Anthelmintics Flashcards
What are Anthelmintics?
drugs that control helminths parasites and disease they cause (nematodes, platyhelminths)
How do we group drugs?
How many classes of drug do horses, sheep and cattle have?
Classified based on their mode of action
Horses and cattle –> 3 classes of drug
Sheep –> 5 major classes
Aim of “control”
reduce transmission and therefore limit the amount of parasites lambs are exposed to
How do we control parasitic infections?
- Prophylactic - PREVENTING
Case of PGE is a FAIL of prophylaxis. - Therapeutic - when a case has been identified, how we treat
- Non drug related parasite control strategies getting more important: faecal collection, grazing strategies
With drugs what do we need to consider?
- Spectrum of activity
- Pharmacokinetics
- Formulation and administration of drug
- Drug efficacy
- Toxicity and specificity Vs host
- Cost
What is a drug’s spectrum of activity?
- gives idea of how broadly each class of anthelmintic works
- Each drug has their own spectrum – can kill x y and z parasite and in what part of lifecycle (e.g L3 and adult telodorsagia for)
- Parasite species and stage
What comes under a drugs pharmacokinetics?
o How well a drug works - Absorption and excretion of drug
o Residual activity – drug given but persists in body
o Drug residues and withdrawal periods – meat and milk. For majority of A there is a withdrawal period
What comes under a drug’s administration
- Oral, pour on, spot on, injectable
Drug efficacy
- the maximum response that can be achieved with a drug
Toxicity and specificity Vs host
o Careful not to overdose
o Some drugs only target molecules parasite has, not host. However some drugs target both host and parasite. So mustn’t harm host
How does the cost of a drug affect things?
drives drug decision for most things. E.g. drug can be used for wrong purpose but cheap. May not be fit for purpose of intended
What are the anthelmintic drug classes?
- 1 B-Z (Benzimidazoles)
- 2-LEV ( Imidazothiazoles, tetrahydropyrimidines)
- 3- ML (Macrocyclic lactones)
- ———2 new classes - 4-AD-Amino acetonitrile derivatives
- 5-SI-Amino acetonitrile derivatives
Examples of Benzimidazoles
- Fenbendazole (in panacole, horses)
- albendazole (often in sheep and human)
- flubendazole (chicken),
- mebendazole (most widely used drug in humans for threadworm
- Triclabendazole - excpetional amongst BZs
- Febantel is a 1BZ that is given and only becomes active inside body
Examples of 2 LEV
Imidazothiazoles, tetrahydropyrimidines
- pyrantel (PYR)
- morantel (used to lesser extent in UK
Examples of 3 ML
Macrocyclic lactones: Avermectins e.g. 1. Ivermectin - toxic to long nosed dogs as crosses blood brain barrier 10 years later 3MLs Milbemycins e.g. 2. Moxidectin
Examples of 4AD
Amino acetonitrile derivatives
1. monepantel - nematode control in sheep (zolvix)
Examples of 5SI
5 - SpiroindoleAmino acetonitrile derivatives
1. Derquantel. To inc efficacy use with abamectin (a 3 ML)
1 BZ spectrum of activity
Benzimidazoles
• Not well absorbed systemically, give orally
• Primarily target nematodes (wouldn’t use for tape or flat worms!)
• Ovicidal – even if eggs released kills eggs so reduces transmission as any eggs won’t develop
• Effective at targeting hypobiosed larvae
2 LEV spectrum of activity
- Probs most limited
- Not well absorbed systemically
- Primarily targets nematodes
- Gut dwelling stages
- Short acting – give product as kill parasites and nematodes within gut but act and then gone
- Note: EXCEPTION – double dose of PYR effective vs tapeworm of horses
- Restricted to killing gut dwelling nematodes
3 MLs spectrum of activity
Macrocyclic lactones
• Well absorbed systemically – given orally and absorbed so can target lots of stages of the parasite
• Effective against nematodes, as absorbed so will also target 4th, 5th larvae, adults, hypobiosed larvae – broad spectrum in terms of targeting multiple stages of nematodes
• Target multiple nematode stages
o Migrating larvae, hypobiotic larvae
• Residual activity
o e.g ivermectin residual activity for 2 weeks, moxidectin 2 weeks persistence at levels that will KILL parasites
• ENDECTOCIDE - target internal (endo) and external (ecto) parasites
What are combination drugs?
• Combine two drugs from different drug classes with different spectrum of activity .
e.g. o Horses e.g moxidectin (nematodes) and praziquantel (tapeworms)
o Cattle e.g ivermectin (nematode) and triclabendazole (fluke)
o Sheep e.g levamisole (N) and triclabendazole (f)
o Dogs and cats e.g pyrantel (n) and praziquantel (tape worms)
