Anti-Helminthic Drugs

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Albendazole—

§    Broad spectrum anti-helminthic drug

§    Route of administration is oral

§    Neurocysticercosis where surgery is not possible Albendazole is used

 

Chemistry—

It is Benzimidazole carbamate

 

Pharmacokinetics—

§    Absorbed adequately but not completely

§    Fatty food increases its absorption

§    Tissue half life is 8-9 hours

§    Excretion is through kidney and small intestine after metabolism

 

Mechanism of Action—

§    Blocks the glucose uptake by the larvae

§    Depletes glycogen storage of the adult worm

§    Decreases the formation of ATP

—as a result the parasite is immobilized and dies.

 

The drug is ovicidal in case of A. lumbricoides

 

Pharmacological effects—no effects on the human body.

 

Clinical uses—

1. Acts against these worms—

Ascaris lumbricoides

Enterobius vermicularis

Ankylostona doudenale

Trichuris trichiura

Hydatid cyst

Strongyloides

2. Neurocysticercosis

3. Cutaneous larva migrans

 

Dose—

§    Dosage is single dose of 400mg in the morning

§    800mg/day (single or divided dose) for 30 days in case of hydatid cyst

 

Contraindication—

Pregnancy

Children below 2 years of age

Allergy to Albendazole

Cirrhosis of liver

 

Adverse effects—

Nausea

Epigastric distress

Diarrhoea

Headache

Dizziness

Lassitude

Insomnia

Jaundice

Alopecia

Pruritus

Leucopenia

Eosinophilioa

Anaemia

Hypotension

 

Contraindicated in pregnancy—teratogenic and embrotoxic

Contraindicated in children below 2 years—there is decreased metabolism, chance of toxicity

 

Mebendazole—

§    Relatively toxic drug

§    Used in Bangladesh for more than 30 years

 

Why Albendazole is better than Mebendazole?—

1. single dose

2. after 15 days an additional dose has to be given in Mebendazole

 

Characteristics—

§    Benzimidazole group

§    It is synthetic

§    Wide spectrum

§    Insoluble in water

§    Taste is not unpleasant and so good for children

 

Pharmacokinetics—

§    Orally given

§    90% is absorbed from GIT (90% acts on the worms)

§    Excreted through the urine after metabolism

§    Peak plasma level occurs in 2-4 hours

 

Mechanism of Action—

§    It inhibits the microtubule formation. So the parasite loses its cytoskeleton and motility and dies.

§    It also impairs glucose uptake and ↓ ATP formation.

—in stool worm is not seen because the clearance of the dead worm is very slow.

 

Clinical uses—

1. Acts against these worms—

Ascaris lumbricoides

Enterobius vermicularis

Ankylostona doudenale

Trichuris trichiura

Tapeworm

Hydatid cyst

2. in Neurocysticercosis when Albendazole does not act

 

Dose—

2 tab of 100mg daily for 3 days

In case of pinworm a single dose can be given

Can be given for 1 month in hydatid cyst or neurocysticercosis

 

*** Laxatives are never indicated in helminthiasis and should not be administered with antihelminthic drugs. But in case of tapeworm infections osmotic laxatives like milk of magnesia can be given to see the head of the worm which will act within 3 hours. Bulk forming laxatives should never be administered.

 

*** in hydatid cyst (from dog) and neurocysticercosis (from uncooked vegetables) albendazole is the 1st choice and Mebendazole is the 2nd choice.

 

Adverse effects (mainly occurs if given for 1 month)—

Nausea

Slight abdominal discomfort

Pruritus

Rash

Eosinophilia

Musculoskeletal pain

Fever

Acute pain in cystic area

Alopecia

Agranulocytosis

Cough

 

 

Contraindication—

1. Pregnancy

2. Children under 2 years of age

3. Hepatic parenchymal diseases

 

Pyrantel Pamoate—

§    Used if the patient is allergic to Albendazole or Mebendazole

§    Broad spectrum

§    If orally given 15% absorbed

§    Excreted in the unchanged form (no metabolism)

 

Mechanism of Action—

Causes depolarizing type of paralysis (spastic paralysis) of the helminthes. So, cannot retain original position and comes out through stool with normal peristalsis.

 

Why usually helminthes do not come out with stool by peristalsis?—

Because they get attached themselves to the intestinal wall.

 

Dose—

11mg/kg body weight (not more than 1gm at a time)

 

Clinical uses—

Effective against these helminthes,

Ascaris lumbricoides

Enterobius vermicularis

Ankylostona doudenale (50% effective)

 

Adverse effects—

Nausea

Headache

Vomiting

Insomnia

Diarrhoea

Rash

Abdominal cramp

Fever

Weakness

 

 

Piperazine—

§    Not used now a days

§    Contraindicated in neurological disorder patients (epilepsy, parkinsonism)

 

Mechanism of Action—

It causes flaccid paralysis of helminthes and they fail to retain their original position. So, come out with the stool by peristalsis.

