Drugs

Definition of Drugs

By definition, drugs are chemical substances that affect or alter the physiology when taken into a living system. They can either be natural or synthetic. Chemically, they are low atomic mass and molecular massstructures. When a drug is therapeutically active and is used for the diagnosis, treatment or prevention of a disease, it is called medicine (legal drugs). They target the macromolecules inside the body and generate a biological response. Most of them interrupt the nervous system (especially brain) for the generation of a proper biological response. However, they can be toxic in higher doses called lethal dose.

Classification of Drugs

Classification of drugs can be done on the basis of different criteria. Some of the criteria for the classification of drugs are given below.

On the basis of pharmacological effect:

 How a drug or medicine affects or influences the cells of an organism is referred to as the pharmacological effect. Drugs have different pharmacological effects on an organism; say, for example, an analgesic reduces the pain while an anti-inflammatory drug reduces the inflammation of the body. Thus, drugs can be classified based on the pharmacological effect.

On the basis of drug action:

Different drugs act differently i.e., each drug has its own way of generating response called drug action.  Drug action is more specified according to how it generates a response. For example, there are lots of medicines to treat hypertension but each type of drug has different drug action. All the hypertension medicines reduce the blood pressure but in a different pathway.

On the basis of chemical structure:

This is a common classification of drugs. Generally, drugs which have same drug action and pharmacological effect have a basic skeletal structure and a minute variation in the branching. This is why some drugs have more potential than the other. For example, all sulphonamides have the same skeletal structure.

On the basis of molecular targets:

Drugs target the macromolecules inside the body to generate a biological response. Such macromolecules are called target molecules or drug targets. Drugs which have the same mechanism of action will have the same target. This basis for classification of drugs is more helpful during clinical trials.

Drug-Target Interaction

Enzymes as Drug Targets

Catalytic Action of Enzymes




Enzymes catalyze different reactions.




The first function is the contact between that affect or alter the physiology when taken into a living system. They can either be natural or synthetic. Chemically, they are low atomic mass and he enzyme and the substrate. Enzyme contain active sites where substrate gets bound. The interaction between the substrate and the enzyme is based on different interaction such as hydrogen bonding, ionic interaction, van der waals forces.








Fig. 1. Substrate Enzyme Interaction



The second function of an enzyme is to provide functional groups that will attack the substrate and carry out enzyme catalyzed reaction.



Drug Enzyme Interaction



Drugs can inhibit the activity of the enzyme by binding to its active site where substrate molecule bind. Thus, by binding to active site of an enzyme, it inhibits the enzyme catalyzed reaction. The chemicals that inhibits the activity of an enzyme are known as enzyme inhibitors.



Drugs acts as inhibitors in two different enzymes:



Some inhibitors act as competitive inhibitors by binding to a site where substrate molecule will bind. But if substrate concentration is much more than the inhibitor, inhibitor will not be able to bind the active site of an enzyme. 







Fig. 2. Drug Enzyme Interaction



Some enzymes known as allosteric enzymes contain allosteric site other than the active site of an enzyme. So, some drugs bind to allosteric site of an enzyme instead of active site of an enzyme. They modify the site in such a way that substrate will not able to recognize the enzyme.

  



Receptors as Drug Targets



Receptors are proteins that are essential for communication. They are mostly embedded in the cell membrane. A small part of receptor is outside the cell membrane and other part is inside the membrane. The outer part of the receptor will interact with the targeted drug.  Neuronal cells also communicate with each other through receptors. Certain chemicals are secreted by neuronal cells which are received by another neuron. These chemicals are known as Chemical Messengers. 







Fig. 3. Types of Enzyme Inhibition



There are a large number of different receptors in the body that interact with different chemical messengers. Receptors show selectivity for one chemical messenger over the other because their binding sites have different shape, structure, and amino acid composition. Drugs that inhibits the natural function of drug is known as Antagonistic Drug. They are used to block the activity of certain enzymes. There are other drugs also that mimics the natural function, such drugs are known as Agonists.











Therapeutic Action of Different Classes of Drugs




Antacids


Hydrochloric acid is produced in stomach to bring out the digestion process. But excess production of acid leads to acidity. Sometimes it may also lead to ulcers in the stomach. Earlier sodium hydrogen carbonate is used to treat acidity. Metal hydroxides are more preferred because of being insoluble and do not increase the pH above neutrality. Studies have reported that Histamine stimulates the release of pepsin and hydrochloric acid in stomach. A drug known as cimetidine prevents the interaction between histamine and the receptors in the stomach. This decreases the amount of released histamine. Later on, another drug came into the market which is known as ranitidine. This drug is still common among the people.







Fig. 1. Structure of Cimetidine



Antihistamines



Histamine is a vasodilator. It contracts the smooth muscles of the gut and the bronchi. Drugs such as brompheniramine (Dimetapp) and terfenadine (Seldane), act as antihistamines. These drugs compete with histamine for binding site on the receptors.



