- Email: [email protected]
Coccidiosis: Selection of the most useful parameters for anticoccidial drug testing
EXPERIMENTAL
28, 160-163
PARASITOLOGY
Coccidiosis:
(1970)
Selection of the Most Useful for Anticoccidial Drug Testing W.
Department
of Poultry
Malcolm
Science, University
Parameters
Reid of Geoqia,
Athens,
Georgia
30601
REID, W. MALCOM. 1970. Coccidiosis: Selection of the most useful parameters for coccidiostat testing. Experimental Puru5itology 28, 160-163. For somewhat different reasons, pharmaceutical houses, governmental regulatory agencies, and poultry producers must pass judgment on new anticoccidial drugs. A diversified group of parameters and formulas for combining them have been developed to assist in making decisions. These formulas have been used for comparisons following laboratory floorpen and field experimentation. Final judgment will ultimately be based on field performance measured by financial savings provided to the poultry producer. INDEX
coccidials;
DESCRIPTORS:
Coccidiosis;
Chemotherapy;
Treatment;
Technique;
Anti-
Coccidiostats.
To conclude this symposium on coccidiosis it may be useful to summarize tests used in selection of an anticoccidial. All participants have faced difficult decisions in judging effectiveness and usefulness of anticoccidial agents (see Experimental Parasitology 28). Three different groups have been represented, each with somewhat different needs for evaluation. These include pharmaceutical houses, governmental regulatory agencies, and the feed manufacturer or poultry producer. Similar parameters may be used in the efficacy evaluations conducted for somewhat different purposes. The pharmaceutical house, which may be working upon a variety of different anticoccidial products, must make difficult preliminary selections involving questions of manufacturing techniques, costs, toxicity in both birds and mammals, susceptibility to development of drug resistance, palatability, absence of electrostatic or hygroscopic properties, suitable carriers, stability, combinability with other medication, as well as efficacy against all species of coccida. This symposium has dealt largely 160
with efficacy judgments. Some type of formula is generally used for combining data and weighting relative importance of different parameters. Several speakers have indicated differences in the parameters selected and their relative weighting in the several formulas described. The oldest and most widely adopted formula ( Cuckler, 1959) is the “anticoccidial index” which combines weight gains, lesion scores, and oocyst counts. Other investigators, who have found wide variability in oocyst counts with different levels of drugs, have developed other formulas. Barwick et al.1 have described the “index of performance,” which includes mean weight gains of survivors as the most sensitive parameter. They also include survival and dropping scores in their “index of performance.” Morehouse and Baron have combined mortality, weight gains, and fecal scores ( = dropping scores) in a slightly different manner. 1 Other papers in this symposium on coccidiosis published herein, are designated by author but are not included in reference lists.
PARAMETER
These formulas are used chiefly in combining results from laboratory or battery experiments to predict performance of an anticoccidial under field conditions. Laboratory experiments have real advantages in reduced cost and greater effectiveness in testing a single variable. This advantage makes such a design the method of choice in testing drug efficacy against different species and strains. Large numbers of isolates can be collected in the field, subpropagated in the laboratory, and then tested. In contrast, field experimentation may encounter a vast number of uncontrollable variables in addition to the inevitable human errors reviewed by Kilgore. Floorpen experiments permit designing trials which include replication, but they require introduction of some artificial conditions. They also share some of the same disadvantages of unexpected variables encountered in field experiments. Two other considerations on design of laboratory experiments require added comment. First, there has been sharp disagreement on the degree of mortality required to demonstrate efficacy in artificial coccidial exposures ( Hunter 1959). Complete against a cocsuppression of mortality cidial challenge producing 5O-100% in unmedicated controls has sometimes been the goal, As indicated by Edgar (see Hunter 1959) a target level of 2030% is more realistic and closer to highest mortality encountered in the field. Thus, a 30% mortality is a satisfactory goal in planning protocols. Second, there has also been disagreement on the day that medication should be started for testing. With preventive drugs introduction of medicated feed 24-48 hours before inoculation with oocysts is usually considered satisfactory. But with treatment, starting the drug 48 hours following inoculation should be considered an acceptable design. A few evaluations (Horton-Smith 1951; Gill, Mal-
SELECTION
161
