Abstract
This Hospital Pharmacy feature is extracted from Off-Label Drug Facts, a publication available from Wolters Kluwer Health. Off-Label Drug Facts is a practitioner-oriented resource for information about specific drug uses that are unapproved by the US Food and Drug Administration. This new guide to the literature enables the health care professional or clinician to quickly identify published studies on off-label uses and determine if a specific use is rational in a patient care scenario. References direct the reader to the full literature for more comprehensive information before patient care decisions are made. Direct questions or comments regarding Off-Label Drug Uses to jgeneral@ku.edu.
Background
Delusional parasitosis or infestation is an uncommon disorder in which patients believe they are infested with pathogens (eg, insects, parasites, or vermin) accompanied by abnormal skin sensations (eg, crawling, tingling).1,2 Symptoms are persistent and often cause the patient to seek medical attention from a variety of physicians before diagnosis is established. Delusional parasitosis occurs more frequently in women than in men, with a typical onset in middle age. It may be chronic or episodic and has been classified as primary or secondary (eg, drug or disease induced). Various treatment modalities have been recommended, including psychotherapy and pharmacological agents. In various pharmacological therapy overviews, the use of antipsychotics with or without antidepressants has been recognized as primary therapy in addition to treatment of any underlying disease.
Patient Population
Adult patients with delusional parasitosis.
Dosage and Duration
Initial doses of 1 to 2 mg daily are titrated slowly (1 mg every 5 to 7 days) to the effective dose that is best tolerated. Typical maintenance doses are between 2 and 4 mg daily. The lowest possible dose of pimozide should be used for the shortest duration, with periodic assessment to determine tolerance and response. Duration documented in the literature has been from a few months to over a year.
Results
A lack of well-controlled trials may be attributed to the difficulty in collecting patients with parasitosis, as this is not a common disorder. Pimozide for the treatment of delusional parasitosis is based primarily on data from case series/reports that demonstrate some efficacy in the majority of patients. The use of the drug is limited by its side-effect profile.
Controlled Trials
In a double-blind, placebo-controlled, crossover trial, 11 patients (mean age, 65.6 years; range, 45-83 years) with delusional parasitosis were treated with pimozide (1-5 mg daily) or placebo for 6 weeks separated by a 4-week washout period. The initial pimozide dose was 2 mg daily and was adjusted at 2 weeks based upon efficacy and tolerance. Two patients did not complete the study. All patients were evaluated at baseline and weekly intervals for subjective (eg, itch, feeling of vermin) and objective symptoms (eg, excoriations and delusions). Pimozide was significantly better than placebo in relieving itch delusions, but it was no different than placebo for feelings of vermin or excoriations. In addition, when compared to placebo, pimozide significantly decreased the Brief Psychiatric Rating Scale score from baseline to end of treatment (mean reduction, 13.5 vs 1.3; P = .012). This study was limited by poor methodology description and small sample size.3
Case Series/Reports
In a case series of 33 patients with delusional parasitosis (median age, 60 years), pimozide was prescribed for 24 patients, 18 of whom took the drug. The dose ranged from 1 to 5 mg daily. No information regarding initial dosing was specified, although the dose was continued for 6 weeks prior to tapering. Of those patients receiving pimozide, 61% (11/18) experienced improvement in or full remission of symptoms; the remaining 39% (7) experienced no change in symptoms. Onset in symptom improvement was noted within 3 to 4 weeks in responders. For those patients not receiving pimozide, only 20% (3/15) experienced relief or resolution of symptoms. This report was limited by poor description of other treatments, lack of specific methodology, and small sample size.4
In several case reports, pimozide has been effective in partially or completely resolving symptoms in the majority of adult patients treated for delusional parasitosis. Daily doses in these reports have ranged from 1 to 5 mg in most cases, but they have been as high as 8 mg, with various adjustment schedules based on tolerance and efficacy. In responders, onset of symptom relief has occurred in 10 days to 4 weeks.5–14
Safety
This is a limited safety profile. Refer to package labeling for complete prescribing information (eg, Warnings/Precautions, Adverse Reactions, Drug Interactions).
Adverse effects that have occurred in the reviewed data include extrapyrimadal symptoms and QT prolongation.5,7,10
Therapy Considerations
Pimozide for the treatment of delusional parasitosis is based primarily on data from case series/ reports that demonstrate some efficacy in the majority of patients. The use of the drug is limited by its side-effect profile.
References
- 1.Freudenmann RW, Lepping P. Delusional infestation. Clin Microbiol Rev. 2009; 22(4):690–732 [DOI] [PMC free article] [PubMed] [Google Scholar]
- 2.Freudenmann RW, Lepping P. Second-generation antipsychotics in primary and secondary delusional parasitosis: Outcome and efficacy. J Clin Psychopharmacol. 2008;28(5):500–508 [DOI] [PubMed] [Google Scholar]
- 3.Hamann K, Avnstrop C. Delusions of infestation treated by pimozide: A double blind crossover clinical study. Acta Dermatol (Stockholm). 1982:62: 55–58 [PubMed] [Google Scholar]
- 4.Zomer SF, De Wit RF, Van Bronswijk JE, Nabarro G, Van Vloten WA. Delusions of parasitosis. A psychiatric disorder to be treated by dermatologists? An analysis of 33 patients. Br J Dermatol. 1998;138(6):1030–1032 [DOI] [PubMed] [Google Scholar]
- 5.Ozten E, Tufan AE, Cerit C, Sayar GH, Ulubil IY. Delusional parasitosis with hyperthyroidism in an elderly woman: A case report. J Med Case Rep. 2013;7(1):17. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 6.Maeda K, Yamamoto Y, Yasuda M, Ishii K. Delusions of oral parasitosis. Prog Neuro-Psychopharmacol Biol Psychiatry. 1998;22:243–248 [DOI] [PubMed] [Google Scholar]
- 7.Hanumantha K, Pradhan PV, Suvarna B. Delusional parasitosis–study of three cases. J Postgrad Med 1994;40(4):222–224 [PubMed] [Google Scholar]
- 8.Monk BE, Rao YJ. Delusion of parasitosis with fatal outcome. Clin Exp Dermatol. 1994;19:341–342 [DOI] [PubMed] [Google Scholar]
- 9.Damiani TJ, Flowers FP, Pierce DK. Pimozide in delusions of parasitosis [letter]. J Am Acad Dermatol 1990;22:312–313 [DOI] [PubMed] [Google Scholar]
- 10.Mitchell C. Successful treatment of chronic delusional parasitosis. Br J Psychiatry 1989;155:556–557 [DOI] [PubMed] [Google Scholar]
- 11.Bond WS. Delusions of parasitosis: A case report and management guidelines. Ann Pharmacotherapy 1989;23:304–306 [DOI] [PubMed] [Google Scholar]
- 12.Reilly TM, Jopling WH, Beard AW. Successful treatment with pimozide of delusional parasitosis. Br J Dermatol 1978;98:457–459 [DOI] [PubMed] [Google Scholar]
- 13.Makhija M, Bhalerao S. Reconsidering pimozide for new-onset delusions of parasitosis. Can J Psychiatry. 2004;49(9):643–644 [DOI] [PubMed] [Google Scholar]
- 14.Nejad AG, Toofani K. Delusion of oral parasitosis in a patient with major depressive disorder. Can J Psychiatry. 2005;50(5):301–302 [DOI] [PubMed] [Google Scholar]