Macrolide antibacterials. Drug interactions of clinical significance

Design, synthesis and biological evaluation of chalcone derivatives as potent and orally active hCYP3A4 inhibitors

Human cytochrome P450 3A4 (hCYP3A4), one of the most important drug-metabolizing enzymes, catalyze the metabolic clearance of ∼50% therapeutic drugs. CYP3A4 inhibitors have been used for improving the in vivo efficacy of hCYP3A4-substrate drugs. However, most of existing hCYP3A4 inhibitors may trigger serious adverse effects or undesirable effects on endogenous metabolism. This study aimed to discover potent and orally active hCYP3A4 inhibitors from chalcone derivatives and to test their anti-hCYP3A4 effects both in vitro and in vivo. Following three rounds of screening and structural optimization, the isoquinoline chalcones were found with excellently anti-hCYP3A4 effects. SAR studies showed that introducing an isoquinoline ring on the A-ring significantly enhanced anti-CYP3A4 effect, generating A10 (IC50 = 102.10 nM) as a promising lead compound. The 2nd round of SAR studies showed that introducing a substituent group at the para position of the carbonyl group on B-ring strongly improved the anti-CYP3A4 effect. As a result, C6 was identified as the most potent hCYP3A4 inhibitor (IC50 = 43.93 nM) in human liver microsomes (HLMs). C6 also displayed potent anti-hCYP3A4 effect in living cells (IC50 = 153.00 nM), which was superior to the positive inhibitor ketoconazole (IC50 = 251.00 nM). Mechanistic studies revealed that C6 could potently inhibit CYP3A4-catalyzed N-ethyl-1,8-naphthalimide (NEN) hydroxylation in a competitive manner (Ki = 30.00 nM). Moreover, C6 exhibited suitable metabolic stability in HLMs and showed good safety profiles in mice. In vivo tests demonstrated that C6 (100 mg/kg, orally administration) significantly increased the AUC(0-inf) of midazolam by 3.63-fold, and strongly prolonged its half-life by 1.66-fold compared with the vehicle group in mice. Collectively, our findings revealed the SARs of chalcone derivatives as hCYP3A4 inhibitors and offered several potent chalcone-type hCYP3A4 inhibitors, while C6 could serve as a good lead compound for developing novel, orally active CYP3A4 inhibitors with improved druglikeness properties.

Individual Pharmacotherapy Management (IPM)—IV: Optimized Usage of Approved Antimicrobials Addressing Under-Recognized Adverse Drug Reactions and Drug-Drug Interactions in Polypharmacy

Antimicrobial therapy is often a life-saving medical intervention for inpatients and outpatients. Almost all medical disciplines are involved in this therapeutic procedure. Knowledge of adverse drug reactions (ADRs) and drug-drug interactions (DDIs) is important to avoid drug-related harm. Within the broad spectrum of antibiotic and antifungal therapy, most typical ADRs are known to physicians. The aim of this study was to evaluate relevant pharmacological aspects with which we are not so familiar and to provide further practical guidance. Individual pharmacotherapy management (IPM) as a synopsis of internal medicine and clinical pharmacology based on the entirety of the digital patient information with reference to drug information, guidelines, and literature research has been continuously performed for over 8 years in interdisciplinary intensive care and trauma and transplant patients. Findings from over 52,000 detailed medication analyses highlight critical ADRs and DDIs, especially in these vulnerable patients with polypharmacy. We present the most relevant ADRs and DDIs in antibiotic and antifungal pharmacology, which are less frequently considered in relation to neurologic, hemostaseologic, hematologic, endocrinologic, and cardiac complexities. Constant awareness and preventive strategies help avoid life-threatening manifestations of these inherent risks and ensure patient and drug safety in antimicrobial therapy.

Colchicine and macrolides: a cohort study of the risk of adverse outcomes associated with concomitant exposure

Colchicine is increasingly used as the number of potential indications expands. However, it also has a narrow therapeutic index that is associated with bothersome to severe side effects. When concomitantly use with medications inhibiting its metabolism, higher plasma levels will result and increase likelihood of colchicine toxicity. We conducted a cohort study using electronic health records comparing encounters with colchicine plus a macrolide and colchicine with an antibiotic non-macrolide. We assessed the relationship between the two groups using adjusted multivariate logistic regression models and the risk of rhabdomyolysis, pancytopenia, muscular weakness, heart failure, acute hepatic failure and death. 12670 patients on colchicine plus an antibiotic non-macrolide were compared to 2199 patients exposed to colchicine plus a macrolide. Patients exposed to colchicine and a macrolide were majority men (n = 1329, 60.4%) and white (n = 1485, 67.5%) in their late sixties (mean age in years 68.4, SD 15.6). Heart failure was more frequent in the colchicine plus a macrolide cohort (n = 402, 18.3%) vs the colchicine non-macrolide one (n = 1153, 9.1%) (p < 0.0001) and also had a higher mortality rate [(85 (3.87%) vs 289 (2.28%), p < 0.0001 macrolides vs non-macrolides cohorts, respectively]. When the sample was limited to individuals exposed to either clarithromycin or erythromycin and colchicine, the adjusted OR for acute hepatic failure was 2.47 (95% CI 1.04–5.91) and 2.06 for death (95% CI 1.07–3.97). There is a significant increase in the risk of hepatic failure and mortality when colchicine is concomitantly administered with a macrolide. Colchicine should not be used concomitantly with these antibiotics or should be temporarily discontinued to avoid toxic levels of colchicine.

[Safety in the selection of oral antibiotic treatment in community infections, beyond COVID-19]

Los antibióticos orales son uno de los fármacos más utilizados en la comunidad. Sus efectos adversos son generalmente poco frecuentes y leves, e incluyen toxicidad e interacciones medicamentosas. El mecanismo de producción es variado y no siempre bien conocido. El conocimiento de los efectos adversos con relevancia clínica puede permitir hacer un uso más juicioso de los antibióticos basados en el principio primero no hacer daño, primun non nocere. En esta revisión exploramos los principales efectos adversos de los antibióticos orales con énfasis en los β-lactámicos, macrólidos y fluoroquinolonas.

A Review: Effects of Macrolides on CYP450 Enzymes

As a kind of haemoglobin, cytochrome P450 enzymes (CYP450) participate in the metabolism of many substances, including endogenous substances, exogenous substances and drugs. It is estimated that 60% of common prescription drugs require bioconversion through CYP450. The influence of macrolides on CYP450 contributes to the metabolism and drug-drug interactions (DDIs) of macrolides. At present, most studies on the effects of macrolides on CYP450 are focused on CYP3A, but a few exist on other enzymes and drug combinations, such as telithromycin, which can decrease the activity of hepatic CYP1A2 and CYP3A2. This article summarizes some published applications of the influence of macrolides on CYP450 and the DDIs of macrolides caused by CYP450. And the article may subsequently guide the rational use of drugs in clinical trials. To a certain extent, poisoning caused by adverse drug interactions can be avoided. Unreasonable use of macrolide antibiotics may enable the presence of residue of macrolide antibiotics in animal-origin food. It is unhealthy for people to eat food with macrolide antibiotic residues. So it is of great significance to guarantee food safety and protect the health of consumers by the rational use of macrolides. This review gives a detailed description of the influence of macrolides on CYP450 and the DDIs of macrolides caused by CYP450. Moreover, it offers a perspective for researchers to further explore in this area.

