Clarithromycin induced digoxin toxicity

A pharmacokinetic study on red ginseng with furosemide in equine

Red ginseng (RG) is a popular ingredient in traditional Korean medicine that has various health benefits. It is commonly taken orally as a dietary supplement; however, its potential interactions with concomitantly administered drugs are unclear. In this study, we examined the pharmacokinetic interaction between furosemide and RG in equine plasma. Liquid chromatography with tandem mass spectrometry analysis was performed to evaluate ginsenosides in the plasma of horses after feeding them RG and furosemide and validate the results. A single bolus of furosemide (0.5 mg/kg) was administered intravenously to female horses that had consumed RG (600 mg/kg/day) every morning for 3 weeks (experimental group), and blood samples were collected from 0 to 24 h, analyzed, and compared with those from female horses that did not consume RG (control group). Four (20s)-protopanaxadiol ginsenosides (Rb1, Rb2, Rc, and Rd) were detected in the plasma. Rb1 and Rc individually showed a high concentration distribution in the plasma. The Cmax, AUC0-t, and AUC0-∞ of furosemide was significantly increased in the experimental group (p < 0.05), while the CL, Vz, and Vss was decreased (p < 0.05, p < 0.01). These changes indicate the potential for pharmacokinetic interactions between furosemide and RG.

Intoxicación digitálica secundaria al tratamiento con claritromicina

OBJECTIVE

The goal of this study was to investigate the percentage of patients concurrently receiving digoxin and clarithromycin who exhibited serum digoxin concentrations above the therapeutic range because of a likely interaction between both drugs, and whether digitalis intoxication ensued.

METHOD

A descriptive, retrospective study carried out from January 2002 to December 2003 in all inpatients concurrently receiving digoxin and clarithromycin whose serum digoxin concentrations were monitored by the Pharmacy Department s Pharmacokinetics Section.

RESULTS

Twenty-six patients having received digoxin and clarithromycin concurrently during their hospital stay were included in the study. Of these, 12 patients (46.2%) had serum digoxin concentrations above the therapeutic range: 7 received digoxin in doses unsuited for their age and/or renal function, and 2 fell short of the mean period of time considered adequate for an interaction to occur. Therefore, only 3 patients had serum digoxin concentrations above the therapeutic range, probably because of an interaction with clarithromycin, and all three had digitalis intoxication symptoms.

CONCLUSIONS

According to the results of our study, 11.5% of patients concurrently receiving digoxin and clarithromycin had serum digoxin concentrations above the therapeutic range because of a likely interaction between these two drugs, with digitalis intoxication ensuing. Thus, we deem it necessary to monitor serum digoxin concentrations in patients receiving clarithtomycin.

Treatment of community-acquired pneumonia in hospitalised patients

Community-acquired pneumonia (CAP) can be life-threatening. The prognosis is generally poorest in elderly patients and/or those with underlying chronic conditions, but fatalities can occur in all age groups. Current challenges in the clinical management of CAP are discussed, and the criteria for identifying those patients who should be treated in hospital with initial intravenous therapy are considered. Rapid initiation of therapy is important, using an agent that provides coverage against the most likely pathogens--Streptococcus pneumoniae and the atypical organisms. There is an increasing tendency to minimise the duration of intravenous therapy, with an early transition to oral therapy and the rapid return of the patient to the community. The efficacy of oral macrolides in the treatment of CAP is well established. Evidence for the use of intravenous azithromycin to provide effective and well-tolerated, first-line intervention in the hospitalized CAP patient is summarised.

Pharmacokinetic aspects of treating infections in the intensive care unit: focus on drug interactions

