Clinical pharmacology becomes a specialty in South Africa.

South Africa recently became the first African country where clinical pharmacology has been approved as a specialty. This article outlines the need for clinical pharmacologists, their role in advancing public health, the potential benefits to the country, and recommendations for ensuring a healthy future for the discipline.

RAT CYP3A and CYP2B1/2 were not associated with nevirapine-induced hepatotoxicity.

Nevirapine is an antiretroviral drug that is used for treatment as well as for the prevention of mother-to-child transmission of the human immunodeficiency virus (HIV). Unfortunately, its adverse effects, mainly hypersensitivity skin reactions and hepatotoxicity, have hampered the use of nevirapine. Since nevirapine-induced hepatotoxicity commonly occurs between 2-12 weeks of treatment, and nevirapine is a known inducer of human CYP3A and CYP2B6 isozymes, it was envisaged that the hepatotoxicity was due to activation of nevirapine to toxic metabolites by the induced enzymes. Therefore, the aim of this study was to use a rat model and determine the role of the rat analogues, rat CYP3A and CYP2B1/2, in nevirapine-induced hepatotoxicity. This was tested by the extent at which hepatotoxicity could be prevented when ketoconazole or thiotepa, known inhibitors of CYP3A and CYP2B1/2, respectively, were given one hour prior to administration of a hepatotoxic dose of nevirapine. It was shown here that nevirapine-induced hepatotoxicity only occurred in animals that were pretreated with an enzyme inducer (dexamethasone or nevirapine); that ketoconazole and thiotepa did not prevent the occurrence of nevirapine-induced hepatotoxicity; and that histopathologic examinations were more accurate than the use of liver enzymes in detecting the liver damage. This suggested that nevirapine-induced hepatotoxicity is closely associated with enzyme induction, and that liver function tests alone might not be good markers for determining nevirapine-induced hepatotoxicity. In conclusion, rat CYP3A and CYP2B1/2 may not be involved in the pathogenesis of nevirapine-induced hepatotoxicity, suggesting that a different enzyme inducible by nevirapine or dexamethasone may be responsible. However, this is yet to be proven in humans.

The effect of surface charge on the disposition of liposome-encapsulated gentamicin to the rat liver, brain, lungs and kidneys after intraperitoneal administration.

The disposition of gentamicin to the normal rat brain, lung, kidney and liver was studied at intervals of 1, 2, 4, 6 and 8h after intraperitoneal injection of gentamicin encapsulated in positive, negative and neutral liposomes. Compared with the control, which was treated with free gentamicin, liposomes were associated with higher concentrations of gentamicin in the brain and liver, while concentrations were lower in the kidney. The average concentrations of gentamicin in the liver and the brain were highest with positive liposomes, while, gentamicin concentrations in the kidneys and lungs were not influenced by surface charge of the liposomes. These observations have important implications on the selective delivery of gentamicin to tissues and on the intraperitoneal route of administration.

The role of cytochrome-P450 inhibitors in the prevention of hepatotoxicity after paracetamol overdose in rats.

Despite the understanding that some cytochrome P450 isoforms are responsible for activation of paracetamol to the hepatotoxic metabolite, N-acetyl-p-benzoquinineimine (NAPQI), the use of enzyme inhibitors for prevention and/or treatment of paracetamol hepatotoxicity is still not well researched. Here, a mixture of ketoconazole, isoniazid and caffeine (inhibitor solution), known inhibitors of CYP3A, CYP2E1 and CYP1A2, was investigated for prevention of hepatotoxicity after paracetamol over-dose in rats. The appropriate doses of paracetamol (1000 mg/kg/day) and the 'inhibitor solution' (ketoconazole 5 mg/kg, isoniazid 5 mg/kg and caffeine 10 mg/kg; =KIC-5-50), were selected in preliminary experiments. Thereafter, two groups of 15 male Sprague-Dawley rats each were treated with the toxic dose of paracetamol intraperitoneally to induce severe hepatotoxicity. But one of the two groups was treated with the KIC-5-50 intraperitoneally 5 min after administration of paracetamol. Five rats were killed at 24, 48 and 72 hours after paracetamol administration. Plasma concentrations of paracetamol were determined by the polarization fluorescent immunoassay and a piece of liver was sent for histopathology examination. Liver function tests at 48 hours were higher in the 'paracetamol only' treated group than in the 'KIC-5-50 + paracetamol' treated group' (P < 0.05), i.e., median (range) AST 2025 (530-4329) i.u./L, ALT 1174 (662-2395) i.u./L versus AST 194 (81-494) i.u./L, ALT 311 (201-945) i.u./L, respectively. The corresponding plasma concentrations of paracetamol were 0.26 (0.13-1.02) microg/mL for the 'paracetamol only' treated group versus 0.17 (0.07-0.33) microg/ml for the 'KIC-5-50 + paracetamol' treated group. Centrilobular necrosis, the pathogmonomic feature of paracetamol hepatotoxicity, was demonstrated only in the 'paracetamol only' treated group. In conclusion, coadministration of paracetamol with inhibitors of cytochrome P450 prevented the development of paracetamol-induced hepatotoxicity in rats, and this calls for research for enzyme inhibitors that may be of therapeutic value.