Effects of rifampicin on plasma pharmacokinetics of tulathromycin in goats

We investigated the pharmacokinetic profile of co-administration of tulathromycin with rifampicin. Healthy male goats were allocated to three groups (n = 8) as Group A (single dose 2.5 mg/kg tulathromycin s.c.), B (10 mg kg^-1  day^-1 rifampicin p.o. daily for 7 days and single dose 2.5 mg/kg tulathromycin s.c. on 8th day), and C (10 mg kg^-1  day^-1 rifampicin p.o. daily for 21 days and single dose 2.5 mg/kg tulathromycin s.c. on 8th day). Blood samples were collected from jugular veins. Plasma samples were analyzed for tulathromycin by liquid chromatography-mass spectrometry (LC-MS/MS). Peak plasma concentration (C_max ) values of tulathromycin were 1,390 ± 173, 958 ± 106, and 807 ± 116 ng/ml in groups A, B, and C, respectively. C_max value of group A was greater than other groups (p < .05). Mean residence time based on time zero to last sample time (MRT_last ) values were 52 ± 1, 56 ± 4 and 66 ± 4 hr in A, B, and C groups, respectively whereas mean residence time based on time zero extrapolated to infinity (MRT_{INF_obs} ) values were 69 ± 4, 85 ± 5, and 86 ± 4 hr, respectively. MRT_last and MRT_{INF_obs} values were greater in B and C groups than group A (p < .05). These findings suggest that rifampicin administration may change several pharmacokinetic parameters of tulathromycin in goats.

Guidelines for Monitoring and Management of Pediatric Patients Before, During, and After Sedation for Diagnostic and Therapeutic Procedures

The safe sedation of children for procedures requires a systematic approach that includes the following: no administration of sedating medication without the safety net of medical/dental supervision, careful presedation evaluation for underlying medical or surgical conditions that would place the child at increased risk from sedating medications, appropriate fasting for elective procedures and a balance between the depth of sedation and risk for those who are unable to fast because of the urgent nature of the procedure, a focused airway examination for large (kissing) tonsils or anatomic airway abnormalities that might increase the potential for airway obstruction, a clear understanding of the medication's pharmacokinetic and pharmacodynamic effects and drug interactions, appropriate training and skills in airway management to allow rescue of the patient, age- and size-appropriate equipment for airway management and venous access, appropriate medications and reversal agents, sufficient numbers of appropriately trained staff to both carry out the procedure and monitor the patient, appropriate physiologic monitoring during and after the procedure, a properly equipped and staffed recovery area, recovery to the presedation level of consciousness before discharge from medical/dental supervision, and appropriate discharge instructions. This report was developed through a collaborative effort of the American Academy of Pediatrics and the American Academy of Pediatric Dentistry to offer pediatric providers updated information and guidance in delivering safe sedation to children.

Guidelines for Monitoring and Management of Pediatric Patients Before, During, and After Sedation for Diagnostic and Therapeutic Procedures: Update 2016

The safe sedation of children for procedures requires a systematic approach that includes the following: no administration of sedating medication without the safety net of medical/dental supervision, careful presedation evaluation for underlying medical or surgical conditions that would place the child at increased risk from sedating medications, appropriate fasting for elective procedures and a balance between the depth of sedation and risk for those who are unable to fast because of the urgent nature of the procedure, a focused airway examination for large (kissing) tonsils or anatomic airway abnormalities that might increase the potential for airway obstruction, a clear understanding of the medication's pharmacokinetic and pharmacodynamic effects and drug interactions, appropriate training and skills in airway management to allow rescue of the patient, age- and size-appropriate equipment for airway management and venous access, appropriate medications and reversal agents, sufficient numbers of staff to both carry out the procedure and monitor the patient, appropriate physiologic monitoring during and after the procedure, a properly equipped and staffed recovery area, recovery to the presedation level of consciousness before discharge from medical/dental supervision, and appropriate discharge instructions. This report was developed through a collaborative effort of the American Academy of Pediatrics and the American Academy of Pediatric Dentistry to offer pediatric providers updated information and guidance in delivering safe sedation to children.

The clinical significance of drug interactions between dermatological and psychoactive medications

Dermatological disease is commonly associated with psychological morbidity because of its visible nature. The burden of living with a chronic dermatological illness can contribute to the development of psychiatric illness and conversely, such conditions can result in the exacerbation of preexisting dermatological disease. It may also reduce a patient's compliance to treatment, result in loss to follow-up and a decreased level of functioning and quality of life. In dermatological patients who suffer from psychiatric symptoms, medical management used in their treatment may have significant interactions with systemic medications used to treat their dermatological condition. A well-known example of this is lithium's ability to exacerbate psoriasis. Such interactions can result in suboptimal treatment of their psychiatric and/or dermatological condition. The present paper aimed to review the literature for documented interactions and the level of clinical significance between dermatological and psychoactive medications. Such information is clinically relevant to the practicing dermatologist in order to minimize adverse effects and drug-drug interactions in dermatological patients.

Autophagy in blood cancers: biological role and therapeutic implications

Autophagy is a cell recycling process the molecular apparatus of which has been identified over the past decade. Autophagy allows cells to survive starvation and inhospitable conditions and plays a key role in numerous physiological functions, including hematopoiesis and immune responses. In hematologic malignancies, autophagy can either act as a chemo-resistance mechanism or have tumor suppressive functions, depending on the context. In addition, autophagy is involved in other important aspects of blood cancers as it promotes immune competence and anti-cancer immunity, and may even help enhance patient tolerance to standard treatments. Approaches exploiting autophagy, either to activate or inhibit it, could find broad application in hematologic malignancies and contribute to improved clinical outcomes. These aspects are discussed here together with a brief introduction to the molecular machinery of autophagy and to its role in blood cell physiology.

Infection and inflammation leading to clozapine toxicity and intensive care: a case series

OBJECTIVE

To describe 3 cases of clozapine toxicity associated with infectious and/or inflammatory processes.

CASE SUMMARIES

Three patients stable on clozapine therapy prior to a medical hospital admission developed clozapine toxicity. It was suspected that an acute infectious and/or inflammatory process in each patient was related to abrupt mental status changes, onset of sialorrhea, myoclonus, and/or need for ventilatory support. Investigations of altered mental status did not reveal alternative causes and presentations were not consistent with neuroleptic malignant syndrome, other acute neurologic complications, or psychiatric decompensation. All patients improved after clozapine dose reductions allowing for transfer from intensive care units. Using the Naranjo ADR Probability Scale for each case, a probable relation between clozapine toxicity and the infectious and/or inflammatory process was determined.

