Drug Interactions between Qualaquin and Uni Bronchial

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.

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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.

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Coadministration with grapefruit juice does not appear to affect the pharmacokinetics of quinine in a clinically relevant manner. Although grapefruit juice is an inhibitor of CYP450 3A4 and quinine is metabolized by this pathway to its major metabolite, 3-hydroxyquinine, a study of ten healthy volunteers found no significant differences in quinine peak plasma concentration (Cmax), time to reach Cmax (Tmax), terminal elimination half-life, systemic exposure (AUC), or apparent oral clearance (Cl/F) when a single 600 mg oral dose of quinine sulfate was administered in combination with 200 mL of orange juice (control), half-strength grapefruit juice, and full-strength grapefruit juice twice daily for 6 days each, separated by a 2-week washout period. Relative to the control period, the apparent renal clearance of quinine was markedly increased by 81% during treatment with half-strength grapefruit juice. However, since renal clearance accounts for approximately 6% of the total clearance of quinine, this change would likely have minimal clinical impact. The lack of a significant interaction is probably due to the fact that grapefruit juice primarily inhibits intestinal rather than hepatic CYP450 3A4, and quinine is not known to undergo significant presystemic metabolism as evidenced by its relatively high oral bioavailability (76% to 88%). Nevertheless, excessive consumption of grapefruit juice and tonic water (which contains quinine) was suspected as the cause of torsade de pointes arrhythmia in a patient with a history of asymptomatic long QT syndrome. Treatment with magnesium sulfate and metoprolol had no effect, but the arrhythmia resolved spontaneously 48 hours after discontinuation of the drinks. Based on current data, moderate grapefruit juice consumption is probably safe for the majority of patients taking quinine.

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