PET D WORM TABLETS

Indications

• Roundworm infections
• Hookworm infections
• Whipworm infections
• Pinworm infections
• Other helminth infections

Dosage

Children: Child 1 month–9 years: Initially 1 mg/kg daily in divided doses on the first day, then increased to 3 mg/kg daily in divided doses, dose to be increased gradually over 3 days. Child 10–17 years: Initially 1 mg/kg daily in divided doses on the first day, then increased to

Adults: 100 mg for 1 dose, if reinfection occurs, a second dose may be needed after 2 weeks.

Mechanism of action

Mebendazole causes degenerative alterations in the tegument and intestinal cells of the worm by binding to the colchicine-sensitive site of tubulin, thus inhibiting its polymerization into microtubules. This leads to impaired glucose uptake and depletion of glycogen stores in the parasites, resulting in decreased ATP production, immobilization, and eventual death of the helminths.

Pharmacodynamics

Mebendazole is a synthetic broad-spectrum anthelmintic. Its principal mode of action is through the inhibition of tubulin polymerization, which results in the loss of cytoplasmic microtubules. This action disrupts organelle movement and interferes with the normal physiological processes of helminths, effectively leading to their death.

Pharmacokinetics

Mebendazole is poorly absorbed from the gastrointestinal tract, which contributes to its effectiveness as an anthelmintic. After oral administration, the drug is primarily metabolized in the liver. Its low solubility limits absorption, but it can still exert its effects on the intestinal parasites present in the gastrointestinal tract. The drug's elimination half-life is variable, and it is not significantly distributed in body tissues.

Contra-indications

• Blood disorders

Adverse effects

• Abnormal sensation in eye
• Anaemia
• Appetite decreased
• Asthenia
• Asthma exacerbated
• Chest discomfort
• Coma
• Confusion
• Conjunctival haemorrhage
• Constipation
• Diarrhoea
• Difficulty standing
• Difficulty swallowing
• Dizziness
• Fever
• Gastrointestinal discomfort
• Headache
• Hepatitis
• Hypotension
• Joint disorders
• Leucopenia
• Lymphatic abnormalities
• Myalgia
• Nausea
• Oedema
• Pain
• Psychiatric disorder
• Seizure
• Severe cutaneous adverse reactions (SCARs)
• Stupor
• Tachycardia
• Tremor
• Urinary incontinence
• Vertigo
• Vomiting

Interactions

• Cimetidine (increases concentration of mebendazole)

Precautions

• Use with caution in patients with epilepsy
• Use with caution in patients with Sjögren’s syndrome

Pregnancy

Embryotoxic in animal studies, avoid if possible.

Breast-feeding

No information available.

Storage

Store in a cool, dry place away from light.

Formulations

• Chewable tablet 100 mg

Indications

• Schistosomiasis caused by Schistosoma mansoni
• Schistosomiasis caused by Schistosoma japonicum
• Tapeworm infections, including Taenia solium and Hymenolepis nana

Mechanism of action

Praziquantel is hypothesized to target the β subunits of voltage-gated Ca2+ channels in parasites such as Schistosoma mansoni and Schistosoma japonicum. This action leads to increased calcium influx, causing rapid contraction and paralysis of the worms. The drug also induces tegumental disintegration and vacuolization in schistosomes, significantly affecting adult worms more than juveniles. Secondary effects include inhibition of glucose uptake and depletion of glycogen levels.

Pharmacodynamics

Praziquantel exhibits a rapid onset of action against trematodes and cestodes, causing significant changes in the permeability of the cell membrane of the parasites. This results in muscle contraction, tegumental damage, and eventual death of the worms. It selectively targets schistosomes and is ineffective against nematodes. The drug's efficacy is notably reduced against juvenile schistosomes and may diminish after a few weeks of treatment.

Pharmacokinetics

Praziquantel is well absorbed from the gastrointestinal tract, with peak plasma concentrations occurring within 1-3 hours post-administration. It undergoes extensive hepatic metabolism, primarily by CYP450 enzymes, and has a half-life of approximately 1-3 hours. The drug is excreted mainly in urine as metabolites, with a small fraction excreted unchanged. The pharmacokinetics can be affected by co-administration with certain other drugs that alter its metabolism.

Adverse effects

• dizziness
• hepatitis
• neutropenia
• seizure
• severe cutaneous adverse reactions

Interactions

• mitotane+praziquantel: Severe (decreases exposure)
• rifampicin+praziquantel: Severe (decreases exposure)
• chloroquine+praziquantel: Moderate (decreases exposure)
• cobicistat+praziquantel: Unknown (increases exposure)
• dexamethasone+praziquantel: Unknown (decreases exposure)
• grapefruit juice+praziquantel: Unknown (increases exposure)
• cimetidine+praziquantel: Unknown (increases exposure)
• idelalisib+praziquantel: Unknown (increases exposure)

Pregnancy

Manufacturer advises avoiding use due to toxicity observed in animal studies.

