The withdrawal syndromes after discontinuance of alcohol, barbiturates, benzodiazepines and other sedative drugs, such as chloral and paraldehyde, are all similar. The severity of a withdrawal reaction is largely determined by the daily dose, the duration of administration and the rate of fall of the drug levels after withdrawal, as well as the propensity of the individual patient. The time course of a withdrawal reaction is determined by the drug's clearance. Alcohol has a half-life of a few hours; withdrawal symptoms may develop within 6-8 hours of abstinence and convulsions in 12-48 hours. After discontinuance of short-or medium-acting barbiturates (half-life 8-40 hours) symptoms may develop in 1-3 days, followed by convulsions and delirium after 3-8 days. Symptoms and seizures may develop in the 1-10 days after withdrawal of benezodiazepines.
In patients with no prior history of epilepsy the types of seizures most commonly induced by drug withdrawal are generalized convulsions, but partial seizures are not uncommon if there is a focal cerebral lesion, or a previous history of partial seizures. Paroxysmal activity and photosensitivity may occur after barbiturate withdrawal in non-epileptics, more commonly in severe withdrawal reactions. Similar EEG changes may be seen after alcohol and benzodiazepine withdrawal, but photosensitivity does not appear to have been shown to be a feature of the benzodiazepine withdrawal syndrome.