MAOIs Antimuscarinics

Excessive central stimulation, usually exhibited as tremors, insomnia and hyperhidrosis, can occur following therapeutic doses of the MAOIs, as can agitation and hypomanic episodes. Peripheral neuropathy, which is largely restricted to the hydrazine type of MAOI, is rare and has been attributed to a drug-induced p)n idoxine deficiency. Such side effects as dizziness and vertigo (presumably associated with hypotension), headache, inhibition of ejaculation (which is often also a problem with the TCAs), fatigue, dry mouth and constipation have also been reported. These side effects appear to be more frequently associated with phenelzine use. They are not associated with any antimuscarinic properties of the drug but presumably arise from the enhanced peripheral sympathetic activity which the MAOIs... 

Hyoscyamine (Anaspaz, Cystospaz, Levsin, Others) [Antispasmodic/Anticholinergic] Uses Spasm w/ GI bladder disorders Action Anticholinergic Dose Adults. 0.125-0.25 mg (1-2 tabs) SL/PO tid-qid, ac hs 1 SR cap ql2h Caution [C, +] T Effects w/ amantadine, antihistamines, antimuscarinics, haloperidol, phenothiazines, TCA, MAOI Contra BOO, GI obst, NAG, MyG, paralytic ileus, ulcerative colitis, MI Disp Caps, tabs SE Dry skin, xerostomia, constipation, anticholinergic SE, heat prostration w/ hot weather Interactions T Effects W/ amantadine, antimuscarinics, haloperidol, phenothiazines,... 

MAOIs ANTIHISTAMINES t occurrence of antimuscarinic effects such as blurred vision, confusion (in elderly patients), restlessness and constipation Additive antimuscarinic effects Warn patients and carers, particularly those managing elderly patients... 

The manufacturer states that nefopam should not be given to patients taking non-selective MAOIs and caution should be used in those taking tricyclic antidepressants, antimuscarinics and sym-pathomimetics. The intensity and incidence of adverse effects are somewhat increased when nefopam is given with codeine, pentazocine or dextropropoxyphene (propoxyphene), and the CNS depressant effect of dihydrocodeine may have contributed to a fatal overdose with nefopam. However, a morphine-sparing effect has been reported. Nefopam may also have a synergistic analgesic effect with ketoprofen. 

Detailed information about adverse interactions between nefopam and other drugs does not seem to be available. The manufacturer advises caution if nefopam is given with a tricyclic antidepressant because they lower the convulsive threshold convulsions have been seen in some patients taking nefopam. In addition, the antimuscarinic adverse effects of nefopam may be additive with those of tricyclics and other drugs with antimuscarinic effects. For example, the CSM in the UK has a number of reports of urinary retention caused by nefopam, which would be expected to be worsened by drugs with antimuscarinic activity. Nefopam appears to have sympathomimetic activity and the manufacturer therefore says it should not be given with the MAOIs (see MAOIs or RIMAs + Sym-pathomimetics Indirectly-acting , p.l 147). 

As with other sedative antihistamines (see MAOIs + Antihistamines , above), the UK manufacturers of cyproheptadine also say that MAOIs prolong and intensify the antimuscarinic effects of antihistamines, but fhere seems to be no clinical data to support this. 

No adverse interactions between the MAOIs and antimuscarinics have been reported, aithough the possibility has been suggested. 

A hyperthermic reaction has been reported in some animals given tranylcypromine or nialamide with procyclidine or benzatropine. It was considered that this might be due to an exaggerated dopamine response. However, there do not appear to be any reports of such an interaction occurring clinically. Nevertheless, some manufacturers of irreversible non-selective MAOIs and antimuscarinics issue cautions about the possibility of increased effects of antimuscarinics when given with MAOIs. This is presumably because, in theory, inhibition of drug-metabolising enzymes by MAOIs may possibly enhance the effects of antimuscarinics. 

A depressed woman taking daily doses of conjugated oestrogens 1.25 mg and amitriptyline 75 mg, was also given furazolidone 300 mg daily and diphenoxylate with atropine sulfate. Two days later she began to experi-enee blurred vision, profuse perspiration followed by alternate chills and hot flushes, restlessness, motor activity, persecutory delusions, auditory hallueinations and visual illusions. The symptoms cleared within a day of stopping the furazolidone. The reasons are not understood but the authors point out that furazolidone has MAO-inhibitory properties and that the symptoms were similar to those seen when the tricyclic antidepressants and MAOIs interaet. However the MAO-inhibitory activity of furazolidone normally develops over several days. Whether the concurrent use of atropine and amitriptyline (both of which have antimuscarinic activity)... 

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