Estavudina

Estavudina is indicated in combination with other antiretroviral medicinal products for the treatment of HIV infected adult patients and paediatric patients (over the age of 3 months) only when other antiretrovirals can not be used. The duration of therapy with Estavudina should be limited to the shortest time possible.

For patients starting therapy with Estavudina, the duration should be limited to the shortest time possible followed by a switch to an alternative appropriate therapy whenever possible. Patients continuing treatment with Estavudina should be assessed frequently and switched to an alternative appropriate therapy whenever possible.

Posology

Adults: the recommended oral dosage is

Paediatric population

Adolescents, children and infants over the age of 3 months: the recommended oral dosage is

The powder formulation of Estavudina should be used for infants under the age of 3 months. Adult patients that have problems swallowing capsules should ask their doctor about the possibility of changing to the powder formulation of this medicine.

Please refer to the Summary of Product Characteristics of the powder formulation.

Dose adjustments

Peripheral neuropathy: if symptoms of peripheral neuropathy develop (usually characterised by persistent numbness, tingling, or pain in the feet and/or hands) patients should be switched to an alternative treatment regimen, if appropriate. In the rare cases when this is inappropriate, dose reduction of stavudine may be considered, while the symptoms of peripheral neuropathy are under close monitoring and satisfactory virological suppression is maintained.

The possible benefits of a dose reduction should be balanced in each case against the risks - which may result from this measure (lower intracellular concentrations).

Special populations

Elderly: Estavudina has not been specifically investigated in patients over the age of 65.

Hepatic impairment: no initial dosage adjustment is necessary.

Renal impairment: the following dosages are recommended

* Patients on haemodialysis should take Estavudina after the completion of haemodialysis, and at the same time on non-dialysis days.

Since urinary excretion is also a major route of elimination of stavudine in paediatric patients, the clearance of stavudine may be altered in paediatric patients with renal impairment. Although there are insufficient data to recommend a specific dosage adjustment of Estavudina in this patient population, a reduction in the dose and/or an increase in the interval between doses proportional to the reduction for adults should be considered. There are no dosage recommendations for paediatric patients under the age of 3 months with renal impairment.

Method of administration

For optimal absorption, Estavudina should be taken on an empty stomach (i.e. at least 1 hour prior to meals) but, if this is not possible, it may be taken with a light meal. Estavudina may also be administered by carefully opening the hard capsule and mixing the contents with food.

Co-administration with didanosine due to the potential for serious and/or life-threatening events notably lactic acidosis, liver function abnormalities, pancreatitis and peripheral neuropathy.

While effective viral suppression with antiretroviral therapy has been proven to substantially reduce the risk of sexual transmission, a residual risk cannot be excluded. Precautions to prevent transmission should be taken in accordance with national guidelines.

Stavudine therapy is associated with several severe side effects, such as lactic acidosis, lipoatrophy and polyneuropathy, for which a potential underlying mechanism is mitochondrial toxicity.).

Liver disease: hepatitis or liver failure, which was fatal in some cases, has been reported. The safety and efficacy of stavudine has not been established in patients with significant underlying liver disorders. Patients with chronic hepatitis B or C and treated with combination antiretroviral therapy are at an increased risk of severe and potentially fatal hepatic adverse reactions. In case of concomitant antiviral therapy for hepatitis B or C, please refer also to the relevant product information for these medicinal products.

Patients with pre-existing liver dysfunction including chronic active hepatitis have an increased frequency of liver function abnormalities during combination antiretroviral therapy and should be monitored according to standard practice. If there is evidence of worsening liver disease in such patients, interruption or discontinuation of treatment must be considered.

In the event of rapidly elevating transaminase levels (ALT/AST, > 5 times upper limit of normal, ULN), discontinuation of Estavudina and any potentially hepatotoxic medicinal products should be considered.

Lipoatrophy: on the basis of mitochondrial toxicity stavudine has been shown to cause loss of subcutaneous fat, which is most evident in the face, limbs and buttocks.

