Changes in the steady-state pharmacokinetics of theophylline during treatment with dirithromycin

Drug metabolism in severe chronic obstructive pulmonary disease: A phenotyping cocktail study

AIMS

To evaluate the effect of severe chronic obstructive pulmonary disease (COPD) on drug metabolism by comparing the pharmacokinetics of patients with severe COPD with healthy volunteers and using the modified Inje drug cocktail.

METHODS

This was a single-centre pharmacokinetic study with 12 healthy participants and 7 participants with GOLD D COPD. Midazolam 1 mg, dextromethorphan 30 mg, losartan 25 mg, omeprazole 20 mg, caffeine 130 mg and paracetamol 1000 mg were simultaneously administered and intensive pharmacokinetic sampling was conducted over 8 hours. Drug metabolism by CYP3A4, CYP2D6, CYP2C9, CYP2C19, CYP1A2, UGT1A6 and UGT1A9 in participants with COPD were compared with phenotypes in healthy controls.

RESULTS

The oral clearance (95% confidence interval) in participants with COPD relative to controls was: midazolam 63% (60-67%); dextromethorphan 72% (40-103%); losartan 53% (52-55%); omeprazole 35% (31-39%); caffeine 52% (50-53%); and paracetamol 73% (72-74%). There was a 5-fold increase in AUC for omeprazole and approximately 2-fold increases for caffeine, losartan, dextromethorphan, and midazolam. The AUC of paracetamol, which is mostly glucuronidated, was increased by about 60%.

CONCLUSION

Severe COPD is associated with a clinically significant reduction in oral drug clearance. This may be greater for cytochrome P450 substrates than for glucuronidated drugs. This supports reduced starting doses when prescribing for patients with severe COPD.

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.

Five-day dirithromycin therapy is as effective as seven-day erythromycin therapy for acute exacerbations of chronic bronchitis

In a meta-analysis of two identically designed, well-controlled, randomized, double-blind clinical trials, we compared 5 days of dirithromycin with 7 days of erythromycin for acute exacerbations of chronic bronchitis. Five hundred and thirty-one patients were randomized to receive dirithromycin (500 mg od) for 5 days and 526 patients were randomized to receive erythromycin (250 mg qid) for 7 days. Clinical and bacteriological responses were assessed 3-5 days after therapy and at termination from the study. Adverse events were collected from both groups and compared with each other, before and after treatment. Of the 690 patients clinically appraisable at the post-therapy visit, 298 (84.2%) dirithromycin-treated patients and 270 (80.4%) erythromycin-treated patients showed a favourable response. At termination, 273 (77.1%) dirithromycin-treated patients and 243 (72.3%) erythromycin-treated patients showed a favourable response. The microbiological cure was equivalent in the two groups (75% of dirithromycin-treated patients and 74.1% of erythromycin-treated patients showed a favourable response at termination). After therapy, dirithromycin was as effective as erythromycin in eradicating Streptococcus pneumoniae (77.8% vs 90.9%), Haemophilus influenzae (71.7% vs 72.2%), Moraxella catarrhalis (93.3% vs 88.9%) and Staphylococcus aureus (81.8% vs 82.1%). Although not statistically significant, fewer dirithromycin-treated patients reported adverse events than did erythromycin-treated patients. Nausea (6.8% vs 7.8%), headache (7.3% vs 8.2%) and diarrhoea (6.6% vs 9.5%) were the most frequently reported adverse events in both groups. In the treatment of acute exacerbations of chronic bronchitis, 5 days of dirithromycin is as effective as 7 days of erythromycin.

Review and comparison of advanced-generation macrolides clarithromycin and dirithromycin

