Treatment and prophylaxis of Pneumocystis carinii pneumonia in AIDS patients

Delivery systems for DNA-binding drugs as gene expression modulators

Despite the large number of publications describing the synthesis and physicocharacterization of the binding between drugs and DNA, relatively few examine drug delivery systems (DDSs) for these molecules. The aim to find DDSs for DNA-binding drugs (DBDs) was prompted mainly to reduce the toxicity and/or enhance the tumor specificity of systemically administered drugs. With this in mind, we have reviewed the biological effects of some DBDs that are currently used as antitumor drugs and describe a brief selection of DDSs currently in clinical trials or on the market.

Dapsone and sulfones in dermatology: overview and update

In their 60-year history, dapsone and the sulfones have been used as both antibacterial and anti-inflammatory agents. Dapsone has been used successfully to treat a range of dermatologic disorders, most successfully those characterized by abnormal neutrophil and eosinophil accumulation. This article reviews and updates the chemistry, pharmacokinetics, clinical application, mechanism of action, adverse effects, and drug interactions of dapsone and the sulfones in dermatology.

Dextran cross-linked gelatin microspheres as a drug delivery system

This paper describes the use of oxidized dextran as a cross-linker for the preparation of gelatin microspheres. Microspheres were obtained by a thermal gelation method and their dissolution kinetic was examined. In order to find evidence of sugar mediated cross-linking, swelling tests and gelatin microspheres dissolution experiments were performed. The obtained results indicated that oxidized dextran can form a cross-linked gelatin network which can reduce the dissolution of gelatin. More interestingly, gelatin microspheres treated by both native and oxidized dextran slow down, even if to a different extent, the release of the antitumor drug TAPP-Br used as a model compound. Taken together, our results suggest that oxidized dextran could be an interesting means to cross-link gelatin microspheres allowing the use of this delivery formulation for controlled release of drugs.

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)

Trimetrexate. A review of its pharmacodynamic and pharmacokinetic properties and therapeutic potential in the treatment of Pneumocystis carinii pneumonia

Trimetrexate is a folinic acid analogue structurally related to methotrexate, whose primary mechanism of action is believed to be inhibition of dihydrofolate reductase. This reduces the production of DNA and RNA precursors and leads to cell death. Trimetrexate is lipophilic and can passively diffuse across cell membranes including those of Pneumocystis carinii and its mammalian host. To minimise toxicity, trimetrexate must be coadministered with calcium folinate (leucovorin calcium), a reduced folate coenzyme, which is transported into, and protects, mammalian host cells but not P. carinii cells. In noncomparative trials trimetrexate was effective in the treatment of P. carinii pneumonia (PCP) in patients with AIDS who were intolerant of or refractory to cotrimoxazole (trimethoprim/sulfamethoxazole) and pentamidine treatment. In these patients, 2- to 4-week survival rates of 48 to 69% were reported. In a comparative trial in the initial therapy of PCP, trimetrexate was less effective than cotrimoxazole in moderate to severe disease as evidenced by a significantly higher failure rate. Trimetrexate was better tolerated than cotrimoxazole when used in this setting, however. Significantly fewer patients receiving trimetrexate plus calcium folinate discontinued treatment because of adverse events than did patients receiving cotrimoxazole. The most common adverse effect associated with trimetrexate is myelosuppression (neutropenia and thrombocytopenia); this is mitigated by coadministration of calcium folinate and is generally reversible upon dosage reduction or discontinuation. Other adverse effects include increases in serum aminotransferase levels, anaemia, fever, rash/pruritus, and increased alkaline phosphatase or serum creatinine levels. Further research into the use of trimetrexate, including its efficacy as prophylaxis, in combination with other agents and as an oral formulation, is needed to clearly define its role in the treatment of PCP and to identify patients most likely to benefit. Currently, trimetrexate should be considered as an alternative treatment option in immunocompromised patients with moderate to severe PCP who have not responded to or are intolerant of first-line therapy.

Antipneumocystis activity of water-soluble lipopeptide L-693,989 in rats

Water-soluble lipopeptide L-693,989 was evaluated for its antipneumocystis activity in rats. Rats from colonies with latent Pneumocystis carinii infections were immunosuppressed with dexamethasone for 6 weeks to facilitate the development of acute P. carinii pneumonia (PCP). After 6 weeks, the rats were maintained on dexamethasone and were treated twice daily for 4 days with various concentrations of L-693,989. At a dose of 0.15 mg/kg of body weight, the compound effectively eliminated 90% of the cysts in 4 days. Trophozoite forms of P. carinii were still present in these animals, as determined by using a P. carinii-specific DNA probe. A 3-week therapy study showed that the trophozoite load did not expand during treatment and that the trophozoites already present at the initiation of therapy appeared to persist. This may be a consequence of the stage specificity of the compound for cyst development and the severe immunosuppressive effects of dexamethasone on rats. When evaluated as a daily parenteral prophylactic agent, L-693,989 was effective in preventing the development of both P. carinii cysts and trophozoites, demonstrating its potential for use in prophylaxis and implying that the cyst stage of P. carinii is an obligatory step in trophozoite multiplication. The foamy exudate commonly associated with P. carinii infections was absent in the lungs of rats on prophylaxis. The compound was also evaluated via oral administration and was found to have a 90% effective dose of 32 mg/kg for therapy of acute infections and 5 mg/kg for daily prophylaxis.