| Identification | More | [Name]
5,5-Diphenylhydantoin | [CAS]
57-41-0 | [Synonyms]
5,5-DIPHENYL-2,4-IMIDAZOLIDINEDIONE
5,5-DIPHENYLHYDANTHOIN
5,5-DIPHENYLHYDANTOIN
DIPHENYLHYDANTOIN
LABOTEST-BB LT00159593
PHENYTION
PHENYTOIN
PHENYTOIN BASE
2,4-Imidazolidinedione, 5,5-diphenyl-
5,5-diphenyl-hydantoi
5,5-Diphenylimidazolidin-2,4-dione
5,5-Dwufenylohydantoina
Aleviatin
Antisacer
Causoin
Citrullamon
Citrulliamon
Comital
Comitoina
component of Mebroin | [EINECS(EC#)]
200-328-6 | [Molecular Formula]
C15H12N2O2 | [MDL Number]
MFCD00005264 | [Molecular Weight]
252.27 | [MOL File]
57-41-0.mol |
| Chemical Properties | Back Directory | [Appearance]
Phenytoin is a crystalline compound | [Melting point ]
293-295 °C (lit.) | [Boiling point ]
395.45°C (rough estimate) | [density ]
1.1562 (rough estimate) | [refractive index ]
1.5906 (estimate) | [Fp ]
11 °C | [storage temp. ]
2-8°C | [solubility ]
DMSO: soluble
| [form ]
Powder | [pka]
pKa 8.43(H2O,t =25,I=0.025) (Uncertain) | [color ]
White to almost white | [Stability:]
Stable. Combustible. Incompatible with strong oxidizing agents, strong bases. | [Water Solubility ]
<0.01 g/100 mL at 19 ºC | [Merck ]
14,7322 | [BRN ]
384532 | [InChIKey]
CXOFVDLJLONNDW-UHFFFAOYSA-N | [CAS DataBase Reference]
57-41-0(CAS DataBase Reference) | [IARC]
2B (Vol. Sup 7, 66) 1996 | [NIST Chemistry Reference]
5,5-Diphenylhydantoin(57-41-0) | [EPA Substance Registry System]
57-41-0(EPA Substance) |
| Safety Data | Back Directory | [Hazard Codes ]
T,Xn,F | [Risk Statements ]
R45:May cause cancer.
R61:May cause harm to the unborn child.
R22:Harmful if swallowed.
R63:Possible risk of harm to the unborn child.
R40:Limited evidence of a carcinogenic effect.
R39/23/24/25:Toxic: danger of very serious irreversible effects through inhalation, in contact with skin and if swallowed .
R23/24/25:Toxic by inhalation, in contact with skin and if swallowed .
R11:Highly Flammable.
R20/21/22:Harmful by inhalation, in contact with skin and if swallowed . | [Safety Statements ]
S53:Avoid exposure-obtain special instruction before use .
S45:In case of accident or if you feel unwell, seek medical advice immediately (show label where possible) .
S36/37:Wear suitable protective clothing and gloves .
S16:Keep away from sources of ignition-No smoking .
S7:Keep container tightly closed . | [RIDADR ]
2811 | [WGK Germany ]
3
| [RTECS ]
MU1050000
| [Autoignition Temperature]
550 °C | [HazardClass ]
6.1(b) | [PackingGroup ]
II | [HS Code ]
29332100 | [Safety Profile]
Confirmed carcinogen
producing lymphoma, Hodgkin's disease,
tumors of the skin and appendages.
Experimental carcinogenic and tumorigenic
data. A human poison by ingestion. Poison
experimentally by ingestion, subcutaneous,
intravenous, and intraperitoneal routes.
Moderately toxic by an unspecified route.
Experimental teratogenic and reproductive
effects. Human systemic effects by
ingestion: dermatitis, change in motor
activity (specific assay), ataxia (loss of
muscle coordmation), degenerative brain
changes, encephalitis, hallucinations,
dtstorted perceptions, irritabihty, and jaundice. Human teratogenic effects by
ingestion: developmental abnormalities of
the central nervous system, carlovascular
(circulatory) system, musculoskeletal system,
craniofacial area, skin and skin appendages,
eye, ear, other developmental abnormalities.
