IVERMECTIN:
The efficacy data for ivermectin alone are located in NADA 140-974 FEDERAL
REGISTER, November 3, 1993 (58FR 58653).
a. Type of Study:
A trial (ASR 14354) was conducted to evaluate the efficacy of ivermectin, in the presence of lincomycin, against endoparasites.
b. Investigator:
Dr. J. E. Holste
Merck Research Farm
6498 Jade Road
Fulton, Missouri 65251
c. General Design:
Forty-eight crossbred piglets were used. There were four treatment groups as follows: nonmedicated control; ivermectin in feed at 2 ppm (1.8 g/ton) from Day 7 to 14; lincomycin in feed at 200 g/ton from Day -7 to 14; and ivermectin in feed at 2 ppm from Day 7 to 14, plus lincomycin at 200 g/ton from Day -7 to 14. For each treatment group, there were six pens of 2 pigs each. On Day -49, each animal was orally administered approximately 20,000 infective larvae of Oesophagostomum spp. The animals were
necropsied by replicate for worm counting on Days 28 or 29.
d. Conclusion:
The numbers of adult Oesophagostomum spp. were reduced
100% in the animals given ivermectin either alone or in combination with
lincomycin (p > 0.01). The effect of lincomycin and the interaction of
lincomycin and ivermectin were not significant (p > 0.10).
(Eds note: The following table consists of 4 columns).
Table 1.
Reduction of counts of Oesophagostomum spp. in pigs given feed containing
ivermectin, lincomycin or a combination of ivermectin and lincomycin.
______________________________________________________________________________________
Reduction Compared to Control
______________________________________________________
Ivermectin(a)
Nematode Ivermectin(a) Lincomycin(b) Lincomycin(b)
______________________________________________________________________________________
Oesophagostomum spp., (Ad) 100% 18.2% 100%
______________________________________________________________________________________
(Ad) = adults
(a) 2 ppm (1.8 g/ton) in feed Days 7 to 14
(b) 200 g/ton in feed Days -7 to 14
e. Adverse Reactions:
None
f. Special Issues:
None
LINCOMYCIN:
Pivotal Dose Confirmation Non-Interference Clinical Study
a. Type of Study:
Assessment of lincomycin efficacy in swine diets at 100 g/ton for 14 days when used in combination with ivermectin at 1.8 g/ton for the first seven days for the treatment of induced swine dysentery.
b. Investigators:
R.A. Rzepkowski, Study Director
Animal Health Therapeutics Research, Unit 7923
The Upjohn Company.
R.J. Yancey, Jr., Study Supervisor
Animal Health Therapeutics Research, Unit 7923
The Upjohn Company.
c. General Design:
* Purpose of Study: To compare in feed the efficacy of lincomycin and
ivermectin alone or in combination for the treatment of induced swine
dysentery.
* Test Animals: Test animals were representative samples from the population
for which these products are intended. Ninety-six (96) crossbred pigs (42
gilts, 54 barrows) that averaged 64 days of age and 50 lb in weight were
allotted to four treatment groups (24 pigs/treatment). To induce swine
dysentery, each pig received two 100 mL oral doses (24 h interval) of
a broth culture containing Serpulina hyodysenteriae.
The experiment design is illustrated in Table 2.
(Eds note: The following table consists of 5 columns).
Table 2.
Experimental design for pigs with experimentally induced swine dysentery.
_________________________________________________________________________________
No. of No. of No. of
Group Treatment Pigs/Group Pens/Group Pigs/Pen
_________________________________________________________________________________
A Combination(ab) 24 12 2
B Control(c) 24 12 2
C Ivermectin(b) 24 12 2
D Lincomycin(a) 24 12 2
_________________________________________________________________________________
(a)Lincomycin at 110 mg/kg (100 g/ton) of feed.
(b)Ivermectin at 2 mg/kg (1.8 g/ton) of feed.
(c)Non-medicated swine feed.
* Controls: A non-medicated infected control group was included in the study.