We reviewed English-language clinical studies, abstracts, and review articles identified from MEDLINE searches from January 1966-August 1998, and bibliographies of identified articles to compare advanced-generation macrolides dirithromycin and clarithromycin and their use for respiratory tract infections. Both agents have superior adverse effect profiles compared with erythromycin, the original macrolide. Both have broad antibacterial coverage, but clarithromycin usually has a lower MIC90 to susceptible organisms than dirithromycin; for most isolates this difference is not clinically significant. Clarithromycin has better in vitro coverage of Haemophilus influenzae, but this activity varies with formation of its bioactive metabolite, 14-hydroxyclarithromycin. Neither agent is ideal for H. influenzae eradication. The agents differ markedly in terms of pharmacokinetics, pharmacodynamics, metabolism, and cost, and thus with respect to drug interaction profiles and dosages. Dirithromycin's drug interaction profile is markedly better than clarithromycin's. Clarithromycin is dosed twice/day; dirithromycin's pharmacokinetics allow once/day dosing. Dirithromycin is less expensive with regard to both cost/day and cost/treatment regimen. Clarithromycin has been studied and approved for administration to children. In adults with respiratory tract infections who are receiving drugs that would interact with clarithromycin, and in those with renal dysfunction with or without coexisting hepatic dysfunction, dirithromycin appears to be superior in terms of safety and equivalent to clarithromycin in terms of efficacy.

Drug interactions of macrolides: emphasis on dirithromycin

OBJECTIVE

To describe the drug interactions of dirithromycin, a new macrolide, and to compare them with those of other macrolides.

DATA SOURCES

A literature search was performed using MEDLINE to identify articles published between January 1980 and July 1995 concerning the drug interactions of macrolides. Published abstracts were also examined. All studies using dirithromycin were performed under the sponsorship of Eli Lilly and Company.

DATA SYNTHESIS

Erythromycin, the first macrolide discovered, is metabolized by the cytochrome P450 enzyme system. By decreasing their metabolism, erythromycin can interact with other drugs metabolized by the cytochrome P450 enzymes. The lack of such interactions would be a desirable feature in a newer macrolide. We describe studies performed to detect any interactions of dirithromycin with cyclosporine, theophylline, terfenadine, warfarin, and ethinyl estradiol. The studies showed that dirithromycin, like azithromycin, is much less likely to cause the interactions detected with clarithromycin and erythromycin. A review of the literature showed differences among macrolides in their abilities to inhibit cytochrome P450 enzymes and, thus, to cause drug-drug interactions. Erythromycin and clarithromycin inhibit cytochrome P450 enzymes, and have been implicated in clinically significant interactions. Azithromycin and dirithromycin neither inhibit cytochrome P450 enzymes nor are implicated in clinically significant drug-drug interactions.

CONCLUSIONS

Dirithromycin, a new macrolide, does not inhibit the cytochrome P450 enzyme system. The concomitant use of dirithromycin with cyclosporine, theophylline, terfenadine, warfarin, or ethinyl estradiol was studied in pharmacokinetic and pharmacodynamic studies. In vitro, dirithromycin did not bind cytochrome P450. In healthy subjects, erythromycin increases the clearance of cyclosporine by 51%, whereas dirithromycin causes no significant changes in the pharmacokinetics of cyclosporine. In kidney transplant recipients, administration of dirithromycin was associated with a significant (p < 0.003) decrease of 17.4% in the clearance of cyclosporine. In patients taking low-dose estradiol, the administration of dirithromycin caused a significant (p < 0.03) increase of 9.9% in the clearance of ethinyl estradiol; escape ovulation did not occur. Unlike erythromycin and clarithromycin, dirithromycin had no significant effects on the pharmacokinetics of theophylline, terfenadine, or warfarin. The alterations typical of drug interactions that are based on inhibition of the cytochrome P450 system occurring with erythromycin and clarithromycin were not observed with dirithromycin.

Comparison of dirithromycin and penicillin for treatment of streptococcal pharyngitis

In the treatment of group A beta-hemolytic streptococcal pharyngitis, penicillin is the drug of choice and erythromycin is the alternative. In a double-blind, randomized study, dirithromycin, a new macrolide, was compared with penicillin for the treatment of streptococcal pharyngitis. Of 121 patients who were treated with dirithromycin, 96.7% manifested a favorable clinical response, and of 136 patients treated with penicillin, 94.2% manifested a favorable clinical response. Streptococci were eradicated from the pharynges of 85.3% of 116 dirithromycin-treated patients and 82.5% of 126 penicillin-treated patients who returned for follow-up. There were no statistically significant differences in efficacy between the two groups. The incidence of abdominal symptoms was higher in dirithromycin-treated patients. Being as efficacious as penicillin and having the advantages over erythromycin of once-daily dosing and the lack of drug interactions, dirithromycin is an alternative to penicillin in the treatment of streptococcal pharyngitis for patients 12 years of age and older.

