Pharmacokinetics of azithromycin in normal and impaired renal function

Comparison of gastrointestinal side effects from different doses of azithromycin for the treatment of gonorrhoea

OBJECTIVES

Azithromycin is commonly used to treat Neisseria gonorrhoeae. We compared its gastrointestinal side effects using 1 g single, 2 g single or 2 g split (i.e. 1 g plus 1 g 6-12 h later) dosing, representing our clinic's changing guidelines over the study period.

METHODS

We recruited consecutive sexual health clinic patients who received azithromycin (and 500 mg ceftriaxone) for uncomplicated gonorrhoea. Each patient received a text message 48 h after their attendance to complete a questionnaire.

RESULTS

Patients received 1 g single (n = 271), 2 g single (218) or 2 g split (105) doses. Vomiting was less common for 1 g versus 2 g single dose [1.1% versus 3.7%; risk difference (RD): -2.6%; 95% CI: -0.2 to -5.4] and 2 g split versus 2 g single dose (0.9% versus 3.7%; RD: -2.8%; 95% CI: -0.3 to -5.8). Nausea was less common for 1 g versus 2 g single dose (13.7% versus 43.1%; RD: -29.5%; 95% CI: -21.7 to -37.2) and 2 g split versus 2 g single dose (16.4% versus 43.1%; RD: -26.8; 95% CI: -17.2 to -36.3). Diarrhoea was less common for 1 g versus 2 g single dose (25.5% versus 50.9%; RD: -25.5%; 95% CI: -17.0 to -33.9) and 2 g split versus 2 g single dose (30.9% versus 50.9%; RD: -20.0; 95% CI: -9.1 to -30.9). Almost all were willing to retake the same dosing for gonorrhoea in the future: 97% for 1 g single; 94% for 2 g single; and 97% for 2 g split dose.

CONCLUSIONS

Azithromycin 2 g split dose for gonorrhoea resulted in significantly less vomiting, nausea and diarrhoea than a 2 g single dose.

Investigating the Critical Variables of Azithromycin Oral Absorption Using In Vitro Tests and PBPK Modeling

Azithromycin is an antibiotic listed in the essential list of medicines for adults and pediatrics. Conflicting evidence has been found regarding azithromycin classification according to the Biopharmaceutics classification system (BCS). The purpose of this study was to identify the critical variables that influence the oral absorption of azithromycin in adults and pediatrics. Azithromycin solubility and dissolution studies (oral suspension) were performed in buffers and biorelevant media simulating the fasted and fed gastrointestinal tract. A PBPK model was developed for azithromycin for healthy adult volunteers and pediatrics (Simcyp® v18.2) informed by in vitro solubility and dissolution studies to predict drug performance after administration of azithromycin as an oral suspension. The developed PBPK model predicted azithromycin plasma concentrations-time profiles after administration of an oral suspension to adults and pediatrics. Sensitivity analysis of solubility vs dose suggests that absorption is independent of solubility within the therapeutic dose range in both adults and pediatrics. The developed PBPK model for adults and pediatrics was consistent with the mechanism of permeation through the intestinal membrane (passive and active processes) being the rate-limiting step of azithromycin's absorption. The physiologically based approach proposed was shown to be useful to determine the factors controlling drug absorption in adults and pediatrics.

Recommendations on off-label use of intravenous azithromycin in children

OBJECTIVE

Intravenous azithromycin (AZM) has been widely used in children worldwide, but there still remains much concern regarding its off-label use, which urgently needs to be regulated. Therefore, we developed a rapid advice guideline in China to give recommendations of rational use of intravenous AZM in children.

METHODS

This guideline focuses on antimicrobial therapy with intravenous AZM in children. The Delphi research method was used to select questions. A systematic literature review was also conducted. Data were pooled and ranked according to the GRADE system. Recommendations were developed based on expert clinical experience, patients' values and preferences, and evidence availability. After an external review, the recommendations were revised and approved.

RESULTS

This guideline included eighteen recommendations that covered four domains: (a) Indications: the treatment of pneumonia caused by atypical but common pathogens, such as Mycoplasma pneumoniae, Chlamydia trachomatis or Chlamydophila pneumoniae and Legionella pneumophila, more typical bacteria as well as the treatment of bronchitis of presumed bacterial aetiologies; (b) Usage and dosage: administration route, infusion concentrations, treatment duration, course of sequential treatment, and dosage stratified by age; (c) Adverse reactions and treatment: the management of gastrointestinal reactions, arrhythmias, pain or phlebitis at the infusion site, and anaphylaxis; and (d) Special population: children with renal or liver dysfunction, congenital heart disease, and obesity. This guideline will hopefully help promote a rational use of intravenous AZM in children worldwide.

