Pharmacokinetics of LY163892 in infants and children

In vitro activity and pharmacodynamics of oral beta-lactam antibiotics against Streptococcus pneumoniae from southeast Missouri

STUDY OBJECTIVES

To determine the frequency of reduced susceptibility to penicillin, and to compare the in vitro activity and pharmacodynamics of oral beta-lactam antibiotics against clinical isolates of Streptococcus pneumoniae from southeast Missouri.

SETTING

Cape Girardeau, Missouri (population 35,500). Interventions. Minimum inhibitory concentrations (MICs) were determined for penicillin, amoxicillin, amoxicillin-clavulanic acid, cefprozil, cefuroxime, cefpodoxime, cefaclor, and loracarbef by E test for 108 isolates of S. pneumoniae. The MIC50, MIC90, and percentage susceptibility were calculated for each agent. Pharmacokinetic variables were obtained from the literature, and serum concentration-time profiles were simulated for a 25-kg child taking pediatric dosages commonly administered to treat otitis media. The average time above MIC (T > MIC) was calculated as percentage of the dosing interval using free concentrations and the MIC for each individual isolate. Analysis of variance (Scheffe post hoc test) was used to determine differences among agents for in vitro activity and T > MIC (level of significance, p<0.05).

MEASUREMENTS AND MAIN RESULTS

The frequency of penicillin-nonsusceptible S. pneumoniae was 28.7% (31/108). For 25 penicillin-intermediate isolates, amoxicillin and amoxicillin-clavulanic acid were significantly more active than cefprozil, cefaclor, and loracarbef. The T > MIC for amoxicillin and amoxicillin-clavulanic acid, simulated at 13.3 mg/kg every 8 hours, was significantly longer than that for all other beta-lactams.

CONCLUSION

Amoxicillin and amoxicillin-clavulanic acid have superior in vitro activity and longer T > MIC for penicillin-intermediate isolates than the other oral beta-lactams.

A national collaborative study of the in vitro activity of oral cephalosporins and loracarbef (LY 163892). Australian Group for the Study of Antimicrobial Resistance (AGAR)

A national collaborative study involving the laboratories of 17 Australian hospitals examined the in vitro activity of loracarbef, cefaclor, cephalexin, amoxycillin and amoxycillin/clavulanate against 2661 recently isolated common bacterial pathogens. Loracarbef was the most active agent against Escherichia coli (MIC90 = 1 mg/l) and had activity comparable to other agents against Klebsiella pneumoniae and Proteus mirabilis. Like the oral cephalosporins, it had no activity against species of Enterobacter and Serratia. beta-lactamase-producing Staphylococcus aureus and Haemophilus influenzae were moderately sensitive to loracarbef (MIC90 = 8 mg/l for both species). Streptococcus pneumoniae was moderately sensitive to loracarbef (MIC90 = 2 mg/l) but strains which were insensitive to penicillin were often highly resistant.

Pharmacokinetic disposition of loracarbef in healthy young men and women at steady state

The pharmacokinetic disposition of 200- and 400-mg doses of a novel carbacephem, loracarbef, was determined over a dose interval on day 8, after ingestion of drug doses twice daily for 7 days, in 20 young, healthy volunteers of both genders. Drug was analyzed in plasma, urine, saliva, vaginal secretions, and fecal filtrate. Peak plasma concentration was proportional to dose for both men (4.0 +/- 1.3 and 8.8 +/- 3.4 mg/L) and women (8.0 +/- 5.6 and 15.3 +/- 3.3 mg/L), and the observed time to peak increased from 1 to 2 hours with the increased dose. Apparent volume of distribution was greater in men than women (0.385 +/- 0.114 versus 0.270 +/- 0.075 L/kg; P < .03). The drug was virtually quantitatively excreted unchanged in urine, and its renal clearance exceeded creatinine clearance in all subjects. Renal loracarbef clearance correlated with neither weight-corrected dose nor creatinine clearance in these healthy subjects. There was no evidence for drug accumulation in the body with chronic ingestion. Loracarbef was detected in the fecal filtrate of seven volunteers, but did not account for more than 7% of the daily dose. Loracarbef was detected in vaginal secretions of two of five volunteers who ingested the 400-mg dose. No drug was detected in saliva obtained just before dose ingestion. These data are consistent with complete bioavailability for an oral beta-lactam antibiotic drug that is virtually completely eliminated unchanged by the kidney.

