|
|
|
|
|
|
|
Medical Pharmacology Chapter 16: Pharmacology of Antipsychotics Drugs
|
|
|
|
|
|
|
Special Topics in Antipsychotic Pharmacotherapy
Emerging Biological Treatments
Transcranial Magnetic Stimulation (TMS)
Repetitive TMS (rTMS) applied to the left dorsolateral prefrontal cortex (DLPFC) has been the most widely studied neurostimulation approach for negative symptoms.
The rationale rests on hypoactivation of the DLPFC in patients with prominent negative symptoms.
Multiple RCTs and meta-analyses report significant reductions in negative symptom severity, though effect sizes are moderate (SMD ~ 0.5), studies are often small, and blinding is imperfect.
A 2020 meta-analysis across 26 RCTs concluded that rTMS produced clinically meaningful improvement in approximately 40–50% of treated patients.
[Knegering R Aleman A De Lange D Repetitive Transcranial magnetic Stimulation for Negative Symptoms of Schizophrenia: Review and Meta-Analysis. J Clin Psychiatry 2010; 71(4): 411-418. https://www.psychiatrist.com/jcp/repetitive-transcranial-magnetic-stimulation-negative/]
Several parameter questions remain unresolved: optimal stimulation frequency (10Hz vs. theta-burst protocols), number of sessions, coil placement accuracy, and patient selection.
The development of neuronavigation-guided TMS, targeting DLPFC identified on individual neuroimaging, may improve response rates.
This is a technically evolving area where early positive results warrant cautious optimism rather than clinical confidence.
Transcranial Direct Current Stimulation (tDCS)
tDCS is lower-cost and more portable than TMS and has been investigated for cognitive and negative symptom benefit.
Anodal stimulation of the DLPFC produces neuromodulatory effects through sustained depolarisation.
The evidence base is smaller than for TMS and meta-analytic conclusions are more cautious, but several high-quality RCTs have reported significant improvements in working memory and modest effects on alogia and blunted affect.
Combined tDCS with cognitive training ('stimulation-enhanced learning') may enhance CR outcomes.
[Mervis J Capizzi R Boroda E MacDonald III Transcranial Direct Current Stimulation over the Dorsolateral Prefrontal Cortex in Schizophrenia: A Quantitative Review of Cognitive Outcomes. Frontiers in Human Neuroscience. February 1, 2017. Sec. Brain Imaging in Stimulation. Volume 11. https://www.frontiersin.org/journals/human-neuroscience/articles/10.3389/fnhum.2017.00044/full]
Phosphodiesterase 10A (PDE10A) inhibitors initially generated excitement as a mechanistically novel approach, targeting striatal signalling pathways implicated in reward processing.
However, pivotal Phase II and III trials failed to separate from placebo on negative symptom outcomes, a pattern depressingly familiar in this area.
Oxytocin enhances social cognition and prosocial behaviour in healthy volunteers.
Intranasal oxytocin has been trialled in schizophrenia with modest, inconsistent results.
The blood-brain penetration of intranasal oxytocin is disputed, and the therapeutic window may be narrow.
Newer oxytocin receptor agonists with better CNS penetration are in early-phase development.
[Feifel D Macdonald K Nguyen A Lefebvre M Gonzales J Hadley A et al. Adjunctive Intranasal Oxytocin Reduces Symptoms in Schizophrenic patients. Biological Psychiatry. Volume 68, Issue 7, 678-680. October 1, 2010. https://www.biologicalpsychiatryjournal.com/article/S0006-3223(10)00479-8/abstract]
Muscarinic agonists.
The recent approval of KarXT (xanomeline-trospium) for schizophrenia marks the first novel mechanism introduced in decades.
As an M1/M4 muscarinic agonist, it acts entirely outside the dopamine pathway.
Phase III data demonstrate significant improvements in both positive and negative symptoms.
Whether effects on negative symptoms reflect genuine primary efficacy or secondary benefit from positive-symptom reduction requires further investigation, but this represents one of the most genuinely promising pharmacological developments for the field.
[Brannan S Sawfchak S Miller A Lieberman J Paul S Breiser A Muscarinica: review Receptor Antagonist in Peripheral Antagonist for Schizophrenia. N Engl J Med 2021; 384 : 717-726. https://www.nejm.org/doi/10.1056/NEJMoa2017015]
Integrated and Stepped-Care Approaches
The complexity of profound negative psychosis argues strongly against single-modality treatment.
The most compelling treatment philosophy is one of systematic integration across pharmacological, psychological, and social domains, sequenced according to individual patient assessment.
First-episode psychosis programs which deliver early, assertive, multimodal intervention have demonstrated that preventing the consolidation of secondary negative symptoms can improve long-term trajectories.
The NAVIGATE programme and the RAISE Early Treatment Program in the United States represent the most rigorous integrated treatment models, combining coordinated antipsychotic management, supported employment and education, family psychoeducation, and individual CBTp.
