Drug Nomenclature and Classification
Understanding how drugs are named and classified is fundamental to pharmaceutical science and pharmacy practice. For the SAPC examination, you must be comfortable with the various naming systems, the ATC classification framework, and the rationale behind pharmaceutical nomenclature of salts, esters, and derivatives.
Drug Naming Systems
Drugs can be identified by several different names. Mastery of all naming systems is required for safe dispensing and for answering SAPC examination questions on pharmaceutical chemistry.
Chemical Name
The chemical name describes the exact molecular structure of the drug substance. It is precise but often impractical for everyday use.
- Generated using IUPAC rules — follows systematic nomenclature
- Example: N-(4-hydroxyphenyl)acetamide = paracetamol (acetaminophen)
- Example: 2-(4-isobutylphenyl)propanoic acid = ibuprofen
Chemical names are used in pharmaceutical analysis, quality control, and regulatory documentation. In the SAPC context, you may encounter questions requiring you to interpret or name drug structures using IUPAC principles.
Generic (INN) Name
The International Nonproprietary Name (INN) is assigned by the World Health Organization (WHO) and provides a unique, universally accepted name for a drug substance.
- Goal: One INN per drug substance worldwide
- Format: Often reflects the pharmacologically important part of the molecule
- Examples: paracetamol, ibuprofen, metformin, amlodipine
- In South Africa: Generic names are used in the pharmacy setting; the Medicines and Related Substances Act (Act 101 of 1965, as amended) promotes generic substitution
Stem patterns in INNs:
| Stem | Meaning | Example |
|---|---|---|
| -lol | beta-blocker | atenolol, metoprolol |
| -pril | ACE inhibitor | enalapril, lisinopril |
| -sartan | ARB | losartan, valsartan |
| -statin | HMG-CoA reductase inhibitor | simvastatin, atorvastatin |
| -caine | local anesthetic | lignocaine, bupivacaine |
| -cillin | penicillin antibiotic | amoxicillin, piperacillin |
| -mycin | aminoglycoside/macrolide | gentamicin, erythromycin |
| -pril | ACE inhibitor | enalapril, lisinopril |
| -mazole | antifungal (azoles) | fluconazole, miconazole |
Brand (Trade) Name
The brand name (proprietary or trademark name) is assigned by the pharmaceutical company and protected as intellectual property.
- Company-assigned — varies by manufacturer
- Example: “Panado” (Aspen) contains paracetamol; “Adco-Paracetamol” also contains paracetamol
- Format: Often chosen for marketing appeal, ease of recall, or therapeutic暗示
- In South Africa: Multiple brands may contain the same active ingredient — pharmacists must be able to identify equivalents
Important: Different brands containing the same active ingredient are considered generically equivalent unless a clinical difference is documented (e.g., modified-release formulations, poorly soluble drugs with bioequivalence concerns).
The ATC Classification System
The Anatomical Therapeutic Chemical (ATC) classification system is the gold standard for drug classification internationally and is used extensively in pharmaceutical science and clinical practice. SAPC expects you to understand its structure and application.
Structure of ATC Codes
An ATC code has 7 characters organized in a hierarchical system:
Level 1: Anatomical main group (1 letter)
Level 2: Therapeutic main group (2 digits)
Level 3: Therapeutic/pharmacological subgroup (1 letter)
Level 4: Chemical/therapeutic/pharmacological subgroup (2 digits)
Level 5: Chemical substance (2 digits)Example — Metformin: A10BA02
| Position | Level | Meaning |
|---|---|---|
| A | 1st level | Alimentary tract and metabolism |
| 10 | 2nd level | Antidiabetic therapy |
| B | 3rd level | Blood glucose lowering drugs |
| A | 4th level | Biguanides |
| 02 | 5th level | Metformin (sequential numbering of substances within the group) |
Anatomical Main Groups
| Code | Anatomical Group |
|---|---|
| A | Alimentary tract and metabolism |
| B | Blood and blood forming organs |
| C | Cardiovascular system |
| D | Dermatologicals |
| G | Genito-urinary system and sex hormones |
| H | Systemic hormonal preparations (excl. sex hormones) |
| J | Anti-infectives for systemic use |
| L | Antineoplastic and immunomodulating agents |
| M | Musculoskeletal system |
| N | Nervous system |
| P | Antiparasitic products, insecticides, and repellents |
| R | Respiratory system |
| S | Sensory organs |
| V | Various |
SAPC Examination Note
Questions on ATC classification may ask you to identify the therapeutic group of a drug given its code, or to determine whether two drugs with similar names belong to the same pharmacological class.
