Drugs and children: methods for therapeutic monitoring

Pharmacokinetic of sulfisoxazole in aqueous humor after topical and subconjunctival application in dogs

This study was undertaken to evaluate the ocular pharmacokinetic of sulfisoxazole. Male, 2-3 years old 10 mix breed dogs weighing 12-15 kg were used. A 2 mg dose/eye of sulfisoxazole was administrated to the animals by either subconjunctivally or by topically. Samples of aqueous humor were collected after 0.083, 0.25, 0.5, 1, 2, 4, 6, 24 and 72 h and level of sulfisoxazole was determined. Pharmacokinetic parameters including absorption rate constant (k(a)), slope factor (beta), absorption half-life (t1/2a), half-life of elimination in aqueous humor (t1/2beta), maximal concentration in aqueous humor (C(max)), time to reach C(max) (t(max)), mean residence time in aqueous humor (MRT) and area under the concentration time curve from zero up to infinity (AUC(0-infinity)) were calculated. Compared to topical application, value of k(a) in subconjunctival application increased while values of t1/2a and t(max) decreased and the value of t1/2beta prolonged (p < 0.05). There was no significant difference between groups regarding other parameters (p > 0.05). These results indicate that sulfisoxazole may not be potent enough to treat intraocular infections caused by bacteria when applied either subconjunctivally or topically at a dose of 2 mg/eye. Furthermore, subconjunctival application of sulfisoxazole could be more efficient for treatment of intraocular infections due to higher absorption of drug and longer remaining time in the eye compared to topical application.

Comparative pharmacokinetics of sulfamethazine in plasma and parotid saliva of sheep

Salivary output in sheep is large enough to be considered a physiologic body fluid compartment. The hypothesis for this work was that pharmacokinetics of sulfamethazine in saliva was similar to that in plasma. A reliable technique was developed to measure parotid salivary output. Mean output of saliva was 3.18 +/- 1.04 L from a single parotid gland per day with a mean flow of 2.21 +/- 0.43 mL/min. Using concentrations of sulfamethazine in parotid saliva made it possible to calculate the total passage of sulfamethazine to parotid saliva, which was calculated to be 3.5% of the total dose. Pharmacokinetic variables obtained for sulfamethazine in plasma and in saliva were closely related (AUC 1408 micrograms.h/mL and AUC 1484 micrograms.h/mL; Vdarea 0.434 L/kg and Vdarea 0.374 L/kg; t 1/2 beta 4.30 h and 3.46 h, respectively) and no substantial differences were observed. The convenience of using salivary concentrations of sulfamethazine for drug monitoring is discussed.

Pharmacokinetic aspects of a sulphachloropyridazine trimethoprim preparation in normal and diseased fowl

1. The pharmacokinetic and residue elimination patterns of sulphachloropyridazine appear to be modified by disease, even without affecting key organs essential for drug metabolism. 2. Drug kinetics and residue elimination data of a sulphachloropyridazine-trimethoprim preparation were compared using infectious coryza-affected (IC) fowl and healthy chickens. 3. The plasma concentrations of sulphachloropyridazine and trimethoprim were higher in affected animals, hence a reduced volume of distribution was obtained. 4. The half-life of sulphachloropyridazine and trimethoprim was reduced in IC-affected fowl and body clearance values were decreased. 5. The rate of drug residue elimination was noticeably slower in the IC-affected group. 6. These results indicate that drug elimination patterns in healthy and diseased animals are not the same.