Theophylline disposition in Korean patients with congestive heart failure

Reduced theophylline clearance due to hepatic congestion secondary to right heart failure - A population pharmacokinetic study

Theophylline, a beneficial drug with bronchodilatory and anti-inflammatory effects, is used for the treatment of respiratory diseases. Pulmonary (PC) and hepatic congestion (HC) are secondary to the development of left- and right-sided heart failure (HF), respectively. This study aimed to evaluate the effects of PC and HC on theophylline clearance (CL) by population pharmacokinetic (PPK) analysis with consideration of the severity of HF assessed by the New York Heart Association (NYHA) functional classification. We obtained 710 minimum steady-state concentrations from 201 Japanese bronchial asthma patients with and without HF. PPK analysis was performed by NONMEM. In the analysis, the left ventricular ejection fraction, smoking (SMK), clarithromycin (CAM), sex, and age were also considered as covariates. The final model of apparent theophylline clearance (CL/F) was as follows: CL/F (L/hr/kg) = 0.0465 × 1.40^SMK × 0.870^CAM × 0.863^{HC(+)NYHA II} × 0.634^{HC(+)NYHA III} × 0.586^{HC(-)NYHA IV} × 0.467^{HC(+)NYHA IV}. SMK is a well-known factor that markedly enhances theophylline clearance through the induction of CYP1A enzymes, while CAM has been reported to inhibit CYP3A4. The final model indicates that HF patients with HC show reduced clearance of theophylline depending on the severity of HF. In this study, no effects of PC were observed.

A review and assessment of potential sources of ethnic differences in drug responsiveness

The International Conference on Harmonization (ICH) E5 guidelines were developed to provide a general framework for evaluating the potential impact of ethnic factors on the acceptability of foreign clinical data, with the underlying objective to facilitate global drug development and registration. It is well recognized that all drugs exhibit significant inter-subject variability in pharmacokinetics and pharmacologic response and that such differences vary considerably among individual drugs and depend on a variety of factors. One such potential factor involves ethnicity. The objective of the present work was to perform an extensive review of the world literature on ethnic differences in drug disposition and responsiveness to determine their general significance in relation to drug development and registration. A few examples of suspected ethnic differences in pharmacokinetics or pharmacodynamics were identified. The available literature, however, was found to be heterologous, including a variety of study designs and research methodologies, and most of the publications were on drugs that were approved a long time ago.

Theophylline metabolism after cardiac surgery

The effect and metabolism of theophylline administration after cardiac surgery has never been reported. Two series of 2-hour intravenous aminophylline administrations (3 mg/kg/h) were conducted in 10 adult patients on the operative day (acute phase) and on the 4th or 5th postoperative day (recovery phase). Both blood and urine samples were collected for 24 hours after dosing. Heart rate increased in both phases, but the cardiac index increased with the decrease of diastolic blood pressure only in the acute phase (p < 0.05). Plasma concentration levels of theophylline tended to be slightly higher in the acute phase, and renal clearance increased in the recovery phase (p < 0.05). The urinary ratio of 3-methylxanthine to theophylline was significantly higher in the acute phase (p < 0.05). This suggests that cytochrome P4501A2 is partially activated rather than depressed and that N-demethylation is promoted more than hydroxylation immediately after surgery.

Effect of ranitidine on theophylline metabolism in healthy Koreans living in China

OBJECTIVE

To evaluate the effect of concurrent ranitidine therapy on theophylline metabolism in healthy Koreans.

DESIGN

A 4-week, double-blind, randomized, placebo-controlled, crossover study.

SETTING

The Clinical Research Unit, Department of Pharmaceutical Sciences, Yanbian Medical College, Yanji, China.

SUBJECTS

Six young, healthy, nonsmoking Korean volunteers residing in China with no known factors that would alter theophylline metabolism.

INTERVENTIONS

Subjects received extended-release oral theophylline at a constant dosage over 4 weeks to yield a serum concentration (Cp) between 5 and 10 micrograms/mL. Week 1 was the dosage titration phase. During week 2 subjects randomly received either ranitidine or a matching placebo. Week 3 was a washout phase, and during week 4 subjects were crossed over to receive either placebo or ranitidine. At the end of each treatment week, serum and urinary metabolite concentrations were measured.

OUTCOME MEASURES

Theophylline serum concentrations and urinary concentrations of 1-methylxanthine, 1-methyluric acid, 3-methylxanthine, and 1,3-dimethyluric acid were measured. Estimates of clearance (Cl), volume of distribution (Vd), and half-life (t1/2) were determined.

RESULTS

Concurrent administration of ranitidine with theophylline did not significantly alter theophylline Cp, Cl, Vd, or t1/2. Urinary concentrations of major theophylline metabolites also were not changed.

CONCLUSIONS

Ranitidine does not significantly alter the metabolism of theophylline in healthy Koreans residing in China.