Pilocarpine concentrations in aqueous humor following single drop application. I. Effect of soft contact lenses.

Following single drop instillation of pilocarpine, drug levels in individual aqueous humor samples of rabbits were determined by high-performance liquid chromatography and correlated with changes in pupillary diameter and intraocular pressure (IOP). Application of higher concentrations of pilocarpine resulted in higher drug levels but these differences were neither statistically significant nor consistently proportional to the strength applied. Maximum miosis occurred between 30 and 60 minutes and the maximum fall in IOP occurred between 1 and 2 hours. The influence of contact lenses with varying water content and thickness upon intraocular penetration of pilocarpine was studied. Contact lenses did not affect 30-minute concentrations of pilocarpine in aqueous humor. Although two-hour levels were significantly lower with contact lenses, miosis and IOP at these time periods were comparable with and without lenses. Neither water content nor thickness appreciably influenced miosis and IOP.

High-performance liquid chromatographic assay for pilocarpine in aqueous humor.

A high-performance liquid chromatographic assay for pilocarpine has been developed for the determination of pilocarpine in aqueous humor. A structurally similar internal standard is used, and pilocarpine is separated from isopilocarpine under the chromatographic conditions used. A 100-microliter sample is mixed with an aliquot of internal standard at pH 8.3 and extracted with methylene chloride. The extract is evaporated to dryness and the alkaloids are quaternized with p-nitrobenzyl bromide. Following the quaternization, the sample is evaporated to dryness, washed and diluted with a mobile phase--triethylamine mixture and analyzed by high-performance liquid chromatography using a reversed-phase octadecylsilane column with detection at a wavelength of 254 nm. This is a highly sensitive, reproducible and selective assay for measuring pilocarpine at physiological levels in individual aqueous humor samples.

Effectiveness of generic acetazolamide.

Comparisons were made between the ocular hypotensive effects and blood levels achieved with the single-dose administration of either generic acetazolamide or brand-name acetazolamide (Diamox). The relative cost of the two products was surveyed. The effect of food on the absorption of acetazolamide was also evaluated. The generic and brand-name acetazolamide were equivalent in their effects on intraocular pressure. Comparable blood levels of acetazolamide were obtained with the two products. The cost of generic acetazolamide was 37% less than brand-name acetazolamide, when available. Food intake did not appear to influence the absorption of acetazolamide.

Inactivation of aminoglycoside-penicillin combinations after subconjunctival injection.

A study was undertaken to determine the extent of inactivation of gentamicin, tobramycin, ticarcillin and carbenicillin when given subconjunctivally in amino-glycoside-penicillin combinations. Rabbits were injected with such a combination in either the same or opposite subconjunctival sites. The aqueous humor was aspirated and bioassayed for antibiotic activity at 1 and 4 hours after injection. The influence of the aqueous humour upon antibiotic inactivation was studied by in vitro experiments. Ticarcillin penetrated into the aqueous humour better than carbenicillin. Some chemical inactivation of all the antibiotics given in combination occurred. There was less inactivation of the aminoglycosides at 4 hours when the antibiotics had been injected at opposite poles. The inactivation occurred primarily within the aqueous humour but to a lesser extent in the subconjunctival space. The degree of inactivation is likely of little clinical significance with the doses usually used.

Antihistamines as prophylaxis against side reactions to intravenous fluorescein.

Systemic antihistamines were administered prior to dye injection in 50 patients undergoing fluorescein angiography. The patients were monitored for side effects. Venous blood samples were obtained before and at three, ten and thirty minutes after intravenous administration of sodium fluorescein and analyzed for histamine levels. Three patients (6%) developed minor side effects of nausea or dizziness; this compares to an incidence of 21% in a previous series of patients from our institution untreated with antihistamines. A three-fold increase in plasma histamine levels occurred in 28% of patients following fluorescein and antihistamine injection; this compares with a 26% incidence of increase in plasma histamine in patients receiving fluorescein without antihistamines (as determined in a previous study). Prophylactic antihistamines should be considered in patients undergoing fluorescein angiography if they have a history of previous allergies or side reactions during prior fluorescein studies. However, complete prophylaxis against severe side reactions to fluorescein injections is not assured with antihistamines.

Effect of local anesthetics on intraocular penetration of subconjunctival antibiotics.

The combination of the subconjunctival injection of lidocaine HCl or procaine HCl with the subconjunctival injection of penicillin G, methicillin, cephaloridine, or gentamicin did not influence their intraocular penetration or subsequent antibiotic activity in aqueous humor of experimental animals.