In randomized controlled trials of treatment-naive patients, clinical lipoatrophy developed in a higher proportion of patients treated with stavudine compared to other nucleosides (tenofovir or abacavir). Dual energy x-ray absorptiometry (DEXA) scans demonstrated overall limb fat loss in stavudine treated patients compared to limb fat gain or no change in patients treated with other NRTIs (abacavir, tenofovir or zidovudine). The incidence and severity of lipoatrophy are cumulative over time with stavudine-containing regimens. In clinical trials, switching from stavudine to other nucleosides (tenofovir or abacavir) resulted in increases in limb fat with modest to no improvements in clinical lipoatrophy. Given the potential risks of using Estavudina including lipoatrophy, a benefit-risk assessment for each patient should be made and an alternative antiretroviral carefully considered. Patients receiving Estavudina should be frequently examined and questioned for signs of lipoatrophy. When such development is found, discontinuation of Estavudina should be considered.

Weight and metabolic parameters: an increase in weight and in levels of blood lipids and glucose may occurr during antiretroviral therapy. Such changes may in part be linked to disease control and life style. For lipids, there is in some cases evidence for a treatment effect, while for weight gain there is no strong evidence relating this to any particular treatment. For monitoring of blood lipids and glucose reference is made to established HIV treatment guidelines. Lipid disorders should be managed as clinically appropriate.

Peripheral neuropathy: up to 20% of patients treated with Estavudina will develop peripheral neuropathy, often starting after some months of treatment.).

Pancreatitis: patients with a history of pancreatitis had an incidence of approximately 5% on Estavudina, as compared to approximately 2% in patients without such a history. Patients with a high risk of pancreatitis or those receiving products known to be associated with pancreatitis should be closely followed for symptoms of this condition.

Immune reactivation syndrome: in HIV-infected patients with severe immune deficiency at the time of institution of combination antiretroviral therapy (CART), an inflammatory reaction to asymptomatic or residual opportunistic pathogens may arise and cause serious clinical conditions, or aggravation of symptoms. Typically, such reactions have been observed within the first few weeks or months of initiation of CART. Relevant examples are cytomegalovirus retinitis, generalised and/or focal mycobacterial infections, and Pneumocystis carinii pneumonia. Any inflammatory symptoms should be evaluated and treatment instituted when necessary. Autoimmune disorders (such as Graves' disease) have also been reported to occur in the setting of immune reactivation; however, the reported time to onset is more variable and these events can occur many months after initiation of treatment.

Osteonecrosis: although the etiology is considered to be multifactorial (including corticosteroid use, alcohol consumption, severe immunosuppression, higher body mass index), cases of osteonecrosis have been reported particularly in patients with advanced HIV-disease and/or long-term exposure to combination antiretroviral therapy (CART). Patients should be advised to seek medical advice if they experience joint aches and pain, joint stiffness or difficulty in movement.

Lactose intolerance: the hard capsule contains lactose. Patients with rare hereditary problems of galactose intolerance, the Lapp lactase deficiency or glucose-galactose malabsorption, should not take this medicine.

Not recommended combinations: pancreatitis (fatal and nonfatal) and peripheral neuropathy (severe in some cases) have been reported in HIV infected patients receiving stavudine in association with hydroxyurea and didanosine. Hepatotoxicity and hepatic failure resulting in death were reported during postmarketing surveillance in HIV infected patients treated with antiretroviral agents and hydroxyurea; fatal hepatic events were reported most often in patients treated with stavudine, hydroxyurea and didanosine. Hence, hydroxyurea should not be used in the treatment of HIV infection.

Elderly: Estavudina has not been specifically investigated in patients over the age of 65.

Paediatric population

Infants under the age of 3 months: safety data are available from clinical trials up to 6 weeks of treatment in 179 newborns and infants < 3 months of age.

Special consideration should be given to the antiretroviral treatment history and the resistance profile of the HIV strain of the mother.

