Introduction to pharmacology

Pharmacology is the study of medications, or chemical compounds, which interact with various living systems, from tiny molecules to cells, to tissues and whole organisms in order to produce a certain effect.Every day, more and more new medications are designed to fight diseases, from infections to cancer, heart failure, and depression.

But the process of developing a new medication can take a lot of time and money, and it typically consists of three steps.

Step 1 is discovery, and that’s when a candidate compound is picked out as a possible therapeutic agent for a specific disease.

Step 2 is preclinical research, during which this compound is tested on cell cultures and animals, like mice and rats, mainly to see if it causes any serious harm on living organisms.

And, finally, step 3 is clinical development, during which clinical trials are performed. That’s where the compound is tested on humans to see if it’s safe and effective in treating diseases.For a new medication, clinical trials are done in 4 phases, which can be remembered with the mnemonic “All medications need the SEAL of approval,” which stands for Safety, Efficacy, Approval, and Long term.

Phase I trials test the medication in a small group of healthy individuals to see if it’s Safe for humans. Phase II trials aim to find out more about how Effective the medication is or how well it works at a certain dose.

This is done by testing it on a moderately sized group of individuals affected by the condition in question. In phase III trials, the new medication is compared to the standard treatment to find out if it’s actually just as good as or even better than the existing one.

Phase III trials generally involve a much larger number of individuals, and aim to replicate the exact setting in which the medication will be administered in real life, which will then be used as the basis for Approval by regulatory organizations for the market.

This whole process can take up to 10 years or more, depending on the compound. But if all this goes well- congratulations!

We’ve got a new medication! Now, that new medication will have at least three names- a chemical one, describing its chemical structure and used mostly in scientific studies, like N-acetyl-p-aminophenol; a generic name, which is usually a shortened version of the chemical name and is mostly used by health professionals, such as paracetamol or acetaminophen; and one or more brand or trade names, given by the pharmaceutical companies that make the medication, such as Panadol or Tylenol.

Okay, but the journey of drug development hasn’t finished quite yet. Once a medication reaches the marketplace, there’s phase IV, which is a final phase of safety surveillance that looks for Long term or rare side effects that might have been missed.

If it’s found to be unsafe, a recall and ban might be needed.Alright, now, once a medication is administered, it starts interacting with the body.

This interaction can be broken down into pharmacokinetics and pharmacodynamics. Pharmacokinetics refers to the movement and modification of the medication inside the body.

In other words, it’s what the body does to this medication. So, once the medication gets administered, it first has to be absorbed into the circulation, then distributed to various tissues throughout the body, metabolized or broken down, and, finally, eliminated or excreted in the urine or feces.

You can remember this as ADME- Absorption, Distribution, Metabolism, and Excretion. Pharmacodynamics, on the other hand, refers to what the medication does to the body.

So, once again, after the administration of a medication, it binds to receptors or specialized proteins located on the surface of or inside a cell.

This gives rise to a signal cascade, which, ultimately, results in some change in the cell’s function, like boosting the production of a particular type of protein or slowing down DNA replication.

An ideal medication would produce a single beneficial or therapeutic effect for a certain disease state. In reality, though, most medications produce several unwanted effects, called side effects like nausea or fatigue.

Now, in order to determine the safety of a medication, we can look at its therapeutic index. The therapeutic index refers to the ratio between the toxic dose and effective dose of a given medication.

We can illustrate this using a nice graph that shows the relationship between the amount of a medication given, also known as dose- on the x axis, usually on a logarithmic scale, with the response produced- on the y axis.

What we get is an S- shaped curve, called dose- response curve. So, to calculate the therapeutic index, we divide the median toxic dose, or TD50, which is the dose that causes a toxic response in 50% of the population; by the median effective dose, or ED50, which is the dose that produces a clinically desired effect in 50% of the population.

The closer the ratio is to 1, the higher the danger of toxicity, so the larger the therapeutic index, the safer a medication is considered to be.Alright, medications that have a low therapeutic index have a narrow margin of safety, which means that there is a thin line between the dose needed to produce the desired effect and the toxic dose.

So these medications, including warfarin, lithium, digoxin, gentamicin, phenytoin, or theophylline, require close monitoring of serum levels.Finally, let’s talk about what happens when two or more medications are administered together.

First of all, there are a whole bunch of ways medications can interact with each other, both at pharmacokinetic and pharmacodynamic levels.

Pharmacokinetic interactions occur when one medication alters the absorption, distribution, metabolism, or excretion of another, thereby changing the amount of medication available to produce the desired effect.

For example, in pharmacokinetics, it might be that two medications are metabolized by the same enzymes, so they compete for the same enzyme sites.

On the other hand, pharmacodynamic interactions occur when medications influence each other’s effects directly. For example, two medications might both increase the blood pressure, producing a synergistic effect where the blood pressure goes up even higher than what you’d expect by simply adding the two medication effects together.

Likewise, a medication might work to increase blood pressure by simply opposing the effect of another medication, thereby having an antagonistic effect.All right, as a quick recap… Each medication is developed in three steps- a discovery, preclinical and clinical step, and has three names- a chemical, generic, and brand name.

Pharmacokinetics studies what the body does to a medication, and pharmacodynamics studies what a medication does to the body, including its beneficial and side effects.

Medications with a narrow therapeutic index need to be closely monitored to prevent toxicity. Drug interactions may occur on both