Clarithromycin-nifedipine interaction as possible cause of vasodilatory shock

Complex Drug-Drug-Gene-Disease Interactions Involving Cytochromes P450: Systematic Review of Published Case Reports and Clinical Perspectives

Drug pharmacokinetics (PK) is influenced by multiple intrinsic and extrinsic factors, among which concomitant medications are responsible for drug-drug interactions (DDIs) that may have a clinical relevance, resulting in adverse drug reactions or reduced efficacy. The addition of intrinsic factors affecting cytochromes P450 (CYPs) activity and/or expression, such as genetic polymorphisms and diseases, may potentiate the impact and clinical relevance of DDIs. In addition, greater variability in drug levels and exposures has been observed when such intrinsic factors are present in addition to concomitant medications perpetrating DDIs. This variability results in poor predictability of DDIs and potentially dramatic clinical consequences. The present review illustrates the issue of complex DDIs using systematically searched published case reports of DDIs involving genetic polymorphisms, renal impairment, cirrhosis, and/or inflammation. Current knowledge on the impact of each of these factors on drug exposure and DDIs is summarized and future perspectives for the management of such complex DDIs in clinical practice are discussed, including the use of advanced Computerized Physician Order Entry (CPOE) systems, the development of model-based dose optimization strategies, and the education of healthcare professionals with respect to personalized medicine.

Hypotension induced by the concomitant use of a calcium-channel blocker and clarithromycin

In the elderly, calcium-channel blockers are the first-line treatment for hypertension, and macrolides are commonly prescribed antibiotics. Here we report a 78-year-old man taking nifedipine, diltiazem and carvedilol who presented with persistent hypotension and bradycardia after clarithromycin was prescribed. He was diagnosed with drug-induced hypotension and treated with fluid resuscitation and vasoactive agents. His symptoms gradually improved. He was transferred out of the intensive care unit 3 days after hospitalisation. Combining calcium-channel blockers and clarithromycin can cause vasodilatory hypotension. The concomitant use of calcium-channel blockers and macrolide antibiotics increases the levels of calcium-channel blockers in the blood as they are metabolised by cytochrome P450 3A4 (CYP3A4), which is inhibited by macrolide antibiotics. Moreover, the addition of another calcium-channel blocker and a β blocker can lower cardiac output due to bradycardia and worsen hypotension. Therefore, it is important to consider drug interactions when the cause of hypotension is unknown.

Population-Based Assessments of Clinical Drug-Drug Interactions: Qualitative Indices or Quantitative Measures?

Population-based assessments of drug-drug interactions have become more common since the introduction and acceptance of the population pharmacokinetic approach. Unlike traditional methods, population-based studies provide clinically relevant results that can be applied directly to a target patient population. Furthermore, population-based studies do not demand the traditional requirements of intensive pharmacokinetic sampling, rigorous inpatient stays, or stringent assessment schedules. As such, the population-based approach can effectively be used to confirm known drug-drug interactions and further characterize anticipated interactions. A prospectively designed analysis can also reveal drug-drug interactions that might otherwise have gone undetected with traditional methods. Ultimately, these results could help to alleviate clinicians' concerns about using widely marketed drugs in combination therapies and also reduce patients' risk of experiencing unacceptable side effects. This article intends to provide a balanced overview of the population-based approach and its merits, drawbacks, and potential utility in the assessment of drug-drug interactions during clinical drug development.

The risk of hypotension following co-prescription of macrolide antibiotics and calcium-channel blockers

BACKGROUND

The macrolide antibiotics clarithromycin and erythromycin may potentiate calcium-channel blockers by inhibiting cytochrome P450 isoenzyme 3A4. However, this potential drug interaction is widely underappreciated and its clinical consequences have not been well characterized. We explored the risk of hypotension or shock requiring hospital admission following the simultaneous use of calcium-channel blockers and macrolide antibiotics.

METHODS

We conducted a population-based, nested, case-crossover study involving people aged 66 years and older who had been prescribed a calcium-channel blocker between Apr. 1, 1994, and Mar. 31, 2009. Of these patients, we included those who had been admitted to hospital for the treatment of hypotension or shock. For each antibiotic, we estimated the risk of hypotension or shock associated with the use of a calcium blocker using a pair-matched analytic approach to contrast each patient's exposure to each macrolide antibiotic (erythromycin, clarithromycin or azithromycin) in a seven-day risk interval immediately before admission to hospital and in a seven-day control interval one month earlier.

RESULTS

Of the 7100 patients admitted to hospital because of hypotension while receiving a calcium-channel blocker, 176 had been prescribed a macrolide antibiotic during either the risk or control intervals. Erythromycin (the strongest inhibitor of cytochrome P450 3A4) was most strongly associated with hypotension (odds ratio [OR] 5.8, 95% confidence interval [CI] 2.3-15.0), followed by clarithromycin (OR 3.7, 95% CI 2.3-6.1). Azithromycin, which does not inhibit cytochrome P450 3A4, was not associated with an increased risk of hypotension (OR 1.5, 95% CI 0.8-2.8). We found similar results in a stratified analysis of patients who received only dihydropyridine calcium-channel blockers.

