 8.7% of itraconazole and 6.1% of fluconazole users. For itraconazole, calcium channel blockers were the most common interacting drugs (3.3%), followed by statins (1.7%) and clarithromycin (1.3%), whereas gestoden + ethynylestradiol (2.5%) and benzodiazepines (1.8%) resulted as the most common interacting drugs among fluconazole users.

CONCLUSION

Data indicate a relevant prevalence of concomitant use of medications potentially leading to drug interactions among azoles users. Because of the wide use of these medications in general practice, they should be used with clinical monitoring in view of their known side effects as well as their potential risk for drug interaction.

The pharmacological importance of cytochrome CYP3A4 in the palliation of symptoms: review and recommendations for avoiding adverse drug interactions

BACKGROUND

Adverse drug interactions are major causes of morbidity, hospitalizations, and mortality. The greatest risk of drug interactions occurs through in the cytochrome system. CYP3A4, the most prevalent cytochrome, accounts for 30-50% of drugs metabolized through type I enzymes.

MATERIALS AND METHODS

Palliative patients received medications for symptoms and co-morbidities, many of which are substrate, inhibitors, or promoters of CYP3A4 activity and expression. A literature review on CYP3A4 was performed pertinent to palliative medicine.

DISCUSSION

In this state of the art review, we discuss the CYP3A4 genetics, and kinetics and common medications, which are substrates or inhibitor/promoters of CYP3A4.

CONCLUSION

We made some recommendations for drug choices to avoid clinically important drug interaction.

Drug-associated disease: cytochrome P450 interactions

Critically ill patients generally are older, frequently have organ failure, and commonly receive multiple medications, all of which make them susceptible to adverse effects of drugs. Drug interactions are a common adverse effect, and many are predictable based on understanding the mechanisms that underlie drug interactions. This article identifies commonly used medications in critically ill patients and the associated drug interactions that may occur with emphasis on the cytochrome P450 enzyme system.

Impact of transgene expression on drug metabolism following systemic adenoviral vector administration

BACKGROUND

Systemic administration of a first-generation adenovirus expressing E. coli beta-galactosidase (AdlacZ) alters expression and function of two hepatic drug-metabolizing enzymes, cytochrome P450 (CYP) 3A2 and 2C11, for 14 days. The objective of these studies was to determine how the transgene cassette influences CYP expression and function.

METHODS

Sprague-Dawley rats were given 5.7 x 10(12) viral particles (vp)/kg of either: AdlacZ, Ad expressing murine erythropoietin (Epo), Ad without a transgene (Null), or phosphate-buffered saline (Vehicle). Hepatic CYP protein expression, activity, mRNA and alanine aminotransferase (ALT) levels were analyzed 0.25, 1, 4, and 14 days following a single intravenous injection.

RESULTS

Administration of Epo did not alter CYP3A2 activity, but induced RNA levels by a factor of 2 at 4 and 14 days (P< or =0.01). This vector suppressed CYP2C11 activity levels by 45% at 1 day (P< or =0.05) and RNA levels throughout the study period (P< or =0.05). The Null vector suppressed CYP3A2 activity by 36, 63, 34, and 45% at 0.25, 1, 4 and 14 days, respectively (P< or =0.05). CYP2C11 activity was suppressed 1 day after administration (41%) and RNA levels were suppressed at 6 h (53%) and 1 day (36%, P< or =0.05). In contrast, AdlacZ suppressed both CYP3A2 and 2C11 at all time points.

CONCLUSIONS

The immunogenic and biological nature of the transgene cassette can influence changes in CYP3A2, but not the 2C11 isoform. The shift in transcription and translation of protein for maintenance of physiologic homeostasis to production of viral proteins and transgene product and their associated toxicity during viral infection may explain our observations.

