Pharmacology
Analgesia and anaesthesia
Pain and anaesthesia medicines are grouped by where they interrupt the pain pathway: at the peripheral inflammatory source, along the conducting nerve, or centrally at the opioid receptor. That location predicts both the usefulness of a drug and the harm it can do.
7 classes across 4 mechanism families.
1. Opioid analgesics
These medicines act at mu, kappa and delta opioid receptors to reduce pain perception. Respiratory depression, tolerance and dependence are properties of the mechanism itself.
- Opioid analgesics — Mu receptor agonists; respiratory depression, tolerance and dependence follow directly from the mechanism.
2. Non-opioid analgesics
These medicines relieve pain without acting at opioid receptors, mostly by inhibiting cyclo-oxygenase or by mechanisms that remain incompletely characterised.
- NSAIDs, including COX-2 selective agents — Cyclo-oxygenase inhibitors; gastrointestinal, renal and cardiovascular risk define their limits.
- Paracetamol and other non-opioid analgesics — Safe at licensed doses and hepatotoxic above them; the mechanism remains incompletely established.
3. Anaesthetic and neuromuscular agents
These agents produce loss of sensation, loss of consciousness or skeletal muscle paralysis, and are used almost exclusively in monitored settings.
- General anaesthetics — Intravenous and inhalational agents producing reversible loss of consciousness.
- Local anaesthetics — Sodium channel blockers acting on conduction; systemic toxicity is the critical hazard.
- Neuromuscular blockers — Depolarising and non-depolarising paralytic agents used only with airway control.
4. Neuropathic pain agents
These medicines act on neuronal excitability rather than on inflammation, which is why conventional analgesics work poorly in nerve-related pain.
- Gabapentinoids and neuropathic pain agents — Alpha-2-delta ligands and related agents; misuse potential and opioid interaction matter.
Studying this the efficient way
Learn the mechanism family first, then the classes inside it. Almost every exam question about spectrum, adverse effects or resistance is really a question about which mechanism a drug belongs to. Each class page ends with a 60-second revision block and the traps students most often fall for.