Independent variation of beta-adrenergic receptor binding and catecholamine-stimulated adenylate cyclase activity in rat erythrocytes

The pharmacokinetics, following i.v. administration of (+)-propranolol (40 mg) have been compared to in vitro measurement of protein binding and biochemical parameters of liver function in six normal subjects and twenty patients with stable chronic liver disease. The clearance of (+)-propranolol decreased with evidence of increasing severity of impairment of liver function correlating significantly with a fall in serum albumin, a rise in bilirubin and a prolongation in prothrombin index. The clearance of (+)-propranolol correlated with and was numerically similar to the clearance of indocyanine green in normal subjects and also in patients with chronic liver disease. Protein binding was decreased in chronic liver disease, but this change was not related to changes in plasma proteins. In normal subjects and patients without ascites the volume of distribution increased with decreases in protein binding. Ascites was associated with a further increase in the volume of distribution. The considerable variation in half-life largely depends on changes in liver blood flow, the degree of protein binding and the plasma protein pool size.     

Clinical pharmacokinetics of nisoldipine coat-core

Nisoldipine, a calcium antagonist of the dihydropyridine type, is the active ingredient of the controlled release nisoldipine coat-core (CC) formulation. In humans, the absorption from nisoldipine CC occurs across the entire gastrointestinal tract with an increase in bioavailability in the colon because of the lower concentrations of metabolising enzymes in the distal gut wall. Although nisoldipine is almost completely absorbed, its absolute bioavailability from the CC tablet is only 5.5%, as a result of significant first-pass metabolism in the gut and liver. Nisoldipine is a high-clearance drug with substantial interindividual and relatively lower intraindividual variability in pharmacokinetics, dependent on liver blood flow. Nisoldipine is highly (> 99%) protein bound. Its elimination is almost exclusively via the metabolic route and renal excretion of metabolites dominates over excretion in the faeces. Although nisoldipine is administered as a racemic mixture, its plasma concentrations are almost entirely caused by the eutomer as a result of highly stereoselective intrinsic clearance. Nisoldipine CC demonstrates linear pharmacokinetics in the therapeutic dose range and its steady-state pharmacokinetics are predictable from single dose data. Steady-state is reached with the second dose when the drug is given once daily and the peak-trough fluctuations in plasma concentration is minimal. Plasma-concentrations of nisoldipine increase with age. Careful dose titration according to individual clinical response is recommended in the elderly. Nisoldipine CC should not be used in patients with liver cirrhosis, though dosage adjustments in patients with renal impairment are not necessary. Inter-ethnic differences in its pharmacokinetics are not evident. Owing to inhibition of metabolising enzymes, a small dosage adjustment decrement for nisoldipine CC may be required when it is given in combination with cimetidine. Concomitant ingestion of nisoldipine with grapefruit juice should be avoided. Inducers of cytochrome P450 (CYP) 3A4, e.g. rifampicin (rifampin) and phenytoin should not be combined with nisoldipine CC, as they may reduce its bioavailability and result in a loss of efficacy. The concomitant use of other drugs which may produce marked induction or inhibition of CYP3A4 is contraindicated. Concomitant intake of the CC tablet with high fat, high calorie foods resulted in an increase in the maximum plasma concentrations of nisoldipine. The 'food-effect' can be avoided by administration of the CC tablet up to 30 minutes before the intake of food [corrected]. Plasma concentrations of nisoldipine are related to its antihypertensive effect via a maximum effect model. Nisoldipine CC once daily produce reductions in blood pressure which are maintained over 24 hours in the absence of relevant effects on heart rate.     