hotra, and La11 1963) have started medication 72 or 96 hours postinoculation. Drug activity is very limited if medication is delayed this long after infection. Treatment instituted after a bird shows symptoms is too late except to assist with other birds in the flock which have acquired infection at a later time. Various governmental regulatory officials must sometimes make judgment on anti-, coccidials to fulfill legal requirements for approvals. These requirements vary greatly between different countries. Industry and governmental committees developing the Food and Drug Administration Guidelines (John Hopkins Press 1989) found some areas with insufficient information or lack of agreement. These discussions have stimulated plans for this seminar. It is hoped that further experimentation will result in continued improvement in methods of testing anticoccidials. New findings can then be incorporated in revisions and interpretations of guidelines. The final decision on use of an anticoccidial rests with the poultry feed manufacturer or the large poultry producer. He cannot become deeply involved until preliminary decisions have been made by the pharmaceutical house and governmental agencies. As indicated by Cover, this final decision constitutes a “fearful responsibility.” Although the prospective user may review the experimental data developed using methods thus far discussed, he will make final judgment in terms of the financial benefits he may expect through use of the product. Financial returns thus become his most important parameter. The best indicator of profits comes from comparing production records of different products. Such data are often summarized in the United States by comparing the “point spread” (average weight of the flock calculated in pounds minus the feed conversion). This method gives a single
I62
REID
useful figure on each flock which can be used in comparing anticoccidial drug performance in addition to other flock management differences. Unfortunately, this point spread formula cannot be used with the metric system. Zuijdam has introduced the “production number,” which has been used in the Netherlands as a method of combining weights, feed consumed, and mortality. Gard and Tonkinson have included samples showing lesion scores along with final bird weight, feed conversion, and mortality for use in floor-pen and field experiments. With proper design, results can be compared using a method involving a “least square analysis.” Field experimentation requires comparisons on large numbers of birds. Since only the large operator is in a position to evaIuate an anticoccidial on a cost basis (Reid 1969; Reid et al. 1969), governmental agencies could assist the poultry industry by expediting the temporary marketing regulations as soon as satisfactory safety data on a drug have been presented. For obvious reasons results from such tests in this highly competitive industry are frequently considered confidential. If properly conducted their value in final selection of an anticoccidial is obvious. ACKNOWLEDGMEXTS
The assistance of the highly qualified scientific personnel employed by the pharmaceutical industries in presentations at the symposium is gratefully acknowledged. The following commercial organizations provided financial support the symposium possible: American making Cyanamid Company, Princeton, New Jersey; Ayerst Laboratories, New York, New York; Chas. Pfizer and Co., Inc., Groton, Connecticut; CIBA Pharmaceutical Co., Three Bridges, New Jersey; The Dow Chemical Co., Midland, Michigan; Eli Lilly and Company, Greenfield, Indiana; HoffmanLaRoche, Inc., Nutley, New Jersey; Merck Institute for Therapeutic Research, Rahway, New Jersey; The Norwich Pharmacal Co., Norwich, New York; Sterwin Laboratories, Inc., New York, New York.
REFEFWNCE~
A. C. 1959. The laboratory evaluation of coccidiostatic drugs. In “Conference on Methods of Testing Coccidiostats,” Section 2, pp. l-14. Merck Chemical Division, Rahway, N. J. GILL, B. S., MALHOTRA, M. N., AND LALL, N. B. 1963. Technical note: Studies on the comparative efficacy of sulphamezathine, sulphaquinoxaline and nitrofurazone given in feed, and their soluble salts administered in drinking water in the control of caecal coccidiosis (Eimeria tenellu) of poultry. Indian Journal of Veterinary Science 33, 56-58. HORTON-&ITH, C. 1951. Sulfaquinoxaline in the treatment of caecal coccidiosis Eimeria tenella (Raillet and Lucet, 1891). Proceedings of the 9th World Poultry Congress, Paris 3, 3-8. HUNTER, J. E. 1959. Considerations for the evaluation of coccidiostats. Proceedings of the Semi-Annzral Nutrition Council, pp. 16 19. American Feed Manufacturers Association, JOAX HOPKINS PRESS. 1969. FDA issues guidelines for efficacy for coccidiostats. Food Chemical News, March 31, pp. 6-8. REID, W. M. 1969. The effects of mechanisms of coccidiostats, histomonostats, and antihelmintics in feed on the performance and health of animals. National Academy of Sciences 1679, 87-99. REID, W. M., BREWER, R. N., JOHNSON, JOYCE, TAYLOR, E. M., HEDGE, K. S., AND KOWALSKI, L. M. 1969. Evaluation of techniques used in studies on efficacy of anticoccidial drugs in chickens. American journal of Veterinary Research 30,447-459. CUCKLER,
COMZWENTS
Dr. .I. C. FrancIsen: I have been impressed throughout the conference with the need for basic research on the biochemistry of the coccidia as an aid in our developing a rational theory of chemotherapeusis based on the chemistry of these parasites. Dr. R. E. McKinley: This group should not that we can significantly ignore the possibility assist in providing solutions to some of the basic consumer protection problems faced by the Food and Drug Administration. We have been discussing the value of and need for field efficacy testing. Field experimenta-