CONCLUSION

This guideline has summarised the evidence and has developed recommendations on the use of intravenous AZM in children worldwide. Further attention and well-designed researches should be conducted on the off-label use of intravenous AZM in children.

Pharmacokinetics under the COVID-19 storm

AIMS

The storm-like nature of the health crises caused by COVID-19 has led to unconventional clinical trial practices such as the relaxation of exclusion criteria. The question remains: how can we conduct diverse trials without exposing subgroups of populations to potentially harmful drug exposure levels? The aim of this study was to build a knowledge base of the effect of intrinsic/extrinsic factors on the disposition of several repurposed COVID-19 drugs.

METHODS

Physiologically based pharmacokinetic (PBPK) models were used to study the change in the pharmacokinetics (PK) of drugs repurposed for COVID-19 in geriatric patients, different race groups, organ impairment and drug-drug interactions (DDIs) risks. These models were also used to predict epithelial lining fluid (ELF) exposure, which is relevant for COVID-19 patients under elevated cytokine levels.

RESULTS

The simulated PK profiles suggest no dose adjustments are required based on age and race for COVID-19 drugs, but dose adjustments may be warranted for COVID-19 patients also exhibiting hepatic/renal impairment. PBPK model simulations suggest ELF exposure to attain a target concentration was adequate for most drugs, except for hydroxychloroquine, azithromycin, atazanavir and lopinavir/ritonavir.

CONCLUSION

We demonstrate that systematically collated data on absorption, distribution, metabolism and excretion, human PK parameters, DDIs and organ impairment can be used to verify simulated plasma and lung tissue exposure for drugs repurposed for COVID-19, justifying broader patient recruitment criteria. In addition, the PBPK model developed was used to study the effect of age and ethnicity on the PK of repurposed drugs, and to assess the correlation between lung exposure and relevant potency values from in vitro studies for SARS-CoV-2.

Azithromycin: An Assessment of Its Pharmacokinetics and Therapeutic Potential in CAPD

Background

Azithromycin is an azalide antibiotic with a similar antibacterial spectrum to erythromycin but with greater gram-negative activity. Azithromycin displays a favorable pharmacokinetic profile, with improved absorption and higher sustained tissue concentrations compared with erythromycin. This results in a prolonged elimination half-life, suggesting a potential for treating continuous ambulatory peritoneal dialysis (CAPD) peritonitis.

Objective

This study aimed to define the potential role of azithromycin in treating CAPD peritonitis.

Design

The pharmacokinetics and peritoneal dialysis (PD) clearance of azithromycin were studied following a single 500-mg oral dose of azithromycin. Blood and dialysate samples were taken over a 10-day period and assayed using high-pressure liquid chromatography.

Setting

The study took place within the Renal Unit at Southend Hospital NHS Trust, a district general hospital in the United Kingdom.

Patients

Eight patients with oliguric end-stage renal failure without peritonitis maintained on CAPD (3 x 2 L/day).

Results

Peak plasma concentrations occurred at 2 -3 hours with 0.35 - 1.35 mg/mL (mean 0.75). The mean elimination half-life was 84.55 hrs, and plasma clearance was 21.93 L/hour. This compares with values of greater than 40 hours and 40.8 L/hour reported in healthy volunteers. After 8 hours, the mean dialysate concentration was 0.07 mg/mL; PD clearance was 0.06 L/hr.

Conclusion

Azithromycin is not substantially removed by CAPD in the absence of peritonitis and cannot be recommended for widespread use in this setting at present. However, the successful use of azithromycin in CAPD peritonitis, due possibly to an intracellular drug transport mechanism, has been reported. Future research should address this possibility.

Sinus Fluid Penetration of Oral Clarithromycin and Azithromycin in Patients with Acute Rhinosinusitis

Background

The aim of this study was to investigate the extracellular concentration and the degree of sinus fluid penetration of newer macrolides, within the first 24–48 hours of treatment in patients with acute bacterial rhinosinusitis (ABRS), choosing clarithromycin and azithromycin as model antibiotics. An open, noninterventional pharmacokinetic study was performed at a tertiary teaching hospital.

Methods

In 36 outpatients with ABRS, sinus fluid aspirates and serum samples were collected 2, 4, 6, 8, and 12 hours or 2, 6, 12, and 24 hours after the administration of three doses of oral clarithromycin, 500 mg, twice daily or two doses of oral azithromycin, 500 mg, once daily, respectively. Drug concentrations were determined in both matrices by high-performance liquid chromatography with fluorometric detection, and the pH was estimated for all sinus fluid samples.

Results

The average clarithromycin sinus fluid concentration was found to be significantly higher than the corresponding azithromycin concentration (2.47 mg/L versus 0.65 mg/L), while the extent of the average sinus fluid penetration, expressed by the ratio of drug concentration in tissue versus serum, was similar for both drugs (115 and 120%, respectively).