INTERPRETATION

In older patients receiving a calcium-channel blocker, use of erythromycin or clarithromycin was associated with an increased risk of hypotension or shock requiring admission to hospital. Preferential use of azithromycin should be considered when a macrolide antibiotic is required for patients already receiving a calcium-channel blocker.

Drug utilization of clarithromycin for gastrointestinal disease treatment

AIM: To evaluate the patterns of use of clarithromycin for gastrointestinal disease treatment and promote its rational use.

METHODS: Using a structured pro forma, we conducted a two-month survey of the electronic prescriptions containing immediate-release (IR) or sustained-release (SR) product of clarithromycin for outpatients with gastrointestinal diseases in a 2200-bed general hospital. Suitability of the prescription was audited retrospectively.

RESULTS: One hundred and sixty-four prescriptions of SR product and 110 prescriptions of IR product were prescribed for gastrointestinal disease treatment. Among prescriptions for anti-Helicobacter pylori (H pylori) therapy, triple therapy take the dominant position (91.8%), followed by quadruple therapy (4.3%) and dual therapy (3.9%). Amoxicillin was the most frequently co-prescribed antibiotic. Furazolidone and levofloxacin are used more widely than metronidazole or tinidazole. Clarithromycin SR was administered at inappropriate time points in all prescriptions. Fifty percent of all prescriptions of clarithromycin SR, and 6.4% of prescriptions of clarithromycin IR, were prescribed at inappropriate dosing intervals. Surprisingly, disconcordance between diagnoses and indications was observed in all prescriptions of clarithromycin SR which has not been approved for treating H pylori infection although off-label use for this purpose was reported in literature. On the contrary, only one prescription (0.9%) of clarithromycin IR was prescribed for unapproved indication (i.e. gastro-oesophageal reflux disease). 1.4% of prescriptions for chronic gastritis or peptic ulcer treatment were irrational in that clarithromycin was not co-prescribed with gastric acid inhibitors. Clinical significant CYP3A based drug interactions with clarithromycin were identified.

CONCLUSION: There is a great scope to improve the quality of clarithromycin prescribing in patients with gastrointestinal disease, especially with regard to administration schedule, concordance between indications and diagnoses and management of drug interactions.

Interaction between midazolam and clarithromycin in the elderly

AIM

To assess the relative contribution of intestinal and hepatic CYP3A inhibition to the interaction between the prototypic CYP3A substrate midazolam and clarithromycin in the elderly.

METHODS

On day 1, 16 volunteers (eight male, eight female) aged 65-75 years weighing 59-112 kg received simultaneous doses of midazolam intravenously (i.v.) (0.05 mg kg(-1) over 30 min) and orally (p.o.) (3.5 mg of a stable isotope, (15)N(3)-midazolam). Starting on day 2, clarithromycin 500 mg was administered orally twice daily for 7 days. On day eight, i.v. and p.o. doses of midazolam were administered 2 h after the final clarithromycin dose. Serum and urine samples were assayed for midazolam, (15)N(3)-midazolam and metabolites by gas chromatography/mass spectometry.

RESULTS

Men and women exhibited similar i.v. (30.4 vs. 36.0 l h(-1)) and p.o. (119 vs. 124 l h(-1)) clearances of midazolam. Midazolam hepatic availability was significantly (P = 0.006) greater in men [0.79, 95% confidence interval (CI) 0.75, 0.84] than in women (0.66, 95% CI 0.59, 0.73), but midazolam intestinal availability (0.39 vs. 0.55) was not different. Following clarithromycin dosing, a significant decrease in systemic (33.2 l h(-1) to 11.5 l h(-1)) and oral (121 l h(-1) to 17.4 l h(-1)) midazolam clearance occurred. Oral, hepatic and intestinal availability was significantly increased after clarithromycin dosing from 0.34 to 0.72, 0.73 to 0.91 and 0.47 to 0.79, respectively. Clarithromycin administration led to an increase in the AUC of midazolam by 3.2-fold following i.v. dosing and 8.0-fold following p.o. dosing. Similar effects were observed for males and females.

CONCLUSIONS

Intestinal and hepatic CYP3A inhibition by clarithromycin significantly reduces the clearance of midazolam in the elderly.

Clarithromycin extended-release in community-acquired respiratory tract infections

Clarithromycin extended-release (ER) is a second-generation macrolide with bactericidal activity against a broad group of pathogens. It allows for convenient once-daily dosing (2 x 500 mg/day), and has less severe adverse effects than the immediate-release (IR) formulation of the drug, which may result in improved patient compliance. Clarithromycin ER has been approved for the treatment of community-acquired pneumonia, acute maxillary sinusitis and acute bacterial exacerbation of chronic bronchitis. In comparison to the IR formulation, clarithromycin ER demonstrates prolonged absorption from the gastrointestinal tract, allowing for once-daily dosing with improved gastrointestinal tolerability. Various double-blind, randomised clinical trials and group studies have found clarithromycin ER to be an efficacious treatment option, comparable with clarithromycin IR, or its other competitors.