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Original research
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Peer reviewed
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Efficacy of ceftiofur sodium for the control of mortality
in neonatal pigs orally inoculated with
K88+ (F4+) enterotoxigenic
Escherichia coli
Beth Hibbard, MA; Fabian M. Kausche, Dr med vet, MS; Kelly F. Lechtenberg, DVM, PhD; Michael S. Hanna, DVM;
Edward J. Robb, DVM, MS; W. Lawrence Bryson, PhD; S. Theodore Chester, Jr, PhD; Kenneth J. Dame
BH, FMK, EJR, WLB, STC, KJD: Pharmacia Animal Health, Kalamazoo, Michigan; KFL, MSH: Midwest Veterinary Services, Oakland, Nebraska. Corresponding author: Beth Hibbard, Pharmacia Animal Health, 7000 Portage Rd, Kalamazoo, MI 49001; Tel: 269-833-2630; Fax: 269-833-3246; E-mail: beth.hibbard@pharmacia.com.
Hibbard B, Kausche FM, Lechtenberg KF, et al. Efficacy of ceftiofur sodium
for the control of mortality in neonatal pigs orally inoculated with
K88+ (F4+) enterotoxigenic
Escherichia coli.J Swine Health Prod. 2003;11(1):7-11.
Also available as a PDF.
Summary
Objective: To evaluate the efficacy of ceftiofur sodium (Naxel/Excenel
Sterile Powder; Pharmacia & Upjohn, Kalamazoo, Michigan) administered IM once daily at
3 or 5 mg ceftiofur per kg BW for 3 days for control of mortality associated with
K88+ (F4+) Escherichia
coli-induced colibacillosis in neonatal piglets.
Methods: Pregnant gilts susceptible to colibacillosis associated with
K88+ E coli were farrowed in farrowing crates
with solid walls to prevent contact between litters. A total of 29 gilts with 240
piglets were enrolled, with litters randomly assigned to study group by order of
farrowing. Groups included uninoculated-no treatment, inoculated-sterile saline
IM, inoculated-ceftiofur sodium IM (3 mg per kg), and inoculated-ceftiofur sodium IM
(5 mg per kg). Treatments were administered on Days 0, 1, and 2. On Day 0, each
inoculated piglet received 20 mL inoculum orally, containing approximately
108 colony forming units per mL of E
coli strain M1823B (O157:K88ac:H43). Clinical observations were conducted twice
daily for 8 days.
Results: Mean mortality rates for the
two ceftiofur-treated groups were lower than for the inoculated-saline group
(P=.003). The proportion of normal stool scores
was higher in ceftiofur-treated groups than in the inoculated-saline group
(P<=.008). Average daily gain for surviving piglets
did not differ among the groups.
Implications: Ceftiofur sodium administered IM daily for 3 consecutive days at
3 or 5 mg per kg significantly reduced mortality and increased percentage
normal stool scores in treated piglets inoculated with
K88+ E coli, compared to
untreated, inoculated piglets.