Drug administration in chronic liver disease

Cirrhosis encompasses a range of pathophysiological changes that may alter drug disposition. Drugs that are dependent primarily on the liver for their systemic clearance are more likely to be subject to reduced elimination and subsequent accumulation. Drug accumulation may lead to excessive plasma drug concentrations and adverse effects, if the adverse effects of the drug are concentration-dependent. The effects of hepatic insufficiency on the pharmacokinetics of drugs are not consistent or predictable. Furthermore, the influence of hepatic disease on the disposition of various drugs can vary, even though those drugs may share the same apparent metabolic pathway. Problems in forecasting drug kinetic behaviour are further enhanced by the additional impairment of kidney function (frequently encountered in patients with advanced liver disease) and by the unpredictability of the glomerular filtration rate using customary methods in patients with cirrhosis. Accordingly, dosages are generally adapted empirically, with the help of serum drug concentrations, when applicable. However, drugs eliminated predominantly by hepatic metabolism are not among those most commonly inducing adverse drug reactions or causing severe complications in patients with cirrhosis. Electrolyte disturbances and the hepatorenal syndrome produced by furosemide (frusemide)-the disposition of which is not substantially modified in liver disease-appear to be the most frequent adverse drug reactions in patients with liver disease. Furthermore, clinically significant alterations in the action of medications at concentrations generally considered to be in the normal therapeutic range are not uncommon. Tissue responsiveness to the pharmacological action of some drugs may be modified, as evidenced by the increased susceptibility of the brain in patients with cirrhosis to the action of many psychoactive agents. Another example is the greater susceptibility of such patients to the nephrotoxic potential of aminogly-cosides, which should not be used in this patient group. Drugs may also interfere with adaptive physiological processes induced by liver disease. ACE inhibitors and nonsteroidal anti-inflammatory drugs counteract the enhanced activity of the renin-angiotensin system in advanced liver disease, thereby generating a high risk of excessive hypotension or acute renal failure, respectively. These drugs are best avoided in patients with cirrhosis. Finally, there may be pharmacological effects that overlap with some pathophysiological modifications related to the process of liver disease, such as increased portal pressure produced by some calcium antagonists, or hypoprothrombinaemia related to the inhibition of synthesis of vitamin K-dependent clotting factors by some beta-lactam antibacterials (especially moxalactam and cefamandole). Accordingly, the use of these drugs should be avoided in advanced liver disease. It is noteworthy that reduced drug metabolism in patients with liver disease does not seem to have a significant impact on the frequency of hepatotoxicity. Special caution should be exercised, however, in patients with alcoholic liver disease because excessive alcohol intake may potentiate the hepatotoxic effect of paracetamol (acetaminophen).     

Role of the liver in interorgan homeostasis of glutathione and cyst(e)ine

There are many pathological changes in patients with cystic fibrosis (CF) which can lead to alterations in drug disposition. Although, in patients with CF, the extent of drug absorption varies widely and the rate of absorption is slower, bioavailability is not altered. Plasma protein binding for the majority of drugs studied did not differ in patients with CF compared with control groups. The difference in volume of distribution of most drugs between patients with CF and healthy individuals vanished when corrected for lean body mass. Despite hepatic dysfunction, patients with CF have enhanced clearance of many, but not all, drugs. Phase I mixed-function oxidases are selectively affected: cytochrome P450 (CYP) 1A2 and CYP2C8 have enhanced activity, while other CYP isoforms such as CYP2C9 and CYP3A4 are unaffected. Increased phase II activities are also demonstrated: glucuronyl transferase, acetyl transferase (NAT1) and sulfotransferase. The increased hepatic clearance of drugs in the presence of CF may be the consequence of disease-specific changes in both enzyme activity and/or drug transport within the liver. The renal clearance (CLR) of many drugs in patients with CF is enhanced although there has been no pathological abnormality identified which could explain this finding: glomerular filtration rate and tubular secretion appear normal in patients with CF. The precise mechanisms for enhanced drug clearance in patients with CF remain to be elucidated. The optimisation of antibiotic therapy in patients with CF includes increasing the dose of beta-lactams by 20 to 30% and monitoring plasma concentrations of aminoglycosides. The appropriate dosage of quinolones has not been definitively established.     

One-stage reconstruction of post-electrical burn forearm and hand defects using microsurgical transfer of an ulnar neuromyotendinocutaneous unit

Epirubicin is known to be metabolized in the liver. Therefore, drugs such as cimetidine, which inhibit the cytochrome P-450 enzyme system or reduce liver blood flow, may reduce the plasma clearance of epirubicin. In a small study, epirubicin 100 mg/m2 every 3 weeks was administered intravenously to eight patients, who also received oral cimetidine (400 mg b.d. for 7 days starting 5 days before chemotherapy) with either the first or second cycles. Epirubicin pharmacokinetics and liver blood flow (idocyanine green clearance) were assessed at each course. The areas under the plasma concentration time curves (AUCs) were used to compare the systemic exposure to epirubicin and its metabolites with each course. The estimated median percentage increase (95% confidence interval CI) in the AUC with cimetidine were: epirubicin 50% (95% CI -18 to 193, epirubicinol 41% (95% CI 1 to 92). Despite the small numbers studied, the increase in the active metabolite epirubicinol was significant (P < 0.05). These changes in exposure were not explained by reduced cytochrome P-450 activity as the 7-deoxy-doxorubicinol aglycone AUC was not reduced (357% increase: 95% CI 17 to 719) or by a decrease in liver blood flow (17% increase: 95% CI -39 to 104). Cimetidine is likely to be coprescribed or self-administered with epirubicin and therefore clinicians should be aware of this potential interaction.     

