Drug Interaction Report
1 potential interaction and/or warning found for the following 2 drugs:
- doxepin topical
- fosphenytoin
Interactions between your drugs
doxepin topical fosphenytoin
Applies to: doxepin topical, fosphenytoin
MONITOR: Tricyclic antidepressants may increase serum phenytoin levels. In vitro studies suggest the mechanism may involve inhibition of CYP450 2C19-catalyzed phenytoin p-hydroxylation by tricyclic antidepressants, especially imipramine and amitriptyline. Phenytoin may induce the hepatic metabolism of desipramine resulting in decreased plasma concentrations. In addition, tricyclic antidepressants may lower the seizure threshold.
MANAGEMENT: Clinical monitoring of patient response, tolerance, and serum phenytoin concentrations is recommended. Patients should be advised to notify their doctor if they experience loss of seizure control or symptoms of phenytoin toxicity (drowsiness, visual disturbances, change in mental status, nausea, or ataxia). Phenytoin dosage may need to be adjusted.
References (9)
- Fogel BS, Haltzman S (1987) "Desipramine and phenytoin: a potential drug interaction of therapeutic relevance." J Clin Psychiatry, 48, p. 387-8
- Houghton GW, Richens A (1975) "Inhibition of phenytoin metabolism by other drugs used in epilepsy." Int J Clin Pharmacol, 12, p. 210-6
- Perucca E, Richens A (1977) "Interaction between phenytoin and imipramine." Br J Clin Pharmacol, 4, p. 485-6
- Shin JG, Park JY, Kim MJ, et al. (2002) "Inhibitory effects of tricyclic antidepressants (TCAs) on human cytochrome P450 enzymes in vitro: mechanism of drug interaction between TCAs and phenytoin." Drug Metab Dispos, 30, p. 1102-7
- Cerner Multum, Inc. "UK Summary of Product Characteristics."
- Cerner Multum, Inc. "Australian Product Information."
- Agencia Española de Medicamentos y Productos Sanitarios Healthcare (2008) Centro de información online de medicamentos de la AEMPS - CIMA. https://cima.aemps.es/cima/publico/home.html
- Cerner Multum, Inc. (2015) "Canadian Product Information."
- Cerner Multum, Inc (2015) "ANVISA Bulário Eletrônico."
Drug and food interactions
No alcohol/food interactions were found with the drugs in your list. However, this does not necessarily mean no food interactions exist. Always consult your healthcare provider.
Therapeutic duplication warnings
No duplication warnings were found for your selected drugs.
Therapeutic duplication warnings are only returned when drugs within the same group exceed the recommended therapeutic duplication maximum.
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Drug Interaction Classification
| Highly clinically significant. Avoid combinations; the risk of the interaction outweighs the benefit. | |
| Moderately clinically significant. Usually avoid combinations; use it only under special circumstances. | |
| Minimally clinically significant. Minimize risk; assess risk and consider an alternative drug, take steps to circumvent the interaction risk and/or institute a monitoring plan. | |
| No interaction information available. |
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