Neurologically Active Drugs



Tranquilizers



These are drugs used to treat stress, or other mental diseases. They also act as sleeping pills. There are different types of tranquilizers. For Example, noradrenaline plays an important role in mood changes. During low level of noradrenaline, person suffers from depression. For this situation, antidepressants are taken. Antidepressants inhibits enzymes that degrades noradrenaline.



Some tranquilizers such as chlordiazepoxide is mild tranquilizer. Equanil is another tranquilizer which is used for controlling depression and hypertension.







Fig. 2. Structure of Equanil



Analgesic



These drugs are used to treat pain without causing any mental illness. Analgesics are classified into- non-narcotic analgesic and narcotic analgesic.



Non-narcotic analgesic such as aspirin acts as inhibitor of prostaglandins. These drugs are also used to treat pain of arthritis. Analgesics are also used to reduce fever. Such drugs are known as Antipyretic.







Fig. 3. Structure of Aspirin



Narcotic analgesic is used to relieve pain and give a feeling of sleepiness. For Example, morphine. Excess dose of morphine may cause convulsions, coma, or even death.



Antimicrobials



Antimicrobials includes bacteria, viruses, fungi etc. it includes:



Antibiotic



These are used to treat infections caused by pathogens. Antibiotics in low dose inhibits the growth of the microorganisms. But these also inhibits the activity of beneficial bacteria. Some antibiotics kills the microorganisms, they are known as Bactericidal. For Example, Penicillin.



Some inhibits the microorganisms instead of killing them. Such drugs are known as Bacteriostatic. For Example, erythromycin, tetracycline.



Some antibiotics target only limited range of microorganisms, they are known as Narrow Spectrum Antibiotics. For Example, Penicillin G. But some target wide range of microorganisms, they are known as Broad Spectrum Antibiotic. For Example, Ampicillin.







Fig. 4. Structure of Ampicillin







Antiseptics and Disinfectants



Antiseptics and disinfectants also acts on microorganisms to kill or inhibit them. Antiseptics acts on living tissues. Such as Soframicine. They are not consumed orally, rather they are applied on infected area. Dettol is one of the commonly used antiseptics. It is a mixture of chloroxylenol and terpineol. Iodine also acts as powerful antiseptic.



Disinfectants are used on non-living objects such as drainage system, floors etc.1% solution of phenol acts as disinfectant. 







Antifertility Drugs



These drugs are used to control the population. They are commonly known as Birth Control Pills. These drugs are composed of synthetic hormones. Norethindrone is an antifertility drug 







Fig. 5. Structure of Norethindrone





which is a derivative of progesterone. Ethynylestradiol (novestrol) is an estrogen derivative which is used in combination with progesterone derivative.






Positive and Negative Effects of Drugs


















Positive effects of drugs











•They cure diseases!
Drugs have numerous positive effects. In fact, all of our medicines are drugs. Cancers and other fatal diseases were impossible to cure before the discovery of drugs like taxol and cisplatin. The wonders drugs have done in the world of medication is indescribable in a few words.











• They make pain bearable.
Drugs having a sedative effect often help patients cope with nail-biting pain and assist doctors to carry on surgical procedures. Pain-killers are a huge discovery that is, until today, the sole basis of ease to patients. Aspirin cures headaches and is a wonder in the case of inflammation.












•They create research and job opportunities
With the rise in drug intake, more and more manufacturing companies are coming up with hundreds of job opportunities. Research scientists are also always on the lookout to find something better than what exists.




• Helps people escape reality
One cannot argue, legal or not, drugs are the best way to escape reality and have a little relaxation period. Along with being a stress buster, it has also been proven to be a performance enhancer. Once on drugs, some people have reported a heightened view of the world as a glorious place. Your mood, creativity, confidence, self-confidence, and perception of life can reach a whole new level with correct administration of drugs.
















Negative effects of drugs







•Drug abuse
Drug abuse refers to the point where a person starts taking drugs without a physician’s guidance and in order to experience pleasure. As drugs induce a feeling of getting “high”, drug abuse is a very common problem today. It has ended in fatality for many unfortunate souls.

• Addiction
Followed by drug abuse, people start getting addicted to drugs. It isn’t uncommon, really! The levels of dopamine released when we take drugs are enough to make our body crave for more. If we give in to the cravings, we are gone – life starts having a singular meaning, “drugs”. As we know, all sorts of addictions are bad for health, so are drugs!

• Legal problems
Often, drugs that are consumed for pleasure are illegal. Also, consumption of drugs is prohibited in many workplaces. Driving and roaming in public under the influence of drugs can also lead to legal action.

• Side effects
Many times, even after a physician’s guidance, drugs may lead to adverse side effects. After all, drugs are chemical substances and not natural. When chemicals infuse with our body, they may spark mutations and problems that may cause various diseases and other problems.

• Money wastage
When addicted, drugs can lead you to money wastage. You start investing all your money and time into drugs. It’s a vicious cycle that never ends. You start going down in debts and losing everything. Your work, home, and health start getting affected – to stabilize which you invest even more money!





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