Promethazine tablets Mechanism Precautions, let us discuss Promethagene. What is this drug, Promethagene? This is one of the drugs that belongs to the chemical category of phenothygenes. We have a few of the other drugs belonging to this chemical category such as clorpromazine, thyroidazine, fluconazine.
All these drugs are phenothygenes, but they are mainly used as antipsychotics. On the other hand, Promethazine is not preferred as antipsychotic. Instead, it is used as antimetic and antiallergic substance. Even this drug is in the phenotagene ring system, but it is not used as antipsychotic because of few of the structural differences between the phenotazine antipsychotics and Promethazine.
In this PromethaGene, we cannot observe any ring substitution. But in the antipsychotics, we can observe in electron with a drawing group at the second position. Lack of ring substitution results in weak activity on dopaminergic neurons.
Similarly, this drug is having a side chain like this, and this side chain is having further side chain at this position, which is not observed in antipsychotics. That’s why Promethagen is having the weak activity on the dopaminergic receptors, but it mainly blocks the H1 receptor and the D2 receptor on the CT J. That’s why it acts as antimicrobic agent.
So Promethagen can be used as antimicrobic to control nausea and vomiting that is observed postoperatively. This drug can also be used to manage motion sickness, where it is used as prophylactic to reduce the motion sickness.
This Promethasic can be given before the travel to prevent the induction of any nause and vomiting. Similarly, this drug can also be used as anti allergic substance. Since this drug acts as antihystic agent, this drug can reduce allergic response. So phenothagin can be classified as anti allergic substance. Since this drug acts on histamine receptors as well as d lopinogenic receptors, it can produce some sedation.
So this drug can also be used to induce the sedation before the surgery. For all these purposes, Promethagen can be used. And this tractorans will be used to control the nauseate and vomiting that is developed during the first trimester of pregnancy. But this is one of the off label purpose of this Promethagen, since complete safety is not established during the pregnancy. Now, let us the chemical nature of this tractorans. So this is a structure of Promethagene. Here we can observe one of the amine group is present on the side chain.
So let us give the numbering. This is one, two and three. So simply it’s a propanamine. At the second portion, amine group is there. So propane, two amine. Now, at the second position, nitrogen is attached with two methyl groups. So NN dimethyl. And at the first position, it is in the heterocyclic ring system.
That ring system is the phenolthiazine, but the numbering is somewhat different. We have to give the least number to the sulfur, so we can start the numbering from this carbon. So this is 1, 2, 3, 4, 5, then 6, 7, 8, 9, and 10. So sulfur is given fifth position and nitrogen is given 10th position. And this entire group is attached by 10th position, so we can write it as phenolthiazine 10L. That is the simple name of Promethagene.
Now, what is the precautions of this drug. One of the important precaution of Promethazine is that this drug on long term therapy can produce bone marrow depression. Because of bone marrow depression, this drug may produce leucopenia, decrease in the nucleoside count, and neutropenia, neutrophil count is going to be reduced. So the chance of anemia and infections can be increased with long term use of Promethagen.
And in those patients who are taking other medications which again reduce the bone marrow depression, such as anti cancer agents and antivirus agents. With such drugs, PromethaGene should be carefully given because of pronounced bone marrow depression. Similarly, this drug can induce one of the syndrome, Neuroleptic Malignant Syndrome, which is commonly observed with many of the Neuroleptics, that is, antipsychotics.
Since PromethaGene can also block the D2 receptors, to some extent, it can also produce one of the side effect associated with antiapileptics, that is the Neuroleptic malignant syndrome. In this condition, we can observe excessive body temperature, resulting in hyperthermia and some muscle rigidity, muscle spasm can be observed, along with increased heart rate, resulting in tachycardia and confusion can be developed within the patients. So all these symptoms are collectively called as neuroleptic malignant syndrome, which is commonly observed with many of the antipsychotics.
Another precaution is that Promethazine can reduce the threshold of seizures. So seizure induction is more pronounced in presence of Promethazine. This is not that much significant in normal patients, but in those patients who are taking other drugs such as opioids, since opioids can also induce the seizures by reducing the threshold.
So the combination of opiates with Promethagene may increase the risk of seizures in the patients. Similarly, low cholinostics at toxic dose, they can induce the seizures. So they should be carefully combined with Promethagene.
Similarly, this drug can produce some respiratory depression, which is more pronounced in the children. That’s why this drug should be carefully given in the asthmatic patients or patients with any chronic obstr uctory pulmonary disorder, COPD. In such patients, this drug should be carefully given as it increase the respiratory depression, d ispnea, wheezing, even it may lead to common death of the patient.
Finally, Promethagene can also produce CNS depression. Because of CNS depression, it can induce the sedation, drowsiness, dizziness in the patients. Again, it is more important when this drug is combined with other drugs like opiates, which again, produce CNS depression. And patients should be given caution while driving the vehicles or working.
with machinery because Promethazine can produce sedation, confusion, and dizziness, which may impair their day time activities, resulting in accidents and injuries. That’s why Promethazine should be carefully used in those patients who are working with machinery and driving the vehicles. Now, let us see how this drug acts.
Promethazine acts on different types of receptors. It can block H 1 receptors. Similarly, to some extent, it can also block D2 receptors. Finally, it can also block muscanic estal colon receptors. By blocking H 1 receptors, it can reduce the allergic reactions. By blocking the D2 receptors at the mesolimbic pathway, it can produce a mild antipsychotic action, and it can also develop fear of the syndromes like neuroleptic malignant syndrome.
It can act on the estal colon receptor, resulting in anti cholinergic side effects such as dry mouth, blood vision, and constipation. But it’s important actions on the MCs where it can block the variety of receptors, including H1 receptors, D2 receptors, and cholinergic.
Ctz is the chemoreceptor trigger zone, which is one of the important center responsible for induction of nausea and vomiting due to any toxic chemicals ingested into the body. This CtZ is expressed with few of the receptor.
such as 5HC3 receptor, which are activated by serotonin, and D2 receptor, which are activated by dopamine. Now, when this CTZ is going to be activated, it can send the signals to the warning center, which is again expressed with a few of the receptor, such as mesconic esterochlorine receptor, as well as H1 receptor.
Now, all these mediators are responsible for induction of emesis. So in order to block the emesis, any of these pathway should be blocked. Now, Promethazine works by multiple mechanisms. It can block the D2 receptors on the CT J. It can also block the muscaneic estal colon receptor on the vomiting center.
And finally, it blocks the important H1 receptor. Thereby, it can reduce the induction of nausea and vomiting. That’s why Promethazine acts as antimic agent. What are the side effects? Promethazine mainly produce sedation, dizziness and confusion. Somnolence and drowsiness is again produced by this drug because of CNS depression.
It can also produce tinnitus, some budging noise in the ears. Even it can produce dry mouth because of anti cholinergic side effects. Dyspnea, difficulty in breathing can be produced because of respiratory depression. Fatigue is another important side effect. It can also produce some blood vision, again, because of anti cholinergic side effects.
How it is given? This drug is available as tablets. It’s also available as solution suppositories. It is available at different strengths such as 12.5 mg, 25 mg, and 50 mg. For the treatment of allergic conditions, this drug can be started at 25 mg dose, which can be given as a single dose.
