Haloperidol decanoate (Haldol Decanoate Injection) and fluphenazine decanoate (Prolixin Decanoate Injection) are long-acting injections of the antipsychotics haloperidol (Haldol) and fluphenazine (Prolixin). In the decanoate formulation, the antipsychotics are suspended in sterile sesame oil to extend the duration of action. The antipsychotic action of the decanoates, however, is not different from that of the oral forms, with the exception of duration of action. The effects of fluphenazine decanoate and haloperidol decanoate can last up to 3 and 4 weeks, respectively.
Both haloperidol and fluphenazine are older, first-generation, high-potency antipsychotics for treating schizophrenia, schizoaffective disorder, psychotic depression, and acute mania in bipolar disorder. A new class of second-generation antipsychotics, such as olanzapine (Zyprexa) and risperidone (Risperdal), has distinct differences and advantages over the older, first-generation agents. Risperidone is also available in a long-acting formulation for injection. When haloperidol decanoate or fluphenazine decanoate is given by intramuscular injection, the drug is “deposited” at the injection site. It is slowly absorbed from the muscle tissues and distributed throughout the body and to the brain, the target organ, where it exerts its antipsychotic effect.
Haloperidol decanoate and fluphenazine decanoate injections are marketed under the trade names Haldol Decanoate Injection and Prolixin Decanoate Injection. Both drugs are available in generic preparations by various manufacturers. Haloperidol decanoate injection comes in concentrations of 50 mg/mL and 100 mg/mL, whereas fluphenazine decanoate injection comes only in a concentration of 25 mg/mL. (Note: The strengths of the decanoates are not equivalent to the strengths of their oral forms on a milligram-per-milligram basis.)
How The Decanoates Are Prescribed
The patient, of course, must agree and cooperate with treatment, which requires routine clinic or office visits to receive maintenance injections of the drug. For the patient who cannot adhere to taking daily oral medications, a decanoate antipsychotic may help prevent psychotic relapse due to ongoing problems with non-compliance. Routine maintenance with haloperidol or fluphenazine decanoate ensures that the patient is receiving the drug and the physician is aware when an injection is missed.
Before receiving haloperidol or fluphenazine decanoate, the patient is treated with the short-acting form to determine response and therapeutic dosage. The dosage is usually determined by taking the patient’s total daily oral dose of haloperidol or fluphenazine and using a conversion ratio to calculate the decanoate dosage. The dosage, however, cannot be determined solely from a formula, but must be individualized and based on the patient’s response and side effects to the drug. For fluphenazine decanoate, the usual dose is 25-50 mg by intramuscular injection every 2-3 weeks. The usual dose for haloperidol decanoate is 100-200 mg intramuscularly every 4 weeks.
Possible Side Effects
Haloperidol decanoate and fluphenazine decanoate are long-acting antipsychotics that exert their action for several weeks. The advantage of the drug’s long action may also be a disadvantage to the patient if there are resultant side effects of the drug. Once the decanoate antipsychotic is administered by injection, it cannot be retrieved or easily reversed. Given these considerations, it is important that the patient be treated initially with short-acting haloperidol or fluphenazine before receiving decanoate injections.
• Drowsiness and feeling of tiredness. Generally, high-potency antipsychotics such as haloperidol and fluphenazine do not induce as much drowsiness as the low-potency antipsychotics such as chlorpromazine (Thorazine). If excessive drowsiness occurs, the patient’s dosage may need to be reduced. Usually, patients develop tolerance to the drug’s side effects.
• Extrapyramidal side effects. Conventional antipsychotics, especially the high-potency agents such as haloperidol and fluphenazine, can induce abnormal movements that mimic Parkinson’s disease. These Parkinson-like symptoms include muscle stiffness, rigidity, tremor, drooling, and a masklike face. The Parkinson-like symptoms and other types of involuntary movements are referred to as extrapyramidal symptoms (EPS). EPS may be treated, and prevented with anticholinergic agents (also called antiparkinson agents), including benztropine (Cogentin), diphenhydramine (Benadryl), trihexyphenidyl (Artane), and procyclidine (Kemadrin).