Modulation by drugs of human hepatic sodium-dependent bile acid transporter (sodium taurocholate cotransporting polypeptide) activity.

Adequate bile flow, maintained in part by the efficient enterohepatic recirculation of bile acids, is critical for normal liver function. One important component of this process is the uptake of bile acids from the portal circulation into hepatocytes by the bile acid uptake transporter sodium taurocholate cotransporting polypeptide (NTCP). Thus, the expression and functional activity of this transporter may affect the rate of bile acid removal from the portal circulation. Accordingly, we assessed NTCP mRNA expression from human livers using a sensitive RNase protection assay. In addition, the ability of various bile acids and drugs to inhibit NTCP activity was determined using a recombinant vaccinia expression system. A 40-fold interindividual variability was found in NTCP mRNA levels determined in eight liver samples of disease-free donors. Expressed NTCP exhibited high-affinity, sodium-dependent uptake of taurocholate, and as expected, this was markedly inhibited by bile acids and organic anions. A number of drugs, including peptidomimetic renin inhibitors, propranolol, cyclosporin, and progesterone, were found to be potent inhibitors, whereas antiarrhythmic agents, including bupivicaine, lidocaine, and quinidine, were found to enhance NTCP activity. Accordingly, these results indicate that large interindividual variability exists in NTCP mRNA level and that a number of drugs currently in clinical use have the potential to interact with and alter NTCP activity, thereby affecting hepatic bile acid uptake.

Fatal multi-organ failure after suicidal overdose with MDMA, 'ecstasy': case report and review of the literature.

A 53-year-old prisoner died of multiorgan failure after a suicidal overdose with 3,4-methylenedeoxymethamphetamine (MDMA, 'Ecstasy'). Twelve hours after ingestion of MDMA, the patient became severely hyperthermic (107.2 degrees F) with evidence of rhabdomyolysis. He subsequently developed acute respiratory distress syndrome (ARDS), disseminated intravascular coagulopathy (DIC) and acute renal failure. At autopsy, plasma concentration of MDMA was 3.05 mg/L. This case shows that MDMA is still abused in our community and clinicians should know the symptoms of MDMA intoxication. In particular, MDMA should be considered when patients have symptoms or signs of increased sympathetic activity. The pathophysiology and treatment of MDMA-induced hyperthermia are discussed.

The role of oxygen free radicals in isoniazid-induced hepatotoxicity.

Isoniazid and its metabolites acetylisoniazid, hydrazine and monoacetylhydrazine were investigated for generation of oxygen free radicals during incubation with rat liver slices. Lipid peroxidation was assessed by the thiobarbituric acid reactive substances test using malonaldehyde as the external standard, while hepatotoxicity was assessed by histopathology studies. Malonaldehyde formed in liver slices after 10 hours of incubation with the drugs was 1.28 +/- 0.24 nmol/mg for isoniazid (control 1.12 +/- 0.17 nmol/mg); 0.88 +/- 0.45 nmol/mg for acetylisoniazid (control 0.84 +/- 0.42 nmol/mg); 1.43 +/- 0.14 nmol/mg for monoacetylhydrazine (control 1.10 +/- 0.12 nmol/mg) and 1.36 +/- 0.02 nmol/mg for hydrazine (control 1.13 +/- 0.04 nmol/mg). Histologically, all slices exhibited hepatic necrosis by 4 hours. However, hydrazine-induced hepatotoxicity was characterized by nuclear hyperchromatsia, karyolysis and karyohexis while monoacetylhydrazine exhibited hydropic karyomegaly only. Isoniazid and acetylisoniazid cytotoxicity exhibited a mixture of the above features such that it could be attributed to the two metabolites, hydrazine and monoacetylhydrazine. In conclusion, there was no evidence implicating oxygen free radicals in isoniazid-induced hepatotoxicity; however, the histopathology findings indicate a need for a review of our knowledge on pathognomonic features of isoniazid hepatotoxicity.