DISCUSSION

Clozapine toxicity may manifest with multiple symptoms, including sedation, sialorrhea, and hypotension. In addition to overdose and drug interactions; infection and/or inflammation may precipitate clozapine toxicity. This may be related to cytokine-mediated inhibition of cytochrome P450 1A2. The likelihood of toxicity via this mechanism has not been well characterized, thus careful monitoring is required for medically ill patients receiving clozapine. Clozapine is extensively bound to the acute phase reactant, α-1 acid glycoprotein, which may unpredictably protect against clinical toxicity. C-reactive protein has also been investigated to relate clozapine toxicity to infection and/or inflammation.

CONCLUSION

Clozapine toxicity developed in 3 patients admitted to a medical setting suspected to be related to infection and/or inflammation. Clinicians should be aware of this potential adverse drug event with clozapine.

Efficacy and safety of long-term antibiotics (macrolides) for the treatment of chronic rhinosinusitis

Long-term treatment of airway inflammation/infection with macrolide antibiotics has now been in use for almost 30 years. Whereas the beneficial clinical effect in cystic fibrosis and COPD have been backed up by randomized controlled trials, the evidence from the upper airways is not as strong. We have identified 22 open studies in chronic rhinosinusitis, with and without polyps, but only 2 randomized controlled trials. Of the controlled trials, the one including CRS patients just without polyps, showed a significant effect in sino-nasal outcome test, saccharine transit time, nasal endoscopy, and IL-8 levels in lavage fluid after 12 weeks of roxithromycin, whereas, in the other RCT with a mixed study group of CRS patients with and without polyps, 12 weeks of azithromycin showed no effect compared to placebo. Concerns regarding the risk of macrolides to induce arrhythmia have been raised. Recent FDA guidelines changes has recommended caution in patients with risk factors such as long QT syndrome, bradycardia, hypokalemia, or hypomagnesemia. Ototoxicity is another concern. Long-term macrolide antibiotics in the treatment of CRS patients is still a viable option in a select group of patients.

Psychotropic drug-drug interactions involving P-glycoprotein

Multidrug resistance P-glycoprotein (P-gp; also known as MDR1 and ABCB1) is expressed in the luminal membrane of the small intestine and blood-brain barrier, and the apical membranes of excretory cells such as hepatocytes and kidney proximal tubule epithelia. P-gp regulates the absorption and elimination of a wide range of compounds, such as digoxin, paclitaxel, HIV protease inhibitors and psychotropic drugs. Its substrate specificity is as broad as that of cytochrome P450 (CYP) 3A4, which encompasses up to 50 % of the currently marketed drugs. There has been considerable interest in variations in the ABCB1 gene as predictors of the pharmacokinetics and/or treatment outcomes of several drug classes, including antidepressants and antipsychotics. Moreover, P-gp-mediated transport activity is saturable, and is subject to modulation by inhibition and induction, which can affect the pharmacokinetics, efficacy or safety of P-gp substrates. In addition, many of the P-gp substrates overlap with CYP3A4 substrates, and several psychotropic drugs that are P-gp substrates are also CYP3A4 substrates. Therefore, psychotropic drugs that are P-gp substrates may cause a drug interaction when P-gp inhibitors and inducers are coadministered, or when psychotropic drugs or other medicines that are P-gp substrates are added to a prescription. Hence, it is clinically important to accumulate data about drug interactions through studies on P-gp, in addition to CYP3A4, to assist in the selection of appropriate psychotropic medications and in avoiding inappropriate combinations of therapeutic agents. There is currently insufficient information available on the psychotropic drug interactions related to P-gp, and therefore we summarize the recent clinical data in this review.

Macrolide therapy in chronic inflammatory diseases

Macrolides are a group of antibiotics with a distinctive macrocyclic lactone ring combined with sugars (cladinose, desosamine). The action of macrolides is to block protein synthesis by binding to the subunit of 50S ribosome of bacteria. Prototype macrolide was erythromycin, which came into clinical practice in the 50s of the 20th century. Its antimicrobial spectrum covers the scope of the penicillins but is extended to the impact of atypical bacteria. In the 90s more drugs of this group were synthesized—they have less severe side effects than erythromycin, extended spectrum of Gram-negative bacteria. Macrolides are effective in treating mycobacterial infections especially in patients infected with HIV. It is now known that in addition to antibacterial abilities, macrolides have immunomodulatory effects—they inhibit the production of proinflammatory cytokines (TNF, IL1, 6, and 8) affect transcription factors (NF-κB) as well as costimulaton (CD 80) and adhesion molecules (ICAM). This review article focused not only on the their antimicrobial abilities but also on efficacy in the treatment of several inflammatory disorders independent of the infectious agent. Their wider use as immunomodulators requires further study, which can lead to an extension of indications for their administration.

Effects of erythromycin on voriconazole pharmacokinetics and association with CYP2C19 polymorphism

PURPOSE

To assess the impacts of erythromycin on the pharmacokinetics of voriconazole and its association with CYP2C19 genotypes in healthy Chinese male subjects.

METHODS

A single-center, open, crossover clinical study with two treatment phases was carried out. Eighteen healthy male volunteers, including 6 CYP2C19 homozygous extensive metabolizers (EMs, *1/*1), 6 heterozygous EMs (HEMs, *1/*2 or *1/*3), and 6 CYP2C19 poor metabolizers (PMs, *2/*2 or *2/*3), were enrolled in this study. A single oral dose of 200 mg voriconazole was administrated to all subjects after 3-day pretreatment with either 500 mg erythromycin or placebo three times daily. Periods were separated by a washout period of 14 days. Serial venous blood samples were collected, and plasma concentrations of voriconazole were determined by HPLC.

RESULTS

C(max), AUC(0-24), and AUC(0-infinity) of voriconazole were increased significantly, while oral clearance of voriconazole was decreased significantly by erythromycin administration (p < 0.001, respectively). Compared with individuals with CYP2C19 PM genotypes, individuals with CYP2C19 EM and HEM genotypes showed significantly decreased T(½), AUC(0-24), AUC(0-infinity), and increased oral clearance of voriconazole (p < 0.05, respectively). In addition, significant increases in AUC(0-24) and AUC(0-infinity) and decreases in oral clearance of voriconazole after erythromycin treatment were observed in CYP2C19 HEMs and PMs (p < 0.05, respectively), but not in CYP2C19 EMs.

CONCLUSION

Both CYP2C19 genotypes and CYP3A4 inhibitor erythromycin can influence the plasma concentration of voriconazole, and erythromycin increases plasma concentration of voriconazole in a CYP2C19 genotype-dependent manner.