Dystonia, which occurs shortly after the patient starts an antipsychotic medication, is another form of EPS. It is often manifested by a sudden spasm of the tongue, jaw, and neck. It is not an allergic reaction to the antipsychotic medication. Although a dystonic reaction may be painful and frightening, it can be rapidly reversed with an injection of an anticholinergic medication, such as benztropine or diphenhydramine. With a dystonic reaction, the patient should immediately seek medical attention.
Akathisia is an inner-driven restlessness caused by antipsychotics. Patients describe it as a feeling of nervousness, with the need to pace and the inability to sit still, and may complain of muscular discomfort. Akathisia can often be misdiagnosed as psychotic agitation. Akathisia responds poorly to anticholinergic medications. Reduction in antipsychotic dose is the usual approach to treating akathisia. Propranolol (Inderal), a beta-blocker, however, may be helpful for some patients.
• Gastrointestinal side effects. Patients may experience dry mouth, nausea, loss of appetite, and constipation. These side effects usually subside over time as the patient develops tolerance to them and may be controlled by reducing the dosage if symptoms persist.
• Photosensitivity. Antipsychotics may sensitize the skin (photosensitivity) and make it more susceptible to sunburn. Photosensitivity may be more frequent with fluphenazine than with haloperidol. Patients should avoid prolong exposure to the sun and use a sunscreen with a high sun protection factor.
• Skin rash. When an allergic skin rash develops, the patient should contact the physician immediately. The physician may prescribe an antihistamine, instructing the patient to take it until the antipsychotic is eliminated from the body.
• Weight gain. Antipsychotic drugs may induce weight gain in some patients. If weight gain becomes a problem, the patient should discuss it with his or her physician.
• Other side effects. Haloperidol and fluphenazine may induce elevated levels of prolactin, a hormone that stimulates breast enlargement and milk secretion. When prolactin levels are elevated, breast enlargement and milk secretion may occur in both women and men. Increased levels of prolactin may also cause sexual dysfunction in men and women and irregular menses in women.
Possible Adverse Reactions
• Tardive dyskinesia (TD). One of the most worrisome side effects of the conventional antipsychotics is tardive dyskinesia. Although it can occur early on, TD is by definition a late-onset movement disorder produced by antipsychotics. The movements, usually involving the mouth, tongue, or extremities, are involuntary and repetitive. Apparently, a higher incidence of TD is associated with age, women, and cumulative doses and prolonged treatment with antipsychotic medications. With early detection of TD, the patient may be switched to an atypical antipsychotic, such as clozapine, which rarely causes this disorder.
• Seizures. Antipsychotics can lower seizure threshold and precipitate seizures in susceptible individuals. High-potency antipsychotics such as haloperidol and fluphenazine are associated with lower incidences of seizures than low-potency antipsychotics such as chlorpromazine. For patients with a history of seizures, the use of antipsychotics must be carefully considered and monitored.
• Neuroleptic malignant syndrome (NMS). The symptoms of NMS, a rare, toxic reaction to antipsychotics, are severe muscle stiffness, rigidity, elevated body temperature, increased heart rate and blood pressure, and increased sweating. NMS may lead to delirium and coma. It may be fatal if medical intervention is not immediately provided. Hence, NMS must be recognized early, for it is a medical emergency requiring immediate cessation of the antipsychotic, timely hospitalization, and intensive medical treatment.
• Heatstroke. Patients may be more susceptible to heatstroke while taking an antipsychotic. It usually occurs in patients who are exposed to very warm temperatures or become dehydrated. To prevent heatstroke, especially during hot weather, patients should drink plenty of fluids and stay in cooler environments.
Pregnancy And Breast Feeding
Haloperidol and fluphenazine are classified in Category C of the U.S. Food and Drug Administration (FDA) Pregnancy Risk Categories. To date, there are no clinical studies, or there is inadequate information, to determine the extent of risks of haloperidol and fluphenazine with pregnancy. In animal studies, however, some fetal abnormalities were found after maternal exposure to haloperidol and fluphenazine. Interpretation of these animal studies in regard to human risk is unclear. When haloperidol or fluphenazine is prescribed during pregnancy, the long-acting decanoate injections are not recommended because of the risks involved.
Haloperidol and fluphenazine are excreted in breast milk. Therefore, it is recommended that women receiving haloperidol or fluphenazine decanoate injections not breastfeed.
If you have any questions about this handout, please consult your physician.