Question

A 32-year-old male patient with asthma with an allergy to penicillin was being treated for asthmatic bronchitis with a standard-dose of oral theophylline and erythromycin. On day 8, he became irrational and confused and was taken to the emergency room by his wife. When his medications were revealed, quantitation of drugs was ordered. The theophylline level was 49 ug/dL (NRI: 10-20 ug/dL). The patient was admitted to the intensive care unit, hydrated and monitored until the theophylline level returned to normal. He then was started on a lower dose of theophylline. The patient recovered without further complications.

1. To what class of drugs does theophylline belong

2. What is meant by steady state?

3. Why is it necessary for drug levels to be at steady-state concentration before quantitation?

4. What is the relationship between drug half-life and steady-state concentration?

5. Can it be determined if this patient achieved steady state theophylline levels before measurement? The half life of theophylline in an adult is 8 hours. He had been taking the drug for 8 days. Calculate the number of half-lives. How many half lives are necessary to determine steady-state?

6. Which drug level would be of greater interest for this patient? Why?

7. At what time should blood be sampled to reflect trough and peak level concentrations? Why should "GEL BARRIER" or "SERUM SEPARATOR" tubes not be used when performing drug levels?

Answer 1

Ans) 1) Theophylline belongs to a class of drugs called methylxanthines. A class of drugs is a group of medications that work in a similar way. These drugs are often used to treat similar conditions. Theophylline works by opening the airways in your lungs.

2) The definition of a steady-state is an unchanging condition, system or physical process that remains the same even after transformation or change. When you have a chemical mix that has certain properties, and the mix retains those properties even after you add a change-agent, this is an example of a steady-state.

3) If you have a drug with a long half life, you can achieve a target steady state level more quickly by using a loading dose. For example, perhaps you want to achieve a steady state of concentration (Css) of 10 ng/mL, which requires a 30 mg dose once daily. However, it will take 10 days to achieve steady state.

4) Steady-state concentration is the time during which the concentration of the drug in the body stays consistent. For most drugs, the time to reach steady state is four to five half-lives if the drug is given at regular intervals—no matter the number of doses, the dose size, or the dosing interval.

- If you double the half-life of a drug, you will double its steady state concentration 1.00 Correct: Steady state concentration is directly proportional to the dosage of a drug and its half life. The time it takes to reach steady state concentration is usually 4-5 half lives.