Chemistry · Ch 15 — Chemistry in Everyday Life
Classification of Drugs
Classification of Drugs
There isn't one single way to classify drugs -- the unit walks through four different, complementary classification schemes, each useful for a different purpose.
By chemical structure: drugs sharing a common molecular skeleton are lumped into one group, regardless of what they actually do. Ampicillin, amoxicillin and methicillin, for instance, all share the same penicillin nucleus (a beta-lactam fused to a thiazolidine ring, carrying a carboxylic acid and a variable R-group amide side chain) and so are all classed as penicillins; opiates, steroids and catecholamines are three more examples of structural families. Sharing a skeleton usually means sharing chemical reactivity -- but NOT necessarily sharing biological action. Every penicillin-group drug happens to act the same biological way, but that is not guaranteed by structure alone: barbiturates and steroids, for example, are each structurally uniform families whose members can still act quite differently in the body.
By pharmacological effect: here drugs are grouped by what they DO to the recipient, regardless of their structure. Anything capable of killing pathogenic bacteria -- amoxicillin, ampicillin, cefixime, cefpodoxime, erythromycin, tetracycline -- is grouped as an antibiotic; anything that lowers blood pressure -- propranolol, atenolol, metoprolol succinate, amlodipine -- is grouped as antihypertensive. This is the classification a physician actually uses at the bedside: it hands over the full menu of options for a given clinical problem, from which the physician picks the one best suited to the patient's specific condition.
By target system (drug action): a tighter classification than the pharmacological one -- drugs are grouped by the specific biological process they interfere with. Streptomycin and erythromycin are both antibiotics that block bacterial protein synthesis, so both land in the same target-system group -- even though the fine mechanism differs: streptomycin blocks the start of protein synthesis, while erythromycin blocks the addition of new amino acids partway through. …
What this figure shows. A structural diagram of the shared penicillin nucleus (the beta-lactam-thiazolidine bicyclic core bearing two methyl groups, a carboxylic acid and an amide side chain R-CO-NH-), followed by a small table pairing the variable R group with the resulting drug name: a benzyl (CH2-C6H5) R group gives Penicillin G, a phenoxymethyl (O-CH2-C6H5) R group gives Penicillin V, an alpha-aminobenzyl R group (bearing -NH2) gives Ampicillin, the same group with an added -OH gives Amoxicillin, and a dimethoxyphenyl R group gives Methicillin -- illustrating how one common chemical …
Worked out. Drugs that share a common chemical skeleton are grouped together -- for example ampicillin, amoxicillin and methicillin all have the penicillin nucleus and are classed together as penicillins, just as opiates, steroids and catecholamines each form their own structural group. Compounds with similar chemical structure tend to share chemical properties, but this does not guarantee similar biological action: all penicillin-group drugs share one biological action, whereas structurally-grouped classes like barbiturates or steroids can have quite different …
Worked out. Drugs are grouped by the biological effect they produce in the recipient -- for instance every medicine able to kill pathogenic bacteria is grouped as an antibiotic (examples: amoxicillin, ampicillin, cefixime, cefpodoxime, erythromycin, tetracycline), while drugs that lower blood pressure are grouped as antihypertensives (propranolol, atenolol, metoprolol succinate, amlodipine). This grouping is useful clinically because it hands the physician the full range of drugs available for a given condition, from which a suitable one is chosen based on the patient' …
Worked out. Drugs are grouped by the biological system or process they act on in the recipient -- a more specific grouping than the pharmacological one. For example, the antibiotics streptomycin and erythromycin are grouped together because both target protein synthesis in bacteria, even though their exact mode of action differs: streptomycin blocks the initiation step of protein synthesis, while erythromycin blocks the incorporation of new amino acids into the growing protei …
Worked out. The most specific classification of all: drugs are grouped by the exact biomolecule -- an enzyme, receptor or other macromolecule -- that they bind to, i.e. their molecular "drug target". Because the target is identical, compounds in the same site-of-action group typically share a common underlying mechanism of action, which is why this section is followed immediately by a dedicated discussion of drug-target interaction (15.1.2). …