PARAMETER
tion provides very limited information concerning efficacy, but a limited amount of field experience is necessary prior to Food and Drug Administration approval, if only to show that commercial conditions the drug can under properly be incorporated in and assayed in commercial feeds without the development of any unexpected adverse effects. This information considered with the results of screening, battery, and floor-pen studies provides the basis for Food and Drug Administration to determine the efficacy in accord with the requirements of the Food, Drug, and Cosmetic Act. However, this is not the end of the Food and Drug Administration’s responsibility. Every time a drug is used constitutes a further trial of the drug regardless of the time elapsed since initial approval. This group made up of consumers, university and industry researchers, and Food and Drug Administration representatives has the the real responsibility of considering, designing, proposing, and effectively accomplishing ways and means of feeding meaningful information concerning field-use experience back to the agency and the industry. An effective records and reports system would permit Food and Drug Administra-
SELECTION
163
tion primary (initial) approval with a minimum of information and the placement of more emphasis upon the consumer’s experience in label revisions, development of and approval of new uses and use patterns, and the development of proper communication with all users of the article.
Dr. E. Waletzky: Do we need floor-pen trials as well as battery trials to show that a drug has anticoccidial efficacy? Dr. W. M. Reid: Performance under floor-pen conditions may be better or worse than anticipated from examination of data from battery trials. Weight gains and feed conversions under the two experimental conditions may be quite different. Some of these differences may reflect subclinical coccidiosis infections. Other unforseen factors may be operative in floor pens. Most commercial poultry producers will place more reliance on results from floor pens than from battery experiments. 07. M. S. Cover: I second the last comment that Dr. Reid made. In my position (Ralston Purina Co.), I want to see feed conversion and weight gain data from floor-pen experiments before further testing in field experimentation.
28, 160-163
PARASITOLOGY
Coccidiosis:
(1970)
Selection of the Most Useful for Anticoccidial Drug Testing W.
Department
of Poultry
Malcolm
Science, University
Parameters
Reid of Geoqia,
Athens,
Georgia
30601
REID, W. MALCOM. 1970. Coccidiosis: Selection of the most useful parameters for coccidiostat testing. Experimental Puru5itology 28, 160-163. For somewhat different reasons, pharmaceutical houses, governmental regulatory agencies, and poultry producers must pass judgment on new anticoccidial drugs. A diversified group of parameters and formulas for combining them have been developed to assist in making decisions. These formulas have been used for comparisons following laboratory floorpen and field experimentation. Final judgment will ultimately be based on field performance measured by financial savings provided to the poultry producer. INDEX
coccidials;
DESCRIPTORS:
Coccidiosis;
Chemotherapy;
Treatment;
Technique;
Anti-
Coccidiostats.
To conclude this symposium on coccidiosis it may be useful to summarize tests used in selection of an anticoccidial. All participants have faced difficult decisions in judging effectiveness and usefulness of anticoccidial agents (see Experimental Parasitology 28). Three different groups have been represented, each with somewhat different needs for evaluation. These include pharmaceutical houses, governmental regulatory agencies, and the feed manufacturer or poultry producer. Similar parameters may be used in the efficacy evaluations conducted for somewhat different purposes. The pharmaceutical house, which may be working upon a variety of different anticoccidial products, must make difficult preliminary selections involving questions of manufacturing techniques, costs, toxicity in both birds and mammals, susceptibility to development of drug resistance, palatability, absence of electrostatic or hygroscopic properties, suitable carriers, stability, combinability with other medication, as well as efficacy against all species of coccida. This symposium has dealt largely 160
with efficacy judgments. Some type of formula is generally used for combining data and weighting relative importance of different parameters. Several speakers have indicated differences in the parameters selected and their relative weighting in the several formulas described. The oldest and most widely adopted formula ( Cuckler, 1959) is the “anticoccidial index” which combines weight gains, lesion scores, and oocyst counts. Other investigators, who have found wide variability in oocyst counts with different levels of drugs, have developed other formulas. Barwick et al.1 have described the “index of performance,” which includes mean weight gains of survivors as the most sensitive parameter. They also include survival and dropping scores in their “index of performance.” Morehouse and Baron have combined mortality, weight gains, and fecal scores ( = dropping scores) in a slightly different manner. 1 Other papers in this symposium on coccidiosis published herein, are designated by author but are not included in reference lists.
