Praziquantel Therapy: Treatment, Effects & Risks

Praziquantel is a pharmacologically active substance used for therapy in parasite infestations. The active ingredient was developed as early as the 1970s and has since been considered the drug of choice for worm infections.

What is praziquantel therapy?

Praziquantel is a so-called antihelminthic, anthelmintic agent. As such, it is used successfully to treat infestations of sucker worms, flatworms, tapeworms, and flukes. Praziquantel is a so-called anthelmintic. As such, it is used with success for infestations with sucking worms, flatworms, tapeworms and leeches. Since its development, the drug has rapidly gained acceptance not only in human medicine, but also in veterinary medicine. The active ingredient was developed as early as the 1970s in cooperation between the two major pharmaceutical companies Bayer and Merck. After a lead time of more than ten years, praziquantel was launched on the market in the early 1980s. Chemically, praziquantel is a quinoline derivative. It exerts its effect locally on the mucous membranes and also acts systemically. Therefore, it is well suited for oral therapy of humans and animals in parasite infestations. The duration of use and method of application always depend on the degree and type of parasite infestation. The active ingredient is effective against a wide range of parasites in humans and animals. Often, even a single dose is required to kill all parasites in the gastrointestinal tract quickly and reliably.

Function, effect and goals

In veterinary medicine, praziquantel is used prophylactically as a worming treatment in dogs and cats. If parasite infestations are already present, they are killed within hours of administration of the drug. Due to the mucosal affinity of praziquantel, the active ingredient also protects to a small extent against reinfestation. In addition to oral administration in the form of tablets with a defined active ingredient content, transdermal application systems have also been developed, but these are used exclusively in veterinary medicine. For prophylaxis or treatment of worm infestation, praziquantel dissolved in water is dripped onto the skin of cats or dogs. The active substance is absorbed through the skin and enters the bloodstream. However, since only a portion of the substance is absorbed through the skin, oral application is considered the standard therapy and drug of choice for worm infestations in the gastrointestinal tract. The goal of praziquantel therapy is the complete killing and elimination of parasites at any stage of development. The mechanism of action of praziquantel is also scientifically proven. The quinoline praziquantel attaches to the mucosal surface of parasites and opens their calcium channels. Very quickly, this leads to overcontraction of the muscles and subsequently to spastic paralysis of worms or flukes, which results in the death of the parasite. However, this is not the only mechanism of action. This is because praziquantel also attacks the intact skin of the parasite and permanently disrupts its metabolism. This enables the pest to be better recognized and attacked by the host’s immune system. In the case of internal worm infestation, the killed parasites are simply excreted in the stool. If the active ingredient enters the blood, it spreads to all organs and organ systems. The efficacy remains fully intact, which is why praziquantel is also well suited for therapy in extraintestinal worm infestations, for example in the brain. To safely kill parasites, it is essential to reach a certain dose per kilogram of body weight. 10-25 mg of praziquantel as a single dose per kilogram of body weight is sufficient for killing in worm infestations in the gastrointestinal tract. In the case of systemic infestation, higher doses, which must then usually be given several times, must be selected. Systemic praziquantel therapy in humans must always be given under strict medical supervision. In the western industrialized nations, infestation with parasites in humans has decreased considerably in recent decades. Praziquantel therefore plays the greater role in veterinary medicine here. In developing countries, however, worm infections are still widespread today. Praziquantel is used here with great success, for example against the dangerous worm disease schistosomiasis. The active ingredient is also approved in pediatrics for body weights of at least 20 kg.

Risks, side effects and hazards

Side effects and intolerance reactions may occur during praziquantel therapy.Adverse effects are often due to overdoses. Vomiting, nausea and abdominal pain, but also weakness, wheal formation on the skin or itching can be signs of an overdose or hypersensitivity during treatment. In these cases, praziquantel should be discontinued immediately and replaced with a similarly acting anthelmintic. Patients treated with the drug also report muscle pain, loss of appetite, dizziness, and fatigue. Because praziquantel therapy in many cases is a single dose and very short, these side effects usually disappear quickly. It is known that some drugs for epilepsy and malaria can significantly reduce the active ingredient content of praziquantel. These groups of medications should therefore not be taken at the same time. In addition, praziquantel is not compatible with the antibiotic rifampicin; unforeseen chemical interactions may occur. Both substances should also not be taken together under any circumstances. During pregnancy and breastfeeding, praziquantel may only be used in justified exceptional medical cases. The active substance also passes into breast milk and can harm the unborn child. Patients with pre-existing conditions such as cardiac arrhythmias or with impaired kidney or liver function must either not take praziquantel at all or only after explicit instructions from the physician. The pharmacological agent cimetidine causes praziquantel to accumulate in the blood. If both substances are taken at the same time, the concentration of praziquantel in the blood may rise sharply; in addition, its half-life is increased because cimetidine makes it more difficult for the liver to break down praziquantel.