Effects on newborn include abnormal
growth statistics (e.g., reduced weight gain),
physical abnormakties, other postnatal
measures or effects, and delayed effects.
Human mutation data reported. A drug for
the treatment of grand mal and
psychomotor seizures. When heated to
decomposition it emits toxic fumes of NOx | [Hazardous Substances Data]
57-41-0(Hazardous Substances Data) | [Toxicity]
LD50 in mice (mg/kg): 92 i.v.; 110 s.c. (Stille, Brunckow) |
| Raw materials And Preparation Products | Back Directory | [Raw materials]
Benzaldehyde-->Ammonium carbonate-->POTASSIUM CYANIDE-->Benzophenone-->Benzeneacetamide, a-amino-a-phenyl--->2-amino-1,5-dihydro-4H-imidazol-4-one-->PARABANIC ACID-->5,5-DIPHENYL-2-THIOHYDANTOIN-->Benzoin | [Preparation Products]
2,4,6-Trifluorophenol-->4,5-dihydroxy-4,5-diphenylimidazolidin-2-one-->1-Imidazolidineacetic acid, 2,5-dioxo-4,4-diphenyl-, ethyl ester-->3a,6a-Diphenyloctahydroimidazo[4,5-d]imidazole-2,5-dione-->Creatinine-->1,3-dibromo-5,5-diphenylimidazolidine-2,4-dione |
| Hazard Information | Back Directory | [General Description]
Fine white or almost white crystalline powder. Odorless or almost odorless. Tasteless. | [Reactivity Profile]
PHENYTOIN(57-41-0) is an amide. Amides/imides react with azo and diazo compounds to generate toxic gases. Flammable gases are formed by the reaction of organic amides/imides with strong reducing agents. Amides are very weak bases (weaker than water). Imides are less basic yet and in fact react with strong bases to form salts. That is, they can react as acids. Mixing amides with dehydrating agents such as P2O5 or SOCl2 generates the corresponding nitrile. The combustion of these compounds generates mixed oxides of nitrogen (NOx). This chemical is incompatible with strong oxidizers and strong bases. | [Air & Water Reactions]
Insoluble in water. | [Potential Exposure]
Phenytoin is an amide pharmaceutical used in the treatment of grand mal epilepsy, Parkinson’s syndrome; and in veterinary medicine. Human exposure to phenytoin occurs principally during its use as a drug. Figures on the number of patients using phenytoin are not available, but phenytoin is given to a major segment of those individuals with epilepsy. The oral dose rate is initially 100 mg given 3 times per day and can gradually increase by 100 mg every 24 weeks until the desired therapeutic response is obtained. The intravenous dose is 200350 mg/day. | [Fire Hazard]
Flash point data for this chemical are not available; however, PHENYTOIN is probably combustible. | [First aid]
Skin Contact: Flood all areas of body that have contacted the substance with water. Don’t wait to remove contaminated clothing; do it under the water stream. Use soap to help assure removal. Isolate contaminated clothing when removed to prevent contact by others. Eye Contact: Remove any contact lenses at once. Flush eyes well with copious quantities of water or normal saline for at least 2030 minutes. Seek medical attention. Inhalation: Leave contaminated area immediately; breathe fresh air. Proper respiratory protection must be supplied to any rescuers. If coughing, difficult breathing or any other symptoms develop, seek medical attention at once, even if symptoms develop many hours after exposure. Ingestion: If convulsions are not present, give a glass or two of water or milk to dilute the substance. Assure that the person’s airway is unobstructed and contact a hospital or poison center immediately for advice on whether or not to induce vomiting. | [Shipping]
UN2811 Toxic solids, organic, n.o.s., Hazard Class: 6.1; Labels: 6.1-Poisonous materials, Technical Name Required. UN3249 Medicine, solid, toxic, n.o.s., Hazard Class: 6.1; Labels: 6.1-Poisonous materials. | [Incompatibilities]
Incompatible with oxidizers (chlorates, nitrates, peroxides, permanganates, perchlorates, chlorine, bromine, fluorine, etc.); contact may cause fires or explosions. Keep away from alkaline materials, strong bases, strong acids, oxoacids, epoxides. Similar organic amides react with azo and diazo compounds, releasing toxic gases. Contact with reducing agents can release flammable gases. Amides are very weak bases but they can react as acids, forming salts. Mixing amides with dehydrating agents such as phosphorus pentoxide or thionyl chloride generates the corresponding nitrile. | [Chemical Properties]
Phenytoin is a crystalline compound | [Chemical Properties]
white crystals or powder | [Originator]
Dilantin ,Parke Davis ,US ,1938 | [Uses]
5,5-Diphenylhydantoin has been used for phenytoin treatment. It has also been used to slow down or prevent mesoendoderm cell migration. | [Uses]
A sodium channel protein inhibitor | [Uses]
Phenytoin has the same main effects on the heart as lidocaine. Its use is essentially limited,
and it is primarily used only as an oral replacement of lidocaine for paroxysmal tachycardia
that is caused particularly by intoxication of digitalis drugs. | [Uses]
Reduces incidence of grand mal seizures; appears to stabilize excitable membranes perhaps through effects on Na+, K+, and Ca2+ channels.