Keywords: swine, bacteria, Escherichia
coli, enterotoxins, diarrhea
Received: August 22, 2001
Accepted: December 14, 2001
Diarrhea occurring in piglets within the first few days after birth (0 to 4 days) is often caused by Escherichia
coli infection of the jejunum and
ileum.1 The disease is economically important in the swine industry due to
the losses observed in the intensive management systems currently used in
farrowing houses.1 Causative bacteria adhere to
the epithelium of the small intestine by means of fimbrial adhesins and produce one
or more enterotoxins that may increase fluid secretion in the small intestine up to
tenfold, causing diarrhea if excess fluid is not absorbed in the large
intestine.1 No primary inflammatory reactions occur in
this type of hypersecretory neonatal
diarrhea.1 However, the ability of the large
intestine to compensate for sudden fluid flux is
easily overwhelmed in neonates.1
Antibiotic therapy is indicated for the treatment of neonatal diarrhea caused
by enterotoxigenic E coli, such as
K88+ (F4+)
strains.1 Therapy should be rapidly
instituted before piglets become severely dehydrated and should seek to inhibit growth
of enterotoxigenic bacteria in the small intestine. Fluid and electrolyte replacement
is useful in treating dehydration and acidosis. Antibacterial treatment should be
coupled with appropriate husbandry techniques, which include providing a draft-free,
warm environment, using farrowing crates designed to keep the piglets away from
fecal material, and maintaining appropriate sanitation of the sow and the
farrowing facility.1
Ceftiofur sodium (Naxcel/Excenel Sterile Powder; Pharmacia & Upjohn,
Kalamazoo, Michigan) is currently approved in the United States and many other countries
for the control and treatment of swine respiratory disease (SRD), administered IM at
3 or 5 mg ceftiofur per kg BW for 3 consecutive days. However, its spectrum of
activity and pharmacokinetic and pharmacodynamic characteristics, including tissue
homogenate data, support a clinical rationale for use of ceftiofur sodium in the
treatment of enterotoxigenic colibacillosis in
neonatal piglets. Ceftiofur was confirmed to be an effective treatment for colibacillosis in
an enterotoxigenic K99+ E coli
challenge model study2 and in field studies
where oral3 and IM4
administration were evaluated for the treatment of naturally
occurring colibacillosis. The present study evaluated the efficacy of ceftiofur sodium
administered IM for 3 consecutive days at 3 or 5 mg ceftiofur per kg BW for the
control of mortality associated with secretory diarrhea in neonatal piglets orally
inoculated with K88+ E coli.
Materials and methods
Experimental design
Gilts were obtained and placed in standard farrowing crates at least 14 days
before their expected farrowing date. Litters (n=29) were randomly assigned in order
of farrowing to one of four study groups (Table 1). Birth weights were
obtained when piglets were processed at the end of farrowing. Piglets in Groups 2, 3, and
4 were inoculated within 7 hours of the end of farrowing (Day 0). Clinical signs
were observed twice daily, beginning 12 hours after the end of farrowing, and
through one observation on Day 8. The first treatment was administered to all
designated piglets 6 hours after inoculation on Day
0, regardless of clinical signs. The first
clinical evaluation was made either before or
after the first treatment, depending on the time of inoculation. Day 1 and Day 2
treatments were administered at 24-hour intervals. The personnel who conducted
the clinical evaluations and necropsies remained blinded to the assigned
treatments throughout the trial. The trial was conducted according to the
Guidelines for Good Target Animal Study
Practices5 and was consistent with applicable laws and
regulations governing the humane care of animals.
Study animals
Pregnant Lancaster or Large White cross gilts (n=31) that had not been
vaccinated against E coli were obtained from a
source that produced piglets susceptible to enterotoxigenic diarrhea associated
with K88+ E coli, with litter mortality rates
between 0 and 60% (unpublished data). Two groups of gilts (n=11 and n=20)
were placed in standard farrowing crates (with solid walls to prevent nose-to-nose
contact between litters) to acclimatize for at
least 14 days before their expected farrowing date. Gilts were observed every 2 to
4 hours to assist in farrowing as needed and to document farrowing times.
Cross-fostering was allowed before inoculation to
balance litter size. All piglets with obvious physical problems, injuries, or birth
weight <0.9 kg were excluded from the study, as was any piglet born after the litter had
been inoculated.
During the entire acclimatization and study periods, the only antibacterials
administered to the piglets were the experimental ceftiofur treatments included in
the study design. No antibacterials were administered to the gilts during the
acclimatization and study periods.
Administration of treatments
Ceftiofur sodium was diluted to 10 mg ceftiofur per mL for accurate dosing
and administered IM using a 20-gauge, 2.5-cm sterile needle. The first treatment (Day
0) was administered in the left neck, and Day 1 and Day 2 treatments were
administered in the right and left neck, respectively.