Cyclosporine A (CsA) affects the pharmacodynamics and pharmacokinetics of the atypical antipsychotic amisulpride probably via inhibition of P-glycoprotein (P-gp)

The importance of P-glycoprotein (P-gp) in the pharmacokinetics of amisulpride and the effects of a P-gp inhibitor cyclosporine A (CsA) was investigated both, in vitro and in vivo. In vitro and in vivo results indicated amisulpride as a substrate of P-gp. Amisulpride was not metabolized by rat liver microsomes. Open field behavior showed time dependent abolishment in locomotion by amisulpride (50 mg kg(-1)). Co-administration of CsA (50 mg kg(-1)) resulted in a higher and significantly longer antipsychotic effect (24 h after drug administration). Accordingly, the area under concentration-time curve in serum and brain was higher in CsA co-treated rats (13.5 vs. 29.8 micromol h l(-1) for serum and 2.16 vs 2.98 micromol h l(-1) for brain tissue) while renal clearance was not affected. These results pointed to a pharmacokinetic drug interaction between CsA and amisulpride most likely caused by inhibition of P-gp.

Herbal interactions involving cytochrome p450 enzymes: a mini review

The metabolism of a drug can be altered by another drug or foreign chemical, and such interactions can often be clinically significant. Cytochrome P450 (CYP) enzymes, a superfamily of enzymes found mainly in the liver, are involved in the metabolism of a plethora of xenobiotics and have been shown to be involved in numerous interactions between drugs and food, herbs and other drugs. The observed induction and inhibition of CYP enzymes by natural products in the presence of a prescribed drug has (among other reasons) led to the general acceptance that natural therapies can have adverse effects, contrary to the popular beliefs in countries where there is an active practice of ethnomedicine. Herbal medicines such as St. John's wort, garlic, piperine, ginseng, and gingko, which are freely available over the counter, have given rise to serious clinical interactions when co-administered with prescription medicines. Such adversities have spurred various pre-clinical and in vitro investigations on a series of other herbal remedies, with their clinical relevance remaining to be established. Although the presence of numerous active ingredients in herbal medicines, foods and dietary supplements complicate experimentation, the observable interactions with CYP enzymes warrant systematic studies, so that metabolism-based interactions can be predicted and avoided more readily. This article highlights the involvement of CYP enzymes in metabolism-related drug-herb interactions and the importance of gaining a mechanism-based understanding to avoid potential adverse drug reactions, in addition to outlining other contributory factors, such as pharmacogenetics and recreational habits that may compound this important health issue.

Current use of anti-infectives in dermatology

Dermatologic diseases encompass a broad category of pathologic situations. Infection remains a significant aspect of the pathology faced in patient encounters, and it is natural to expect that anti-infectives play a major element in the armamentarium utilized by dermatologists. Aside from the treatment of the classic bacterial and fungal infections, there are now new uses for antiviral agents to help suppress recurrent disease, such as herpes simplex. There is also the novel approach of using anti-infectives, or agents that have been thought to have antimicrobial activity, to treat inflammatory diseases. This review describes anti-infectives, beginning with common antibiotics used to treat bacterial infections. The discussion will then cover the current use of antivirals. Finally, the description of antifungals will be separated, starting with the oral agents and ending with the topical antimycotics. The use of anti-infectives in tropical dermatology has been purposefully left out, and perhaps should be the subject of a separate review. Cutaneous bacterial infections consist chiefly of those microorganisms that colonize the skin, such as species of staphylococcus and streptococcus. Propionibacterium acnes and certain other anaerobes can be involved in folliculitis, pyodermas and in chronic conditions such as hidradenitis suppurativa.

Potential elevation of tacrolimus trough concentrations with concomitant metronidazole therapy

OBJECTIVE

To report the occurrence of a potential tacrolimus elevation in a renal transplant recipient after adding metronidazole to the medication regimen.