Mitochondrial dysfunction following exposure in utero: nucleos(t)ide analogues may impact mitochondrial function to a variable degree, which is most pronounced with stavudine, didanosine and zidovudine.); these have predominantly concerned treatment with regimens containing zidovudine. The main adverse reactions reported are haematological disorders (anaemia, neutropenia) and metabolic disorders (hyperlactatemia, hyperlipasemia). These events have often been transitory. Late-onset neurological disorders have been reported rarely (hypertonia, convulsion, abnormal behaviour). Whether such neurological disorders are transient or permanent is currently unknown. These findings should be considered for any child exposed in utero to nucleos(t)ide analogues, that present with severe clinical findings of unknown etiology, particularly neurologic findings. These findings do not affect current national recommendations to use antiretroviral therapy in pregnant women to prevent vertical transmission of HIV.

No studies on the effects on the ability to drive and use machines have been performed. Stavudine may cause dizziness and/or somnolence. Patients should be instructed that if they experience these symptoms they should avoid potentially hazardous tasks such as driving or operating machinery.

Summary of the safety profile

Stavudine therapy is associated with several severe adverse reactions, such as lactic acidosis, lipoatrophy and polyneuropathy, for which a potential underlying mechanism is mitochondrial toxicity. Given these potential risks, a benefit-risk assessment for each patient should be made and an alternative antiretroviral should be carefully considered.

Cases of lactic acidosis, sometimes fatal, usually associated with severe hepatomegaly and hepatic steatosis, have been reported in < 1% of patients taking stavudine in combination with other antiretrovirals.

Motor weakness has been reported rarely in patients receiving combination antiretroviral therapy including Estavudina. Most of these cases occurred in the setting of symptomatic hyperlactatemia or lactic acidosis syndrome. The evolution of motor weakness may mimic the clinical presentation of Guillain-Barré syndrome (including respiratory failure). Symptoms may continue or worsen following discontinuation of therapy.

Hepatitis or liver failure, which was fatal in some cases, has been reported with the use of stavudine.

Lipoatrophy was commonly reported in patients treated with stavudine in combination with other antiretrovirals.

Peripheral neuropathy was seen in combination studies of Estavudina with lamivudine plus efavirenz; the frequency of peripheral neurologic symptoms was 19% (6% for moderate to severe) with a rate of discontinuation due to neuropathy of 2%. The patients usually experienced resolution of symptoms after dose reduction or interruption of stavudine.

Pancreatitis, occasionally fatal, has been reported in up to 2-3% of patients enrolled in monotherapy clinical studies. Pancreatitis was reported in < 1% of patients in combination therapy studies with Estavudina.

Tabulated summary of adverse reactions

Adverse reactions of moderate or greater severity with at least a possible relationship to treatment regimen (based on investigator attribution) reported from 467 patients treated with Estavudina in combination with lamivudine and efavirenz in two randomised clinical trials and along-term follow-up study (follow-up: median 56 weeks ranging up to 119 weeks) are listed below. Also listed are adverse reactions observed post-marketing in association with stavudine-containing antiretroviral treatment. The frequency of adverse reactions listed below is defined using the following convention: very common (> 1/10); common (> 1/100 to < 1/10); uncommon (> 1/1,000 to < 1/100); rare (> 1/10,000 to < 1/1,000); very rare (< 1/10,000). Within each frequency grouping, undesirable effects are presented in order of decreasing seriousness.

* Adverse reactions observed post-marketing in association with stavudine-containing antiretroviral treatment

** See Section Description of selected adverse reactions for more details.

Description of selected adverse reactions

Immune reactivation syndrome: in HIV-infected patients with severe immune deficiency at the time of initiation of combination antiretroviral therapy (CART), an inflammatory reaction to asymptomatic or residual opportunistic infections may arise. Autoimmune disorders (such as Graves' disease) have also been reported; however, the reported time to onset is more variable and these events can occur many months after initiation of treatment.

