|
Many side effects are related to tricyclics antimuscarinic
actions. The antimuscarinic side effects are relatively
common and include:
- Dry mouth (salivary secretion is affected)
- Dry nose
- Blurred vision (accommodation in the eye is affected)
- Decreased gastro-intestinal motility and secretion.
This may lead to constipation
- Urinary retention or difficulty with urination
- Hyperthermia
Tolerance to these adverse effects often develops if
treatment is continued, side effects may also be less
troublesome if treatment is initiated with low dose
and then gradually increased, although this may delay
the clinical effect.
Other side effects may include drowsiness, anxiety,
restlessness, cognitive and memory difficulties, confusion,
dizziness, akathisia, hypersensitivity reactions, increased
appetite with weight gain, sweating, decrease in sexual
ability and desire, muscle twitches, weakness, nausea
and vomiting, hypotension, tachycardia, and rarely,
irregular heart rhythms. Rhabdomyolysis or muscle breakdown
has been rarely reported with this class of drugs.
Interactions
TCAs are highly metabolized by the cytochrome P450
hepatic enzymes. Drugs that inhibit cytochrome P450
(for example cimetidine, methylphenidate, antipsychotics,
and calcium channel blockers) may produce decreases
in the tricyclic's metabolism leading to increases in
tricyclic blood concentrations and accompanying toxicity.
Drugs which prolong the QT interval including antiarrythmics
such as quinidine, the antihistamines astemizole and
terfenadine, and some antipsychotics may increase the
chance of ventricular dysrhythmias. TCAs may enhance
the response to alcohol and the effects of barbiturates
and other CNS depressants. Side effects may also be
enhanced by other drugs which have antimuscarinic properties.
|