| [Definition]
ChEBI: A imidazolidine-2,4-dione that consists of hydantoin bearing two phenyl substituents at position 5. | [Manufacturing Process]
10 g of benzophenone (1 mol), 4 g of potassium cyanide (1.22 mols) and 16 g of ammonium carbonate (3.3 mols) are dissolved in 100 cc of 60% (by volume) ethyl alcohol and the mixture warmed under a reflux condenser without stirring at 58° to 62°C. After warming the mixture for 10 hours apartial vacuum is applied and the temperature is raised enough to permit concentration of the reaction mixture to two-thirds of its initial volume.
A slight excess of mineral acid, such as sulfuric or hydrochloric acid is added to acidify the mixture which is then chilled and the solid which separates is filtered off. It is then treated with an aqueous solution of dilute sodium hydroxide to dissolve the hydantoin from the solid unreacted benzophenone. After filtration, the alkaline extract is then acidified to cause the separation of solid pure diphenylhydantoin which is filtered off and dried. It melts at 293° to 296°C.
A net yield of about 95% is obtained by the procedure described above. If the time of warming the reaction mixture is increased three-or four-fold, practically 100% net yields are obtained. The same high net yields are also obtained by heating for even longer periods of time. For example, by heating for 90 hours, a 100% net yield, or 67% gross yield, is obtained. | [Brand name]
Anticonvulsant.
Dilantin (Pfizer) [Name previously used:
Diphenylhydantoin.]. | [Therapeutic Function]
Antiepileptic | [Biological Functions]
Phenytoin is a valuable agent for the treatment of generalized
tonic–clonic seizures and for the treatment of
partial seizures with complex symptoms. The establishment
of phenytoin (at that time known as diphenylhydantoin)
in 1938 as an effective treatment for epilepsy
was more than simply the introduction of another drug
for treatment of seizure disorders. Until that time the
only drugs that had any beneficial effects in epilepsy
were the bromides and barbiturates, both classes of
compounds having marked CNS depressant properties.
The prevailing view among neurologists of that era was
that epilepsy was the result of excessive electrical activity in the brain and it therefore seemed perfectly reasonable
that CNS depressants would be effective in antagonizing
the seizures. Consequently,many patients received
high doses of barbiturates and spent much of
their time sedated. Also, since CNS depression was considered
to be the mechanism of action of AEDs, the
pharmaceutical firms were evaluating only compounds
with profound CNS depressant properties as potential antiepileptic agents. It was, therefore, revolutionary
when phenytoin was shown to be as effective as phenobarbital
in the treatment of epilepsy without any significant
CNS depressant activity. This revolutionized the
search for new anticonvulsant drugs as well as immediately
improving the day-to-day functioning of epileptic
patients.