Systemic sclerosis and bilateral lung transplantation: a single centre experience

Lung involvement is the leading cause of death in systemic sclerosis (SSc), but lung transplantation (LT) for systemic disease remains controversial. Our objective was to comprehensively evaluate post-LT outcomes for SSc compared to idiopathic pulmonary fibrosis (IPF). We retrospectively evaluated bilateral LT recipients (LTRs) with SSc or IPF at our centre between January 1, 2003 and December 31, 2007. The primary end-point was all-cause mortality at 1 yr post-LT. Secondary end-points included assessments of acute rejection (AR), pulmonary function, infection and chronic rejection. 14 patients with SSc and 38 patients with IPF underwent LT. Apart from a younger SSc cohort (53.2 versus 58.8 yrs; p = 0.02), the two groups were well matched. 1-yr all-cause mortality was no different between SSc (6.6%) and IPF (13.1%) groups, after adjusting for age (p = 0.62). Rates of (AR) ≥2 were significantly increased for the SSc compared with the IPF group (hazard ratio (HR) 2.91; p = 0.007). Other end-points, including chronic rejection, infection and pulmonary function, showed no differences. SSc LTRs experience similar survival 1 yr post-LT when compared to IPF. AR rates may be significantly higher in the SSc group. Longer follow-up is necessary to determine the effects of gastrointestinal dysfunction and AR on late allograft function in SSc LTR.

Synthesis and evaluation of inhibitors of cytochrome P450 3A (CYP3A) for pharmacokinetic enhancement of drugs

The HIV protease inhibitor ritonavir (RTV) is also a potent inhibitor of the metabolizing enzyme cytochrome P450 3A (CYP3A) and is clinically useful in HIV therapy in its ability to enhance human plasma levels of other HIV protease inhibitors (PIs). A novel series of CYP3A inhibitors was designed around the structural elements of RTV believed to be important to CYP3A inhibition, with general design features being the attachment of groups that mimic the P2-P3 segment of RTV to a soluble core. Several analogs were found to strongly enhance plasma levels of lopinavir (LPV), including 8, which compares favorably with RTV in the same model. Interestingly, an inverse correlation between in vitro inhibition of CYP3A and elevation of LPV was observed. The compounds described in this study may be useful for enhancing the pharmacokinetics of drugs that are metabolized by CYP3A.

Short-term clarithromycin administration impairs clearance and enhances pharmacodynamic effects of trazodone but not of zolpidem

The kinetic and dynamic interactions of 5 mg zolpidem and 50 mg trazodone with 500 mg clarithromycin (4 doses given over 32 h) were investigated in a 5-way double crossover study with 10 healthy volunteers. The five treatment conditions were: placebo + placebo; zolpidem + placebo; zolpidem + clarithromycin; trazodone + placebo; and trazodone + clarithromycin. Coadministration of clarithromycin increased trazodone area under the curve, prolonged elimination half-life, increased peak plasma concentration (C(max)), and reduced oral clearance. In contrast, clarithromycin had no significant effect on any kinetic parameter for zolpidem. Clarithromycin did not potentiate sedation caused by zolpidem. However, clarithromycin coadministered with trazodone significantly increased self- and observer-rated sedation and ratings of feeling "spacey." Thus, short-term clarithromycin coadministration significantly impairs trazodone clearance, elevates plasma concentrations, and enhances sedative effects. However, clarithromycin has no significant kinetic or dynamic interaction with zolpidem.

Risk management of simvastatin or atorvastatin interactions with CYP3A4 inhibitors

BACKGROUND

Co-administration of cytochrome P450 (CYP) 3A4 inhibitors with simvastatin or atorvastatin is associated with increased risk of developing myopathy or rhabdomyolysis.

OBJECTIVE

To detect co-prescriptions of CYP3A4 inhibitors with simvastatin or atorvastatin in community pharmacies and assess the risk-preventive actions taken by the prescribing physicians who were alerted about the co-prescription by the pharmacist.

METHODS

This naturalistic study was performed during four separate 6-week periods in 2004 and 2005, and involved 110 Norwegian community pharmacists (25-30 in each period). Co-prescription of the selected CYP3A4 inhibitors diltiazem, verapamil, clarithromycin, erythromycin, fluconazole, itraconazole and ketoconazole with either simvastatin or atorvastatin was detected with the aid of a simple computer programme. In instances where the pharmacist alerted the prescribing physician about the co-prescription, information on possible strategies to minimize the risk associated with the interaction was also provided. Odds ratios (ORs) were estimated to describe the associations between prescription variables and frequencies of physician information and prescription change, respectively.

RESULTS

In total, 245 co-prescriptions of CYP3A4 inhibitors with simvastatin (134 events) or atorvastatin (111) were detected. Diltiazem (86 events), verapamil (72), erythromycin (48) and clarithromycin (29) were the most commonly co-prescribed CYP3A4 inhibitors. Physicians were informed in 168 out of 245 cases (68.6%). The prescription was subsequently changed in 100 out of 168 cases (59.5%). Another 50 physicians (29.8%) responded that they would consult the patient and monitor potential adverse effects, while only 18 physicians (10.7%) replied that they had already managed the interactions or considered the issue as irrelevant. The adjusted OR for the informing of the physician was 1.89 (95% CI 0.98, 3.63) in patients receiving a daily HMG-CoA reductase inhibitor ('statin') dose of >or=40 mg compared with patients receiving a statin dose of <40 mg/day. The adjusted OR for prescription change was 4.98 (95% CI 2.36, 10.52) if co-prescription was detected prior to the initiation of concurrent use compared with if it was detected during concurrent use.

CONCLUSION

Nine out of ten physicians changed prescriptions or monitored potential adverse effects when informed by community pharmacists about the risk associated with co-prescription of CYP3A4 inhibitors with simvastatin or atorvastatin. This suggests that an important risk factor for myotoxicity due to these statins could be minimized through interdisciplinary co-operation.

Role of cytochrome P450 in drug interactions

Drug-drug interactions have become an important issue in health care. It is now realized that many drug-drug interactions can be explained by alterations in the metabolic enzymes that are present in the liver and other extra-hepatic tissues. Many of the major pharmacokinetic interactions between drugs are due to hepatic cytochrome P450 (P450 or CYP) enzymes being affected by previous administration of other drugs. After coadministration, some drugs act as potent enzyme inducers, whereas others are inhibitors. However, reports of enzyme inhibition are very much more common. Understanding these mechanisms of enzyme inhibition or induction is extremely important in order to give appropriate multiple-drug therapies. In future, it may help to identify individuals at greatest risk of drug interactions and adverse events.