Pharmaceutical Nomenclature of Salts and Esters
Many drug substances are formulated as salts or esters to improve their physicochemical properties — solubility, stability, bioavailability, or taste.
Salt Naming
The general format is: Active moiety + salt form
| Salt type | Naming convention | Example |
|---|---|---|
| Hydrochloride | - hydrochloride | metformin hydrochloride |
| Sulphate | - sulphate | quinine sulphate |
| Sodium | - sodium | amoxicillin sodium |
| Potassium | - potassium | furosemide potassium |
| Calcium | - calcium | cefotaxime calcium |
| Mesilate (methanesulphonate) | - mesilate | haloperidol mesilate |
Key points for pharmacy practice:
- The salt form can affect bioavailability — e.g., doxycycline hyclate vs doxycycline base
- In dispensing, the salt form must be specified on the prescription
- Different salts may have different storage requirements
Ester Naming
Esters are named using the acyl group followed by the parent alcohol: e.g., acetyl-salicylic acid (aspirin), benzyl penicillin (penicillin G).
Ester prodrugs are inactive compounds that are metabolically converted to the active drug. The ester designation in the name (e.g., -pril → fosphenytoin is not a prodrug but a phosphate ester of phenytoin) gives a clue to the metabolic activation step.
SAPC Examination Note
Questions frequently test the relationship between a drug’s chemical name, its salt form, and its therapeutic use. Be sure you can identify:
- The pharmacologically active moiety
- The salt or ester component
- Why the salt/ester form was chosen
Drug Classification by Legal Status
For the SAPC examination, you must know South Africa’s scheduling system:
| Schedule | Description | Examples |
|---|---|---|
| Schedule 0 | General sale — no prescription needed | Certain multivitamins, basic analgesics |
| Schedule 1 | Prescription medicine — pharmacist-initiated | Some antihypertensives, oral hypoglycemics |
| Schedule 2 | Pharmacist-only medicine | Chlorpheniramine, certain NSAIDs |
| Schedule 3 | Prescription only — controlled dispensing | Benzodiazepines, certain opioids |
| Schedule 4 | Prescription only medicine | Most prescription drugs |
| Schedule 5 | Controlled substances — permit required | Cocaine, amphetamine derivatives |
| Schedule 6 | Dangerous drugs — custody of practitioner | Opium, cannabis |
| Schedule 7 | Unlawful possession — prohibitted | Heroin, methaqualone |
| Schedule 8 | Abuse potential — registers maintained | Methylphenidate, certain opioids |
Critical distinction for pharmacy practice: The schedule determines what can be dispensed without a prescription and whether record-keeping requirements apply. Schedule 5 and above require permits; Schedule 8 drugs require a register.
Drug Classification by Pharmacological Action
Classification by Mechanism of Action
| Class | Mechanism | Example |
|---|---|---|
| Agonist | Activates receptor | Morphine (μ-opioid agonist) |
| Antagonist | Blocks receptor | Naloxone (opioid antagonist) |
| Partial agonist | Submaximal activation | Buprenorphine (partial μ agonist) |
| Inverse agonist | Negative constitutive activity | Hydroxyzine (H1 inverse agonist) |
| Enzyme inhibitor | Blocks enzyme activity | Captopril (ACE inhibitor) |
| Channel blocker | Blocks ion channels | Verapamil (Ca²⁺ channel blocker) |
| Reuptake inhibitor | Blocks neurotransmitter reuptake | Fluoxetine (SSRI) |
SAPC Examination Tips
- INN vs brand names — SAPC questions often present a scenario where a patient brings a brand name and you must identify the generic drug. Practice converting between brand and generic names for common medications on the South African market.
- ATC codes — Be able to decode an ATC code to determine the anatomical system and therapeutic group. In practice, this helps with drug information retrieval and identifying interactions.
- Scheduling — Know the scheduling system thoroughly. Questions frequently involve determining whether a particular drug requires a prescription or can be dispensed OTC.
- Salt forms — Always check the salt when identifying drugs — ” Atenolol” and “atenolol 100mg tablets” may need to be distinguished from “atenololchlorthalidone” combination products.
- Stem recognition — Learning pharmacological stems (-olol, -pril, -statin, -caine, etc.) will help you identify drug classes rapidly in the exam and in practice.
- Generic substitution — Understand the legal and scientific basis for generic substitution in South Africa. Know when a generic may or may not be substituted (e.g., narrow therapeutic index drugs, modified-release products).
Common Examination Trap
Students frequently confuse trade/brand names with generic names. The SAPC consistently uses generic nomenclature in pharmaceutical science questions. Always practice answering questions using the INN or chemical name, not the brand name. For example, Panado® is NOT a drug name — paracetamol is the correct drug name.