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Drug Interactions between Climara and Theomar GG

This report displays the potential drug interactions for the following 2 drugs:

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Interactions between your drugs

Moderate

theophylline estradiol

Applies to: Theomar GG (guaifenesin / theophylline) and Climara (estradiol)

MONITOR: The coadministration with contraceptive steroids may increase the plasma concentrations of theophylline and other methylxanthines. The proposed mechanism is inhibition of methylxanthine metabolism via hepatic microsomal enzymes, of which estrogens and progestins are also substrates. In one study, theophylline clearance was approximately 30% lower in oral contraceptive users than in nonusers. However, clinical data have been conflicting.

MANAGEMENT: Caution is advised during concomitant therapy with methylxanthines and hormonal contraceptives. Serum theophylline levels and pharmacologic response should be monitored and the dosage adjusted accordingly, particularly following initiation or discontinuation of hormonal contraceptives in patients who are stabilized on their theophylline regimen. Patients should be advised to notify their physician if they experience signs and symptoms of theophylline toxicity such as nausea, vomiting, diarrhea, headache, restlessness, insomnia, and irregular heartbeat.

References

  1. Tornatore KM, Kanarkowski R, McCarthy TL, et al. "Effect of chronic oral contraceptive steroids on theophylline disposition." Eur J Clin Pharmacol 23 (1982): 129-34
  2. Gardner MJ, Tornatore KM, Jusko WJ, Kanarkowski R "Effects of tobacco smoking and oral contraceptive use on theophylline disposition." Br J Clin Pharmacol 16 (1983): 271-80
  3. Roberts RK, Grice J, McGuffie, Heilbronn L "Oral contraceptive steroids impair the elimination of theophylline." J Lab Clin Med 101 (1983): 821-25

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Drug and food interactions

Moderate

theophylline food

Applies to: Theomar GG (guaifenesin / theophylline)

GENERALLY AVOID: Coadministration with caffeine may increase the serum concentrations of theophylline. The proposed mechanism involves competitive inhibition of theophylline metabolism via CYP450 1A2, as well as metabolic conversion of caffeine to theophylline in vivo and saturation of theophylline metabolism at higher serum concentrations. In six healthy male volunteers (all smokers), serum concentrations of theophylline (administered as aminophylline 400 mg single oral dose) were significantly higher following consumption of caffeine (2 to 7 cups of instant coffee over 24 hours, equivalent to approximately 120 to 630 mg of caffeine) than after caffeine deprivation for 48 hours. Caffeine consumption also increased the apparent elimination half-life of theophylline by an average of 32% and reduced its total body clearance by 23%. In another study, steady-state concentration and area under the concentration-time curve of theophylline (1200 mg intravenously over 24 hours) increased by 23% and 40%, respectively, in eight healthy volunteers following administration of caffeine (300 mg orally three times a day).

MANAGEMENT: Given the narrow therapeutic index of theophylline, patients should limit or avoid significant fluctuations in their intake of pharmacologic as well as dietary caffeine.

ADJUST DOSING INTERVAL: Administration of theophylline with continuous enteral nutrition may reduce the serum levels or the rate of absorption of theophylline. The mechanism has not been reported. In one case, theophylline levels decreased by 53% in a patient receiving continuous nasogastric tube feedings and occurred with both theophylline tablet and liquid formulations, but not with intravenous aminophylline.

MANAGEMENT: When administered to patients receiving continuous enteral nutrition , some experts recommend that the tube feeding should be interrupted for at least 1 hour before and 1 hour after the dose of theophylline is given; rapid-release formulations are preferable, and theophylline levels should be monitored.

