Pharmacokinetic drug interactions with anti-ulcer drugs

Effects of calcium carbonate, sevelamer hydrochloride or pantoprazole on the pharmacokinetics of cinacalcet

BACKGROUND AND OBJECTIVES

Secondary hyperparathyroidism is a common consequence of chronic kidney disease. Cinacalcet (Sensipar(®)) is often prescribed in combination to reduce elevated levels of parathyroid hormone, calcium and phosphorus. The objective of this study was to assess the effects of concomitantly administered therapies of calcium carbonate (CaCO(3); TUMS(®)), sevelamer hydrochloride (HCl; Renagel(®)) and pantoprazole sodium (Protonix(®)) on the pharmacokinetics and safety of cinacalcet in healthy subjects.

METHODS

Three randomized, open-label, two-way crossover pharmacokinetic studies were conducted in healthy subjects. Participants received single doses of cinacalcet alone or in combination with either CaCO(3), sevelamer HCl or pantoprazole. The pharmacokinetic profile of cinacalcet was characterized. Safety assessments including adverse event reporting, changes in vital signs and clinical laboratory measurements were conducted throughout the studies.

RESULTS

The 90 % confidence intervals for the area under the concentration-time curve from time zero to the last quantifiable concentration (AUC(last)), area under the concentration-time curve from time zero to infinity (AUC(0-∞)) and maximum plasma concentration (C(max)) of cinacalcet were within the accepted range of 80-125 % for both CaCO(3) and sevelamer HCl co-administration with cinacalcet. No severe or serious adverse events or clinically relevant changes in physical or laboratory findings occurred during the studies.

CONCLUSION

The pharmacokinetic parameters of cinacalcet were not affected by co-administration of CaCO(3), sevelamer HCl or pantoprazole. Co-administration of these agents with cinacalcet does not require an adjustment of the dose of cinacalcet.

Therapeutic options for the treatment of tinea capitis: Griseofulvin versus fluconazole

BACKGROUND

Tinea capitis is a relatively common fungal infection of childhood. Griseofulvin has been the mainstay of treatment for many years. However, newer oral antifungal agents are being used more frequently.

OBJECTIVE

Our purpose was to evaluate the therapeutic efficacy of fluconazole in comparison with griseofulvin in the treatment of tinea capitis.

METHODS

We performed a single-blind, randomized, prospective evaluation of 40 patients with a clinical and mycologic diagnosis of tinea capitis. One group received fluconazole for 4 weeks. The other group received griseofulvin for 6 weeks. Five clinical parameters were evaluated. Mycologic examinations were performed at baseline and at the end of 8 weeks.

RESULTS

Patients ranged in age from 1 to 16 years; 80% were boys and 20% were girls. Mycologic examinations disclosed Trichophyton verrucosum in 40% of patients, T. violaceum in 40% and Microsporum canis in 20%. At week 8, the griseofulvin-treated group showed a cure rate of 76%, and the fluconazole-treated group 78%. The cure rates were not statistically significant.

CONCLUSION

Fluconazole constitutes an alternative but, because of greater availability and lower cost, griseofulvin remains the treatment of choice for tinea capitis.

Role of cytochrome P450 in drug interactions

Drug-drug interactions have become an important issue in health care. It is now realized that many drug-drug interactions can be explained by alterations in the metabolic enzymes that are present in the liver and other extra-hepatic tissues. Many of the major pharmacokinetic interactions between drugs are due to hepatic cytochrome P450 (P450 or CYP) enzymes being affected by previous administration of other drugs. After coadministration, some drugs act as potent enzyme inducers, whereas others are inhibitors. However, reports of enzyme inhibition are very much more common. Understanding these mechanisms of enzyme inhibition or induction is extremely important in order to give appropriate multiple-drug therapies. In future, it may help to identify individuals at greatest risk of drug interactions and adverse events.

