Nematicides – Antihelmintic Drugs

by Pravin Shukle, MD

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    00:00 So let's move on to the antihelminthic agents.

    00:04 We'll start of with the nematodes.

    00:06 So the nematicidal agents start off with albendazole.

    00:11 It's probably first in alphabet but it's also first in choices.

    00:15 It's a very, very good agent.

    00:17 It inhibits microtubule assembly which is essential for the structural stability of the organism.

    00:24 It kills the ova or eggs in ascariasis and these other agents.

    00:30 It is also going to kill the larva in ascariasis and cysticercosis which is also called the pork tapeworm.

    00:39 It is larvicidal in hookworm.

    00:41 And it is also larvicidal in hydatid disease.

    00:44 So we use this agent in a number of different types of infections that are listed there.

    00:51 In terms of toxicity from this agent, because the agent is used for such a short duration or time, toxicity is really quite rare.

    01:00 Sometimes we'll see a reversible drop in white cell count.

    01:03 And sometimes we'll see a short time rise in liver enzymes with prolonged used.

    01:08 But the times that we actually use this for prolonged usages is really quite rare.

    01:13 So becomes mostly a non issue.

    01:18 Diethylcarbamazine is quite an interesting drug.

    01:23 We actually use it to immobilize the microfilariae by an unknown mechanism.

    01:30 And it is used in eye worm.

    01:31 So this is actually an image of an eye worm.

    01:34 So you can actually see them in the square, in the iris of a patient.

    01:41 It looks like a white line that actually moves around.

    01:43 It's actually quite a horrific thing to see if you've ever seen it live.

    01:48 Toxicity to this medication, reactions to proteins of dying filariae include fever, rash and ocular damage.

    01:55 So it's not so much the drug itself that's causing the toxic reaction.

    02:00 It's a fact that when these filariae are dying, those break down proteins are causing all kinds of reaction.

    02:07 And that's where you get run into trouble.

    02:11 Ivermectin is another well known agent.

    02:15 It's a nematicidal.

    02:17 This is cutaneous larva migrans and you will see this in your practice at some point or another.

    02:23 These are worms that are actually under the skin.

    02:25 It's one dose, so ivermectin is one dose.

    02:29 It intensifies the GABA neurotransmission in the nematodes.

    02:33 And the nematodes become spastic and immobilize.

    02:36 And they can't feed.

    02:38 They can't do anything and they die.

    02:39 We use it in cutaneous larva migrans, strongylodiasis and filariasis.

    02:49 Toxicity to ivermectin is quite rare.

    02:52 Remember that the actual toxicity to the drug is almost non-existent because it's just a single dose.

    02:58 Where you get the toxicity is from the dying worms.

    03:01 And so the agents that are being released from the dying worms includes fever.

    03:06 The side effects include fever, rash and ocular damage if it's in the eye.

    03:11 Now this disgusting picture is an infection of ascariasis.

    03:19 This was removed from a 4 year old child who ended up having a bowel obstruction.

    03:23 And they couldn't figure out why.

    03:25 And the found out that his valve was full of these worms.

    03:27 So mebendazole is the treatment for this.

    03:31 It's absorbed minimally.

    03:34 So less than 10 percent of this agent can be absorbed from the bowel.

    03:37 It inhibits microtubule synthesis.

    03:40 And it also inhibits the glucose uptake in the nematodes so they die very quickly.

    03:45 It is the primary drug for ascariasis, pinworm and whipworm.

    03:49 And it is the backup drug for visceral or tissue larva migrans.

    03:58 Thiabendazole is another nematicidal agent.

    04:00 It's a structural cogener of mebendazole.

    04:03 In terms of how it is working, it's absorb systemically and it has much more systemic side effects then the other agents.

    04:13 It works through inhibiting microtubule synthesis and glucose uptake in nematodes.

    04:18 It's an alternative for systemic infections things like strongyloides or trichinosis which are the adult worms.

    04:25 In terms of toxicity GI irritation is quite common.

    04:28 You can also get intrahepatic cholestasis, liver failure.

    04:33 And in terms of neurological symptoms you can sometimes get headache, dizziness and drowsiness.

    04:38 A drop in white count leukopenia is common.

    04:42 Hematuria is something that we have to be aware of and can occur.

    04:46 And allergic reactions not just to the dying organisms but also to the drug itself are also present.

    04:52 You can also get a Stevens Johnson syndrome which can be fatal.

    04:57 We're not entirely sure if this is due to the drug itself or if it's due to the dying organisms, we haven't quite figured that one out yet.

    05:05 And any rate be quite aware that this is a potential problem with this agent.

    About the Lecture

    The lecture Nematicides – Antihelmintic Drugs by Pravin Shukle, MD is from the course Antimicrobial Pharmacology.

    Author of lecture Nematicides – Antihelmintic Drugs

     Pravin Shukle, MD

    Pravin Shukle, MD

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