Conclusion

In patients with ABRS, clarithromycin and azithromycin present adequate penetration into sinus fluid to eradicate erythromycin-sensitive strains of Streptococcus pneumoniae. Considering their comparative in vitro activity, the sinus fluid pH effect, and their sinus fluid penetration profile, we may conclude that among the erythromycin-resistant S. pneumoniae strains, clarithromycin might be advantageous over azithromycin in eradicating some of the low-level resistant strains.

Azithromycin: mechanisms of action and their relevance for clinical applications

Azithromycin is a macrolide antibiotic which inhibits bacterial protein synthesis, quorum-sensing and reduces the formation of biofilm. Accumulating effectively in cells, particularly phagocytes, it is delivered in high concentrations to sites of infection, as reflected in rapid plasma clearance and extensive tissue distribution. Azithromycin is indicated for respiratory, urogenital, dermal and other bacterial infections, and exerts immunomodulatory effects in chronic inflammatory disorders, including diffuse panbronchiolitis, post-transplant bronchiolitis and rosacea. Modulation of host responses facilitates its long-term therapeutic benefit in cystic fibrosis, non-cystic fibrosis bronchiectasis, exacerbations of chronic obstructive pulmonary disease (COPD) and non-eosinophilic asthma. Initial, stimulatory effects of azithromycin on immune and epithelial cells, involving interactions with phospholipids and Erk1/2, are followed by later modulation of transcription factors AP-1, NFκB, inflammatory cytokine and mucin release. Delayed inhibitory effects on cell function and high lysosomal accumulation accompany disruption of protein and intracellular lipid transport, regulation of surface receptor expression, of macrophage phenotype and autophagy. These later changes underlie many immunomodulatory effects of azithromycin, contributing to resolution of acute infections and reduction of exacerbations in chronic airway diseases. A sub-group of post-transplant bronchiolitis patients appears to be sensitive to azithromycin, as may be patients with severe sepsis. Other promising indications include chronic prostatitis and periodontitis, but weak activity in malaria is unlikely to prove crucial. Long-term administration of azithromycin must be balanced against the potential for increased bacterial resistance. Azithromycin has a very good record of safety, but recent reports indicate rare cases of cardiac torsades des pointes in patients at risk.

Azithromycin: more lethal than chloramphenicol?

Azithromycin is commonly used in sexual health and respiratory medicine, often when the diagnosis is presumptive. A recent article by Ray et al. reported that 1 out of 20 000 courses of low-dose azithromycin was associated with (sudden) cardiovascular death (including 1 out of 4000 courses in high-risk cardiovascular patients), ascribing these deaths to azithromycin itself. Here, we critique the actual study and examine conflicting data from randomised control trials, animal studies and observational data.

Azithromycin as a cause of QT-interval prolongation and torsade de pointes in the absence of other known precipitating factors

During treatment with azithromycin, a 55 year-old woman developed a newly prolonged QT interval and torsade de pointes in the absence of known risk factors. Female gender and acute renal failure may be considerations in patients treated with azithromycin.

Acute renal failure in CF patients chronically infected by the Liverpool epidemic Pseudomonas aeruginosa strain (LES)

Although acute renal failure has been described in children with CF in relation to intravenous aminoglycoside use, there are no reports in the adult CF literature. We describe 8 cases of acute renal failure in adult CF patients, all occurring during the use of intravenous aminoglycosides for the treatment of pulmonary exacerbations with an epidemic multi-resistant Pseudomonas aeruginosa strain. Potential contributory factors are discussed. These cases demonstrate another complication of infection by epidemic Pseudomonas strains in CF, and confirm the need for effective segregation policies to prevent this.

In vitro activity and pharmacodynamics of azithromycin and clarithromycin against Streptococcus pneumoniae based on serum and intrapulmonary pharmacokinetics

BACKGROUND

Multidrug-resistant strains of Streptococcus pneumoniae are increasingly common worldwide, but the clinical significance of their resistance to the macrolide antibiotics is controversial. Applying pharmacokinetic and pharmacodynamic principles can assist in the selection of appropriate antimicrobial therapy.

OBJECTIVES

The purpose of this study was to determine the in vitro activity of penicillin, azithromycin, clarithromycin, and clindamycin against clinical isolates of S. pneumoniae and to evaluate the pharmacodynamics of azithromycin and clarithromycin based on serum and epithelial lining fluid (ELF) concentrations.