PARAMETER
These formulas are used chiefly in combining results from laboratory or battery experiments to predict performance of an anticoccidial under field conditions. Laboratory experiments have real advantages in reduced cost and greater effectiveness in testing a single variable. This advantage makes such a design the method of choice in testing drug efficacy against different species and strains. Large numbers of isolates can be collected in the field, subpropagated in the laboratory, and then tested. In contrast, field experimentation may encounter a vast number of uncontrollable variables in addition to the inevitable human errors reviewed by Kilgore. Floorpen experiments permit designing trials which include replication, but they require introduction of some artificial conditions. They also share some of the same disadvantages of unexpected variables encountered in field experiments. Two other considerations on design of laboratory experiments require added comment. First, there has been sharp disagreement on the degree of mortality required to demonstrate efficacy in artificial coccidial exposures ( Hunter 1959). Complete against a cocsuppression of mortality cidial challenge producing 5O-100% in unmedicated controls has sometimes been the goal, As indicated by Edgar (see Hunter 1959) a target level of 2030% is more realistic and closer to highest mortality encountered in the field. Thus, a 30% mortality is a satisfactory goal in planning protocols. Second, there has also been disagreement on the day that medication should be started for testing. With preventive drugs introduction of medicated feed 24-48 hours before inoculation with oocysts is usually considered satisfactory. But with treatment, starting the drug 48 hours following inoculation should be considered an acceptable design. A few evaluations (Horton-Smith 1951; Gill, Mal-
SELECTION
161
hotra, and La11 1963) have started medication 72 or 96 hours postinoculation. Drug activity is very limited if medication is delayed this long after infection. Treatment instituted after a bird shows symptoms is too late except to assist with other birds in the flock which have acquired infection at a later time. Various governmental regulatory officials must sometimes make judgment on anti-, coccidials to fulfill legal requirements for approvals. These requirements vary greatly between different countries. Industry and governmental committees developing the Food and Drug Administration Guidelines (John Hopkins Press 1989) found some areas with insufficient information or lack of agreement. These discussions have stimulated plans for this seminar. It is hoped that further experimentation will result in continued improvement in methods of testing anticoccidials. New findings can then be incorporated in revisions and interpretations of guidelines. The final decision on use of an anticoccidial rests with the poultry feed manufacturer or the large poultry producer. He cannot become deeply involved until preliminary decisions have been made by the pharmaceutical house and governmental agencies. As indicated by Cover, this final decision constitutes a “fearful responsibility.” Although the prospective user may review the experimental data developed using methods thus far discussed, he will make final judgment in terms of the financial benefits he may expect through use of the product. Financial returns thus become his most important parameter. The best indicator of profits comes from comparing production records of different products. Such data are often summarized in the United States by comparing the “point spread” (average weight of the flock calculated in pounds minus the feed conversion). This method gives a single
I62
REID
useful figure on each flock which can be used in comparing anticoccidial drug performance in addition to other flock management differences. Unfortunately, this point spread formula cannot be used with the metric system. Zuijdam has introduced the “production number,” which has been used in the Netherlands as a method of combining weights, feed consumed, and mortality. Gard and Tonkinson have included samples showing lesion scores along with final bird weight, feed conversion, and mortality for use in floor-pen and field experiments. With proper design, results can be compared using a method involving a “least square analysis.” Field experimentation requires comparisons on large numbers of birds. Since only the large operator is in a position to evaIuate an anticoccidial on a cost basis (Reid 1969; Reid et al. 1969), governmental agencies could assist the poultry industry by expediting the temporary marketing regulations as soon as satisfactory safety data on a drug have been presented. For obvious reasons results from such tests in this highly competitive industry are frequently considered confidential. If properly conducted their value in final selection of an anticoccidial is obvious. ACKNOWLEDGMEXTS
The assistance of the highly qualified scientific personnel employed by the pharmaceutical industries in presentations at the symposium is gratefully acknowledged. The following commercial organizations provided financial support the symposium possible: American making Cyanamid Company, Princeton, New Jersey; Ayerst Laboratories, New York, New York; Chas. Pfizer and Co., Inc., Groton, Connecticut; CIBA Pharmaceutical Co., Three Bridges, New Jersey; The Dow Chemical Co., Midland, Michigan; Eli Lilly and Company, Greenfield, Indiana; HoffmanLaRoche, Inc., Nutley, New Jersey; Merck Institute for Therapeutic Research, Rahway, New Jersey; The Norwich Pharmacal Co., Norwich, New York; Sterwin Laboratories, Inc., New York, New York.
