RESP. PHARMCO - Methylxanthines

Question 1

Give the examples of methylxanthines

Answer 1

Theophylline
Aminophylline
Oxtriphylline
Tea , Coffee and Cocoa

Question 2

Give the Moa of Methylxanthines

Answer 2

Inhibit phosphodiesterase ( they breakdown cGMP and CAMP) thus increase the cGMP and cCAMP levels and causes bronchodilation

Question 3

Give two main effects of Theophylline

Answer 3

1) Adenosine receptor antagonism that is associated with arrhythmias and seizures
2) Deacytylation of histones that reduces transcription of proinflammatory genes
3) Inhibits synthesis and secretion of inflammatory mediators from mast cells and neutrophils

Question 4

Does tolerance to Methylxanthines occur

Answer 4

No thus no need to adjust does because of this

Question 5

Give the effects of Methylxanthines at CNS , CVS , GIT and Kidney

Answer 5

CNS - increase alertness , nervousness , insomnia and at high doses tremors and convulsions
CVS - increase CO and PVR but BP is only slightly raised , has positive inotropic and chronotropic effects due to increased influx of calcium due to increased cCAMP , decrease blood viscosity
GIT - increase gastric acid secretion
Kidney - weak diuretics
Skeletal muscle - improve contractility of diaphragm and reverse fatigue in patients with COPD

Question 6

Give the ROA of Methylxanthines

Answer 6

Oral - well absorbed
IV and IM
Rectal - slow and unreliable

Question 7

What effect does food have on Theophylline

Answer 7

It slows its rate of absorption but not the extent

Question 8

Methylxanthines are widely distributed and can be found in placenta and breast milk , true or false

Answer 8

True

Question 9

Give the percentage of plasma protein binding of Theophylline and give situations that may reduce this binding

Answer 9

60%
Hepatic cirrhosis and newborns

Question 10

Methylxanthines are metabolized in the

Answer 10

Liver

Question 11

Half life of Theophylline varies in preterms , young children and adults .

Answer 11

Preterms - 20-36hrs
Young children - 3.5 hrs.
Adults - 8-9hrs

Question 12

Give factors that usually reduce the half life of Theophylline

Answer 12

Phenytoin and Barbiturates
Oral contraceptives
Rifampin
Children (1-16yrs)
Cigarette and Marijuana smoking
High protein diet
Barbecued meat

Question 13

Give some situations that may increase the half life of Theophylline

Answer 13

Old age
High carbohydrate diet
Vaccination
Pulmonary edema
Hepatic cirrhosis
Congestive heart failure
Infections

Question 14

Give three drugs that increase the half life

Answer 14

Allopurinol
Erythromycin
Ciprofloxacin
Cimetidine

Question 15

Give the main adverse effects of Methylxanthines in
1) CNS
2) CVS
3) Kidney

Answer 15

CNS - seizures and convulsions
Learning difficulties in children
Tremors , Headaches

CVS - Arrhythmias
Kidney - diuresis

Question 16

Give three drugs that may be used to treat convulsions from Methylxanthines

Answer 16

Diazepam
Phenytoin
Phenobarbital

Question 17

Theophylline is converted to what in preterms and how does this differ in adults

Answer 17

Caffeine
Minimal detection in adults

Question 18

Give the theruputic index of Theophylline (long or short)

Answer 18

Short thus requires drug monitoring

Question 19

Describe two mechanisms of action of Methylxanthines as bronchodilators

Answer 19

1) Inhibit phosphodiesterase (PDE2) which usually convert cAMP and cGMP to AMP amd GMP thus accumulation. Bronchodilation occurs when cAMP rises.

2) Theophylline is an adenosine receptor antagonist . Adenosine can cause bronchoconstriction in asthmatics and thus inhibiting adenosine action causes Bronchodilation