Local anaesthetics: pulling the plug on the signal
A nerve carries its message as an electrical wave, and that wave depends on sodium rushing in through voltage-gated sodium channels — a kind of ion channel. A local anaesthetic (lidocaine and its relatives) blocks those channels from the inside. No sodium influx, no wave, no signal: the nerve simply cannot fire. Injected near a nerve, it produces a numb, pain-free zone while the rest of the body stays fully awake. This is pure interruption of nociception along the wire — it does not touch consciousness at all.
Two practical quirks fall straight out of the chemistry. First, local anaesthetics work poorly in infected, inflamed tissue: the acidic environment shifts the drug toward its charged form, which crosses the nerve membrane badly — a real-world case of the pH partition idea. Second, they are often co-injected with adrenaline, which narrows local blood vessels so the anaesthetic is washed away more slowly, lasting longer and staying where it is needed. The danger is escape into the bloodstream: if too much reaches the heart and brain, it can block their sodium channels too, causing arrhythmias and seizures. Dose limits exist for exactly this reason.
Corticosteroids: shutting inflammation down from the top
Where an NSAID blocks one enzyme low in the inflammation pathway, a corticosteroid reaches further up and turns the whole programme down. These drugs are synthetic versions of the body's glucocorticoid hormone. They cross into the cell and bind a nuclear receptor; the receptor then travels into the nucleus and changes which genes are switched on and off. The net effect is broad: less of the enzymes that make prostaglandins and other inflammatory mediators, fewer inflammatory cells recruited, and a powerful, wide-ranging anti-inflammatory action. That is why steroids work on inflammation that NSAIDs barely dent — severe arthritis, asthma flares, autoimmune disease.
Like opioids, corticosteroids are tapered, not stopped abruptly: long use makes the body's own steroid factory go quiet, and it needs time to wake up again. Whenever you can, steroids are aimed locally — inhaled for asthma, injected into a single joint — to get the anti-inflammatory effect where it is wanted while sparing the rest of the body.