Protease inhibitors in patients with HIV disease. Clinically important pharmacokinetic considerations

Since its introduction in 1987, zidovudine monotherapy has been the treatment of choice for patients with HIV infection. Unfortunately it has been established that the beneficial effects of zidovudine are not sustained due to the development of resistant viral strains. This has led to the strategy of combination therapy, and in 1995 treatment with zidovudine plus didanosine, or zidovudine plus zalcitabine, was demonstrated to be more effective than zidovudine monotherapy in preventing disease progression and reducing mortality in patients with HIV disease. Recent work demonstrates an even greater antiviral effect from triple therapy with 2 nucleosides, zidovudine plus zalcitabine with the addition of saquinavir, a new protease inhibitor drug. The HIV protease enzyme is responsible for the post-translational processing of gag and gag-pol polyprotein precursors, and its inhibition by drugs such as saquinavir, ritonavir, indinavir and VX-478 results in the production of non-infectious virions. As resistance may also develop to the protease inhibitors they may be used in combination, and future strategies may well include quadruple therapy with 2 nucleoside analogues plus 2 protease inhibitors. Administration of protease inhibitors alone or in combination with other drugs does raise a number of important pharmacokinetic issues for patients with HIV disease. Some protease inhibitors (e.g. saquinavir) have kinetic profiles characterised by reduced absorption and a high first pass effect, resulting in poor bioavailability which may be improved by administrating with food. Physiological factors including achlorhydria, malabsorption and hepatic dysfunction may influence the bioavailability of protease inhibitors in HIV disease. Protease inhibitors are very highly bound to plasma proteins (> 98%), predominantly to alpha 1-acid glycoprotein. This may influence their antiviral activity in vitro and may also predispose to plasma protein displacement interactions. Such interactions are usually only of clinical relevance if the metabolism of the displaced drug is also inhibited. This is precisely the situation likely to pertain to the protease inhibitors, as ritonavir may displace other protease inhibitor drugs, such as saquinavir, from plasma proteins and inhibit their metabolism. Protease inhibitors are extensively metabolised by the cytochrome P450 (CYP) enzymes present in the liver and small intestine. In vitro studies suggest that the most influential CYP isoenzyme involved in the metabolism of the protease inhibitors is CYP3A, with the isoforms CYP2C9 and CYP2D6 also contributing. Ritonavir has an elimination half-life (t1/2 beta) of 3 hours, indinavir 2 hours and saquinavir between 7 and 12 hours. Renal elimination is not significant, with less than 5% of ritonavir and saquinavir excreted in the unchanged form. As patients with HIV disease are likely to be taking multiple prolonged drug regimens this may lead to drug interactions as a result of enzyme induction or inhibition. Recognised enzyme inducers of CYP3A, which are likely to be prescribed for patients with HIV disease, include rifampicin (rifampin) [treatment of pulmonary tuberculosis], rifabutin (treatment and prophylaxis of Mycobacterium avium complex), phenobarbital (phenobarbitone), phenytoin and carbamazepine (treatment of seizures secondary to cerebral toxoplasmosis or cerebral lymphoma). These drugs may reduce the plasma concentrations of the protease inhibitors and reduce their antiviral efficacy. If coadministered drugs are substrates for a common CYP enzyme, the elimination of one or both drugs may be impaired. Drugs which are metabolised by CYP3A and are likely to be used in the treatment of patients with HIV disease include the azole antifungals, macrolide antibiotics and dapsone; therefore, protease inhibitors may interact with these drugs. (ABSTRACT TRUNCATED)     

