Anticholinergics drug interactions

Contraindications, precautions, and interactions of die anticholinergic drug are discussed in Chapter 25. 

Methylxanthines are no longer considered first-line therapy for COPD. Inhaled bronchodilator therapy is preferred over theophylline for COPD because of theophylline s risk for drug interactions and the interpatient variability in dosage requirements. Theophylline may be considered in patients who are intolerant or unable to use an inhaled bronchodilator. A methylxanthine may also be added to the regimen of patients who have not achieved an optimal clinical response to an inhaled anticholinergic and [i2-agonist. 

Thus, the anticholinergic activity of the alkaloid hyoscyamine is almost entirely confined to the (—)-isomer, and the (+)-isomer is almost devoid of activity. The racemic ( )-form, atropine, has approximately half the activity of the laevorotatory enantiomer. An anticholinergic drug blocks the action of the neurotransmitter acetylcholine, and thus occupies the same binding site as acetylcholine. The major interaction with the receptor involves that part of the molecule that mimics acetylcholine, namely the appropriately positioned ester and amine groups. The chiral centre is adjacent to the ester, and also influences binding to the receptor. 

Drugs that may interact with darifenacin include moderate and potent CYP3A4 inhibitors, anticholinergic drugs, CYP2D6 substrates, and digoxin. 

Drugs that may interact with pilocarpine include beta blockers and anticholinergics. Drug/Food interactions The rate of absorption of pilocarpine is decreased when taken with a high-fat meal. Maximum concentration is decreased and time to reach maximum concentration is increased. 

Tricyclic antidepressants are notorious for their risk to be involved in drug-drug interactions. Additive anticholinergic effects can be expected in combination with antihistamines, antipsychotics and anticholinergic-type anti-Parkinson agents. Hepatic enzyme-inducing agents increase their hepatic metabolism while enzyme inhibitors may potentiate the effects of tricyclics. Concomitant use with monoamine oxidase inhibitors will produce hypertension, hyperpyrexia and convulsions. 

Several drug interactions involving amantadine and rimantadine are clinically significant. Anticholinergic drugs can potentiate the toxicity of amantadine. Thiazide-triamterene, trimethoprim-sulfamethoxazole, quinine, and quinidine increase plasma amantadine levels. Cimetidine decreases rimantadine clearance, and aspirin and acetaminophen decrease rimantadine plasma levels. 

Amoxapine and maprotiline share most drug interactions common to the TCA group. Both are CYP2D6 substrates and should be used with caution in combination with inhibitors such as fluoxetine. Amoxapine and maprotiline also both have anticholinergic and antihistaminic properties that may be additive with drugs that share a similar profile. 

This pharmacodynamic interaction suggests that donepezil should be avoided in patients with Alzheimer s disease who are taking anticholinergic drugs. 

The use of cisapride and its benefit to harm balance in children has been reviewed (25). Overall it is well tolerated. The most common adverse effects are diarrhea, abdominal cramps, borborygmi, and colic. Serious adverse events are rare and include isolated cases of extrapyramidal reactions, seizures in epileptic patients, cholestasis, QT interval prolongation and ventricular dysrhythmias, anorexia, and enuresis. Interactions of cisapride with other drugs are similar to those reported in adults. Co-administration of drugs that inhibit CYP3A4, such as imidazoles, macrolide antibiotics, the antidepressant nefazodone, and protease inhibitors such as ritonavir, are contraindicated. Furthermore, co-administration of anticholinergic drugs can compromise the beneficial effects of cisapride. 

Drug interactions Additive CNS depressant effects may occur when antihistamines are administered concomitantly with other CNS depressants, including barbiturates, benzodiazepines, alcohol, and other sedatives. Additive anticholinergic effect also may occur when used in combination with other anticholinergic agents. 

The Hi antagonists display a variety of. significant drug interactions when coadministered with other therapeutic agents. For example. MAO inhibitors prolong and intensify the anticholinergic actions of the antihistamines. - " ... 

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