Interaction with drugs

MAOIs must not be used to treat a patient if the patient is also taking drugs that depend on enzymes affected by MAOI for their metabolism, for example:-

• sympathomimetic amines eg adrenaline, noradrenaline
• cold cures containing phenylpropanolamine and ephedrine
• methyl dopa
• antihistamines
• some local anaesthetics
• morphine, pethidine, procaine, alcohol, insulin, barbiturates. The effects of oral hypoglycaemic drugs may be heightened.

There may be dangerous interactions between tricyclics and MAOIs, which means that a tricyclic should not be given for about 2 weeks after stopping a MAOI. A drug- free interval is not required if the tricyclic is given first, which is a reason why tricyclics are used first in depressive illness and having a MAOI as a reserve.