An understanding of absorption, binding, metabolism,
and excretion is more important for phenytoin
than it is for most drugs. Following oral administration,
phenytoin absorption is slow but usually complete, and
it occurs primarily in the duodenum. Phenytoin is highly
bound (about 90%) to plasma proteins, primarily
plasma albumin. Since several other substances can also
bind to albumin, phenytoin administration can displace
(and be displaced by) such agents as thyroxine, triiodothyronine,
valproic acid, sulfafurazole, and salicylic
acid. | [Mechanism of action]
Phenytoin is indicated for initial monotherapy or adjunct treatment of complex partial or tonic-clonic seizures, convulsive status
epilepticus, and prophylaxis. It often is selected for initial monotherapy because of its high efficacy and relatively low incidence
of side effects. Phenytoin is not used in the treatment of absence seizures, because it may increase their frequency of
occurrence. Phenytoin binds to and stabilizes the inactivated state of sodium channels, thus producing a
use-dependent blockade of repetitive firing and inhibition of the spread of seizure activity to adjacent cortical areas. | [Pharmacokinetics]
Phenytoin may be administered either orally or intravenously and is absorbed slowly after oral
administration, with peak plasma levels achieved after 3 to 12 hours. It is extensively plasma protein
bound (~90%), and the elimination half-life is between 15 and 30 hours. These large ranges reflect
the considerable variability observed from patient to patient. Parenteral administration of phenytoin
is usually limited to the intravenous route. Phenytoin for injection is dissolved in a highly alkaline
vehicle (pH 12). This alkaline vehicle is required because phenytoin is weakly acidic and has very
poor solubility in its un-ionized form. Reportedly, however, its phosphate ester fosphenytoin has
water solubility advantages over phenytoin for injection. Intramuscular phenytoin generally is
avoided, because it results in tissue necrosis at the site of injection and erratic absorption because
of high alkalinity. In addition, intermittent intravenous infusion is required to reduce the incidence of
severe phlebitis.
Phenytoin metabolism is relatively slow and predominantly involves aromatic hydroxylation to
p-hydroxylated inactive metabolites. Phenytoin also induces its own metabolism
and is subject to large interindividual variability. The major metabolite, 5-p-hydroxyphenyl-
5-phenylhydantoin, accounts for approximately 75% of a dose. This metabolite is excreted through
the kidney as the β-glucuronide conjugate. Phenytoin clearance is strongly influenced by its
metabolism; therefore, agents that affect phenytoin metabolism may cause intoxication. In addition,
because phenytoin is highly plasma protein bound, agents that displace phenytoin also may cause
toxicity. | [Pharmacology]
In terms of its effect on the CNS, phenytoin is considered an excellent antiepileptic drug
with insignificant sedative effects. Even in large doses it does not cause hypnosis. It is presumed that phenytoin facilitates secretion of sodium ions from nerve cells, which reduces
the stimulation of neurons. This in turn prevents the activation of neurons upon receiving
impulses from the epileptogenic center. In addition, phenytoin reduces the incoming flow
of potassium ions during repolarization. It is possible that phenytoin significantly slows the
distribution of excitation in the brain as a direct result of the redistribution of the ion flow. | [Clinical Use]
Phenytoin (Dilantin) was originally introduced for the
control of convulsive disorders but has
now also been shown to be effective in the treatment of
cardiac arrhythmias. Phenytoin appears to be particularly
effective in treating ventricular arrhythmias in children.
Phenytoin, like lidocaine, is more effective in the treatment
of ventricular than supraventricular arrhythmias.
It is particularly effective in treating ventricular arrhythmias
associated with digitalis toxicity, acute myocardial
infarction, open-heart surgery, anesthesia, cardiac
catheterization, cardioversion, and angiographic
studies.
Phenytoin finds its most effective use in the treatment
of supraventricular and ventricular arrhythmias
associated with digitalis intoxication. The ability of
phenytoin to improve digitalis-induced depression of
A-V conduction is a special feature that contrasts with
the actions of other antiarrhythmic agents. | [Clinical Use]
Phenytoin is one of very few drugs that displays
zero-order (or saturation) kinetics in its metabolism.At
low blood levels the rate of phenytoin metabolism is
proportional to the drug’s blood 1evels (i.e., first-order
kinetics). However, at the higher blood levels usually
required to control seizures, the maximum capacity of
drug-metabolizing enzymes is often exceeded (i.e., the
enzyme is saturated), and further increases in the dose
of phenytoin may lead to a disproportionate increase in
the drug’s blood concentration. Since the plasma levels
continue to increase in such a situation, steady-state levels
are not attained, and toxicity may ensue. Calculation
of half-life (t1/2) values for phenytoin often is meaningless,
since the apparent half-life varies with the drug
blood level.
