Papaverine – Effects, Application and Risks

Papaverine is a substance from the group of alkaloids and belongs to the class of antispasmodics. The alkaloid is found in the dried milky sap of the opium poppy. However, it can also be produced synthetically.

What is papaverine?

Papaverine is a natural substance found in the milky sap of the opium poppy and other related poppy species. Raw opium contains about one-tenth of papaverine. The pure substance papaverine is effective and, at the same time, does not have the entire spectrum of possible side effects. Like the chemical derivative of papaverine, papaverine is a cAMP phosphodiesterase inhibitor. It thus acts on numerous subforms of the phosphodiesterase family.

Papaverine is mainly used as a vasodilating drug. It belongs to the group of antispasmodics. Antispasmodics are antispasmodic drugs that reduce the state of tension in the smooth muscles and relieve their spasms.

The first complete synthesis of papaverine was carried out in 1909 by the researchers Pictet and Gams. The Austrian, Guido Goldschmiedt, managed to solve the entire structure a few years later. Today, papaverine hydrochloride is used pharmaceutically as a monopreparation or in combination preparations.

Pharmacological action

Papaverine is a cAMP phosphodiesterase inhibitor. Phosphodiesterases are enzymes found in almost every tissue in the body. Every environmental change is perceived by the body and causes a stimulus. This is transmitted to the interior of the cell by messenger substances. These messenger substances are also referred to as “second messengers.” The second messengers include the substances cAMP (cyclic adenosine monophosphate) and cGMP (cyclic guanosine monophosphate). They are responsible for the stimulus response in the cell. This stimulus response can take place, for example, through a change in the metabolism of the cell. Signal transmission within the cell can be inhibited by phosphodiesterases. Phosphodiesterases can split messenger substances such as cAMP or cGMP and thus render them ineffective.
Phosphodiesterase inhibitors, on the other hand, disrupt the enzymes in their work and thus promote signal transmission within the cell. Papaverine is a phosphodiesterase inhibitor that inhibits phosphodiesterases that disable cAMP. As a result, they prolong the effects of the messenger substance and enhance the effects of various stimuli. Since cAMP has a relaxing effect on smooth muscles, papaverine has an antispasmodic and vasoconstrictive effect.

Medical Application and Use

Papaverine is mainly used in heart surgery. There, the drug prevents blood vessel spasms when arteries are harvested for bypass operations. Papaverine is also used as an antispasmodic drug for stomach cramps, biliary colic and urinary tract spasms. However, for these indications it is increasingly being replaced by the spasmolytic propiverine, as this not only has an anticonvulsant but also anticholinergic effect.

Another area of ​​application for papaverine causes erectile dysfunction in men. For this, the drug is injected into the erectile tissue of the male penis. The vasodilation then leads to increased blood flow to the penis and thus to an erection. This therapy is also known as cavernous autoinjection therapy (SCAT).

In rare cases, papaverine is also used to treat peripheral or cerebral circulatory disorders. However, therapy with the drug is controversial for these indications.

Risks and side effects

When taking papaverine, neurological deficits such as hemiplegia, epileptic seizures, pupillary disorders, or clouding of consciousness can occur. The vasodilating effect of the drug can lead to a life-threatening drop in blood pressure. In addition, intracranial pressure may increase. Overall, however, side effects are rare.
However, the injection of papaverine during the cavernous autoinjection therapy is associated with more risks. This can lead to a painful permanent erection. This form of permanent erection without arousal is called priapism. The erection lasts longer than two hours and, if left untreated, can lead to severe erectile dysfunction.

Severe allergic reactions can also occur after the injection of papaverine. These show up as a rash, hives, tightness in the chest, or swelling in the body. If you have these symptoms, you should see a doctor immediately. Excessive tiredness, abnormal heart rhythms, nausea, vomiting, and yellowing of the skin and eyes (icterus) also require immediate medical attention.

Milder side effects include diarrhea, constipation, dizziness, loss of appetite, upset stomach, or slight redness at the injection site. If these side effects persist or worsen, a doctor should also be consulted.

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