Clinical efficacy of dirithromycin in patients with bacteremic pneumonia

Dirithromycin is a new macrolide antimicrobial drug with a long half-life (44 hours) that reaches high tissue concentrations, thus permitting once-daily oral dosing and shorter courses of therapy. Soon after absorption, dirithromycin enters the tissue so rapidly that serum concentrations are comparatively low. It could be hypothesized that these low serum levels could endanger the outcome in patients with bacteremic pneumonia. We reviewed the database on dirithromycin pneumonia (consisting of 1108 patients randomized to receive dirithromycin or erythromycin in two double-masked trials) to ascertain its efficacy in patients with community-acquired pneumonia and concomitant bacteremia. Fourteen (2.5%) of 555 dirithromycin-treated patients and 10 (1.8%) of 553 erythromycin-treated patients had bacteremia. A favorable clinical response posttherapy was observed in 92.3% and 88.9% of these patients with a response assigned, respectively. Overall, favorable response rates were comparable between the two groups in the bacteremic subsets: patients with pneumococcal bacteremia, patients with nonbacteremic pneumococcal pneumonia, and all patients enrolled with acute pneumonia who had a posttherapy clinical response. In the treatment of patients with mild or moderate community-acquired pneumonia, including those with unsuspected and incidental bacteremia, dirithromycin is an effective macrolide antimicrobial drug.

Dirithromycin: a new macrolide

OBJECTIVE

To review the clinical microbiology and therapeutic use of dirithromycin, emphasizing comparative data between dirithromycin and the standard macrolide erythromycin, as well as clarithromycin and azithromycin.

DATA SOURCES

A MEDLINE search of English-language literature during the years 1966-1996, and an extensive review of journals were conducted to prepare this article.

DATA EXTRACTION

The data on pharmacokinetics, adverse effects, and drug interactions were obtained from open and controlled studies. Controlled single- or double-blind studies were evaluated to assess the efficacy of dirithromycin in the treatment of various upper and lower respiratory tract infections, as well as skin and soft tissue infections.

DATA SYNTHESIS

The spectrum of activity of dirithromycin is similar to that of erythromycin, clarithromycin, or azithromycin, with some notable exceptions. Dirithromycin was more active in vitro against Campylobacter jejuni and Borrelia burgdorferi than was erythromycin or clarithromycin, but in general demonstrated less activity than erythromycin, clarithromycin, or azithromycin against a majority of microorganisms. The pharmacokinetic profile of dirithromycin offers the advantages of once-daily dosing and high and prolonged tissue concentrations; dosing adjustments are not needed in the elderly or in patients with renal or mild hepatic impairment. Clinical efficacy and bacteriologic eradication rates with dirithromycin and erythromycin are comparable for the treatment of respiratory and skin and soft tissue infections due to susceptible pathogens. Dirithromycin appears to have adverse effect profiles similar to those of the other macrolides, with reported problems most often related to the gastrointestinal tract. Dirithromycin does not seem to cause clinically important interactions with drugs such as theophylline, oral contraceptives, cyclosporine, or terfenadine.

CONCLUSIONS

Dirithromycin offers some attractive pharmacokinetic properties. The long elimination half-life of dirithromycin allows once-daily dosing and higher and more prolonged tissue concentrations than are achievable with erythromycin. The spectrum of activity, adverse effect profile, clinical efficacy, and bacteriologic eradication rate of dirithromycin may be similar to those of erythromycin. No significant drug interactions with dirithromycin have been reported. Based on available data, dirithromycin may not offer any unique clinical advantage over clarithromycin or azithromycin. Future clinical trials may reveal a special role for dirithromycin in patient care.

Macrolides versus azalides: a drug interaction update

OBJECTIVE

To describe the current drug interaction profiles for all approved and investigational macrolide and azalide antimicrobials, and to comment on the clinical impact of these interactions when appropriate.

DATA SOURCES

MEDLINE was searched to identify all pertinent studies, review articles, and case reports from 1975 to 1995. When appropriate information was not available in the literature, data were obtained from the product manufacturers.