Inoculum
Each inoculated piglet received 20 mL of inoculum orally, containing
approximately 108 colony forming units (CFUs) per
mL of E coli strain M1823B (O157:K88ac:H43) suspended in trypticase soy broth.
This isolate, a hemolytic strain originally isolated from the intestine of a pig with
post-weaning diarrhea, produces the heat labile enterotoxin (LT) and the heat stable
toxin (STb).6 The ceftiofur minimum
inhibitory concentration (MIC) for this organism
is 0.5 mg per mL. The inoculum was administered in 10-mL portions, with all
piglets in a litter receiving the first 10 mL
before any piglet received the second 10 mL. Inocula were administered orally with the
aid of a 13-cm, 14-gauge catheter (Angiocath; BD Medical Systems, Franklin Lakes,
New Jersey) with the stylet removed. A new catheter was used for each litter.
Throughout the study, personnel changed gloves after handling a litter and before moving
to the next, to minimize the possibility of spreading the challenge organism
between litters. In addition, care was taken when cleaning crates to avoid splashing fecal
material into adjacent crates.
Clinical observations and scoring
 Observers recorded weights, determined a stool score using the scoring system
described in Table 2, and noted an illness index score and other relevant clinical
ob-servations.Clinical scoring was performed by evaluators who remained blinded to
the assigned study groups throughout the study.
Moribund or savaged piglets were euth-anized. All piglets removed from the
study or found dead were necropsied. Deaths were categorized as due to colibacillosis
if evidence of dehydration was present at necropsy.
Mortality due to enterotoxigenic colibacillosis was calculated as the
proportion of piglets in a litter that died due to dehydration associated with
enterotoxi-genic colibacillosis. Percent normal
stool scores was calculated for each surviving piglet as the number of normal stool
scores divided by the number of stool evaluations for that piglet. Average daily gain was
calculated for the surviving piglets as the final weight of each piglet minus the
birth weight, divided by the number of days the piglet was on study.
No rectal swabs, fecal samples, or tissue samples were collected for culturing
during this study.
Statistical analysis
Data from all piglets that died or were euthanized prior to inoculation, or
that were born after the rest of the litter was inoculated, were excluded from the
analysis data set. The primary variable in this
randomized block design study was mortality associated with dehydration due to
entero-toxigenic colibacillosis. Stool scores and ADG were secondary variables.
Mortality was analyzed as a general linear mixed model using the PROC MIXED
procedure from SAS.7 Mortality was expressed as
the Freeman-Tukey angularly transformed proportion of piglets within a litter that
died due to enterotoxigenic colibacillosis (using n + 0.5 as weights, where n = number
of piglets assigned to the study within the litter). The mixed model included the
fixed effects of period (farrowing period for
the two groups of gilts), treatment, and period by treatment interaction, and the
random effect of gilt-litter within period by
treatment. The random effect of gilt-litter within period was used as the error term
to test the fixed effects of treatment.
Stool scores for the surviving piglets were analyzed as a general linear mixed
model using the PROC MIXED procedure from SAS. Stool scores were expressed as
the Freeman-Tukey angularly transformed proportion of normal stool scores for each
piglet (using n + 0.5 as weights, where n = number of stool evaluations). The
mixed model included the fixed effects of period (farrowing period), treatment, and
period by treatment interaction, and the random effects of gilt-litter within period by
treatment and residual. The random effect of gilt-litter within period was used as
the error term to test the fixed effects of treatment.
The ADG for surviving piglets was analyzed as a general linear mixed model
using the PROC MIXED procedure from SAS. The mixed model included the fixed
effects of period (farrowing period), treatment, and period by treatment interaction,
and the random effects of gilt-litter within period by treatment and residual. The
random effect of gilt-litter within period was used as the error term to test the fixed
effects of treatment.
