Evaluation of low-dose, extended-interval clindamycin regimens against Staphylococcus aureus and Streptococcus pneumoniae using a dynamic in vitro model of infection

In vitro elution of amikacin, cefazolin, gentamicin, ampicillin/sulbactam, and meropenem from a commercially available calcium sulfate delivery kit

Introduction

The use of implantable antibiotic beads has become a frequent treatment modality for the management of surgical site infections in human and veterinary medicine. The objective of this study is to describe the elution kinetics of five antibiotics from a commercially available calcium sulfate antibiotic delivery kit. A secondary goal was to compare elution concentrations with minimal inhibitory concentrations (MIC) for commonly encountered bacteria from the University of Florida's veterinary microbiology laboratory database.

Methods

Calcium sulfate powder was combined with amikacin, cefazolin, gentamicin, ampicillin/sulbactam, and meropenem. Triplicates of three antibiotic-loaded beads were immersed in 5 mL of phosphate-buffered saline (PBS) and kept at 37°C under constant agitation. Antibiotic-conditioned PBS was sampled at 14 time points from 1-h to 30 days and analyzed by liquid chromatography to determine the antibiotic concentration.

Results

All beads eluted concentrations of antibiotics for the 30-day sampling period, except for ampicillin/sulbactam, with the most antibiotics being eluted within the first week. The concentration of antibiotics within the eluent within the first 3-9 days (3- and 5-mm beads, respectively) was greater than the MIC of common isolates. The 5 mm bead samples were superior in maintaining higher concentrations for a longer period, compared to the 3-mm beads.

Discussion

CSH beads eluted antibiotics over the 30-day course of the study. Most of the antibiotic elution occurred within the first week and was maintained above the MIC of commonly encountered isolates. This information may be useful for clinical decision making for treatment of local infections encountered in practice.

A Pharmacoepidemiologic Study of the Safety and Effectiveness of Clindamycin in Infants

BACKGROUND

Despite the absence of adequate safety or efficacy data, clindamycin is widely prescribed in the neonatal intensive care unit. We evaluated the association between clindamycin exposure and adverse events, as well as antibiotic effectiveness in infants.

METHODS

This was a retrospective cohort study of infants receiving clindamycin before postnatal day 121 who were discharged from a Pediatrix Medical Group neonatal intensive care unit (1997-2015). Using a previously developed pharmacokinetic model, we performed simulations to predict clindamycin exposure based on available dosing data. We used multivariable logistic regression to evaluate the association between clindamycin exposure and safety outcomes during and after clindamycin therapy. We reported the proportion of infants with methicillin-resistant Staphylococcus aureus (MRSA) bacteremia and clearance of MRSA bacteremia.

RESULTS

A total of 4089 infants received clindamycin at a median (25th-75th percentile) dose of 15 mg/kg/d (12-16). Clearance increased with older gestational age. Infants with the highest total clindamycin exposure had marginally increased odds of necrotizing enterocolitis within 7 days (adjusted odds ratio = 1.95 [1.04-3.63]), but exposure was not associated with death, sepsis, seizures, intestinal perforation or intestinal strictures. Of 25 infants who had MRSA bacteremia, 19 (76%) cleared the infection by the end of the clindamycin course.

CONCLUSIONS

Higher clindamycin exposure was not associated with increased odds of death or nonlaboratory adverse events. The use of pharmacokinetic models combined with available electronic health record data offers a valuable, cost-effective approach to analyzing the safety and effectiveness of drugs in infants when large-scale trials are not feasible.

Pharmacokinetics of intravenous clindamycin phosphate in captive Bennett's wallabies (Macropus rufogriseus)

This study was designed to investigate the pharmacokinetics of clindamycin, a lincosamide antibiotic, in Bennett's wallabies. The pharmacokinetic properties of a single intravenous (IV) dose of clindamycin were determined in six wallabies. A single 20-min IV infusion of 20 mg/kg of clindamycin was administered, followed by blood collection prior to, and up to 12 hr after clindamycin administration. Plasma clindamycin concentrations were determined by high-pressure liquid chromatography (HPLC) with ultraviolet (UV) detection. Pharmacokinetic variables were calculated using a two-compartment model with first order elimination which best fit the data. The mean volume of distribution at steady-state, distribution half-life, and elimination half-life were 898.25 ml/kg, 0.16 hr, 1.79 hr, respectively. No adverse effects were noted after IV administration.

Elution of Clindamycin and Enrofloxacin From Calcium Sulfate Hemihydrate Beads In Vitro

OBJECTIVE

To compare the in vitro elution characteristics of clindamycin and enrofloxacin from calcium sulfate hemihydrate beads containing a single antibiotic, both antibiotics, and each antibiotic incubated in the same eluent well.

