Clinical trials selection

Class Drug Name and Oral Dose (mg/day) Compelling Indications2 Clinical Trials Select Adverse Events Comments... 

In order to minimise harms there is first a need to identify and assess the impact of unexpected potential hazards. For most medicines, serious ADRs are rare otherwise their detection would result in the drug not reaching or being withdrawn from the market. For products which do reach the market, serious hazards are seldom identified during pre-marketing clinical trials because sample sizes are almost invariably too small to detect them. In addition, the prevailing conditions of clinical trials - selected patients, short durations of treatment, close monitoring and specialist supervision - almost invariably mean that they will underestimate the frequency of ADRs relative to what will really occur in ordinary practice. 

Selected for clinical trials as a compound to calm agitated patients, imipramine was relatively ineffective. However, it was observed to be effective in the treatment of certain depressed patients (38). Early studies on the mechanism of action showed that imipramine potentiates the effects of the catecholamines, primarily norepinephrine. This finding, along with other evidence, led to the hypothesis that the compound exerts its antidepressant effects by elevating norepinephrine levels at central adrenergic synapses. Subsequent studies have shown that the compound is a potent inhibitor of norepinephrine reuptake and, to a lesser extent, the uptake of serotonin, thus fitting the hypothesis that had been developed to explain the antidepressant actions ofMAOIs. 

Development of a peptide vaccine is derived from the identification of the immunodominant epitope of an antigen (141). A polypeptide based on the amino acid sequence of the epitope can then be synthesized. Preparation of a peptide vaccine has the advantage of allowing for large-scale production of a vaccine at relatively low cost. It also allows for selecting the appropriate T- or B-ceU epitopes to be included in the vaccine, which may be advantageous in some cases. Several vaccines based on peptide approaches, such as SPf66 (95) for malaria and an HIV-1 peptide (142) have been in clinical trials. No peptide vaccines are Hcensed as yet. 

The use of selective P-antagonists for treatment of CHF has included the P -blocker metoprolol (Table 1) and results of clinical trials suggest long-term beneficial effects. Selective P -antagonists have also been tested, an example of which is xamoterol [81801 -12-9], C2 H25N20, which is (i)-A/-(2-hydroxy-3-(4-hydroxyphenoxy)propylamino)ethylmorphine-4-carboxamide. Xamoterol exhibits approximately 50% of the activity of isoproterenol, and serves to provide modest inotropic effects (128,129). 

At the in vivo assay level, the classic ip-ip (iateraperitoneal) in vivo model has been replaced as a selection criteria for advancement of new dmg candidates to clinical trial. More stringent alternative models iaclude subcutaneous or subrenal capsule implantation of tumor followed by iatravenous dmg dosiag (7) and the human tumor xenograft models ia aude mice (8). 

Out of the numerous compounds these investigators made, they eventually selected /S-hydroxyethyla oquinine for clinical trial owing to its low toxicity, relatively high bacteriostatic power and lack of deleterious side-effects. The following table summarises the data available on these two points for this drug and its near relatives. The name opocupreine is used by Cretcher for opoquinine (p. 452). 

Selective AR agonists are undergoing clinical trials for cardiac arrhythmias and pain (Ai) cardiac imaging and inflammation (A2a) colon cancer, rheumatoid arthritis, psoriasis, and dry eye (A3). Selective AR antagonists are either in or advancing toward clinical trials for kidney disorders (Ax) Parkinson s disease (A2a) diabetes and asthma (A2B) cancer and glaucoma (A3). 

The first two selective COX-2 inhibitors to be marketed and subjected to in depth clinical trials were celecoxib and rofecoxib. Both compounds are as effective as standard NSAIDs in rheumatoid arthritis, osteoarthritis and for pain following orthopaedic or dental surgery. Gastrointestinal side effects were far fewer than with comparator diugs and in fact were no... 

Celecoxib, which has a low selectivity for COX-2 compared to COX-1, is still available, although its more selective successor, valdecoxib has been withdrawn. Etoricoxib, the successor to rofecoxib, is marketed in Europe but not in the USA. In a large multinational clinical trial, etoricoxib caused no more thromboembolic events than diclofenac, but after 18 months the incidence of gastrointestinal ulcers and bleeding was the same for both drugs [4]. 

A number of rationally designed MMP inhibitors have shown some promise in the treatment of pathologies, which MMPs are suspected to be involved in. However, most of these, such as Marimastat (BB-2516), a broad spectrum MMP inhibitor, or trocade (Ro 32-3555), an MMP-1 selective inhibitor, have performed poorly in clinical trials. The failure of Marimastat was partially responsible for the folding of British Biotech, which developed it. The failure of... 

A number of inhibitors directed towards the active site of PKC have been developed [4]. Many of these have therapeutic potential and some are in clinical trials. The drug enzastaurin (LY317615) shows selectivity towards inhibiting PKC 3 and is currently in clinical trials for cancer. This drug has particular potential as a treatment for colon cancer because of the specific role ofPKC (311 in this disease (see above). A separate PKC (3 inhibitor, ruboxistaurin (LY333531) has been developed as a drug to treat the microvasculature complications of diabetes hyperactivation of both PKC (311 and PKC (31 contribute to diabetic retinopathy and microvasculature complications. 

Proteasomal inhibition represents a novel strategy in cancer treatment and the small molecule Bortezomid (PS-341, Velcade ) has been approved for the treatment of refractory and relapsed multiple myeloma, a proliferative disease of plasma cells. Bortezomid inhibits an active site in a proteasome subunit and remarkably shows selective cytotoxicity to cancer cells. Although the underlying mechanisms are not completely understood bortezomid apparently induces a cell stress response in these tumor cells followed by caspase-dependent apoptosis. Whether bortezomid is beneficial for the treatment of other proliferative disease is currently being tested in clinical trials. 

Compound 34 (BCZ-1812, RWJ-270201, peramivir) showed selective inhibition of influenza virus sialidases over bacterial and mammalian sialidases (Babu et al. 2000 Bantia et al. 2001 Sidwell and Smee 2002). Successful inhibition of influenza virus infectivity in vitro (Smee et al. 2001) and upon oral administration in vivo [mice (Bantia et al. 2001) and ferrets, reviewed in Sidwell and Smee 2002] led to human clinical trials of orally administered peramivir (Barroso et al. 2005). While orally administrated peramivir successfully completed animal studies and Phase I and Phase II clinical trials, in which the compound was showing neither major side effects nor toxicity (Sidwell and Smee 2002), preliminary results of the Phase III trials (June 2002) demonstrated no statistically significant difference in the primary efficacy endpoint, possibly due to low bioavailability (Barroso et al. 2005). 

The first study to demonstrate the activity of enfuvirtide in HIV-infected patients (Kilby et al. 1998) showed that patients receiving the maximum 100 mg intravenous dose had maximum median declines in HIV-1 RNA of -1.96 logjo copies/mL through 14 days. Several additional studies (Kilby et al. 2002 Lalezari et al. 2003a, b) further demonstrated the safety and efficacy of enfuvirtide and led to the selection of twice-daily subcutaneous injections of a 90 mg nominal dose for testing in the TORO (T-20 vs. optimized regimen only) pivotal clinical trials. 

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