Symptoms in the Pharmacy :Respiratory Problems (7)

Cough remedies: other constituents
 

Antihistamines

 
Examples used in OTC products include diphenhydramine and
promethazine. Theoretically these reduce the frequency of coughing
and have a drying effect on secretions, but in practice they also induce
drowsiness. Combinations of antihistamines with expectorants are
illogical and best avoided. 

 A combination of an antihistamine and a cough suppressant may be useful in that antihistamines can help to dry up secretions and, when the combination is given as a night-time dose if the cough is disturbing sleep, a good night’s sleep will invariably
follow. This is one of the rare occasions when a side-effect proves
useful. The non-sedating antihistamines are less effective in symptomatic
treatment of coughs and colds because of their less pronounced
anticholinergic actions.

Interactions:Traditional antihistamines should not be used by patients
who are taking phenothiazines and tricyclic antidepressants because
of additive anticholinergic and sedative effects. Increased sedation will
also occur with any drug that has a CNS depressant effect. Alcohol
should be avoided because this will also lead to increased drowsiness.

Sympathomimetics

Pseudoephedrine is the most commonly used oral decongestant included
in cough and cold remedies  for its bronchodilatory
and decongestant actions. It has a stimulant effect that may lead
to a sleepless night if taken close to bedtime. It may be useful if the
patient has a blocked nose as well as a cough and an expectorant/
decongestant combination can be useful in productive coughs. 

Sympathomimetics can cause raised blood pressure, stimulation of the
heart and alterations in diabetic control. Oral sympathomimetics
should be used with caution in patients with

• diabetes
• coronary heart disease (e.g. angina)
• hypertension
• hyperthyroidism

Interactions: Sympathomimetics should be avoided by patients taking

• monoamine oxidase inhibitors (e.g. phenelzine)
• reversible inhibitors of monoamine oxidase A (e.g. moclobemide)
• beta-blockers
• tricylic antidepressants (e.g. amitriptyline); a theoretical interaction

which does not seem to cause problems in practice.
 

Theophylline

 
Theophylline is sometimes included in cough remedies for its bronchodilator
effect. OTC medicines containing theophylline should
not be taken at the same time as prescribed theophylline since
toxic blood levels and side-effects may occur. The action of theophylline
can be potentiated by some drugs, e.g. cimetidine and  erythromycin.

  

Levels of theophylline in the blood are reduced by smoking and
drugs such as carbamazepine, phenytoin and rifampicin that induce
liver enzymes, so that the metabolism of theophylline is increased and
lower serum levels result.

Side-effects include GI irritation, nausea, palpitations, insomnia and
headaches. The adult dose is typically 120 mg three or four times daily.
It is not recommended in children. Before selling any OTC product
containing theophylline, check that the patient is not already taking
the drug on prescription.