Humanity has been plagued with illness from times immemorial,and we have tried to alleviate our illnesses with medicines for just as long. In the beginning, medicines were composed of plants and animals.
The oldest evidence of drug preparation is 5000 years old found written on a clay slab in Nagpur. There were several ingredients mixed in specific quantities to come up with just the right cure.
Though the same rules apply today, it is now a chemical process. It is a science of precision and takes tremendous patience. Chemicals which are either newly isolated from plants and animals or whose information we already possess are studied and then produced artificially and used to compose our medicines.
Composition of Medicine
A series of raw ingredients are mixed in a specific quantity to be pharmacologically effective against the disease.
Most medicines have two types of ingredients:
- Active Substance – Accountable for therapeutic effect on a particular disease or condition.
This active substance is the actual ingredient meant to treat.
- Inactive substance – It has no therapeutic effect but is necessary to make the drug stable in specific dosage forms like tablets, capsules, syrup, etc.
This ingredient is called the excipient,and they are pharmacologically inactive.
This process of composition of medicine is called formulation.
While discovering new drugs, molecules of interest have to be synthesized and evaluated.
This used to be a difficult and protracted process.
Combinatorial chemistry is a synthetic chemical method of synthesizing a large number of potential drug molecules in a single process of synthesis.
These compounds are then stored on the compound libraries. These libraries are established by computer software.
The structure and biological activity of each of these molecules can be screened on the library.
First, an active substance is chosen from the combinatorial library.
Then its chemical, mechanical and physical properties are studied during a process called pre-formulation.
These properties offer a framework for compatibility with another ingredient in the dose.
The pre-formulation study aims to develop the effective, stable and safe dosage form by establishing a profile of kinetic rate profile and acquiring information on Physio-chemical parameters of new drug substances.
The other properties studied during pre-formulation are solubility, dissolution rate, partition coefficient, polymorphic forms, and stability.
The process of making a new drug is long and painstaking.
It goes through a clinical trial before coming out in the market. Usually, clinical trials take as long as 15 years before the drug is even released to the market.
This stage is designed to test the safety, toxicity, dose quantity, and formulation method for the drug.
Drug loading is also an important aspect of this phase. It is the ratio of the active component in the medicine to the total content of the medicine.
By phase III clinical trials, the formulation of the drug has reached a stage close to the composition that will be ultimately used in the market.
This composition of the drug must be stable. Unless the drug is stable, you cannot know what, the dose will be when taken by the patient.
Stability studies are carried out for the testing effect ofhumidity, temperature,oxidation, or photolysis (U.V light or visible light) on the drug, and the composition is also the tested for the formation of degradation products.
Orally taken formulations are usually solid formulations.
This composition is the most commonly used medicine by patients.
Solid medicinesare given in the form of tablets.
Tablet is in the shape of a disc and is madewith granulated powder compressed by suitable machinery.
The tablet is coated starch like substance, so when it comes in contact with the GI tract, it swells up and dissolves.These substances are called excipients.
There are also binding agents to hold the mixture ofthetablet together.
Tablets can be sugar or film coated.
- Metrogyl tablet is composed of active substance metronidazole.
Excipients ethylcellulose, lactose, silica colloidal anhydrous, disodium edetate, magnesium stearate, sodium starch glycollate, guar gum may also be present.
Enteric Coated Tablets
When the tablets are enteric coated they are protected against the acidic contents of the stomach and do not disintegrate.
They do disintegrate in the alkaline medium of the intestine.
Capsules can come in Hard and Soft form.
Hard comprises a solid drug formation,and the soft comprises the drug in liquid or semi-solid form.
When a drug is applied to an area directly for treatment, it is called topical application.
This application can be to skin, hair,mouth, vagina, rectum, and entire GI tract during surgeries.
Isotonic solutions are used in eye and nose drops to prevent reaction, discomfort, and pain on application.
Ear drops are oily solutions so that they stick to the oral cavity.