Toxicological Significance of Mechanism-Based Inactivation of Cytochrome P450 Enzymes by Drugs

Cytochrome P450 (P450) enzymes oxidize xenobiotics into chemically reactive metabolites or intermediates as well as into stable metabolites. If the reactivity of the product is very high, it binds to a catalytic site or sites of the enzyme itself and inactivates it. This phenomenon is referred to as mechanism-based inactivation. Many clinically important drugs are mechanism-based inactivators that include macrolide antibiotics, calcium channel blockers, and selective serotonin uptake inhibitors, but are not always structurally and pharmacologically related. The inactivation of P450s during drug therapy results in serious drug interactions, since irreversibility of the binding allows enzyme inhibition to be prolonged after elimination of the causal drug. The inhibition of the metabolism of drugs with narrow therapeutic indexes, such as terfenadine and astemizole, leads to toxicities. On the other hand, the fate of P450s after the inactivation and the toxicological consequences remains to be elucidated, while it has been suggested that P450s modified and degraded are involved in some forms of tissue toxicity. Porphyrinogenic drugs, such as griseofulvin, cause mechanism-based heme inactivation, leading to formation of ferrochelatase-inhibitory N-alkylated protoporphyrins and resulting in porphyria. Involvement of P450-derived free heme in halothane-induced hepatotoxicity and catalytic iron in cisplatin-induced nephrotoxicity has also been suggested. Autoantibodies against P450s have been found in hepatitis following administration of tienilic acid and dihydralazine. Tienilic acid is activated by and covalently bound to CYP2C9, and the neoantigens thus formed activate immune systems, resulting in the formation of an autoantibodydirected against CYP2C9, named anti-liver/kidney microsomal autoantibody type 2, whereas the pathological role of the autoantibodies in drug-induced hepatitis remains largely unknown.

Rational prescription of drugs within similar therapeutic or structural class for gastrointestinal disease treatment: Drug metabolism and its related interactions

AIM: To review and summarize drug metabolism and its related interactions in prescribing drugs within the similar therapeutic or structural class for gastrointestinal disease treatment so as to promote rational use of medicines in clinical practice.

METHODS: Relevant literature was identified by performing MEDLINE/Pubmed searches covering the period from 1988 to 2006.

RESULTS: Seven classes of drugs were chosen, including gastric proton pump inhibitors, histamine H₂-receptor antagonists, benzamide-type gastroprokinetic agents, selective 5-HT₃ receptor antagonists, fluoroquinolones, macrolide antibiotics and azole antifungals. They showed significant differences in metabolic profile (i.e., the fraction of drug metabolized by cytochrome P450 (CYP), CYP reaction phenotype, impact of CYP genotype on interindividual pharmacokinetics variability and CYP-mediated drug-drug interaction potential). Many events of severe adverse drug reactions and treatment failures were closely related to the ignorance of the above issues.

CONCLUSION: Clinicians should acquaint themselves with what kind of drug has less interpatient variability in clearance and whether to perform CYP genotyping prior to initiation of therapy. The relevant CYP knowledge helps clinicians to enhance the management of patients with gastrointestinal disease who may require treatment with polytherapeutic regimens.

Treatment and dosing of Helicobacter pylori infection: when pharmacology meets clinic

Helicobacter pylori infection is a major cause of diseases located in the upper gastrointestinal tract. Successful eradication of the bacteria may improve H. pylori-related symptomatic complaints in functional dyspepsia, cure peptic ulcer disease and prevent gastric cancer. As vaccines are not available, the search for the optimal drug regimen has dominated the last decade. Today, most countries prefer a 7- to 10-day regimen containing a proton pump inhibitor, clarithromycin and amoxicillin as first-line treatment. An alternative (or second-line) treatment contains a proton pump inhibitor, bismuth, tetracycline and metronidazole. This review also highlights the impact of new drugs, new drug combinations, and their optimal dosing required to maximise clinical outcome.

Macrolides inhibit IL17-induced IL8 and 8-isoprostane release from human airway smooth muscle cells

Lung transplantation is hampered by bronchiolitis obliterans syndrome (BOS), although recently azithromycin treatment has a published response rate of about 42% in patients with established BOS. We linked this improvement to a reduction in airway neutrophilia and IL8. In the present study, we further investigated the intracellular mechanisms of azithromycin, looking at the possible involvement of mitogen-activated-protein kinases (MAPK) and oxidative stress. Simultaneously, currently used immunosuppressive agents were investigated. Human primary airway smooth muscle cells were stimulated with IL17 and incubated with increasing concentrations of steroids, immunosuppressive agents (tacrolimus, cyclosporine and rapamycin) or macrolides (erythromycin and azithromycin). We measured supernatant IL8 protein, 8-isoprostane and cell lysate MAPK. IL17-induced IL8 production was decreased by both erythromycin and azithromycin. In nonstimulated condition, IL8 production only increased at the highest dose of azithromycin. Dexamethasone failed to attenuate IL8 production, whereas immunosuppressive agents significantly increased IL8 production in both IL17-stimulated and nonstimulated conditions. 8-isoprostane production and MAPK activation proved to be decreased by the macrolides. We conclude that macrolides (but not steroids/immunosuppressive agents) inhibit IL17-induced IL8 production in human primary airway smooth muscle cells via a reduction in MAPK activation and 8-isoprostane production. In BOS patients, these phenomena may explain the anti-inflammatory effects of azithromycin.

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.

Guidelines for monitoring and management of pediatric patients during and after sedation for diagnostic and therapeutic procedures: an update

The safe sedation of children for procedures requires a systematic approach that includes the following: no administration of sedating medication without the safety net of medical supervision; careful presedation evaluation for underlying medical or surgical conditions that would place the child at increased risk from sedating medications; appropriate fasting for elective procedures and a balance between depth of sedation and risk for those who are unable to fast because of the urgent nature of the procedure; a focused airway examination for large tonsils or anatomic airway abnormalities that might increase the potential for airway obstruction; a clear understanding of the pharmacokinetic and pharmacodynamic effects of the medications used for sedation, as well as an appreciation for drug interactions; appropriate training and skills in airway management to allow rescue of the patient; age- and size-appropriate equipment for airway management and venous access; appropriate medications and reversal agents; sufficient numbers of people to carry out the procedure and monitor the patient; appropriate physiologic monitoring during and after the procedure; a properly equipped and staffed recovery area; recovery to presedation level of consciousness before discharge from medical supervision; and appropriate discharge instructions. This report was developed through a collaborative effort of the American Academy of Pediatrics and the American Academy of Pediatric Dentistry to offer pediatric providers updated information and guidance in delivering safe sedation to children.

Clinically relevant drug interactions with antiepileptic drugs

Some patients with difficult-to-treat epilepsy benefit from combination therapy with two or more antiepileptic drugs (AEDs). Additionally, virtually all epilepsy patients will receive, at some time in their lives, other medications for the management of associated conditions. In these situations, clinically important drug interactions may occur. Carbamazepine, phenytoin, phenobarbital and primidone induce many cytochrome P450 (CYP) and glucuronyl transferase (GT) enzymes, and can reduce drastically the serum concentration of associated drugs which are substrates of the same enzymes. Examples of agents whose serum levels are decreased markedly by enzyme-inducing AEDs, include lamotrigine, tiagabine, several steroidal drugs, cyclosporin A, oral anticoagulants and many cardiovascular, antineoplastic and psychotropic drugs. Valproic acid is not enzyme inducer, but it may cause clinically relevant drug interactions by inhibiting the metabolism of selected substrates, most notably phenobarbital and lamotrigine. Compared with older generation agents, most of the recently developed AEDs are less likely to induce or inhibit the activity of CYP or GT enzymes. However, they may be a target for metabolically mediated drug interactions, and oxcarbazepine, lamotrigine, felbamate and, at high dosages, topiramate may stimulate the metabolism of oral contraceptive steroids. Levetiracetam, gabapentin and pregabalin have not been reported to cause or be a target for clinically relevant pharmacokinetic drug interactions. Pharmacodynamic interactions involving AEDs have not been well characterized, but their understanding is important for a more rational approach to combination therapy. In particular, neurotoxic effects appear to be more likely with coprescription of AEDs sharing the same primary mechanism of action.

