Praziquantel

BRAND NAMES

• Biltricide (most widely known international brand) 

• Droncit (mainly veterinary use, also used in some parasite treatments in animals)

• Distocide (used in certain regions for human infections)

MECHANISM OF ACTION

Praziquantel acts against parasitic worms by increasing the permeability of their cell membranes to calcium ions. It binds to the tegument (outer surface) of susceptible helminths and causes a rapid influx of Ca²⁺ into the parasite cells. This leads to sustained muscle contraction (spastic paralysis) and disruption of the parasite’s tegument. As a result, the worms lose their ability to maintain attachment to host tissues and become damaged, making them more susceptible to destruction by the host immune system. Ultimately, the paralyzed and damaged parasites are dislodged and eliminated from the body.

PHARMACOKINETICS

Absorption 

Praziquantel is rapidly and almost completely absorbed after oral administration, but its bioavailability is variable due to extensive first-pass metabolism in the liver. Peak plasma concentrations are typically reached within 1 to 3 hours after ingestion.

Distribution

Praziquantel has a relatively large volume of distribution, reflecting its wide tissue penetration. The approximate volume of distribution is about 0.6 to 0.8 L/kg, which corresponds to roughly 42 to 56 litres in an average 70 kg adult.

Metabolism

Praziquantel undergoes extensive hepatic metabolism, primarily through the cytochrome P450 enzyme system, especially CYP3A4. It is rapidly converted into several inactive metabolites via oxidation and hydroxylation processes.

Elimination

Praziquantel is eliminated primarily through the kidneys after hepatic metabolism. The drug is excreted mostly in the form of inactive metabolites in urine, with only a small amount appearing unchanged. A minor portion of the drug and its metabolites is also excreted via bile into the feces.

PHARMACODYNAMICS

Praziquantel exerts its pharmacological effects by increasing the permeability of the parasite’s cell membranes to calcium ions. It binds to the tegument of susceptible helminths, causing a rapid influx of Ca²⁺ into muscle cells. This leads to sustained muscle contraction (spastic paralysis) and severe damage to the parasite’s outer surface (tegument disruption). The damaged tegument exposes parasite antigens, enhancing recognition and attack by the host immune system.

ADMINISTRATION

Praziquantel is administered orally in the form of tablets. The tablets are usually taken with water, and it is recommended to take them with food, especially a high-fat meal, to improve absorption and increase bioavailability. The dosing schedule depends on the type of parasitic infection being treated and may be given as a single dose or divided doses over 1 day, and in some cases repeated after a few weeks for certain infections like schistosomiasis. Tablets should be swallowed whole, although they can be broken if necessary for dose adjustment in children. 

DOSAGE AND STRENGTH

Praziquantel is commonly available in tablet form, with the most widely used strength being 600 mg tablets, although lower strengths such as 150 mg may also be available in some regions. The dosage of praziquantel depends on the type of parasitic infection and the patient’s body weight. For schistosomiasis, it is usually given at a total dose of 40–60 mg/kg in a single day, divided into two or three doses. For tapeworm infections, a lower single dose of about 5–10 mg/kg is often sufficient, while liver fluke infections may require 25 mg/kg taken three times in one day.

DRUG INTERACTIONS

Praziquantel is primarily metabolized by the hepatic enzyme CYP3A4, so drugs that affect this enzyme can significantly alter its blood levels. Enzyme inducers such as rifampicin, carbamazepine, phenytoin, and phenobarbital can increase the metabolism of praziquantel, leading to reduced plasma concentrations and decreased therapeutic effectiveness. 

FOOD INTERACTIONS

Food has a significant effect on the absorption of praziquantel. When taken with food, especially a high-fat meal, the drug’s bioavailability increases markedly, leading to higher plasma concentrations and improved therapeutic effect.

CONTRAINDICATIONS

Praziquantel is contraindicated in patients with known hypersensitivity or allergy to the drug or any of its components. It should not be used in individuals with ocular cysticercosis, as destruction of larvae in the eye can lead to severe inflammatory reactions and potential vision damage.

SIDE EFFECTS

• Headache 

• Dizziness 

• Drowsiness or fatigue 

• Nausea and vomiting 

• Abdominal pain or cramps 

• Diarrhea 

• Mild fever 

• Itching (pruritus) 

• Skin rash 

• Muscle pain (myalgia) 

• Loss of appetite 

• Transient increase in liver enzymes 

• Malaise (general discomfort) 

• Rare: allergic reactions 

• Rare (especially in neurocysticercosis): neurological symptoms due to inflammatory response to dying parasites 

OVER DOSE

Overdose of praziquantel is uncommon, but excessive intake may intensify its known adverse effects. Symptoms may include severe headache, marked dizziness, nausea, vomiting, abdominal pain, fatigue, and excessive drowsiness. In higher doses, central nervous system effects such as confusion or impaired coordination may occur.

TOXICITY

Praziquantel has a relatively wide therapeutic index, so true toxicity is rare. However, at high doses or in susceptible individuals, toxicity mainly presents as exaggerated pharmacological and adverse effects. Central nervous system toxicity may include severe dizziness, headache, drowsiness, confusion, and impaired coordination.