ADRs are best avoided as this acute neurological side effect is painful, frightening and, in the case of laryngeal dystonia, potentially life-threatening. Common presentations include dystonic contractions of the neck muscles, leading to the head pulled to the side (torticollis), and oculogyric crises (deviation of the eyes upwards). However, other muscle groups can be involved. The muscle contractions can be intermittent or lead to rather sustained postures; symptoms ADRs may also fluctuate and are often transient. A complaint of a swollen tongue is a common ADR complaint (pseudomacroglossia).
They almost always occur in antipsychotic-naïve patients, particularly young males or in patients otherwise sensitive to extrapyramidal side effects. An ADR is most likely to occur when treatment is initiated and can occur within a few hours after the first dose if an oral antipsychotic is given; the onset of an ADR can be quite delayed, by days or weeks, if treatment is initiated with a LAI. The clinical situation is usually obvious enough to make this diagnosis without the need for further work-up for other, unlikely conditions that can lead to dystonias (e.g., tetanus, focal seizures, strychnine poisoning, hypocalcemia).
- Prevention is better than treatment: most patients who had an ADR even many decades ago remember this experience, particularly if they had a severe reaction. Using prophylactic benztropine in high-risk patients (i.e., young, antipsychotic-naïve patient who are given an intramuscular first-generation antipsychotic) remains a common practice in the emergency room. However, the prophylactic use of anticholinergics is otherwise not recommended to prevent acute dystonic reactions when starting antipsychotics.
- An ADR requires recognition and urgent action. In general, patients should be evaluated in person and not just managed over the phone, particularly if the larynx is affected (dysphonia, stridor). Most people have diphenhydramine (Benadryl) at home that they should take immediately, before heading to the ED.
- In the emergency room or clinic, the parenteral administration of an anticholinergic (1 to 2 mg benztropine or 25-50 mg diphenhydramine) usually leads to rapid and complete resolution of the ADR. However, the dose may need to be repeated. Intravenous administration is preferred over intramuscular administration if diphenhydramine is used due to its faster action. IV administration is reserved for the emergency room.
- Do not forget to discharge patients from the ED with a prescription for an anticholinergic such as benztropine 2 mg twice daily. If a LAI was involved (e.g., loading dose strategy), the treatment may need to continue for several weeks.
- For patients who have been on an anticholinergic for more than one week, the agent should be withdrawn slowly (e.g., 1 mg benztropine or 25 mg diphenhydramine every 2 weeks) to avoid rebound effects (sleep disturbances, increased extrapyramidal symptoms).