Attention here is directed at those medications that cause diffuse disturbances of cerebral function manifested particularly by alterations in the level of consciousness. Coma is a common sequel to overdosage with various drugs, including hypnotics, sedatives, neuroleptics, antidepressants, anticonvulsants, and analgesics. Spontaneous and reflex ocular movements are typically impaired, even at an early stage, in barbiturate and phenytoin intoxication. Depending on the depth of coma, the corneal reflex may be lost, and painful stimuli to the trunk or extremities may lead to purposive movements, decorticate or decerebrate posturing, or absence of motor response. Flaccidity and hyporeflexia of the limbs are common, but spasticity, hyperreflexia, and extensor plantar responses are sometimes found.
Examination often reveals tremor, asterixis, and myoclonus in addition to mental disturbances.
Nystagmus may also be present, particularly when CNS depressant drugs or anticonvulsants have been taken. A similar clinical disturbance may result from withdrawal of certain medications, such as benzodiazepines or barbiturates. Some encephalopathies may be related to the infectious and neoplastic complications associated with immunosuppressive agents. Among other medications prescribed for the treatment of cardiac disorders, lidocaine and related agents may cause seizures, tremor, paresthesias, and confusional states. Calcium channel blockers, beta blockers, digoxin, and thiazide diuretics can also cause encephalopathies.