Loracarbef. A review of its antimicrobial activity, pharmacokinetic properties and therapeutic efficacy

Loracarbef is an orally administered member of a new synthetic class of beta-lactam antibiotics, the carbacephems, which is characterised by enhanced chemical stability. At low concentrations (< 2 mg/L) in vitro, it inhibits Streptococcus pneumoniae, S. pyogenes, beta-haemolytic streptococci groups B, C and G. Proteus mirabilis and Moraxella catarrhalis, including beta-lactamase-producing strains. At therapeutic plasma concentrations it is also active in vitro against most strains of Staphylococcus aureus, S. saprophyticus, Escherichia coli and beta-lactamase-positive and -negative strains of Haemophilus influenzae. Like other beta-lactams, loracarbef is inactive against methicillin-resistant strains of S. aureus. When administered at dosages of 200 to 400 mg twice daily, the clinical and bacteriological efficacy of loracarbef is comparable with that of amoxicillin and amoxicillin/clavulanic acid in patients with upper or lower respiratory tract infections, and comparable with that of cefaclor in treating infections of the lower respiratory tract, skin and skin structures and urinary tract. Loracarbef and phenoxymethylpenicillin (penicillin V) were equally effective in treating streptococcal pharyngitis and tonsillitis. Loracarbef is generally well tolerated by all age groups and causes less diarrhoea than amoxicillin/clavulanic acid. It is administered twice daily. It offers a suitable alternative to other orally administered antibiotics for the treatment of mild to moderate infections caused by susceptible organisms.

Loracarbef: a new orally administered carbacephem antibiotic

OBJECTIVE

To discuss the in vitro activity, pharmacokinetics, clinical efficacy, adverse effects, and relative merits of loracarbef, a new orally administered carbacephem antibiotic.

DATA SOURCES

Pertinent literature was identified by a review of selected journals and a MEDLINE search. Additional information was provided by the manufacturer of loracarbef.

STUDY SELECTION

All studies that have evaluated the clinical efficacy of loracarbef were included. In vitro studies were included if they used similar methodologies. Additional information was incorporated regarding the chemistry, pharmacokinetics, and adverse effects of loracarbef.

DATA SYNTHESIS

Loracarbef has antibacterial activity against most community-acquired respiratory tract, skin and skin structure, and urinary tract pathogens. The drug is well absorbed after oral administration and plasma concentrations achieved in patients are greater than the in vitro minimum inhibitory concentrations for most of the above bacteria. Although the majority of the clinical studies with loracarbef have methodologic deficiencies, loracarbef therapy has demonstrated similar efficacy in the treatment of upper respiratory tract (except otitis media), lower respiratory tract, skin and skin-structure, and urinary tract infections compared with accepted antibiotics. Potential advantages of the new carbacephem may be improved patient compliance with its less frequent dosing schedule (once or twice a day, depending on the infection), and a low incidence of adverse effects.

CONCLUSIONS

Preliminary data indicate that loracarbef may be an alternative agent for the treatment of a variety of community-acquired infections. Additional clinical experience and rigorously controlled comparative clinical trials are necessary to enable practitioners to fully define the therapeutic role of loracarbef.

Pharmacokinetics of loracarbef in pediatric patients

Loracarbef is an investigational oral antibiotic but its pharmacokinetics have not been studied after multiple oral doses in pediatric patients. The pharmacokinetics of loracarbef were determined in 18 pediatric patients after multiple oral doses. 8 patients with streptococcal pharyngitis received 7.5 mg/kg every 12 h, and 10 patients with otitis media were given 15 mg per kg every 12h. Multiple blood and urine samples were collected to measure loracarbef concentrations. In patients with streptococcal pharyngitis, the mean maximum serum concentration (Cmax), the time to achieve maximum concentration (Tmax), area under the serum concentration-time curve (AUC) and elimination half-life (t1/2) were 10.6 +/- 3.6 mcg/ml, 0.78 +/- 0.21 h, 21.4 +/- 7.2 mcg.h/ml, and 1.2 + 0.4 h, respectively. The mean Cmax, Tmax, AUC and t1/2 were 18.0 +/- 5.4 mcg/ml, 0.83 +/- 0.44 h, 35.6 +/- 9.4 mcg.h/ml, and 1.1 +/- 0.5 h, respectively, in patients with otitis media. The Cmax exceeded the minimum inhibitory concentration of common susceptible pathogens causing pharyngitis and otitis media by severalfold. Nearly 60% of the dose was excreted unchanged in the urine during the dosage interval. The pharmacokinetics were independent of dose. Loracarbef was well tolerated in all patients. These data suggest that loracarbef may be used safely at doses of 7.5 mg/kg every 12 h in pediatric patients with streptococcal pharyngitis and 15 mg/kg every 12 h in those with otitis media.