Drug interactions during therapy with three major groups of antimicrobial agents

This review focuses on drug-drug interactions with three major groups of antimicrobial agents: macrolides (including azalides and ketolides), quinolones, which are widely used for the treatment of bacterial infections, and azoles, which are used for antifungal therapy. Macrolides and the ketolide telithromycin are potent inhibitors of CYP3A4 and thus interfere with the pharmacokinetics of many other drugs that are metabolised by this enzyme. In contrast, although closely related, azithromycin is not a cytochrome inhibitor. All quinolones form complexes with di- and trivalent cations and, therefore, the absorption of quinolones can be dramatically reduced when given concomitantly with mineral antacids, zinc or iron preparations. Ciprofloxacin exhibits an inhibitory potential for the cytochrome isoenzyme 1A2, resulting in an inhibition of theophylline metabolism. Other quinolones, such as levofloxacin or moxifloxacin, do not interfere with theophylline metabolism. The systemic azoles, such as ketoconazole, itraconazole, fluconazole and voriconazole, are inhibitors of CYP isoenzymes, such as CYP3A4, CYP2C9 and CYP2C19, to varying degrees. In addition, some are substrates of the MDR-1 gene product, P-glycoprotein. These features are the basis for most of the interactions occurring during azole therapy (e.g., in severely ill patients in the hospital who are treated with multiple drugs).

Macrolides in cystic fibrosis

Macrolide antibiotics have been licensed since the 1950s and have an important role in the treatment of a diverse range of infectious diseases. Macrolide antibiotics have antibacterial activity against gram-positive bacteria, some gram-negative bacteria and intracellular pathogens. The spectrum of antibacterial activity combined with excellent intracellular and tissue penetration has led to the extensive use of this class of drugs in respiratory disease. Macrolide antibiotics also have demonstrated anti-inflammatory properties in various in vitro and in vivo model systems. Novel antimicrobial and anti-inflammatory properties of macrolide may result in clinical benefits, particularly in conditions where the infectious agent is inherently resistant to macrolides. Three randomized control trials have demonstrated improved lung function in patients treated with the macrolide antibiotic, azithromycin. Azithromycin was generally well tolerated and resulted in reduction in the inflammatory response which may be due to an immunomodulatory role. Short term studies (three to six months) have not demonstrated the development of increased bacterial resistance or the emergence of new pathogens following azithromycin.

Mechanism-based inhibition of cytochrome P450 3A4 by therapeutic drugs

Consistent with its highest abundance in humans, cytochrome P450 (CYP) 3A is responsible for the metabolism of about 60% of currently known drugs. However, this unusual low substrate specificity also makes CYP3A4 susceptible to reversible or irreversible inhibition by a variety of drugs. Mechanism-based inhibition of CYP3A4 is characterised by nicotinamide adenine dinucleotide phosphate hydrogen (NADPH)-, time- and concentration-dependent enzyme inactivation, occurring when some drugs are converted by CYP isoenzymes to reactive metabolites capable of irreversibly binding covalently to CYP3A4. Approaches using in vitro, in silico and in vivo models can be used to study CYP3A4 inactivation by drugs. Human liver microsomes are always used to estimate inactivation kinetic parameters including the concentration required for half-maximal inactivation (K(I)) and the maximal rate of inactivation at saturation (k(inact)). Clinically important mechanism-based CYP3A4 inhibitors include antibacterials (e.g. clarithromycin, erythromycin and isoniazid), anticancer agents (e.g. tamoxifen and irinotecan), anti-HIV agents (e.g. ritonavir and delavirdine), antihypertensives (e.g. dihydralazine, verapamil and diltiazem), sex steroids and their receptor modulators (e.g. gestodene and raloxifene), and several herbal constituents (e.g. bergamottin and glabridin). Drugs inactivating CYP3A4 often possess several common moieties such as a tertiary amine function, furan ring, and acetylene function. It appears that the chemical properties of a drug critical to CYP3A4 inactivation include formation of reactive metabolites by CYP isoenzymes, preponderance of CYP inducers and P-glycoprotein (P-gp) substrate, and occurrence of clinically significant pharmacokinetic interactions with coadministered drugs. Compared with reversible inhibition of CYP3A4, mechanism-based inhibition of CYP3A4 more frequently cause pharmacokinetic-pharmacodynamic drug-drug interactions, as the inactivated CYP3A4 has to be replaced by newly synthesised CYP3A4 protein. The resultant drug interactions may lead to adverse drug effects, including some fatal events. For example, when aforementioned CYP3A4 inhibitors are coadministered with terfenadine, cisapride or astemizole (all CYP3A4 substrates), torsades de pointes (a life-threatening ventricular arrhythmia associated with QT prolongation) may occur.However, predicting drug-drug interactions involving CYP3A4 inactivation is difficult, since the clinical outcomes depend on a number of factors that are associated with drugs and patients. The apparent pharmacokinetic effect of a mechanism-based inhibitor of CYP3A4 would be a function of its K(I), k(inact) and partition ratio and the zero-order synthesis rate of new or replacement enzyme. The inactivators for CYP3A4 can be inducers and P-gp substrates/inhibitors, confounding in vitro-in vivo extrapolation. The clinical significance of CYP3A inhibition for drug safety and efficacy warrants closer understanding of the mechanisms for each inhibitor. Furthermore, such inactivation may be exploited for therapeutic gain in certain circumstances.

Drug bioactivation, covalent binding to target proteins and toxicity relevance

A number of therapeutic drugs with different structures and mechanisms of action have been reported to undergo metabolic activation by Phase I or Phase II drug-metabolizing enzymes. The bioactivation gives rise to reactive metabolites/intermediates, which readily confer covalent binding to various target proteins by nucleophilic substitution and/or Schiff's base mechanism. These drugs include analgesics (e.g., acetaminophen), antibacterial agents (e.g., sulfonamides and macrolide antibiotics), anticancer drugs (e.g., irinotecan), antiepileptic drugs (e.g., carbamazepine), anti-HIV agents (e.g., ritonavir), antipsychotics (e.g., clozapine), cardiovascular drugs (e.g., procainamide and hydralazine), immunosupressants (e.g., cyclosporine A), inhalational anesthetics (e.g., halothane), nonsteroidal anti-inflammatory drugs (NSAIDSs) (e.g., diclofenac), and steroids and their receptor modulators (e.g., estrogens and tamoxifen). Some herbal and dietary constituents are also bioactivated to reactive metabolites capable of binding covalently and inactivating cytochrome P450s (CYPs). A number of important target proteins of drugs have been identified by mass spectrometric techniques and proteomic approaches. The covalent binding and formation of drug-protein adducts are generally considered to be related to drug toxicity, and selective protein covalent binding by drug metabolites may lead to selective organ toxicity. However, the mechanisms involved in the protein adduct-induced toxicity are largely undefined, although it has been suggested that drug-protein adducts may cause toxicity either through impairing physiological functions of the modified proteins or through immune-mediated mechanisms. In addition, mechanism-based inhibition of CYPs may result in toxic drug-drug interactions. The clinical consequences of drug bioactivation and covalent binding to proteins are unpredictable, depending on many factors that are associated with the administered drugs and patients. Further studies using proteomic and genomic approaches with high throughput capacity are needed to identify the protein targets of reactive drug metabolites, and to elucidate the structure-activity relationships of drug's covalent binding to proteins and their clinical outcomes.