Practical treatment guide for dose individualisation in cancer chemotherapy

Dosages of anticancer drugs are usually calculated on the basis of a uniform standard, the body surface area (BSA). Although many physiological functions are proportionate to BSA, overall drug clearance is only partially related to this parameter. Consequently, following administration of equivalent drug dosages based on BSA, a wide variability in plasma drug concentrations can be found between patients, as a result of which some patients experience little toxicity while others may show severe toxic symptoms. A clear pharmacokinetic/pharmacodynamic correlation has been demonstrated for some anticancer drugs, and this relationship provides a background against which rational dose optimisation can be implemented for individual patients. The 3 strategies that can be employed for optimising dosage regimens, none based on BSA, are described and criticised. A priori adaptive dosage determination is based on the relative contribution of identifiable characteristics of patient, drug therapy and disease state that influence plasma drug concentrations; the dosage regimen is based on each patient's profile with regard to these characteristics. Although this approach is most successful with drugs whose clearance is closely tied to renal function, patient characteristics such age, obesity, serum albumin or hepatic function may be useful. The anticancer drug most closely identified with this approach is carboplatin, although dosage reduction strategies for etoposide, taxanes, anthracyclines, topotecan, oxazaphosphorines, vinca alkaloids or melphalan are advocated for patients with renal or hepatic dysfunction. The importance of pharmacogenetics for fluorouracil and mercaptopurine is also briefly discussed. The second approach consists of adaptive dosage adjustments during repetitive or continuous administration of a drug. It has been used for several years to administer methotrexate therapy and, more recently, it has been developed more fully and applied to continuous infusion of fluorouracil or etoposide. It was based, after determination of a target plasma concentration or area under the plasma drug concentration-time curve (AUC), on modification of the drug dosage during the cycle of chemotherapy or for the next cycle. Finally, the third approach of adaptive dosage adjustment with feedback control, based on population pharmacokinetics, with limited sampling strategy, may allow a feedback revision of the dosage following measurement of plasma drug concentration and comparison with the population previously studied. This approach is a theoretical strategy which has not, until now, been used prospectively in clinical oncology. For drugs such as anticancer agents with a very narrow therapeutic index, every effort should be made to minimise interpatient variability in drug exposure in order to maximise the benefit while keeping the risk of serious adverse effects at an acceptable level. This is particularly important when treatment is being given with curative intent.     

Lorazepam-valproate interaction: studies in normal subjects and isolated perfused rat liver

Valproate (VPA) has been shown to interact with all the major antiepileptic drugs (AEDs) through two mechanisms of action: displacement from albumin binding sites and inhibition of drug metabolism. More recently, evidence showed that VPA inhibits the elimination of drugs metabolized by glucuronide conjugation. Lorazepam (LZP), which is primarily eliminated by conjugation with glucuronic acid, is administered concurrently with VPA both in treatment of epilepsy and in patients treated with VPA for psychiatric disorders. Therefore, a significant drug interaction is likely. We investigated such interaction both in in vitro isolated perfused rat liver (IPRL) and in normal subjects. LZP [2 mg, intravenous (i.v.) bolus] was administered to 8 normal volunteers before and after chronic dosing with VPA. In 6 of 8 subjects, VPA significantly decreased LZP plasma clearance by an average of 40% (p < 0.05) and increased LZP concentrations by decreasing formation clearance of the LZP glucuronide. In the IPRL studies, VPA also significantly decreased formation of LZP glucuronide (from 0.72 +/- 0.14 to 0.22 +/- 0.15 ml/h/kg, p < 0.05), indicating that IPRL is a useful tool for evaluation of the effect of VPA on drugs eliminated by glucuronide conjugation.     

Caffeine clearance by two point analysis: a measure of liver function in chronic liver disease

This study attempted to compare the pharmacokinetic parameters of caffeine in patients with chronic liver disease and in normal subjects and to define the two sampling times which are suitable for determining caffeine clearance in these patients. Ten decompensated and eight compensated cirrhotic patients, and nine patients with chronic hepatitis were given a 3.5 mg/kg single oral dose of caffeine, followed by measurement of serum caffeine concentrations at 0, 30, 60, 90 minutes and 3, 5, 10, 24 and 36 hours using the HPLC technique. Caffeine clearance and its elimination rate constant in the decompensated cirrhotic patients were significantly lower than those in the compensated cirrhotic patients and much lower than in normal subjects (p > 0.01). Caffeine clearance in chronic hepatitis patients was also significantly lower than in normal subjects. The volumes of distribution of caffeine in compensated and decompensated cirrhotic patients and normal subjects were significantly different. There was also a significant difference between normal subjects and the chronic hepatitis group. Serum caffeine clearance showed a good correlation with Child Pugh's score at r = -0.788. Two sampling times within 10 to 24 hours after oral dose of caffeine served as the best sampling points for determination of caffeine clearance by the simple equation; Cl = kel approximately Vd (Vd is a fixed value in each group). It was clearly shown that caffeine clearance, calculated by two point analysis, would be a simple and useful method for measuring liver function in chronic liver disease.     