Antibiotic therapy for urinary tract infections

Loracarbef, a member of the carbacephem class of beta-lactam antibiotics, was tested in randomized, double-blind, parallel studies for the treatment of uncomplicated urinary tract infections (UTIs). In one study conducted in the United States, a 7-day course of once-daily doses of loracarbef (200 mg) was compared with a 7-day course of multiple daily doses of cefaclor (250 mg three times a day). Analysis of data from a small, homogeneous patient population of 108 college-aged women showed that loracarbef produced clinical and bacteriologic responses similar to those produced by cefaclor. At 5-9 days posttherapy, bacteriologic cure was observed in 96% of patients in the loracarbef group and 90% of patients in the cefaclor group (p = 0.614); at 4-6 weeks post-therapy, the same cure rate (81%) was observed in both groups. Analysis of the larger (333 patients) and more heterogeneous study population containing several male and elderly female patients showed that loracarbef again produced responses similar to those produced by cefaclor, with no statistically significant differences seen between the groups at 5-9 days or at 4-6 weeks posttherapy. The adverse events reported by the loracarbef and cefaclor groups were also comparable in both the small and large patient populations analyzed. Similarly favorable results were seen when a 7-day regimen of loracarbef (200 mg once a day) was compared with a 7-day regimen of norfloxacin (400 mg twice a day) in a large European study of approximately 300 patients with uncomplicated cystitis. These studies demonstrate that the safety and efficacy of once-daily loracarbef are comparable to the safety and efficacy of multiple-dose/day therapy with other antimicrobial agents commonly used in the treatment of uncomplicated UTIs.

Bactericidal titers of loracarbef (LY 163892) in serum and killing rates in volunteers receiving 400 versus 200 milligrams

In a randomized crossover trial, six volunteers received 200- and 400-mg doses of loracarbef (LY 163892), a new oral cephalosporin. Mean +/- standard error of the mean concentrations in serum obtained after 1.5 and 3 h were 13.2 +/- 2.8 and 4.3 +/- 0.7 mg/liter, respectively, after the 400-mg dose and 6.9 +/- 1.0 and 1.7 +/- 0.2 mg/liter, respectively, after the 200-mg dose. Bactericidal reciprocal titers measured against respiratory pathogens in serum suggested that loracarbef would be highly effective against Streptococcus pneumoniae and Streptococcus pyogenes (median titers, 8 to 128 at 1.5 h and less than 2 to 32 at 3 h) and beta-lactamase-negative Haemophilus influenzae (median titers, 4 at 1.5 h and 2 to 4 at 3 h). Other species (Branhamella catarrhalis, Streptococcus anginosus, Staphylococcus aureus) were associated with lower bactericidal titers. Killing curves performed against 12 strains demonstrated that the bioactivity of loracarbef (measured by the reduction in the area under the control growth curve) was significantly correlated with the concentration/MIC ratio, whereas the initial rate of killing was not, once the concentration was greater than the MIC. Our results suggest that administration of 400 mg of loracarbef every 8 h might be associated with more favorable pharmacodynamic parameters against target bacteria.