Possible involvement of organic anion transporter 2 on the interaction of theophylline with erythromycin in the human liver

Organic anion transporter 2 (Oat2 [SLC22A7]) is a multispecific organic anion transporter. Although several substrates of human Oat2 (hOat2) have been elucidated, a possible involvement of hOat2 in drug interaction is less defined. The purpose of this study was to investigate the interaction of theophylline with erythromycin mediated by hOat2 using a Xenopus laevis oocyte expression system. When expressed in Xenopus oocytes, hOat2 mediated the transport of theophylline and erythromycin. The finding indicates that the two compounds are novel substrates for hOat2. The apparent K(m) values for the uptake of hOat2 that mediated the transport of theophylline and erythromycin were 12.6 muM and 18.5 muM, respectively. The hOat2-mediated uptake of [(14)C]theophylline and [(14)C]erythromycin was cis-inhibited by adding erythromycin and theophylline, respectively. Our present findings suggest that hOat2 may, at least in part, be involved in the theophylline-erythromycin interaction in the human liver.

Ketolides: an emerging treatment for macrolide-resistant respiratory infections, focusing on S. pneumoniae

Resistance to antibiotics in community acquired respiratory infections is increasing worldwide. Resistance to the macrolides can be class-specific, as in efflux or ribosomal mutations, or, in the case of erythromycin ribosomal methylase (erm)-mediated resistance, may generate cross-resistance to other related classes. The ketolides are a new subclass of macrolides specifically designed to combat macrolide-resistant respiratory pathogens. X-ray crystallography indicates that ketolides bind to a secondary region in domain II of the 23S rRNA subunit, resulting in an improved structure-activity relationship. Telithromycin and cethromycin (formerly ABT-773) are the two most clinically advanced ketolides, exhibiting greater activity towards both typical and atypical respiratory pathogens. As a subclass of macrolides, ketolides demonstrate potent activity against most macrolide-resistant streptococci, including ermB- and macrolide efflux (mef)A-positive Streptococcus pneumoniae. Their pharmacokinetics display a long half-life as well as extensive tissue distribution and uptake into respiratory tissues and fluids, allowing for once-daily dosing. Clinical trials focusing on respiratory infections indicate bacteriological and clinical cure rates similar to comparators, even in patients infected with macrolide-resistant strains.

Macrolide and occult infection in asthma

PURPOSE OF REVIEW

A small percentage of asthma exacerbations are linked with infection by an atypical bacterium, such as Chlamydia pneumoniae or Mycoplasma pneumoniae. These bacteria also have been proposed to cause occult chronic lower airway inflammation and to initiate nonatopic asthma in adults. Consequently, the logical procedure would be to eliminate these pathogens as soon and as thoroughly as possible using antibiotics. Nonetheless, antibiotics are not recommended even for the treatment of acute asthma exacerbations except as needed for comorbid conditions. These discrepancies highlight the need to define the role, if any, of antimicrobials that are active against atypical pathogens, mainly macrolides, but also tetracyclines and fluoroquinolones, in the treatment of asthma.

RECENT FINDINGS

Macrolides are antibiotics with both antimicrobial and antiinflammatory activities. Some studies have documented that these agents could be useful in the treatment of occult infection in asthma because of their antimicrobial activity against atypical pathogens. They could also lead to reduction of the airways inflammation by decreasing the transcription of mRNA for a variety of cytokines and inhibiting interleukin-8 release by eosinophils, and therefore improvement of symptoms and pulmonary function. These effects are not caused by bronchodilation, elevation of serum theophylline level, or steroid-sparing mechanism.

SUMMARY

The available clinical evidence seems to support use of macrolides in the treatment of asthma because of their antimicrobial activity. However, studies that may confirm this hypothesis are scarce and with limited scientific value because of their open, uncontrolled design.

No clinically significant effect of erythromycin or azithromycin on the pharmacokinetics of voriconazole in healthy male volunteers

AIMS

The antibiotic erythromycin is a potent inhibitor of cytochrome P450 CYP3A4 metabolism. As CYP isozymes, including CYP3A4, are involved in the metabolism of the new triazole voriconazole, this study investigated the effects of multiple-dose erythromycin or azithromycin on the steady-state pharmacokinetics of voriconazole in healthy male subjects.

METHODS

In an open, randomized, parallel-group, single-centre study, 30 healthy male subjects aged 20-41 years received oral voriconazole 200 mg twice daily for 14 days plus either erythromycin (1 g twice daily on days 8-14), azithromycin (500 mg once daily on days 12-14) or placebo (twice daily on days 8-14). Only morning doses were administered on day 14. Plasma concentrations of voriconazole were measured up to 12 h postdose on days 7 and 14, and plasma pharmacokinetic parameters were calculated. Adverse events and standard laboratory test results were recorded before and throughout the study.

RESULTS

Comparison of the voriconazole Cmax day 14/day 7 ratio for the voriconazole + erythromycin group with that of the voriconazole + placebo group yielded a ratio of 107.7%[90% confidence interval (CI) 90.6, 128.0]; for the voriconazole + azithromycin group, the ratio was 117.5% (90% CI 98.8, 139.7). Comparison of the voriconazole AUCtau day 14/day 7 ratios of the voriconazole + erythromycin and voriconazole + azithromycin groups with that of the voriconazole + placebo group showed ratios of 101.2% (90% CI 89.1, 114.8) and 107.9% (90% CI 95.1, 122.4), respectively. For voriconazole tmax, the differences between the day 14-day 7 calculations for the voriconazole + erythromycin or the voriconazole + azithromycin groups and that of the voriconazole + placebo group were - 0.2 h (90% CI - 0.8, 0.3) and - 0.1 h (90% CI - 0.7, 0.5), respectively. None of these changes was considered clinically relevant. The study drugs were well tolerated by subjects in all groups; the most common study drug-related adverse events were visual disturbances, reported in all groups, and abdominal pain, present in the voriconazole + erythromycin group.

CONCLUSIONS

Coadministration of erythromycin or azithromycin does not affect the steady-state pharmacokinetics of voriconazole in a clinically relevant manner in healthy male subjects.

