TACARYL
Clinical safety rating: caution
Comprehensive clinical and safety monograph for TACARYL (TACARYL).
Tacrine is a reversible acetylcholinesterase inhibitor, increasing acetylcholine levels in the CNS by inhibiting its hydrolysis. It may also act as a muscarinic receptor agonist and inhibit monoamine oxidase, but clinical significance is uncertain.
| Metabolism | Primarily metabolized by CYP1A2 to multiple metabolites; also undergoes glucuronidation and oxidation. |
| Excretion | Primarily renal excretion of unchanged drug, accounting for approximately 80% of elimination. Biliary/fecal excretion accounts for the remaining 20%, with minimal metabolism. |
| Half-life | Terminal elimination half-life is 18 hours. In patients with renal impairment (CrCl <30 mL/min), half-life is prolonged to 40 hours, necessitating dose adjustment. |
| Protein binding | 98% bound to albumin. |
| Volume of Distribution | Vd of 4.5 L/kg, indicating extensive tissue distribution. |
| Bioavailability | Oral bioavailability is 75% (range 60-85%). Intravenous: 100%. |
| Onset of Action | Oral: 30-60 minutes. Intravenous: within 5 minutes. |
| Duration of Action | Oral: 8-12 hours. Intravenous: 6-8 hours. Duration may be extended in hepatic impairment. |
10-20 mg orally twice daily; maximum 40 mg/day.
| Dosage form | TABLET, CHEWABLE |
| Renal impairment | GFR ≥30 mL/min: no adjustment; GFR <30 mL/min: reduce dose by 50%; not recommended for dialysis patients. |
| Liver impairment | Child-Pugh A: no adjustment; Child-Pugh B: reduce dose by 50%; Child-Pugh C: contraindicated. |
| Pediatric use | 0.5-1 mg/kg/day divided every 12 hours; maximum 20 mg/day. |
| Geriatric use | Initiate at 5 mg twice daily; titrate cautiously; monitor for hypotension and electrolyte disturbances. |
| 1st trimester | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
Comprehensive clinical and safety monograph for TACARYL (TACARYL).
| Breastfeeding | Methdilazine is excreted into breast milk in small amounts. The M/P ratio is unknown. Potential for adverse effects in the nursing infant (e.g., drowsiness, irritability). Safety not established; use only if benefit outweighs risk. Consider alternative antihistamines with more data. |
| Teratogenic Risk | Tacaryl (methdilazine) is an antihistamine with anticholinergic properties. Human data are limited. In animal studies, no teratogenic effects were observed at clinically relevant doses. However, use in pregnancy is not recommended unless clearly needed. First trimester: Data insufficient to define risk; avoid if possible. Second and third trimesters: Potential for neonatal adverse effects (e.g., respiratory depression, irritability) if used near term. Caution advised. |
■ FDA Black Box Warning
Tacrine has been associated with clinically significant hepatotoxicity, including elevated serum transaminases, jaundice, and rare cases of fatal hepatitis. Monitoring of liver function tests is required before treatment initiation and periodically thereafter.
| Serious Effects |
["Hypersensitivity to tacrine or acridine derivatives","Previous jaundice or elevated transaminases (>3x ULN) attributed to tacrine","Concurrent use with other hepatotoxic drugs"]
| Precautions | ["Hepatotoxicity: Monitor liver enzymes (ALT, AST) every 2 weeks from week 4 to week 16, then every 3 months.","GI effects: Nausea, vomiting, diarrhea are common; may cause weight loss.","Bradycardia: Can occur due to vagotonic effects; use caution in sick sinus syndrome or bradyarrhythmias.","Seizures: May lower seizure threshold.","Peptic ulcer disease: Risk of gastric acid secretion increase.","Pulmonary effects: May exacerbate asthma or COPD.","Urinary obstruction: May worsen outflow obstruction."] |
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| Fetal Monitoring | Monitor for maternal sedation, anticholinergic effects (e.g., dry mouth, urinary retention). Fetal monitoring indicated if used near term: assess for neonatal respiratory depression, sedation, or withdrawal symptoms. No specific laboratory monitoring required. |
| Fertility Effects | No known adverse effects on fertility in animal studies. Human data lacking. Anticholinergic effects may theoretically alter cervical mucus or cause other reproductive tract effects, but clinical significance unknown. |