High-performance liquid chromatographic determination of loracarbef, a potential metabolite, cefaclor and cephalexin in human plasma, serum and urine

A high-performance liquid chromatographic (HPLC) method is reported for the determination of a new carbacephem antibiotic, loracarbef, a hydroxylated analogue, and two cephalosporins, cefaclor and cephalexin, in plasma, serum, and urine. The antibiotics are extracted from plasma by means of C18 solid-phase cartridges. Urine samples are diluted with water and directly injected on the HPLC system. The HPLC system utilizes a Supelcosil LC-18-DB (250 mm x 4.6 mm I.D.) reversed-phase column and ultraviolet detection at 265 nm. The limit of quantitation is 0.5 micrograms/ml for each compound. Excellent correlation of plasma concentrations is shown between results determined by HPLC and those obtained by microbiological agar-well diffusion assays. Stability studies of loracarbef in human plasma show the antibiotic to be stable for at least 24 h at room temperature and for at least twelve months at -20 degrees C.

Comparative evaluation of loracarbef and amoxicillin-clavulanate for acute otitis media

One hundred five infants and children with acute otitis media were randomized to therapy with loracarbef, an experimental carbacephem antibiotic, or amoxicillin-clavulanate (Augmentin), an approved drug for this disease. Ninety-two were evaluable (46 in each group). Middle ear fluid samples obtained for culture before therapy grew Haemophilus spp. in 30% of cases, pneumococci in 29% of cases, and Moraxella catarrhalis in 15% of cases. beta-Lactamase-producing bacteria were found in 37% of patients. Clinical failure occurred in four loracarbef-treated patients and one amoxicillin-clavulanate-treated patient (P = 0.361). Recurrence of acute otitis media was more common in the 2 to 3 weeks after loracarbef treatment (eight patients) than it was after amoxicillin-clavulanate therapy (three patients), but not significantly so (P = 0.197). Thus, combined failure and recurrence occurred in 12 loracarbef-treated patients and four amoxicillin-clavulanate-treated patients (P = 0.052). Gastrointestinal side effects occurred in 13 loracarbef-treated and 21 amoxicillin-clavulanate-treated patients (P = 0.13). Diaper rash was more common with amoxicillin-clavulanate (22 patients) than with loracarbef (10 patients; P = 0.016). Satisfactory results were achieved with both antibiotics, and adverse effects, although common, were minor.

Loracarbef versus cefaclor in the treatment of urinary tract infections in women

In a double-blind, prospective, randomized study, 108 college women with acute urinary tract infections were treated for 7 days with either loracarbef (LY163892) at 200 mg once daily (n = 53) or cefaclor at 250 mg three times daily (n = 55). The cure rates at 5 to 9 days after treatment in the loracarbef and cefaclor groups were 96 and 90%, respectively. Both loracarbef and cefaclor are safe, well tolerated, and effective in the treatment of urinary tract infections in women.

Effect of loracarbef on the normal oropharyngeal and intestinal microflora

20 healthy volunteers received loracarbef capsules 200 mg b.i.d. for 7 days. Saliva and stool specimens were taken before loracarbef administration and on the 2nd, 5th, and 7th day during the administration period, and again 2, 5 and 9 days after withdrawal of the antibiotic to study the effect of loracarbef on the normal microflora. The concentrations of loracarbef in serum, saliva and faeces were determined by an agar diffusion method. The mean serum peak concentration attained after 1 h was 6.8 mg/l and the saliva concentrations were in the range 0-0.9 mg/l. The loracarbef concentrations in faeces ranged from 0 to 0.9 mg/kg. The changes in the the oropharyngeal microflora were minor and only bacteroides rods were affected. In the intestinal aerobic microflora, the number of enterococci and streptococci slightly increased while staphylococci, micrococci, corynebacteria, bacillus and enterobacteria were not affected. The number of bifidobacteria and eubacteria in the anaerobic microflora decreased while no other bacterial groups were affected. One week after withdrawal of loracarbef, both the oropharyngeal and intestinal microflora had returned to normal. No new colonizing loracarbef resistant microorganisms were observed during the investigation period.

Loracarbef concentrations in middle ear fluid

Loracarbef concentrations in plasma and middle ear fluid (MEF) were measured in specimens obtained approximately 2 h after doses of 7.5 or 15 mg/kg. The mean +/- standard deviation concentrations in MEF were 2.0 +/- 2.6 mg/liter (48% of the concentration in plasma) after the smaller dose and 3.9 +/- 2.6 mg/liter (42% of the concentration in plasma) after the larger dose. With the larger dose, the concentrations in MEF were greater than the MIC for 90% of strains of the usual pathogens of acute otitis media tested in 16 of 17 specimens.