A guide to selection and appropriate use of macrolides in skin infections

Dermatologists must be aware of the adverse effects of antimicrobial agents as well as various drug interactions that may influence the choice of drug as well as specific drug schedules. The development of modern antibacterials has improved the treatment of cutaneous bacterial infections. Macrolide antibacterials continue to be an important therapeutic class of drugs with established efficacy in a variety of skin infections. All macrolides inhibit protein synthesis by reversibly binding to the 23S ribosomal RNA in the 50S-subunit. Erythromycin, the prototype of macrolide antibacterials, was isolated from the metabolic products of a strain of Streptomyces erytherus in 1952. Originally, erythromycin was introduced as an alternative to penicillin because of its activity against the Gram-positive organisms. Numerous studies have demonstrated the efficacy and safety of erythromycin for various infectious diseases. Unfortunately, erythromycin is associated with a number of drawbacks including a narrow spectrum of activity, unfavorable pharmacokinetic properties, poor gastrointestinal tolerability, and a significant number of drug-drug interactions. Newer macrolides have been developed to address these limitations. The pharmacokinetics of azithromycin and clarithromycin allow for shorter dosing schedules because of prolonged tissue levels. The efficacy of azithromycin for the treatment of skin and soft tissue infections in adults and children is well established. The unique pharmakinetics of azithromycin makes it a suitable agent for the treatment of acne. Clarithromycin represents a clear advance in the macrolide management of patients with leprosy and skin infections with atypical mycobacteria. Dirithromycin and roxithromycin display no clinical or bacteriological adcantage over erythromycin despite a superior pharmacokinetic profile. An area of concern is the increasing macrolide resistance that is being reported with some of the common pathogens which may limit the clinical usefulness of this class of antimicrobial agents in future.

Differential pharmacokinetics of theophylline in elderly patients

The clinical use of theophylline as a first-line bronchodilator has declined during the last two decades. However, in many clinical settings, such as an emergency bronchial asthma attack, theophylline may have a first-line role, in combination with beta(2)-adrenoreceptor agonists and corticosteroids, for improving the asthmatic status. Furthermore, many therapeutic mechanisms of theophylline for bronchial asthma have been reported, and recent studies have suggested that theophylline therapy may have a beneficial role in the management of chronic stable asthma as well as exacerbated disease. However, theophylline has a low therapeutic index because the bronchodilation it produces has a linear relationship with logarithmic increases in serum concentration for the therapeutic range of 5-20 mg/L. Thus, the knowledge of its basic pharmacokinetics and the factors that can alter its clearance is clinically relevant for physicians. Especially when used in elderly asthmatic patients, dosage adjustment of theophylline is a requisite since the elderly have several risk factors that may increase the plasma theophylline level, such as reduced clearance, various underlying diseases and multiple coadministered drugs. After theophylline treatment has been initiated, therapeutic drug monitoring is required.

The effect of erythromycin on the pharmacokinetics of rosuvastatin

RATIONALE OBJECTIVE

To examine in vivo the effect of erythromycin on the pharmacokinetics of rosuvastatin [an inhibitor of 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase]. Erythromycin is a potent inhibitor of CYP3A4 that markedly increases circulating levels of some other HMG-CoA reductase inhibitors.

METHODS

In this randomised, double-blind, two-way cross-over, placebo-controlled trial 14 healthy volunteers were given 500 mg erythromycin or placebo four times daily for 7 days. A single dose of 80 mg rosuvastatin was co-administered on day 4 of dosing. Plasma concentrations of rosuvastatin and active and total HMG-CoA reductase inhibitors were measured up to 96 h after dosing.

RESULTS

Eleven volunteers had data available from both dosing periods. There was no increase in rosuvastatin plasma exposure following co-administration with erythromycin compared to placebo. In fact, following co-administration with erythromycin, rosuvastatin geometric least square mean AUC((0-t)) and C(max) were 20% and 31%, respectively, lower than with placebo. Individual treatment ratios for AUC((0-t)) ranged from 0.48 to 1.17, and for C(max) ranged from 0.33 to 2.19. Essentially all of the circulating active HMG-CoA reductase inhibitors and most (>94%) of the total inhibitors were accounted for by rosuvastatin. Erythromycin did not affect the proportion of circulating active or total inhibitors accounted for by circulating rosuvastatin.

CONCLUSIONS

Erythromycin did not produce any increase in rosuvastatin plasma exposure. This indicates that CYP3A4 metabolism is not an important clearance mechanism for rosuvastatin, a result consistent with previous findings. The small decreases in rosuvastatin AUC((0-t)) and C(max) that occurred as a consequence of short-term treatment with erythromycin are unlikely to have relevance to long-term treatment with rosuvastatin.

Interaction of cytochrome P450 3A inhibitors with P-glycoprotein

Many clinically important drug interactions occur due to inhibition of human liver cytochrome P450 3A (CYP3A) metabolism. The drug efflux pump P-glycoprotein (Pgp) can be an additional locus contributing to these drug interactions because there is overlap in drugs that are substrates for both proteins. We screened a number of CYP3A inhibitors (macrolide antibiotics, azole antifungals, and ergotpeptides) for their ability to interact with Pgp, compared with prototypical Pgp inhibitors. We used cell lines expressing human, mouse, and rat mdr1 genes. Pgp antagonism was defined by interactions of the drugs with four cell lines (LLC-PK1, L-MDR1, L-mdr1a, and L-mdr1b) using a microfluorometric calcein-AM assay and characterized for their inhibitor constant (K(i)) toward calcein-AM. The compounds were further defined for their ability to inhibit MDR1 by their effect on vinblastine accumulation into L-MDR1 cells. Representative compounds from each class of drugs were further tested as Pgp substrates, defined by the ability of human Pgp or mouse mdr1a/Pgp to transport them across a polarized kidney epithelial cell in vitro. These same compounds were administered radiolabeled in vivo to mdr1a (+/+) and (-/-) mice and the distribution of radioactivity compared. The results are summarized as follows: 1) Some drug interactions with Pgp were substrate- and/or assay-dependent. 2) Ergot alkaloids were identified as a class of MDR1/Pgp chemosensitizers. 3) The Ergot alkaloids revealed species differences in the structure-activity relationships for inhibition of Pgp. Simultaneous inhibition of Pgp by many CYP3A inhibitors contributes to human variation in the extent of drug-drug interactions.

Bradycardia associated with intravenous methadone administered for sedation in a patient with acute respiratory distress syndrome

The use of low tidal volumes with permissive hypercapnia in patients with acute respiratory distress syndrome may require heavy sedation to allow them to tolerate mechanical ventilation. Administration of methadone for sedation is an alternative to using other opioids, given its longer elimination half-life and incomplete cross-tolerance with other mu-receptor-active opioids. Methadone appears to have a molecular structure similar to that of verapamil, a calcium channel blocker, and may exhibit similar cardiac properties as well. A 43-year-old man with acute respiratory distress syndrome experienced bradycardia while receiving a continuous infusion of methadone for sedation and mechanical ventilation management. This case report demonstrates that caution is warranted when high dosages of methadone are administered because of its potential cardiac effects.