Lack of effect of aciclovir on metabolism of theophylline and expression of hepatic cytochrome P450 1A2 in rats

There is an interesting clinical report indicating that aciclovir, which is mainly excreted into urine, decreases the systemic clearance of theophylline by inhibiting cytochrome P450 (CYP) 1A2-mediated metabolism. In this study, we investigated the effect of aciclovir on the metabolism of theophylline, and on the activity and expression of hepatic CYP1A2 in rats. Theophylline (10 mg/kg) was injected intravenously into rats treated with two different dosages of aciclovir. When theophylline was simultaneously administered with aciclovir (50 mg/kg), the systemic clearance of theophylline and metabolic clearance of its major metabolites, 1-methyluric acid and 1,3-dimethyluric acid, were unchanged. In place of theophylline, when 1-methyl-3-propylxanthine (2.5 mg/kg), which is almost metabolized by CYP1A2 in rats, was coadministered intravenously with aciclovir (50 mg/kg), the pharmacokinetics of 1-methyl-3-propylxanthine was also unchanged. When theophylline was administered to rats pretreated with repeated intraperitoneal injections of aciclovir (25 mg/kg twice daily for 3 d), no significant differences in the systemic clearance of theophylline and its metabolic clearance to 1-methyluric acid and 1,3-dimethyluric acid were observed between the control and aciclovir-treated rats. This dosage of aciclovir did not change the activity of 7-ethoxyresorufin O-dealkylation, which is represented as CYP1A2 activity. In Western blot analysis, no significant change in the protein levels of hepatic CYP1A2 was observed between the control and aciclovir-treated rats. The present study suggests that aciclovir has no effect on the pharmacokinetics and metabolism of theophylline and on the activity and expression of hepatic CYP1A2 in rats.

Effect of omeprazole on the pharmacokinetics of paricalcitol in healthy subjects

Paricalcitol capsules are indicated for the prevention and treatment of secondary hyperparathyroidism in chronic kidney disease (CKD). Proton pump inhibitors are prescribed to CKD patients to treat gastroesophageal reflux. This was a single dose, crossover study evaluating the effect of omeprazole, change in gastric pH as a result thereof, on the pharmacokinetics (PK) of paricalcitol. Twenty-six healthy subjects were administered paricalcitol capsules (16 microg) alone (regimen A), and following a single dose of OMP (40 mg) (regimen B), with a washout of at least 7 days. Plasma samples for paricalcitol concentrations were collected for 48 h post-paricalcitol dose. The plasma paricalcitol concentrations were measured using an LC-MS/MS assay (LOQ=0.02 ng/ml) and paricalcitol pharmacokinetic parameters were estimated using non-compartmental methods. The point estimates and the corresponding 90% confidence intervals for Cmax and AUC0-infinity to evaluate paricalcitol-omeprazole interaction were 1.032 [0.920-1.158] and 1.041 [0.951-1.139], respectively. No significant differences in Tmax (regimen A: 2.9 h vs regimen B: 2.6 h) or t1/2 (6.83 h vs 6.6 h) between the regimens were observed. Hence, the co-administration of omeprazole does not affect the PK of paricalcitol. Both regimens were well tolerated and no apparent differences among the regimens with respect to safety were observed.

Reduced oral itraconazole bioavailability by antacid suspension

AIMS

To investigate the effects of antacid suspension on oral absorption of itraconazole.

METHODS

A randomized, open-labelled, two-period, crossover study with a 1-week washout period was conducted in 12 healthy Thai male volunteers. The participants were allocated in either treatment A or B in the first period. In treatment A, the volunteers were orally administered with 200 mg of itraconazole alone. In treatment B, the volunteers were administered orally with 200 mg of itraconazole co-administered with antacid suspension. Serial serum samples were collected over the period of 24 h and subsequently analysed by using a validated high-pressure liquid chromatographic method with ultraviolet detection. Pharmacokinetic parameters were determined by non-compartmental analysis.

RESULTS

Time to reach maximal concentration (Tmax), maximal concentration (Cmax) and area under the curve (AUC0-infinity) were markedly decreased in antacid-treated group. Tmax for treatment A was 3.0 +/- 0.4 and 5.1 +/- 2.7 h for treatment B. Cmax and AUC0-infinity of treatments A and B were 146.3 +/- 70.5 vs. 43.6 +/- 16.9 (ng/mL) and 1928.5 +/- 1114.6 vs. 654.8 +/- 452.2 (ng x h/mL) respectively. 90% Confidence interval (90% CI) of Cmax and AUC0--infinity were 24.1-42.1 and 16.2-65.9 respectively.