METHODS

The minimum inhibitory concentrations (MICs) of penicillin, azithromycin, clarithromycin, and clindamycin were determined for 307 isolates of S. pneumoniae using broth microdilution. Using serum and ELF concentrations after standard dosing, we calculated the proportion of isolates against which it would be possible to obtain a ratio of azithromycin area under the curve to MIC > or =25 and clarithromycin concentrations that exceeded the MIC for > or =40% of the dosing interval.

RESULTS

Overall, 19.5%, 25.4%, 25.1%, and 7.2% of the 307 pneumococcal isolates were resistant to penicillin, azithromycin, clarithromycin, and clindamycin, respectively. However, 71.7% of penicillin-resistant strains were also resistant to azithromycin and clarithromycin. Based on serum concentrations, clarithromycin achieved its pharmacodynamic target in 76.9% of isolates, compared with 59.9% for azithromycin. Based on ELF concentrations, clarithromycin achieved its pharmacodynamic target in 93.5% of isolates, compared with 74.6% for azithromycin. Based on ELF concentrations, clarithromycin achieved its pharmacodynamic target in 86.7% of penicillin-resistant isolates, compared with 28.3% for azithromycin.

CONCLUSIONS

On the basis of serum and ELF concentrations, clarithromycin achieved pharmacodynamic targets against a greater proportion of S. pneumoniae isolates than did azithromycin. Clinical studies are needed to determine the efficacy of these agents against pneumococci that demonstrate in vitro resistance using current susceptibility breakpoints.

Treatment of typhoid fever with azithromycin versus chloramphenicol in a randomized multicentre trial in India

To compare the clinical and bacteriological efficacies of azithromycin and chloramphenicol for treatment of typhoid fever, 77 bacteriologically evaluable adults, with blood cultures positive for Salmonella typhi or Salmonella paratyphi A susceptible to their assigned drugs, were entered into a randomized open trial at four hospitals in India. Forty-two patients were randomized to receive azithromycin 500 mg p.o. od for 7 days and 35 to receive chloramphenicol 2-3 g p.o. od in four divided doses for 14 days. Thirty-seven patients (88%) in the azithromycin group responded with clinical cure or improvement within 8 days and 30 patients (86%) in the chloramphenicol group responded with cure or improvement. By day 14 after the start of treatment, all patients treated with azithromycin and all except two of the patients treated with chloramphenicol (94%) were cured or improved. Blood cultures repeated on day 8 after start of therapy showed eradication of organisms in 100% of patients in the azithromycin group and 94% of patients in the chloramphenicol group. By day 14 the eradication rate in the chloramphenicol group had increased to 97%. Stool cultures on days 21 and 35 after start of treatment showed no prolonged faecal carriage of Salmonella spp. in either group. These results indicate that azithromycin given once daily for 7 days was effective therapy for typhoid fever in a region endemic with chloramphenicol-resistant S. typhi infection and was equivalent in effectiveness to chloramphenicol given to patients with chloramphenicol-susceptible infections.

Disposition of oral azithromycin in humans

BACKGROUND

The oral bioavailability of azithromycin is approximately 37% in healthy subjects; little is known about the disposition of the remaining 63% of the dose. This study attempted to describe the fate of azithromycin before absorption.

METHODS

Twelve subjects with ileostomies in place for > 1 month were studied in this open-label, randomized, three-center, two-period, two-treatment crossover study. Subjects randomly received single 500 mg intravenous infusion (over 1 hour) or two 250 mg oral capsules after a fast for > 12 hours. Blood and ileostomy samples were collected serially after each administration and analyzed for azithromycin and two metabolites (descladinose and 9a-N-desmethyl metabolites) by HPLC with electrochemical detection.

RESULTS

Mean +/- SD peak concentration values after oral and intravenous administration were 0.21 +/- 0.08 and 3.40 +/- 1.12 microgram/ml. Mean values for area under the serum concentration versus time curve were 1.27 +/- 0.65 and 7.14 +/- 1.34 micrograms x hr/ml, respectively. The absolute bioavailability of 16.2% was approximately one-half the value observed previously in healthy subjects. Recovery in ileostomy fluid (percent of dose in 24 hours) or azithromycin, descladinose, and 9a-N-desmethyl metabolites were 13%, 0.5%, and 1% (total, 15%) after intravenous dosing and 47%, 13%, and 2% (total, 62%) after oral dosing. Total and ileal clearances were 776 +/- 126 and 158 +/- 63 ml/min after intravenous dosing.

CONCLUSION

Because more descladinose metabolite was detected after oral dosing, acid degradation of azithromycin before absorption contributed to some loss in oral bioavailability. Further, ileal clearance (biliary plus intestinal excretion clearance) in this population represented 21% of total clearance. Taken together, these data suggest that the cause of low oral bioavailability of azithromycin is the result of incomplete absorption rather than acid degradation or extensive first-pass metabolism.