THE NEW PENICILLINS

Hydrazyl hydroxycoumarins as new potential conquerors towards Pseudomonas aeruginosa

A class of unique hydrazyl hydroxycoumarins (HHs) as novel structural scaffold was developed to combat dreadful bacterial infections. Some HHs could effectively suppress bacterial growth at low concentrations, especially, pyridyl HH 7 exhibited a good inhibition against Pseudomonas aeruginosa 27853 with a low MIC value of 0.5 μg/mL, which was 8-fold more active than norfloxacin. Furthermore, pyridyl HH 7 with low hemolytic activity and low cytotoxicity towards NCM460 cells showed much lower trend to induce the drug-resistant development than norfloxacin. Preliminarily mechanism exploration indicated that pyridyl HH 7 could eradicate the integrity of bacterial membrane, result in the leakage of intracellular proteins, and interact with bacterial DNA gyrase via non-covalent binding, and ADME analysis manifested that compound 7 gave good pharmacokinetic properties. These results suggested that the newly developed hydrazyl hydroxycoumarins as potential multitargeting antibacterial agents should be worthy of further investigation for combating bacterial infection.

Amoxicillin/clavulanate for infections in infants and children: past, present and future

Chemical synthesis of the penicillin nucleus in the 1950s made introduction of a broad array of new and important antimicrobials, including ampicillin and amoxicillin, possible. Ampicillin was introduced in 1962 in oral and parenteral forms as the first of the semisynthetic penicillins to provide increased activity against Gram-negative bacteria. Amoxicillin replaced oral ampicillin beginning in 1974 because amoxicillin resulted in higher and more prolonged serum concentrations than did equivalent doses of ampicillin. Amoxicillin/clavulanate (Augmentin) was introduced in the United States in 1984 to enhance the activity of amoxicillin by addition of the beta-lactamase inhibitor, clavulanic acid. During the past 20 years, amoxicillin/clavulanate has proven effective for a variety of pediatric infectious diseases, particularly acute otitis media (AOM). In 2001, a new pediatric formulation, high dose amoxicillin/clavulanate (Augmentin ES-600) was approved for use in the United States. The high dose preparation addressed the needs of pediatricians by providing greater amounts of amoxicillin while maintaining the same daily dose of clavulanic acid as the regular strength formulation. Doubling the dose of amoxicillin for management of recurrent and persistent AOM was recommended in 1999 by the Centers for Disease Control and Prevention because of concern about the increased incidence of nonsusceptible strains of Streptococcus pneumoniae. The original formulation combined amoxicillin/clavulanate in a 4:1 ratio and was followed by a 7:1 ratio formulation. The high dose formulation (600 mg of amoxicillin per 5 ml) provides a 14:1 ratio of amoxicillin to clavulanate. Although management of AOM will likely undergo changes in the coming years, amoxicillin is expected to remain first line therapy for AOM. For children who fail initial therapy with amoxicillin, high dose amoxicillin/clavulanate, an oral cephalosporin or parenteral ceftriaxone is recommended.

Penetration of imipenem into human aqueous and vitreous humor

Twenty-five patients about to undergo cataract surgery and ten patients about to undergo vitrectomy received a 1-g intravenous dose of imipenem before surgery. Specimens of aqueous or vitreous humor were then obtained and assayed for antibiotic content with a microbiologic disk agar technique. A mean peak aqueous humor level of 2.99 micrograms/ml was found at approximately two hours after administration, and a mean vitreous level of 2.53 micrograms/ml was found from two hours to three hours 15 minutes after administration. These concentrations were well above the minimum inhibitory concentration of imipenem for 90% (MIC90) of Staphylococcus epidermidis, S. aureus, and the Enterobacteriaceae commonly involved in bacterial endophthalmitis.