Breast-feeding

Amount present in milk is too small to be harmful; however, the manufacturer advises avoiding use.

Storage

Store in a cool, dry place away from light.

Formulations

• tablets
• oral suspension

Indications

• Ascariasis
• Partial intestinal obstruction due to Ascaris lumbricoides

Dosage

Children: Refer to BNF for Children for specific dosing information.

Adults: Refer to BNF for specific dosing information.

Mechanism of action

Piperazine functions as a GABA receptor agonist, selectively binding to muscle membrane GABA receptors in nematodes. This binding induces hyperpolarization of nerve endings, leading to flaccid paralysis of the worms. By blocking the response of worm muscle to acetylcholine, piperazine alters cell membrane permeability to ions, resulting in hyperpolarization and suppression of spontaneous spike potentials, thereby facilitating the expulsion of the worm through normal intestinal peristalsis.

Pharmacodynamics

Piperazine is effective as an anthelminthic, particularly for treating infections from Ascaris lumbricoides. It induces reversible muscle paralysis in nematode parasites by hyperpolarizing their cell membranes. The primary clinical use is in addressing complications such as partial intestinal obstruction caused by these worms, a condition more frequently encountered in children.

Pharmacokinetics

The pharmacokinetics of piperazine, including absorption, distribution, metabolism, and excretion, have not been well-characterized in the available literature. However, it is generally understood that piperazine is absorbed from the gastrointestinal tract and is metabolized in the liver. Further detailed studies may be required to elucidate its complete pharmacokinetic profile.

Adverse effects

• Nausea
• Vomiting
• Abdominal pain
• Diarrhea
• Headache
• Dizziness

Precautions

• Use with caution in patients with renal impairment
• Consider potential interactions with other central nervous system depressants

Pregnancy

Limited data are available on the safety of piperazine during pregnancy. Use only if the potential benefit justifies the potential risk to the fetus.

Breast-feeding

Piperazine is excreted in breast milk; use with caution and consider the need for monitoring the infant.

Storage

Store in a cool, dry place away from light. Keep out of reach of children.

Formulations

• Piperazine citrate
• Piperazine hydrate

Mechanism of action

Mebendazole causes degenerative alterations in the tegument and intestinal cells of the worm by binding to the colchicine-sensitive site of tubulin, thus inhibiting its polymerization or assembly into microtubules. The loss of the cytoplasmic microtubules leads to impaired uptake of glucose by the larval and adult stages of the susceptible parasites, and depletes their glycogen stores. Degenerative changes in the endoplasmic reticulum, the mitochondria of the germinal layer, and the subsequent release of lysosomes result in decreased production of adenosine triphosphate (ATP), which is the energy required for the survival of the helminth. Due to diminished energy production, the parasite is immobilized and eventually dies. Although the exact mechanism of anthelmintic activity of mebendazole has not been fully elucidated, the drug appears to cause selective and irreversible inhibition of the uptake of glucose and other low molecular weight nutrients in susceptible helminths; inhibition of glucose uptake appears to result in endogenous depletion of glycogen stores in the helminth. Mebendazole does not inhibit glucose uptake in mammals. Mebendazole appears to cause degenerative changes in the intestine of nematodes and in the absorptive cells of cestodes. The principal anthelmintic effect of the drug appears to be degeneration of cytoplasmic microtubules within these intestinal and absorptive cells. Microtubular deterioration results in inhibition of organelle movement and interferes with the absorptive and secretory function. As a result of excessive accumulation of intracellular transport secretory granules, hydrolytic and proteolytic enzymes are released and cause cellular autolysis. This irreversible damage leads to death of the parasite. Vermicidal; may also be ovicidal for ova or most helminths; mebendazole causes degeneration of parasite's cytoplasmic microtubules and thereby selectively and irreversibly blocks glucose uptake in susceptible adult intestine-dwelling helminths and their tissue-dwelling larvae; inhibition of glucose uptake apparently results in depletion of the parasite's glycogen stores; this, in turn, results in reduced formation of adenosine triphosphate (ATP) required for survival and reproduction of the helminth; corresponding energy levels are gradually reduced until death of the parasite ensues; mebendazole does not appear to affect serum glucose concentrations in humans, however. Benzimidazoles produce many biochemical changes in susceptible nematodes, eg, inhibition of mitochondrial fumarate reductase, reduced glucose transport, and uncoupling of oxidative phosphorylation ... /but/ the primary action ... /should be/ to inhibit microtubule polymerization by binding to beta-tubulin. The selective toxicity of these agents derives from the fact that specific, high-affinity binding to parasite beta-tubulin occurs at much lower concn than does binding to the mammalian protein ... Benzimidazole-resistant Haemonchus contortus display reduced high-affinity drug binding to beta-tubulin and alterations in beta-tubulin isotype gene expression that correlate with drug resistance ... Two identified mechanisms of drug resistance in nematodes involve both a progressive loss of "susceptible" beta-tubulin gene isotypes together with emergence of a "resistant" isotype with a conserved point mutation that encodes a tyrosine instead of phenylalanine at position 200 of beta-tubulin. While this mutation may not be required for benzimidazole resistance in all parasites, eg, Giardia lamblia, benzimidazole resistance in parasitic nematodes is unlikely to be overcome by novel benzimidazole analogs, because tyrosine also is present at position 200 of human beta-tubulin. /Benzimidazoles/

Pharmacodynamics

Mebendazole is a (synthetic) broad-spectrum anthelmintic. The principal mode of action for Mebendazole is by its inhibitory effect on tubulin polymerization which results in the loss of cytoplasmic microtubules.

