Schizophrenia is a chronic mental illness. Patients often present with hallucinations, delusions, disorganized thinking, emotional blunting, and abnormal behaviors. Pharmacological treatment is the cornerstone of the therapeutic process, as it can effectively control symptoms and reduce relapse.
First-Generation Antipsychotics (Typical Antipsychotics, Conventional Antipsychotics)
First-generation antipsychotics are the earliest medications used in the treatment of schizophrenia. They have been widely prescribed since the 1950s. Their primary mechanism of action is blocking dopamine D2 receptors in the brain, thereby reducing excessive dopamine activity that leads to hallucinations, delusions, and disorganized thought. Because dopamine plays a crucial role in the brain’s reward, emotional, and motor systems, these drugs are effective in controlling positive symptoms but are also prone to causing side effects.
Representative Medications
- Sulpiride (Dogmatil)
- Trifluoperazine (Stelazine)
- Pericyazine (Neulactil)
- Thioridazine (Melleril)
- Pimozide (Orap)
- Flupenthixol (Fluanxol) and its injectable form Flupenthixol Decanoate
- Zuclopenthixol (Clopixol) and its injectable form Zuclopenthixol Decanoate
- Haloperidol (Haldol) and its injectable form Haloperidol Decanoate
- Fluphenazine Decanoate (Modecate Depot)
Advantages
- Highly effective for positive symptoms such as hallucinations, delusions, and disorganized thinking.
- Long history of clinical use, with extensive physician experience.
- Relatively affordable compared to newer agents.
- Some medications are available in long-acting injectable forms, which improve adherence and reduce relapse.
Disadvantages and Side Effects
Because of their strong dopamine receptor blockade, these drugs often cause:
- Extrapyramidal side effects: muscle rigidity, tremors, akathisia (restlessness).
- Tardive dyskinesia: involuntary movements that may develop with long-term use.
- Anticholinergic side effects: dry mouth, constipation, blurred vision, urinary retention.
- Cardiovascular side effects: hypotension, arrhythmias.
Clinicians must balance efficacy with side effects and may prescribe adjunctive medications (such as the anticholinergic agent Trihexyphenidyl) to reduce adverse effects.
Comprehensive Guide to Second-Generation Antipsychotics
Second-generation antipsychotics (Atypical Antipsychotics, new-generation antipsychotics) have gradually replaced first-generation drugs since the 1990s, becoming the primary choice for treating schizophrenia. Their mechanism of action is not limited to blocking dopamine D2 receptors; they also modulate serotonin receptors. This dual regulation allows them to control positive symptoms (such as hallucinations, delusions, and disorganized thinking) while also exerting therapeutic effects on negative symptoms (such as emotional blunting and lack of motivation).
In terms of side effects, second-generation antipsychotics generally cause fewer extrapyramidal symptoms, such as muscle rigidity or tremors, compared to first-generation drugs. However, some agents may lead to metabolic abnormalities, including weight gain, elevated blood sugar, and lipid disturbances. Clinically, physicians must balance efficacy with side effects, tailoring medication choices to the patient’s physical condition, lifestyle, and adherence. With rational drug selection and regular monitoring, patients can achieve symptom control while maintaining a more stable and healthier life.
Amisulpride (Solian)
Mechanism of Action: Primarily blocks dopamine D2/D3 receptors, particularly effective for negative symptoms.
Advantages: Improves lack of motivation and emotional blunting; relatively mild side effects.
Disadvantages: May cause hyperprolactinemia, leading to menstrual irregularities or breast enlargement.
Aripiprazole (Abilify) and its injectable form (Abilify Maintena)
Mechanism of Action: Partial dopamine receptor agonist, suppresses excessive activity while providing stimulation when activity is low.
Advantages: Minimal weight gain, low metabolic side effects; long-acting injectable improves adherence.
Disadvantages: Some patients may experience agitation or insomnia.
Brexpiprazole (Rexulti)
Mechanism of Action: Similar to aripiprazole but with gentler activity, resulting in fewer side effects.
Advantages: Less agitation, good tolerability.
Disadvantages: Relatively new in clinical use, higher cost.
Clozapine (Clozaril)
Mechanism of Action: Acts on multiple receptors; considered the gold standard for treatment-resistant schizophrenia.
Advantages: Effective for patients unresponsive to other medications; reduces suicide risk.
Disadvantages: Requires regular blood monitoring to prevent agranulocytosis; may cause weight gain and sedation.
Indications: Treatment-resistant schizophrenia.
Lurasidone (Latuda)
Mechanism of Action: Acts on dopamine and serotonin receptors, with potential cognitive benefits.
Advantages: Low metabolic side effects, minimal weight gain.
Disadvantages: May cause anxiety or insomnia.
Risperidone (Risperdal) and its injectable form (Risperdal Consta)
Mechanism of Action: Blocks dopamine and serotonin receptors.
Advantages: Widely used, well-established efficacy; available in long-acting injectable form.
Disadvantages: May cause hyperprolactinemia and weight gain.
Paliperidone (Invega) and its injectable forms (Invega Sustenna, Invega Trinza, Invega Hafyera)
Mechanism of Action: Active metabolite of risperidone, providing more stable effects.
Advantages: Monthly or quarterly injectable options improve adherence.
Disadvantages: Side effects similar to risperidone, including elevated prolactin.
Olanzapine (Zyprexa)
Mechanism of Action: Acts on multiple receptors, providing broad efficacy.
Advantages: Effective for both positive and negative symptoms.
Disadvantages: Significant weight gain and high risk of metabolic abnormalities.
Quetiapine (Seroquel)
Mechanism of Action: Acts on dopamine and serotonin receptors, with sedative properties.
Advantages: Improves sleep and anxiety; relatively mild side effects.
Disadvantages: Prominent sedation, requires divided dosing.
Indications: Patients with comorbid insomnia or anxiety.
Ziprasidone (Zeldox)
Mechanism of Action: Blocks dopamine and serotonin receptors.
Advantages: Minimal weight gain, low metabolic side effects.
Disadvantages: May affect cardiac conduction (QT interval prolongation).
Indications: Patients concerned about weight gain or metabolic risks.
Side Effects and Special Risks of Second-Generation Antipsychotics
Although second-generation agents generally cause fewer side effects, clinicians must remain vigilant for:
- Metabolic abnormalities: weight gain, diabetes risk, dyslipidemia.
- Hyperprolactinemia: particularly with risperidone and paliperidone.
- Cardiac conduction abnormalities: especially with ziprasidone.
- Hematological risks: clozapine requires strict blood monitoring.
Side Effect Management and Monitoring
- Metabolic monitoring: regular checks of weight, blood glucose, and cholesterol.
- Prolactin testing: indicated if menstrual irregularities or breast changes occur.
- Cardiac evaluation: routine electrocardiograms for patients on ziprasidone.
- Blood tests: mandatory for patients on clozapine.
Second-generation antipsychotics have become the mainstream in clinical practice in Hong Kong, balancing efficacy with side effect management. Through rational drug selection, regular monitoring, and the use of long-acting injectables, patients can significantly reduce relapse and improve quality of life.