REFEFWNCE~
A. C. 1959. The laboratory evaluation of coccidiostatic drugs. In “Conference on Methods of Testing Coccidiostats,” Section 2, pp. l-14. Merck Chemical Division, Rahway, N. J. GILL, B. S., MALHOTRA, M. N., AND LALL, N. B. 1963. Technical note: Studies on the comparative efficacy of sulphamezathine, sulphaquinoxaline and nitrofurazone given in feed, and their soluble salts administered in drinking water in the control of caecal coccidiosis (Eimeria tenellu) of poultry. Indian Journal of Veterinary Science 33, 56-58. HORTON-&ITH, C. 1951. Sulfaquinoxaline in the treatment of caecal coccidiosis Eimeria tenella (Raillet and Lucet, 1891). Proceedings of the 9th World Poultry Congress, Paris 3, 3-8. HUNTER, J. E. 1959. Considerations for the evaluation of coccidiostats. Proceedings of the Semi-Annzral Nutrition Council, pp. 16 19. American Feed Manufacturers Association, JOAX HOPKINS PRESS. 1969. FDA issues guidelines for efficacy for coccidiostats. Food Chemical News, March 31, pp. 6-8. REID, W. M. 1969. The effects of mechanisms of coccidiostats, histomonostats, and antihelmintics in feed on the performance and health of animals. National Academy of Sciences 1679, 87-99. REID, W. M., BREWER, R. N., JOHNSON, JOYCE, TAYLOR, E. M., HEDGE, K. S., AND KOWALSKI, L. M. 1969. Evaluation of techniques used in studies on efficacy of anticoccidial drugs in chickens. American journal of Veterinary Research 30,447-459. CUCKLER,
COMZWENTS
Dr. .I. C. FrancIsen: I have been impressed throughout the conference with the need for basic research on the biochemistry of the coccidia as an aid in our developing a rational theory of chemotherapeusis based on the chemistry of these parasites. Dr. R. E. McKinley: This group should not that we can significantly ignore the possibility assist in providing solutions to some of the basic consumer protection problems faced by the Food and Drug Administration. We have been discussing the value of and need for field efficacy testing. Field experimenta-
PARAMETER
tion provides very limited information concerning efficacy, but a limited amount of field experience is necessary prior to Food and Drug Administration approval, if only to show that commercial conditions the drug can under properly be incorporated in and assayed in commercial feeds without the development of any unexpected adverse effects. This information considered with the results of screening, battery, and floor-pen studies provides the basis for Food and Drug Administration to determine the efficacy in accord with the requirements of the Food, Drug, and Cosmetic Act. However, this is not the end of the Food and Drug Administration’s responsibility. Every time a drug is used constitutes a further trial of the drug regardless of the time elapsed since initial approval. This group made up of consumers, university and industry researchers, and Food and Drug Administration representatives has the the real responsibility of considering, designing, proposing, and effectively accomplishing ways and means of feeding meaningful information concerning field-use experience back to the agency and the industry. An effective records and reports system would permit Food and Drug Administra-
SELECTION
163
tion primary (initial) approval with a minimum of information and the placement of more emphasis upon the consumer’s experience in label revisions, development of and approval of new uses and use patterns, and the development of proper communication with all users of the article.
Dr. E. Waletzky: Do we need floor-pen trials as well as battery trials to show that a drug has anticoccidial efficacy? Dr. W. M. Reid: Performance under floor-pen conditions may be better or worse than anticipated from examination of data from battery trials. Weight gains and feed conversions under the two experimental conditions may be quite different. Some of these differences may reflect subclinical coccidiosis infections. Other unforseen factors may be operative in floor pens. Most commercial poultry producers will place more reliance on results from floor pens than from battery experiments. 07. M. S. Cover: I second the last comment that Dr. Reid made. In my position (Ralston Purina Co.), I want to see feed conversion and weight gain data from floor-pen experiments before further testing in field experimentation.