1. Clinical Overview
Glutathione (GSH) is a tripeptide thiol (γ-L-glutamyl-L-cysteinylglycine) that serves as the body's primary endogenous antioxidant and detoxifying agent. In the Indian pharmaceutical context, oral formulations of 600mg are widely marketed as dietary supplements and adjunctive therapy for various conditions related to oxidative stress, liver health, and skin lightening. Its clinical efficacy via oral route is debated due to significant first-pass metabolism, but it remains a popular OTC choice.
| Onset | Duration | Bioavailability |
|---|---|---|
| Peak plasma concentrations (Tmax) for oral reduced glutathione are typically observed within 1 to 2 hours post-administration, but systemic antioxidant effects may take several days to weeks of consistent dosing to manifest clinically. | The elimination half-life is short (approx. 10-15 minutes for free GSH), but its indirect effects on cellular redox balance and enzyme systems can persist, necessitating multiple daily doses or sustained-release formulations for maintained effect. | Oral bioavailability of reduced glutathione is very low, estimated to be less than 10% in some studies, due to extensive hydrolysis by intestinal and hepatic gamma-glutamyl transpeptidase (GGT) and dipeptidases. Liposomal, sublingual, or acetylated forms claim higher bioavailability. |
2. Mechanism of Action
Glutathione (GSH) is the most abundant intracellular non-protein thiol. It functions as a critical redox buffer, maintaining the reduced state of cellular components. It directly neutralizes reactive oxygen species (ROS) like hydrogen peroxide, hydroxyl radicals, and peroxynitrite via the glutathione peroxidase (GPx) reaction, where GSH is oxidized to glutathione disulfide (GSSG). GSSG is then reduced back to GSH by glutathione reductase (GR), using NADPH. It also conjugates with xenobiotics, toxins, and carcinogens (Phase II detoxification), forming mercapturates excreted in bile and urine. It regenerates other antioxidants like vitamins C and E.
3. Indications & Uses
- Adjunctive therapy in non-alcoholic fatty liver disease (NAFLD) and alcoholic liver disease
- As an antioxidant supplement in conditions of increased oxidative stress
- Supportive therapy in drug-induced hepatotoxicity (e.g., antitubercular drugs, chemotherapy)
4. Dosage & Administration
Adult Dosage: 600mg to 1200mg per day, divided into two or three doses (e.g., 600mg once or twice daily). Often taken on an empty stomach for better absorption, though evidence is mixed.
Administration: Oral tablet/capsule. Should be taken with a full glass of water. For potential better absorption, it is often recommended to take on an empty stomach, 30 minutes before meals or 2 hours after meals. Avoid taking with high-protein meals simultaneously as it may compete for absorption.
5. Side Effects
Common side effects may include:
- Generally well-tolerated. Rarely, mild gastrointestinal discomfort, bloating, or flatulence.
6. Drug Interactions
| Drug | Effect | Severity |
|---|---|---|
| Chemotherapy drugs (e.g., Cisplatin, Doxorubicin) | Theoretical: May reduce efficacy of certain chemotherapies that rely on oxidative stress for cytotoxicity. However, it may also protect against chemotherapy-induced toxicity. Evidence is conflicting and context-dependent. | Major - Requires medical supervision. |
| Acetaminophen (Paracetamol) | Glutathione is crucial in detoxifying N-acetyl-p-benzoquinone imine (NAPQI), the toxic metabolite of acetaminophen. Supplementation may support liver protection in overdose but does not replace N-acetylcysteine (NAC) as the antidote. | Moderate |
| Immunosuppressants (e.g., Cyclosporine, Tacrolimus) | Theoretical concern that by modulating lymphocyte function, it may alter immunosuppression. Clinical significance for oral doses is unknown. | Moderate |
7. Patient Counselling
- DO take consistently as directed, as effects are cumulative.
- DO store in a cool, dry place away from light and moisture.
- DO inform your doctor about all supplements you are taking.
- DONT take double doses to make up for a missed dose.
- DONT use oral glutathione as a substitute for a balanced diet.
- DONT expect immediate results; skin lightening effects, if any, may take 2-3 months.
8. Toxicology & Storage
Overdose: No well-documented cases of acute oral overdose. Theoretical symptoms based on mechanism could include nausea, vomiting, abdominal pain, and diarrhea due to osmotic and gastrointestinal effects of a large peptide load.
Storage: Store below 30°C, in a cool, dry place. Protect from light and moisture. Keep the container tightly closed. Keep out of reach of children.