Monimax® is a registered coccidiostat that combines the strengths of the synthetic compound nicarbazin with the ionophore monensin, resulting in a unique new product for coccidiosis control.
Here are three benefits of using the combination of nicarbazin and monensin as found in Monimax®.
1. Broader activity
Intrinsically, both monensin and nicarbazin are efficacious against all seven Eimeria species that infect chickens. Nicarbazin shows more activity against caecal species but when combining it with monensin, efficacy against the complete set of Eimeria species is guaranteed, even at lower dosages.
Also, nicarbazin and monensin act during different stages of the Eimeria life cycle which gives Monimax® a broader activity and efficacy (Figure 1):
- Extracellular: Monensin interacts with the parasite early in the life cycle during the motile stage (sporozoites and merozoites) and does not penetrate the intestinal cells
- Intracellular: Nicarbazin interacts later during the life cycle of the parasite and can penetrate the intestinal cells (1st and 2nd generation schizonts)
These different modes of action make sure that any parasite that escapes the early action of monensin is likely to be subsequently killed by nicarbazin in the later life cycle stages.
This benefit of combining monensin and nicarbazin was shown in a clinical trial. The combination of nicarbazin with monensin was shown to be more effective against Eimeria species than either drug used alone at the same concentrations.
In the clinical trial, also called an anticoccidial sensitivity trial (AST), groups of birds reared in cages were challenged at 17 days of age with relevant European Eimeria field strains (Figure 2). The effect of different anticoccidial products on the development of the disease was evaluated by performing lesion scoring.
Table 1 shows the results of the groups receiving different anticoccidials and compares them to the control groups: an uninfected untreated control (UUC) and an infected untreated control (IUC).
The results show that the combination of monensin and nicarbazin (both at 40 ppm) resulted in significantly lower lesion scores in comparison to nicarbazin and monensin alone (at 40 ppm). Since the reduction in the lesion scores of the combination of nicarbazin and monensin was stronger than the sum of the effects of the individual products, this indicates a synergistic effect between monensin and nicarbazin.
2. Reduced risk of toxicity
Making efficient drug combinations generally allows the dosage of active compounds to be reduced without any reduction in efficacy. In the case of nicarbazin, when it is combined with monensin, the dose can be reduced by 30 - 40% compared to the dose when nicarbazin is used alone. The benefit here is a reduction in the risk of toxicity which is generally recognised with high doses of nicarbazin in acute heat stress conditions. And due to the lower dose, Monimax® can be used in chickens reared for laying. Other products containing higher dosages of nicarbazin are not allowed due to the adverse effects on egg production.
Zero-day withdrawal time
The lower dosages also reduce the withdrawal time since a lower dosage typically means lower residues. In the case of Monimax®, a zero-day withdrawal period applies, which is not the case when the individual compounds are used at a higher dosage.
3. Avoid resistance
The practice of prophylactic control of coccidiosis, in which large numbers of broilers are given coccidiostats continously in the feed, has resulted in the inevitable development of drug resistance. When the parasite is constantly exposed throughout its life cycle to coccidiostats, resistance develops and the coccidiostats become less effective. When using drug combinations, the development of this resistance is reduced or delayed.
Although resistance development to nicarbazin and monensin is considered to develop slowly, reduced sensitivity can occur, especially since the worldwide popularity and use of both compounds has increased. The chance of selecting resistant mutants when using drug combinations is less than if those compounds are used alone. It is important to note that differences exist between different combinations, possible because of the extent of use but also because of intrinsic differences: Chapman (1994) highlighted that resistance to a mixture of 50 ppm nicarbazin and 50 ppm narasin could be developed after 11 serial passages of E. tenella in medicated birds whereas as many as 60 generations of selection were required for resistance to develop in E. acervulina and E. tenella when a mixture of nicarbazin and monensin was used.
One plus one is more than two
Combining nicarbazin and monensin in Monimax® delivers more benefits than the sum of the two active parts. Nevertheless, in order to preserve long-term efficacy, it is still advisable to apply rotation programs including different coccidiostats as well as coccidiosis vaccines to minimise development of reduced sensitivity. In this way, the coccidiosis-control-arsenal is kept in optimal shape to face the different challenges.