====== N-acetyl cysteine (NAC) ======

**Definition:**  
*N-acetyl cysteine (NAC)* is a synthetic derivative of the amino acid L-cysteine. It serves as a precursor to **glutathione**, a key intracellular antioxidant, and has **mucolytic, antioxidant, anti-inflammatory**, and **neuroprotective** properties.

===== Mechanism of Action =====

  * **Glutathione precursor:** NAC provides cysteine for the synthesis of glutathione (GSH), enhancing cellular redox capacity.
  * **Mucolytic effect:** Breaks disulfide bonds in mucus glycoproteins, reducing viscosity.
  * **Antioxidant activity:** Scavenges free radicals and reactive oxygen species (ROS).
  * **Anti-inflammatory effect:** Modulates NF-κB and cytokine production.
  * **Neuroprotective properties:** May reduce oxidative stress and excitotoxicity in neurodegenerative and neuropsychiatric conditions.

===== Clinical Uses =====

^ Indication                             ^ Use/Effect                                                   ^
| **Acetaminophen overdose**           | Antidote—restores hepatic glutathione and prevents hepatotoxicity. |
| **Chronic respiratory diseases**     | Mucolytic agent in COPD, cystic fibrosis, bronchitis.         |
| **Psychiatric disorders**            | Investigated in schizophrenia, bipolar disorder, OCD.         |
| **Neurological disorders**           | Studied in Parkinson’s, Alzheimer’s, and traumatic brain injury. |
| **Contrast-induced nephropathy**     | Proposed renal protective effect (evidence inconclusive).     |

===== Dosage & Administration =====

  * **Oral:** Common in chronic use (e.g., 600–1800 mg/day).
  * **Intravenous:** High-dose protocols for acetaminophen toxicity.
  * **Inhaled (nebulized):** For mucolytic purposes.

===== Safety and Side Effects =====

  * Generally well tolerated.
  * May cause nausea, vomiting, diarrhea, or rare allergic reactions.
  * IV form may induce anaphylactoid reactions in sensitive individuals.

===== Research and Emerging Roles =====

  * **COVID-19:** Investigated for reducing oxidative stress and cytokine storm.
  * **Cancer:** Explored for its role in modulating redox-sensitive oncogenic pathways.
  * **Prophylactic use:** In chronic diseases involving oxidative stress and inflammation.

===== References =====
  * Samuni Y, et al. (2013). The chemistry and biological activities of N-acetylcysteine. *Biochim Biophys Acta*.
  * Millea PJ. (2009). N-acetylcysteine: multiple clinical applications. *Am Fam Physician*.