CASE SUMMARY

A 24-year-old white man status post living-related renal transplant who had been stabilized on tacrolimus 4 mg twice daily (trough concentrations 7-10 ng/mL) for 2 months and prednisone 20 mg daily presented to the clinic with severe diarrhea. Stool cultures were positive for Clostridium difficile, and therapy with metronidazole 500 mg 4 times daily was initiated. Between days 4 and 14 of metronidazole therapy, the patient's tacrolimus trough concentration and serum creatinine level increased to maximum levels of 26.3 ng/mL and 3.3 mg/dL (baseline 1.6-1.8 mg/dL), respectively. Tacrolimus was withheld for one dose and then decreased to 1 mg twice daily. Two days after metronidazole discontinuation, tacrolimus trough concentrations dropped to 9.4 ng/mL and serum creatinine to 2.3 mg/dL, warranting a tacrolimus dose increase to 3 mg daily.

DISCUSSION

As of April 15, 2005, one other case has been reported documenting an elevation in tacrolimus concentrations with the addition of metronidazole. The possible mechanism may be related to metronidazole's weak inhibition of CYP3A4 and, possibly, P-glycoprotein. According to the Naranjo probability scale, metronidazole was the probable cause of this adverse reaction.

CONCLUSIONS

Coadministration of tacrolimus with metronidazole may result in elevated tacrolimus concentrations, possibly leading to tacrolimus toxicity. Practitioners should be aware of this potential interaction and closely monitor tacrolimus concentrations and renal function.

Drug interactions in the management of HIV infection

The availability of antiretroviral therapy has significantly reduced the morbidity and mortality of HIV infection. In addition, improved treatment of opportunistic infections and comorbidities common to patients with HIV is further prolonging the lives of patients. Improvement in the treatment of HIV has led to a significant increase in the number of medications which caregivers are able to utilise to manage HIV/AIDS. Antiretroviral medications, as well as many of the drugs used in the management of opportunistic infections and primary care (e.g., macrolide antibiotics, azole antifungals, cholesterol-lowering medications), are particularly prone to drug interactions. The interpretation of clinically significant interactions is complicated by the rate at which new information on drug metabolism and transport is becoming available. Management of drug interactions in HIV is further confounded by conflicting study results and differences between documented and theoretical inter-actions. The mechanisms and significance of interactions involving antiretrovirals, drugs used for opportunistic infections, and other medications commonly used in HIV patients will be reviewed.

Pharmacotherapy of onychomycosis

Fungal infections of the nails are frequent in some segments of the population. Dermatophytes, yeasts and moulds are potential pathogens. A series of antifungal treatments are available to the clinician, differing by both their mechanistic nature and mode of administration. The pharmacodynamic and pharmacokinetic properties of each antifungal agent are distinct. This review focuses on the characteristics of amorolfine, bifonazole, ciclopirox, fluconazole, griseofulvin, itraconazole, ketoconazole, ravuconazole, R126638 and terbinafine. Single drug treatments and combined therapies are presented. None of the current drug regimens have demonstrated reliable efficacy against all cases of onychomycosis. Treatment failures, relapses and reinfections remain stubborn problems in the management of onychomycosis.

Skin and Psyche : Diversionary Symbiosis

A significant proportion of patients with skin diseases have associated psychosocial factors. Not only does psychopathology manifest on the skin in absence of any real skin disease, primary skin disorders can also be exacerbated by emotional stress adversely influencing the homeostasis of immunological and inflammatory processes in deeper layers of the skin. Furthermore, many patients develop emotional problems as a result of having disfiguring skin diseases. In addition, some patients having solely sensory disturbances in absence of primary dermatoses or identifiable medical or neurological conditions, as well as some purely dermatologic conditions such as post-herpetic neuralgia may preferentially need psychotherapeutic modalities to address their underlying psychopathology irrespective of the presenting dermatologic manifestation arising out of 'somatisation' of a psychopathology into physical problems. The most obvious course of action of referral to a psychiatrist or another mental health professional may unfortunately not be readily tenable either due to the perceived stigma associated with psychiatric illness or lack of insight on the part of patients. In the interregnum, effective management of the psychologic or/and psychiatric problems can only be done by the dermatologist provided he has an adequate knowledge base and experience to undertake psychotherapeutic modalities.