Carbidopainteractions

Drugs metabolized by COMT: use with caution Anti-hypertensive agents: dose adjustment may be required Tricyclic antidepressants: risk of hypertension and dyskinesia reported during concomitant use with carbidopa/levodopa Dopamine D2 receptor antagonists, isoniazid, phenytoin, papaverine and iron salts: may reduce efficacy of carbidopa, levodopa and entacapone tablets Drugs that interfere with biliary excretion, glucuronidation and intestinal beta-glucuronidase: dose adjustment of carbidopa, levodopa and entacapone tablets may be required Drugs metabolized by CYP2C9 (e.g., coumadin): dose adjustment of carbidopa, levodopa and entacapone tablets may be required; monitor INR when initiating carbidopa, levodopa and entacapone tablets in patients on coumadin

7.1 MAO Inhibitors

Patients receiving nonselective MAO inhibitors and carbidopa, levodopa and entacapone may be at risk of increased adrenergic tone. Therefore, the use of carbidopa, levodopa and entacapone tablets is contraindicated in patients receiving nonselective MAO inhibitors.

7.2 Drugs Metabolized by

Catechol-O-Methyltransferase (COMT) Drugs known to be metabolized by COMT, such as isoproterenol, epinephrine, norepinephrine, dopamine, dobutamine, alpha-methyldopa, apomorphine, isoetherine, and bitolterol should be administered with caution in patients receiving entacapone regardless of the route of administration (including inhalation), as their interaction may result in increased heart rates, possibly arrhythmias, and excessive changes in blood pressure.

7.3 Antihypertensive

Agents Symptomatic postural hypotension has occurred when carbidopa/levodopa was added to the treatment of patients receiving antihypertensive drugs. When starting therapy with carbidopa, levodopa and entacapone tablets, dosage adjustment of antihypertensive drug may be required.

7.4 Tricyclic

Antidepressants There have been reports of adverse reactions, including hypertension and dyskinesia, resulting from the concomitant use of tricyclic antidepressants and carbidopa/levodopa.

7.5 Dopamine D2

Receptor Antagonists Dopamine D2 receptor antagonists (e.g., metoclopramide, phenothiazines, butyrophenones, risperidone) may reduce the therapeutic effects of levodopa.

7.6 Isoniazid

Isoniazid may reduce the therapeutic effects of levodopa, a dose increase may be necessary.

7.7 Phenytoin

The beneficial effects of levodopa in Parkinson’s disease have been reported to be reversed by phenytoin. Patients taking phenytoin with carbidopa/levodopa should be carefully observed for loss of therapeutic response. Carbidopa, levodopa and entacapone tablets dosage should be increased as clinically needed in patients receiving phenytoin.

7.8 Papaverine

The beneficial effects of levodopa in Parkinson’s disease have been reported to be reversed by papaverine. Patients taking papaverine with carbidopa/levodopa should be carefully observed for loss of therapeutic response. Carbidopa, levodopa and entacapone tablets dosage should be increased as clinically needed in patients receiving papaverine.

7.9 Iron Salts

Iron salts or multi vitamins containing iron salts should be coadministered with caution. Iron salts can form chelates with levodopa, carbidopa and entacapone and consequently reduce bioavailability of levodopa, carbidopa and entacapone.

7.10 Drugs Known to

Interfere with Biliary Excretion, Glucuronidation, and Intestinal Beta-glucuronidase As most entacapone excretion is via the bile, caution should be exercised when drugs known to interfere with biliary excretion, glucuronidation, and intestinal beta-glucuronidase are given concurrently with entacapone. These include probenecid, cholestyramine, and some antibiotics (e.g., erythromycin, rifampicin, ampicillin and chloramphenicol). 7.11 Drugs Metabolized via CYP2C9 (e.g., coumadin) The dosage of carbidopa, levodopa and entacapone tablets should be adjusted as clinically needed in patients using other drugs metabolized via CYP2C9. An interaction study in healthy volunteers, entacapone increased the AUC of R-warfarin on average by 18%, and the INR values on average by 13%. Cases of increased INR in patients concomitantly using warfarin have been reported during the post-approval use of entacapone. Thus, monitoring of INR is recommended when carbidopa, levodopa and entacapone tablets treatment is initiated for patients receiving warfarin.