Basic Pharmacology

Pharmacology
is the study (ology) of drugs (pharmacy). Psychopharmacology is the study of (ology)
drugs (pharmacology/y) that produce their effects on the mind or brain (psycho
or psyche). There are five basic classes of psycho-active drugs: 1) the opioids
(i.e., heroin and methadone), 2) the stimulants (i.e., cocaine, nicotine), 3)
the depressants (i.e., tranquilizers, antipsychotics, alcohol), 4) hallucinogens
(i.e., LSD), and 5) marijuana and hashish (Cooper, Bloom and Roth, 1991).

Most
compounds, including opioids exist in two forms, one form in active and one
inactive — that are distinguished by levo or dextro preceding the compounds
name (Goldstein, 1994). Sometimes just the first letter, l
or d
is used to indicate the form of the compound.

 

left
handed = levo-methadone = l-methadone
= methadone

right
handed = dextro-methadone = d-methadone

 Generally
speaking the active form is usually the -levo form and very often levo- is
dropped from the compounds name completely. The best way to think of these
two forms is your two hands. Both the right and left hand have the same
structures (i.e., one thumb and four fingers) but they are mirror images of one
another. And like hands, the levo and dextro form are very different from one
another, one active, one inactive, yet similar — the same basic three
dimensional structure.

Administration

An
important factor in how a psychoactive drug exerts it effects is how it is
administered. Administration refers to the mechanisms by which drugs are
transported from the point of entry into the bloodstream. Drugs are commonly
administered in five ways: 1) orally, 2) rectally, 3) parentally (injection), 4)
the membranes of the mouth or nose, and 5) by inhalation. Each method of
administration has its advantages and disadvantages (see Table 1) (Cooper, Bloom
and Roth, 1991).
 

After
a drug is administered the next important determinant in the drugs ability to
exert its effect is how the drug is distributed throughout the body (Barchas,
Berger, Ciaranello and Elliot, 1977). Once the drug reaches the bloodstream it
is distributed throughout the body. However, it must be able to pass across
various barriers in order to reach the site of action. Only a very small portion
of the total amount of a drug in the body at any one time is in direct contact
with the specific cells that produce the pharmacological effect of the drug.
Most of the drug is found in areas of body that are remote from the drug’s site
of action. In the case of psychoactive drugs, most of the drug is to be found
outside of the brain and is therefore not directly contributing to the
psychopharmacological effect. Four types of membranes are most important in the
way a drug is distributed throughout the body (Barchas, Berger, Ciaranello and
Elliot, 1977). 
These are: 
1) cell Walls, 2) Walls of capillary vessels of the circulatory system,
3) the blood-brain barrier (BBB), and 4) the placental barrier.

Cell
Membranes:
In
order to be absorbed from the intestine or gain access to the interior of a
cell, a drug must be able to penetrate the cell membranes (Spence and Mason,
1979). The characteristic feature of cell membranes are fat molecules coated by
a protein layer on each surface. Like a bimolecular Sandwich the fat molecules
(cheese) are sandwiched between two layers of protein (the bread). Only drugs
that are soluble in fat are permeable and can pass through the cell membrane.
The cell membrane also contains small pores that allow water-soluble molecules
to pass through. Most drugs are too large to pass through the pores and, thus,
most water-soluble, fat-insoluble drugs cannot pass through the cellular
barrier.

Blood
Capillaries:
Within a minute or so of a drug entering the bloodstream, it is
distributed fairly evenly through the circulatory system (Cooper, Bloom and
Roth, 1991).  However, most drugs
are not confined to the bloodstream and are readily exchanged back and forth
across the blood capillaries. The capillary walls contain pores that are large
enough for most drugs to pass through, therefore it does not matter whether a
drug is fat-soluble or insoluble for it to pass through.