STUDY SELECTION

All available data were reviewed to give 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 from company-supplied materials. Although the data were not always entirely explicative, the best attempt was made to deliver the 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

Since the introduction of erythromycin into clinical practice, there have been several clinically significant drug interactions identified throughout the literature associated with this drug. These interactions have been caused mostly by inhibition of the CYP3A subclass of hepatic enzymes, thereby decreasing the metabolism of any other agent given concurrently that is also cleared through this mechanism. With the development and marketing of several new macrolides, it was hoped that the drug interaction profile associated with this class would improve. This has been met with variable success. Although some of the extensions of the 14-membered ring macrolides have shown an incidence of interactions equal to that of erythromycin, others have shown improved profiles. In contrast, the 16-membered ring macrolides have demonstrated a much improved, though not absent, interaction profile. The most success in avoiding drug interactions through structure modification has been accomplished with the development of the azalide class, of which azithromycin is the first to be approved for marketing. This agent has to date produced none of the classic drug interactions that most macrolides have demonstrated in patient care.

CONCLUSIONS

The introduction of new 14- and 16-membered ring macrolides appears to have had a variable effect in modifying the incidence of drug interactions associated with this class. Azithromycin, a member of the new azalide class, has to date produced fewer clinically significant interactions than other azalides with any agent that is cleared through the CYP3A system.(ABSTRACT TRUNCATED AT 250 WORDS)

Macrolide antibacterials. Drug interactions of clinical significance

Macrolide antibiotics can interact adversely with commonly used drugs, usually by altering metabolism due to complex formation and inhibition of cytochrome P-450 IIIA4 (CYP3A4) in the liver and enterocytes. In addition, pharmacokinetic drug interactions with macrolides can result from their antibiotic effect on microorganisms of the enteric flora, and through enhanced gastric emptying due to a motilin-like effect. Macrolides may be classified into 3 different groups according to their affinity for CYP3A4, and thus their propensity to cause pharmacokinetic drug interactions. Troleandomycin, erythromycin and its prodrugs decrease drug metabolism and may produce drug interactions (group 1). Others, including clarithromycin, flurithromycin, midecamycin, midecamycin acetate (miocamycin; ponsinomycin), josamycin and roxithromycin (group 2) rarely cause interactions. Azithromycin, dirithromycin, rikamycin and spiramycin (group 3) do not inactivate CYP3A4 and do not engender these adverse effects. Drug interactions with carbamazepine, cyclosporin, terfenadine, astemizole and theophylline represent the most frequently encountered interactions with macrolide antibiotics. If the combination of a macrolide and one of these compounds cannot be avoided, serum concentrations of concurrently administered drugs should be monitored and patients observed for signs of toxicity. Rare interactions and those of dubious clinical importance are those with alfentanil and sufentanil, antacids and cimetidine, oral anticoagulants, bromocriptine, clozapine, oral contraceptive steroids, digoxin, disopyramide, ergot alkaloids, felodipine, glibenclamide (glyburide), levodopa/carbidopa, lovastatin, methylprednisolone, phenazone (antipyrine), phenytoin, rifabutin and rifampicin (rifampin), triazolam and midazolam, valproic acid (sodium valproate) and zidovudine.

Steady-state pharmacokinetics of theophylline in COPD patients treated with dirithromycin

Steady-state theophylline pharmacokinetic parameters were studied in a panel of 14 patients with chronic obstructive pulmonary disease (COPD). Pharmacokinetic parameters were evaluated before, during, and after a 10-day regimen of the macrolide antibiotic, dirithromycin. The addition of dirithromycin (500 mg orally once daily at 7:00 AM) to a sustained-release theophylline dosing regimen (every 12 hours) elicited small changes in the steady-state pharmacokinetics of theophylline, which were not statistically significant. Mean steady-state plasma theophylline trough concentrations (Css,min) were invariant before, during, and after dirithromycin treatment. Mean average steady-state plasma theophylline concentrations (Cav) declined by 7% during dirithromycin treatment (NS), and mean peak plasma concentrations (Css,max) declined by 12% (NS). Theophylline clearance (CL/F) also remained relatively unchanged during dirithromycin treatment exhibiting an increase of only 11% (NS). Dirithromycin treatment does not significantly affect the steady-state pharmacokinetics of theophylline, and its use in COPD patients is not likely to modify treatment outcomes with theophylline.