Human vitreous levels of selected antistaphylococcal antibiotics

Staphylococcus epidermidis and S. aureus are the most common causes of bacterial endophthalmitis. A study of the penetration of selected antistaphylococcal antibiotics into human vitreous was undertaken in 58 patients. After 2-g intravenous doses of cephalothin, cefazolin, methicillin, oxacillin, or nafcillin were given to patients about to undergo vitreous surgery, mean vitreous levels for each antibiotic were as follows: cephalothin, 0.97 microgram/ml in diabetics and 0.69 microgram/ml in nondiabetics; cefazolin, 0.84 microgram/ml in diabetics and 1.6 microgram/ml in nondiabetics; methicillin, 2.56 micrograms/ml in diabetics and 2.64 micrograms/ml in nondiabetics; oxacillin, 0.62 microgram/ml in diabetics and 0.34 microgram/ml in nondiabetics; and nafcillin, 0.73 microgram/ml in diabetics and 0.75 microgram/ml in nondiabetics. Only cefazolin produced vitreous concentrations consistently above its minimum inhibitory concentration for 90% of S. epidermidis isolates. Staphylococcus aureus isolates were not similarly covered. There was a trend toward higher vitreous antibiotic concentrations in patients with proliferative vitreoretinopathy and rubeosis.

The cephalosporin antibiotic agents--I. Considered as a group

This review of the cephalosporin antibiotic family will appear in three parts. The first part will provide general information on the cephalosporins as a class, highlighting the history, chemistry, pharmacokinetics, toxicity, and the segregation of these agents into “generations.” The second segment will discuss the antimicrobial spectra of activity of the first- and second-generation agents, while the last article will focus on the third-generation and investigational cephalosporins under evaluation.

Despite a confusing, and somewhat overwhelming array of cephalosporin antimicrobial agents presently available to the clinician, more are on the way. Since 1962 and the introduction of cephalothin, the first agent in this family, there has been a constant parade of new cephalosporins from various pharmaceutical manufacturers. Drug manufacturers are attempting to develop a more effective drug with attractive pharmacokinetic features and less toxicity by modifying the basic cephalosporin molecule.

Reversible neutropenia associated with ampicillin therapy in pediatric patients

Hematologic abnormalities associated with penicillin compounds are uncommon, and neutropenia associated with ampicillin is reported even less frequently. Neutropenia developed in three pediatric patients after high-dose (150-400 mg/kg) ampicillin therapy over a period of 3 to 12 days. In all cases, the white blood cell and neutrophil counts returned towards normal within 4 to 11 days after discontinuation of the antibiotic. Bone marrow examination revealed a maturation arrest in one and slight shift to the left in the maturation of granulocytic cells in another. Other marrow components were normal. Red blood cells, reticulocytes, platelets, and hemoglobin did not show any abnormal alteration in any of the patients. Physicians administering ampicillin, particularly in high doses, should be alert to the possible development of neutropenia; however, all reported neutropenias have been reversible.

Antimicrobial prophylaxis for recurrent acute otitis media

Antimicrobial prophylaxis for children who have frequently recurring, severe episodes of acute otitis media appears to constitute a reasonable management option, even though it is not yet clear whether the advantages outweigh the disadvantages and risks. It remains for well-designed and well-executed studies that extend over relatively long periods to indicate whether this approach to management is the best of the available options, and if so, which of the available drugs is preferable.

Penetrance of nafcillin into human ventricular fluid: correlation with ventricular pleocytosis and glucose levels

Fourteen hydrocephalic pediatric patients with suspected shunt infections were studied for penetrance of nafcillin into the ventricular fluid after intravenous administration. In seven patients with bacterial ventriculitis, the concentration of nafcillin in ventricular fluid was 0.8 to 20.4% of the peak concentration in serum. In the remaining seven patients without bacterial ventriculitis, ventricular fluid levels ranged between less than or equal to 0.02 to 4% of peak serum concentrations. Although the degree of pleocytosis correlated poorly with penetrance, ventricular fluid glucose levels correlated inversely with penetrance of nafcillin (r = -0.7275, P less than 0.001).

Ampicillin penetration into the rabbit eye

Distribution of intravenously injected ampicillin of 50 mg/kg was studied in the rabbit eye using radioactive tracer method. Antibiotic concentration regarded as therapeutic in the treatment of gram-negative organisms was obtained in all vascularized ocular structures. Intermediate values were measured from the cornea and aqueous humour. In the vitreous body and lens, ampicillin was unable to approach a concentration that would be effective against the common gram-negative organisms. The low ampicillin concentration in the vitreous body and lens was unchanged by systemically administered probenecid, which in other parts of the eye caused significantly higher ampicillin levels.