STUDY DESIGN

Experimental in vitro study.

METHODS

Calcium sulfate hemihydrate beads were formed by mixing with clindamycin and/or enrofloxacin to create 4 study groups: (1) 160 mg clindamycin/10 beads; (2) 160 mg enrofloxacin/10 beads; (3) 160 mg clindamycin + 160 mg enrofloxacin/10 beads; and (4) 160 mg clindamycin/5 beads and 160 mg enrofloxacin/5 beads. Chains of beads were formed in triplicate and placed in 5 mL phosphate buffered saline (PBS; pH 7.4 and room temperature) with constant agitation. Antibiotic-conditioned PBS was sampled at 14 time points from 1 hour to 30 days. Clindamycin and enrofloxacin concentrations in PBS were determined using high-performance liquid chromatography.

RESULTS

Eluent concentrations from clindamycin-impregnated beads failed to remain sufficiently above minimum inhibitory concentration (MIC) for common infecting bacteria over the study period. Enrofloxacin eluent concentrations remained sufficiently above MIC for common wound pathogens of dogs and cats and demonstrated an atypical biphasic release pattern. No significant differences in elution occurred as a result of copolymerization of the antibiotics into a single bead or from individual beads co-eluting in the same eluent well.

CONCLUSION

Clindamycin-impregnated beads cannot be recommended for treatment of infection at the studied doses; however, use of enrofloxacin-impregnated beads may be justified when susceptible bacteria are cultured.

Augmenting Effect of Antibiotics on Endotoxin Activity May Cause a Safety Problem

Enhancing/interfering effect of antibiotics on endotoxin was evaluated using the endotoxin test and the cell line assay in 28SC cells that has a responsiveness consistent with that of human peripheral blood. When a total of 21 products of seven different kinds of antibiotics were tested, none showed any significant effect on the endotoxin test at its therapeutic dose. However, aminoglycosides showed a significant augmenting effect on IL-6 induction of endotoxin in 28SC cells. Detailed examination of the augmenting effect was made on spectinomycin in the in vitro cell line assay and also in the lethal endotoxin challenge assay in D -galactosamine-treated mice. Spectinomycin also enhanced the endotoxin lethality in D -galactosamine-treated mice. A kinetic analysis in endotoxin-sensitized 28SC cells revealed that the augmentation takes place as quickly as 10 min after spectinomycin treatment. Accordingly, a special caution concerning the augmenting effect was assumed necessary for the safety control of antibiotic products as well as for selecting antibiotics for the therapeutic use.

Serum pharmacokinetics of clindamycin hydrochloride in normal dogs when administered at two dosage regimens

The aim of this cross-over study was to compare clindamycin pharmacokinetics in the serum of clinically normal dogs when administered orally at two dosage regimens (5.5 mg/kg, twice daily, and 11 mg/kg, once daily), separated by a 1 week wash-out period. Serum samples were obtained from six clinically normal laboratory beagles before, 3, 6, 9 and 12 h after the first and fifth dose of clindamycin at 5.5 mg/kg, twice daily, and before, 3, 6, 9, 12, 18 and 24 h after the first and third dose at 11 mg/kg, once daily. Serum clindamycin concentrations were determined by reverse-phase liquid chromatography coupled with mass spectrometry. Results were analysed using Student's paired t-test, at a 5% level of significance. Values of pharmacokinetic parameters that differed significantly between the two dosage regimens included the following: maximal concentration and area under the concentration-time curve were higher at 11 mg/kg, once daily, than at 5.5 mg/kg, twice daily; and, more importantly, the ratio of AUC(0-24) to the minimal inhibitory concentration (MIC) value of 0.5 μg/mL for a 24 h period (AUC(0-24)/MIC) was higher when clindamycin was administered at 11 than at 5.5 mg/kg, at least during the first day of drug administration. Therefore, a better pharmacokinetic profile may be expected when clindamycin is administered at 11 mg/kg, once daily, for the treatment of canine pyoderma caused by Staphylococcus pseudintermedius.