Lipoatrophy: stavudine has been shown to cause loss of subcutaneous fat, which is most evident in the face, limbs and buttocks. The incidence and severity of lipoatrophy are related to cumulative exposure, and is often not reversible when stavudine treatment is stopped. Patients receiving Estavudina should be frequently examined and questioned for signs of lipoatrophy. When such development is found, treatment with Estavudina should not be continued.

Metabolic parameters: weight and levels of blood lipids and glucose may increase during antiretroviral therapy.

Osteonecrosis: cases of osteonecrosis have been reported, particularly in patients with generally acknowledged risk factors, advanced HIV disease or long-term exposure to combination antiretroviral therapy (CART). The frequency of this is unknown.

Laboratory abnormalities: laboratory abnormalities reported in these two trials and an ongoing follow-up study included elevations of ALT (> 5 x ULN) in 3%, of AST (> 5 x ULN) in 3%, of lipase (> 2.1 ULN) in 3% of the patients in the Estavudina group. Neutropenia (< 750 cells/mm³) was reported in 5%, thrombocytopenia (platelets < 50,000/mm³) in 2%, and low haemoglobin (< 8 g/dl) in < 1% of patients receiving Estavudina.

Macrocytosis was not evaluated in these trials, but was found to be associated with Estavudina in an earlier trial (MCV > 112 fl occurred in 30% of patients treated with Estavudina).

Paediatric population

Adolescents, children and infants: adverse reactions and serious laboratory abnormalities reported to occur in paediatric patients ranging in age from birth through adolescence who received stavudine in clinical studies were generally similar in type and frequency to those seen in adults. However, clinically significant peripheral neuropathy is less frequent. These studies include ACTG 240, where 105 paediatric patients ages 3 months to 6 years received Estavudina 2 mg/kg/day for a median of 6.4 months; a controlled clinical trial where 185 newborns received Estavudina 2 mg/kg/day either alone or in combination with didanosine from birth through 6 weeks of age; and a clinical trial where 8 newborns received Estavudina 2 mg/kg/day in combination with didanosine and nelfinavir from birth through 4 weeks of age.

The HIV status for the newborns and infants ≤ 3 months of age was negative, for older infants it tended to be positive. The profile of the adverse events for newborns and infants ≤ 3 months of age showed increases in lactic acid levels, neutropenia, anaemia, thrombocytopenia, hepatic transaminase increases and increased lipids, including hypertriglyceridaemia. The number of reports in older infants was too small to identify a pattern.

Reporting of suspected adverse reactions

Reporting suspected adverse reactions after authorisation of the medicinal product is important. It allows continued monitoring of the benefit/risk balance of the medicinal product. Healthcare professionals are asked to report any suspected adverse reactions via the Yellow Card Scheme at: www.mhra.gov.uk/yellowcard.

Experience in adults treated with up to 12 times the recommended daily dosage revealed no acute toxicity. Complications of chronic overdosage could include peripheral neuropathy and hepatic dysfunction. The mean haemodialysis clearance of stavudine is 120 ml/min. The contribution of this to the total elimination in an overdose situation is unknown. It is not known whether stavudine is removed by peritoneal dialysis.

Pharmacotherapeutic group: antivirals for systemic use, nucleoside and nucleotide reverse transcriptase inhibitors, ATC code: J05AF04

Mechanism of action

Stavudine, a thymidine analogue, is phosphorylated by cellular kinases to stavudine triphosphate which inhibits HIV reverse transcriptase by competing with the natural substrate, thymidine triphosphate. It also inhibits viral DNA synthesis by causing DNA chain termination due to a lack of the 3'-hydroxyl group necessary for DNA elongation. Cellular DNA polymerase γ is also sensitive to inhibition by stavudine triphosphate, while cellular polymerases α and β are inhibited at concentrations 4,000-fold and 40-fold higher, respectively, than that needed to inhibit HIV reverse transcriptase.

