Learning Objective
By the end of this section, learners will be able to identify common neurologic adverse drug reactions, associate them with their causative agents, and apply these associations to USMLE Step 1–style clinical vignettes.
| Neurologic Reaction | Causal Agents | Key Clinical Features / Notes |
|---|---|---|
| Cinchonism | Quinidine, quinine | Tinnitus, hearing loss, visual disturbances, headache, nausea, psychosis, cognitive impairment |
| Parkinson-like syndrome (drug-induced parkinsonism) | Antipsychotics, metoclopramide | Bradykinesia, rigidity, resting tremor; classic cogwheel rigidity on exam |
| Peripheral neuropathy | Platinum agents (eg, cisplatin), isoniazid, vincristine, paclitaxel, phenytoin | Stocking–glove sensory loss, paresthesias, pain; isoniazid neuropathy prevented with vitamin B₆ (pyridoxine) |
| Idiopathic intracranial hypertension (pseudotumor cerebri) | Corticosteroids (withdrawal), danazol, vitamin A, growth hormone, tetracyclines | Headache, papilledema, transient visual obscurations; ↑ intracranial pressure with normal imaging |
| Seizures | Isoniazid, bupropion, imipenem/cilastatin, tramadol | Lowered seizure threshold; INH-related seizures respond to pyridoxine |
| Tardive dyskinesia | Antipsychotics, metoclopramide | Late-onset, involuntary choreoathetoid movements (eg, lip smacking, tongue protrusion); often irreversible |
| Visual disturbances | Topiramate, hydroxychloroquine, digoxin, isoniazid, ivabradine, PDE-5 inhibitors, ethambutol | – Topiramate: blurred vision, diplopia, halos – Hydroxychloroquine: ↓ visual acuity, visual field defects – Digoxin: yellow-tinged vision – Ethambutol: optic neuritis, red–green color vision loss |
USMLE Step 1 Pearl
- Dopamine blockade (antipsychotics, metoclopramide) → Parkinsonism & tardive dyskinesia
- INH → seizures & peripheral neuropathy (treat/prevent with vitamin B₆)
- Tetracyclines + vitamin A → pseudotumor cerebri
- Ethambutol → color vision changes (red–green)