Disposition of nafcillin in patients with cirrhosis and extrahepatic biliary obstruction

Nafcillin, a semisynthetic penicillin effective against penicillinase-producing staphylococci, is eliminated largely in man via the liver. This study assessed the effect of cirrhosis and extrahepatic biliary obstruction in man on the pharmacokinetics of nafcillin. The plasma clearance of nafcillin controls was 583 +/- 144.2 ml per min (mean +/- SD) and fell strikingly to 291 +/- 147.6 and 163 +/- 56.3 ml per min in patients with cirrhosis and extrahepatic obstruction, respectively (P less than 0.001). In the latter two groups nafcillin excreted in urine increased from about 30 to 50% of administered dose (P less than 0.02), suggesting that renal disease superimposed on hepatic disease would further decrease over-all nafcillin clearance. The depression of nafcillin clearance with hepatobiliary disease did not correlate with any conventional liver laboratory test. The initial volume of distribution of nafcillin (V1) was unaltered but at steady state (Vd()) there was a significant reduction in the distribution volume in the patients with liver disease. Accordingly, the impairment in drug elimination, as assessed by its clearance from plasma, was underestimated by the prolongation of the nafcillin elimination half-life (t1/2(beta)) which was 1.02 +/- 0.20 hr in controls, and 1.23 +/- 0.31 (P greater than 0.05) and 1.73 +/- 0.44 hr (P less than 0.03), respectively, in patients with cirrhosis and extrahepatic obstruction.     

Change in serum hyaluronan: a simple index of short-term drug-induced changes in hepatic sinusoidal perfusion

BACKGROUND: Hyaluronan is an endogenous polysaccharide whose clearance from the plasma is predominantly by liver sinusoidal cells and is sinusoidal flow dependent. This study was designed to determine if a change in serum hyaluronan might reliably reflect short-term drug-induced changes in sinusoidal perfusion. METHODS: Hemodynamic changes following an oral dose of ketanserin were compared with changes in serum hyaluronan levels in 12 patients with alcoholic liver disease and portal hypertension. Indices determined comprised heart rate, mean arterial pressure (MAP), cardiac output (CO), systemic vascular resistance, hepatic venous pressure gradient (HVPG), indocyanine green (ICG) clearance and extraction, and total hepatic blood flow. Measurements were made in a basal state 1 hour after ketanserin ingestion and expressed as a ratio of values post- to pre-ketanserin administration. RESULTS: Ketanserin had variable effects comprising both increases and decreases in all indices. On univariate and multivariate analysis, changes in serum hyaluronan concentration (1.05 +/- 0.13, mean +/- SD) significantly correlated with only one index: changes in ICG clearance (0.93 +/- 0.17, r = -0.65, P = 0.02). CONCLUSIONS: Changes in serum hyaluronan levels reflect short-term drug-induced changes in sinusoidal perfusion in patients with alcoholic liver disease and portal hypertension. Serial measurement of serum hyaluronan levels may offer a simple method of screening vasoactive drugs for their short-term effects on sinusoidal perfusion.     

Pharmacokinetic basis for the safety of glimepiride in risk groups of NIDDM patients

The pharmacokinetics of the sulfonylurea, glimepiride, in risk groups of NIDDM patients are reviewed with regard to pharmacokinetic-effect relationships. A variety of factors, such as regulatory processes, glucose absorption, insulin sensitivity, might prevent the definition of a clear concentration-effect relationship for sulfonylureas. However, when these processes are minimized, as with the glucose clamp technique, such relationships can be defined. This is true for glibenclamide or glimepiride, for which saturation of effect is apparent in the upper therapeutic dose range in healthy subjects. However, pharmacokinetic-pharmacodynamic relationships are less readily defined during long-term treatment of NIDDM patients. In kidney or liver disease, the hypoglycemic effect of sulfonylureas can be increased and prolonged, mainly due to a decrease in insulin metabolism or of hepatic glucose output; the risk of hypoglycemia is increased. The pharmacokinetics of most sulfonylureas have not been well characterised in patients with kidney or liver disease. Generally, sulfonylureas are eliminated by renal excretion of metabolites, some of which have similar pharmacological activity to the parent drug e.g. glibenclamide, chlorpropamide, tolbutamide. In renal disease, elimination of these metabolites can be impaired. In 31 NIDDM patients with kidney disease, elimination of unchanged glimepiride was greater in patients with more severe renal disease, probably due to a decrease in the plasma protein-bound fraction. Elimination of the renally excreted metabolites was also impaired in the same group of patients. 12 of 16 NIDDM patients with kidney disease who continued glimepiride treatment for three months maintained fasting blood glucose levels of less than 9.99 mmol/l at a daily dose of 1-6 mg, the typical dose range for patients with normal renal function. Pharmacokinetic data on sulfonylureas are generally inconsistent in cirrhotic patients. In 11 patients with liver disease, the pharmacokinetics of glimepiride were similar to those of healthy volunteers. In conclusion, pharmacokinetics, pharmacodynamics and their relationships can be defined for glimepiride under controlled conditions. Such information is lacking for many commonly used sulfonylureas in risk group NIDDM patients. Studies described here show that the pharmacokinetics of glimepiride are altered in renal disease but may not be seriously affected in patients with liver disease.     

