Anthelmintic Drugs & Insecticides: Mechanisms, Side Effects, and Efficacy Worldwide

1. Medical University of Sofia, Faculty of Medicine Department of Pharmacology and Toxicology Anthelmintic drugs Insecticides (Abstract) Assoc. Prof. Ivan Lambev e-mail: itlambev@mail.bg

2. Relative incidence of helminth infections worldwide

3. Cestodes (tapeworms) Beef tapeworm – Taenia saginata Pork tapeworm – Taenia solium Cysticercosis – Taenia solium Fish tapeworm – Diphyllobothrium latum Hydatid disease – Echinococcus granulosus

5. Life cycle of Taenia saginata (beef tapeworm).

6. Life cycle of Trichinella spiralis (cosmopolitan)

7. Trichinella larva encysted in a characteristic hyalinized capsule in striated muscle tissue

8. Elephantiasis (Lymphatic filariasis) of the lower extremityassociated with Wuchereria bancrofti infection

9. Global distribution of Schistosoma mansoni and S. intercalatum

11. Niclosamideblocks glucose uptake by intestinal tapeworms. It may cause some mild gastrointestinal symptoms. Piperazine may cause hypersensitivity reactions, neurological symptoms (including “worm wobble”) and may precipitate epilepsy. Praziquantel paralyses both adult worms and larvae. It is extensively metabolised. Praziquantel may cause nausea, headache, dizziness and drowsiness; it cures with a single dose (or divided doses in one day).

12. Mebendazoleblocks glucose uptake by nematodes. Mild GI distarbunces may be caused, and it should not be used in preg- nancy or in children under the age of 2. Albendazole is similar to mebendazole. Levamisoleparalyses the musculature of sensitive nematodes which, unable to maintain their anchorage, are expelled by normal peristalsis. It is may cause abdominal pain, nausea, vomiting, headache and dizziness.

13. Thiabendazole inhibits cellular enzymes of susceptible helminths. Gastrointestinal, neuro- logical and hypersensitivity reactions, liver damage and crystalluria may be induced. Pyranteldepolarises neuromuscular junctions of susceptible nematodes which are expelled in the faeces. It cures with a single dose. It may induce GI disturbance, headache, dizziness, drowsiness and insomnia.

14. Diethylcarbamazine kills both microfilariae and adult worms. Fever, headache, anorexia, malaise, urticaria, vomiting and asthmatic attacks following the first dose are due to products of destruction of the parasite, and reactions are minimised by slow increase in dosage over the first 3 days. Ivermectin may cause immediate reactions due to the death of the microfilaria. It can be effective in a single dose, but is best repeated at 6–12-month intervals.

15. Insecticides Whereas fleas can be effectively dealt with by disinfection of clothes, lice and mites require the topical application of insecticides to the infected subject. Chlorphenothane (DDT) kills insects after absorption of a very small amount, e.g., via foot contact with sprayed surfaces (contact insecticide). The cause of death is nervous system damage and seizures. In humans DDT causes acute neurotoxicity only after absorption of very large amounts.

16. DDT is chemically stable and degraded in the environment and body at extremely slow rates. As a highly lipophilic sub- stance, it accumulates in fat tissues. Widespread use of DDT in pest control has led to its accumulation in food chains to alarming levels. For this rea- son its use has now been banned in many countries.

17. Lindane is the active gama-isomer of hexachlorocyclohexane. It also exerts a neurotoxic action on insects (as well as humans). Irritation of skin or mucous membranes may occur after topical use. Lindane is active also against intrader- mal mites (Sarcoptes scabiei, causative agent of scabies), besides lice and fleas. It is more readily degraded than DDT. Permethrin, a synthetic pyrethroid, exhibits similar anti-ectoparasitic activity and may be the drug of choice due to its slower cutaneous absorption, fast hydrolytic inactivation, and rapid renal elimination