CONCLUSIONS

Rate and extent of itraconazole oral absorption were markedly decreased by concurrent use of antacid suspension. Hence, co-administration of itraconazole and antacid suspension should be avoided.

Delivering health information about self-medication to older adults: use of touchscreen-equipped notebook computers

Preventing Drug Interactions in Active Older Adults is an educational intervention to prevent prescription and over-the-counter (OTC) drug and alcohol interactions in active, community-living older adults. The objectives of the program are to increase older adults' knowledge of potential interactions of prescription medications with OTC drugs and alcohol and to increase their confidence (self-efficacy) about how to avoid such interactions. An interactive multimedia computer software program (Personal Education Program or PEP) was designed for the learning styles and psychomotor skills of older adults. Focus groups of older adults evaluated PEP components in a formative manner during development. The program content dealing with antacids, calcium supplements, and acid reducers was pilot tested with 60 older adults recruited from local senior centers. Participants used the PEP on notebook computers equipped with infrared-sensitive touchscreens. Users of PEP had greater knowledge and self-efficacy scores than controls. Participants indicated a high degree of satisfaction with the PEP and reported their intent to make specific changes in self-medication behaviors.

Pharmacokinetic considerations in the eradication of Helicobacter pylori

As Helicobacter pylori plays an important role in the aetiopathogenesis of peptic ulcer, therapeutic strategies aimed at maintaining long term remission have shifted from the control of intragastric pH to targeting H. pylori. According to recent international guidelines the clinical goals--rapid ulcer healing and prevention of relapse--can be best accomplished by combination therapy consisting of an antisecretory drug (proton pump inhibitor or ranitidine) and 2 antimicrobial agents (preferable amoxicillin, clarithromycin or metronidazole). When applying such multidrug regimens, possible synergy between the agents suggests that pharmacokinetic considerations might help to improve H. pylori eradication rates, which should be above 85 to 90% on an intention-to-treat basis. The present review summarises the pharmacokinetic properties and interaction potential of all drugs presently used in the various H. pylori eradication regimens, with emphasis on particular patient populations such as the elderly and those with renal impairment. The drugs considered are omeprazole, lansoprazole, pantoprazole, rabeprazole, ranitidine and ranitidine bismutrex, bismuth salts, amoxicillin, clarithromycin, azithromycin, roxithromycin, metronidazole, tinidazole and tetracycline. When addressing the clinically important questions of the efficacy, safety and costs of the recommended regimens, the impact of drug disposition on H. pylori eradication should not be neglected.

Clinically significant pharmacokinetic drug interactions with benzodiazepines

The reports of interactions between benzodiazepines (BZPs) and other drugs (e.g., antidepressants, selective serotonin reuptake inhibitors, antiulcer drugs, antiepileptic drugs, macrolide antibiotics) during their combined use are reviewed. In general, metabolism of BZPs is delayed when combined with a number of other drugs but some reports have suggested otherwise. In recent years, the cytochrome P450 (P450 or CYP) isoenzyme that catalyses the metabolism of BZPs has also been identified. BZPs are mainly catalysed by CYP3A4. When published reports are studied, it appears necessary to be exceptionally careful about interactions mainly between BZPs and selective serotonin reuptake inhibitors, cimetidine, antiepileptic drugs, macrolide antibiotics and antimycotics. More information is necessary to identify individuals at greatest risk of drug interactions and adverse events.

Clinically important pharmacokinetic drug-drug interactions: role of cytochrome P450 enzymes

Drug-drug interactions have become an important issue in health care. It is now realized that many drug-drug interactions can be explained by alterations in the metabolic enzymes that are present in the liver and other extra-hepatic tissues and many of the major pharmacokinetic interactions between drugs are due to hepatic cytochrome P450 (P450 or CYP) enzymes being affected by previous administration of other drugs. After coadministration, some drugs act as potent enzyme inducers, whereas others are inhibitors. However, reports of enzyme inhibition are very much more common. Understanding these mechanisms of enzyme inhibition or induction is extremely important in order to give appropriate multiple-drug therapies. In the future, it may help to identify individuals at greatest risk of drug interactions and adverse events.