Mechanism of action

Although the exact mechanism of action is unknown, praziquantel was hypothesized to target the β subunits of voltage-gated Ca₂₊ channels, particularly in Schistosoma mansoni and Schistosoma japonicum, due to the lack of two conserved serine residues in these subunits. This is supported by the finding that co-administration of calcium channel blockers like nicarpidine and nifedipine renders 50% of Schistosoma mansoni resistant to praziquantel. Increased exposure of antigens on the worm surface was also observed, but little research has been done to elucidate on the mechanism of action.

Pharmacodynamics

In vitro studies on trematodes and cestodes have shown that praziquantel induces a rapid contraction of schistosomas by a specific effect on the permeability of the cell membrane. The drug further causes vacuolization and disintegration of the schistosome tegument. The effect is more marked on adult worms compared to young worms. An increased Ca2⁺-influx may play an important role. Secondary effects are inhibition of glucose uptake, lowering of glycogen levels and stimulation of lactate release. The action of praziquantel is specific to trematodes and cestodes; nematodes (including filariae) are not affected. Praziquantel is active against schistosoma (for example, Schistosoma mekongi, Schistosoma japonicum, Schistosoma mansoni and Schistosoma hematobium), and infections due to the liver flukes, Clonorchis sinensis/Opisthorchis viverrini. Published in vitro data have shown a potential lack of efficacy of praziquantel against migrating schistosomulae. An interesting quirk of praziquantel is that it is relatively ineffective against juvenile schistosomes. While initially effective, effectiveness against schistosomes decreases until it reaches a minimum at 3-4 weeks. Effectiveness then increases again until it is once again fully effective at 6-7 weeks.

Mechanism of action

Piperazine is a GABA receptor agonist. Piperzine binds directly and selectively to muscle membrane GABA receptors, presumably causing hyperpolarization of nerve endings, resulting in flaccid paralysis of the worm. While the worm is paralyzed, it is dislodged from the intestinal lumen and expelled live from the body by normal intestinal peristalsis. Piperazine blocks the response of the /target species/ worm muscle (best studied in Ascaris), causing flaccid paralysis of the worm. While the worm is paralyzed, it is dislodged from the intestinal lumen and expelled live from the body by normal intestinal peristalsis. The predominant effect of piperazine on /the target species/ Ascaris is to cause a flaccid paralysis that results in expulsion of the worm by peristalsis. ... Piperazine blocks the response of Ascaris muscle to acetylcholine, apparently by altering the permeability of the cell membrane to ions that are responsible for the maintenance of the resting potential. The drug causes hyperpolarization and suppression of spontaneous spike potentials with accompanying paralysis. Piperazine citrate causes reversible muscle paralysis in intestinal nematodes, presumably by causing hyperpolarization of nerve endings /in this target species/. /Piperazine citrate/ Piperazine and its salts, as a gamma-aminobutyric acid (GABA)-like substance, induce a reversible flaccid paralysis in the /target/ nematode parasites. This is provoked by a hyperpolarization of the cell membrane followed by suppression of spontaneous spike potentials. THe paralyzed nematodes are expelled from the gut lumen by normal peristaltic actions. In mammals, motorcortical GABAa inhibition is important for initiation of smooth flexion and/or extension movements of the extremities affecting motor and postural control. When injected into the hand motor cortical area of three infant macaque monkeys, the GABA agonist muscimol disrupted forelimb movement showing a posture of dropped wrist and fingers as if the radial nerve were paralysed. Interestingly, the three investigated animals exhibited large inter-individual differences in sensitivity to the action of the same dose of muscimol, being low in one, moderate in the second and substantial in the third. Injection into the medial segment of globus pallidus elicited choreiform movements and injections into substantia nigra pars reticulata provoked severe axial posture anomalies with rotational behaviour as well as contralateral hypotonia. Although the symptoms induced by piperazine in sensitive species exhibits some of these features, it is possible that its effects in mammals also involve other modes of action as well, in as much as a nicotinic action on rat sympathetic ganglia in vitro was reported in one series of experiments.

Pharmacodynamics

Piperazine is an anthelminthic especially useful in the treatment of partial intestinal obstruction caused by Ascaris worms, which is a condition primarily seen in children. Piperazine hydrate and piperazine citrate are the main anthelminthic piperazines.