Pharmacokinetic interactions involving anti-infective drugs may be important in the intensive care unit (ICU). Although some interactions involve absorption or distribution, the most clinically relevant interactions during anti-infective treatment involve the elimination phase. Cytochrome P450 (CYP) 1A2, 2C9, 2C19, 2D6 and 3A4 are the major isoforms responsible for oxidative metabolism of drugs. Macrolides (especially troleandomycin and erythromycin versus CYP3A4), fluoroquinolones (especially enoxacin, ciprofloxacin and norfloxacin versus CYP1A2) and azole antifungals (especially fluconazole versus CYP2C9 and CYP2C19, and ketoconazole and itraconazole versus CYP3A4) are all inhibitors of CYP-mediated metabolism and may therefore be responsible for toxicity of other coadministered drugs by decreasing their clearance. On the other hand, rifampicin is a nonspecific inducer of CYP-mediated metabolism (especially of CYP2C9, CYP2C19 and CYP3A4) and may therefore cause therapeutic failure of other coadministered drugs by increasing their clearance. Drugs frequently used in the ICU that are at risk of clinically relevant pharrmacokinetic interactions with anti-infective agents include some benzodiazepines (especially midazolam and triazolam), immunosuppressive agents (cyclosporin, tacrolimus), antiasthmatic agents (theophylline), opioid analgesics (alfentanil), anticonvulsants (phenytoin, carbamazepine), calcium antagonists (verapamil, nifedipine, felodipine) and anticoagulants (warfarin). Some lipophilic anti-infective agents inhibit (clarithromycin, itraconazole) or induce (rifampicin) the transmembrane transporter P-glycoprotein, which promotes excretion from renal tubular and intestinal cells. This results in a decrease or increase, respectively, in the clearance of P-glycoprotein substrates at the renal level and an increase or decrease, respectively, of their oral bioavailability at the intestinal level. Hydrophilic anti-infective agents are often eliminated unchanged by renal glomerular filtration and tubular secretion, and are therefore involved in competition for excretion. Beta-lactams are known to compete with other drugs for renal tubular secretion mediated by the organic anion transport system, but this is frequently not of major concern, given their wide therapeutic index. However, there is a risk of nephrotoxicity and neurotoxicity with some cephalosporins and carbapenems. Therapeutic failure with these hydrophilic compounds may be due to haemodynamically active coadministered drugs, such as dopamine, dobutamine and furosemide, which increase their renal clearance by means of enhanced cardiac output and/or renal blood flow. Therefore, coadministration of some drugs should be avoided, or at least careful therapeutic drug monitoring should be performed when available. Monitoring may be especially helpful when there is some coexisting pathophysiological condition affecting drug disposition, for example malabsorption or marked instability of the systemic circulation or of renal or hepatic function.

Macrolide drug interactions: an update

OBJECTIVE

To describe the current drug interaction profiles for the commonly used macrolides in the US and Europe, and to comment on the clinical impact of these interactions.

DATA SOURCES

A MEDLINE search (1975-1998) was performed to identify all pertinent studies, review articles, and case reports. When appropriate information was not available in the literature, data were obtained from the product manufacturers.

STUDY SELECTION

All available data were reviewed to provide an unbiased account of possible drug interactions.

DATA EXTRACTION

Data for some of the interactions were not available from the literature, but were available from abstracts or company-supplied materials. Although the data were not always explicit, the best attempt was made to deliver pertinent information that clinical practitioners would need to formulate practice opinions. When more in-depth information was supplied in the form of a review or study report, a thorough explanation of pertinent methodology was supplied.

DATA SYNTHESIS

Several clinically significant drug interactions have been identified since the approval of erythromycin. These interactions usually were related to the inhibition of the cytochrome P450 enzyme systems, which are responsible for the metabolism of many drugs. The decreased metabolism by the macrolides has in some instances resulted in potentially severe adverse events. The development and marketing of newer macrolides are hoped to improve the drug interaction profile associated with this class. However, this has produced variable success. Some of the newer macrolides demonstrated an interaction profile similar to that of erythromycin; others have improved profiles. The most success in avoiding drug interactions related to the inhibition of cytochrome P450 has been through the development of the azalide subclass, of which azithromycin is the first and only to be marketed. Azithromycin has not been demonstrated to inhibit the cytochrome P450 system in studies using a human liver microsome model, and to date has produced none of the classic drug interactions characteristic of the macrolides.

CONCLUSIONS

Most of the available data regarding macrolide drug interactions are from studies in healthy volunteers and case reports. These data suggest that clarithromycin appears to have an interaction profile similar to that of erythromycin. Given this similarity, it is important to consider the interaction profile of clarithromycin when using erythromycin. This is especially necessary as funds for further studies of a medication available in generic form (e.g., erythromycin) are limited. Azithromycin has produced few clinically significant interactions with any agent cleared through the cytochrome P450 enzyme system. Although the available data are promising, the final test should come from studies conducted in patients who are taking potentially interacting compounds on a chronic basis.