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
Monitoring
- acetylcholinesterase inhibitor may increase gastric acid secretion, so patients should be monitored closely for GI bleeding, especially those receiving concurrent NSAID drugs.
- check body weight regularly
- monitor the cognitive, global functions, and ADL activities
- monitor the sleeping quality
Drug interaction
Hepatic metabolism of donepezil via the cytochrome P450 will be affected by drugs that inhibit the isoenzyme CYP3A4 and CYP2D6 Interactions do not generally apply to steroid used for topical action including inhalation, unless specified.
| Drugs given with donepezil | Potential Effect |
|---|---|
| CYP2D6 inhibitors:
SSRI, such as Paroxetine, Quinidine, Amitriptyline |
May increase plasma-donepezil concentration, increasing the risk of severe adverse reactions. |
| CYP3A4 inhibitors:
Erythromycin, Itraconazole, Ketoconazole |
May increase plasma-donepezil concentration, increasing the risk of severe adverse reactions |
| CYP3A4 inducers & CYP2D6 inducers:
Rifampicin, Phenytoin, Carbamazepine |
May reduce plasma-donepezil concentration |
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 9ml/minute. Patients with known hypersensitivity to galantamine hydrobromide
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
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 Galantamine be taken?
Galantamine comes in three forms: as 8mg and 12mg tablets; as Galatamine XL in 8mg, 16mg and 24mg prolonged release capsules; and as an oral solution 4mg/ml. Tablets and oral solution should be administered twice a day, preferably with morning and evening meals. Drink plenty of liquids to keep yourself hydrated.
What should I avoid while taking?
Avoid abruptly discontinue the medication.
What happen if I overdose?
Contact your primary care doctor. If emergency situation, call 999
What happen if I miss a dose?
Take it as soon as you remember. If it is near the time of the next dose, skip the missed dose. Take your next dose at the regular time. Do not double the dose to catch up.