References

  1. Jonkman JH, Sollie FA, Sauter R, Steinijans VW "The influence of caffeine on the steady-state pharmacokinetics of theophylline." Clin Pharmacol Ther 49 (1991): 248-55
  2. Sato J, Nakata H, Owada E, Kikuta T, Umetsu M, Ito K "Influence of usual intake of dietary caffeine on single-dose kinetics of theophylline in healthy human subjects." Eur J Clin Pharmacol 44 (1993): 295-8
  3. Wohlt PD, Zheng L, Gunderson S, Balzar SA, Johnson BD, Fish JT "Recommendations for the use of medications with continuous enteral nutrition." Am J Health Syst Pharm 66 (2009): 1438-67

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Moderate

theophylline food

Applies to: Theomar GG (guaifenesin / theophylline)

GENERALLY AVOID: Coadministration with caffeine may increase the serum concentrations of theophylline. The proposed mechanism involves competitive inhibition of theophylline metabolism via CYP450 1A2, as well as metabolic conversion of caffeine to theophylline in vivo and saturation of theophylline metabolism at higher serum concentrations. In six healthy male volunteers (all smokers), serum concentrations of theophylline (administered as aminophylline 400 mg single oral dose) were significantly higher following consumption of caffeine (2 to 7 cups of instant coffee over 24 hours, equivalent to approximately 120 to 630 mg of caffeine) than after caffeine deprivation for 48 hours. Caffeine consumption also increased the apparent elimination half-life of theophylline by an average of 32% and reduced its total body clearance by 23%. In another study, steady-state concentration and area under the concentration-time curve of theophylline (1200 mg intravenously over 24 hours) increased by 23% and 40%, respectively, in eight healthy volunteers following administration of caffeine (300 mg orally three times a day).

MANAGEMENT: Given the narrow therapeutic index of theophylline, patients should limit or avoid significant fluctuations in their intake of pharmacologic as well as dietary caffeine.

References

  1. Jonkman JH, Sollie FA, Sauter R, Steinijans VW "The influence of caffeine on the steady-state pharmacokinetics of theophylline." Clin Pharmacol Ther 49 (1991): 248-55
  2. Sato J, Nakata H, Owada E, Kikuta T, Umetsu M, Ito K "Influence of usual intake of dietary caffeine on single-dose kinetics of theophylline in healthy human subjects." Eur J Clin Pharmacol 44 (1993): 295-8

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Minor

estradiol food

Applies to: Climara (estradiol)

Coadministration with grapefruit juice may increase the bioavailability of oral estrogens. The proposed mechanism is inhibition of CYP450 3A4-mediated first-pass metabolism in the gut wall induced by certain compounds present in grapefruits. In a small, randomized, crossover study, the administration of ethinyl estradiol with grapefruit juice (compared to herbal tea) increased peak plasma drug concentration (Cmax) by 37% and area under the concentration-time curve (AUC) by 28%. Based on these findings, grapefruit juice is unlikely to affect the overall safety profile of ethinyl estradiol. However, as with other drug interactions involving grapefruit juice, the pharmacokinetic alterations are subject to a high degree of interpatient variability. Also, the effect on other estrogens has not been studied.

References

  1. Weber A, Jager R, Borner A, et al. "Can grapefruit juice influence ethinyl estradiol bioavailability?" Contraception 53 (1996): 41-7
  2. Schubert W, Eriksson U, Edgar B, Cullberg G, Hedner T "Flavonoids in grapefruit juice inhibit the in vitro hepatic metabolism of 17B-estradiol." Eur J Drug Metab Pharmacokinet 20 (1995): 219-24

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Therapeutic duplication warnings

No warnings were found for your selected drugs.

Therapeutic duplication warnings are only returned when drugs within the same group exceed the recommended therapeutic duplication maximum.

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Drug Interaction Classification

These classifications are only a guideline. The relevance of a particular drug interaction to a specific individual is difficult to determine. Always consult your healthcare provider before starting or stopping any medication.
Major Highly clinically significant. Avoid combinations; the risk of the interaction outweighs the benefit.
Moderate Moderately clinically significant. Usually avoid combinations; use it only under special circumstances.
Minor Minimally clinically significant. Minimize risk; assess risk and consider an alternative drug, take steps to circumvent the interaction risk and/or institute a monitoring plan.
Unknown No interaction information available.

Further information

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