Acute adverse effects seen after phenytoin administration
usually result from overdosage. They are generally
characterized by nystagmus, ataxia, vertigo, and
diplopia (cerebellovestibular dysfunction). Higher
doses lead to altered levels of consciousness and cognitive
changes.
A variety of idiosyncratic reactions may be seen
shortly after therapy has begun. Skin rashes, usually
morbilliform in character, are most common.
Exfoliative dermatitis or toxic epidermal necrolysis
(Lyellís syndrome) has been observed but is infrequent.
Other rashes occasionally have been reported, as have a
variety of blood dyscrasias and hepatic necrosis. | [Side effects]
The most common side effect in children receiving
long-term therapy is gingival hyperplasia, or overgrowth
of the gums (occurs in up to 50% of patients).
Although the condition is not serious, it is a cosmetic
problem and can be very embarrassing to the patient.
Hirsutism also is an annoying side effect of phenytoin,
particularly in young females. Thickening of subcutaneous
tissue, coarsening of facial features, and enlargement
of lips and nose (hydantoin facies) are often seen
in patients receiving long-term phenytoin therapy.
Peripheral neuropathy and chronic cerebellar degeneration
have been reported, but they are rare.
There is evidence that phenytoin is teratogenic in
humans, but the mechanism is not clear. However, it is
known that phenytoin can produce a folate deficiency,
and folate deficiency is associated with teratogenesis.
Only a few well-documented drug combinations
with phenytoin may necessitate dosage adjustment.
Coadministration of the following drugs can result in
elevations of plasma phenytoin levels in most patients:
cimetidine, chloramphenicol, disulfiram, sulthiame, and
isoniazid (in slow acetylators). Phenytoin often causes a
decline in plasma carbamazepine levels if these two
drugs are given concomitantly.
Ethotoin and mephenytoin are congeners of phenytoin
that are marketed as AEDs in the United States.
They are not widely used.
| [Side effects]
The rapid IV administration of phenytoin can present a
hazard. Respiratory arrest, arrhythmias, and hypotension
have been reported. | [Synthesis]
Phenytoin, 5,5-diphenylimidazolidinedione (9.1.1) is synthesized in two different
ways. The first involves a rearrangement on the reaction of benzil with urea to form the desired
product (9.1.1) .
The second method involves the reaction of benzophenone with sodium cyanide in the
presence of ammonium carbonate, followed by the simultaneous cyclization of the resulting product (carboxyaminonitrile) and its rearrangement under the reaction conditions to
form phenytoin .
 | [Drug interactions]
Plasma phenytoin concentrations are increased in the
presence of chloramphenicol, disulfiram, and isoniazid,
since the latter drugs inhibit the hepatic metabolism of
phenytoin. A reduction in phenytoin dose can alleviate
the consequences of these drug–drug interactions. | [Carcinogenicity]
Phenytoin and its sodium salt are reasonably anticipated to be human carcinogens based on sufficient evidence from studies in experimental animals. | [Environmental Fate]
Routes and Pathways
Exposure is usually oral, but the intravenous route may be used
to treat status epilepticus.
Relevant Physicochemical Properties
Appearance: clear, colorless, or slightly yellow in solution
Solubility: ethyl alcohol | [Metabolism]
Phenytoin is hydroxylated in the liver to inactive
metabolites chiefly 5-(4-hydroxyphenyl)-5-
phenylhydantoin by an enzyme system which is
saturable. Phenytoin undergoes enterohepatic recycling
and is excreted in the urine, mainly as its hydroxylated
metabolite, in either free or conjugated form. | [storage]
Store at -20°C | [Purification Methods]
Crystallise the hydantoin from EtOH. [Beilstein 24 III/IV 1748.] | [Toxicity evaluation]
Since metabolism of the drug is a saturable process, much of
the toxicity of phenytoin is thought to be due to increased
concentrations of the drug, especially of nonprotein-bound
drug. The free drug may cross the blood–brain barrier, and if
present in excess, could produce some of the adverse neurological
manifestations. Other toxicities may be related to folic
acid deficiency induced by phenytoin. Reactive intermediates
formed during metabolism of phenytoin may also be responsible
for some of the drug’s toxicity. | [Precautions]
Phenytoin either should not be used or should be used
cautiously in patients with hypotension, severe bradycardia,
high-grade A-V block, severe heart failure, or
hypersensitivity to the drug.
