12. Drug Interactions
OVERVIEW
1. One drug may alter the absorption, metabolism or excretion of another.
2. Drugs may have additive or inhibitory interactions at the receptor site.
3. Idiosyncratic interactions are those wherein one drug enhances or antagonizes the action of another through a mechanism that is not discernible.
4. Two or more psychotropic drugs from different therapeutic groups may increase the sedative, hypotensive, or anticholinergic effects of one another.
5. Nonpsychotropic drugs may produce additive sedation, hypotension, and anticholinergic effects with psychotropic drugs.
6. Psychotropic drugs may prevent therapeutic effects of some nonpsychotropic drugs (eg, TCA. block hypotensive effects of guanethidine and clonidine).
7. One drug may inhibit metabolism and increase serum concentration of another (eg, methylphenidate, neuroleptics, and triiodothyronine may increase serum concentration or therapeutic effects of TCAs.)
8. ACE inhibitors (eg, captopril) may produce profound hypotension when coadministered with chlorpromazine.
9. Meperidine may produce fatal reaction (hyperthermia, hypertension, seizures) in MAOI treated patients.
10.Calcium channel blockers, ACE inhibitors, and carbamazepine administered along with lithium can provoke lithium neurotoxicity.
11.Erythromycin and calcium channel blockers can inhibit metabolism of carbamazopine and provoke carbamazepine neurotoxicity.
12.A detailed medication history before prescribing psychotropic drugs is essential, as is periodic review of all prescribed and nonprescribed medications the patient is taking.