Treatments and controls were randomly assigned to pens within the 12 blocks of
eight pigs each. All personnel conducting the study were unaware of the
medications in the feed for treatments A, B, C and D.
* Diagnosis: A trained technician diagnosed swine dysentery based on the
clinical signs of diarrhea, dysentery and shedding of S. hyodysenteriae
in the feces. Treatment was initiated in each group when at least 50% of the
pigs were shedding S. hyodysenteriae and at least 25% of the pigs were
exhibiting bloody feces.
* Dosage Forms: LINCOMIX® 50 and IVOMEC® Premixes for
swine were mixed into the basal diet at the described levels to produce the
medicated feeds.
* Route of Administration: Orally via medicated feed.
* Dosages Used:
Group A:
Medicated feed containing 110 mg lincomycin plus 2 mg
ivermectin per kg feed (100 g lincomycin and 1.8 g ivermectin per ton of
feed).
Group B:
Unmedicated swine grower diet.
Group C:
Medicated feed containing 2 mg ivermectin per kg feed (1.8 g/ton).
Group D:
Medicated feed containing 110 mg lincomycin per kg feed (100
g/ton).
* Test Duration: Twenty-eight (28) day combined treatment and observation
period.
* Pertinent Parameters Measured: Mortality, survival days, dysenteric days,
physical activity, and spirochetal shedding days were the pertinent parameters
measured.
* Decision Variables: Percent dysenteric days and percent shedding of
S. hyodysenteriae were the primary decision variables.
d. Statistical Analysis:
Statistical analysis was performed on an experimental unit (pen) basis using Type III sums of squares from the general linear models (GLM) procedure of SAS® according to the analysis of variance described in Table 3. The percentages were expressed as pen percentages and a test of normality of the residuals was performed using Wilks'
W statistic (alpha= 0.05). The homogeneity of the elements of the
test terms was tested using Levene's test at alpha = 0.01.
(Eds note: The following table consists of 9 columns).
Table. 3.
Description of source of variation, degrees of freedom (DF) and
test term for statistical analysis of treatment effects, and mean
squares (MS), F-values (F) and P-values (P) for the significance
tests of treatment effects for the two variables used to evaluate
the combination feed.
_________________________________________________________________________________
Source DF Test Term Percent Dysenteric Percent Spirochetal
Days Shedding Days
__________________________________________________
MS F P MS F P
_________________________________________________________________________________
Block 11 49.11 0.78 0.655 46.41 0.28 0.985
Treatment 3 Residual 328.28 5.23 0.005 1441.67 8.81 0.001
Residual 33 62.75 163.72
_________________________________________________________________________________
e. Results:
The results are presented in Table 4.
(Eds note: The following table consists of 5 columns).
Table 4.
Overall means (1,2) of variables by treatment for pigs
challenged with Serpulina hyodysenteriae.
________________________________________________________________________________
Variable Treatment Groups
_______________________________________________________
A Combination B Control C Ivermectin D Lincomycin
________________________________________________________________________________
Percent Mortality 4.2 4.2 4.2 0.0
Percent Survival Days 96.0 96.0 97.9 100
Percent Dysenteric Days 8.0a 16.6b 17.5b 8.0a
Percent Spirochetal 12.4a 28.4b 34.7b 13.8a
Shedding Days
________________________________________________________________________________
1 For all variables except Percent Dysenteric Days and Percent Spirochetal Shedding Days, means indicated are arithmetic means calculated with the pens as the experimental units. Least Squares Means are given for Percent Dysenteric Days and Percent Spirochetal Shedding Days.
2 Significant differences (p < 0.05) among treatment means on each
row are indicated with differing superscripts.
f. Conclusions:
These results show that the addition of ivermectin to lincomycin-containing feed did not interfere with the efficacy of lincomycin as therapy for swine dysentery.
g. Adverse Reactions:
None.
h. Special Issues:
None.