Resistance

Stavudine treatment can select for and/or maintain thymidine analogue mutations (TAMs) associated with zidovudine resistance. The decrease of susceptibility in vitro is subtle requiring two or more TAMs (generally M41L and T215Y) before stavudine susceptibility is decreased (> 1.5 fold).

These TAMs are seen at a similar frequency with stavudine and zidovudine in virological treatment. The clinical relevance of these findings suggest that stavudine should be generally avoided in the presence of TAMs, especially M41L and T215Y.

The activity of stavudine is also affected by multi-drug resistance associated mutations such as Q151M. In addition, K65R has been reported in patients receiving stavudine/didanosine or stavudine/lamivudine, but not in patients receiving stavudine monotherapy. V75T is selected in vitro by stavudine and reduces susceptibility to stavudine by 2-fold. It occurs in ~1% of patients receiving stavudine.

Clinical efficacy and safety

Estavudina has been studied in combination with other antiretroviral agents, e.g. didanosine, lamivudine, ritonavir, indinavir, saquinavir, efavirenz, and nelfinavir.

In antiretroviral naive patients

Study AI455-099 was a 48-week, randomised, double-blind study with Estavudina (40 mg twice daily), in combination with lamivudine (150 mg twice daily) plus efavirenz (600 mg once daily), in 391 treatment-naive patients, with a median CD4 cell count of 272 cells/mm³ (range 61 to 1,215 cells/mm³) and a median plasma HIV-1 RNA of 4.80 log₁₀ copies/ml (range 2.6 to 5.9 log ₁₀ copies/ml) at baseline. Patients were primarily males (70%) and non-white (58%) with a median age of 33 years (range 18 to 68 years).

Study AI455-096 was a 48-week, randomised, double-blind study with Estavudina (40 mg twice daily), in combination with lamivudine (150 mg twice daily) plus efavirenz (600 mg once daily), in 76 treatment-naive patients, with a median CD4 cell count of 261 cells/mm³ (range 63 to 962 cells/mm³) and a median plasma HIV-1 RNA of 4.63 log₁₀ copies/ml (range 3.0 to 5.9 log₁₀ copies/ml) at baseline. Patients were primarily males (76%) and white (66%) with a median age of 34 years (range 22 to 67 years).

The results of AI455-099 and AI455-096 are presented in Table 1. Both studies were designed to compare two formulations of Estavudina, one of which was the marketed formulation dosed as currently approved in product labelling. Only the data from the marketed formulation are presented.

Table 1: Efficacy Outcomes at Week 48 (Studies AI455-099 and AI455-096)

^a Number of patients evaluable.

Paediatric population

Absorption

The absolute bioavailability is 86±18%. After multiple oral administration of 0.5-0.67 mg/kg doses, a C_max value of 810±175 ng/ml was obtained. C_max and AUC increased proportionally with dose in the dose ranges, intravenous 0.0625-0.75 mg/kg, and oral 0.033-4.0 mg/kg.

In eight patients receiving 40 mg twice daily in the fasted state, steady-state AUC_0-12h was 1284±227 ng·h/ml (18%) (mean ± SD [% CV]), C_max was 536±146 ng/ml (27%), and C_min was 9±8 ng/ml (89%). A study in asymptomatic patients demonstrated that systemic exposure is similar while C_max is lower and T_max is prolonged when stavudine is administered with a standardised, high-fat meal compared with fasting conditions. The clinical significance of this is unknown.

Distribution

The apparent volume of distribution at steady state is 46±21 l. It was not possible to detect stavudine in cerebrospinal fluid until at least 2 hours after oral administration. Four hours after administration, the CSF/plasma ratio was 0.39±0.06. No significant accumulation of stavudine is observed with repeated administration every 6, 8, or 12 hours.

Binding of stavudine to serum proteins was negligible over the concentration range of 0.01 to 11.4 µg/ml. Stavudine distributes equally between red blood cells and plasma.

