OBJECT DRUGS

• Metoclopramide (Reglan, etc.)

PRECIPITANT DRUGS

Antipsychotics:

• Chlorpromazine (Thorazine)
• Fluphenazine (Prolixin)
• Haloperidol (Haldol)
• Loxapine (Loxitane)
• Mesoridazine (Serentil)
• Perphenazine (Trilafon)
• Prochlorperazine (Compazine)
• Promethazine (Phenergan)
• Thioridazine (Mellaril)
• Thiothixene (Navane)
• Triethylperazine (Torecan)
• Trifluoperazine (Stelazine)

Comment:

Metoclopramide is a dopamine D₂ receptor antagonist and can cause extrapyramidal reactions and tardive dyskinesias. Phenothiazines also increase the risk of these movement disorders, so it is likely that a person taking metoclopramide with a phenothiazine would be at greater risk of extrapyramidal reactions than a person taking either drug alone. Theoretically, one would expect an increased risk of this interaction in patients with low CYP2D6 activity due to genetics or therapy with CYP2D6 inhibitors, since metoclopramide is a CYP2D6 substrate. Also metoclopramide is partially eliminated unchanged in the urine, so patients with severe renal impairment may also be at greater risk.

Class 2: Use Only If Benefit Felt to Outweigh Risk

• Use Alternative: If possible, avoid using metoclopramide and phenothiazines concurrently. The product information states that metoclopramide is contraindicated with drugs known to cause extrapyramidal reactions.
• Monitor: If the combination is used, limit metoclopramide use to as short a period as possible, and monitor for evidence of extrapyramidal symptoms and tardive dyskinesias.