Phenytoin toxicity due to concomitant antituberculosis therapy.

Isoniazid inhibits the metabolism of phenytoin. Slow acetylators, who comprise roughly 50% of the South African population, are likely to develop clinical and biochemical features of phenytoin toxicity when this drug is given together with antituberculosis therapy. We describe a patient in whom this interaction caused a series of dangerous clinical events. Seventy-four per cent of patients with epileptogenic disorders seen at the Emergency Unit at Groote Schuur Hospital were on phenytoin and 11.6% of these had blood levels in the toxic range. The wide use of phenytoin during the recent tuberculosis epidemic makes it imperative to suspect this drug interaction in patients exhibiting clinical features that might be related to phenytoin toxicity. Knowledge of this interaction and adjustment of the dose of phenytoin should enable clinicians to avoid this adverse drug interaction.

Oxidative stress during antituberculous therapy in young and elderly patients.

Using allantoin (ATN) as a marker for reactive oxygen species (ROS), oxidative stress during antituberculous (anti-TB) therapy was compared in 10 young and 9 elderly patients. Before treatment, ATN plasma concentrations in patients were similar to that of volunteers. Administration of a combination of isoniazid (INH), rifampicin (RIF) and pyrazinamide (PZA) increased plasma ATN in both groups of patients. ATN concentrations (M +/- SE) at six hours were higher (P < 0.05) in elderly than in young patients on day one, 8.22 +/- 1.50 vs 1.89 +/- 0.98 microgram/mL); day 30, (5.85 +/- 0.82 vs 0.87 +/- 0.57 microgram/mL; and day 90, (4.84 +/- 1.24 vs 0.52 +/- 0.50 microgram/mL). Because total amount of ATN excreted was similar in both groups on the three occasions, more ATN was formed in elderly than young patients. In conclusion, there was more oxidative stress in elderly than young patients. It is thereby suggested that Anti-TB drugs induce formation of ROS and elderly patients are at a greater risk of toxicity probably because of poor antioxidant mechanisms.

Comprehensive assay for pyrazinamide, rifampicin and isoniazid with its hydrazine metabolites in human plasma by column liquid chromatography.

A comprehensive assay for determination of pyrazinamide (PZA), rifampicin (RIF), isoniazid (INH) and hydrazine metabolites is described. The method involves organic solvent extraction of PZA and RIF, followed by derivatization of INH, monoacetylhydrazine (mHYD) and hydrazine (HYD) with salicylaldehyde and extraction with diethyl ether. Acetylisoniazid (acINH) and diacetylhydrazine (dHYD) were hydrolyzed to INH and mHYD, respectively, and processed as above. Using a gradient solvent programmer, PZA and RIF were analyzed on a C8 (5 microns) column at 248 nm, while INH and metabolites were analyzed on a C18 (5 microns) ODS2 column at 280 nm.

Hydrazine--a possible cause of isoniazid--induced hepatic necrosis.

Pharmacokinetic parameters of isoniazid, hydrazine (a metabolite of isoniazid), rifampicin and pyrazinamide in a 74-year-old man with pulmonary tuberculosis who died of submassive hepatic necrosis eight days after starting antituberculosis therapy were compared with those of other elderly patients who did not develop hepatotoxicity. Steady-state plasma hydrazine and rifampicin concentrations in this patient exceeded twice the mean +/- 2 SD value for the group of patients without hepatotoxicity, while concentrations for isoniazid and pyrazinamide were comparable. The findings suggest that HYD may have a role in isoniazid-induced hepatic necrosis.

The disposition of antituberculous drugs in plasma of elderly patients. I. Isoniazid and hydrazine metabolite.

