Download - Class antihelmintics agents
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ANTIHELMINTICS
Dr. RAGHU PRASADA M SMBBS,MDASSISTANT PROFESSOR DEPT. OF PHARMACOLOGYSSIMS & RC.
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Antihelmintics
Drugs used to treat parasitic worm infections: helmintic infections
Unlike protozoa, helminths are large and have complex cellular structures
Drug treatment is very specific It is very important to identify the causative worm Done by finding the parasite ova or larvae in
feces, urine, blood, sputum, or tissue
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HELMINTHSNEMATELMINTHS(ROUND)
ROUND.W-ASCARIS.L HOOK W-NECATOR A WHIP W-TRICHURIS T THREAD W-
STRONGYLOIDES.S PIN W-ENTEROBIUS V FILARIASIS-W BANCROFTI ONCHOCERCIASIS-
O.VOLVULUS GUINEA W-
DRACANCULUS M
PLATYHELMINTHS
TREMATODES-FLUKES BLOOD F-
SCISTOSOMIASIS LIVER F-CLONORCHIASIS INTESTINAL F-
FASCIOLOPSIASIS LUNG F-
PARAGONIMIASISCESTODESBEEF TW-T.SAGINATPORK TW-T.SOLIUMFISH TW-DIPHYLLOBO
THRIUM DWARF TW-
HYMENOLEPIS.NANA
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LIFE CYCLE OF HELMINTHS
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Classification
Against Nematodes-ALBENDAZOLE, MEBENDAZOLEPYRANTEL PAMOATE, LEVIMASOLE, PIPERAZINE,
IVERMECTIN, DIETHYLCARBAMAZINE, THIABENDAZOLE, DOXYCYCLINE
Against trematodesMETRIFONATE, OXAMNIQUINE, BITHIONOL,
TRICLABENDAZOLEAgainst CestodesNICLOSAMIDEAgainst trematodes and Cestodes-PRAZIQUANTEL
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Against Nematodes
PYRANTEL PAMOATEMOA-Blocks acetylcholine at the neuromuscular
junction, resulting in paralysis of the worms, which are then expelled through the GI tract
P/K-small amount is absorbed, so high levels are achieved in intestinal walls luminal helminths
Uses –round w, hook w, Pin w—10mg/kgS/E-may cause hypersensitivity reactions, neurological
symptoms (including “worm wobble”) and may precipitate epilepsy.
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Against Nematodes
Benzimidazoles (ALBENDAZOLE & MEBENDAZOLE )MOA-binds to beta tubulinprevents
polymerisationbreak down of cytoplasmic microtubulesthey Inhibit uptake of glucose and other nutrients, depletion of glycogen stores decrease of ATPleading to autolysis and death of the parasitic worm
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Benzimidazoles -Pharmacokinetics
Mebendazole is absorbed after oral – 10% Fatty meal increases absorption Albendazole,
mebendazoleIt is rapidly metabolised, the products being excreted
in the urine and the bile within 24-48 hours. Single dose for threadworm, BD daily for 3 days for hookworm and roundworm
infestations.Thiabendazole is rapidly absorbed orallyAlbendazole is metabolised extensively by first-pass
metabolism to the sulfoxide so has t1/2 -8-10 hrs
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Against nematodes
Benzimidazoles-ADR-Well tolerated, less side effectsIf used for >3months as in hydatid diseaseEpigastric distress, alopacia, insomnia, Teratogenic in
animalsThiabendazole inhibits cellular enzymesof susceptible helminths. Inhibits the helminth-
specific enzyme, fumarate reductaseS/E-Gastrointestinal, neurological and hypersensitivity
reactions, liver damage, and crystallurea may be induced.
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LEVAMISOLE
It is effective in infections with the common round-worm as well as hook worm
MOA: It has a nicotine-like action, stimulating and subsequently blocking the neuromuscular junctions. The paralysed worms are then expelled in the faeces. Ova are not killed.
Phamacokinetics:The drug is given orally, is rapidly absorbed and is widely distributed. It
crosses the blood-brain barrier. Side effects:They include gastrointestinal disturbances,
Dizziness and skin eruptions. High concentrations can have nicotinic actions on autonomic
ganglia in the mammalian host. There are some reports of encephalopathy
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Piperazine
MOA-It reversibly inhibits neuromuscular transmission in the worm
It probably by acting like GABA/GABA-gated chloride channels in nematode muscle. The paralyzed worms are expelled alive
-used for Ascariasis -4g * 2 daysand Pin worm- 4g * 7 daysADR- nausea, vomiting,
rarely neurotoxic and allergic reactionsnitrosamine metabolite-carcinogenic and
teratogenic potentialD/I- should not be used concurrently with pyrantel pamoate
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Ivermectin
It is highly effective broad-spectrum antiparasitic First choice of drug for the treatment of filarial infections
and is very effective in onchocerciasisMOA: It kill the worm by opening glutamate-gated chloride
channels (found only in invertebrates) and increasing Cl- conductance; by binding to a novel allosteric site on the acetylcholine nicotinic receptor to cause an increase in transmission, leading to motor paralysis; or by binding to aminobutyric acid receptors.
