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This is how diphenhydramine works

The body's own messenger substance histamine plays an important role in defense reactions against invading germs and toxins. In the event of an infection or ingestion of poison, the immune system prompts the so-called mast cells to release stored histamine and other messenger substances. As a result, the affected tissue is supplied with more blood. In addition, more white blood cells are attracted and the blood vessels become more permeable. Last but not least, the tissue swells so that the immune cells can migrate better. In short: there is an inflammatory reaction.

In some cases, however, this protective reaction of the immune system is undesirable, for example when it manifests itself as an allergic reaction to pollen, food or insect bites. This can then be specifically suppressed with a so-called antihistamine such as diphenhydramine. This active ingredient occupies the docking points (receptors) for the body's own histamine, so that it can no longer work.

Diphenhydramine as an antihistamine of the first generation (i.e. as one of the first substances in this class to be discovered) also crosses the blood-brain barrier very well. In the brain, the body's own messenger substance histamine is involved, among other things, in the regulation of the wake-sleep rhythm - if this regulation is disturbed by antihistamines, fatigue occurs as a side effect. Second-generation antihistamines can barely cross the blood-brain barrier, which prevents tiredness.

In addition, diphenhydramine also has a dampening effect on the vomiting center in the brain stem and thus suppresses nausea and nausea.

Absorption, breakdown and excretion of diphenhydramine

The active ingredient is taken in the form of its salt diphenhydramine hydrochloride (diphenhydramine hydrochloride) as a tablet and enters the blood through the intestinal mucosa. When used as a rectal capsule, the active ingredient enters the blood through the mucous membrane of the rectum. The highest blood levels are reached after one to four hours.

Diphenhydramine is broken down into ineffective metabolic products in the liver and excreted in the urine via the kidneys. After about four hours, half of the active ingredient is eliminated from the body.

When is diphenhydramine used?

In the meantime, no drugs containing diphenhydramine to alleviate allergic reactions are approved in Germany. The newer antihistamines are preferred because they have fewer side effects. However, diphenhydramine is still a component of some sleep aids as an aid to sleep and sleep through.

In addition, it is still used against nausea and vomiting, but the related active ingredient dimenhydrinate is now used more frequently.

Diphenhydramine should only be used for a short time as self-medication.

This is how diphenhydramine is used

To treat sleep disorders, a 50 milligram tablet of diphenhydramine is taken about 30 to 15 minutes before bedtime. Care should be taken to ensure that the duration of sleep is long enough, otherwise the active ingredient will still work the next morning and can lead to fatigue and impaired reactions. The intake should be a few days, but a maximum of two weeks.

As a remedy for nausea and vomiting, diphenhydramine rectal capsules are inserted into the anus just like suppositories. Insertion can be made easier if the capsule is moistened with water beforehand. . If symptoms persist, a rectal capsule can be inserted up to three times a day.

Tablets are less useful in the case of nausea and vomiting, as vomiting sometimes prevents them from entering the intestine and releasing their active ingredient.

What are the side effects of diphenhydramine?

Most often, after taking diphenhydramine as a sleep aid, people complain of tiredness, drowsiness and difficulty concentrating the next day, especially after insufficient sleep time. When taken against nausea, fatigue is a common side effect.

Other possible diphenhydramine side effects include dizziness, muscle weakness and the associated risk of falling, headache, nausea, diarrhea, vomiting, constipation, dry mouth, heartburn, visual disturbances and urination problems.

The skin becomes more seldom sensitive to strong sunlight. Sometimes changes in the blood count occur and the intraocular pressure increases.

What should be considered when taking diphenhydramine?

While taking diphenhydramine, you should not take any sedative or sedative drugs (sleeping pills, sedatives, pain relievers, agents for depression or convulsions) or drink alcohol. Otherwise this would increase the effect excessively. The effects of diphenhydramine can also be increased by antihypertensive agents.

Diphenhydramine and some other drugs slow down the conduction of stimuli in the heart muscle (so-called QT time prolongation). If someone already has a QT time prolongation (“Long QT Syndrome”) or is taking medication with a QT time prolonging effect, diphenhydramine must not be taken - not even after the other medications. Otherwise life-threatening cardiac arrhythmias can occur. Examples of such drugs are agents for arrhythmias, certain antibiotics, antimalarials, other antihistamines, diuretics, and agents for psychosis and schizophrenia.

Diphenhydramine should not be used during pregnancy and breastfeeding. Studies have shown that it can be teratogenic and inhibit the flow of milk in breastfeeding women.

Children from the age of twelve and older patients may take diphenhydramine in reduced doses. The latter, however, must not have an enlarged prostate, otherwise urinary retention threatens.

Do not operate heavy machinery or drive traffic after taking diphenhydramine.

How to get medicines with diphenhydramine

Preparations with single doses of up to 50 milligrams of diphenhydramine for ingestion as tablets, rectal capsules or suppositories can be purchased without a prescription in pharmacies.

How long has diphenhydramine been known?

The active ingredient diphenhydramine was discovered in 1943 by Professor George Rieveschl at the University of Cincinnati in the USA. Just three years later, it was the first antihistamine to be approved as a drug by the US FDA. In the following years, the related active ingredient dimenhydrinate was developed from diphenhydramine, which is less sleep-inducing. In the 1960s, it was discovered that diphenhydramine increases serotonin levels in the brain and thus potentially acts against depression - it was the model of the first SSRI (selective serotonin reuptake inhibitor) fluoxetine. There are now numerous generic drugs available as over-the-counter sleep aids with the active ingredient Diphenhydramine.

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