The plasma profiles of isoniazid (INH) and hydrazine (HYD) metabolite were compared in 18 elderly patients (67-89 years of age) and 19 young adult patients (19-59 years of age) on the first day and at one month after treatment for tuberculosis with INH, rifampicin (RIF) and pyrazinamide (PZA). There was no difference in the pharmacokinetics of INH between the two age groups. The clearance for INH at steady-state was significantly lower than after the first dose. After the first dose the maximum concentration (Cmax) for HYD was significantly higher (p less than 0.05) in the elderly (0.4 +/- 0.07 microgram/ml) than in the young (0.24 +/- 0.08 microgram/ml). HYD is produced in significant amounts during INH metabolism and this should not be neglected when evaluating INH related toxicity.

The disposition of antituberculous drugs in plasma of elderly patients. II. Isoniazid, rifampicin and pyrazinamide.

The pharmacokinetics of isoniazid (INH), rifampicin (RIF) and pyrazinamide (PZA) were studied in 18 elderly patients (67-89 years of age) and 19 young adult patients (19-59 years of age) on the first day and at one month of treatment for pulmonary tuberculosis. Elderly patients exhibited more side effects but there were no age-related changes in the pharmacokinetics of any of the three drugs when used in this combination. The clearance for INH and RIF at steady-state were significantly lower than after first-dose, while that of PZA remained unchanged. At steady-state the clearances for INH and RIF were not characteristic of polymorphic metabolism and auto-enzyme induction, respectively. Elderly patients are more sensitive to antituberculous (anti-TB) drugs; therefore, a modification in the dosage for this patient group should be considered.

Simultaneous assay for isoniazid and hydrazine metabolite in plasma and cerebrospinal fluid in the rabbit.

A simple procedure for the simultaneous determination of isoniazid and hydrazine metabolite in plasma and cerebrospinal fluid in the rabbit is described. The assay involves organic extraction before and after derivatization of the two compounds and the internal standard, phenelzine. The extract of the derivatized compounds was evaporated to dryness at 40 degrees C and the residue redissolved in the mobile phase (50 microliters). A 25-microliters aliquot was injected into the liquid chromatograph and eluted with acetonitrile-water-triethylamine (70:30:0.4, v/v) containing 5 mM heptanesulphonic acid on a 30-microns C8 precolumn linked to a 10-microns C18 microBondapak column at ambient temperature (25 +/- 1 degree C). The eluate was detected by ultraviolet detection at 320 nm.

The pharmacokinetics of isoniazid and hydrazine metabolite in plasma and cerebrospinal fluid of rabbits.

The pharmacokinetics of isoniazid (INH) and hydrazine metabolite (HYD) in plasma and cerebrospinal fluid (CSF) of ten rabbits was studied after separate intravenous (i.v.) and oral (p.o.) administration in a crossover study. The concentrations of INH and HYD in the biological fluids were determined by high performance liquid chromatography (HPLC). There was no difference in the area under plasma concentration-time curves, indicating that oral absorption was complete. The mean apparent volume of distribution after i.v. (3.02 +/- 0.55 L) was smaller (p less than 0.01) than that after p.o. (4.29 +/- 1.25 L) dosing. The elimination t1/2 of INH in CSF was longer (p less than 0.005) than that in plasma after either route of administration. There was no significant barrier to the penetration of INH into the CSF from the general circulation. The HYD plasma concentrations were similar after either route. HYD was eliminated at a slower rate (Ke = 0.17 h-1) than INH (Ke = 0.59 h-1). There was prolonged exposure of the body to HYD (greater than 6 h - above 0.1 micrograms/ml).

An overview of the use of anti-tuberculous drugs in Uganda and Hong Kong.

Anti-tuberculous (Anti-TB) chemotherapy in Uganda is outlined. Its pattern of use and the subsequent shortcomings have prompted the need for the present review. A collateral comparison to that of Hong Kong was run to emphasize the correlation of anti-TB chemotherapy with economic development and regional variation in the population of the two areas. Tuberculosis of the central nervous system (CNS) has a high fatality rate. In the search for a more comprehensive anti-TB dosage regimen, the difficulty in treating tuberculosis of the CNS has attracted special attention with emphasis on the fate of anti-TB drugs across the meninges. The choice of a method for drug analysis in routine therapeutic drug monitoring for a country is likewise determined by factors similar to those for the anti-TB regimen. Uganda needs an inexpensive, precise and selective method for TB treatment tailored to its financial and manpower resources.