Activities of clindamycin, daptomycin, doxycycline, linezolid, trimethoprim-sulfamethoxazole, and vancomycin against community-associated methicillin-resistant Staphylococcus aureus with inducible clindamycin resistance in murine thigh infection and in vitro pharmacodynamic models

Controversy exists about the most effective treatment options for community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) and about the ability of these strains to develop inducible resistance to clindamycin during therapy. Using both in vitro pharmacodynamic and murine thigh infection models, we evaluated and compared several antimicrobial compounds against CA-MRSA. Strains with inducible macrolide lincosamide-streptogramin type B (iMLS(B)) resistance and strains in which resistance was noninducible were evaluated. Two levels of inocula (10(5) and 10(7)) were evaluated for clindamycin activity in the in vivo model. In both models, the antimicrobial evaluation was performed in triplicate, and bacterial quantification occurred over 72 h, with drug doses that were designed to simulate the free drug area-under-the-concentration-time curve values (fAUCs) obtained from human samples. When the activity of clindamycin against the iMLS(B) strains was evaluated, constitutive resistance was noted at 24 h (MIC of >256), and failure was noted at an inoculum of > or =10(6) in the in vivo models. However, at a low inoculum (10(5)) in the murine thigh-infection model, clindamycin demonstrated modest activity, reducing the CFU/thigh count for clindamycin resistance-inducible strains at 72 h (0.45 to 1.3 logs). Overall, administration of daptomycin followed by vancomycin demonstrated the most significant kill against all strains in both models. Against the clindamycin noninducible strain, clindamycin and doxycycline demonstrated significant kill. Doxycycline, linezolid, and trimethoprim-sulfamethoxazide (not run in the murine model) demonstrated bacteriostatic activity against clindamycin resistance-inducible isolates. This study demonstrates that clindamycin's activity against the iMLS(B) strains tested is partially impacted by inoculum size. At present, there are several alternatives that appear promising for treating clindamycin resistance-inducible strains of CA-MRSA.

Clindamycin bioavailability and pharmacokinetics following oral administration of clindamycin hydrochloride capsules in dogs

Oral bioavailability and pharmacokinetic behaviour of clindamycin in dogs was investigated following intravenous (IV) and oral (capsules) administration of clindamycin hydrochloride, at the dose of 11 mg/kg BW. The absorption after oral administration was fast, with a mean absorption time (MAT) of 0.87+/-0.40 h, and bioavailability was 72.55+/-9.86%. Total clearance (CL) of clindamycin was low, after both IV and oral administration (0.503+/-0.095 vs. 0.458+/-0.087 L/h/kg). Volume of distribution at steady-state (IV) was 2.48+/-0.48 L/kg, indicating a wide distribution of clindamycin in body fluids and tissues. Elimination half-lives were similar for both routes of administration (4.37+/-1.20 h for IV, vs. 4.37+/-0.73 h for oral). Serum clindamycin concentrations following administration of capsules remained above the MICs of very susceptible microorganisms (0.04-0.5 microg/mL) for 12 or 10 h, respectively. Time above the mean inhibitory concentration (MIC) is considered as the index predicting the efficacy of clindamycin (T(>MIC) must be at least 40-50% of the dosing interval), so a once-daily oral administration of 11 mg/kg BW of clindamycin can be considered therapeutically effective. For less susceptible bacteria (with MICs of 0.5-2 microg/mL) the same dose should be given but twice daily.

Pharmacokinetic/pharmacodynamic relationships of antimicrobial drugs used in veterinary medicine

The rise in incidence of antimicrobial resistance, consumer demands and improved understanding of antimicrobial action has encouraged international agencies to review the use of antimicrobial drugs. More detailed understanding of relationships between the pharmacokinetics (PK) of antimicrobial drugs in target animal species and their action on target pathogens [pharmacodynamics (PD)] has led to greater sophistication in design of dosage schedules which improve the activity and reduce the selection pressure for resistance in antimicrobial therapy. This, in turn, may be informative in the pharmaceutical development of antimicrobial drugs and in their selection and clinical utility. PK/PD relationships between area under the concentration time curve from zero to 24 h (AUC(0-24)) and minimum inhibitory concentration (MIC), maximum plasma concentration (C(max)) and MIC and time during which plasma concentrations exceed the MIC have been particularly useful in optimizing efficacy and minimizing resistance. Antimicrobial drugs have been classified as concentration-dependent where increasing concentrations at the locus of infection improve bacterial kill, or time-dependent where exceeding the MIC for a prolonged percentage of the inter-dosing interval correlates with improved efficacy. For the latter group increasing the absolute concentration obtained above a threshold does not improve efficacy. The PK/PD relationship for each group of antimicrobial drugs is 'bug and drug' specific, although ratios of 125 for AUC(0-24):MIC and 10 for C(max):MIC have been recommended to achieve high efficacy for concentration-dependent antimicrobial drugs, and exceeding MIC by 1-5 multiples for between 40 and 100% of the inter-dosing interval is appropriate for most time-dependent agents. Fluoroquinolones, aminoglycosides and metronidazole are concentration-dependent and beta-lactams, macrolides, lincosamides and glycopeptides are time-dependent. For drugs of other classes there is limited and conflicting information on their classification. Resistance selection may be reduced for concentration-dependent antimicrobials by achieving an AUC(0-24):MIC ratio of greater than 100 or a C(max):MIC ratio of greater than 8. The relationships between time greater than MIC and resistance selection for time-dependent antimicrobials have not been well characterized.

