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Guidance for Industry 

Effectiveness of Anthelmintics: 

Specific Recommendations for Poultry-GALLUS GALLUS

VICH GL21 

FINAL GUIDANCE 

This final guidance is intended to standardize and simplify methods used in the evaluation of 

new anthelmintics submitted for approval to the European Union, Japan, and the United States. 

Comments and suggestions regarding the document should be submitted to Division of Dockets 

Management (HFA-305), Food and Drug Administration, 5630 Fishers Lane, Rm. 1061, 

Rockville, MD 20852. Submit electronic comments to http://www.regulations.gov. All comments 

should be identified with the Docket No. 00D-1629. 

For questions regarding this document, contact Janis Messenheimer, Center for Veterinary 

Medicine, (HFV-135), Food and Drug Administration, 7500 Standish Place, Rockville, MD 20855, 

240-276-8348, e-mail: janis.messenheimer@fda.hhs.gov. 

U.S. Department of Health and Human Services 

Food and Drug Administration 

Center for Veterinary Medicine 

June 19, 2002
VICH GL21 (ANTHELMINTICS: POULTRY – GALLUS GALLUS) 

June 2002 

For implementation at Step 7 

EFFECTIVENESS OF ANTHELMINTICS: SPECIFIC RECOMMENDATIONS FOR 

POULTRY - GALLUS GALLUS

Recommended for Implementation 

on June 2001 

by the VICH Steering Committee 

THIS GUIDANCE HAS BEEN DEVELOPED BY THE APPROPRIATE VICH EXPERT WORKING GROUP AND WAS 

SUBJECT TO CONSULTATION BY THE PARTIES, IN ACCORDANCE WITH THE VICH PROCESS. AT STEP 7 OF 

THE PROCESS THE FINAL DRAFT IS RECOMMENDED FOR ADOPTION TO THE REGULATORY BODIES OF THE 

EUROPEAN UNION, JAPAN AND USA. 

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EFFECTIVENESS OF ANTHELMINTICS: 

SPECIFIC RECOMMENDATIONS FOR POULTRY - GALLUS GALLUS

Endorsed by the VICH Steering Committee at Step 7 of the 

VICH process at its meeting from June 2001 

This guidance represents the agency's current thinking on the subject matter and does not 

create or confer any rights for or on any person and does not operate to bind FDA or the public. 

An alternative method may be used as long as it satisfies the requirements of the applicable 

statutes and regulations. 

Introduction 

The present guidance for poultry (Gallus gallus) was developed by the Working Group established by 

the Veterinary International Cooperation on Harmonization (VICH), Anthelmintic Guidances. It should 

be read in conjunction with the VICH Effectiveness of Anthelmintic: General Recommendations 

(EAGR) which should be referred to for discussion of broad aspects for providing pivotal data to 

demonstrate product anthelmintic effectiveness. The present document is structured similarly to the 

EAGR with the aim of simplicity for readers comparing both documents. 

This guidance for poultry is part of this EAGR and the aim is (1) to be more specific for certain 

specific issues for poultry not discussed in the EAGR; (2) to highlight differences with the EAGR on 

effectiveness data recommendations and (3) to give explanations for disparities with the EAGR. 

Although technical procedures to be followed are not the aim of this guidance, some details are given 

as until now the pertinent procedures have not been described elsewhere. 

A. General Elements 

1- The Evaluation of Effectiveness Data 

Only controlled tests based on parasite counts of adults/larvae should be acceptable both for the 

dose determination and dose confirmation studies, since critical tests generally are not considered to 

be reliable for chickens. Egg counts with identification of the genus should be the preferred method to 

evaluate the effectiveness in field studies. Adequate parasite infection should be defined in the 

protocol according to regional prevalence or historic and/or statistical data. 

2- Use of Natural or Induced Infections 

Dose determination studies generally should be conducted using induced infections with either 

laboratory or recent field isolates. 

Dose confirmation studies could be conducted using naturally infected birds which can have 

superimposed induced infections. This procedure should allow a wide range of parasites to be 

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present in the experimental birds. Also, induced infections in one of the studies should be acceptable. 

Studies for larval stages should be conducted with induced infections only. 

The history of the parasites used in the induced infection studies should be included in the final 

report. 

3- Number of Infective Forms Recommended for Induced Infections 

Table 1 indicates the number of eggs/cysticercoids recommended to be used and will depend on the 

isolate that is used. The final number of eggs/cysticercoids used in the infection should be included in 

the final report. 

