Fenoterol Hbr -Beta agonist- Anti-asthmatic - Investigational Drug
Drug Name:Fenoterol Hbr -Beta agonist- Anti-asthmatic - Investigational Drug
List Of Brands:
Indication Type Description:
Indication
Adverse Reaction
Pharmacology/ Pharmacokinetics
Indication:
Moderate to severe asthma
Summary
Fenoterol by inhalation appears to be safe and effective treatment for prophylaxis of excercise- induced bronchospasm, acute attacks of mild to moderate asthma and maintenance therapy for chronic asthma or COPD. However, no apparent advantage of fenoterol over equioment doses of the currently available Beta- selective agonists , albertorol, salbutamol, has yet been demonstrated.
A New Drug Apllication (NDA) is pending.
Fenoterol will be marketed as Berotac from Boehringer Ingelham. Further information on
this period can be received from Boehringer-Ingelheim Canada
Adverse Reaction:
Side effects-
After inhalation of therapeutic doses of fenoterol, side effects are rare.
After oral therapy, skeletal muscle tremor, tachcardia, palpitations, and nervousness occur
occassionally.
Fenoterol is not recommended for use in patients with hyperthyroid ism. Use with caution in
patients with cardiovascular disease, diabetes mellitus and hepatic or renal function
Pharmacology/ Pharmacokinetics:
Pharmacology-
Fenoterol Hbr is an adrenoergic agonist undergoing investigation in the U.S. as a brochodilating agent. It has been available outside the U.S, since the early 1970s as metered dose inhaler(MDI), a solution for neubulization, a powder for inhaltion and an oral dosage form.
Stimulation of Beta-adrenergic activates adenyl cyclase which converts adenosine triphosphate into cCMP, increased levels of cCMP inhibit mediator release and produce bronchodilation.
Although controversial, an increase in mucocilliary transport may also occur. In addition,
Beta- stimulation causes vasodilation of peripheral blood vessels. This effect can result in
baro-receptor- mediated reflux- positive chronotropic response ( increase in heart rate)
and stimulation of skeletol muscle leading to tremor.
Fenoterol has greater beta selectivitivity than metaproternol, but is approximately equal in
selectivity to albuterol and terbutaline. Bronchoselectivity is enhanced by administering
fenoterol, by inhaltion this allows the use of lower dose to acheive therapeutic effects and
reduce side effects
Usual therapeutic doses of (200 to 400mg) of inhaled fenoterol do not significantly affect the
cardiovascular system , however marked cardiovascular effects have been observed after
oral, SC,IM or IV admininstration. Fenoterol prevents immediate antigen induced bronchospasm but does not prevent delayed allergic reactions.
Pharmacokinetics-
Approximately 60% of an oral dose is absorbed, with peak plasma levels reached in 2 hours.
After inhalition fenoterol appears to undergo a two-stage absorption process , the final stage
is independent of dose, while the second is similar to that seen after oral admin. This is
consistent with the observation that, when a drug is administred by inhalation, as much as
90% of the dose is swallowed.
Fenoterol undergoes extensive first-pass metabolism. The half-life of the radio- labelled
drug is 7 hours, however this dose does not represent true half-life for the parent compond.
Although maximim effect of inhaled fenoterol is not acheived for 1 to 2 hours, 60% of the
maximum response is seen within the first few minutes. The duration of action is
app 4- 6 hours . However since the lower therapeutic dose produces near mamimal
bronchodilation, increasing the dose to near maximal effective concentration will increase
the duration of action without affecting the intensity of the peak response.
After oral administration, <2% of the dose is eliminated unchanged in the urine, the balance
is excreted as conjugates in the urine and faces (40%)
Clinical trials-
Clinical trials have established the efficacy of fenoterol for maintenance therapy in patients
with moderate to severe asthma, therapy in chronic obstructive pumonary disease(CPOD),
protection against acute asthmatic atacks.
It is difficult to evaluate many of these studies becaase they are single-dose studies, or
because they do not compare equipotent doses when evaluated against albuterol
and terbutaline.
However, at equipotent doses, ( 1 puff fenoterol 200mcg/puff) = 2puffs albeterol (100mcg/puff) = 2 puffs terbutaline (250mcg/puff , there appears to be no clinically significant difference in duration of action, bronchoselectivity or therapeutic efficacy among the three agents.
The dose of fenoterol used to treat acute asthma is 200mcg( 1 puff) repeated once in 5 minutes for children and 1 to 3 puffs for adults.
Maintenance therapy is 1 to 2 puffs 2 to 4 times a daily for adults, give 1 puff twice daily for
children. Increasing an inhaled dose of fenoterol to > 600mcg( 3 puffs) does not appear to
increase the therapeutic response but may increase incidence of side effects.