Effectiveness Study:
Lincomycin added at the rate of 200 g of lincomycin per 2000 lb of feed is
approved as therapy to reduce the severity of lesions caused by Mycoplasma
hyopneumoniae in swine. The purpose of this study was to evaluate the in
vitro antimicrobial activity of lincomycin and ivermectin, alone and in
combination, against strains of M. hyopneumoniae.
The in vitro activity of lincomycin and ivermectin, alone and in
combination, against 15 strains of M. hyopneumoniae was determined. In
addition, the effect of the glycerol-formal solvent used for ivermectin
reference standard on the activity of lincomycin was tested. Against the
strains tested, ivermectin was not active with minimum inhibitory
concentrations (MIC) for all isolates > 32.0 ug/mL. Lincomycin,
lincomycin/ivermectin at a 3.1:1 (w/w) ratio, lincomycin/ivermectin at a 10:1
(w/w) ratio; and lincomycin dissolved in the glycerol-formal ivermectin solvent
all yielded MIC values of (< or =) 0.5 ug/mL for all the strains tested.
Lincomycin, lincomycin/ivermectin at a 3.1:1 (w/w) ratio, and
lincomycin/ivermectin at a 10:1 (w/w) ratio were chosen because they reflect
the range of in vivo blood concentrations foe each drug. The MIC values
for lincomycin alone and in combination with ivermectin and the solvent, were
within one serial dilution with all the strains tested. These results suggest
that combining ivermectin with lincomycin does not affect the in vitro
activity of lincomycin against M. hyopneumoniae. Table 5 summarizes
these data.
Table 5.
Summary of minimum inhibitory concentrations (MICs) results obtained
with isolates of M. hyopneumoniae against lincomycin and ivermectin,
alone and in combination.
Antimicrobial MIC Range (ug/mL)
_____________ _________________
Lincomycin (< or =) 0.03-0.5
L/I 3.1:1(a) 0.06-0.5
L/I 10:1(b) (< or =) 0.03-0.5
Ivermectin > 32.0
L/GF(c) < 0.03-0.5
_____________________________________________________________________
(a) LI/3.1:1=lincomycin/ivermectin 3.1:1, lincomycin value reported.
(b) LI/10:1=lincomycin/ivermectin 10:1, lincomycin value reported.
(c) L/GF, lincomycin/glycerol-formal solvent.
Pivotal Pharmacokinetic Study - Non-Interference Study:
a. Type of Study:
Pharmacokinetic - Plasma concentrations after either
lincomycin alone or lincomycin and ivermectin administered to swine.
b. Investigator:
Scott A. Brown, Study Director
Animal Health Drug Metabolism, Unit 7926
The Upjohn Company.
c. General Design:
* Purpose of Study: To compare the steady-state plasma concentrations of
lincomycin after administration of lincomycin alone and after administration of
lincomycin and ivermectin in swine feed.
* Test Animals:
Thirty-two (32) healthy Yorkshire cross pigs (16 male/16 female), 2-4 months of age weighing 13.7-22.2 kg (30-49 lb). The pigs were randomly assigned to one of two treatment groups with an equal number of males and females allocated into each of the two treatment groups. Both treatment
groups received lincomycin for 7 consecutive days (first through seventh day of the study). Treatment Group A then received lincomycin for 7 consecutive days (eighth through fourteenth day of the study), whereas Group B received lincomycin feed for 7 consecutive days (days 15-21 of the study). Treatment Group B received lincomycin plus ivermectin for 7 consecutive days
(days 8-14 of the study), whereas Treatment Group A received lincomycin plus ivermectin for 7 consecutive days (days 15-21 of the study). The treatment periods are illustrated by the following diagram.
Day 0 Day 7 Day 14 Day 21
Group A |---------------------------------|================|
Group B |----------------|================|----------------|
--- lincomycin
=== lincomycin plus ivermectin
* Controls: The design and type of study required no unmedicated control
group.
* Dosage Forms: LINCOMIX® 50 and IVOMEC® Premixes for
swine were mixed into the basal diet at the described levels to produce the
medicated feeds.