Table 1. Range of infective stages recommended to produce adequate infections in chickens for 

anthelmintic evaluation. 

Parasites Range 

Ascaridia galli 200-500 

Capillaria obsignata 100-300 

Heterakis gallinarum 200-300 

Raillietina cesticillus 

Syngamus trachea 

50-100 

200 - 600 

Some factors to consider for induced infections in chickens are: 

a) Young birds should be used in the studies; 

b) To maximize the establishment of adequate infections it is recommended to use low numbers of 

infective stages; 

c) Stress (e.g., poor diets) is not recommended to generate helminth infections; 

d) Housing conditions should not allow accidental infections. 

4- Recommendations for the Calculation of Effectiveness 

4.1 Criteria to grant a claim 

To be granted a claim, the following pivotal data should be included: 

a) Two dose confirmation studies conducted with a minimum of six adequately infected birds in each 

of the non-medicated group and the treated group; 

b) The differences in parasite counts between treated and control birds should be statistically 

significant (p<0.05); 

c) Effectiveness should be 90% or higher calculated using transformed (geometric means) data of 

worm counts; 

d) The infection of the birds in the study should be deemed adequate based on historical, 

parasitological and/or statistical criteria. 

4.2 Number of Animals (Dose Determination and Dose Confirmation Trials) 

The minimum number of birds used per experimental group is a crucial point. Although the number of 

birds will depend on the ability to process the data according to the adequate statistical analysis, it 

has been recommended, to achieve harmonization, that the inclusion of at least six birds in each 

experimental group is a minimum. 

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4.3 Adequacy of Infection 

Concerning the minimum adequate number of helminths, the decision should be made when the final 

report is submitted based on statistical and historical data, literature review, or expert testimony. The 

range of chicken helminths (adults) considered adequate to grant a claim will vary according to the 

species. Generally a mean number of 20 adult A. galli is considered to be adequate. Lower counts 

may be expected with H. gallinarum, C. obsignata and R. cesticellus. Necropsies should be 

conducted within 10 days of treatment.

4.4 Label Claims 

For adult claims, as a general rule, the treatment should not be administered earlier than 28 days 

after infection. It is recommended to include at least six sentinel birds for helminth characterization 

and quantification before treatment is initiated. For L4 claims, treatments should be given, as a 

general rule, seven days after infection, except for A. galli and H. gallinarum which should be 16 days 

after infection. 

5 - Treatment Procedures 

The method of administration (oral, parenteral, topical, slow release, etc.), formulation and extent of 

activity of a product will influence the protocol design. 

When the drug is to be administered in the water or in a premix, it should be done as much as 

possible following the labelling recommendations. Palatability/consumption studies may be 

recommended for medicated premixes. Samples of medicated water or feed should be collected to 

confirm drug concentration. The amount of medicated product provided to each animal should be 

recorded to ensure that the treatment satisfies the label recommendations. 

6 - Bird Selection, Allocation and Handling 

Test birds should be clinically healthy and representative of the age, sex, and class for which the 

claim of the test anthelmintic is to be made. In general, birds should be young and from a breed that 

is susceptible to helminth infections. Birds should be randomly assigned to each group. Blocking in 

replicates by weight, sex, age, and/or exposure to parasites may aid in reducing trial variance. Faecal 

egg counts are also acceptable to allocate the experimental birds. Control birds should be of the 

same weight, age, breed, sex and history as the treated group. For induced infections, the use of 

helminth naive birds is recommended. 

Animal housing, feeding and care should follow recommendations for welfare, including vaccination 

according to local practices. This information should be provided in the final report. A minimum 10-

day acclimatization period is recommended. Housing and feed/water should be adequate according 

to the geographical location. Birds should be monitored daily to determine adverse reactions. 

B. Specific Evaluation Studies 

1- Dose Determination Studies 

If the treatment recommends extended administration, one or more studies are recommended to 

determine the minimum treatment period for effectiveness. 

2 - Dose Confirmation 

No species specific recommendations. 

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3 - Field Effectiveness Studies 

Due to commercial constraints the experimental unit in these studies invariably should be the 

shed/house. A shed/house should receive only one treatment, i.e., control or medicated. 

Clinical observations, production variables, and records of mortality should be maintained and 

compared to historical data of the commercial establishment. Slaughterhouse inspection reports 

should be included in the final report, when the number of test animals can not be confirmed.