The antiproteinuric effect of angiotensin antagonism in human IgA nephropathy is potentiated by indomethacin

Evidence is available from animal and human studies that protein traffic through the glomerular capillary has a pathogenetic role in subsequent renal damage and that angiotensin-converting enzyme (ACE) inhibitors appear superior to other drugs in lowering proteinuria and the rate of renal function decline. This study compares the effect of ACE inhibition or angiotensin II (AngII) receptor blockade on urinary protein excretion and renal hemodynamics in 20 patients with IgA glomerulonephritis randomized to receive enalapril (20 mg/d) or irbesartan (100 mg/d) for 28 d in a double-blind study with two parallel groups. This study also evaluated whether addition of indomethacin (75 mg twice a day) to each of the two treatments resulted in a more potent antiproteinuric effect. Enalapril alone reduced total protein excretion (61% change from baseline) and fractional clearance of albumin without changes in GFR and minor elevation in renal plasma flow. Also, patients randomized to receive the AngII receptor antagonist irbesartan for 28 d had lower proteinuria (55% change from baseline) and fractional clearance of albumin at the end of the treatment period with similar renal hemodynamic changes. When indomethacin was added to enalapril treatment, a further significant reduction in urinary proteins and fractional albumin clearance was observed. In patients given irbesartan, the addition of indomethacin further reduced proteinuria and fractional clearance of albumin. The combined therapy with enalapril or irbesartan and indomethacin did not significantly affect GFR and renal plasma flow compared with baseline. These findings indicate that in patients with IgA glomerulonephritis the antiproteinuric effect of blocking AngII activity by either ACE inhibitors or AngII receptor antagonists is potentiated by indomethacin, an effect that occurred without impairment of renal function.     

Treatment of concomitant illnesses in patients receiving anticonvulsants: drug interactions of clinical significance

As epilepsy often is a chronic condition requiring prolonged therapy with anticonvulsants, patients being treated for epilepsy can be at risk when they are prescribed other drugs for concomitant diseases. Pharmacokinetic interactions can occur at each step of drug disposition (absorption, distribution, metabolism and elimination). Although such interactions may occur frequently with some drugs, only some will be clinically relevant. Alterations in the hepatic biotransformation of metabolised drugs due to hepatic isoenzyme induction or inhibition is of particular concern. The consequences of pharmacokinetic interactions are either accumulation of the drug leading to toxicity, or lowering of plasma concentrations resulting in reduced efficacy. Clinically relevant interactions depend on the structure, dosage and duration of administration of interacting agents, and on the individual's genetic make-up. In the past, drug interactions have been analysed empirically. At present, at least for interactions between drugs that are biotransformed in the liver, the risk should be predicted by considering the individual cytochrome P450 isoforms involved in the metabolism of coadministered drugs. Although drug-drug interactions can be predicted, their extent cannot be due to large interindividual variability. Even if nearly all drug combinations could be used with close clinical surveillance and blood concentration determinations, drugs that are not metabolised and are not highly protein bound, as are several of the new anticonvulsants, such as gabapentin, lamotrigine and vigabatrin, have a clear advantage in terms of a lower interaction potential.     

Long-term improvement in renal function after cyclosporine reduction in renal transplant recipients with histologically proven chronic cyclosporine nephropathy

BACKGROUND: Chronic cyclosporine (CsA) nephropathy, which has been unequivocally documented in recipients of heart, heart-lung, liver, or bone marrow transplants, as well as in nontransplant situations, usually results in a progressive deterioration of renal function. In this study, we assessed the potential reversibility of chronic CsA nephropathy in renal transplant recipients. PATIENTS AND METHODS: Twenty-three renal transplant patients with biopsy-proven CsA nephropathy associated with long-term CsA administration (27+/-4 months) were followed up for more than 2 years after CsA reduction (18/23 patients) or withdrawal (5/23 patients) and addition of azathioprine. Changes in effective renal plasma flow and glomerular filtration rate were assessed before and 2 years after CsA reduction, whereas serum creatinine, proteinuria, blood pressure, and CsA concentrations were monitored up to 5 years. RESULTS: At 2-year follow-up, glomerular filtration rate increased from 40+/-3 to 47+/-4 (P<0.05) and effective renal plasma flow from 217+/-23 to 244+/-24 ml/min/1.73 m2 (NS). Mean arterial pressure significantly decreased from 98.7+/-2.9 to 93.1+/-2.7 mmHg (P<0.05). There was no significant change in renal vascular resistance, filtration fraction, or albumin excretion. A significant decrease in serum creatinine was also observed during the whole follow-up (73+/-6.5 months). CsA reduction was followed by only one episode of acute reversible rejection; chronic rejection developed in three patients 2 years or later after CsA reduction. CONCLUSIONS: These data suggest that CsA nephropathy participates in graft dysfunction in a small group of renal transplant recipients. In addition, graft dysfunction may be reversible when CsA dosage is reduced early after diagnosis of chronic CsA nephropathy.     

