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Pharmaceutical technology & biopharmacy.College 2-12
The amount of drug that is delivered to the site of action is determined by the following processes:
- The amount of drug that is released from the dosage form.
- The site where the drug is released from the dosage form.
- The transport of the drug from the released site to the site of action.
A drug is taken in, where after it will dissolve (the drug must be dissolved) and pass a membrane and
be absorbed in the systemic circulation. The drug will then go to the site of action that has receptors
to receive the drug. Exceptions to this process are intravenously injected drugs, these will enter the
systemic circulation straight away. Targeted drugs are also an exception, these will only go to the site
of action.
Pharmacokinetics is about what the body does with the drug after administration. There are four
steps in this process, this process is called ADME: Absorption, uptake of the drug in the systemic
blood circulation. Distribution, the distribution of the drug to the different compartments of the
body. Metabolism, the chemical conversion of drug substance by the body (enzymes) to different
active or inactive substances called metabolites. Excretion, the removal of the drug or its metabolites
from the body, via urine, bile, sweat or breath.
Administration via the intravenous injection, is the most direct way of administering a drug. It will
enter the systemic blood circulation straight away and has a bioavailability of 100%. The drug needs
to be dissolved in an aqueous solution, generally the fastest way to get the therapeutic effect. The
bioavailability is the amount of administered drug that reaches the systemic circulation.
The volume of distribution (Vd) is the apparent volume in which the drug is dissolved after
administration. When there is no concentration of the drug in organs, fluids or tissues the Vd will not
be larger than the body volume. When there is a concentration in organs, tissues or fluids, the Vd can
be greater than the body volume.
Drugs that are administered via non-intravenous routes undergo an absorption process. The drug is
released from the dosage form then it will dissolve in aqueous fluids and transport over the
membrane where it can be taken up in the blood. The pharmaceutical availability is the amount of
drug that is in solution. Hence why the pharmaceutical availability is always greater or the same than
the bioavailability.
Relevant Physic-chemical properties can also influence the way a drug acts in the body. Such as
diffusion: this is spontaneous transport cause by a difference in concentration from one part to
another part through a permeable membrane. Solubility is important because a drug needs to be
dissolved in order to drive the diffusion in the body and thus the transport of the drug. It is
determined by a crystalline habit, salt form, solvent and the particle size. The dissolution rate is the
rate at which a drug is released from the dosage form. To increase the dissolution, rate the surface of
the particle needs to increase, the charge can change the dissolution rate, the salt form and the
crystalline habit or amorphous material can change the dissolution rate. Also, the specific surface
area of a certain powder is related to the particle size of that powder. The charge is also important
because a charged molecule is unable to cross a membrane. A salt form has a higher dissolution rate
than a free acid or base. The ions in the salt change the environment of the stagnant layer
surrounding the dissolving particle, which increases the solubility of the drug in the stagnant layer.
Polymorphism, crystalline materials dissolve slower than amorphous material. The dissolving
molecule does not need to be released from the crystalline lattice, the amorphous materials however
are mostly unstable and will transform back into the crystalline state again.
The bioavailability is determined by the AUC of the orally injected drug divided by the AUC of the
drug if it were to be administered via an injection. Through parameters such as Cmax & Tmax the
bioavailability can be described in terms of absorption rate.
,Membranes can be passed due to passive transport, para-cellular uptake is an example of this. The
drug passes through the tight junctions in between the mucosal cells. Trans-cellular transport can be
passive or active, active transport can be accomplished using transport proteins that require energy,
thus it is active transport. When it passes through the membrane passively, there can be spoken of
passive transport. This can either happen inside the lipid bilayer or across the lipid bilayer. The way
of transport is decided by the properties of the drug. Ionisation (charge) can also influence passive
drug absorption, charged molecules are less lipophilic than the charged acids or bases. The driving
for transport is the non-ionised fraction of the dissolved drug. Protonated acids and deprotonated
bases are the driving force for the absorption process. The more non-ionised fractions (NIF) the
faster and more complete the absorption will be.
The pH can also play a major role in the drug absorption, pH in
the stomach is between 1.5 & 5.0, in the small intestine it
varies between 2.0 & 7.4 and the pH in the colon (large
intestine) is between 6.0 & 7.4. The rate of absorption
depends on the pH and the form of the drug. Weak acids are
mostly absorbed in the upper part of the duodenum because
the walls of the stomach. Weak bases are best absorbed in the
upper intestines, this is due to their good dissolution that takes place in the stomach.
In general, one charged group is not responsible for restricting passive absorption, but more groups
are. The driving force is the non-ionised fraction multiplied by the logarithm of the non-ionised
molecule. Milk increases the pH in the stomach and Cola decreases it.
The Biopharmaceutical Classification System (BCS) helps to group different drugs in categories. Class I
has a high permeability and a high solubility. Class II has a high permeability and a low solubility.