* Route of Administration: Orally via medicated feed.
* Dosages Used: 220 g lincomycin/1000 kg feed (200 g/2000 lb) either alone or
with 2.0 g ivermectin/1000 kg feed (1.82 g/2000 lb).
* Test Duration: Twenty-one (21) days.
* Pertinent Parameters Measured:
Average lincomycin plasma concentrations
(Cavg) were evaluated for each pig/treatment by dividing the area under the
curve (AUC) determined on Day 13 and on Day 21 (hours 2 and 4 following the 8
AM and 4 PM doses) by the total blood sampling interval (12 hours). All blood
samples were analyzed for lincomycin free base by Gas Chromatography/Mass
Spectrometry (GC/MS) with electron impact detection.
* Decision Criteria:
To confirm the absence of bias in the treatment
comparison due either to a lack of steady state conditions or to the presence
of a period by treatment interaction, Cavg values were obtained for each
treatment and period (see Table 6). The 90% confidence intervals for
lincomycin concentrations on Days 13 and 21 were used to assess potential drug
interactions. If the 90% confidence interval for the difference between
lincomycin plasma concentrations after lincomycin alone subtracted from those
after lincomycin plus ivermectin was greater than -0.20 times the mean
lincomycin concentrations after lincomycin alone, the conclusion was that
ivermectin did not interfere with lincomycin.
d. Results and Statistical Analysis:
Consistent with the mean values presented in Table 6, no statistically significant period by treatment interactions were observed (P = 0.1550). This verifies that the evaluation of the treatment effects represents an unbiased comparison.
(Eds note: The following table consists of 3 columns).
Table 6.
Comparison of Average Lincomycin Blood Levels in Periods 1 and 2 for
Each Treatment Group.
____________________________________________________________
Period Treatment Cavg (ug/mL)
LSMEAN ____________________________________________________________
1 lincomycin 0.37383906
1 linco/ivermectin 0.41850469
2 lincomycin 0.32698437
2 linco/ivermectin 0.38898438
The statistical analysis of average plasma concentration after lincomycin
alone versus lincomycin plus ivermectin are summarized in Table 7.
(Eds note: The following table consists of 6 columns).
Table 7.
Comparisons of least squares means of lincomycin concentrations with
and without adjustment for feed consumption. Unadjusted concentrations
are reported in ug/mL, adjusted concentrations are reported in
[(ug/mL)/(kg feed/kg BW)].
__________________________________________________________________________________________
Adjusted for Least Squares Means of Significance 90% CI of -0.20x Linco
Relative Concentration Level of Difference LSMean
Feed (Standard Errors) Difference
Consumption
__________________________
Linco Alone Lincomycin+
Ivermectin
__________________________________________________________________________________________
No 0.351 0.404 0.0512 0.028 to 0.07 -0.070
(0.019) (0.019)
Yes 6.55 7.52 0.0787 0.436 to 1.49 -1.31
(0.376) (0.376)
__________________________________________________________________________________________
e. Conclusions:
The presence of ivermectin (2.0 g ivermectin/1000 kg feed) in swine feed containing lincomycin hydrochloride (220 g lincomycin/1000 kg feed) does not reduce the systemic concentrations of lincomycin. This demonstrates lack of substantial interference caused by ivermectin on lincomycin
pharmacokinetics in swine administered both lincomycin and ivermectin in the feed.
f. Adverse Reactions:
None.
g. Special Issues:
None.
A. Toxicity Tests:
The original NADAs and Freedom of Information summaries for each individual
drug establish the acceptable daily intake of each for human consumption.
Ivermectin:
NADA 140-974
FEDERAL REGISTER, November 3, 1993 (58 FR 58653).
Lincomycin:
NADA 97-505
41 FR 26855, Jun. 30, 1976;
47 FR 52145, Nov. 19, 1982;
51 FR 12137, Apr. 9, 1986;
55 FR 23423, Jun. 8, 1990.
B. Safe Concentration of Residues:
For swine the marker residue tolerance and/or safe concentration of residues
for ivermectin and lincomycin are as specified in 21 CFR 556.344 and 21 CFR
556.360, respectively.