Effects of acetylsalicylic acid on peripheral hemodynamics in patients with chronic heart failure treated with angiotensin-converting enzyme inhibitors

Cyclooxygenase inhibitors may affect the hemodynamic status of patients with heart failure adversely and may also block the vasodilatory effects of angiotensin-converting enzyme (ACE) inhibitors in such patients. Relatively low doses of the cyclooxygenase inhibitor acetylsalicylic acid (ASA) are now used routinely in ischemic heart disease, the most important cause of heart failure. Therefore, we investigated the hemodynamic interaction between ASA and captopril in heart failure. In a randomized, cross-over study, 13 patients with congestive heart failure (CHF) who were already receiving maintenance treatment with an ACE inhibitor received a single dose of 25 mg captopril combined with 236 mg ASA or placebo. Peripheral blood flow was studied noninvasively by venous occlusion plethysmography of the calves. Liver blood flow was estimated from indocyanine green (ICG) clearance. Administration of captopril alone significantly decreased blood pressure (BP), and ICG clearance. Calf blood flow remained unchanged. However, after arterial occlusion, hyperemic calf blood flow persisted for longer. Captopril alone did not significantly change the plasma levels of the vasodilating prostaglandins PGI2 and PGE2 or the vasoconstricting thromboxane A2 (TXA2). In contrast, captopril combined with ASA reduced the plasma levels of these vasoactive substances, with significant decreases in PGE2 and TXA2 as compared with captopril alone, yet the hemodynamic alterations after captopril plus ASA were similar to those observed after captopril alone. A single antithrombotic dose of ASA (236 mg) in 13 patients with CHF [New York Heart Association (NYHA) class II-IV] undergoing chronic treatment with ACE inhibitors had no discernible effect on hemodynamic status.(ABSTRACT TRUNCATED AT 250 WORDS)     

Pharmacokinetics and metabolism in mice of a phosphorothioate oligonucleotide antisense inhibitor of C-raf-1 kinase expression

The plasma and tissue disposition of CGP 69846A (ISIS 5132) was characterized in male CD-1 mice following iv bolus injections administered every other day for 28 days (total of 15 doses). The doses ranged from 0.8 mg/kg to 100 mg/kg. Urinary excretion of oligonucleotide was also monitored over a 24-hr period following single dose administration over the same dose range. Pharmacokinetic plasma profiles were determined following single dose administration (dose 1) and after multiple doses (dose 15) at doses of 4 and 20 mg/kg. Concentrations in kidney, liver, spleen, heart, lung, and lymph nodes were characterized following doses 1, 8, and 15 for all doses. Capillary gel electrophoresis was used to quantitate intact (full-length) oligonucleotide and its metabolites (down to N - 11 base deletions) in both plasma and tissue at all time points. The plasma and tissue disposition of CGP 69846A was characterized by a rapid distribution into all tissues analyzed. Rapid plasma clearance of the parent oligonucleotide (9.3-14.3 ml/min/kg) was predominantly the result of distribution to tissue and, to a lesser extent, metabolism. Appearance and pattern of chain-shortened metabolites seen in plasma and tissue were consistent with predominantly exonuclease-mediated base deletion. No measurable accumulation of oligonucleotide was observed in plasma following multiple-dose administration, but both the liver and the kidney exhibited 2-3-fold accumulations. In general, the tissues exhibited half-lives for the elimination of parent oligonucleotide of 16-60 hr compared with plasma half-lives of 30-45 min. After repeated administrations, significant decreases in plasma clearance and volume of distribution at steady state (Vss) were observed following dose 15 at the dose of 20 mg/kg but not at the dose of 4 mg/kg. Changes in tissue accumulation and evidence for saturation of tissue distribution at the high doses may explain the plasma disposition changes observed in the absence of alteration of metabolism or plasma accumulation. Urinary excretion was a minor pathway for elimination of oligonucleotide over the 24-hr period immediately following iv administration. However, the amount of oligonucleotide excreted in the urine increased as a function of dose from less than 1% to approximately 13% of the administered dose over a dose range of 0.8 mg/kg to 100 mg/kg.     

