Antipsychotics and Dopamine Antagonists
One of the most well-documented causes of drug-induced trismus is the use of antipsychotic medications. These drugs primarily work by blocking dopamine receptors in the brain. However, this action can also affect the extrapyramidal system, which controls motor function. The resulting side effects are known as extrapyramidal symptoms (EPS) and can manifest as dystonia—involuntary muscle contractions or spasms—which can affect the muscles of the jaw and face, causing trismus.
- First-generation antipsychotics: Older or typical antipsychotics, such as haloperidol, phenothiazines (e.g., perphenazine, trifluoperazine), and zuclopenthixol, are more likely to cause EPS and, by extension, trismus.
- Second-generation antipsychotics: Atypical antipsychotics, like risperidone, aripiprazole, and paliperidone, have a lower risk of causing EPS but can still induce trismus, particularly at higher doses.
- Anti-nausea medications: Certain antiemetics with a similar pharmacological profile to antipsychotics, such as metoclopramide (Reglan) and prochlorperazine, are potent dopamine receptor blockers and are known to cause acute dystonic reactions, including trismus.
Antidepressants
While less common than with antipsychotics, certain antidepressants have been linked to trismus or severe jaw clenching, also known as bruxism, which can lead to trismus. The mechanism is thought to involve the modulation of serotonin and norepinephrine pathways, which can indirectly affect the dopamine system.
- Selective Serotonin Reuptake Inhibitors (SSRIs): Drugs such as fluoxetine, sertraline, and paroxetine have been reported to cause jaw stiffness and bruxism, which can present as trismus in some patients.
- Serotonin-Norepinephrine Reuptake Inhibitors (SNRIs): Some SNRIs, like venlafaxine and duloxetine, have also been associated with drug-induced dystonia and trismus, sometimes within the first few weeks of starting the medication.
Anesthetic Agents
The muscle relaxant succinylcholine is used during anesthesia to temporarily paralyze muscles for surgical procedures, including intubation. In some patients, particularly children, it can induce a phenomenon called masseter muscle rigidity (MMR) or severe trismus. This is a critical side effect, as it can be an early sign of malignant hyperthermia, a rare but life-threatening hypermetabolic condition. The sustained contraction of the masseter muscles makes it difficult or impossible to open the jaw.
Other Medications Linked to Trismus
A variety of other drugs can cause trismus, though the incidence and mechanism may vary.
- Chemotherapy drugs: Medications like capecitabine, oxaliplatin, and vinca alkaloids (vinflunine) have been associated with trismus in cancer patients, often due to their effect on nerves.
- Sympathomimetic stimulants: Stimulants like amphetamines can cause jaw clenching (bruxism) and lead to trismus over time.
Comparison of Trismus-Inducing Drug Classes
| Drug Class | Primary Mechanism | Common Examples | Onset of Action | Management Options |
|---|---|---|---|---|
| Antipsychotics / Dopamine Antagonists | Dopamine receptor blockade, leading to acute dystonia. | Haloperidol, risperidone, metoclopramide. | Rapid (acute dystonia), sometimes within days of starting or changing dose. | Discontinue drug, administer anticholinergic (procyclidine), benzodiazepines. |
| Antidepressants (SSRIs/SNRIs) | Serotonergic effects indirectly affecting dopamine; can cause bruxism. | Fluoxetine, sertraline, duloxetine. | Days to weeks after initiation or dose change. | Dose reduction, drug change, buspirone augmentation, mouthguard for bruxism. |
| Anesthetic Agents (e.g., Succinylcholine) | Depolarizing neuromuscular blockade, causing masseter muscle rigidity. | Succinylcholine. | Immediately after administration. | Suspend triggering agent, administer dantrolene if malignant hyperthermia is suspected. |
| Chemotherapy | Neurotoxicity. | Capecitabine, oxaliplatin. | Variable. | Symptomatic treatment, manage underlying cancer. |
Management of Drug-Induced Trismus
The most important step in managing drug-induced trismus is to recognize the adverse effect and identify the causative agent. In many cases, discontinuing the offending medication or adjusting the dosage can lead to a resolution of symptoms. For severe acute dystonic reactions, an anticholinergic medication like procyclidine or a benzodiazepine such as diazepam can be administered for rapid symptom relief.
Physical therapy and jaw exercises are also recommended for long-term management, especially if the trismus has led to prolonged muscle stiffness. Jaw-stretching devices may also be beneficial in some cases.
For anesthesia-related masseter muscle rigidity caused by succinylcholine, a rapid evaluation for malignant hyperthermia is necessary, and dantrolene should be administered promptly if indicated.
Additional strategies include resting the jaw, applying moist heat to the area, and adjusting diet to softer foods to reduce strain on the jaw muscles. Patients should always consult their healthcare provider before making any changes to their medication regimen.
For more detailed information on managing head and neck cancer side effects like trismus, you can consult resources like the OncoLink website.
What to Do If You Experience Trismus
First, contact your prescribing healthcare provider immediately to discuss your symptoms. Do not stop taking your medication abruptly unless advised, as this could have other serious consequences. Rest your jaw and avoid chewing gum or hard foods. Applying moist heat to the jaw area for 15-20 minutes at a time may help relax the muscles. For mild cases associated with jaw clenching, a mouthguard may be beneficial. If the trismus is severe and you have difficulty breathing, speaking, or swallowing, seek emergency medical attention.
Conclusion
Trismus, or lockjaw, can be a distressing side effect of various medications, most notably antipsychotics, certain antidepressants, and the anesthetic agent succinylcholine. The underlying mechanisms often involve disruptions in the brain's dopamine pathways, leading to extrapyramidal symptoms. Proper management depends on accurate identification of the causative drug and can include discontinuation, dosage adjustment, or administering specific antidotes like anticholinergics. Timely intervention, in consultation with a healthcare professional, is crucial for resolving the condition and preventing complications.