Two-year outcomes showed significantly better quality-of-life gains compared with standard community care, particularly for those with shorter duration of untreated psychosis.
[Kane J Robinson D Schooler N Mueser K Penn D Rosenheck R Addington J et al and Heinssen R Comprehensive Versus Usual Community Care for First-Episode Psychosis: 2-Year Outcomes NIMH From the NIMH RAISE Early Treatment Program. The American Journal of Psychiatry. Volume 173, Number 4.https://psychiatryonline.org/doi/10.1176/appi.ajp.2015.15050632]
For patients with established, chronic deficit-state negative symptoms, stepped-care models prioritize:
(1) ensuring antipsychotic treatment is optimized or switched to clozapine if indicated;
(2) screening for and treating secondary causes such as depression, EPS, institutionalism
(3) maximizing environmental enrichment and structured activity;
(4) initiating targeted psychological work where engagement is achievable; and
(5) considering neurostimulation in partial responders.
This hierarchy is not universal as clinical judgement must account for individual patient capacity, preference, and context.
Critical Challenges and Honest Uncertainties
The treatment of profound negative psychosis confronts clinicians with a range of inter-related challenges that no single treatment approach has resolved:
Measurement heterogeneity
The field uses over twenty rating scales for negative symptoms, with inconsistent domains and scoring, making cross-trial comparison unreliable.
The PANSS Negative Subscale, SANS, BNSS, and CAINS all capture overlapping but non-identical constructs, and none is accepted as a universal gold standard.
Placebo response
Negative symptom trials suffer from high and variable placebo response rates, particularly where secondary symptoms are admitted alongside primary ones.
This inflates placebo arms and reduces the chance of detecting true drug signals.
Patient engagement
The very symptoms under treatment, avolition, alogia, asociality compromise patients' ability to engage with and sustain psychological interventions.
Trial retention in this population is chronically poor.
Therapeutic optimism must be balanced against realistic appraisal of what engagement is achievable.
Therapeutic nihilism
Clinician pessimism about the treatability of negative symptoms has historically led to under-referral for psychological and social interventions and over-reliance on pharmacology alone.
This constitutes a form of iatrogenic harm.
Translational failure
Animal models of negative symptoms, largely based on pharmacological induction or genetic manipulation, have poor predictive validity for human trials.
Multiple promising agents have failed in Phase II/III due to this translational gap.
[Blanchard J Cohen A The Structure of Negative Symptoms Within Schizophrenia: Implications for Assessment. Schizophrenia Bulletin, Volume 32, Issue 2, April 2006, 238-245. https://academic.oup.com/schizophreniabulletin/article-abstract/32/2/238/1897273?redirectedFrom=fulltext]
It must also be acknowledged that the clinical category 'profound negative psychosis' does not map cleanly onto a single neurobiological entity.
Heterogeneity within this grouping in terms of genetic architecture, premorbid functioning, comorbidities, illness trajectory, and social history means that treatment response will always be variable.
Precision psychiatry approaches, utilising biomarkers, neuroimaging, and genetic stratification, aim to identify treatment-responsive subgroups, but this aspiration remains largely unrealised in clinical practice.
[Insel T The NIMH Reserved Domain Criteria (RDoC) Project: Precision Medicine for Psychiatry. American Journal of Psychiatry. Volume 171, Number 4. April 1, 2014.https://psychiatryonline.org/doi/10.1176/appi.ajp.2014.14020138]
Profound negative psychosis remains among the most clinically challenging conditions in all of medicine.
No treatment reliably produces large, durable reductions in primary negative symptoms, and intellectual honesty demands that this be communicated clearly to patients and families while simultaneously maintaining therapeutic engagement and hope.
Several principles emerge from this critical review.
Secondary negative symptoms should always be actively assessed and treated before concluding that symptoms are primary and fixed.
Pharmacological treatment should be optimized, with clozapine trialed where appropriate and cariprazine considered in those with predominant negative symptomatology.
Adjunctive strategies remain empirically weak, though adjunctive antidepressants have a defensible evidence base for secondary symptom overlap.
Psychological and social interventions, especially those targeting motivational and reward systems, supported employment, and family psychoeducation should be integrated into care regardless of anticipated pharmacological response.
Neurostimulation approaches deserve consideration in treatment-resistant cases, with rTMS the most evidenced option.
The emergence of novel mechanisms particularly muscarinic receptor agonism with KarXT and advancing neurostimulation protocols offers the most credible grounds for cautious optimism in recent years.
However, the track record of this field demands epistemic humility: treatments that appear promising in early trials have repeatedly disappointed in larger, more rigorous studies.
Progress may ultimately depend less on any single breakthrough than on sustained investment in integrated, personalised, multi-domain care and on the willingness of systems to fund and deliver it.
|
|
|
|
|
|
 |
|
DISCLAIMER
|
