Intravitreal, retinal, and central nervous system foscarnet concentrations after rapid intravenous administration to rabbits

Overton's rule helps to estimate the penetration of anti-infectives into patients' cerebrospinal fluid

In 1900, Ernst Overton found that the entry of anilin dyes through the cell membranes of living cells depended on the lipophilicity of the dyes. The brain is surrounded by barriers consisting of lipid layers that possess several inward and outward active transport systems. In the absence of meningeal inflammation, the cerebrospinal fluid (CSF) penetration of anti-infectives in humans estimated by the ratio of the area under the concentration-time curve (AUC) in CSF (AUC(CSF)) to that in serum (AUC(CSF)/AUC(S)) correlated positively with the lipid-water partition coefficient at pH 7.0 (log D) (Spearman's rank correlation coefficient r(S) = 0.40; P = 0.01) and negatively with the molecular mass (MM) (r(S) = -0.33; P = 0.04). The ratio of AUC(CSF) to the AUC of the fraction in serum that was not bound (AUC(CSF)/AUC(S,free)) strongly correlated with log D (r(S) = 0.67; P < 0.0001). In the presence of meningeal inflammation, AUC(CSF)/AUC(S) also correlated positively with log D (r(S) = 0.46; P = 0.002) and negatively with the MM (r(S) = -0.37; P = 0.01). The correlation of AUC(CSF)/AUC(S,free) with log D (r(S) = 0.66; P < 0.0001) was as strong as in the absence of meningeal inflammation. Despite these clear correlations, Overton's rule was able to explain only part of the differences in CSF penetration of the individual compounds. The site of CSF withdrawal (lumbar versus ventricular CSF), age of the patients, underlying diseases, active transport, and alterations in the pharmacokinetics by comedications also appeared to strongly influence the CSF penetration of the drugs studied.

Efeitos do Foscarnet sobre a infecção pelos herpesvírus bovino tipos 1 e 5 em coelhos

O efeito antiviral do Foscarnet (PFA) foi demonstrado anteriormente em células de cultivo infectadas com três herpesvírus bovino (BoHV). No presente estudo, investigaram-se os seus efeitos sobre a infecção e doença causadas pelo BoHV-1 e BoHV-5 em coelhos infectados experimentalmente. Coelhos inoculados com o BoHV-5 pela via intraconjuntival (IC) e tratados com o PFA (100mg/kg/dia) a partir do dia 1 pós-inoculação (pi) apresentaram uma redução nos títulos de vírus excretados entre os dias 2 e 6 pi em comparação com o grupo não-tratado; essa diferença foi significativa no dia 3 pi [F(9,108) = 2,23; P<0,03)]. Os coelhos inoculados com o BoHV-5 e tratados com o PFA apresentaram uma redução significativa nos índices de morbidade e mortalidade (95,4% [21/22] nos controles; 50% [11/22] nos tratados; [P<0,0008]). Em coelhos inoculados com o BoHV-1 pela via IC, o tratamento com o PFA resultou em redução nos títulos de vírus excretados, entre os dias 1 e 4, e 6 e 7 pi. Esses animais apresentaram um período de incubação mais curto e um curso clínico mais longo comparando-se com o grupo controle não tratado (P<0,005 e P<0,04, respectivamente). O PFA também reduziu a freqüência e severidade da doença ocular nos coelhos inoculados com o BoHV-1. Esses resultados demonstram que o PFA possui atividade frente ao BoHV-1 e BoHV-5 in vivo e são promissores para o uso desse fármaco em terapias experimentais das infecções herpéticas dos animais domésticos.

Cidofovir and foscarnet for treatment of human herpesvirus 6 encephalitis in a neutropenic stem cell transplant recipient

We report a stem cell transplant recipient who developed human herpesvirus 6 encephalitis. Human herpesvirus 6 load indicated massive intrathecal viral replication. Administration of cidofovir followed by foscarnet was associated with total clearance of human herpesvirus 6 infection. Cidofovir and foscarnet combination therapy may be beneficial for reducing mortality of (neutropenic) stem cell transplant recipients with human herpesvirus 6 encephalitis.

Determination of foscarnet (trisodium phosphonoformate) in pharmaceutical preparations by high-performance liquid chromatography with ultraviolet detection

An isocratic high-performance liquid chromatographic method with UV detection has been developed and validated for the quantitative determination of foscarnet in isoosmotic sodium chloride aqueous solution. The mobile phase consisted of mixture of methanol:water (30:70 v/v), containing 1 mm tetrahexylammonium hydrogen sulphate at pH 5.80. The analyte was separated on a reversed-phase C(18) column packed with 4 microm spherical particles of octadecylsilane. Hydrochlorothiazide was used as internal standard. UV detection at 232 nm allowed a quantification limit of 50 microg/mL. The assay was linear from 50 to 4000 microg/mL. The coefficient of variation was < or =2.52% for intra-assay precision and < or =3.49% for inter-assay precision. The deviation from the nominal value ranged from -0.57 to 0.47% for the same-day accuracy and from -0.75 to 3.06% for day-to-day accuracy.

Factors affecting delivery of antiviral drugs to the brain

Although the CNS is in part protected from peripheral insults by the blood-brain barrier and the blood-cerebrospinal fluid barrier, a number of human viruses gain access to the brain, replicate within this organ, or sustain latent infection. The efficacy of antiviral drugs towards the cerebral viral load is often limited as both blood-brain interfaces impede their cerebral distribution. For polar compounds, the major factor restricting their entry lies in the tight junctions that occlude the paracellular pathway across these barriers. For compounds with more favourable lipid solubility properties, CNS penetration will be function of a number of physicochemical factors that include the degree of lipophilicity, size and ability to bind to protein or red blood cells, as well as other factors inherent to the vascular and choroidal systems, such as the local cerebral blood flow and the surface area available for exchange. In addition, influx and efflux transport systems, or metabolic processes active in both capillary endothelial cells and choroid plexus epithelial cells, can greatly change the bioavailability of a drug in one or several compartments of the CNS. The relative importance of these various factors with respect to the CNS delivery of the different classes of antiviral drugs is illustrated and discussed.

Drug delivery to the retina: challenges and opportunities

Retinal drug delivery is a challenging area in the field of ophthalmic drug delivery. An ideal drug delivery system for the retina and vitreous humor has not yet been found, despite extensive research. Drug delivery to retinal tissue and vitreous via systemic administration is constrained due to the presence of a blood-retinal barrier (BRB) which regulates permeation of substances from blood to the retina. Although intravitreal administration overcomes this barrier, it is associated with several other problems. In recent years, transporter targeted drug delivery has become a clinically significant drug delivery approach for enhancing the bioavailabilities of drug molecules with poor membrane permeability characteristics. Various nutrient transporters, which include peptide, amino acid, folate, monocarboxylic acid transporters and so on, have been reported to be expressed on the retina and BRB. Prodrug derivatisation of drug molecules which target these transporters could result in enhanced ocular bioavailability. Highlighted in this review are various strategies currently employed for drug delivery to the posterior chamber, and novel opportunities that can be exploited to enhance ocular bioavailability of drugs.