Pharmacokinetic drug interactions of macrolides

The macrolide antibiotics include natural members, prodrugs and semisynthetic derivatives. These drugs are indicated in a variety of infections and are often combined with other drug therapies, thus creating the potential for pharmacokinetic interactions. Macrolides can both inhibit drug metabolism in the liver by complex formation and inactivation of microsomal drug oxidising enzymes and also interfere with microorganisms of the enteric flora through their antibiotic effects. Over the past 20 years, a number of reports have incriminated macrolides as a potential source of clinically severe drug interactions. However, differences have been found between the various macrolides in this regard and not all macrolides are responsible for drug interactions. With the recent advent of many semisynthetic macrolide antibiotics it is now evident that they may be classified into 3 different groups in causing drug interactions. The first group (e.g. troleandomycin, erythromycins) are those prone to forming nitrosoalkanes and the consequent formation of inactive cytochrome P450-metabolite complexes. The second group (e.g. josamycin, flurithromycin, roxithromycin, clarithromycin, miocamycin and midecamycin) form complexes to a lesser extent and rarely produce drug interactions. The last group (e.g. spiramycin, rokitamycin, dirithromycin and azithromycin) do not inactivate cytochrome P450 and are unable to modify the pharmacokinetics of other compounds. It appears that 2 structural factors are important for a macrolide antibiotic to lead to the induction of cytochrome P450 and the formation in vivo or in vitro of an inhibitory cytochrome P450-iron-nitrosoalkane metabolite complex: the presence in the macrolide molecules of a non-hindered readily accessible N-dimethylamino group and the hydrophobic character of the drug. Troleandomycin ranks first as a potent inhibitor of microsomal liver enzymes, causing a significant decrease of the metabolism of methylprednisolone, theophylline, carbamazepine, phenazone (antipyrine) and triazolam. Troleandomycin can cause ergotism in patients receiving ergot alkaloids and cholestatic jaundice in those taking oral contraceptives. Erythromycin and its different prodrugs appear to be less potent inhibitors of drug metabolism. Case reports and controlled studies have, however, shown that erythromycins may interact with theophylline, carbamazepine, methylprednisolone, warfarin, cyclosporin, triazolam, midazolam, alfentanil, disopyramide and bromocriptine, decreasing drug clearance. The bioavailability of digoxin appears also to be increased by erythromycin in patients excreting high amounts of reduced digoxin metabolites, probably due to destruction of enteric flora responsible for the formation of these compounds. These incriminated macrolide antibiotics should not be administered concomitantly with other drugs known to be affected metabolically by them, or at the very least, combined administration should be carried out only with careful patient monitoring.(ABSTRACT TRUNCATED AT 400 WORDS)

The new macrolide antibiotics: azithromycin, clarithromycin, dirithromycin, and roxithromycin

OBJECTIVE

To review the chemistry, antimicrobial spectrum, pharmacokinetics, clinical trials, adverse effects, and drug interactions of four new macrolide antibiotics: azithromycin, clarithromycin, dirithromycin, and roxithromycin.

DATA SOURCES

Information was obtained from comparative clinical trials, abstracts, conference proceedings, and review articles. Indexing terms included azithromycin, clarithromycin, dirithromycin, erythromycin, roxithromycin, and macrolide antibiotics.

STUDY SELECTION

Emphasis was placed on comparative clinical trials involving the new macrolide antibiotics.

DATA EXTRACTION

Data from human studies published in the English language were evaluated. Trials were assessed by sample size, macrolide dosage regimen, and therapeutic response.

DATA SYNTHESIS

The erythromycins have gained widespread use in treating a variety of infections. Although they are effective, limitations include the need to administer four times a day and the intolerable adverse gastrointestinal effects. Four of the more extensively studied agents, azithromycin, clarithromycin, dirithromycin, and roxithromycin, are currently being studied in patients. Based on the studies to date, the newer macrolides may offer several advantages over erythromycin, including: (1) greater antimicrobial activity against certain organisms; (2) longer elimination half-life, thus allowing less frequent administration; and (3) lower incidence of adverse gastrointestinal effects.

CONCLUSIONS

The new macrolide antibiotics appear to offer an improvement over erythromycin. Definitive conclusions about the role of these drugs should await completion of ongoing clinical studies.