Metabolism

Unchanged stavudine was the major drug-related component in total plasma radioactivity circulating after an oral 80 mg dose of ¹⁴C-stavudine in healthy subjects. The AUC(inf) for stavudine was 61% of the AUC(inf) of the total circulating radioactivity. Metabolites include oxidised stavudine, glucuronide conjugates of stavudine and its oxidised metabolite, and an N-acetylcysteine conjugate of the ribose after glycosidic cleavage, suggesting that thymine is also a metabolite of stavudine.

Elimination

Following an oral 80-mg dose of ¹⁴C-stavudine to healthy subjects, approximately 95% and 3% of the total radioactivity was recovered in urine and faeces, respectively. Approximately 70% of the orally administered stavudine dose was excreted as an unchanged drug in urine. Mean renal clearance of the parent compound is approximately 272 ml/min, accounting for approximately 67% of the apparent oral clearance, indicating active tubular secretion in addition to glomerular filtration.

In HIV-infected patients,total clearance of stavudine is 594±164 ml/min, and renal clearance is 237±98 ml/min. The total clearance of stavudine appears to be higher in HIV-infected patients, while the renal clearance is similar between healthy subjects and HIV-infected patients. The mechanism and clinical significance of this difference are unknown. After intravenous administration, 42% (range: 13% to 87%) of dose is excreted unchanged in the urine. The corresponding values after oral single and multiple dose administration are 35% (range: 8% to 72%) and 40% (range: 12% to 82%), respectively. The mean terminal elimination half-life of stavudine is 1.3 to 2.3 hours following single or multiple doses, and is independent of dose. In vitro, stavudine triphosphate has an intracellular half-life of 3.5 hours in CEM T-cells (a human T-lymphoblastoid cell line) and peripheral blood mononuclear cells, supporting twice daily dosing.

The pharmacokinetics of stavudine was independent of time, since the ratio between AUC_(ss) at steady state and the AUC_(0-t) after the first dose was approximately 1. Intra- and interindividual variation in pharmacokinetic characteristics of stavudine is low, approximately 15% and 25%, respectively, after oral administration.

Special Populations

Renal impairment: the clearance of stavudine decreases as creatinine clearance decreases; therefore, it is recommended that the dosage of Estavudina be adjusted in patients with reduced renal function.

Hepatic impairment: stavudine pharmacokinetics in patients with hepatic impairment were similar to those in patients with normal hepatic function.

Paediatric population

Adolescents, children and infants: total exposure to stavudine was comparable between adolescents, children and infants > 14 days receiving the 2 mg/kg/day dose and adults receiving 1 mg/kg/day. Apparent oral clearance was approximately 14 ml/min/kg for infants ages 5 weeks to 15 years, 12 ml/min/kg for infants ages 14 to 28 days, and 5 ml/min/kg for infants on the day of birth. Two to three hours post-dose, CSF/plasma ratios of stavudine ranged from 16% to 125% (mean of 59%±35%).

Animal data showed embryo-foetal toxicity at very high exposure levels. An ex vivo study using a term human placenta model demonstrated that stavudine reaches the foetal circulation by simple diffusion. A rat study also showed placental transfer of stavudine, with the foetal tissue concentration approximately 50% of the maternal plasma concentration.

Stavudine was genotoxic in in vitro tests in human lymphocytes possessing triphosphorylating activity (in which no no-effect level was established), in mouse fibroblasts, and in an in vivo test for chromosomal aberrations. Similar effects have been observed with other nucleoside analogues.

Stavudine was carcinogenic in mice (liver tumours) and rats (liver tumours: cholangiocellular, hepatocellular, mixed hepatocholangiocellular, and/or vascular; and urinary bladder carcinomas) at very high exposure levels. No carcinogenicity was noted at doses of 400 mg/kg/day in mice and 600 mg/kg/day in rats, corresponding to exposures ~ 39 and 168 times the expected human exposure, respectively, suggesting an insignificant carcinogenic potential of stavudine in clinical therapy.

Not applicable.

Any unused medicinal product or waste material should be disposed of in accordance with local requirements.