Galantamine
Drug class: Acetylcholinesterase Inhibitor
Galantamine (REMINYL)(中文: 加蘭他敏) is a reversible inhibitor of acetylcholinesterase. It also has an intrinsic action on nicotinic receptors. It is used for the treatment of mild to moderate dementia in Alzheimer’s disease.
Common Strengths of Galantamine
- Extended-Release Capsules: 8 mg, 16 mg, 24 mg.
Drug Trade Names
- Reminyl Prolonged release (Extended Release)
Drug Usage
Galantamine is primarily prescribed for:
- Mild to moderate dementia associated with Alzheimer's disease.
- Cognitive impairment in conditions like Down syndrome and vascular dementia.
Mechanism of Action
Galantamine act as an acetylcholinesterase inhibitor, preventing the breakdown of acetylcholine, thereby increasing the concentration of acetylcholine in the brain, which is crucial for memory and cognitive functions.
Route of Administration
Galantamine is administered orally in various forms:
- Oral
Dosage
Initial: 8 mg/day; Maintenance: 16 to 24 mg/day
Side Effects
| Frequency | Adverse reactions |
|---|---|
| Common Side Effects | Nausea |
| Vomiting | |
| Diarrhea | |
| Dizziness | |
| Loss of appetite | |
| Serious Side Effects | Severe allergic reactions (e.g. rash, difficulty breathing) |
| Slow heart rate, chest pain, or irregular heart rhythms, which could lead to fainting or cardiac arrest. Patients with pre-existing heart conditions should be monitored closely. | |
| Seizures | |
| Urinary retention | |
| Gastrointestinal bleeding (symptoms such as tarry stools, or vomiting that resembles coffee grounds) |
Pharmacokinetics
Galantamine has:
- Absorption: Approximately 90% bioavailability.
- Onset Time: Effects typically observed within an hour post-administration.
- Time to Peak Concentration (Tmax): After oral administration, galantamine reaches peak plasma approximately 4 hours for extended-release formulations.
- Metabolic Pathways: Approximately 75% of galantamine is metabolized in the liver primarily by cytochrome P450 enzyme CYP2D6 and CYP3A4.
- Genetic Variability: There are genetic variations affecting metabolism, particularly involving CYP2D6. Poor metabolizers may experience higher plasma concentrations and prolonged effects of galantamine compared to extensive metabolizers.
- Half-Life: The elimination half-life of galantamine ranges from about 7 to 8 hours, allowing for twice-daily dosing in clinical practice.
Drug Precautions
Pregnancy
It is generally advised that galantamine should be avoided during pregnancy unless necessary due to potential risk to fetal development.
Breastfeeding
Du to the lack of data, galantamine is typically not recommended for breastfeeding women unless the benefits outweigh the risks.
Children and Elderly
Galantamine is generally not recommended for children due to limited safety data. In elderly patients, dosing should be cautions due to increased sensitivity and potential for side effects.
Hepatic Impairment
- No dose adjustment of galantamine is necessary in mild hepatic impairment.
- For immediate-release tablet, in moderate impairment, initially 4mg once daily, preferably in the morning, for at least one week, then 4 mg twice daily for at least 4 weeks. Maximum 8 mg twice daily. Avoid in severe impairment
- For modified-release capsules in moderate impairment, initially 8 mg on alternate days, preferably in the morning for 1 week, then 8 mg once daily for 4 weeks. Maximum 16 mg daily. Avoid in severe impairment
Renal Impairment
- No dose adjustment is necessary for galantamine in mild or moderate renal impairment.
- Avoid if eGFR less than 9ml/minute/1.73m2
Drug Monitoring Items
Monitoring should include:
- Heart rate and rhythm (due to potential bradycardia)
- Weight monitoring: galantamine may contribute to weight loss
- Renal function (especially in those with kidney disease)
- Signs of gastrointestinal distress or allergic reactions.
- Cognitive assessments to evaluate the effectiveness of treatment and monitor for adverse effects
Drug Interactions Galantamine may interact with:
- Other cholinesterase inhibitors (increased risk of side effects)
- Anticholinergic medications (may reduce effectiveness)
- Medications affecting heart rhythm (increased risk of bradycardia)
Caution
- Cardiovascular conduction disorders such as sick-sinus syndrome
- Susceptibility to peptic ulcers
- Asthma, chronic obstructive pulmonary disease
- People who have a predisposition to seizures
- Concomitant antipsychotic treatment
- Increased risk of neuroleptic malignant syndrome
Contraindications
- Patients with severe impairment (creatinine clearance less than 9 mL/minute)
- Patients with known hypersensitivity to galantamine hydrobromide
Effects on ability to drive and use machinery
Donepezil can cause fatigue, dizziness and muscles, mainly when initiating or increasing the dose. The treating doctor should routinely evaluate the ability of patients on donepezil to continue driving or operating complex machines.
FAQ
How Should I Take the Tablet?
Take galantamine with food to minimize gastrointestinal upset.
What Should I Avoid While Taking?
Avoid alcohol and medications that can further lower heart rate on affect cognitive function without consulting your healthcare provider.
What Happens if I Miss a Dose?
If you miss a dose, take it as soon as you remember unless it is close to the time for your next dose. Do not double up on doses.