Blood-Brain
Barrier (BBB): (BBB):
For drugs to enter the central nervous system (CNS) they must be able to
penetrate the BBB (Cooper, Bloom and Roth, 1991). The BBB increases the
permeability of the capillary membranes thus protecting the brain from various
substances that would otherwise be harmful (Spence and Mason, 1979). Capillaries
of the brain are tightly joined making them smaller and more difficult to
traverse. But, a second barrier protects the CNS. The outer cell walls are
covered by a foot-like sheaf structure that arises from a nearby cell called an
astrocyte. Thus, for a substance to enter the brain it must traverse not only
the capillary wall but also the membranes of the astrocytes in order to reach
their target cells.

Placental
Barrier:
Among all the membrane systems of the body, the placenta is unique: it separates
two distinct human beings with differing genetic compositions, physiological
responses, and sensitivities to drugs (Barchas, Berger, Ciaranello and Elliot,
1977). The fetus obtains essential nutrients and eliminates metabolic waste
products through the placenta without depending on its own organs, many of which
are not yet functioning. This dependence of the fetus on the mother places it at
the mercy of the placenta when foreign substances appear in the mother’s blood.

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Bibliography
List 

Understanding
pharmacology can be difficult for the person without a scientific background. 
This does not mean that one should ignore this area of methadone because
it is important for patients to have some basic knowledge in order to know about
their dose.  Below
are some classic texts with information about pharmacology. 
Some are more difficult than others and you should first look through a
text prior to purchasing it to insure that you have the correct information.

Brecher, E.M.,  1972.  Licit
and Illicit Drugs.  The Consumers
Union Report on Narcotics, Stimulants, Depressants, Inhalants, Hallucinogens,
and Marijuana.  Boston:
Little, Brown and Company.

 

Cooper, J.R.; Bloom, F.E.; Roth,
R.H.,  1991. The Biochemical Basis of
Neuropharmacology (6th Edition). New York:  Oxford University Press.

Eccles, J.C.,  1977. The
Understanding of the Brain. New York: McGraw-Hill.

 

 

Gilman, A.G., Rail, T.W., Niles,
A.S. and Taylor, P. (eds),  1990. 
Goodman
and Gilman’s The Pharmacological Basis of Therapeutics (8th
Edition). New York: Pergamon Press.

 

 

Goldstein, A.  1994.  Addiction. 
From Biology to Drug Policy. 
New York:  W.H. Freeman
& Company.

 

 

Lowinson, J.H., Ruiz, P.,
Millman, R.B. and Langrod, J.G.  (eds)
1992.  Substance
Abuse: A Comprehensive Textbook. 
Ed.  Baltimore: Williams
and Wilkens.

 

 

Pratt, W.B.; Taylor, P. (eds) ,
1990.  The Principles of Drug Action. The Basis
of Pharmacology (3rd Edition). New York:  Churchill Livingstone.

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References

 

Barchas, J.D., Berger, P.A.,
Ciaranello, R.D. and Elliot, G.R. (1977). Psychopharmacology.
From Theory to Practice. New York: Oxford University Press.

 

Cooper, J.R., Bloom, F.E. and
Roth, R.H. (1991). The
Biochemical Basis of Neuropharmacology (6th Edition). New York: 
Oxford University Press.

 

Goldstein, A.  (1994).  Addiction. 
From Biology to Drug Policy. 
New York:  W.H. Freeman
& Company.

Gilman,
A.G., Rail, T.W., Niles, A.S. and Taylor, P. (eds) (1990). Goodman
and Gilman’s The Pharmacological Basis of Therapeutics (8th
Edition). New York: Pergamon Press.

 

Spence, A.P. and Mason, E.B.
(1979). Human
Anatomy and Physiology. Menlo Park, California: The
Benjamin/Cummings Publishing Company.

 

Zweben,
J.E. and Sorensen, J.L. (Jul-Sep 1988). Misunderstandings about methadone. Journal
of Psychoactive Drugs 20(3): 275-281.

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