For each variable, pairwise comparisons were made between Groups 3 and 4
and Group 2. The farrowing period by treatment interaction for each comparison
was accomplished through contrast statements. No statistical comparisons were made
between Group 1 and the other study groups or between Groups 3 and 4. All
analyses were conducted using [alpha]=.05.
Results
A total of 29 gilts with 240 piglets were included in the statistical analyses.
Data from five piglets whose deaths were not related to colibacillosis were excluded
before the analyses of stool scores and ADG.
Results of analysis of mean mortality due to colibacillosis, proportion of normal
stool scores in surviving piglets, and ADG in surviving piglets are presented in Table
3. Mean mortality rates for Groups 3 and 4 were lower than for Group 2, and
the proportionof normal stool scores during the entire study period was higher
in Groups 3 and 4 than in Group 2. Daily stool scores (which were not analyzed
statistically) were numerically higher through Day 4 for Group 2 compared to Groups
3 and 4 (Figure 1). There were no significant differences in ADG between Group 2
and Groups 3 or 4 (P>.05).
 
Discussion
The results of this study provide clinical confirmation of the effectiveness
of ceftiofur for the treatment of enterotoxi-genic colibacillosis in neonatal
piglets. These data are consistent with the pharmacokinetics and pharmacodynamics
of ceftiofur.8
Salmon et al9 determined ceftiofur
MIC for 84 swine E coli isolates using the microdilution method of the
National Committee on Clinical Laboratory Standards with appropriate quality
control strains. The MIC50 (which represents
the MIC for the most sensitive 50% of the isolates) was 0.5
mg per mL and the MIC90 (which represents the MIC for the
most sensitive 90% of the isolates) was 1.0 mg per mL (range 0.25 to 4.0
mg per mL, mode 0.5 mg per mL). These values are comparable to the ceftiofur MICs for
Salmonella serovar Choleraesuis, the
least ceftiofur-sensitive pathogen associated with SRD for which ceftiofur sodium
and ceftiofur hydrochloride have label
claims.10,11 In addition, 885 swine
enteric isolates, including E coli, collected in
Missouri in 1996-1997, were susceptible to
ceftiofur.12 The ceftiofur MIC for the enterotoxigenic
E coli inoculation strain used in the present study was 0.5
mg per mL, in agreement with the mode and
MIC50 of previously reported swine E
coli isolates.9
In a pharmacokinetic study evaluating the plasma concentrations of ceftiofur
sodium or ceftiofur hydrochloride in
pigs,8 the critical pharmacokinetic parameters
(maximum plasma concentration achieved after treatment administration, area under
the plasma concentration-time curve, and time the plasma concentration remained
above 0.2 mg per mL) were similar for pigs receiving either ceftiofur sodium or ceftiofur
hydrochloride in the same dosage. The dosing regimens tested for the treatment
of colibacillosis in our study included the range of dosing regimens approved by
the Food and Drug Administration Center for Veterinary Medicine for the treatment
and control of swine bacterial respiratory disease.
A tissue distribution study conducted in pigs provides further evidence
supporting the effectiveness of ceftiofur for
enteric colibacillosis.13 Pigs received a single
IM dose of ceftiofur sodium at 3 mg ceftiofur per kg BW, the lower end of the dose
range approved in the United States for the treatment of SRD. Ceftiofur concentrations
in the washed homogenate of the distal 1 m of jejunum and in mesenteric lymph
node were 1.00 and 1.09 mg per g, respectively, 7.5 hours after treatment.
