About Theophylline, Part 2 Print E-mail



Theophylline products exist in numerous forms. A recent listing of all FDA-approved prescription drugs lists 126 different preparations that contain theophylline. This gives your doctor great flexibility if he needs to prescribe theophylline for you.

Selecting a theophylline product, and determining the best dose and time between doses, must integrate the patient's clinical needs, the absorption characteristics of different formulations, and the drug's removal rate in the particular patient. The dose and dose interval decided on, plus the rates of theophylline's absorption and removal, each affect the fluctuation of its concentration in the blood. For maximum benefit from the drug, the blood concentration must be maintained within the narrow therapeutic range around the clock. This means that the above four factors must be coordinated to keep fluctuations at a minimum.

The optimal theophylline formulation, dose, and dosage interval can only be determined via the patient's blood concentration measurements.

Once a patient has invested the time and money that this requires, he should continue using the brand that was finally decided upon. The generic equivalent is not equivalent when it comes to theophylline. Your doctor's prescriptions should always include the instruction: Do not substitute.

Understanding the relative strengths of different types of theophylline preparations is very important for the patient. A preparation's strength is determined by the actual amount of theophylline in it (called anhydrous theophylline). The amount of medicine that you take each time refers to the amount of your preparation, not the amount of anhydrous theophylline. So the identical dose of different preparation will not each give you the same amount of anhydrous theophylline. If your doctor changes your theophylline medication, don't be alarmed if your dose and/or dose interval are also changed.

For example, if you have been taking 400-milligram doses of a pure theophylline preparation and then switch to 400-milligram doses of a theophylline salt (for example, Choledyl), you would suddenly get only 256 milligrams of anhydrous theophylline per doseone-half the previous amount. To get the same therapeutic benefits as you did with the pure theophylline preparation, you would have to take about 626 milligrams on the same schedule, or 315 milligrams twice as often.

Administration

Theophylline preparations basically fall into two groups: rapidly absorbed and slowly absorbed. The rapid absorption productsnormally given intravenouslyare usually used during an acute asthma attack. The sustained-release (or slow release) theophylline preparations are used for COPD maintenance therapy because they can be scheduled for longer intervals. They also reduce fluctuation in blood concentration, which in turn improves symptom control. And the longer dosage intervals result in better patient compliance.

The patient's drug removal rate must be accounted for in determining this interval. Patients with particularly rapid removal rates and a strong asthma component may have to take a sustained-release preparation every 8 hours instead of every 12 to prevent symptoms from breaking through before the next dose. COPD/asthma patients with particularly slow rates can control their symptoms adequately with one dose every 24 hours.

Slow-release theophylline products are given by mouth, usually in a tablet or a bead-filled capsule. The beads can be sprinkled on soft food (for example, applesauce or yogurt) for people who find tablets difficult to swallow. If you prefer a liquid syrup (which is generally for children, despite the extremely bitter taste), your prescription should state the dose in milligrams. And ask your pharmacist to give you a measuring device to use that will ensure accurate dosage.

Interactions

Beta-2 Stimulator: The first type of interaction to consider is the synergistic reaction when theophylline is teamed with a beta-2 stimulator. Theophylline is certainly an important drug for patients with advanced COPD because of its help in clearing mucus and strengthening the diaphragm. At the same time, its bronchodilating effects counter any tendency toward the asthmatic's hyperreactive airways. But some COPD patients with a substantial asthma component may find that theophylline alone cannot satisfactorily control their asthma symptoms. Then a beta-2 stimulator is added to their "menu." Giving these two asthma drugs together means the effective dose of each can be lowered, which then reduces the risk of side effects. This is particularly helpful when the optimum theophylline dose otherwise needed for maximum bronchodilation is above the nontoxic range.

Drugs Affecting Theophylline's Removal: A different type of drug interaction involving theophylline occurs when another medication that the patient is taking changes theophylline's removal rate.

Theophylline's Effects on Other Drugs: In two cases, theophylline alters the effect of another drug. Phenytoinan anticonvulsantseems weakened when it is taken together with theophylline. Lithiumtaken to control manic-depressive psychosisis eliminated from the patient's system much more quickly. Because researchers are not yet sure whether it is only the initial simultaneous dose(s) or each individual dose that acts so dramatically, lithium blood levels should be monitored regularly whenever a patient is also using a theophylline preparation.


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