Because of the increase in A-V transmission observed
with phenytoin administration, it should not be
given to patients with atrial flutter or atrial fibrillation.
Phenytoin will probably not restore normal sinus
rhythm and may dangerously accelerate the ventricular
rate. |
| Questions And Answer | Back Directory | [Description]
Phenytoin is a first- generation antiepileptic drug (AED) known with the proprietary brand name of Epanutin® (Pfizer, Tadworth) in the UK and Dilantin® (Pfizer, New York, NY) in the USA.
| [Generic formulation]
MHRA/ CHM advice to minimize risk when switching patients with epilepsy between different manufacturers’ products (incl. generic products):
- Doctors are advised to ensure that their patients are maintained on a specific manufacturer’s product.
| [Indications]
Epilepsy
Monotherapy and adjunctive therapy of focal and generalized tonic- clonic seizures.
Recommendations summarized from NICE (2012)
- Seizure types: on referral to tertiary care (focal seizures), contraindicated (generalized tonic- clonic seizures if there are absence or myoclonic seizures or if juvenile myoclonic epilepsy is suspected, absence seizures, myoclonic seizures).
- Epilepsy types: on referral to tertiary care (benign epilepsy with centrotemporal spikes, Panayiotopoulos syndrome, late- onset childhood occipital epilepsy), contraindicated (absence syndromes, juvenile myoclonic epilepsy, idiopathic generalized epilepsy, Dravet syndrome).
| [Dose titration]
Epilepsy
150–300 mg od or divided into two doses, then increased to 200– 500 mg daily (dose to be increased gradually as necessary, with plasma phenytoin concentration monitoring).
| [Plasma levels monitoring]
Phenytoin has a narrow therapeutic index and the relationship between dose and plasma. Phenytoin concentration is non- linear: small dosage increases in some patients may produce large increases in plasma concentration with acute toxic adverse effects. Similarly, a few missed doses or a small change in phenytoin absorption may result in a marked change in plasma phenytoin concentration. Monitoring of plasma phenytoin concentration improves dosage adjustments. The usual total plasma phenytoin concentration for optimum response is 0– 20 mg/ L (careful interpretation of total plasma phenytoin concentration is necessary in pregnancy, the elderly, and certain disease states where protein binding may be reduced and it may be more appropriate to measure free plasma phenytoin concentration).
| [Cautions]
Patients with acute porphyrias (contraindication).
| [Interactions]
With AEDs
- Phenytoin is extensively bound to serum plasma proteins and is prone to competitive displacement. Phenytoin is metabolized by hepatic enzymes (cytochrome P450 CYP2C9 and CYP2C9) and is particularly susceptible to inhibitory drug interactions because it is subject to saturable metabolism.
- Several AEDs, including eslicarbazepine, oxcarbazepine, topiramate, and valproate, potentially increase phenytoin serum levels.
- Vigabatrin may decrease phenytoin plasma levels.
- Carbamazepine, phenobarbital, and valproate may either increase or decrease phenytoin serum levels.
- Phenytoin is a potent inducer of hepatic drug- metabolizing enzymes and may reduce the levels of drugs metabolized by these enzymes.
- Phenytoin may alter serum levels and/ or effects of carbamazepine, lamotrigine, phenobarbital, and valproate.
With other drugs
- Phenytoin serum levels are potentially increased by analgesic/ anti- inflammatory agents (such as azapropazone, phenylbutazone, salicylates), anaesthetics (halothane), antibacterial agents (such as chloramphenicol, erythromycin, isoniazid, sulfadiazine, sulfamethizole, sulfamethoxazoletrimethoprim, sulfaphenazole, sulfisoxazole, sulfonamides), antifungal agents (such as amphotericin b, fluconazole, itraconazole, ketoconazole, miconazole, voriconazole), antineoplastic agents (such as capecitabine, fluorouracil), psychotropic agents (such as chlordiazepoxide, diazepam, disulfiram, fluoxetine, fluvoxamine, methylphenidate, sertraline, trazodone, viloxazine), cardiovascular agents (such as amiodarone, dicoumarol, diltiazem, nifedipine, ticlopidine), H2- antagonists (such as cimetidine), HMG- CoA reductase inhibitors (such as fluvastatin), hormones (such as oestrogens), immunosuppressant drugs (such as tacrolimus), oral hypoglycaemic agents (such as tolbutamide), proton pump inhibitors (such as omeprazole).