C. Residue Depletion Non-Interference Study:
A residue assay non-interference study was conducted. The non-interference by
lincomycin in the ivermectin assay was shown in two phases. The derivatization
of standards containing 29.0 or 58.0 mcg/mL lincomycin, 100 ng/mL
ivermectin or a combination of both analytes demonstrated that (a) lincomycin
does not produce a fluorescent derivative either with or without the presence
of ivermectin and (b) it does not change the retention time or sensitivity of
the ivermectin fluorescent peak. In the second phase, control porcine liver
from the study was fortified with approximately 2300 ppb lincomycin,
approximately 20 ppb ivermectin or a combination of both. No fluorescent peaks
were produced in the analysis of lincomycin by the ivermectin assay. No peaks
representing lincomycin were observed under the ivermectin HPLC conditions.
The recovery of ivermectin alone from the three fortified samples was 89, 92
and 95%. The recovery of ivermectin from the three samples fortified with
about 100 times as much lincomycin as ivermectin was 95, 89 and 95%. These
equivalent results indicate that the presence of lincomycin in porcine liver
does not interfere with the ivermectin assay. Also, ivermectin at 2 mcg/g was
found not to interfere with the microbiological cylinder plate assay for
lincomycin.
A tissue residue depletion study was conducted to determine the depletion of
the marker residues of ivermectin and lincomycin in liver (target tissue) of
swine administered lincomycin at its highest use level of 200 g/ton in
combination with ivermectin at its use level of 2 ppm (approximately 100
mcg/kg/day) in complete feed. Medicated animals were given a basal ration
containing lincomycin at 200 g/ton on Day 0 through Day 14, then a ration
containing lincomycin at 200 g/ton and ivermectin at 2 ppm from Day 15 through
Day 21, followed by a non-medicated basal ration until study termination.
Three barrows and three gilts were sacrificed at each withdrawal time.
The withdrawal times following the end of the combination medication period
were 0 (within six hours after removal of medicated feed), 1, 2, 3 and 5 days.
One barrow and one gilt served as non-medicated control animals. Marker
residue assays were performed on swine livers using the high pressure
liquid chromatography-fluorescence and microbiological cylinder/plate assay
determinative methods for ivermectin and lincomycin, respectively. The average
or mean marker residue concentrations found were as follows:
(Eds note: The following table consists of 5 columns).
Ivermectin (ppb) Lincomycin (ppm)
Withdrawal _______________________ _______________________
day average range mean range
0 53 35 - 76 0.251 0.153 - 0.414
1 33 19 - 53 0 0
2 17* 10 - 25 0 0
3 8 4 - 13 0 0
5 3 0 - 8 0 0
* Due to illness of one pig from this group, its residue value was discarded
and not included in the average. If not excluded the average would be 15 ppb
and the range would be 2-25 ppb.
The marker residue tolerance (Rm) for ivermectin in swine liver is 20 ppb.
Statistical analysis of the depletion data, using the upper tolerance limit
containing 99 percentile of the population with 95% confidence, yields a
withdrawal period of 5 days. The withdrawal periods for both ivermectin and
lincomycin are unaltered for use of these drugs in combination at their highest
approved use levels.
D. Regulatory Methods:
The validated regulatory analytical methods for detection of the marker
residue of ivermectin are filed in the Food Additives Manual on display in
FDA's Freedom of Information Public Room (Room 12A-30, 5600 Fishers Lane,
Rockville, MD 20857).
A microbiological assay method is used to assay tissues for lincomycin
residues. The method titled "Determination of Lincomycin Residues in
Broiler Chicken Tissues" is filed in the Food Additives Manual on display in
FDA's Freedom of Information Public Room (Room 12A-30, 5600 Fishers Lane,
Rockville, MD 20857).
