Optimisation of itraconazole therapy using target drug concentrations

Area of Science:

• Pharmacology
• Mycology
• Clinical Pharmacy

Background:

• Itraconazole is a broad-spectrum triazole antifungal agent used for fungal infections, particularly in immunocompromised individuals.
• Its lipophilic nature and ionization at low pH influence its absorption and distribution.
• Hydroxy-itraconazole, a major metabolite, possesses similar antifungal activity and higher plasma concentrations than the parent drug.

Purpose of the Study:

• To review the pharmacokinetic properties of itraconazole.
• To discuss factors affecting its absorption, distribution, metabolism, and excretion.
• To highlight the clinical relevance of itraconazole pharmacokinetics, including drug interactions and therapeutic drug monitoring.

Main Methods:

• Literature review of itraconazole pharmacokinetics.
• Analysis of data on drug absorption, protein binding, volume of distribution, metabolism, and clearance.
• Evaluation of factors influencing itraconazole pharmacokinetics, such as food intake, disease states, and co-administered drugs.
• Review of clinical studies correlating plasma concentrations with efficacy.

Main Results:

• Itraconazole absorption is variable (55% in fasting state, increased with food) and affected by gastrointestinal disorders.
• The drug is highly protein-bound (99.8%) with a large volume of distribution (11 L/kg) and extensively metabolized by the liver.
• Hydroxy-itraconazole is a key active metabolite; itraconazole is a potent inhibitor of CYP3A4, leading to significant drug interactions.
• Pharmacokinetics exhibit dose-dependency, and renal failure does not impact properties, while hepatic insufficiency effects are less understood.
• Therapeutic drug monitoring is suggested, with target concentrations of >250 µg/L for itraconazole or 750–1000 µg/L for itraconazole + hydroxy-itraconazole for prophylaxis.

Conclusions:

• Significant inter- and intra-patient variability in itraconazole pharmacokinetics complicates dose-efficacy relationships.
• Regular monitoring of itraconazole plasma concentrations is essential to ensure adequate exposure and optimize antifungal activity, particularly in patients with life-threatening infections.
• Understanding itraconazole's pharmacokinetic profile and interactions is critical for safe and effective clinical use.