Chemistry is one of the life requirements in this age. It can play a great role in changing of life around us. Also, it significantly helps people to get their needs in an easier and faster way.
Chemistry is also involved in many organic and plastic industries, in agriculture, and in the synthesis of manure. It is also involved in weapons industries and technology, making them an important elements in the progress of society. As well as, chemistry contributes in the production of various drugs, which treat many diseases.
So, what is the chemistry? what are its types, and especially, how it contributes in all processes related to drug and its prescription for treating the disorders?
Chemistry, a branch of science, is the study of the composition, properties and behavior of matter. It is concerned with atoms and their interactions with other atoms and molecules.
Chemistry is divided into five major Branches;
- Organic: is the study of essential all substances containing carbon
- Inorganic : is the study of substances that do not contain carbon
3- Analytical: is the study of the composition of substances.
4. Physical: is the study of theories and experiments that describe the behavior of chemicals and energy involved.
5. Biochemistry: is the study of the chemistry of living organisms.
What is the importance of chemistry in Pharmacy?
Chemistry is used in medicine quite a lot. All the synthetic medicines that we receive are made from various chemicals and their chemical reactions.
Therefore, it is important to medicine because it helps us in finding the cure to most diseases and to understand how vitamins, supplements and drugs can help or harm us. Chemical reactions occur when you breathe, eat or even sleep.
Furthermore, because of most diseases, injuries, and treatments involve chemicals and chemical processes. So, understanding chemistry, we are able to develop drugs that fight disease, develop better nutrition, and develop healthier environments to avoid disease.
How do you use chemistry in a pharmacy?
Pharmacies deal with medicines, and most medical compounds are small molecules like aspirin or ethanol, to larger biological molecules, mostly proteins like insulin or prolactin. So a pharmacist is doing a fair bit of chemistry, in addition to doing biology, medicine, and retail sales.
Pharmacists are not just concerned with how their chemicals affect the body of the patient, but they are also concerned with how the molecules interact with one another, how they affect the body in combination, and how they are delivered. To make a pill that survives the stomach acid, and is delivered into the intestines, can be complicated without chemistry background.
Some drugs must be injected or delivered through the skin in some other way, because they can’t pass through the digesting tract unaltered – most proteins are in this category. Some are inhaled for the same reason, or because they act faster that way. Knowing how chemistry affects drug delivery is an important part of designing pills, capsules, injectables, and inhalants.
In other cases, a drug might cause the body to produce an enzyme that breaks down another drug the patient might be taking. Understanding chemistry allows the pharmacist to suggest that the pills be taken at different times, or that another drug be substituted for one of the originals.
Chemistry helps us to understand; physicochemical properties of drugs that is useful in dosage forms designing and in achieving drug: stability, drugs-receptor binding interaction which is useful in managing bioavailability and in mechanism of action of medicines and their side effects.
Physical and chemical Properties and Drug:
Physicochemical Properties and Drug depend on:
- Ionisation ( hydrophilicity).
- Acidity or Basicity of a compound.
- 3- Lipophilicity ( Partition coefficients)
- 4- Hydrogen bonding
- 5- Molecular size.
- Ionisation (hydrophilicity) :
Ionisation (hydrophilicity) is the protonation or deprotonation resulting in charged molecules, about 85% of marketed drugs contain functional groups that are ionised to some extent at physiological pH (pH 1.5 – 8).
The extent of ionisation of a compound can have a large effect on many biological properties, such as receptor/enzyme binding, binding to plasma proteins, CNS penetration, solubility and absorption. Once the pKa value of a molecule is known, then it is possible to calculate the proportion of ionised and neutral species at any pH.
So, the same compound will be ionised to different extents in different parts of the body. This means that, for example, basic compounds will not be so well absorbed in the stomach than acidic compounds since it is generally the unionised form of the drug which diffuses into the blood stream.
2. Acidity or Basicity of a compound:
The acidity or basicity of a compound plays a major role in controlling: Absorption and transport to site of action, solubility, bioavailability, absorption and cell penetration, plasma binding, and volume of distribution.
The pH of different cellular compartments, body fluids, and organ is usually tightly regulated in a process called acid-base homeostasis. The pH of blood is usually slightly basic with a value of pH 7.4. This value is often referred to as physiological pH in biological and medicine (table 1).
Table1: pH value of different biological fluids and tissues of the human body
Drugs are only absorbed passively when they are unionised. This is because the compound has to pass through a lipophilic (‘fat loving’) membrane and this process will be unfavourable for charged molecules. . In a more acidic medium, such as the stomach, the percentage ionised for an acidic compound will be less than at pH 7.4 and so more compound will have the capacity to be passively absorbed. In comparison, a basic compound in an acidic medium will be more ionised and so less of the compound will be in the neutral form and have the capacity to undergo passive absorption. This may well be the reason for the observation that acidic compounds generally have better fraction absorbed (hence bioavailability) than bases with neutral compounds lying between them.
Lipophilicity (‘fat-liking’) is the most important physical property of a drug in relation to its absorption, distribution, potency and elimination. It is often an important factor in all of the following, which include both biological and physicochemical properties:
- Plasma protein binding
- CNS penetration
According to this property, the compound that binds too strongly to plasma proteins and therefore the free blood concentration will be too low to produce the desired effect. Conversely, if the compound is too polar (hydrophilic), it may not be absorbed through the gut wall due to lack of membrane solubility. So it is important that the lipophilicity of a potential drug molecule is correct in design.
Hydrophobic means ‘water hating’. This principle also applies to the physical properties of drug molecules. If a compound is too lipophilic, it may be insoluble in aqueous media (e.g. gastrointestinal fluid or blood).
4. Hydrogen bonding
Hydrogen bonding is the attractive force between a hydrogen atom covalently bound to an electronegative atom (the donor) and a second electropositive atom (the acceptor). You don’t want too many hydrogen bond donors or acceptors, otherwise the drug won’t get from the gut into the blood.
5. Molecular size
Molecular size is one of the most important factors affecting biological activity, but it’s also one of the most difficult to measure. There are various ways of investigating the molecular size, including measurement of:
1- Molecular weight (most important)
It is probably the most useful measure of molecular size as it is very easy to calculate, but you may also come across other measures
- Polar surface area.
For example, is a measure of what proportion of the surface of the molecule is comprised of polar groups, compared to the proportion of hydrophobic groups.
The application of Chemistry in Pharmacy:
The most obvious is that pharmacy is dealing with chemicals. It is pure chemistry and understanding how the chemicals interact with a living being, to know what medicines are made of and how they interact with each other and environment.
Additionally, chemistry help us to know of potential side effects a patient may incur due to the specific medication or a combination of medicines and to calculate the correct dosage prescribed by a physician.
Finally, Chemistry is important in separation of drugs mixtures by various chromatography methods in which both the random samples and the standard solution are passed through a high performance liquid chromatography (HPLC) and the quantities are compared.
HPLC is widely used to check the quantities of active ingredients in medicines. The result of this process show if the average content of the medicine lies within the accepted limits of variation as an application of Chemistry.
The Organic Chemistry of Drug Design and Drug Action 3rd Edition by Richard B. Silverman, Mark W. Holladay.
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