Nafcillin treatment of Staphylococcus aureus meningitis

Serial serum and cerebrospinal fluid nafcillin concentrations were determined in a patient successfully treated with nafcillin (200 mg/kg per day) for Staphylococcus aureus bacteremia and meningitis. Nafcillin and methicillin cerebrospinal fluid concentrations were compared.

Intravitreal oxacillin in experimental staphylococcal endophthalmitis

We compared combined intravitreal and systemic oxacillin to combined subconjunctival and systemic oxacillin in the treatment of experimental staphylococcal endophthalmitis. Intravitreal injection of 500 mcg was nontoxic to all intraocular structures and produced concentrations in the vitreous bactericidal to all susceptible strains of Staphylococcus aureus for almost 24 hours. In eyes treated 8, 10, and 12 hours after intravitreal inoculation of 10000 to 20000 penicillinase-producing S. aureus organisms, intravitreal injection of 500 mcg of oxacillin was superior to subconjunctival injection of 100 mg when each was combined with seven days of intensive intramuscular oxacillin.

5-Fluorocytosine in human cryptococcosis

Because there are few persuasive data for selecting one semisynthetic penicillin or cephalosporin over another for treatment of serious staphylococcal infections, 118 recent clinical isolates of Staphylococcus aureus were studied to determine to what extent the presence of β-lactamase affected the relative anti-staphylococcal activity of six penicillins and seven cephalosporins. In addition, the effect of inoculum was studied for its possible effect on the anti-staphylococcal activity of the 13 β-lactam antibiotics. By all criteria, methicillin and nafcillin were clearly more resistant to both the inoculum effect and the production of staphylococcal β-lactamase, whereas benzylpenicillin and cephaloridine (especially benzyl-penicillin) were the most susceptible to these effects. Cephazolin was clearly more susceptible to staphylococcal β-lactamase and heavy inocula than the other cephalosporins (with the exception of cephaloridine), whereas cephalothin was the most resistant cephalosporin to these factors. The minimal inhibitory concentration for benzylpenicillin for tests with undiluted inoculum, compared to results with inoculum diluted 10⁻⁴, differed by a factor up to 16,384, whereas with methicillin and nafcillin the differences were rarely more than twofold. Ratios for the other 10 antibiotics fell between these extremes. These results suggest that methicillin or nafcillin is most stable to staphylococcal β-lactamase, and that benzylpenicillin and cephaloridine are the most susceptible.

Bacterial endocarditis following aortic valve replacement. Clinical and pathologic correlations

The clinical and pathologic findings in three patients with bacterial infection at the sites of prosthetic aortic valves are described. Each presented typical clinical features of acute bacterial endocarditis followed by the sudden development of severe and ultimately fatal aortic regurgitation. Pathologically the infectious process was characterized by extensive necrosis of the aortic annulus, disruption of the aortic wall, and the formation of abscesses in the periaortic tissues. In two patients the prosthetic valve was partially detached from the annulus, whereas in the other it was totally dislodged and impacted in the aortic arch shortly before death. In all, secondary operative intervention would have been fruitless because of the extent of the infection and the character of the tissue at the aortic root. In one patient fatal staphylococcal endocarditis followed dental extractions despite penicillin prophylaxis. A more comprehensive antibiotic regimen for patients with prosthetic cardiac valves is suggested.

Comparative In Vitro Activities of Lysostaphin and Other Antistaphylococcal Antibiotics on Clinical Isolates of Staphylococcus aureus

The in vitro activity of lysostaphin against clinical isolates of Staphylococcus aureus was determined by conventional tube-dilution methods. For comparison, minimal inhibitory concentration (MIC) values were also determined for penicillin G, ampicillin, methicillin, ristocetin, vancomycin, and erythromycin. Phage type and penicillinase and coagulase production were determined for each isolate. The MIC values for lysostaphin ranged from <0.047 to 12.5 μg/ml; 96% of the penicillinase-positive strains were inhibited by 1.56 μg/ml of lysostaphin, whereas 3.12 μg/ml of vancomycin and methicillin were required to attain the same degree of inhibition.