Selecting antibacterials for outpatient parenteral antimicrobial therapy : pharmacokinetic-pharmacodynamic considerations

Some infectious diseases require management with parenteral therapy, although the patient may not need hospitalisation. Consequently, the administration of intravenous antimicrobials in a home or infusion clinic setting has now become commonplace. Outpatient parenteral antimicrobial therapy (OPAT) is considered safe, therapeutically effective and economical. A broad range of infections can be successfully managed with OPAT, although this form of treatment is unnecessary when oral therapy can be used. Many antimicrobials can be employed for OPAT and the choice of agent(s) and regimen should be based upon sound clinical and microbiological evidence. Assessments of cost and convenience should be made subsequent to these primary treatment outcome determinants. When designing an OPAT treatment regimen, the pharmacokinetic and pharmacodynamic characteristics of the individual agents should also be considered. Pharmacokinetics (PK) is the study of the time course of absorption, distribution, metabolism and elimination of drugs (what the body does to the drug). Clinical pharmacokinetic monitoring has been used to overcome the pharmacokinetic variability of antimicrobials and enable individualised dosing regimens that attain desirable antimicrobial serum concentrations. Pharmacodynamics (PD) is the study of the relationship between the serum concentration of a drug and the clinical response observed in a patient (what the drug does to the body). By combining pharmacokinetic properties (peak [C(max)] or trough [C(min)] serum concentrations, half-life, area under the curve) and pharmacodynamic properties (susceptibility results, minimum inhibitory concentrations [MIC] or minimum bactericidal concentrations [MBC], bactericidal or bacteriostatic killing, post-antibiotic effects), unique PK/PD parameters or indices (t > MIC, C(max)/MIC, AUC(24)/MIC) can be defined. Depending on the killing characteristics of a given class of antimicrobials (concentration-dependent or time-dependent), specific PK/PD parameters may predict in vitro bacterial eradication rates and correlate with in vivo microbiologic and clinical cures. An understanding of these principles will enable the clinician to vary dosing schemes and design individualised dosing regimens to achieve optimal PK/PD parameters and potentially improve patient outcomes. This paper will review basic principles of useful PK/PD parameters for various classes of antimicrobials as they may relate to OPAT. In summary, OPAT has become an important treatment option for the management of infectious diseases in the community setting. To optimise treatment course outcomes, pharmacokinetic and pharmacodynamic properties of the individual agents should be carefully considered when designing OPAT treatment regimens.

What do we really know about antibiotic pharmacodynamics?

Antibiotic pharmacodynamics is an evolving science that focuses on the relationship between drug concentration and pharmacologic effect, which is an antibiotic-induced bacterial death that also can manifest as an adverse drug reaction. The pharmacologic action of antibiotics usually can be described as concentration dependent or independent, although such classifications are highly reliant on the specific antibiotic and bacterial pathogen being studied. Quantitative pharmacodynamic parameters, such as ratio of the area under the concentration-time curve during a 24-hour dosing period to minimum inhibitory concentration (AUC0-24:MIC), ratio of maximum serum antibiotic concentration to MIC (Cmax:MIC), and duration of time that antibiotic concentrations exceed MIC (T>MIC), have been proposed as likely predictors of clinical and microbiologic success or failure for different pairings of antibiotic and bacteria. Thus far, most pharmacodynamic data reported have focused on fluoroquinolones, but work has been conducted on vancomycin, beta-lactams, macrolides, aminoglycosides, and other antibiotics. Despite the development of a number of different pharmacodynamic modeling systems, remarkable agreement exists between in vitro, animal, and limited human data. Although still somewhat premature and requiring additional clinical validation, antibiotic pharmacodynamics will likely advance on four fronts: the science should prove to be extremely useful and represent a cost-effective and efficient method to help develop new antibiotics; formulary committees will likely use pharmacodynamic parameters to assist in differentiating antibiotics of the same chemical class in making antibiotic formulary selections; pharmacodynamic principles will likely be used to design optimal antibiotic strategies for patients with severe infections; and limited data to date suggest that the application of pharmacodynamic concepts may limit or prevent the development of antibiotic resistance. The study of antibiotic pharmacodynamics appears to hold great promise and will likely become a routine part of our daily clinical practices.