Internal and External Antiparasitics: How and When to Dose

Antiparasitics include internal products for worms and external ones for ticks, fleas and mange, and some act on both. They are used heavily on Egyptian farms and in homes, but a mistake in dose or timing can cause treatment failure or poisoning. Parasites do not disappear with random spraying; they require a plan based on weight, parasite type and life cycle. This article explains the main groups, how dosing is calculated, and why some treatments must be repeated.

Groups of antiparasitics

The first group is the macrocyclic lactones such as ivermectin and doramectin, active against roundworms and some arthropods. The second is the pyrethroids such as permethrin and deltamethrin for ticks and fleas. The third includes fipronil and imidacloprid for fleas. The fourth is tapeworm drugs such as praziquantel, and the fifth is benzimidazoles for roundworms and liver flukes.

Each group has a different spectrum, and no product kills everything. Mixing an internal and an external product can cause toxicity, especially in cats. Reading the active ingredient rather than the brand name is the first step, followed by checking the age group, weight and species.

• Macrocyclic lactones: roundworms and some external parasites.
• Pyrethroids: ticks and fleas, with great caution in cats.
• Fipronil and imidacloprid: mainly fleas.
• Praziquantel: tapeworms.
• Benzimidazoles: roundworms and liver flukes.

Dose by weight, not age

The dose is calculated on real weight, and the animal is weighed before treatment or a reliable sample is used. Puppies and kittens do not get an adult dose reduced by guesswork; they need a product labelled for their age and weight. An overdose can cause tremors, drooling or lethargy, while an underdose leaves surviving parasites that build resistance.

For cattle, use a weigh tape or scale, and for poultry calculate the amount from daily water or feed intake. A sick or stressed animal may need treatment delayed or the dose adjusted under veterinary guidance. Never assume the same dose for the whole herd when weights differ.

Internal: worms and coccidia

Roundworms are treated with albendazole, fenbendazole or ivermectin depending on the species. Tapeworms need praziquantel. Coccidia are not worms but protozoa and require dedicated anticoccidials such as toltrazuril or amprolium, along with better hygiene and drier litter.

Repeat treatment depends on the parasite life cycle: some worms need a second dose after two weeks to kill stages that were not adult at the first dose. In sheep and cattle, milk and meat withdrawal periods must be respected. Do not use one drug for all animals without diagnosis, because some parasites need a different product.

External: ticks, fleas and mange

Ticks and fleas are controlled with spot-on products, tablets or sprays. Mange needs longer treatment and sometimes injections under veterinary supervision, plus environmental cleaning because the parasite survives off the animal. Cats are highly sensitive to permethrin, and dog products must never be used on them.

Full control covers the animal, bedding, floors and vehicles. Repeat treatment according to the parasite life cycle, often after two to three weeks. The environment can be supported with products from our pest control, and animal products such as Dectomax or Sebason used as your vet advises.

Resistance and the control calendar

Resistance comes from repeated use of the same product at an insufficient dose. The answer is annual rotation of groups, not switching products every week, with results measured by faecal testing or tick counts. Large farms run regular herd checks and treat only the animals that need it instead of treating all.

The calendar depends on region and weather: the Egyptian summer increases ticks and fleas, and humidity favours mange. Start before the peak season and record every treatment date and product. Do not use more than one systemic product at the same time without advice, because the interaction can be toxic. If treatment fails, review with the vet instead of doubling the dose.

Conclusion

Parasite control starts with identifying the parasite and weighing the animal, then choosing the right group and repeating it at the right time. Do not treat by habit or double the dose. Record every treatment and consult the vet when failure repeats.

This article is general guidance and is not a substitute for examining your animal by a licensed veterinarian. In emergencies, contact your vet immediately.