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Ivermectin
Uses :It has also given good results against W. bancrofti, which causes elephantiasis.
A single dose kills the immature microfilariae of O. volvulus- river blindness
The drug also has activity against infections with some roundworms: common roundworms, whipworms, and threadworms
It works best if repeated at 6–12-month intervals.Side effects: skin rashes, fever, giddiness, headaches
and pains in muscles, joints and lymph glands
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Diethylcarbamazine
Diethylcarbamazine is a piperazine deri.It is active in filarial infections caused by W. bancrofti It mainly act by make opsonisation of worm that detected
by our immune systemThe drug is absorbed by oral administration and clear from
body within 48 hrsSide effects Fever, headache, anorexia, malaise,urticaria, vomiting, and asthmatic attacks followingthe first dose are due to products of destruction ofthe parasite, and reactions are minimised by slowincrease in dosage over the first 3 days.
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Against cestodes- NICLOSAMIDEMOA: Its action has been ascribed to inhibition of the parasite's
mitochondrial anaerobic phosphorylation of ADP which produces usable energy
The scolex and a proximal segment are irreversibly damaged by the drug
The worm separates from the intestinal wall and is expelledThere is negligible absorption of the drug from the
gastrointestinal tract.Taenia solium, the drug is given in a single dose after a light
meal, followed by a purgative 2 hoursUnwanted effects are few, infrequent and transient. Nausea
and vomiting can occur.
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Adverse effects Drowsiness, dizziness, Malaise, anorexia, as well as gastrointestinal upsets.
It is contradicted in pregnant women or nursing mothers. Drug interaction:
Enzyme inducers dexamethasone, phenytoin, and carbamazepine increase metabolism
Cimetidine, known to inhibit cytochrome P-450 isozymes, causes increased praziquantel levels.
NICLOSAMIDE
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Against trematodes and Cestodes-PRAZIQUANTELPRAZIQUANTEL-It is the drug of choice for all forms of schistos
and for cestode infections like cysticercosis.
MOA: Permeability of the cell membrane to calcium is increased, causing contracture and paralysis of the both adult worms and larvae.
Pharmacokinetics: It is rapidly absorbed after oral administration and distributes into the cerebrospinal fluid.
S/E-It may cause nausea, headache, dizziness, and drowsiness; it cures with a single dose (or divided doses in one day).
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Against trematodes
METRIFONATE, OXAMNIQUINE, BITHIONOL, TRICLABENDAZOLE
MIRTIFONATE –organophosphorus compound so is cholinesterase inhibitors. It is safe and coast effective for schistosoma infection.It has good oral absorptionOrally active and t1/2 =1-5 hrsS/E-cholinergic side effects
-diarrhoea, tremors, bronchospasmC/I- pregnancy
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Against trematodes
OXAMNIQUINE-tertahydroquinoline dervtUsed against Scistosoma mansoniIt is the drug of choice for all forms of schistosomiasis
-given orallyMOA- flukes esterifies drug to produce reactive
metabolite that alkylates DNA of flukes. It intercalated with parasite DNA and inactivate it
S/E- CNS-drowsiness, dizziness pruritis, urticaria
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Against trematodes
BITHIONOL-orally well absorbedDOC-for fascioliasis(sheep liver fluke)
30-50mg for 10-15 days on alternate daysADR- anorexia, nausea, vomiting
avoided in children below 8yrsTRICLABENDAZOLE
narrow spectrum benzimidazoleDOC for treating human fasciola hepatica
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Worms (helminths) Drug of choice
Tapeworms (cestodes) Niclosamide or Praziquantel or Albendazole
Roundworms (nematodes)•Enterobius vermicularis (pinworm)•Ascaris lumbricoides•Trichuris trichiura (whipworm)•Trichinella spiralis (trichinellosis)
•Strongyloides stercoralis•Necator americanus (hookworm)•Ancylostoma duodenale
•Onchocerca volvulus (Onchocercosis)•Wuchereria bancrofti (Elephantiasis)
Mebendazole or PyrantelMebendazole or PyrantelMebendazole or AlbendazoleMebendazoleand ThiabendazoleThiabendazoleMebendazole or PyrantelMebendazole, Pyrantel, or AlbendazoleIvermectinDiethylcarbamazine
Flukes (trematodes)•Schistzoma (Schistozomes) Praziquantel
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