- Phenytoin plasma levels may be decreased by antibacterial agents (such as ciprofloxacin, rifampicin), antineoplastic agents (such as bleomycin, carboplatin, cisplatin, doxorubicin, methotrexate), antiulcer agents (such as sucralfate), antiretrovirals (such as fosamprenavir, nelfinavir, ritonavir), bronchodilators (such as theophylline), cardiovascular agents (such as reserpine), folic acid, hyperglycaemic agents (such as diazoxide), St John抯 wort (Hypericum perforatum).
- Phenytoin serum levels may be either increased or decreased by antibacterial agents (such as ciprofloxacin), antineoplastic agents, and psychotropic agents (such as chlordiazepoxide, diazepam, and phenothiazines).
- Phenytoin may alter serum levels and/ or effects of the following drugs: antibacterial agents (such as doxycycline, rifampicin, tetracycline), antifungal agents (such as azoles, posaconazole, voriconazole), antihelminthics (such as albendazole, praziquantel), antineoplastic agents (such as teniposide), antiretrovirals (such as delavirdine, efavirenz, fosamprenavir, indinavir, lopinavir/ ritonavir, nelfinavir, ritonavir, saquinavir), bronchodilators (such as theophylline), cardiovascular agents (such as digitoxin, digoxin, mexiletine, nicardipine, nimodipine, nisoldipine, quinidine, verapamil), coumarin anticoagulants (such as warfarin), ciclosporin, diuretics (such as furosemide), HMG- CoA reductase inhibitors (such as atorvastatin, fluvastatin, simvastatin), hormones (such as oestrogens, oral contraceptives), hyperglycaemic agents (such as diazoxide), immunosuppressant drugs, neuromuscular blocking agents (such as alcuronium, cisatracurium, pancuronium, rocuronium, vecuronium), opioid analgesics (such as methadone), oral hypoglycaemic agents (such as chlorpropamide, glyburide, tolbutamide), psychotropic agents (such as clozapine, paroxetine, quetiapine, sertraline), vitamin D.
With alcohol/food
Acute alcohol intake may increase phenytoin serum levels while chronic alcoholism may decrease serum levels. There are no specific foods that must be excluded from diet when taking phenytoin (phenytoin doses should be taken preferably with or after food).
| [Special populations]
Hepatic impairment
Reduce dose to avoid toxicity.
Renal impairment
Nil.
Pregnancy
- Phenytoin may produce congenital abnormalities in the offspring of a small number of epileptic patients. Therefore, phenytoin should only be used during pregnancy, especially early pregnancy, if in the judgement of the physician the potential benefits clearly outweigh the risk.
- In addition to the reports of increased incidence of congenital malformations, such as cleft lip/ palate and heart malformations in children of women receiving phenytoin, there have been reports of a foetal hydantoin syndrome, consisting of prenatal growth deficiency, micro- encephaly, and mental deficiency in children born to mothers who have received phenytoin. There have been isolated reports of malignancies, including neuroblastoma, in children whose mothers received phenytoin during pregnancy.
- ?An increase in seizure frequency during pregnancy occurs in a proportion of patients, possibly due to altered phenytoin absorption or metabolism. Therefore, periodic measurement of serum phenytoin levels is particularly valuable in the management of a pregnant patient with epilepsy as a guide to an appropriate adjustment of dosage; however, postpartum restoration of the original dosage will probably be indicated.
- Breast- feeding is not recommended for women taking phenytoin because phenytoin appears to be secreted in low concentrations in human milk.
| [Behavioural and cognitive effects in patients with epilepsy]
Phenytoin has an overall favourable behavioural profile, although it has been occasionally associated with negative effects on mood and psychotic symptoms (especially at higher doses). The cognitive profile is more problematic, especially in the attention and memory domains. Cognitive adverse effects associated with phenytoin are often dose- dependent and may be particularly obvious in visually guided motor functions.
| [Psychiatric use]
Phenytoin has no approved indications in psychiatry, although the results of small randomized studies have shown that it may be useful in the maintenance treatment of bipolar disorder, major depressive disorder, and impulsive aggression.
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