Class III has low permeability and a high solubility. Class IV has low permeability and low solubility. A
drug is highly soluble when it dissolves in a 250 mL aqueous buffer with a pH between 2 & 7.5. a drug
is highly permeable when the bioavailability is >90%. DN = d/(V*Cs), Dose number (DN) is a
dimensionless parameter that links solubility (Cs) to dose (d) and volume available for dissolution (V).
DN < 0.1 no effect of solubility on absorption rate, DN > 10 solubility will affect absorption rate and
bioavailability, DN 0.1-10 solubility may affect absorption rate and bioavailability.
College 3-12
Definitions and general aspects
A patient can experience different sorts of pain, acute pain which is heavy and immediately. Chronic
pain, the pain lasts for a longer time. Specific pain, the pain has a purpose or a reoccurring effect, for
example with a surgery or migraine. Pharmacologically active compound (API) in a suitable dosage
form is called a medicine. Dosage form consists of active compounds and excipients.
Biopharmaceutics decide how the dosage form and the route of administration are designed. Before
a drug is brought on the market it is first authorized on quality, clinical efficacy and safety.
Biopharmaceutics also study and describe the fate of an API in the body from the time of
administration until the moment it exerts its effect and how an API is metabolised and excreted.
(L)ADME is the system which can be used to give this a systematic overview. There are two types of
drug action, it can be systemic; the API will reach the site of action via the systematic circulation. Or it
can be local; this means it is released at the site of action. The pharmaceutical availability is the
amount of API released from the dosage form. The bioavailability is the amount of API that reaches
the systematic circulation. Due to the First-pass effect there is some of dissolved drug is taken up by
the body hence why the bioavailability is always smaller than or equal to the pharmaceutical
availability.
Routes of administration can vary depending on the drug that is used. The dosage form however can
, also differ for the same administration route. The desired effect decides the route of administration
and the dosage form.
Efficacy of a medicine is biopharmaceutically influenced by:
- API: content of the drug, its physicochemical properties
- Dosage form: structure and composition of the drug and its preparation method.
- Route of administration: dosage form is connected with route of administration
- How the body copes with the API: ADME
Excipients are part of each formulation so that the production can be facilitated, the quality can be
improved, the performance can be optimised and the acceptability and compliance of the patient to
be increased.
Oral drug delivery
The dosage form is ingested via the mouth, this can either be one of two forms. Solid oral dosage
form (tablet, capsule, powder and oromucosal preparations) and liquid oral dosage form.
Biopharmaceutics orally, tablet or capsule needs to disintegrate so that the API can be dissolved in
the body and the first-pass effect needs to be taken in count. For the drug to be released at the right
site, pH, residence time, digestive and metabolising enzymes should be taken in count. The route
orally is as follows: mouthoesophagusstomachsmall intestinelarge intestinerectum.
Absorption from gastrointestinal tract, dissolution of API in aqueous environment, the absorbing
membrane acts as lipophilic barrier so that the drug can be absorbed. The crossing of the
membranes is related to its lipophilicity. API needs to be uncharged in order to cross a lipid
membrane. API is a weak base when its uncharged at 2 pH above its pKa, it is a weak acid when its
uncharged at 2 pH below its pKa.
Tablets have a few characteristics, they are patient friendly and easy to use, the dose is accurate, the
production is fast and can be done on a large scale, they are stable and have advanced delivery
forms. It is mostly built up of the following elements, API, Filler, Disintegrating agent, Binder,
Lubricant, Matrix and coating. An oral medicine can have either an immediate or modified release.
When it has an immediate release of the drug the onset is rapid, it has a fast effect and short
duration of the effect. When the release is modified, the release rate is mostly slow it is released on a
predefined time point and has a specific site of release. Using immediate release there will be a
higher drug concentration but also for a shorter amount of time whereas sustained release keeps the
drug level close to constant.
Capsules can have two forms; it can be hard or soft and again there can be immediate release and
modified release. Hard capsules have a hard shell, the drug consists of a body and a cap. The capsule
masks the taste and odour. The shell will dissolve, and the content will be liberated. It is suitable for
patients that have swallowing problems, the content can be mixed with semi-liquid food. Soft
capsules are industrially manufactured, are softgels, suitable for poorly water-soluble, oily API, a way
to transform a liquid API to a solid dosage form and the API is in solution or in matrix.
Oromucosal preparations are solid, semi-solid or liquid preparations, containing active substances
intended for administration to the oral cavity and/or the throat to obtain a local or systemic effect.
The active substance will be swallowed and absorbed via the gastrointestinal tract. Oromucosal
preparations are patient friendly, have a rapid action and are lipophilic drugs.
Oral liquids are always in a mixture, aqueous solution, a suspension, dispersion of particles in
aqueous liquid, or an emulsion, dispersion of fat droplets in aqueous liquid. Oral liquids are a good
alternative for tablet or capsules if the patient has swallowing problems. The dose is easily adjustable
and its suitable for administration through feeding tube. However, they are less stable than solid oral
dosage forms. Properties API important for choice pharmaceutical form and dosing mistakes are
made easily. A suspension is a solid substance finely dispersed in liquid, sedimentation can take
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