Hydroxyurea is used in the treatment of various forms of cancer, sickle-cell anaemia and HIV infection. Oral absorption of the drug is virtually complete, the volume of distribution is equivalent to total body water and elimination is through both renal and nonrenal mechanisms. Nonrenal elimination of hydroxyurea is characterised by Michaelis-Menten kinetics. Further studies are necessary to clarify several aspects of the pharmacokinetics and pharmacodynamics of hydroxyurea: the effect of age and disease state, concentration-effect relationship, the role of therapeutic drug monitoring, and the mechanisms of renal and nonrenal elimination. The recent development of improved assays for hydroxyurea should have benefits for future pharmacokinetic studies.

The article reviews the effect of diabetes on the pharmacokinetics and pharmacodynamics of drugs in humans. For most drugs which cross the gastrointestinal wall by passive diffusion, oral absorption is unlikely to be affected by diabetes, although a delay in the absorption of tolazamide and a decrease in the extent of absorption of ampicillin have been reported. Subcutaneous absorption of insulin is more rapid in diabetic patients, whereas the intramuscular absorption of several drugs is slower. The binding of a number of drugs in the blood is reduced in diabetes, which may be due to glycosylation of plasma proteins or displacement by plasma free fatty acids, the level of which is increased in diabetic patients. Plasma concentrations of albumin and alpha 1-acid glycoprotein do not appear to be changed by the disease. The distribution of drugs with little or no binding in the blood is generally not altered, although the volume of distribution of phenazone (antipyrine) is reduced by 20% in insulin-dependent diabetes mellitus (IDDM). In contrast to animal studies, the metabolic clearance of most drugs in humans appears to be unaffected or slightly reduced by the disease. The presence of fatty liver in non-insulin-dependent diabetes mellitus (NIDDM) may contribute to a reduced hepatic clearance, whereas decreased binding in the blood may cause an increase in clearance. The effect of diabetes on hepatic blood flow in humans appears to be unknown. Diabetes affects kidney function in a significant number of diabetic patients. During the first 10 years after the onset of the disease, glomerular filtration is elevated in these patients. Thus, the renal clearance of a number of antibiotics has been shown to be increased in diabetic children. As the disease progresses, renal function is impaired and glomerular function declines from the initial elevated state. In diabetic adults the renal clearance of drugs either is comparable with that found in nondiabetic individuals or is reduced. A limited number of studies have been conducted comparing the dose-response of cardiovascular drugs in diabetic patients with that in nondiabetic controls. Decreased, increased and unchanged responses have been reported. It is apparent that in some cases an altered response may be observed for a drug when administered to a diabetic patient compared with a similar nondiabetic individual. At the present time, it is not possible to ascertain whether these studies reflect true pharmacodynamic changes or merely alterations in pharmacokinetics.(ABSTRACT TRUNCATED AT 400 WORDS)

Osteotropicity of novel bone-targeted HPMA copolymer conjugates has been demonstrated previously with bone histomorphometric analysis. The pharmacokinetics and biodistribution of this delivery system were investigated in the current study with healthy young BALB/c mice. The 125 Ilabeled bone-targeted and control (non-targeted) HPMA copolymers were administered intravenously to mice and their distribution to different organs and tissues were followed using a gamma counter and single photon emission computed tomography (SPECT). Both the invasive and non-invasive data further confirmed that the incorporation of D-aspartic acid octapeptide (D-Asp 8 ) as bone-targeting moiety could favorably deposit the HPMA copolymers to the entire skeleton, especially to the high bone turnover sites. To evaluate the influence of molecular weight, three fractions (M w of 24, 46, and 96 kDa) of HPMA copolymer -D-Asp 8 conjugate were prepared and evaluated. Higher molecular weight of the conjugate enhanced the deposition to bone due to the prolonged half-life in circulation, but it weakened the bone-selectivity. A higher content of bonetargeting moiety (D-Asp 8 ) in the conjugate is desirable to achieve superior hard tissue selectivity. Further validation of the bone-targeting efficacy of the conjugates in animal models of osteoporosis and other skeletal diseases is needed in the future.

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