Creams and Ointments
Skin treatment generally requires ointments and creams.Ointments have a lipid base and Cream an aqueous base
Ointments have a significant absorption into the tissue as they vacuum the skin from the air when applied. Hence drug does not evaporate as much.
Creams, on the other hand,remain on the superficial layer of the skin,andnot much is absorbed.
- Metrogyl M ointment is composed of metronidazole and mupirocin,and it can treat certain bacterial and parasitic of the joints, vagina, and respiratory tract.
- Metrogyl P skin ointment contains povidone iodine topical and metronidazole topical and can be used to treat rosacea, chronic wounds, post-surgery infections, and abrasions.
- Metrogyl P plus ointment has ornidazole and povidone iodine as the active substances,and it destroys amoeba.
Pastes are made up of powder and repel water which makes them useful in protecting the skin from humidity and moisture.
Gels and Lotions
They have an alcohol base. Can be applied on surfaces with hair.
It has fast evaporation and very small drug penetration.
- Metrogyl Dg gel is composed of chlorhexidine gluconate and metronidazole.
It is used for the treatment of dental infections.
- Metrogyl gel is composed of only metronidazole and used for trichomoniasis or bacterial vaginosis treatment which is an infection of the genitals.
- Metrogyl gel Plus has active component Ornidazole and can treat acne and genital infections.
Oral Liquid Preparations
Such preparations are easier to swallow than other forms of medicines.
Flavors could be added to make the composition more palatable.
But to avoid drug abuse mostly sorbitol (sugar alcohols) is now added instead of sugar.
It has an added benefit because of its action as an osmotic laxative.
If the drug cannot dissolve in water,then alcohol can be used as a dissolving substance.
Situations where the drug is in solid form,but alcohol is not used for dissolving purpose then the solution is a suspension.
- Metrogyl oral suspension is composed of metronidazole in 5ml solution. It should be shaken before use and taken by mouth with a meal.
These are drugs being administered high up the vagina.This will make sure that the drug coats the maximal vaginal surface and thus maximal absorption occurs.
The drug gets absorbed by the vaginal mucosa and directly into the bloodstream.
Such a form is used when a patient is not the conscious and oral administration isn’t possible.
Suppositories can be useful in patients who have trouble swallowing, nausea, to skip first pass metabolism by the liver, and where it is troublesome to find a vein.
- Metrogyl V3 suppository has clotrimazole and clindamycin. But clotrimazole is in higher quantity then clindamycin. It can treat bacterial infections of the genitals, lung, digestive system, etc
- Metrogyl V7 suppository has clotrimazole and clindamycin in the same quantity. It is used to treat toxoplasmosis, soft tissue infections, bacterial vaginosis.
Injectable Drug Formulation
These drug formulations are either present in a lyophilized form or if stable then in liquid form.
Injectable drug compositions require cold temperatures for storage as they get destroyed at high temperatures.
Method of drug administration that by-passes the GI tract is called parental administration. Drugs can be injected into any body part with the help of needles.
The drug is injected into the dermis.
Not used often as absorption is slow and large quantities cannot be given. E.g., Local Anaesthesia
The drug is injected below the skin and into the fatty area.
Drug absorption is slow and used mainly for drugs that don’t have oral preparations. Insulin.
When adrenaline is added to the injection, it decreases bleeding but slows the absorption.
This happens because adrenaline has receptors on the blood vessels and causes vasoconstriction (narrowing of the blood vessels) by acting on these receptors.
If a drug like a hyaluronidaseis added, it will destroy the tissue collagen,andthe drug absorption will be faster.
The drug is injected into the muscle.
Muscles have a larger surface area and are also more vascular than dermis or subcutaneous tissue.
This makes the drug absorption faster than either intradermal or subcutaneous injections. Lipid soluble drugs are more easily absorbed as opposed to lipophobic drugs.
Sometimes the drug solution is oil based. Such mixtures are called depot injections and disintegration may take several weeks.
The drug is administered directly into the blood circulation.
This makes it the fastest route of drug administration. This administration avoids the process of absorption and hence very fast action can be achieved.
- A metrogyl infusion is an injectable form of metronidazole given intravenously.
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