Abnormal regulation of plasma pyridoxal 5'-phosphate in patients with liver disease

Pyridoxal 5'-phosphate (PLP), the coenzyme form of vitamin B6, is essential for many biochemical reactions in the body. Studies in experimental animals have suggested that the liver is a primary site for the formation of PLP circulating in the plasma, and that it may also participate in its degradation. This study evaluates, for the first time, the effects of liver disease in man on the regulation of plasma PLP. The plasma PLP level was measured before and sequentially after the rapid intravenous administration of 50 mg of pyridoxine to patients with alcoholic cirrhosis, acute hepatitis, and extrahepatic obstruction, and to normal control subjects. The base line plasma PLP concentration was significantly lower in cirrhotic patients than in normal persons (P less than 0.025), and there was a tendency for it to be reduced in patients with extrahepatic obstruction. After administration of pyridoxine there was a significant increase in the plasma PLP level over a 2- to 12-hr period, after which the concentration returned gradually toward the initial value. The area under the concentration/time curve was from 2 to 8 times smaller (P less than 0.002) in the patients with liver disease. To assess possible mechanisms of this change, 5 mg of PLP were intravenously administered to the various patient groups and the pharmacokinetics of the disposition were assessed. The initial and steady state volumes of distribution of PLP were comparable in cirrhotics and controls (P greater than 0.05), but the clearance of plasma PLP in cirrhotics was much faster (63.0 +/- 7.4 versus 31.7 +/- 2.7 ml per min, P less than 0.004). Similar findings were obtained in the other liver disease subjects. The in vitro plasma binding of PLP at supracirculatory concentrations was comparable in cirrhotics and controls (99.4 versus 99.5%, P greater than 0.05). In conclusion: (1) plasma PLP regulation in patients with liver disease is abnormal, (2) a significant factor in the decrease in plasma PLP after intravenous pyridoxine administration in these patients appears to be an increase in the total plasma clearance of the coenzyme, and (3) it is postulated that this may be due to increased degradation of PLP by the diseased liver.     

Update on the use of metabolic probes to quantify liver function: caffeine versus lidocaine

The search for continues for a safe, accurate and reliable method to quantify liver function similar in principle to renal creatinine clearance or pulmonary function spirometry tests. When evaluating patients in the more advanced stages of chronic liver disease, one's clinical judgement regarding the degree of liver dysfunction usually suffices, but in patients with early or only intermediate disease, and estimate based on routine blood tests and/or clinical severity scores is often unreliable. A more quantitative approach under investigation at present has been to monitor specific pharmacokinetic parameters of 'probe' drugs metabolized primarily by hepatic cytochrome P-450. These parameters include the plasma or salivary clearance rate of the parent compound and/or the formation rate of its metabolites. Following a review of basic hepatic pharmacology relevant to this topic, we shall explore the advantages and disadvantages of two 'metabolic probes' that have shown the most promise to date, caffeine and lidocaine.     

Evaluation of [14C]aminopyrine breath test, peripheral clearance of [99mTc]EHIDA, and serum bile acid levels in liver function and disease

The purpose of this study is to evaluate the diagnostic value of the following tests in the assessment of patients with chronic liver disease (CLD) and cholestatic syndrome (CS): (1) aminopyrine breath test, measuring 14CO2 excretion in the expired air, (2) peripheral clearance of [99mTc]EHIDA, and (3) postprandial levels of glycocholic acid (GCA) and glycochenodeoxycholic acid (GCDCA). The results indicate that: (1) 14CO2 2-hr excretion rate is a specific and sensitive marker of liver function, with good correlation with postprandial bile acid levels, [99mTc]EHIDA retention, and the conventional tests of serum albumin and prothrombin time. (2) Peripheral clearance and retention of [99mTc]EHIDA increased in both groups of CLD and CS vs controls, but it does not discriminate between the two. (3) Postprandial bile acids were elevated in CLD, particularly those of GCDCA, whereas GCA levels were significantly elevated in CS compared with CLD. This may be due to increased synthesis and entry into the blood. (4) The combination of [14C]aminopyrine breath test and postprandial levels of GCDCA enhance the diagnostic value, specificity, and sensitivity in the assessment of patients with CLD.