Although a formal dose proportionality study evaluating the pharmacokinetics
of ceftiofur when administered at several incremental dose levels has not been
conducted in swine, previous studies support dose proportionality in
swine.14 Assuming dose proportionality, the tissue
concentrations in the distal portion of the
jejunum would be expected to remain above the
MIC90 for the E coli strains
tested9 for approximately 18.5 to 19.5 hours after
a single IM dose of 5 mg ceftiofur per kg BW, and tissue concentrations are
estimated to be approximately 0.68 mg ceftiofur per mL at the 24-hour dosing
interval. Since current technology cannot accurately measure the amount of
ceftiofur that bacteria encounter at the site of
colonization, namely, the luminal surface of the small intestine, it is not technically
feasible to determine the ratio of the drug concentration at the site of infection to the
MIC. While therapeutic levels of ceftiofur-related residues were detected in tissue samples
of the small intestine13 when pigs were
administered ceftiofur, rapid degradation of ceftiofur in the large intestine and
fecal material of animals15,16 would likely
limit its effectiveness against infections in the large intestine.
The results of this inoculation study confirm and extend previous work that
evaluated the efficacy of ceftiofur for the treatment of colibacillosis. In a similar
study conducted with a K99+ E
coli, a single dose of ceftiofur hydrochloride at 0.5 or 2.0
mg ceftiofur per kg BW was administered IM to piglets 6 hours after
inoculation.2 In pigs treated with either dose compared
to untreated controls, mortality and abnormal stool scores were significantly lower,
there was significantly less shedding of the challenge organism, and weight gain was
significantly greater. Groups treated orally were also included in this study and a
second challenge study.2 All oral
treatment regimens reduced mortalityand abnormal stool scores and
improvedweight gain relative to untreated controls. The efficacy
of the oral treatments was later confirmed in two field
studies.3,4 In a multilocation field efficacy
study3 of ceftiofur for treatment of naturally occurring colibacillosis, a
single oral dose of 13.5 mg ceftiofur per pig was effective, ie, reduced mortality and
diarrhea in the surviving piglets compared with
placebo-treated controls. The oral use of ceftiofur is no longer considered to be
prudent use of a third generation cephalosporin. A second field study
evaluated IM single-dose and 3-day regimens of 8
mg ceftiofur per kg (pigs <10 days old) and 11 mg ceftiofur per kg (pigs
>=10 days old) compared to untreated
controls.4 Clinical recovery rates and weight gains were
higher for ceftiofur-treated groups. The
efficacy demonstrated in these clinical studies
supports the conclusion that ceftiofur is present at the mucosal surface of the
small intestine at concentrations adequate for the treatment of colibacillosis in pigs.
While the present study provided clinical confirmation of the efficacy of ceftiofur
for reduction of mortality associated with enterotoxigenic colibacillosis in
neonatal swine, it is important to note that this
is extra-label use of ceftiofur. A dose titration has not been performed for this use
of ceftiofur, and the doses tested in the present study were those currently
approved by the FDA and other regulatory bodies worldwide for the treatment
and control of bacterial SRD. Although there are no systematic sampling studies
currently conducted to evaluate trends in enterotoxigenic
E coli antimicrobial resistance, data suggest that resistance may
develop in some swine pathogens.17 This
emphasizes the importance of having a definitive diagnosis and knowledge of
the MIC(s) for the pathogens prior to initiation of antimicrobial treatment.
These clinical data are provided for practitioner information only to assist in the
decision-making process regarding treatment selection.
Implications
- Under the conditions of this study, in neonatal pigs orally inoculated
with K88+ E coli, mortality was lower
and the percentage of normal stool scores was higher in groups treated IM
with ceftiofur sodium (3 or 5 mg ceftiofur per kg BW) compared to groups
that received no ceftiofur treatment.
- Ceftiofur sodium (Naxcel/Excenel Sterile Powder; Pharmacia &
Upjohn) administered IM at the dose labeled for the treatment of SRD appears
to be an effective treatment for reducing losses due to neonatal pig
diarrhea caused by K88+ enterotoxigenic
strains of E coli.
Acknowledgments
The authors thank Trevor Preston and Rich Pounds for their technical support
during the animal phase of this study.
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JM, Turnquist SE, Johnson GC, Gosser HS. Minimal inhibitory concentration
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Determination of tissue concentrations of
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