 

Clinical uses—

Acts against these worms,

Ascaris lumbricoides

Enterobius vermicularis

 

Pharmacokinetics—

Readily absorbed from the GIT.

Maximum plasma level is reached in 2-4 hours.

Most of the drugs excreted unchanged through the urine.

 

Dose—

75mg/kg/day (maximum 3.5gm) for 2 days before and after breakfast.

For heavy infections treatment should be continued for 3-4 days or be repeated after 1 week.

 

Adverse effects—

Usual mild adverse effects—

Nausea, vomiting, diarrhoea, abdominal pain, dizziness and headache.

 

Rare neurotoxic adverse effects—

Somnolence, dizziness, ataxia, seizures, chorea, visual disturbances.

 

 

Nicolsamide—

§    Drug of choice for tapeworm

§    Salicylamide derivative

§    Usually given orally

§    It kills the head of the tapeworm

 

Mechanism of Action—

It will inhibit oxidative phosphorylation of tapeworm, so the head will be killed.

 

Clinical uses—

Taenia saginata

Hymenolepis nana

Other tapeworms (Hymenolepis diminuta, Dipylidium caninum)

Intestinal fluke infections (Fasciolopsis buski, Heterophyes heterophyes)

 

Dose—

Adults—2gm (4 tablets of 500mg) in the early morning before breakfast

Children of more than 34kg weight—3 tablets

Children with 11-34kg weight—2 tablets

Children below 11 kg weight—1 tablet

—after 3 hours laxatives should be given, so the head will come out and through that worm can be searched.

—tablets must be chewed thoroughly.

 

Contraindication—

Pregnancy

Alcohol intakers

Children below 2 yrs of age

 

Adverse effects—

Mild nausea

Diarrhoea

Abdominal discomfort

Headache

Skin rash

Pruritus

Vertigo

 

 

Ivermectin—

§    It is the drug of choice in Strongyloidiasis  and Onchocerciasis (Onchocerca volvulus)

§    It is also an alternative drug for scabies.

§    May prove useful in treatment of other forms of Filariasis and cutaneous larvae migrans.

 

Chemistry—

It is a semisynthetic macrocyclic lactone and is a mixture of Avermectin Bla and Blb.

 

Source—

It is derived from the soil actinomycete Streptomyces avermitilis.

 

Pharmacokinetics—

§    Given orally, rapidly absorbed and has wide tissue distribution.

§    Its half life is 16 hours and reaches the highest plasma level (50 μg/l) at 4 hours after 12mg dose.

 

Mechanism of Action—

§    Ivermectin appears to paralyze nematodes and arthropods by intensifying GABA mediated transmission of signals in the peripheral nerves.

§    In Onchcerciasis, Ivermectin is microfilaricidal and affects embryogenesis.

 

Clinical uses—

Onchocerciasis (single dose of 150 μg/kg with water in empty stomach), Strongyloidiasis (single dose of 200 μg/kg), Bancroftian Filariasis and other parasites.

 

Adverse effects—

§    Fatigue, dizziness, nausea, vomiting, abdominal pain and rashes.

§    In the treatment of onchocerciasis the adverse effect is called Mazotti reaction, which includes fever, headache, dizziness, somnolence, weakness, rash, pruritus, diarrhoea, joint and muscle pain, hypotension, tachycardia and lymphadenitis, lymphangitis and oedema.

 

Contraindication—

Because Ivermectin enhances GABA activity, it should not be used with drugs of similar effects like barbiturates, BDZs and Valproic acid. Should not be used in pregnancy and children below 5 years of age. Should not be used in the diseases when there is impairment of BBB like in the diseases, Meningitis and African sleeping sickness.

 

 

Praziquantel—

§    Praziquantel is effective in the treatment of Schistosomiasis and Most flukes.

§    Also used against Taeniasis, Diphyllobothriasis, and neurocysticercosis.

§    It is a synthetic Isoquinoline-Pyrazine derivative.

§    Rapidly absorbed, bioavailability is about 80% after oral administration.

§    The drug increases cell membrane permeability to calcium resulting in vacuolization, marked contraction, paralysis, dislodgement and death.

§    Adverse effects are headache, dizziness, lassitude, nausea, loose stool, pruritus, abdominal pain, urticaria and Arthralgia.

 

Diethylcarbamazine—

§    Drug of choice in the treatment of Filariasis, Loasis and tropical eosinophilia

§    Ivermectin is better drug and should be used if available avoiding Diethylcarbamazine.

§    It is a synthetic Pipeazine derivative.

§    Immobilize microfilariae and alters their surface structure making them more susceptible to destruction by host defense mechanism.

 

Adverse effects—

Drug induced reactions—

Headache, malaise, anorexia, weakness, nausea, vomiting, dizziness and sleepiness (less often).

 

Reaction induced by dying parasites—

Due to release of foreign proteins from the dying microfilariae there may be eosinophilia and leukocytosis.